Prevalence and morphological features of acetabular dysplasia with coexisting femoroacetabular impingement-related findings in a Japanese population: a computed tomography-based cross-sectional study

Prevalence and morphological features of acetabular dysplasia with coexisting femoroacetabular... Journal of Hip Preservation Surgery Vol. 5, No. 2, pp. 137–149 doi: 10.1093/jhps/hny006 Advance Access Publication 12 March 2018 Research article Prevalence and morphological features of acetabular dysplasia with coexisting femoroacetabular impingement-related findings in a Japanese population: a computed tomography-based cross-sectional study Tomohiro Mimura*, Kanji Mori, Yuki Furuya, Shin Itakura, Taku Kawasaki and Shinji Imai Department of Orthopedic Surgery, Shiga University of Medical Science, Tsukinowa-cho, Seta, Otsu, Shiga 520-2192, Japan *Correspondence to: T. Mimura. E-mail: tmimura@belle.shiga-med.ac.jp Submitted 19 August 2017; Revised 14 January 2018; revised version accepted 11 February 2018 ABSTRACT The coexistence of acetabular dysplasia (AD) and femoroacetabular impingement (FAI) has not been well dis- cussed. This study was performed to elucidate the prevalence and morphological features of AD with coexisting FAI-related findings in a Japanese population. Computed tomography images were retrospectively evaluated. AD was classified as definite or borderline. The morphological findings that defined cam deformity were an a angle of55 , head–neck offset ratio (HNOR) of<0.13, pistol grip deformity positivity and herniation pit positivity. The morphological findings that defined pincer deformity were acetabular index of0 and a retroverted acet- abulum. In total, 128 hips (male, 64; female, 64) were analyzed. The prevalence of coexistence of AD and FAI- related findings was detected in 23.4% of hips (definite AD and FAI, 7.8%; borderline AD and FAI, 15.6%). The percentages of hips with AD containing cam or pincer deformities among all were 54.3% and 4.3%, respectively. The percentage of AD with coexisting cam and that of AD with coexisting combined deformities was significantly higher in men, respectively. On the other hand, the most major morphological feature of FAI detected in hips with AD was a HNOR of<0.13. The coexistence of AD and FAI-related findings was common in a Japanese population, and 65.2% of hips with AD had some FAI-related findings. In discussing and managing AD, we rec- ommend paying attention to the coexistence with FAI-related findings, especially in men and in borderline AD. In such hips, the most notable parameter as a morphological feature of FAI is a reduced HNOR. deformity, pincer deformity, combined deformities and INTRODUCTION sports impingement, where a hip with normal anatomy im- Acetabular dysplasia (AD) is a well-recognized cause of pinges in extreme positions in sporting activity. osteoarthritis (OA) of the hip [1]. In Japan, AD is a major The anatomical abnormalities associated with AD and FAI risk factor for OA [2], and the prevalence of AD is higher have been discussed as independent anatomical features. in Japanese than in Western populations [3]. Furthermore, Several recent reports have described the coexistence of definite AD and borderline AD are often distinguished in AD and FAI-related findings in patients with symptomatic the clinical setting [4, 5]. Femoroacetabular impingement AD or FAI [8–11]. However, the prevalence and morpho- (FAI) has also been highlighted, and an association be- logical features of the coexistence of AD (especially border- tween FAI and hip OA has been identified [6, 7]. FAI has line AD) and FAI-related findings are not well known in been thought to be divided into four categories: cam V C The Author(s) 2018. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 138  T. Mimura et al. Japanese populations who are generally assumed to have AD rather than Western populations. The aim of this study was to investigate the detailed prevalence and morpho- logical features of AD with coexisting FAI-related findings using multislice computed tomography (CT) images in a Japanese population. MATERIALS AND METHODS Patients and parameters The ethics committee of our institution approved the study protocol. We conducted a retrospective patient-based study of patients who had undergone CT imaging of the chest, abdomen and pelvis. We reviewed all CT data from 1 July 2013–14 August 2013 in our institution. First, we selected the scans that had been ordered by other departments at our institution and confirmed that the CT examination had been performed for conditions unrelated to hip disorders based on the information in the clinical record. Next, we se- lected 65 consecutive patients irrespective of sex who ful- filled the criteria described below. The inclusion criteria for the present study were as follows: (1) involvement of the Fig. 1. Measurement of CE angle, Sharp angle and AI. These whole pelvis and both hip joints, (2) reconstructed axial angles were measured on a slice of femoral head center in the slice thickness of1 mm and (3) normal pelvic rotations coronal plane. h1, h2, and h3 is CE angle, Sharp angle and AI, re- and tilt (specified below in the section describing standard- spectively. CE angle was measured as the angle between the line ization of CT images). The exclusion criteria were as joining the lateral aspect of the acetabulum and the femoral head center, and the line perpendicular to the line parallel to the trans- follows: (1) age of<20 years, (2) inability to clearly detect verse axis of the pelvis. Sharp angle was measured as the angle the center of the femoral head, such as in patients with between the line joining the lateral aspect of the weight bearing an elliptical femoral head and (3) inability to correctly zone and the inferior point of teardrop, and the line parallel to measure the parameters, such as clear hip OA that had the transverse axis of the pelvis. AI was measured as the angle be- the osteophyte formation, the loss of joint space and tween the line joining the medial and lateral aspects of the weight subchondral bone cysts [12]. bearing zone, and the line parallel to the transverse axis of the Both hips were analyzed in each patient. Two male hips pelvis. were excluded because of a metaphyseal bone tumor in each. As a result, 128 hips (64 male hips and 64 female hips) were evaluated. The examined parameters and find- HP as a cystic-like lesion underneath the anterior cortex at ings were age, sex, center-edge (CE) angle [13], Sharp the anterosuperior femoral head–neck junction with a clear angle [14], acetabular index (AI) [15], acetabular version demarcation [26] and a diameter of>3mm [27](Fig. 4). angle [16], a angle [17], head–neck offset ratio (HNOR) HP was evaluated at the above-described multiradial slices. [18], herniation pit (HP) [19] and pistol grip deformity The presence of a PGD was subjectively determined using (PGD) [20, 21]. reconstructed three-dimensional CT images (Fig. 5). AD CE angle, Sharp angle and AI were measured on a slice was classified into definite AD and borderline AD. Definite of the femoral head center in the coronal plane (Fig. 1). AD was defined as a CE angle of<20 or a Sharp angle The acetabular anteversion angle was measured in four of>45 . Borderline AD was defined as a CE angle of 20 axial slices (Fig. 2). We defined an acetabulum with a nega- to<25 or a Sharp angle of>42 to 45 (hips already tive acetabular anteversion angle in any slice (A1, A2, A3 defined as definite AD were excluded). We investigated or A4) as a retroverted acetabulum (RA) [22]. RA of these the prevalence of these morphological findings and then slices was representing crossover sign positive on plain determined the prevalence of AD with coexisting radio- radiograph. The a angle and HNOR were measured in logical FAI. FAI was classified into cam and pincer multiple radial slices, namely clockwise system, using previ- deformities. Cam deformity was defined as an a angle ously described methods [23–25](Fig. 3). We defined an of55 [28], HP positivity [29], PGD positivity [29]or Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 Acetabular dysplasia with coexisting femoroacetabular impingement  139 Fig. 2. Measurement of the acetabular version angle in four axial slices. (A) Reference plane for measuring the acetabular version angle. Each line represents one of the four slices; a slice at the level of the superior margin of the femoral head (slice A1), a slice 5 mm below the superior margin of the femoral head (slice A2), a slice 10 mm below the superior margin of the femoral head (slice A3) and a slice 15 mm below the superior margin of the femoral head (slice A4). (B) Axial slice of A1. Angle ø is the acetabular ver- sion angle. Fig. 3. Measurement of the a-angle and HNOR in multiple radial slices (clockwise system). (A) Reference plane for measuring the a-angle and HNOR. The dotted line is the axis through the center of the femoral neck. It is adjusted to be parallel to the femoral neck–shaft angle. The solid line is the reference plane for radial angle reconstruction. (B) The reconstructed three-dimensional image demonstrates superimposed radial reference lines at 15 intervals. R1 (3:00 o’clock) is the oblique axial slice (dotted line in A). R2 (2:30 o’clock) is a plane rotated 15 from R1. R3 (2:00 o’clock) is a plane rotated 30 from R1. R4 (1:30 o’clock) is a plane rotated 45 from R1. R5 (1:00 o’clock) is a plane rotated 60 from R1. R6 (12:30 o’clock) is a plane rotated 75 from R1. (C) Angle ø is the a-angle. The a-angle is the angle between the line joining the center of the femoral head and the center of the femoral neck, and the line from the center of the femoral head to the point where the spherical image of the femoral head is lost. The HNOR was calculated by dividing the anterior offset (asterisk) by the maximum diameter of the femoral head of each slice. The anterior offset is the thick- ness of the femoral head that lies anterior to a line passing the anterior wall of the femoral neck that is parallel to a line crossing the center of the femoral head and neck. an HNOR of<0.13 [28]. Pincer deformity was defined as Radiological examination and standardization of CT images AI of0 [29] or the presence of an RA. Hips with both All CT images were axial and sequential and were obtained cam and pincer deformities were considered to have a in the supine position without gantry tilt (120 kV, 160 mA, combined deformity. Prevalence was defined as the pro- 0.5 s) using a Toshiba Aquilion CX (Toshiba Medical portion of hips that fulfilled a specific definition among all Systems Corporation, Tokyo, Japan). The data were of the hips in this study. Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 140  T. Mimura et al. any horizontal distance was present between the tip of the coccyx and the pubic symphysis [30]) and (3) the neutral pelvic tilt (investigated the distance between the upper border of the symphysis and the midportion of the sacro- coccygeal joint, as described previously [29, 30]). In this study, 32 mm6 10 mm in men and 476 10 mm in women were considered neutral [30]. Statistical methods Data are expressed as mean6 standard deviation. All stat- istical analyses were performed using StatView version 5.0 (SAS Institute, Cary, NC, USA). The significance of differ- ences between men and women was evaluated using the Wilcoxon rank-sum test and v test. Values of P< 0.05 were considered to indicate statistical significance. The 95% confidence interval (CI) was estimated based on the score test for prevalences. To evaluate the intraobserver re- liability and interobserver reliability between the two ob- servers (senior orthopedic surgeons) who were blinded to the each other’s results, the intraclass correlation coeffi- Fig. 4. We defined an HP as a cystic-like lesion underneath the anterior cortex at the anterosuperior femoral head–neck junction cients (ICCs) of the CE angle, Sharp angle, AI, acetabular with clear demarcation and a diameter of>3 mm. A HP (arrow) version angle, a angle and HNOR were evaluated using was evaluated in multiradial six slices. SPSS statistics 22.0 for Windows (IBM Corp., Armonk, NY, USA) at least 2 weeks apart. Observer agreement was considered unacceptable if the value was less than 0.40, moderate if the value was 0.41–0.60, substantial if the value was 0.61–0.80, and almost perfect if the value was greater than 0.80. RESULTS Table I shows the mean age and parameters of all patients and of men and women. Table II shows the prevalence of each type of AD and FAI-related findings in all patients, men and women. Overall, AD was detected in 35.9% of hips (46/128) [29.7% (19/64) in men, 42.2% (27/64) in women; P¼ 0.140] (data not shown). A total of 76.6% of hips (98/128) met at least one criterion of the definition of cam or pincer deformity [89.1% (57/64) in men, 64.1% (41/64) in women; P< 0.001] (data not shown). Fig. 5. The presence of a PGD was subjectively judged on recon- structed three-dimensional reconstructed computed tomography Table III shows the prevalence of each combination images. This case was judged to be PGD-positive bilaterally of the coexistence of AD and FAI-related deformities. (arrow). Figure 6 was the representative case of definite AD with coexisting cam deformity. The prevalence of borderline AD with coexisting FAI (15.6%, 20/128) was times higher reconstructed under conditions suitable for bone evalu- ation using AquariusNet Viewer software (TeraRecon Inc., than that of definite AD with coexisting FAI (7.8%, 10/ San Francisco, CA, USA). We used the three-dimensional 128). Altogether, the coexistence of AD and any type of reconstructed CT images to confirm the pelvic rotation FAI-related deformity was detected in 23.4% (30/128) of all hips. The prevalence of AD with a coexisting cam de- and tilt. We confirmed (1) the rotation in the coronal plane (confirmed whether the teardrop line was horizon- formity was higher than that of AD with a coexisting pincer tal), (2) the rotation in the axial plane (examined whether deformity regardless of sex. No significant difference was Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 Acetabular dysplasia with coexisting femoroacetabular impingement  141 Table I. Mean age and data for each parameter in all patients, men and women All subjects (128 hips) Males (64 hips) Females (64 hips) P-value Age (years) 56.3615.8 (21–84) 57.2616.1(21–83) 55.5615.48 (31–84) 0.520* CE angle ( ) 31.667.0 (15.4–47.8) 32.366.5 (17.6–45.7) 30.967.3 (15.4–47.8) 0.315* Sharp angle ( ) 40.1 6 6.9 (31.8–54.8) 39.3 6 4.1 (31.8–54.8) 40.9 6 3.3 (31.9–49.1) 0.003* Acetabular index ( ) 6.769.2 (7.9–22.8) 6.6611.3 (7.5–22.8) 6.866.4 (7.9–22.3) 0.195* Acetabular version A1 ( ) 9.068.6 (14.9–31.3) 7.869.9 (7.2–29.0) 10.368.8 (14.9–31.3) 0.043* A2 ( ) 12.069.0 (10.6–34.0) 9.968.6 (7.5–34.0) 14.068.8 (10.6–32.7) 0.003* A3 ( ) 16.768.7 (7.5–33.4) 15.168.1 (1.3–33.3) 18.269.1 (7.5–33.4) 0.025* A4 ( ) 19.667.8 (3.8–35.6) 18.266.8 (1.51–35.6) 20.968.5 (3.8–35.6) 0.030* a-angle R1 ( ) 40.365.1 (21.6–55.0) 41.665.0 (30.5–55.0) 39.065.0 (21.6–48.7) 0.011* R2 ( ) 42.865.7 (30.8–60.3) 44.066.1 (30.8–60.3) 41.764.9 (31.6–52.9) 0.025* R3 ( ) 46.065.9 (32.3–64.6) 46.966.5 (32.3–64.6) 45.065.1 (33.9–58.2) 0.130* R4 ( ) 48.565.9 (35.9–68.6) 49.066.5 (35.9–68.6) 47.965.2 (39.2–63.9) 0.413* R5 ( ) 49.066.9 (34.7–75.0) 51.467.0 (39.2–75.0) 47.765.9 (34.7–72.1) <0.001* R6 ( ) 46.967.4 (33.1–74.7) 49.567.4 (34.1–74.7) 44.364.9 (33.1–53.7) <0.001* HNOR R1 0.24560.03 (0.159–0.371) 0.24360.03 (0.159–0.333) 0.24860.04 (0.165–0.371) 0.504* R2 0.24160.07 (0.123–0.349) 0.24560.09 (0.123–0.305) 0.23660.04 (0.156–0.349) 0.784* R3 0.20560.04 (0.080–0.336) 0.21160.05 (0.080–0.307) 0.20060.04 (0.115–0.336) 0.099* R4 0.16760.05 (0.036–0.323) 0.16560.05 (0.036–0.306) 0.16860.04 (0.113–0.323) 0.628* R5 0.14060.03 (0.054–0.270) 0.13660.03 (0.057–0.248) 0.14560.03 (0.054–0.270) 0.113* R6 0.14160.03 (0.056–0.263) 0.13260.03 (0.056–0.191) 0.15060.03 (0.065–0.263) 0.002* HP positive 17.2% (10.6%–23.7%) 24.6% (17.14%–32.06%) 9.2% (6.65%–11.75%) 0.019† PGD positive 14.0% (7.98%–20.01%) 20.0% (13.07%–26.92%) 12.3% (17.32%–28.68%) 0.041† Data are presented as mean6 standard deviation (range) or as percentage (95% CI). CE angle, center-edge angle; HNOR, head–neck offset ratio; HP, herniation pit; PGD, pistol grip deformity. A1, axial slice at the level of the superior margin of the femoral head; A2, axial slice 5 mm below the superior margin of the femoral head; A3, axial slice 10 mm below the superior margin of the femoral head; A4, axial slice 15 mm below the superior margin of the femoral head; R1, oblique axial plane through the center of the femoral neck, adjusted to be parallel to the femoral neck–shaft angle (3:00 o’clock); R2, radial plane cranially rotated 15 from R1 (2:30 o’clock); R3, ra- dial plane cranially rotated 30 from R1 (2:00 o’clock); R4, radial plane cranially rotated 45 from R1 (1: 30 o’clock); R5, radial plane cranially rotated 60 from R1 (1: 00 o’clock); R6, radial plane cranially rotated 75 from R1 (12:30 o’clock). *Male versus female, evaluated with the Wilcoxon rank-sum test. P-values of<0.05 were considered statistically significant. † 2 Male versus female, evaluated with v test. P-values of<0.05 were considered statistically significant. Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 142  T. Mimura et al. Table II. Detailed prevalence of AD and FAI-related findings in all patients, men, and women All subjects (128 hips) Males (64 hips) Females (64 hips) P-value* Definite AD CE angle <20 6.3% (8/128) 3.1% (2/64) 9.4% (6/64) 0.144 [3.2%–11.8%] [0.9%–10.7%] [4.4%–19.0%] Sharp angle >45 7.8% (10/128) 6.3% (4/64) 9.4% (6/64) 0.439 [4.3%–13.8%] [2.5%–15.0%] [4.4%–19.0%] Total 11.7% (15/128) 7.8% (5/64) 15.6% (10/64) 0.169 [7.2%–18.4%] [3.4%–17.0%] [8.7%–26.4%] Borderline AD 20  CE angle <25 12.5% (16/128) 12.5% (8/64) 12.5% (8/64) 1 [7.8%–19.3%] [6.5%–22.8%] [6.5%–22.8%] 42 < Sharp angle 45 21.9% (28/128) 15.6% (10/64) 28.1% (18/64) 0.087 [15.6%–29.8%] [8.7%–26.4%] [18.6%–40.1%] Total 24.2% (31/128) 21.9% (14/64) 26.6% (17/64) 0.536 [17.6%–32.3%] [13.5%–33.4%] [17.3%–38.5%] Cam deformity a angle 55 28.9% (37/128) 40.6% (26/64) 17.2% (11/64) 0.003 [21.8%–37.3%] [29.5%–52.9%] [9.9%–28.2%] HNOR <0.13 58.6% (75/128) 65.6% (42/64) 51.6% (33/64) 0.106 [49.9%–66.9%] [53.4%–76.1%] [39.6%–63.4%] PGD positive 14.1% (18/128) 20.3% (13/64) 7.8% (5/64) 0.041 [9.1%–21.1%] [12.3%–31.7%] [3.4%–17.0%] HP positive 17.2% (22/128) 25.0% (16/64) 9.4% (6/64) 0.016 [11.6%–24.7%] [16.0%–36.8%] [4.4%–19.0%] Total 68.0% (87/128) 79.7% (51/64) 56.3% (36/64) 0.004 [59.5%–75.4%] [68.3%–87.7%] [44.1%–67.7%] Pincer deformity Acetabular index 0 18.0% (23/128) 20.3% (13/64) 15.6% (10/64) 0.489 [12.3%–25.5%] [12.3%–31.7%] [8.7%–26.4%] RA 12.5% (16/128) 17.2% (11/64) 7.8% (5/64) 0.108 [7.8%–19.3%] [9.9%–28.2%] [3.4%–17.0%] Total 28.9% (37/128) 37.5% (24/64) 20.3% (13/64) 0.031 [21.8%–37.3%] [26.7%–49.7%] [12.3%–31.7%] Combined deformity 20.3% (26/128) 28.1% (18/64) 12.5% (8/64) 0.028 [14.3%–28.1%] [18.6%–40.1%] [6.5%–22.8%] Data are shown as percentage [95% CI]. AD, acetabular dysplasia; FAI, femoroacetabular impingement; CE, center-edge angle; PGD, pistol grip deformity; HP, her- niation pit; HNOR, head–neck offset ratio; RA, retroverted acetabulum. *Male versus female, evaluated with v test. P-values of<0.05 were considered statistically significant. Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 Acetabular dysplasia with coexisting femoroacetabular impingement  143 Table III. Prevalence of each combination of coexistence of AD and FAI-related deformities All subjects Males Females P-value* (128 hips) (64 hips) (64 hips) Definite AD and FAI-related deformities 7.8% (10/128) 7.8% (5/64) 7.8% (5/64) 1 [4.3%–13.8%] [3.4%–17.0%] [3.4%–17.0%] Definite AD þ cam deformity 6.3% (8/128) 4.7% (3/64) 7.8% (5/64) 0.465 [3.2%–11.8%] [1.6%–12.9%] [3.4%–17.0%] Definite AD þ pincer deformity 0% (0/128) 0% (0/64) 0% (0/64) – [0%–2.9%] [0%–5.7%] [0%–5.7%] Definite AD þ combined deformity 1.6% (2/128) 3.1% (2/64) 0% (0/64) 0.154 [0.4%–5.5%] [0.9%–10.7%] [0%–5.7%] Borderline AD and FAI-related deformities 15.6% (20/128) 20.3% (13/64) 10.9% (7/64) 0.144 [10.3%–22.9%] [12.3%–31.7%] [5.4%–20.9%] Borderline AD þ cam deformity 13.3% (17/128) 17.2% (11/64) 9.4% (6/64) 0.193 [8.5%–20.2%] [9.9%–28.2%] [4.4%–19.0%] Borderline AD þ pincer deformity 1.6% (2/128) 1.6% (1/64) 1.6% (1/64) 1 [0.4%–5.5%] [0.3%–8.3%] [0.3%–8.3%] Borderline AD þ combined deformity 0.8% (1/128) 1.6% (1/64) 0% (0/64) 0.315 [0.1%–4.3%] [0.3%–8.3%] [0%–5.7%] AD in total (definite and borderline) and 23.4% (30/128) 28.1% (18/64) 18.7% (12/64) 0.210 FAI-related deformities [16.9%–31.5%] [18.6%–40.1%] [11.1%–30.0%] AD in total (definite and borderline) þ cam deformity 19.5% (25/128) 21.9% (14/64) 17.2% (11/64) 0.504 [13.6%–27.2%] [13.5%–33.4%] [9.9%–28.2%] AD in total (definite and borderline) þ pincer deformity 1.6% (2/128) 1.6% (1/64) 1.6% (1/64) 1 [0.4%–5.5%] [0.3%–8.3%] [0.3%–8.3%] AD in total (definite and borderline) þ combined deformity 2.3% (3/128) 4.7% (3/64) 0% (0/64) 0.079 [0.8%–6.7%] [1.6%–12.9%] [0%–5.7%] Data are shown as percentage [95% CI]. AD, acetabular dysplasia; FAI, femoroacetabular impingement. *Male versus female, evaluated with v test. P-values of<0.05 were considered statistically significant. observed in any combination of AD and FAI-related de- words, 65.2% of hips (30/46) with AD had some FAI- formity between men and women. related findings. Table IV shows the percentage of each type of AD with Table V shows the detailed percentage of each type of coexisting cam, pincer and combined deformities com- AD with coexisting cam, pincer and combined deformities pared with total AD (definite and borderline). The per- in men and women compared with total AD. There was no centage of AD with a coexisting cam deformity (54.3%, combination of AD and FAI-related findings which showed 25/46) was much higher than that of AD with coexisting that the corresponding percentage in women was higher pincer (4.3%, 2/46). The percentage of AD without coex- than that in men. The percentages of total AD with a coex- isting FAI-related findings was 34.8% (16/46); in other isting cam deformity and total AD with a coexisting Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 144  T. Mimura et al. Fig. 6. The representative case of the hip of AD with coexisting FAI-related findings. This case was 50 years old women, left hip was defined as a hip of borderline AD with coexisting cam deformity. (A) CE angle, Sharp angle and AI was 21 ,44 and 20 , respectively. (B) The acetabular version angle was 7 at a slice at the level of the superior margin of the femoral head (slice A1). (C) The a-angle and HNOR at a slice of R4 (1:30 o’clock) was 57 and 0.125, respectively. HP was also positive. (D) PGD was negative. According to the CE and Sharp angle, this hip was defined as a borderline AD. On the other hand, this hip was also defined as a cam deformity due to a-angle> 55 , HNOR< 0.13 and HP positive. However, this hip did not coexist with a pincer deformity, because the AI was over 0 and acetabular version angle was not negative. Table IV. Corresponding percentage of each type of AD with coexisting cam, pincer and combined deformities and without coexisting FAI-related findings compared with all numbers of each type of AD in all patients With coexisting With coexisting With coexisting Without coexisting cam deformity pincer deformity combined deformity FAI-related findings Definite AD (n ¼ 15) 53.3% (8/15) 0% (0/15) 13.3% (2/15) 33.3% (5/15) [30.1%–75.2%] [0%–20.4%] [3.7%–37.9%] [15.2%–58.3%] Borderline AD (n ¼ 31) 54.8% (17/31) 6.5% (2/31) 3.2% (1/31) 35.5% (11/31) [37.8%–70.8%] [1.8%–20.7%] [0.6%–16.2%] [21.1%–53.1%] AD in total (definite and borderline) (n ¼ 46) 54.3% (25/46) 4.3% (2/46) 6.5% (3/46) 34.8% (16/46) [40.2%–67.8%] [1.2%–14.5%] [2.2%–17.5%] [22.7%–49.2%] Data are shown as percentage [95% CI]. AD, acetabular dysplasia; FAI, femoroacetabular impingement. combined deformity were significantly higher in men than The ICCs of the intraobserver and interobserver reli- women (P¼ 0.0272 and P¼ 0.0327, respectively). ability of all parameters were almost perfect (0.80). Conversely, the percentages of total AD without coexisting FAI-related findings were significantly higher in women DISCUSSION (P¼ 0.0004). AD and FAI have been thoroughly discussed as a cause of hip OA [1, 2, 6, 7]. However, the prevalence and morpho- Table VI shows the corresponding percentages of the combinations of the coexistence of each type of AD and logical features of the coexistence of AD and FAI have not each FAI-related finding compared with all hips. The most been well discussed. In the present study, we showed the major features of cam deformities coexisting with definite prevalence of AD with coexisting pincer, cam and com- AD and borderline AD were an HNOR of<0.13. On the bined deformities, and also the frequency with which FAI- other hand, the major feature of pincer deformities coexist- related findings coexist with definite and borderline AD in ing with definite AD and borderline AD were RA. No sig- asymptomatic Japanese population. To the best of our nificant differences were found in the corresponding knowledge, there is scarce literature on this topic. percentages of the coexistence of each type of AD and Several authors have discussed the coexistence of cam each FAI-related finding between men and women. deformity and AD in symptomatic populations. Ida et al. [9] Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 Acetabular dysplasia with coexisting femoroacetabular impingement  145 Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 Table V. Comparison of corresponding percentage of AD with coexisting cam, pincer and combined deformities and without coexisting FAI- related findings compared with all numbers of each type of AD between men and women With coexisting With coexisting With coexisting Without coexisting cam deformity pincer deformity combined deformity FAI-related findings Definite AD (n ¼ 5 in male, Male Female Male Female Male Female Male Female n ¼ 10 in female) 60% (3/5) 50% (5/10) 0% (0/5) 0% (0/10) 40% (2/5) 0% (0/10) 0%(0/5) 50%(5/10) [23.1%–88.2%] [23.7%–76.3%] [0%–43.4%] [0%–27.8%] [11.8%–76.9%] [0%–27.8%] [0%–43.3%] [23.7%–76.3%] P¼0.7144 P¼0.0317P¼0.0528 Borderline AD (n ¼ 14 in male, Male Female Male Female Male Female Male Female n ¼ 17 in female) 78.6% (11/14) 35.3% (6/17) 7.1% (1/14) 5.9% (1/17) 7.1% (1/14) 0% (0/17) 7.1% (1/14) 58.8% (10/17) [52.4%–92.4%] [17.3%–58.7%] [1.3%–31.5%] [1.0%–27.0%] [1.3%–31.5%] [0%–18.4%] [1.3%–31.5%] [36.0%–78.4%] P¼0.0032P¼0.8869P¼0.3113P¼0.00276 AD in total (n ¼ 19 in male, Male Female Male Female Male Female Male Female n ¼ 27 in female) 73.7% (14/19) 40.7% (11/27) 5.3% (1/19) 3.7% (1/27) 15.8% (3/19) 0% (0/27) 5.3% (1/19) 55.6% (15/27) [51.2%–88.2%] [24.5%–59.3%] [0.9%–24.6%] [0.7%–18.3%] [5.5%–37.6%] [0%–12.5%] [0.9%–24.6%] [37.3%–72.4%] P¼0.0272P¼0.7984P¼0.0327P¼0.0004 Data are shown as percentage [95% CI]. AD, acetabular dysplasia; FAI, femoroacetabular impingement. P values were evaluated with the v test. P values of<0.05 were considered statistically significant. 146  T. Mimura et al. Table VI. Corresponding percentage of combination of coexistence with each type of AD and each FAI-related finding compared with all hips with coexistence of each type of AD (definite or borderline) and each FAI- related deformity (cam or pincer deformity) All subjects Males Females P-value* Definite AD þ cam deformity Definite AD þ a angle 55 40% (4/10) 40.0% (2/5) 40.0% (2/5) 1 [16.8%–68.7%] [11.8%–76.9%] [11.8%–76.9%] Definite AD þ HNOR < 0.13 100% (10/10) 100% (5/5) 100% (5/5) – [72.2%–100%] [56.6%–100%] [56.6%–100%] Definite AD þ PGD positive 10% (1/10) 20% (1/5) 0% (0/5) 0.292 [1.8%–40.4%] [3.6%–62.4%] [0%–43.3%] Definite AD þ HP positive 20% (2/10) 20% (1/5) 20% (1/5) 1 [5.7%–51.0%] [3.6%–62.4%] [3.6%–62.4%] Definite AD þ pincer deformity Definite AD þ acetabular index 0 0% (0/2) 0% (0/2) (0/0) – [0%–65.8%] [0%–65.8%] Definite AD þ RA 100% (2/2) 100% (2/2) (0/0) – [34.2%–100%] [34.2%–100%] Borderline AD þ cam deformity Borderline AD þ a angle 55 55.6% (10/18) 41.7% (5/12) 83.3% (5/6) 0.094 [33.7%–75.4%] [19.3%–68.0%] [43.6%–97.0%] Borderline AD þ HNOR < 0.13 88.9% (16/18) 83.3% (10/12) 100% (6/6) 0.249 [67.2%–96.9%] [55.2%–95.3%] [61.0%–100%] Borderline AD þ PGD positive 27.8% (5/18) 25.0% (3/12) 33.3% (2/6) 0.709 [12.5%–50.9%] [8.9%–53.2%] [9.7%–70.0%] Borderline AD þ HP positive 22.2% (4/18) 33.3% (4/12) 0% (0/6) 0.109 [9.0%–45.2%] [13.8%–60.9%] [0%–39.0%] Borderline AD þ pincer deformity Borderline AD þ acetabular index 0 33.3% (1/3) 0% (0/2) 100% (1/1) 0.083 [6.1%–79.2%] [0%–65.8%] [20.7%–100%] Borderline AD þ RA 66.7% (2/3) 100% (2/2) 0% (0/1) 0.083 [20.8%–93.9%] [34.2%–100%] [0%–79.3%] Data are shown as percentage [95% CI]. AD, acetabular dysplasia; FAI, femoroacetabular impingement; PGD, pistol grip deformity; HP, herniation pit; HNOR, head–neck offset ratio; RA, retroverted acetabulum. *Male versus female, evaluated with v test. P-values of<0.05 were considered statistically significant. reported the frequency of cam deformity in hips with Clohisy et al. [8] found that femoral head asphericity symptomatic AD. They found that 40% of patients with was present in 72% and reduced head–neck offset was also AD had radiological evidence of cam deformity (a angle presented in 75% of symptomatic AD. Furthermore, Wyles of>55 ) on lateral roentgenograms. On the other hand, et al. [11] reported that patients with coexisting AD and Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 Acetabular dysplasia with coexisting femoroacetabular impingement  147 cam deformity developed hip OA more rapidly rather plain radiograph examination (Inoue et al. [3], 8.1%; Umer than patients with AD. From this study, we are agreed to et al. [32], 7.3%). However, direct comparison of our re- these previous reports showed the high prevalence of sults with their results is difficult because the evaluation coexistence of AD and cam-related findings, and clinical methods were different. We recognize that these angles importance of them. However, previous studies have showed discrepancy between CT images and plain radio- evaluated the coexistence of AD and cam-related findings graphs. Actually, Chadayammuri et al. [33] reported dis- only using simple plain radiographs. In the present study, crepancies in the CE angle between plain radiographs and we revealed the coexistence of several FAI-related findings CT images. They found that the CE angle measured on and AD (including borderline) using multislice CT images CT images was 2.1 larger than that of measured on plain and also compared the results between men and women. radiographs. Considering these facts, our results might We emphasized the prevalence of borderline AD with coex- overestimate the prevalence of AD rather than the studies isting cam deformity was 15.6%, which was two times higher that measured these parameters using plain radiograph. than that of definite AD with coexisting cam deformity. However, we believe that CT images are more suitable Therefore, we consider that more attention should be given than plain radiographs with respect to correct measure- to the coexistence of borderline AD and cam deformity. ment of AD parameters because we can more easily detect Furthermore, the percentage of hips with AD and a coexist- the bony morphological features of the acetabulum, espe- ing cam deformity was significantly higher in men than cially the lateral point of the acetabular dome, and we can women. Therefore, we also suppose that more attention also accurately evaluate the acetabular bony coverage in should be given to the coexistence of AD and cam the center of the femoral head. Furthermore, the ICCs for deformity especially in men. Additionally, we showed that the interobserver reliability of the CE angle and Sharp the most major feature of cam-related findings detected in angle were 0.83 and 0.94 in this study, respectively. Mast definite and borderline AD in Japanese hips was reduced et al. [34] and Tan et al. [35] reported that the ICCs for HNOR. the interobserver reliability of the CE angle evaluated on The percentage of hips with definite AD with coexisting plain radiographs were 0.73 and 0.51, respectively. We be- pincer-related findings compared with all hips with definite lieve that CT images allow for calculation of a more accur- AD was 0%, and the prevalence of borderline AD with co- ate prevalence of AD than do plain radiographs. existing pincer-related findings compared with all hips with In the present study, we defined a CE angle of<20 as borderline AD was only 6.5%. Fujii et al. [10] reported indicative of definite AD and a CE angle of 20 to<25 as that an RA was observed in 18% of Japanese patients with indicative of borderline AD. These cut-off values have been symptomatic AD. They showed that AD with an RA was widely utilized in the literature [4, 5]. We also defined a associated with an earlier onset of pain than AD with ante- Sharp angle of>45 as indicative of definite AD and a version. However, Troelsen et al. [31] reported that an RA Sharp angle of>42 to 45 as indicative of borderline AD. was found in one-third of hips with AD when assessed on A Sharp angle of>45 has been widely used to define the weight-bearing pelvic radiographs. They also reported that presence of definite AD in the literature [5]. However, few the prevalence of an RA may be underestimated if the eval- reports have described the cut-off of Sharp angle for the uated images are obtained from patients in the supine pos- definition of borderline AD. Paliobeis and Villar [4] re- ition. Therefore, we might have underestimated the ported that a Sharp angle of>39 to 42 was indicative of coexistence of AD and pincer-related findings in the pre- borderline AD and that a Sharp angle of>42 was indica- sent study because we used CT images and excluded the tive of definite AD. If we had used these definitions in the pelvis anteriorly rotated rather than normal range from present study, the prevalence of borderline AD as diag- present study. Although the percentage of AD with coexist- nosed by a Sharp angle of>39 to 42 would have been ing pincer deformity was lower than that of AD with coex- 28.9%, and that of definite AD as diagnosed by a Sharp isting cam deformity, we had better understand that the angle of>42 would have been 29.7%; the prevalence of coexistence of pincer deformity in men was slightly higher total AD would have been 58.6%. However, these preva- than that in women. In such hips, we should pay more at- lences are much higher than those defined using the CE tention to a RA as a morphological finding of pincer angle in our study and much higher than the previously re- deformity. ported prevalences of definite AD [3, 32]. Sharp [14] ori- We employed two parameters for the definition of AD ginally reported that angles of 39 –42 were within the in the present study. As a result, we detected definite AD upper limit of normality. Therefore, we defined a Sharp in 11.7% of the Japanese hip joints in this study, which is angle of>45 as indicative of definite AD and a Sharp relatively higher than in previous Asian studies based on angle of>42 to 45 as indicative of borderline AD in the Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 148  T. Mimura et al. present study. On the other hand, we did not define AD percentages did not generally change, if HP and PGD posi- using AI in the present study. Namely, we did not distin- tivity were excluded from the parameter of cam deformity. guish between ‘flat roof (short roof) dysplasia’ and ‘sloping Although, AD and FAI were originally independent roof dysplasia’ [36, 37]. Brockwell et al. [36] suggested concepts, we consider that simultaneous evaluation of AD that a sloping roof dysplasia was so-called primary dyspla- and FAI would be informative from the viewpoint of pre- sia or classical dysplasia which has instability and a flat roof venting the progression of hip OA. Actually, we found that dysplasia was essentially taking with cam impingement. only 34.8% of hips with AD were free from the coexistence They described that a flat roof dysplasia was brought by of FAI-related findings when we investigated AD using the impingement between iliac acetabular epiphysis and multislice CT images in Japan. Furthermore, we revealed cam deformity in adolescence. In the present study, we did that the major and notable parameter of a cam deformity not discuss these morphologies of AD. If we classified and detected in hips with AD was a HNOR. We consider that discussed these morphologies of AD, we believed that the it is important to correctly evaluate the coexistence of AD results would be different. and radiological FAI-related findings when discussing mor- This study has some limitations. First, it was not phological disorders of the hip joint. However, it still re- population-based, but patient-based. This is an inescapable mains unclear what additional procedure (debridement, limitation of this study. However, our aim in this study was labral fixation or osteochodroplasty of cam lesion) is not to simply investigate the prevalence of AD with coex- needed and suitable when we perform acetabular osteot- isting radiological FAI but to evaluate its prevalence using omy for AD with coexisting FAI [38]. Further research will detailed multislice and multiplane examinations. Therefore, be needed to indicate how to manage FAI-related findings we investigated the patients’ CT images from scans that coexisting with AD. had been requested by other departments at our institution In conclusion, we found that the coexistence of AD and for evaluation of conditions unrelated to hip disorders. FAI-related findings was common in Japanese population, Second, we excluded clear hip OA in order to precisely and 65.2% of hips with AD had some FAI-related findings. measure morphological parameters. We understand that The prevalence of borderline AD with coexisting FAI was AD and FAI are generally thought to be lead to hip OA. much higher than that of definite AD with coexisting FAI, Therefore, we recognized that this might lead to potential and the percentage of AD with coexisting FAI-related find- selection bias and an underestimation of the prevalence of ings in men was higher rather than that in women. We also AD or FAI. Third, the sample size was relatively small, and found that AD with coexisting cam-related findings was this study was performed in a single hospital. We recognize considerably more common than AD with coexisting that it might be incorrect to generalize our results to region pincer-related findings, and the most notable parameter as throughout Japan. Finally, we employed four parameters to a morphological feature of cam deformity detected in such define cam deformity, and we employed two parameters to hips was a HNOR. define pincer deformity. We recognize that the prevalence of AD with coexisting FAI-related findings would be differ- CONFLICT OF INTEREST STATEMENT ent if we had employed other parameters for definition of None declared. FAI-related deformities or altered the number of param- eters used to define cam or pincer deformity. For example, a HP is generally thought to be a predictor of FAI [29, REFERENCES 25]. However, Kim et al. [27] indicate that a HP may have 1. Murphy SB, Ganz R, Muller ME. The prognosis in untreated dys- limited significance as a predictor of FAI. Furthermore, a plasia of the hip. A study of radiographic factors that predict out- angle would be naturally more than 55 , if PGD was come. J Bone Joint Surg Am 1995 Jul; 77: 985–9. existed. Therefore, we supposed that the results would be 2. Takeyama A, Naito M, Shiramizu K, Kiyama T. Prevalance of different, if HP and PGD positivity were excluded as a par- femoroacetabular impingement in Asian patients with osteoarth- ritis of the hip. 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J Bone Joint Surg Br 21. Harris WH. Aetiology of osteoarthritis of the hip. Clin Orthop 1991; 73: 423–9. Relat Res 1986 Dec; 213: 20–33. 38. Goronzy J, Franken L, Hartmann A et al. What were the results of 22. Reynolds D, Lucas J, Klaue K. Retroversion of the acetabulum. A surgical treatment of hip dysplasia with concomitant cam deform- cause of hip pain. J Bone Joint Surg Br 1999; 81: 281–8. ity? Clin Orhop Relat Res 2017; 475: 1128–37. Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Hip Preservation Surgery Oxford University Press

Prevalence and morphological features of acetabular dysplasia with coexisting femoroacetabular impingement-related findings in a Japanese population: a computed tomography-based cross-sectional study

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Journal of Hip Preservation Surgery Vol. 5, No. 2, pp. 137–149 doi: 10.1093/jhps/hny006 Advance Access Publication 12 March 2018 Research article Prevalence and morphological features of acetabular dysplasia with coexisting femoroacetabular impingement-related findings in a Japanese population: a computed tomography-based cross-sectional study Tomohiro Mimura*, Kanji Mori, Yuki Furuya, Shin Itakura, Taku Kawasaki and Shinji Imai Department of Orthopedic Surgery, Shiga University of Medical Science, Tsukinowa-cho, Seta, Otsu, Shiga 520-2192, Japan *Correspondence to: T. Mimura. E-mail: tmimura@belle.shiga-med.ac.jp Submitted 19 August 2017; Revised 14 January 2018; revised version accepted 11 February 2018 ABSTRACT The coexistence of acetabular dysplasia (AD) and femoroacetabular impingement (FAI) has not been well dis- cussed. This study was performed to elucidate the prevalence and morphological features of AD with coexisting FAI-related findings in a Japanese population. Computed tomography images were retrospectively evaluated. AD was classified as definite or borderline. The morphological findings that defined cam deformity were an a angle of55 , head–neck offset ratio (HNOR) of<0.13, pistol grip deformity positivity and herniation pit positivity. The morphological findings that defined pincer deformity were acetabular index of0 and a retroverted acet- abulum. In total, 128 hips (male, 64; female, 64) were analyzed. The prevalence of coexistence of AD and FAI- related findings was detected in 23.4% of hips (definite AD and FAI, 7.8%; borderline AD and FAI, 15.6%). The percentages of hips with AD containing cam or pincer deformities among all were 54.3% and 4.3%, respectively. The percentage of AD with coexisting cam and that of AD with coexisting combined deformities was significantly higher in men, respectively. On the other hand, the most major morphological feature of FAI detected in hips with AD was a HNOR of<0.13. The coexistence of AD and FAI-related findings was common in a Japanese population, and 65.2% of hips with AD had some FAI-related findings. In discussing and managing AD, we rec- ommend paying attention to the coexistence with FAI-related findings, especially in men and in borderline AD. In such hips, the most notable parameter as a morphological feature of FAI is a reduced HNOR. deformity, pincer deformity, combined deformities and INTRODUCTION sports impingement, where a hip with normal anatomy im- Acetabular dysplasia (AD) is a well-recognized cause of pinges in extreme positions in sporting activity. osteoarthritis (OA) of the hip [1]. In Japan, AD is a major The anatomical abnormalities associated with AD and FAI risk factor for OA [2], and the prevalence of AD is higher have been discussed as independent anatomical features. in Japanese than in Western populations [3]. Furthermore, Several recent reports have described the coexistence of definite AD and borderline AD are often distinguished in AD and FAI-related findings in patients with symptomatic the clinical setting [4, 5]. Femoroacetabular impingement AD or FAI [8–11]. However, the prevalence and morpho- (FAI) has also been highlighted, and an association be- logical features of the coexistence of AD (especially border- tween FAI and hip OA has been identified [6, 7]. FAI has line AD) and FAI-related findings are not well known in been thought to be divided into four categories: cam V C The Author(s) 2018. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 138  T. Mimura et al. Japanese populations who are generally assumed to have AD rather than Western populations. The aim of this study was to investigate the detailed prevalence and morpho- logical features of AD with coexisting FAI-related findings using multislice computed tomography (CT) images in a Japanese population. MATERIALS AND METHODS Patients and parameters The ethics committee of our institution approved the study protocol. We conducted a retrospective patient-based study of patients who had undergone CT imaging of the chest, abdomen and pelvis. We reviewed all CT data from 1 July 2013–14 August 2013 in our institution. First, we selected the scans that had been ordered by other departments at our institution and confirmed that the CT examination had been performed for conditions unrelated to hip disorders based on the information in the clinical record. Next, we se- lected 65 consecutive patients irrespective of sex who ful- filled the criteria described below. The inclusion criteria for the present study were as follows: (1) involvement of the Fig. 1. Measurement of CE angle, Sharp angle and AI. These whole pelvis and both hip joints, (2) reconstructed axial angles were measured on a slice of femoral head center in the slice thickness of1 mm and (3) normal pelvic rotations coronal plane. h1, h2, and h3 is CE angle, Sharp angle and AI, re- and tilt (specified below in the section describing standard- spectively. CE angle was measured as the angle between the line ization of CT images). The exclusion criteria were as joining the lateral aspect of the acetabulum and the femoral head center, and the line perpendicular to the line parallel to the trans- follows: (1) age of<20 years, (2) inability to clearly detect verse axis of the pelvis. Sharp angle was measured as the angle the center of the femoral head, such as in patients with between the line joining the lateral aspect of the weight bearing an elliptical femoral head and (3) inability to correctly zone and the inferior point of teardrop, and the line parallel to measure the parameters, such as clear hip OA that had the transverse axis of the pelvis. AI was measured as the angle be- the osteophyte formation, the loss of joint space and tween the line joining the medial and lateral aspects of the weight subchondral bone cysts [12]. bearing zone, and the line parallel to the transverse axis of the Both hips were analyzed in each patient. Two male hips pelvis. were excluded because of a metaphyseal bone tumor in each. As a result, 128 hips (64 male hips and 64 female hips) were evaluated. The examined parameters and find- HP as a cystic-like lesion underneath the anterior cortex at ings were age, sex, center-edge (CE) angle [13], Sharp the anterosuperior femoral head–neck junction with a clear angle [14], acetabular index (AI) [15], acetabular version demarcation [26] and a diameter of>3mm [27](Fig. 4). angle [16], a angle [17], head–neck offset ratio (HNOR) HP was evaluated at the above-described multiradial slices. [18], herniation pit (HP) [19] and pistol grip deformity The presence of a PGD was subjectively determined using (PGD) [20, 21]. reconstructed three-dimensional CT images (Fig. 5). AD CE angle, Sharp angle and AI were measured on a slice was classified into definite AD and borderline AD. Definite of the femoral head center in the coronal plane (Fig. 1). AD was defined as a CE angle of<20 or a Sharp angle The acetabular anteversion angle was measured in four of>45 . Borderline AD was defined as a CE angle of 20 axial slices (Fig. 2). We defined an acetabulum with a nega- to<25 or a Sharp angle of>42 to 45 (hips already tive acetabular anteversion angle in any slice (A1, A2, A3 defined as definite AD were excluded). We investigated or A4) as a retroverted acetabulum (RA) [22]. RA of these the prevalence of these morphological findings and then slices was representing crossover sign positive on plain determined the prevalence of AD with coexisting radio- radiograph. The a angle and HNOR were measured in logical FAI. FAI was classified into cam and pincer multiple radial slices, namely clockwise system, using previ- deformities. Cam deformity was defined as an a angle ously described methods [23–25](Fig. 3). We defined an of55 [28], HP positivity [29], PGD positivity [29]or Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 Acetabular dysplasia with coexisting femoroacetabular impingement  139 Fig. 2. Measurement of the acetabular version angle in four axial slices. (A) Reference plane for measuring the acetabular version angle. Each line represents one of the four slices; a slice at the level of the superior margin of the femoral head (slice A1), a slice 5 mm below the superior margin of the femoral head (slice A2), a slice 10 mm below the superior margin of the femoral head (slice A3) and a slice 15 mm below the superior margin of the femoral head (slice A4). (B) Axial slice of A1. Angle ø is the acetabular ver- sion angle. Fig. 3. Measurement of the a-angle and HNOR in multiple radial slices (clockwise system). (A) Reference plane for measuring the a-angle and HNOR. The dotted line is the axis through the center of the femoral neck. It is adjusted to be parallel to the femoral neck–shaft angle. The solid line is the reference plane for radial angle reconstruction. (B) The reconstructed three-dimensional image demonstrates superimposed radial reference lines at 15 intervals. R1 (3:00 o’clock) is the oblique axial slice (dotted line in A). R2 (2:30 o’clock) is a plane rotated 15 from R1. R3 (2:00 o’clock) is a plane rotated 30 from R1. R4 (1:30 o’clock) is a plane rotated 45 from R1. R5 (1:00 o’clock) is a plane rotated 60 from R1. R6 (12:30 o’clock) is a plane rotated 75 from R1. (C) Angle ø is the a-angle. The a-angle is the angle between the line joining the center of the femoral head and the center of the femoral neck, and the line from the center of the femoral head to the point where the spherical image of the femoral head is lost. The HNOR was calculated by dividing the anterior offset (asterisk) by the maximum diameter of the femoral head of each slice. The anterior offset is the thick- ness of the femoral head that lies anterior to a line passing the anterior wall of the femoral neck that is parallel to a line crossing the center of the femoral head and neck. an HNOR of<0.13 [28]. Pincer deformity was defined as Radiological examination and standardization of CT images AI of0 [29] or the presence of an RA. Hips with both All CT images were axial and sequential and were obtained cam and pincer deformities were considered to have a in the supine position without gantry tilt (120 kV, 160 mA, combined deformity. Prevalence was defined as the pro- 0.5 s) using a Toshiba Aquilion CX (Toshiba Medical portion of hips that fulfilled a specific definition among all Systems Corporation, Tokyo, Japan). The data were of the hips in this study. Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 140  T. Mimura et al. any horizontal distance was present between the tip of the coccyx and the pubic symphysis [30]) and (3) the neutral pelvic tilt (investigated the distance between the upper border of the symphysis and the midportion of the sacro- coccygeal joint, as described previously [29, 30]). In this study, 32 mm6 10 mm in men and 476 10 mm in women were considered neutral [30]. Statistical methods Data are expressed as mean6 standard deviation. All stat- istical analyses were performed using StatView version 5.0 (SAS Institute, Cary, NC, USA). The significance of differ- ences between men and women was evaluated using the Wilcoxon rank-sum test and v test. Values of P< 0.05 were considered to indicate statistical significance. The 95% confidence interval (CI) was estimated based on the score test for prevalences. To evaluate the intraobserver re- liability and interobserver reliability between the two ob- servers (senior orthopedic surgeons) who were blinded to the each other’s results, the intraclass correlation coeffi- Fig. 4. We defined an HP as a cystic-like lesion underneath the anterior cortex at the anterosuperior femoral head–neck junction cients (ICCs) of the CE angle, Sharp angle, AI, acetabular with clear demarcation and a diameter of>3 mm. A HP (arrow) version angle, a angle and HNOR were evaluated using was evaluated in multiradial six slices. SPSS statistics 22.0 for Windows (IBM Corp., Armonk, NY, USA) at least 2 weeks apart. Observer agreement was considered unacceptable if the value was less than 0.40, moderate if the value was 0.41–0.60, substantial if the value was 0.61–0.80, and almost perfect if the value was greater than 0.80. RESULTS Table I shows the mean age and parameters of all patients and of men and women. Table II shows the prevalence of each type of AD and FAI-related findings in all patients, men and women. Overall, AD was detected in 35.9% of hips (46/128) [29.7% (19/64) in men, 42.2% (27/64) in women; P¼ 0.140] (data not shown). A total of 76.6% of hips (98/128) met at least one criterion of the definition of cam or pincer deformity [89.1% (57/64) in men, 64.1% (41/64) in women; P< 0.001] (data not shown). Fig. 5. The presence of a PGD was subjectively judged on recon- structed three-dimensional reconstructed computed tomography Table III shows the prevalence of each combination images. This case was judged to be PGD-positive bilaterally of the coexistence of AD and FAI-related deformities. (arrow). Figure 6 was the representative case of definite AD with coexisting cam deformity. The prevalence of borderline AD with coexisting FAI (15.6%, 20/128) was times higher reconstructed under conditions suitable for bone evalu- ation using AquariusNet Viewer software (TeraRecon Inc., than that of definite AD with coexisting FAI (7.8%, 10/ San Francisco, CA, USA). We used the three-dimensional 128). Altogether, the coexistence of AD and any type of reconstructed CT images to confirm the pelvic rotation FAI-related deformity was detected in 23.4% (30/128) of all hips. The prevalence of AD with a coexisting cam de- and tilt. We confirmed (1) the rotation in the coronal plane (confirmed whether the teardrop line was horizon- formity was higher than that of AD with a coexisting pincer tal), (2) the rotation in the axial plane (examined whether deformity regardless of sex. No significant difference was Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 Acetabular dysplasia with coexisting femoroacetabular impingement  141 Table I. Mean age and data for each parameter in all patients, men and women All subjects (128 hips) Males (64 hips) Females (64 hips) P-value Age (years) 56.3615.8 (21–84) 57.2616.1(21–83) 55.5615.48 (31–84) 0.520* CE angle ( ) 31.667.0 (15.4–47.8) 32.366.5 (17.6–45.7) 30.967.3 (15.4–47.8) 0.315* Sharp angle ( ) 40.1 6 6.9 (31.8–54.8) 39.3 6 4.1 (31.8–54.8) 40.9 6 3.3 (31.9–49.1) 0.003* Acetabular index ( ) 6.769.2 (7.9–22.8) 6.6611.3 (7.5–22.8) 6.866.4 (7.9–22.3) 0.195* Acetabular version A1 ( ) 9.068.6 (14.9–31.3) 7.869.9 (7.2–29.0) 10.368.8 (14.9–31.3) 0.043* A2 ( ) 12.069.0 (10.6–34.0) 9.968.6 (7.5–34.0) 14.068.8 (10.6–32.7) 0.003* A3 ( ) 16.768.7 (7.5–33.4) 15.168.1 (1.3–33.3) 18.269.1 (7.5–33.4) 0.025* A4 ( ) 19.667.8 (3.8–35.6) 18.266.8 (1.51–35.6) 20.968.5 (3.8–35.6) 0.030* a-angle R1 ( ) 40.365.1 (21.6–55.0) 41.665.0 (30.5–55.0) 39.065.0 (21.6–48.7) 0.011* R2 ( ) 42.865.7 (30.8–60.3) 44.066.1 (30.8–60.3) 41.764.9 (31.6–52.9) 0.025* R3 ( ) 46.065.9 (32.3–64.6) 46.966.5 (32.3–64.6) 45.065.1 (33.9–58.2) 0.130* R4 ( ) 48.565.9 (35.9–68.6) 49.066.5 (35.9–68.6) 47.965.2 (39.2–63.9) 0.413* R5 ( ) 49.066.9 (34.7–75.0) 51.467.0 (39.2–75.0) 47.765.9 (34.7–72.1) <0.001* R6 ( ) 46.967.4 (33.1–74.7) 49.567.4 (34.1–74.7) 44.364.9 (33.1–53.7) <0.001* HNOR R1 0.24560.03 (0.159–0.371) 0.24360.03 (0.159–0.333) 0.24860.04 (0.165–0.371) 0.504* R2 0.24160.07 (0.123–0.349) 0.24560.09 (0.123–0.305) 0.23660.04 (0.156–0.349) 0.784* R3 0.20560.04 (0.080–0.336) 0.21160.05 (0.080–0.307) 0.20060.04 (0.115–0.336) 0.099* R4 0.16760.05 (0.036–0.323) 0.16560.05 (0.036–0.306) 0.16860.04 (0.113–0.323) 0.628* R5 0.14060.03 (0.054–0.270) 0.13660.03 (0.057–0.248) 0.14560.03 (0.054–0.270) 0.113* R6 0.14160.03 (0.056–0.263) 0.13260.03 (0.056–0.191) 0.15060.03 (0.065–0.263) 0.002* HP positive 17.2% (10.6%–23.7%) 24.6% (17.14%–32.06%) 9.2% (6.65%–11.75%) 0.019† PGD positive 14.0% (7.98%–20.01%) 20.0% (13.07%–26.92%) 12.3% (17.32%–28.68%) 0.041† Data are presented as mean6 standard deviation (range) or as percentage (95% CI). CE angle, center-edge angle; HNOR, head–neck offset ratio; HP, herniation pit; PGD, pistol grip deformity. A1, axial slice at the level of the superior margin of the femoral head; A2, axial slice 5 mm below the superior margin of the femoral head; A3, axial slice 10 mm below the superior margin of the femoral head; A4, axial slice 15 mm below the superior margin of the femoral head; R1, oblique axial plane through the center of the femoral neck, adjusted to be parallel to the femoral neck–shaft angle (3:00 o’clock); R2, radial plane cranially rotated 15 from R1 (2:30 o’clock); R3, ra- dial plane cranially rotated 30 from R1 (2:00 o’clock); R4, radial plane cranially rotated 45 from R1 (1: 30 o’clock); R5, radial plane cranially rotated 60 from R1 (1: 00 o’clock); R6, radial plane cranially rotated 75 from R1 (12:30 o’clock). *Male versus female, evaluated with the Wilcoxon rank-sum test. P-values of<0.05 were considered statistically significant. † 2 Male versus female, evaluated with v test. P-values of<0.05 were considered statistically significant. Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 142  T. Mimura et al. Table II. Detailed prevalence of AD and FAI-related findings in all patients, men, and women All subjects (128 hips) Males (64 hips) Females (64 hips) P-value* Definite AD CE angle <20 6.3% (8/128) 3.1% (2/64) 9.4% (6/64) 0.144 [3.2%–11.8%] [0.9%–10.7%] [4.4%–19.0%] Sharp angle >45 7.8% (10/128) 6.3% (4/64) 9.4% (6/64) 0.439 [4.3%–13.8%] [2.5%–15.0%] [4.4%–19.0%] Total 11.7% (15/128) 7.8% (5/64) 15.6% (10/64) 0.169 [7.2%–18.4%] [3.4%–17.0%] [8.7%–26.4%] Borderline AD 20  CE angle <25 12.5% (16/128) 12.5% (8/64) 12.5% (8/64) 1 [7.8%–19.3%] [6.5%–22.8%] [6.5%–22.8%] 42 < Sharp angle 45 21.9% (28/128) 15.6% (10/64) 28.1% (18/64) 0.087 [15.6%–29.8%] [8.7%–26.4%] [18.6%–40.1%] Total 24.2% (31/128) 21.9% (14/64) 26.6% (17/64) 0.536 [17.6%–32.3%] [13.5%–33.4%] [17.3%–38.5%] Cam deformity a angle 55 28.9% (37/128) 40.6% (26/64) 17.2% (11/64) 0.003 [21.8%–37.3%] [29.5%–52.9%] [9.9%–28.2%] HNOR <0.13 58.6% (75/128) 65.6% (42/64) 51.6% (33/64) 0.106 [49.9%–66.9%] [53.4%–76.1%] [39.6%–63.4%] PGD positive 14.1% (18/128) 20.3% (13/64) 7.8% (5/64) 0.041 [9.1%–21.1%] [12.3%–31.7%] [3.4%–17.0%] HP positive 17.2% (22/128) 25.0% (16/64) 9.4% (6/64) 0.016 [11.6%–24.7%] [16.0%–36.8%] [4.4%–19.0%] Total 68.0% (87/128) 79.7% (51/64) 56.3% (36/64) 0.004 [59.5%–75.4%] [68.3%–87.7%] [44.1%–67.7%] Pincer deformity Acetabular index 0 18.0% (23/128) 20.3% (13/64) 15.6% (10/64) 0.489 [12.3%–25.5%] [12.3%–31.7%] [8.7%–26.4%] RA 12.5% (16/128) 17.2% (11/64) 7.8% (5/64) 0.108 [7.8%–19.3%] [9.9%–28.2%] [3.4%–17.0%] Total 28.9% (37/128) 37.5% (24/64) 20.3% (13/64) 0.031 [21.8%–37.3%] [26.7%–49.7%] [12.3%–31.7%] Combined deformity 20.3% (26/128) 28.1% (18/64) 12.5% (8/64) 0.028 [14.3%–28.1%] [18.6%–40.1%] [6.5%–22.8%] Data are shown as percentage [95% CI]. AD, acetabular dysplasia; FAI, femoroacetabular impingement; CE, center-edge angle; PGD, pistol grip deformity; HP, her- niation pit; HNOR, head–neck offset ratio; RA, retroverted acetabulum. *Male versus female, evaluated with v test. P-values of<0.05 were considered statistically significant. Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 Acetabular dysplasia with coexisting femoroacetabular impingement  143 Table III. Prevalence of each combination of coexistence of AD and FAI-related deformities All subjects Males Females P-value* (128 hips) (64 hips) (64 hips) Definite AD and FAI-related deformities 7.8% (10/128) 7.8% (5/64) 7.8% (5/64) 1 [4.3%–13.8%] [3.4%–17.0%] [3.4%–17.0%] Definite AD þ cam deformity 6.3% (8/128) 4.7% (3/64) 7.8% (5/64) 0.465 [3.2%–11.8%] [1.6%–12.9%] [3.4%–17.0%] Definite AD þ pincer deformity 0% (0/128) 0% (0/64) 0% (0/64) – [0%–2.9%] [0%–5.7%] [0%–5.7%] Definite AD þ combined deformity 1.6% (2/128) 3.1% (2/64) 0% (0/64) 0.154 [0.4%–5.5%] [0.9%–10.7%] [0%–5.7%] Borderline AD and FAI-related deformities 15.6% (20/128) 20.3% (13/64) 10.9% (7/64) 0.144 [10.3%–22.9%] [12.3%–31.7%] [5.4%–20.9%] Borderline AD þ cam deformity 13.3% (17/128) 17.2% (11/64) 9.4% (6/64) 0.193 [8.5%–20.2%] [9.9%–28.2%] [4.4%–19.0%] Borderline AD þ pincer deformity 1.6% (2/128) 1.6% (1/64) 1.6% (1/64) 1 [0.4%–5.5%] [0.3%–8.3%] [0.3%–8.3%] Borderline AD þ combined deformity 0.8% (1/128) 1.6% (1/64) 0% (0/64) 0.315 [0.1%–4.3%] [0.3%–8.3%] [0%–5.7%] AD in total (definite and borderline) and 23.4% (30/128) 28.1% (18/64) 18.7% (12/64) 0.210 FAI-related deformities [16.9%–31.5%] [18.6%–40.1%] [11.1%–30.0%] AD in total (definite and borderline) þ cam deformity 19.5% (25/128) 21.9% (14/64) 17.2% (11/64) 0.504 [13.6%–27.2%] [13.5%–33.4%] [9.9%–28.2%] AD in total (definite and borderline) þ pincer deformity 1.6% (2/128) 1.6% (1/64) 1.6% (1/64) 1 [0.4%–5.5%] [0.3%–8.3%] [0.3%–8.3%] AD in total (definite and borderline) þ combined deformity 2.3% (3/128) 4.7% (3/64) 0% (0/64) 0.079 [0.8%–6.7%] [1.6%–12.9%] [0%–5.7%] Data are shown as percentage [95% CI]. AD, acetabular dysplasia; FAI, femoroacetabular impingement. *Male versus female, evaluated with v test. P-values of<0.05 were considered statistically significant. observed in any combination of AD and FAI-related de- words, 65.2% of hips (30/46) with AD had some FAI- formity between men and women. related findings. Table IV shows the percentage of each type of AD with Table V shows the detailed percentage of each type of coexisting cam, pincer and combined deformities com- AD with coexisting cam, pincer and combined deformities pared with total AD (definite and borderline). The per- in men and women compared with total AD. There was no centage of AD with a coexisting cam deformity (54.3%, combination of AD and FAI-related findings which showed 25/46) was much higher than that of AD with coexisting that the corresponding percentage in women was higher pincer (4.3%, 2/46). The percentage of AD without coex- than that in men. The percentages of total AD with a coex- isting FAI-related findings was 34.8% (16/46); in other isting cam deformity and total AD with a coexisting Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 144  T. Mimura et al. Fig. 6. The representative case of the hip of AD with coexisting FAI-related findings. This case was 50 years old women, left hip was defined as a hip of borderline AD with coexisting cam deformity. (A) CE angle, Sharp angle and AI was 21 ,44 and 20 , respectively. (B) The acetabular version angle was 7 at a slice at the level of the superior margin of the femoral head (slice A1). (C) The a-angle and HNOR at a slice of R4 (1:30 o’clock) was 57 and 0.125, respectively. HP was also positive. (D) PGD was negative. According to the CE and Sharp angle, this hip was defined as a borderline AD. On the other hand, this hip was also defined as a cam deformity due to a-angle> 55 , HNOR< 0.13 and HP positive. However, this hip did not coexist with a pincer deformity, because the AI was over 0 and acetabular version angle was not negative. Table IV. Corresponding percentage of each type of AD with coexisting cam, pincer and combined deformities and without coexisting FAI-related findings compared with all numbers of each type of AD in all patients With coexisting With coexisting With coexisting Without coexisting cam deformity pincer deformity combined deformity FAI-related findings Definite AD (n ¼ 15) 53.3% (8/15) 0% (0/15) 13.3% (2/15) 33.3% (5/15) [30.1%–75.2%] [0%–20.4%] [3.7%–37.9%] [15.2%–58.3%] Borderline AD (n ¼ 31) 54.8% (17/31) 6.5% (2/31) 3.2% (1/31) 35.5% (11/31) [37.8%–70.8%] [1.8%–20.7%] [0.6%–16.2%] [21.1%–53.1%] AD in total (definite and borderline) (n ¼ 46) 54.3% (25/46) 4.3% (2/46) 6.5% (3/46) 34.8% (16/46) [40.2%–67.8%] [1.2%–14.5%] [2.2%–17.5%] [22.7%–49.2%] Data are shown as percentage [95% CI]. AD, acetabular dysplasia; FAI, femoroacetabular impingement. combined deformity were significantly higher in men than The ICCs of the intraobserver and interobserver reli- women (P¼ 0.0272 and P¼ 0.0327, respectively). ability of all parameters were almost perfect (0.80). Conversely, the percentages of total AD without coexisting FAI-related findings were significantly higher in women DISCUSSION (P¼ 0.0004). AD and FAI have been thoroughly discussed as a cause of hip OA [1, 2, 6, 7]. However, the prevalence and morpho- Table VI shows the corresponding percentages of the combinations of the coexistence of each type of AD and logical features of the coexistence of AD and FAI have not each FAI-related finding compared with all hips. The most been well discussed. In the present study, we showed the major features of cam deformities coexisting with definite prevalence of AD with coexisting pincer, cam and com- AD and borderline AD were an HNOR of<0.13. On the bined deformities, and also the frequency with which FAI- other hand, the major feature of pincer deformities coexist- related findings coexist with definite and borderline AD in ing with definite AD and borderline AD were RA. No sig- asymptomatic Japanese population. To the best of our nificant differences were found in the corresponding knowledge, there is scarce literature on this topic. percentages of the coexistence of each type of AD and Several authors have discussed the coexistence of cam each FAI-related finding between men and women. deformity and AD in symptomatic populations. Ida et al. [9] Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 Acetabular dysplasia with coexisting femoroacetabular impingement  145 Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 Table V. Comparison of corresponding percentage of AD with coexisting cam, pincer and combined deformities and without coexisting FAI- related findings compared with all numbers of each type of AD between men and women With coexisting With coexisting With coexisting Without coexisting cam deformity pincer deformity combined deformity FAI-related findings Definite AD (n ¼ 5 in male, Male Female Male Female Male Female Male Female n ¼ 10 in female) 60% (3/5) 50% (5/10) 0% (0/5) 0% (0/10) 40% (2/5) 0% (0/10) 0%(0/5) 50%(5/10) [23.1%–88.2%] [23.7%–76.3%] [0%–43.4%] [0%–27.8%] [11.8%–76.9%] [0%–27.8%] [0%–43.3%] [23.7%–76.3%] P¼0.7144 P¼0.0317P¼0.0528 Borderline AD (n ¼ 14 in male, Male Female Male Female Male Female Male Female n ¼ 17 in female) 78.6% (11/14) 35.3% (6/17) 7.1% (1/14) 5.9% (1/17) 7.1% (1/14) 0% (0/17) 7.1% (1/14) 58.8% (10/17) [52.4%–92.4%] [17.3%–58.7%] [1.3%–31.5%] [1.0%–27.0%] [1.3%–31.5%] [0%–18.4%] [1.3%–31.5%] [36.0%–78.4%] P¼0.0032P¼0.8869P¼0.3113P¼0.00276 AD in total (n ¼ 19 in male, Male Female Male Female Male Female Male Female n ¼ 27 in female) 73.7% (14/19) 40.7% (11/27) 5.3% (1/19) 3.7% (1/27) 15.8% (3/19) 0% (0/27) 5.3% (1/19) 55.6% (15/27) [51.2%–88.2%] [24.5%–59.3%] [0.9%–24.6%] [0.7%–18.3%] [5.5%–37.6%] [0%–12.5%] [0.9%–24.6%] [37.3%–72.4%] P¼0.0272P¼0.7984P¼0.0327P¼0.0004 Data are shown as percentage [95% CI]. AD, acetabular dysplasia; FAI, femoroacetabular impingement. P values were evaluated with the v test. P values of<0.05 were considered statistically significant. 146  T. Mimura et al. Table VI. Corresponding percentage of combination of coexistence with each type of AD and each FAI-related finding compared with all hips with coexistence of each type of AD (definite or borderline) and each FAI- related deformity (cam or pincer deformity) All subjects Males Females P-value* Definite AD þ cam deformity Definite AD þ a angle 55 40% (4/10) 40.0% (2/5) 40.0% (2/5) 1 [16.8%–68.7%] [11.8%–76.9%] [11.8%–76.9%] Definite AD þ HNOR < 0.13 100% (10/10) 100% (5/5) 100% (5/5) – [72.2%–100%] [56.6%–100%] [56.6%–100%] Definite AD þ PGD positive 10% (1/10) 20% (1/5) 0% (0/5) 0.292 [1.8%–40.4%] [3.6%–62.4%] [0%–43.3%] Definite AD þ HP positive 20% (2/10) 20% (1/5) 20% (1/5) 1 [5.7%–51.0%] [3.6%–62.4%] [3.6%–62.4%] Definite AD þ pincer deformity Definite AD þ acetabular index 0 0% (0/2) 0% (0/2) (0/0) – [0%–65.8%] [0%–65.8%] Definite AD þ RA 100% (2/2) 100% (2/2) (0/0) – [34.2%–100%] [34.2%–100%] Borderline AD þ cam deformity Borderline AD þ a angle 55 55.6% (10/18) 41.7% (5/12) 83.3% (5/6) 0.094 [33.7%–75.4%] [19.3%–68.0%] [43.6%–97.0%] Borderline AD þ HNOR < 0.13 88.9% (16/18) 83.3% (10/12) 100% (6/6) 0.249 [67.2%–96.9%] [55.2%–95.3%] [61.0%–100%] Borderline AD þ PGD positive 27.8% (5/18) 25.0% (3/12) 33.3% (2/6) 0.709 [12.5%–50.9%] [8.9%–53.2%] [9.7%–70.0%] Borderline AD þ HP positive 22.2% (4/18) 33.3% (4/12) 0% (0/6) 0.109 [9.0%–45.2%] [13.8%–60.9%] [0%–39.0%] Borderline AD þ pincer deformity Borderline AD þ acetabular index 0 33.3% (1/3) 0% (0/2) 100% (1/1) 0.083 [6.1%–79.2%] [0%–65.8%] [20.7%–100%] Borderline AD þ RA 66.7% (2/3) 100% (2/2) 0% (0/1) 0.083 [20.8%–93.9%] [34.2%–100%] [0%–79.3%] Data are shown as percentage [95% CI]. AD, acetabular dysplasia; FAI, femoroacetabular impingement; PGD, pistol grip deformity; HP, herniation pit; HNOR, head–neck offset ratio; RA, retroverted acetabulum. *Male versus female, evaluated with v test. P-values of<0.05 were considered statistically significant. reported the frequency of cam deformity in hips with Clohisy et al. [8] found that femoral head asphericity symptomatic AD. They found that 40% of patients with was present in 72% and reduced head–neck offset was also AD had radiological evidence of cam deformity (a angle presented in 75% of symptomatic AD. Furthermore, Wyles of>55 ) on lateral roentgenograms. On the other hand, et al. [11] reported that patients with coexisting AD and Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 Acetabular dysplasia with coexisting femoroacetabular impingement  147 cam deformity developed hip OA more rapidly rather plain radiograph examination (Inoue et al. [3], 8.1%; Umer than patients with AD. From this study, we are agreed to et al. [32], 7.3%). However, direct comparison of our re- these previous reports showed the high prevalence of sults with their results is difficult because the evaluation coexistence of AD and cam-related findings, and clinical methods were different. We recognize that these angles importance of them. However, previous studies have showed discrepancy between CT images and plain radio- evaluated the coexistence of AD and cam-related findings graphs. Actually, Chadayammuri et al. [33] reported dis- only using simple plain radiographs. In the present study, crepancies in the CE angle between plain radiographs and we revealed the coexistence of several FAI-related findings CT images. They found that the CE angle measured on and AD (including borderline) using multislice CT images CT images was 2.1 larger than that of measured on plain and also compared the results between men and women. radiographs. Considering these facts, our results might We emphasized the prevalence of borderline AD with coex- overestimate the prevalence of AD rather than the studies isting cam deformity was 15.6%, which was two times higher that measured these parameters using plain radiograph. than that of definite AD with coexisting cam deformity. However, we believe that CT images are more suitable Therefore, we consider that more attention should be given than plain radiographs with respect to correct measure- to the coexistence of borderline AD and cam deformity. ment of AD parameters because we can more easily detect Furthermore, the percentage of hips with AD and a coexist- the bony morphological features of the acetabulum, espe- ing cam deformity was significantly higher in men than cially the lateral point of the acetabular dome, and we can women. Therefore, we also suppose that more attention also accurately evaluate the acetabular bony coverage in should be given to the coexistence of AD and cam the center of the femoral head. Furthermore, the ICCs for deformity especially in men. Additionally, we showed that the interobserver reliability of the CE angle and Sharp the most major feature of cam-related findings detected in angle were 0.83 and 0.94 in this study, respectively. Mast definite and borderline AD in Japanese hips was reduced et al. [34] and Tan et al. [35] reported that the ICCs for HNOR. the interobserver reliability of the CE angle evaluated on The percentage of hips with definite AD with coexisting plain radiographs were 0.73 and 0.51, respectively. We be- pincer-related findings compared with all hips with definite lieve that CT images allow for calculation of a more accur- AD was 0%, and the prevalence of borderline AD with co- ate prevalence of AD than do plain radiographs. existing pincer-related findings compared with all hips with In the present study, we defined a CE angle of<20 as borderline AD was only 6.5%. Fujii et al. [10] reported indicative of definite AD and a CE angle of 20 to<25 as that an RA was observed in 18% of Japanese patients with indicative of borderline AD. These cut-off values have been symptomatic AD. They showed that AD with an RA was widely utilized in the literature [4, 5]. We also defined a associated with an earlier onset of pain than AD with ante- Sharp angle of>45 as indicative of definite AD and a version. However, Troelsen et al. [31] reported that an RA Sharp angle of>42 to 45 as indicative of borderline AD. was found in one-third of hips with AD when assessed on A Sharp angle of>45 has been widely used to define the weight-bearing pelvic radiographs. They also reported that presence of definite AD in the literature [5]. However, few the prevalence of an RA may be underestimated if the eval- reports have described the cut-off of Sharp angle for the uated images are obtained from patients in the supine pos- definition of borderline AD. Paliobeis and Villar [4] re- ition. Therefore, we might have underestimated the ported that a Sharp angle of>39 to 42 was indicative of coexistence of AD and pincer-related findings in the pre- borderline AD and that a Sharp angle of>42 was indica- sent study because we used CT images and excluded the tive of definite AD. If we had used these definitions in the pelvis anteriorly rotated rather than normal range from present study, the prevalence of borderline AD as diag- present study. Although the percentage of AD with coexist- nosed by a Sharp angle of>39 to 42 would have been ing pincer deformity was lower than that of AD with coex- 28.9%, and that of definite AD as diagnosed by a Sharp isting cam deformity, we had better understand that the angle of>42 would have been 29.7%; the prevalence of coexistence of pincer deformity in men was slightly higher total AD would have been 58.6%. However, these preva- than that in women. In such hips, we should pay more at- lences are much higher than those defined using the CE tention to a RA as a morphological finding of pincer angle in our study and much higher than the previously re- deformity. ported prevalences of definite AD [3, 32]. Sharp [14] ori- We employed two parameters for the definition of AD ginally reported that angles of 39 –42 were within the in the present study. As a result, we detected definite AD upper limit of normality. Therefore, we defined a Sharp in 11.7% of the Japanese hip joints in this study, which is angle of>45 as indicative of definite AD and a Sharp relatively higher than in previous Asian studies based on angle of>42 to 45 as indicative of borderline AD in the Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/137/4931209 by Ed 'DeepDyve' Gillespie user on 20 June 2018 148  T. Mimura et al. present study. On the other hand, we did not define AD percentages did not generally change, if HP and PGD posi- using AI in the present study. Namely, we did not distin- tivity were excluded from the parameter of cam deformity. guish between ‘flat roof (short roof) dysplasia’ and ‘sloping Although, AD and FAI were originally independent roof dysplasia’ [36, 37]. Brockwell et al. [36] suggested concepts, we consider that simultaneous evaluation of AD that a sloping roof dysplasia was so-called primary dyspla- and FAI would be informative from the viewpoint of pre- sia or classical dysplasia which has instability and a flat roof venting the progression of hip OA. Actually, we found that dysplasia was essentially taking with cam impingement. only 34.8% of hips with AD were free from the coexistence They described that a flat roof dysplasia was brought by of FAI-related findings when we investigated AD using the impingement between iliac acetabular epiphysis and multislice CT images in Japan. Furthermore, we revealed cam deformity in adolescence. In the present study, we did that the major and notable parameter of a cam deformity not discuss these morphologies of AD. If we classified and detected in hips with AD was a HNOR. We consider that discussed these morphologies of AD, we believed that the it is important to correctly evaluate the coexistence of AD results would be different. and radiological FAI-related findings when discussing mor- This study has some limitations. First, it was not phological disorders of the hip joint. However, it still re- population-based, but patient-based. This is an inescapable mains unclear what additional procedure (debridement, limitation of this study. However, our aim in this study was labral fixation or osteochodroplasty of cam lesion) is not to simply investigate the prevalence of AD with coex- needed and suitable when we perform acetabular osteot- isting radiological FAI but to evaluate its prevalence using omy for AD with coexisting FAI [38]. Further research will detailed multislice and multiplane examinations. Therefore, be needed to indicate how to manage FAI-related findings we investigated the patients’ CT images from scans that coexisting with AD. had been requested by other departments at our institution In conclusion, we found that the coexistence of AD and for evaluation of conditions unrelated to hip disorders. FAI-related findings was common in Japanese population, Second, we excluded clear hip OA in order to precisely and 65.2% of hips with AD had some FAI-related findings. measure morphological parameters. We understand that The prevalence of borderline AD with coexisting FAI was AD and FAI are generally thought to be lead to hip OA. much higher than that of definite AD with coexisting FAI, Therefore, we recognized that this might lead to potential and the percentage of AD with coexisting FAI-related find- selection bias and an underestimation of the prevalence of ings in men was higher rather than that in women. We also AD or FAI. Third, the sample size was relatively small, and found that AD with coexisting cam-related findings was this study was performed in a single hospital. We recognize considerably more common than AD with coexisting that it might be incorrect to generalize our results to region pincer-related findings, and the most notable parameter as throughout Japan. Finally, we employed four parameters to a morphological feature of cam deformity detected in such define cam deformity, and we employed two parameters to hips was a HNOR. define pincer deformity. We recognize that the prevalence of AD with coexisting FAI-related findings would be differ- CONFLICT OF INTEREST STATEMENT ent if we had employed other parameters for definition of None declared. FAI-related deformities or altered the number of param- eters used to define cam or pincer deformity. For example, a HP is generally thought to be a predictor of FAI [29, REFERENCES 25]. However, Kim et al. [27] indicate that a HP may have 1. Murphy SB, Ganz R, Muller ME. The prognosis in untreated dys- limited significance as a predictor of FAI. Furthermore, a plasia of the hip. A study of radiographic factors that predict out- angle would be naturally more than 55 , if PGD was come. J Bone Joint Surg Am 1995 Jul; 77: 985–9. existed. Therefore, we supposed that the results would be 2. Takeyama A, Naito M, Shiramizu K, Kiyama T. Prevalance of different, if HP and PGD positivity were excluded as a par- femoroacetabular impingement in Asian patients with osteoarth- ritis of the hip. 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Journal of Hip Preservation SurgeryOxford University Press

Published: Mar 12, 2018

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