Muscle-tendon-related pain in 100 patients with hip dysplasia: prevalence and associations with self-reported hip disability and muscle strength

Muscle-tendon-related pain in 100 patients with hip dysplasia: prevalence and associations with... Journal of Hip Preservation Surgery Vol. 5, No. 1, pp. 39–46 doi: 10.1093/jhps/hnx041 Advance Access Publication 17 November 2017 Research article Muscle-tendon-related pain in 100 patients with hip dysplasia: prevalence and associations with self- reported hip disability and muscle strength 1,2 3 3 4 Julie Sandell Jacobsen *, Per Ho¨lmich , Kristian Thorborg , Lars Bolvig , 5 5 6 Stig Storgaard Jakobsen , Kjeld Søballe and Inger Mechlenburg Department of Physiotherapy, Faculty of Health Sciences, VIA University College, Hedeager 2, 8200, Aarhus N, Denmark, Department of Physiotherapy and Occupational Therapy, Aarhus University Hospital, Tage-Hansens Gade 2, 8000 Aarhus C, Denmark, Department of Orthopaedic Surgery, Sports Orthopedic Research Center-Copenhagen (SORC-C), Copenhagen University Hospital, Amager and Hvidovre, Italiensvej 1, 2300 Copenhagen S, Denmark, Department of Radiology, Aarhus University Hospital, Tage-Hansens Gade 2, 8000 Aarhus C, Denmark, Department of Orthopaedic Surgery, Aarhus University Hospital, Tage-Hansens Gade 2, 8000 Aarhus C, Denmark and Centre of Research in Rehabilitation (CORIR), Institute of Clinical Medicine, Aarhus University, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark *Correspondence to: J. S. Jacobsen. E-mail: jsaj@via.dk Submitted 5 April 2017; Revised 22 August 2017; revised version accepted 16 September 2017 ABSTRACT The primary aim was to identify muscle-tendon-related pain in 100 patients with hip dysplasia. The secondary aim was to test whether muscle-tendon-related pain is associated with self-reported hip disability and muscle strength in patient with hip dysplasia. One hundred patients (17 men) with a mean age of 29 years (SD 9) were included. Clinical entity approach was carried out to identify muscle-tendon-related pain. Associations between muscle-tendon-related pain and self-reported hip disability and muscle strength were tested with multiple regres- sion analysis, including adjustments for age and gender. Self-reported hip disability was recorded with the Copenhagen Hip and Groin Outcome Score (HAGOS), and muscle strength was assessed with a handheld dyna- mometer. Iliopsoas- and abductor-related pain were most prevalent with prevalences of 56% (CI 46; 66) and 42% (CI 32; 52), respectively. Adductor-, hamstrings- and rectus abdominis-related pain were less common. There was a significant inverse linear association between muscle-tendon-related pain and self-reported hip disability ranging from 3.35 to  7.51 HAGOS points in the adjusted analysis (P< 0.05). Besides the association between muscle-tendon-related pain and hip extension a significant inverse linear association between muscle- tendon-related pain and muscle strength was found ranging from 0.11 to  0.12 Nm/kg in the adjusted analysis (P< 0.05). Muscle-tendon-related pain exists in about half of patients with hip dysplasia with a high prevalence of muscle-tendon-related pain in the iliopsoas and the hip abductors and affects patients’ self-reported hip disabil- ity and muscle strength negatively. and intra-articular injury has been reported as one INTRODUCTION important predisposing factor to development of osteoarth- Symptomatic hip dysplasia normally presents in early life ritis [2]. Labrum injury or degeneration is present in 49– [1] and left untreated, hip dysplasia may lead to develop- 83% of patients with hip dysplasia [2, 5], and causes pain at ment of early osteoarthritis [2, 3]. The aetiology of hip the groin and/or lateral to the hip [5, 6]. Moreover, the osteoarthritis in hip dysplasia is unknown and often shallow acetabulum and the reduced weight bearing are described as multifactorial [2]. However, the lack of acetab- associated with increased load on the muscles acting close ular support to the femoral head [4] and the compromised to the hip joint [7, 8], and muscle-tendon-related pain may passive stability of the hip joint lead to an increased mech- potentially coexist with intra-articular pathology. anical pressure on the acetabular labrum and cartilage [2], V C The Author 2017. 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/5/1/39/4638269 by Ed 'DeepDyve' Gillespie user on 16 March 2018 40  J. S. Jacobsen et al. The acetabular labrum functions as an important anterior the hip, knee or ankle, (iv) Neurological, rheumatological or stabilizer to the dysplastic hip [9], and the location of the medical conditions affecting the function of the hip joint, iliopsoas muscle close to the capsule–labral complex en- (v) Tenotomy of the iliopsoas tendon or z-plastic of the ilio- ables the muscle to work as an anterior stabilizer to the hip tibial band and (vi) Steroid-injection in the iliopsoas tendon joint [10]. The gluteus medius and minimus muscles work and/or bursa trochanterica within the last 6 weeks. together with the iliopsoas muscle as important lateral sta- bilizers to maintain a level led pelvis during ambulation Study design [11]. The stabilizing role of the iliopsoas and gluteus med- All outcomes measures were collected prior to PAO during ius and minimus muscles may be increased in hip dysplasia a clinical examination. The clinical examination was com- due to the morphology of the hip joint [7, 10], and poten- pleted by two experienced physical therapists (CMS and tially higher load on the muscles may lead to overuse- JSJ) with 5 and 7 years of experience assessing patients related pain in the muscles and tendons. with hip dysplasia, respectively. The patients were ran- Muscle-tendon-related pain is present in hip dysplasia domly assessed by the two physical therapists with approxi- [6, 12], and abnormality of the iliopsoas muscle identified mately equal distribution between the two (60:40). The as internal snapping hip has been verified in 18% using hip examination included recording of self-reported hip disabil- arthroscopy [12]. In patients with femoroacetabular im- ity, examination of muscle-tendon-related pain in clinical pingement muscle-tendon-related pain frequently coexist entities and hip muscle strength tests. with the morphology of the hip joint [13], and in sports- active subjects with long-standing groin pain, muscle-ten- Self-reported hip disability don-related pain has been identified with the clinical entity The Copenhagen Hip and Groin Outcome Score approach [14, 15]. In patients with hip dysplasia, however, (HAGOS) questionnaire was completed by all patients no previous studies have systematically examined the pres- prior to the clinical examinations [18]. HAGOS has shown ence of muscle-tendon-related pain in a consecutive cohort to be a valid, reliable and responsive measure of hip disabil- scheduled for periacetabular osteotomy. ity and associated problems in young to middle-aged phys- The primary aim was to identify muscle-tendon-related ically active patients with longstanding hip and/or groin pain in 100 patients with hip dysplasia in the following pain including patients undergoing hip arthroscopy [18, clinical entities: (i) iliopsoas, (ii) abductors, (iii) adductors, 19]. HAGOS consists of six separate subscales rating hip (iv) hamstrings, and (v) rectus abdominis. The secondary disability from 0 to 100 points, where zero points indicates aim was to test if muscle-tendon-related pain is associated the lowest outcome [18]. The six subscales measure pain, with self-reported hip disability and muscle strength in pa- symptoms, physical function in daily living (ADL), physical tient with hip dysplasia. function in sports and recreation, participation in physical activity and quality of life [18]. MATERIALS AND METHODS This study complies with the Helsinki Declaration and was Muscle-tendon-related pain notified to the Danish Committee on Biomedical and Research Ethics at 14 January 2014 (5/2014). The Danish A standardized clinical entity approach was carried out to Data Protection Agency gave permission for the handling identify muscle-tendon-related pain in clinical entities as- of personal data (1-16-02-47-14), and the study was regis- sessed in the limb scheduled for PAO [14, 15, 20]. The tered at ClinicalTrials.gov (20140401PAO). standardized entity approach includes a number of pain provocation tests covered by anatomic palpation, resistance Subjects testing and passive muscle stretch (Table I). The approach In a consecutive sample, patients with bilateral or unilateral includes five entities, and the entities were tested in the fol- hip dysplasia were invited to participate from May 2014 to lowing order: adduction-related pain, iliopsoas-related August 2015 from the Department of Orthopedics at pain, rectus abdominis-related pain, abductor-related pain Aarhus University Hospital in Denmark. Inclusion criteria and hamstring-related pain. Rectus abdominis-related pain were Wiberg’s center-edge (CE) angle<25 [16], groin is in the Doha consensus covered by the term inguinal- pain for at least 3 months and scheduled periacetabular oste- related pain [20]. Inguinal-related pain is less relevant otomy (PAO) [17]. Patients were excluded based on the among patients with hip dysplasia as many of these pa- following criteria: (i) Calve´ Perthes and epiphysiolysis, tients are women in which the inguinal canal anatomy is (ii) Surgery due to herniated disc and spondylodesis, somewhat different from males, and therefore rectus- (iii) Previous joint preservation procedure or arthroplasty of abdominis-related pain was the focus in the present study. Downloaded from https://academic.oup.com/jhps/article-abstract/5/1/39/4638269 by Ed 'DeepDyve' Gillespie user on 16 March 2018 Muscle-tendon-related pain in 100 patients with hip dysplasia  41 Table I. Diagnostic criteria for each individual entity Clinical entities Diagnostic criteria Iliopsoas-related pain Palpatory pain of the muscle through the lower lateral part of the abdomen and/or just dis- tal of the inguinal ligament and pain with passive stretching during modified Thomas’ test [14, 20, 21] Abductor-related pain Palpatory pain at the insertion point at the greater trochanter and pain with side-lying ab- duction against resistance Adductor-related pain Palpatory pain at the muscle origin at the pubic bone and pain with adduction against resistance [14, 20] Hamstring-related pain Palpatory pain at the muscle origin at the tuber ischii and pain with extension against resistance Rectus abdominis-related pain Palpatory pain of the distal tendon and/or the insertion at the pubic bone, and pain at con- traction against resistance [14, 20] Muscle strength measures was investigated. Twenty-five patients were Isometric muscle strength tests were performed using a reli- tested 6 weeks after PAO by two physiotherapists, rater A able dynamometer technique [22]. Muscle strength was and B (CMS and JSJ), with a 2-day period between a first tested with a handheld dynamometer (powertrack II coman- and second test. Each patient was randomized to whether dor, JTECH Medical, Salt Lake City, Utah). Isometric hip rater A or B performed the initial testing. adduction, abduction, flexion and extension strength were measured in the limb scheduled for PAO, and the order of Sample size the individual tests was randomized before each session to Since it was not possible to calculate the sample size based avoid systematic bias. The examiner applied resistance 5 cm on the prevalence of muscle-tendon-related pain, we chose proximal to the proximal edge of the lateral malleolus for hip to calculate it based on the secondary outcome of the abduction, adduction and extension. Resistance in hip flexion study. The sample size calculation was based on the was performed 5 cm proximal to the proximal border of pa- HAGOS ADL subscore with an estimated difference of tella. In all the isometric tests, the patients exerted 5-s 11.8 points and an estimated standard deviation of 18.5 Maximal Voluntary Isometric Contraction (MVIC) against points between patients with and without muscle-tendon- the dynamometer. The highest value of four repeated meas- related pain. The estimated difference was based on the urements for each test was used in the analysis. To avoid fa- Minimal Important Change of 11.8 points reported in a co- tigue, patients rested for 30 s between each measurement. All hort study on patients with femoroacetabular impingement strength values were weight-adjusted and reported as scheduled for hip arthroscopy [19], and the standard devi- Newton meters per kilogram of the bodyweight. ation was based on the standard deviation of the HAGOS ADL subscore of 18.5 points reported in a cohort study on Baseline characteristics patients with intra-articular hip lesions undergoing hip Baseline characteristics were registered using standardized arthroscopy [24]. Based on a significance level of 5% and a questions. Pain was measured on a numeric rating scale power of 80%, 80 patients were needed, and considering (NRS) in rest while sitting and lying. The center-edge the risk of dropouts, we included 100 patients. (CE) angle [16], To¨nnis’ acetabular index (AI) angle [23] and To¨nnis’ osteoarthritis grade [23] were measured by a Statistics single rater (SSJ) using anteroposterior radiographs, Normal distribution was checked with histograms and whereas hospital charts was used to record unilateral or bi- probability plots. Multiple linear regression analyses were lateral hip involvement and other pathologies. performed with muscle-tendon-related pain as the inde- pendent variable (i.e. the sum of positive clinical entities Inter-rater reliability of the test battery for each patient) and each HAGOS subscale as the de- Two different testers assessed muscle-tendon-related pain pendent variable (pain, symptoms, ADL, physical function and muscle strength and the inter-rater reliability of these in sports and recreation, participation in physical activity Downloaded from https://academic.oup.com/jhps/article-abstract/5/1/39/4638269 by Ed 'DeepDyve' Gillespie user on 16 March 2018 42  J. S. Jacobsen et al. Table II. Baseline characteristics in 100 consecutive patients with hip dysplasia Outcomes Patients (SD) Men 17 Bilateral symptoms 89 Osteoarthritis grade 0/1 97/3 Congenital hip dislocation 6 Age, years 29.9 (9.2) BMI, kg/m 23.2 (3.0) Duration of pain, years 4.9 (5.6) NRS pain lying, 0–10 3.1 (2.4) Fig. 1. Flowchart of the study process. One hundred consecutive NRS pain sitting, 0–10 3.8 (2.7) patients with unilateral and bilateral symptoms were included CE angle preoperatively, degrees 17.4 (4.7) from the Division of Hip Surgery, Department of Orthopedics, Aarhus University Hospital in Denmark from May 2014 to AI angle preoperatively, degrees 13.8 (4.9) August 2015. Abbreviations: HD, hip dysplasia; ADHD, atten- tion deficit/hyperactivity disorder; MRSA, methicillin-resistant HAGOS pain, 0–100 50.3 (18.0) Staphylococcus aureus. HAGOS symptoms, 0–100 49.2 (17.4) and quality of life). Crude and adjusted b-coefficients were HAGOS ADL, 0–100 55.5 (22.4) estimated, and adjustments were made for age and gender. HAGOS sport/recreation, 0–100 39.3 (20.7) Likewise, multiple linear regression analyses were per- formed with muscle-tendon-related pain as the independ- HAGOS participation, 0–100 23.0 (24.7) ent variable (i.e. the sum of positive clinical entities for HAGOS quality of life, 0–100 29.4 (14.3) each patient) and strength of each muscle group as the de- pendent variable (i.e. flexion, abduction, adduction and ex- Hip flexion, Nm/kg 1.2 (0.5) tension). Crude and adjusted b-coefficients were Hip abduction, Nm/kg 1.2 (0.4) estimated, and adjustments were made for age and gender. The assumptions (independent observations, linear associ- Hip adduction, Nm/kg 1.1 (0.4) ation, constant variance of residuals, normally distribution Hip extension, Nm/kg 1.8 (0.7) of residuals) for the multiple and linear regression analyses were met. The significance level was 0.05 and STATA 14 Baseline characteristics are presented as mean (SD) values and as numbers. (StataCorp, College Station, TX) software package was BMI, body mass index; CE, center-edge; AI, To¨nnis’ acetabular index; HAGOS, Copenhagen hip and groin outcome score; ADL, activities of daily living; NRS, used for data analysis. Numeric Rating Scale. RESULTS measurements (0.72–0.92) and the standard error of meas- A consecutive sample of 135 patients was assessed for eligi- bility and out of those, 100 patients were included in this urement ranged between 9.45% and 14.44%. The prevalence of muscle-tendon-related pain accord- study (Fig. 1). Baseline characteristics of the included pa- tients are reported in Table II. ing to specific entities was: iliopsoas-related pain 56% (CI 46; 66), abductor-related pain 42% (CI 32; 52), adductor- The inter-rater reliability of the standardized clinical en- tity approach is reported in Supplementary Appendix related pain 14% (CI 8; 22), Hamstring-related pain 6% (CI 2; 13) and rectus abdominis-related pain 4% (CI 1; Table S1 and the inter-rater reliability of the muscle strength test is reported in Supplementary Appendix Table 10). Twenty-six percent of the patients reported no muscle-related pain, as defined by non-existence of pain in S2. Agreement between rater A and rater B ranged from 64% to 100% with kappa-coefficients ranging from 0.17 to any of the predefined clinical entities, and the maximum number of pain-full clinical entities in individual patients 0.60. The ICC was >0.70 for all muscle strength Downloaded from https://academic.oup.com/jhps/article-abstract/5/1/39/4638269 by Ed 'DeepDyve' Gillespie user on 16 March 2018 Muscle-tendon-related pain in 100 patients with hip dysplasia  43 was four. The distribution of muscle-tendon-related pain in (58% and 36%, respectively). The higher prevalence of clinical entities was as follows: pain in one entity (38%), adductor-related pain in that study probably reflects that pain in two entities (27%), pain in three entities (6%) and the population is dominated by males and soccer players pain in four entities (3%). opposed to our female and non-specific sports-active study Both the crude and adjusted linear regression proved an population [15, 20, 25]. What was notable in our cohort inverse linear association between muscle-tendon-related was the large proportion of patients (42%) with abductor- pain and the self-reported HAGOS score (Table III). related pain. This fits well with the results of a previous Besides the adjusted association between muscle-tendon study reporting increased hip abduction and external rota- related pain and hip extension an inverse linear association tion torques in patients with hip dysplasia [7]. Possibly, between muscle-tendon-related pain and isometric hip the higher torques reported among patients with hip dys- muscle strength was found in both crude and adjusted ana- plasia exist due to the shallow acetabulum and reduced lyses (Table IV). weightbearing of the hip, where the muscles acting close to the hip may present with overuse-related pain in order to DISCUSSION maintain a levelled pelvis during ambulation. Patients with symptomatic hip dysplasia are characterized Abductor- and iliopsoas-related pain may potentially be improved by introducing heavy slow strength training by a high prevalence of muscle-tendon-related pain as- sessed with the clinical entity approach, and muscle-ten- using the side-lying hip abduction exercise and the stand- ing hip flexion exercise [26, 27], both performed in full ac- don-related pain evidently affects patients’ self-reported hip disability and muscle strength. Moreover, the findings tive range of motion [26, 27]. The heavy slow strength training including an eccentric emphasis could be an effect- suggest that muscle strength and hip disability may poten- tially be improved through exercise therapy focusing on ive way of reducing muscle-tendon-related pain and im- prove hip disability as has been shown in patients with reducing muscle-tendon-related lower extremity pain. To our knowledge, no previous studies have systematic- achilles and patellar tendinopathy [28–30]. In a random- ized trial, improvement in adductor-related pain was docu- ally assessed presence of muscle-tendon-related pain in a large cohort of hip dysplasia patients scheduled for PAO. mented in sports-active persons with longstanding groin pain [31], and in a cohort study, reduction of pain and suc- One cross-sectional study on 16 patients with symptomatic hip dysplasia documented pathology of the psoas tendon cessful return to sport were reported in runners with ilioti- bial band syndrome [32]. Similar exercise approaches seem in three hips [12], and another cross-sectional study on hip dysplasia patients treated with PAO 24 months earlier feasible in patients with symptomatic hip dysplasia. Our results showed significant associations between reported non-specific soft-tissue injury in 17% [6]. In a sample of sports-active persons with long-standing groin muscle-tendon-related pain and all six subscales of HAGOS, and the associations proved a linear relationship pain muscle-tendon-related pain in clinical entities was sys- tematically assessed [15], and adductor- and iliopsoas- between the number of clinical entities with muscle-ten- don-related pain and the reported HAGOS scores. This related pain were reported as the most prevalent entities Table III. Associations between muscle-tendon-related pain and self-reported disability (n ¼ 100) Crude Adjusted HAGOS points (0-100) b Coefficient (95% CI) P value b Coefficient (95% CI) P value HAGOS Pain 6.79 (10.12; 3.46) <0.001 6.90 (10.18; 3.61) <0.001 HAGOS Symptoms 6.26 (9.52; 3.01) <0.001 6.34 (9.61; 3.07) <0.001 HAGOS ADL 7.17 (11.41; 2.93) 0.001 7.51 (11.53; 3.49) <0.001 HAGOS Sport/rec 7.12 (11.01; 3.23) <0.001 7.39 (11.22; 3.56) <0.001 HAGOS Participation 5.73 (10.55; 0.92) 0.020 6.08 (10.89; 1.27) 0.014 HAGOS Quality of life 3.19 (5.98; 0.41) 0.025 3.35 (6.12; 0.58) 0.018 Linear regression of muscle-tendon-related pain on the self-reported HAGOS score reported as crude and adjusted b coefficients (95% confidence interval). Adjustments were made for age and gender. ADL, activities of daily living; sport/rec, sport/recreation. Downloaded from https://academic.oup.com/jhps/article-abstract/5/1/39/4638269 by Ed 'DeepDyve' Gillespie user on 16 March 2018 44  J. S. Jacobsen et al. Table IV. Associations between muscle-tendon-related pain and muscle strength (n ¼ 100) Crude Adjusted Hip muscle strength (Nm/kg) b Coefficient (95% CI) P value b Coefficient (95% CI) P value Flexion 0.12 (0.23; 0.02) 0.021 0.11 (0.21; 0.01) 0.038 Abduction 0.10 (0.19; 0.01) 0.023 0.11 (0.19; 0.03) 0.011 Adduction 0.12 (0.21; 0.03) 0.009 0.12 (0.20; 0.03) 0.010 Extension 0.14 (0.28; 0.01) 0.037 0.12 (0.25; 0.01) 0.077 Linear regression of muscle-tendon-related pain on the muscle strength values reported as crude and adjusted b coefficients (95% confidence interval). Adjustments were made for age and gender. means that per added painful entity a patient experiences, reported inter-rater values of a previous study on sports- the lower that patient will score in HAGOS. Patients with active people with long-standing groin pain our values are muscle-tendon-related pain in more than one entity is nor- systematically lower [14]. This discrepancy may exist be- mally presented in our cohort (represent 36%). The cause the second test was performed 3 days after the first HAGOS ADL score among these patients is minimum 15 test and not on the same day, and because the kappa coeffi- points lower than in patients with no pain [i.e. a patient cient depends on the prevalence [34]. The prevalence of with pain in one entity reports a 7.5 points lower score pain is low in the iliopsoas palpation lower abdomen (LA) than a patients with no pain, and a patient with pain in two test, the hamstrings palpation test and the hamstrings entities reports a 15 points (27.5) lower score than a pa- against resistance test, and the k values of these three tests tient with no pain, Table III (adjusted analysis)]. A should be interpreted with caution. The assessment of iso- HAGOS ADL score of 15 points is higher than the metric hip muscle strength are also exposed to measure- Minimal Important Change of 11.8 points [19]. This ment error because of the assessor-dependent approach. means, that the impact of muscle-tendon-related pain on Our values of the SEM% are similar but higher than the re- hip disability is of clinical relevance among patients with sults reported in a previous study on inter-tester reliability muscle-tendon-related pain, presenting with more than of isometric hip muscle strength test using belt fixation one entity. Based on this, the clinical entity approach may [35]. However, the SEM% is lower than the 20% border be used as a fast and in-expensive screening approach to se- reported by the Cochrane Musculoskeletal Group [33], lect hip dysplasia patients with substantial disability in and we included a large cohort where the measurement activities of daily living that is associated with the presence error has lesser impact. Based on the latter two arguments, of muscle-tendon-related pain. we find the variability of our muscle strength tests accept- The isometric muscle strength tests likewise showed a able. Another limitation is that we did not include a control linear and significant association between the number of group, and therefore we have no knowledge of the pres- clinical entities with muscle-tendon-related pain and ence of muscle-tendon-related pain in healthy subjects. muscle strength. This means that per added clinical entity Presence of muscle-tendon-related pain in our study was with muscle-tendon-related pain the lower strength will however based on provocation of earlier experienced pain, that patient have. The relative lower strength values in a which are probably unusual in subjects categorizing them- patient with muscle-tendon related pain in one clinical selves as healthy. A third limitation is, that we included pa- entity is approximately 10% and in two clinical entities is tients with both uni- and bilateral symptoms, which is approximately 20%. The latter is the same as the recom- similar to previous studies in this area [6, 36–38]. It cannot mended meaningful difference of 20% reported by the be ruled out that presence of hip dysplasia in one side of Cochrane Musculoskeletal Group [33] and higher than the the body could have had influence on muscle-tendon- SEM% values reported in this study, and the lower related pain of the other side. strength values indicate the relevance of muscle strength The results of this study provide evidence that there is a training. high prevalence of muscle-tendon-related pain in patients Our study has a number of limitations. The analysis of with symptomatic hip dysplasia. Previously, labral tears and inter-rater reliability showed slight to moderate agreement acetabular cartilage lesions have been described as the of the clinical entity approach. Compared with the primary cause of pain at the groin and/or lateral to the hip Downloaded from https://academic.oup.com/jhps/article-abstract/5/1/39/4638269 by Ed 'DeepDyve' Gillespie user on 16 March 2018 Muscle-tendon-related pain in 100 patients with hip dysplasia  45 exercises for patients with dysplastic hips. Isokinetics Exerc Sci [5, 6]. In the present study, we also found, a high preva- 2013; 21: 95–100. lence of muscle-tendon-related pain in clinical entities 9. Henak CR, Ellis BJ, Harris MD et al. Role of the acetabular la- dominated by a high prevalence of iliopsoas- and abductor- brum in load support across the hip joint. J Biomech 2011; 44: related pain. The implications of our results are that clin- 2201–6. icians and scientists have to re-evaluate the cause of pain 10. 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Muscle-tendon-related pain in 100 patients with hip dysplasia: prevalence and associations with self-reported hip disability and muscle strength

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Journal of Hip Preservation Surgery Vol. 5, No. 1, pp. 39–46 doi: 10.1093/jhps/hnx041 Advance Access Publication 17 November 2017 Research article Muscle-tendon-related pain in 100 patients with hip dysplasia: prevalence and associations with self- reported hip disability and muscle strength 1,2 3 3 4 Julie Sandell Jacobsen *, Per Ho¨lmich , Kristian Thorborg , Lars Bolvig , 5 5 6 Stig Storgaard Jakobsen , Kjeld Søballe and Inger Mechlenburg Department of Physiotherapy, Faculty of Health Sciences, VIA University College, Hedeager 2, 8200, Aarhus N, Denmark, Department of Physiotherapy and Occupational Therapy, Aarhus University Hospital, Tage-Hansens Gade 2, 8000 Aarhus C, Denmark, Department of Orthopaedic Surgery, Sports Orthopedic Research Center-Copenhagen (SORC-C), Copenhagen University Hospital, Amager and Hvidovre, Italiensvej 1, 2300 Copenhagen S, Denmark, Department of Radiology, Aarhus University Hospital, Tage-Hansens Gade 2, 8000 Aarhus C, Denmark, Department of Orthopaedic Surgery, Aarhus University Hospital, Tage-Hansens Gade 2, 8000 Aarhus C, Denmark and Centre of Research in Rehabilitation (CORIR), Institute of Clinical Medicine, Aarhus University, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark *Correspondence to: J. S. Jacobsen. E-mail: jsaj@via.dk Submitted 5 April 2017; Revised 22 August 2017; revised version accepted 16 September 2017 ABSTRACT The primary aim was to identify muscle-tendon-related pain in 100 patients with hip dysplasia. The secondary aim was to test whether muscle-tendon-related pain is associated with self-reported hip disability and muscle strength in patient with hip dysplasia. One hundred patients (17 men) with a mean age of 29 years (SD 9) were included. Clinical entity approach was carried out to identify muscle-tendon-related pain. Associations between muscle-tendon-related pain and self-reported hip disability and muscle strength were tested with multiple regres- sion analysis, including adjustments for age and gender. Self-reported hip disability was recorded with the Copenhagen Hip and Groin Outcome Score (HAGOS), and muscle strength was assessed with a handheld dyna- mometer. Iliopsoas- and abductor-related pain were most prevalent with prevalences of 56% (CI 46; 66) and 42% (CI 32; 52), respectively. Adductor-, hamstrings- and rectus abdominis-related pain were less common. There was a significant inverse linear association between muscle-tendon-related pain and self-reported hip disability ranging from 3.35 to  7.51 HAGOS points in the adjusted analysis (P< 0.05). Besides the association between muscle-tendon-related pain and hip extension a significant inverse linear association between muscle- tendon-related pain and muscle strength was found ranging from 0.11 to  0.12 Nm/kg in the adjusted analysis (P< 0.05). Muscle-tendon-related pain exists in about half of patients with hip dysplasia with a high prevalence of muscle-tendon-related pain in the iliopsoas and the hip abductors and affects patients’ self-reported hip disabil- ity and muscle strength negatively. and intra-articular injury has been reported as one INTRODUCTION important predisposing factor to development of osteoarth- Symptomatic hip dysplasia normally presents in early life ritis [2]. Labrum injury or degeneration is present in 49– [1] and left untreated, hip dysplasia may lead to develop- 83% of patients with hip dysplasia [2, 5], and causes pain at ment of early osteoarthritis [2, 3]. The aetiology of hip the groin and/or lateral to the hip [5, 6]. Moreover, the osteoarthritis in hip dysplasia is unknown and often shallow acetabulum and the reduced weight bearing are described as multifactorial [2]. However, the lack of acetab- associated with increased load on the muscles acting close ular support to the femoral head [4] and the compromised to the hip joint [7, 8], and muscle-tendon-related pain may passive stability of the hip joint lead to an increased mech- potentially coexist with intra-articular pathology. anical pressure on the acetabular labrum and cartilage [2], V C The Author 2017. 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/5/1/39/4638269 by Ed 'DeepDyve' Gillespie user on 16 March 2018 40  J. S. Jacobsen et al. The acetabular labrum functions as an important anterior the hip, knee or ankle, (iv) Neurological, rheumatological or stabilizer to the dysplastic hip [9], and the location of the medical conditions affecting the function of the hip joint, iliopsoas muscle close to the capsule–labral complex en- (v) Tenotomy of the iliopsoas tendon or z-plastic of the ilio- ables the muscle to work as an anterior stabilizer to the hip tibial band and (vi) Steroid-injection in the iliopsoas tendon joint [10]. The gluteus medius and minimus muscles work and/or bursa trochanterica within the last 6 weeks. together with the iliopsoas muscle as important lateral sta- bilizers to maintain a level led pelvis during ambulation Study design [11]. The stabilizing role of the iliopsoas and gluteus med- All outcomes measures were collected prior to PAO during ius and minimus muscles may be increased in hip dysplasia a clinical examination. The clinical examination was com- due to the morphology of the hip joint [7, 10], and poten- pleted by two experienced physical therapists (CMS and tially higher load on the muscles may lead to overuse- JSJ) with 5 and 7 years of experience assessing patients related pain in the muscles and tendons. with hip dysplasia, respectively. The patients were ran- Muscle-tendon-related pain is present in hip dysplasia domly assessed by the two physical therapists with approxi- [6, 12], and abnormality of the iliopsoas muscle identified mately equal distribution between the two (60:40). The as internal snapping hip has been verified in 18% using hip examination included recording of self-reported hip disabil- arthroscopy [12]. In patients with femoroacetabular im- ity, examination of muscle-tendon-related pain in clinical pingement muscle-tendon-related pain frequently coexist entities and hip muscle strength tests. with the morphology of the hip joint [13], and in sports- active subjects with long-standing groin pain, muscle-ten- Self-reported hip disability don-related pain has been identified with the clinical entity The Copenhagen Hip and Groin Outcome Score approach [14, 15]. In patients with hip dysplasia, however, (HAGOS) questionnaire was completed by all patients no previous studies have systematically examined the pres- prior to the clinical examinations [18]. HAGOS has shown ence of muscle-tendon-related pain in a consecutive cohort to be a valid, reliable and responsive measure of hip disabil- scheduled for periacetabular osteotomy. ity and associated problems in young to middle-aged phys- The primary aim was to identify muscle-tendon-related ically active patients with longstanding hip and/or groin pain in 100 patients with hip dysplasia in the following pain including patients undergoing hip arthroscopy [18, clinical entities: (i) iliopsoas, (ii) abductors, (iii) adductors, 19]. HAGOS consists of six separate subscales rating hip (iv) hamstrings, and (v) rectus abdominis. The secondary disability from 0 to 100 points, where zero points indicates aim was to test if muscle-tendon-related pain is associated the lowest outcome [18]. The six subscales measure pain, with self-reported hip disability and muscle strength in pa- symptoms, physical function in daily living (ADL), physical tient with hip dysplasia. function in sports and recreation, participation in physical activity and quality of life [18]. MATERIALS AND METHODS This study complies with the Helsinki Declaration and was Muscle-tendon-related pain notified to the Danish Committee on Biomedical and Research Ethics at 14 January 2014 (5/2014). The Danish A standardized clinical entity approach was carried out to Data Protection Agency gave permission for the handling identify muscle-tendon-related pain in clinical entities as- of personal data (1-16-02-47-14), and the study was regis- sessed in the limb scheduled for PAO [14, 15, 20]. The tered at ClinicalTrials.gov (20140401PAO). standardized entity approach includes a number of pain provocation tests covered by anatomic palpation, resistance Subjects testing and passive muscle stretch (Table I). The approach In a consecutive sample, patients with bilateral or unilateral includes five entities, and the entities were tested in the fol- hip dysplasia were invited to participate from May 2014 to lowing order: adduction-related pain, iliopsoas-related August 2015 from the Department of Orthopedics at pain, rectus abdominis-related pain, abductor-related pain Aarhus University Hospital in Denmark. Inclusion criteria and hamstring-related pain. Rectus abdominis-related pain were Wiberg’s center-edge (CE) angle<25 [16], groin is in the Doha consensus covered by the term inguinal- pain for at least 3 months and scheduled periacetabular oste- related pain [20]. Inguinal-related pain is less relevant otomy (PAO) [17]. Patients were excluded based on the among patients with hip dysplasia as many of these pa- following criteria: (i) Calve´ Perthes and epiphysiolysis, tients are women in which the inguinal canal anatomy is (ii) Surgery due to herniated disc and spondylodesis, somewhat different from males, and therefore rectus- (iii) Previous joint preservation procedure or arthroplasty of abdominis-related pain was the focus in the present study. Downloaded from https://academic.oup.com/jhps/article-abstract/5/1/39/4638269 by Ed 'DeepDyve' Gillespie user on 16 March 2018 Muscle-tendon-related pain in 100 patients with hip dysplasia  41 Table I. Diagnostic criteria for each individual entity Clinical entities Diagnostic criteria Iliopsoas-related pain Palpatory pain of the muscle through the lower lateral part of the abdomen and/or just dis- tal of the inguinal ligament and pain with passive stretching during modified Thomas’ test [14, 20, 21] Abductor-related pain Palpatory pain at the insertion point at the greater trochanter and pain with side-lying ab- duction against resistance Adductor-related pain Palpatory pain at the muscle origin at the pubic bone and pain with adduction against resistance [14, 20] Hamstring-related pain Palpatory pain at the muscle origin at the tuber ischii and pain with extension against resistance Rectus abdominis-related pain Palpatory pain of the distal tendon and/or the insertion at the pubic bone, and pain at con- traction against resistance [14, 20] Muscle strength measures was investigated. Twenty-five patients were Isometric muscle strength tests were performed using a reli- tested 6 weeks after PAO by two physiotherapists, rater A able dynamometer technique [22]. Muscle strength was and B (CMS and JSJ), with a 2-day period between a first tested with a handheld dynamometer (powertrack II coman- and second test. Each patient was randomized to whether dor, JTECH Medical, Salt Lake City, Utah). Isometric hip rater A or B performed the initial testing. adduction, abduction, flexion and extension strength were measured in the limb scheduled for PAO, and the order of Sample size the individual tests was randomized before each session to Since it was not possible to calculate the sample size based avoid systematic bias. The examiner applied resistance 5 cm on the prevalence of muscle-tendon-related pain, we chose proximal to the proximal edge of the lateral malleolus for hip to calculate it based on the secondary outcome of the abduction, adduction and extension. Resistance in hip flexion study. The sample size calculation was based on the was performed 5 cm proximal to the proximal border of pa- HAGOS ADL subscore with an estimated difference of tella. In all the isometric tests, the patients exerted 5-s 11.8 points and an estimated standard deviation of 18.5 Maximal Voluntary Isometric Contraction (MVIC) against points between patients with and without muscle-tendon- the dynamometer. The highest value of four repeated meas- related pain. The estimated difference was based on the urements for each test was used in the analysis. To avoid fa- Minimal Important Change of 11.8 points reported in a co- tigue, patients rested for 30 s between each measurement. All hort study on patients with femoroacetabular impingement strength values were weight-adjusted and reported as scheduled for hip arthroscopy [19], and the standard devi- Newton meters per kilogram of the bodyweight. ation was based on the standard deviation of the HAGOS ADL subscore of 18.5 points reported in a cohort study on Baseline characteristics patients with intra-articular hip lesions undergoing hip Baseline characteristics were registered using standardized arthroscopy [24]. Based on a significance level of 5% and a questions. Pain was measured on a numeric rating scale power of 80%, 80 patients were needed, and considering (NRS) in rest while sitting and lying. The center-edge the risk of dropouts, we included 100 patients. (CE) angle [16], To¨nnis’ acetabular index (AI) angle [23] and To¨nnis’ osteoarthritis grade [23] were measured by a Statistics single rater (SSJ) using anteroposterior radiographs, Normal distribution was checked with histograms and whereas hospital charts was used to record unilateral or bi- probability plots. Multiple linear regression analyses were lateral hip involvement and other pathologies. performed with muscle-tendon-related pain as the inde- pendent variable (i.e. the sum of positive clinical entities Inter-rater reliability of the test battery for each patient) and each HAGOS subscale as the de- Two different testers assessed muscle-tendon-related pain pendent variable (pain, symptoms, ADL, physical function and muscle strength and the inter-rater reliability of these in sports and recreation, participation in physical activity Downloaded from https://academic.oup.com/jhps/article-abstract/5/1/39/4638269 by Ed 'DeepDyve' Gillespie user on 16 March 2018 42  J. S. Jacobsen et al. Table II. Baseline characteristics in 100 consecutive patients with hip dysplasia Outcomes Patients (SD) Men 17 Bilateral symptoms 89 Osteoarthritis grade 0/1 97/3 Congenital hip dislocation 6 Age, years 29.9 (9.2) BMI, kg/m 23.2 (3.0) Duration of pain, years 4.9 (5.6) NRS pain lying, 0–10 3.1 (2.4) Fig. 1. Flowchart of the study process. One hundred consecutive NRS pain sitting, 0–10 3.8 (2.7) patients with unilateral and bilateral symptoms were included CE angle preoperatively, degrees 17.4 (4.7) from the Division of Hip Surgery, Department of Orthopedics, Aarhus University Hospital in Denmark from May 2014 to AI angle preoperatively, degrees 13.8 (4.9) August 2015. Abbreviations: HD, hip dysplasia; ADHD, atten- tion deficit/hyperactivity disorder; MRSA, methicillin-resistant HAGOS pain, 0–100 50.3 (18.0) Staphylococcus aureus. HAGOS symptoms, 0–100 49.2 (17.4) and quality of life). Crude and adjusted b-coefficients were HAGOS ADL, 0–100 55.5 (22.4) estimated, and adjustments were made for age and gender. HAGOS sport/recreation, 0–100 39.3 (20.7) Likewise, multiple linear regression analyses were per- formed with muscle-tendon-related pain as the independ- HAGOS participation, 0–100 23.0 (24.7) ent variable (i.e. the sum of positive clinical entities for HAGOS quality of life, 0–100 29.4 (14.3) each patient) and strength of each muscle group as the de- pendent variable (i.e. flexion, abduction, adduction and ex- Hip flexion, Nm/kg 1.2 (0.5) tension). Crude and adjusted b-coefficients were Hip abduction, Nm/kg 1.2 (0.4) estimated, and adjustments were made for age and gender. The assumptions (independent observations, linear associ- Hip adduction, Nm/kg 1.1 (0.4) ation, constant variance of residuals, normally distribution Hip extension, Nm/kg 1.8 (0.7) of residuals) for the multiple and linear regression analyses were met. The significance level was 0.05 and STATA 14 Baseline characteristics are presented as mean (SD) values and as numbers. (StataCorp, College Station, TX) software package was BMI, body mass index; CE, center-edge; AI, To¨nnis’ acetabular index; HAGOS, Copenhagen hip and groin outcome score; ADL, activities of daily living; NRS, used for data analysis. Numeric Rating Scale. RESULTS measurements (0.72–0.92) and the standard error of meas- A consecutive sample of 135 patients was assessed for eligi- bility and out of those, 100 patients were included in this urement ranged between 9.45% and 14.44%. The prevalence of muscle-tendon-related pain accord- study (Fig. 1). Baseline characteristics of the included pa- tients are reported in Table II. ing to specific entities was: iliopsoas-related pain 56% (CI 46; 66), abductor-related pain 42% (CI 32; 52), adductor- The inter-rater reliability of the standardized clinical en- tity approach is reported in Supplementary Appendix related pain 14% (CI 8; 22), Hamstring-related pain 6% (CI 2; 13) and rectus abdominis-related pain 4% (CI 1; Table S1 and the inter-rater reliability of the muscle strength test is reported in Supplementary Appendix Table 10). Twenty-six percent of the patients reported no muscle-related pain, as defined by non-existence of pain in S2. Agreement between rater A and rater B ranged from 64% to 100% with kappa-coefficients ranging from 0.17 to any of the predefined clinical entities, and the maximum number of pain-full clinical entities in individual patients 0.60. The ICC was >0.70 for all muscle strength Downloaded from https://academic.oup.com/jhps/article-abstract/5/1/39/4638269 by Ed 'DeepDyve' Gillespie user on 16 March 2018 Muscle-tendon-related pain in 100 patients with hip dysplasia  43 was four. The distribution of muscle-tendon-related pain in (58% and 36%, respectively). The higher prevalence of clinical entities was as follows: pain in one entity (38%), adductor-related pain in that study probably reflects that pain in two entities (27%), pain in three entities (6%) and the population is dominated by males and soccer players pain in four entities (3%). opposed to our female and non-specific sports-active study Both the crude and adjusted linear regression proved an population [15, 20, 25]. What was notable in our cohort inverse linear association between muscle-tendon-related was the large proportion of patients (42%) with abductor- pain and the self-reported HAGOS score (Table III). related pain. This fits well with the results of a previous Besides the adjusted association between muscle-tendon study reporting increased hip abduction and external rota- related pain and hip extension an inverse linear association tion torques in patients with hip dysplasia [7]. Possibly, between muscle-tendon-related pain and isometric hip the higher torques reported among patients with hip dys- muscle strength was found in both crude and adjusted ana- plasia exist due to the shallow acetabulum and reduced lyses (Table IV). weightbearing of the hip, where the muscles acting close to the hip may present with overuse-related pain in order to DISCUSSION maintain a levelled pelvis during ambulation. Patients with symptomatic hip dysplasia are characterized Abductor- and iliopsoas-related pain may potentially be improved by introducing heavy slow strength training by a high prevalence of muscle-tendon-related pain as- sessed with the clinical entity approach, and muscle-ten- using the side-lying hip abduction exercise and the stand- ing hip flexion exercise [26, 27], both performed in full ac- don-related pain evidently affects patients’ self-reported hip disability and muscle strength. Moreover, the findings tive range of motion [26, 27]. The heavy slow strength training including an eccentric emphasis could be an effect- suggest that muscle strength and hip disability may poten- tially be improved through exercise therapy focusing on ive way of reducing muscle-tendon-related pain and im- prove hip disability as has been shown in patients with reducing muscle-tendon-related lower extremity pain. To our knowledge, no previous studies have systematic- achilles and patellar tendinopathy [28–30]. In a random- ized trial, improvement in adductor-related pain was docu- ally assessed presence of muscle-tendon-related pain in a large cohort of hip dysplasia patients scheduled for PAO. mented in sports-active persons with longstanding groin pain [31], and in a cohort study, reduction of pain and suc- One cross-sectional study on 16 patients with symptomatic hip dysplasia documented pathology of the psoas tendon cessful return to sport were reported in runners with ilioti- bial band syndrome [32]. Similar exercise approaches seem in three hips [12], and another cross-sectional study on hip dysplasia patients treated with PAO 24 months earlier feasible in patients with symptomatic hip dysplasia. Our results showed significant associations between reported non-specific soft-tissue injury in 17% [6]. In a sample of sports-active persons with long-standing groin muscle-tendon-related pain and all six subscales of HAGOS, and the associations proved a linear relationship pain muscle-tendon-related pain in clinical entities was sys- tematically assessed [15], and adductor- and iliopsoas- between the number of clinical entities with muscle-ten- don-related pain and the reported HAGOS scores. This related pain were reported as the most prevalent entities Table III. Associations between muscle-tendon-related pain and self-reported disability (n ¼ 100) Crude Adjusted HAGOS points (0-100) b Coefficient (95% CI) P value b Coefficient (95% CI) P value HAGOS Pain 6.79 (10.12; 3.46) <0.001 6.90 (10.18; 3.61) <0.001 HAGOS Symptoms 6.26 (9.52; 3.01) <0.001 6.34 (9.61; 3.07) <0.001 HAGOS ADL 7.17 (11.41; 2.93) 0.001 7.51 (11.53; 3.49) <0.001 HAGOS Sport/rec 7.12 (11.01; 3.23) <0.001 7.39 (11.22; 3.56) <0.001 HAGOS Participation 5.73 (10.55; 0.92) 0.020 6.08 (10.89; 1.27) 0.014 HAGOS Quality of life 3.19 (5.98; 0.41) 0.025 3.35 (6.12; 0.58) 0.018 Linear regression of muscle-tendon-related pain on the self-reported HAGOS score reported as crude and adjusted b coefficients (95% confidence interval). Adjustments were made for age and gender. ADL, activities of daily living; sport/rec, sport/recreation. Downloaded from https://academic.oup.com/jhps/article-abstract/5/1/39/4638269 by Ed 'DeepDyve' Gillespie user on 16 March 2018 44  J. S. Jacobsen et al. Table IV. Associations between muscle-tendon-related pain and muscle strength (n ¼ 100) Crude Adjusted Hip muscle strength (Nm/kg) b Coefficient (95% CI) P value b Coefficient (95% CI) P value Flexion 0.12 (0.23; 0.02) 0.021 0.11 (0.21; 0.01) 0.038 Abduction 0.10 (0.19; 0.01) 0.023 0.11 (0.19; 0.03) 0.011 Adduction 0.12 (0.21; 0.03) 0.009 0.12 (0.20; 0.03) 0.010 Extension 0.14 (0.28; 0.01) 0.037 0.12 (0.25; 0.01) 0.077 Linear regression of muscle-tendon-related pain on the muscle strength values reported as crude and adjusted b coefficients (95% confidence interval). Adjustments were made for age and gender. means that per added painful entity a patient experiences, reported inter-rater values of a previous study on sports- the lower that patient will score in HAGOS. Patients with active people with long-standing groin pain our values are muscle-tendon-related pain in more than one entity is nor- systematically lower [14]. This discrepancy may exist be- mally presented in our cohort (represent 36%). The cause the second test was performed 3 days after the first HAGOS ADL score among these patients is minimum 15 test and not on the same day, and because the kappa coeffi- points lower than in patients with no pain [i.e. a patient cient depends on the prevalence [34]. The prevalence of with pain in one entity reports a 7.5 points lower score pain is low in the iliopsoas palpation lower abdomen (LA) than a patients with no pain, and a patient with pain in two test, the hamstrings palpation test and the hamstrings entities reports a 15 points (27.5) lower score than a pa- against resistance test, and the k values of these three tests tient with no pain, Table III (adjusted analysis)]. A should be interpreted with caution. The assessment of iso- HAGOS ADL score of 15 points is higher than the metric hip muscle strength are also exposed to measure- Minimal Important Change of 11.8 points [19]. This ment error because of the assessor-dependent approach. means, that the impact of muscle-tendon-related pain on Our values of the SEM% are similar but higher than the re- hip disability is of clinical relevance among patients with sults reported in a previous study on inter-tester reliability muscle-tendon-related pain, presenting with more than of isometric hip muscle strength test using belt fixation one entity. Based on this, the clinical entity approach may [35]. However, the SEM% is lower than the 20% border be used as a fast and in-expensive screening approach to se- reported by the Cochrane Musculoskeletal Group [33], lect hip dysplasia patients with substantial disability in and we included a large cohort where the measurement activities of daily living that is associated with the presence error has lesser impact. Based on the latter two arguments, of muscle-tendon-related pain. we find the variability of our muscle strength tests accept- The isometric muscle strength tests likewise showed a able. Another limitation is that we did not include a control linear and significant association between the number of group, and therefore we have no knowledge of the pres- clinical entities with muscle-tendon-related pain and ence of muscle-tendon-related pain in healthy subjects. muscle strength. This means that per added clinical entity Presence of muscle-tendon-related pain in our study was with muscle-tendon-related pain the lower strength will however based on provocation of earlier experienced pain, that patient have. The relative lower strength values in a which are probably unusual in subjects categorizing them- patient with muscle-tendon related pain in one clinical selves as healthy. A third limitation is, that we included pa- entity is approximately 10% and in two clinical entities is tients with both uni- and bilateral symptoms, which is approximately 20%. The latter is the same as the recom- similar to previous studies in this area [6, 36–38]. It cannot mended meaningful difference of 20% reported by the be ruled out that presence of hip dysplasia in one side of Cochrane Musculoskeletal Group [33] and higher than the the body could have had influence on muscle-tendon- SEM% values reported in this study, and the lower related pain of the other side. strength values indicate the relevance of muscle strength The results of this study provide evidence that there is a training. high prevalence of muscle-tendon-related pain in patients Our study has a number of limitations. The analysis of with symptomatic hip dysplasia. Previously, labral tears and inter-rater reliability showed slight to moderate agreement acetabular cartilage lesions have been described as the of the clinical entity approach. Compared with the primary cause of pain at the groin and/or lateral to the hip Downloaded from https://academic.oup.com/jhps/article-abstract/5/1/39/4638269 by Ed 'DeepDyve' Gillespie user on 16 March 2018 Muscle-tendon-related pain in 100 patients with hip dysplasia  45 exercises for patients with dysplastic hips. Isokinetics Exerc Sci [5, 6]. In the present study, we also found, a high preva- 2013; 21: 95–100. lence of muscle-tendon-related pain in clinical entities 9. Henak CR, Ellis BJ, Harris MD et al. Role of the acetabular la- dominated by a high prevalence of iliopsoas- and abductor- brum in load support across the hip joint. J Biomech 2011; 44: related pain. The implications of our results are that clin- 2201–6. icians and scientists have to re-evaluate the cause of pain 10. 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Journal of Hip Preservation SurgeryOxford University Press

Published: Jan 1, 2018

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