TY - JOUR
AU - Tanaka, Sakae
AB - Abstract Objectives. This study aimed to evaluate the clinical safety and wear-resistance of the novel highly cross-linked polyethylene (HXLPE) acetabular liner with surface grafting of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) at 3 years after total hip replacement (THR). Methods. Eighty consecutive patients underwent cementless THR using a 26-mm diameter cobalt–chromium–molybdenum alloy femoral head and a PMPC-grafted HXLPE liner for the bearing couplings. We evaluated the clinical and radiographic outcomes of 76 patients at 3 years after the index surgery. Results. The clinical results at 3 years were equivalent to a Harris hip score of 95.6 points. No adverse events were associated with the implanted PMPC-grafted HXLPE liner, and no periprosthetic osteolysis was detected. The mean femoral head penetration rate was 0.002 mm/year, representing marked reduction compared with other HXLPE liners. Conclusions. A PMPC-grafted HXLPE liner is a safe option in THR and probably reduces the generation of wear particles. Arthroplasty, Hip prosthesis, Joint replacement, Polyethylene (UHMWPE), Wear Introduction Total hip replacement (THR) is an established treatment modality for patients with end-stage hip disorders such as osteoarthritis and rheumatoid arthritis. However, periprosthetic osteolysis has been recognized as a notable complication affecting the long-term survival of THR; extensive research has shown that wear particles from the polyethylene (PE) liners are responsible for osteolysis [1]. Hence, many approaches have been adopted for reducing the generation of wear particles thereby improving the survival of THR. Recent observations of the healthy mammalian articular cartilage surface have disclosed that it is covered with a nanometer-scaled phospholipid layer that protects the articulating surface from mechanical wear and facilitates a smooth motion of joints during daily activities [2,3]. Hence, grafting a polymer with a phospholipid-like layer on the liner surface may mimic the surface conditions of healthy articular cartilage. Based on this hypothesis, we have successfully produced a biocompatible and highly hydrophilic surface via nanometer-scaled grafting of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) onto highly cross-linked polyethylene (HXLPE) [4]. Our hip simulator studies revealed that such grafting remarkably reduced the wear of an HXLPE liner up to 20 × 106 cycles [5–7]. We reported that PMPC-grafted surfaces captured water molecules and reduced the friction between the bearing surfaces via the hydration lubrication mechanism [8]. In addition, we reported that the PMPC-grafted particles were biologically inert and did not cause subsequent bone-resorptive responses [4], indicating that this technology prevents wear particle production and biological reactions to such particles in THR. Since then, PMPC-grafted HXLPE liners have been used in hip replacement surgery to address the concerns of wear and osteolysis. From the perspective of material engineering, the PMPC-grafted HXLPE liner is a new medical implant prepared from MPC polymer, which has been used on the surface of artificial lungs [9], intravascular stents [10], soft contact lenses [11], and the artificial hearts [12]. Such implants were introduced into clinical practice from 1997, and since then, no adverse reactions to MPC polymer have been reported. The major difference between other devices and the PMPC-grafted HXLPE liner is the method used for its MPC polymer coating, the photo-induced graft polymerization, which is considered appropriate for withstanding weight [4]. The purpose of this follow-up for a prospective cohort study, in which 80 primary cementless THRs were performed using a PMPC-grafted HXLPE liner [13], was to report the clinical and radiographic outcomes, including femoral head penetration, at 3 years after the index surgery. The outline of this study was disclosed as UMIN000003681. Methods Between April 2007 and September 2008, 80 consecutive patients who underwent THR for a Charnley Class A or Class B painful, non-infectious hip disorder were recruited from five participating hospitals [14]. The institutional review board of each participating hospital granted ethical approval, and informed consent was obtained from all participants before the study commenced. All patients received the K-MAX cementless THR (KYOCERA Medical Corporation, Osaka, Japan) consisting of a collarless femoral stem (K-MAX HS-6) and a low-profile porous-coated acetabular component with four peripheral fins (K-MAX Q5LP). For the bearing coupling, a 26-mm-diameter cobalt–chromium–molybdenum (Co–Cr–Mo) alloy femoral head and a PMPC-grafted HXLPE liner were employed. PMPC grafting of the surfaces of the HXLPE liner was performed using a photoinduced polymerization technique as previously reported [4]. The surgeries were performed by 10 surgeons of 5 institutions, who used the posterior approach. Patients underwent the routine thromboprophylaxis regimen and postoperative rehabilitation program of each institution. All patients were prospectively followed for 3 years after the index surgery. During the course of the study, all adverse events suspected to correlate with the implanted PMPC-grafted HXLPE liner were recorded. Orthopedic surgeons other than the operators evaluated clinical performance using the evaluation chart of hip joint function authorized by the Japanese Orthopaedic Association (JOA score) [15]. The JOA score consists of four categories: pain (40 points), range of motion (20 points), gait (20 points), and activities of daily living (20 points). Fujisawa et al. reported that there was an excellent correlation between the JOA and Harris hip scores (coefficient of correlation = 0.843) [16]. Therefore, we calculated the equivalent Harris hip score using the following regression formula: Harris hip score = JOA score × 0.979 + 4.363. Anteroposterior pelvic radiographs were obtained with the patient in supine, immediately after surgery and at 3 weeks, 3 months, 6 months, 1 year, and 3 years postoperatively. The distance between the X-ray tube and the imaging plate was set to 100 cm, and the center of the X-ray beam was directed at the cranial end of the pubic symphysis. The digitized image data were stored at a resolution of 0.13–0.20 mm/pixel. We compared the radiographs obtained at 3 weeks with those obtained at up to 3 years for detecting periprosthetic osteolysis and assessing implant stability. Periprosthetic osteolysis was defined as new cystic lucency localized on the endosteal surface of the bone [17]. Migration of the femoral component was defined as a change of 3 mm or above in the position of the implant [18]. To assess the stability of the acetabular component, we modified the method described by Engh et al. [19]. The acetabular component was defined as stable, suboptimally stable (migrated ≤ 2 mm or tilted ≤ 5°), or unstable (migrated > 2 mm or tilted > 5°). In addition, three independent reviewers measured the position of the femoral head on digitized radiographic images obtained at 3 weeks, 6 months, 1 year, and 3 years after implantation, without any clinical information. They employed a 2D computerized method—the PolyWare technique (Draftware Inc., Vevay, IN) [20]. Each reviewer measured the position of the femoral head thrice on a radiograph and recorded the median as the measured value. The authors calculated the average value of the three measured values recorded by the three reviewers and stored it in a database as the observed data. Then, they calculated the change in the femoral head position in each patient as the amount of femoral head penetration using the position at 3 weeks as the original position. Several authors have reported a biphasic pattern in the progression of femoral head penetration into an HXLPE liner [19,21–25]. In the first phase, the femoral head rapidly moves into the liner; this phenomenon is called “bedding-in” and is largely attributed to permanent plastic deformation of the material and setting of the liner in the metal shell [22]. In the second phase, the femoral head slowly moves into the liner; this phenomenon is largely attributed to true wear—material loss in the form of particles—and is considered the “steady-state wear rate”. We used these terms to describe the measurement results. Statistical methods The paired t-test was used to compare the JOA scores recorded before surgery and at 3 years after surgery. Pearson's correlation coefficient or the Mann–Whitney U test was employed to test the correlations between the measurement of femoral head penetration and patient characteristics, such as body mass index (BMI). Results Of the original 80 patients, 1 died of a cause unrelated to the joint replacement and 3 were lost or refused to return for follow-up at 3 years postoperatively. Thus, the study group comprised 76 patients (Table 1). Table 1. Preoperative demographic data. Items All patients Patients (%) 76 Sex Male 14 (18.4) Female 62 (81.6) Age (years) 40–49 5 (6.6) 50–59 30 (39.5) 60–69 22 (28.9) 70–75 19 (25.0) Diagnosis Osteoarthritis 73 (96.1) Osteonecrosis 3 (3.9) Charnley Category A 40 (52.6) B 36 (47.4) Side Right 42 (55.3) Left 34 (44.7) Body Height (cm) > 140 to ≦ 150 17 (22.4) > 150 to ≦ 160 40 (52.6) > 160 to ≦ 170 18 (23.7) > 170 to ≦ 180 1 (1.3) Mean ± SD 155.5 ± 6.5 Body Weight (kg) > 30 to ≦ 40 4 (5.3) > 40 to ≦ 50 17 (22.4) > 50 to ≦ 60 41 (53.9) > 60 to ≦ 70 13 (17.1) > 70 to ≦ 80 1 (1.3) Mean ± SD 54.4 ± 7.4 Body Mass Index > 15 to ≦ 20 11 (14.5) > 20 to ≦ 25 49 (64.5) > 25 to ≦ 30 16 (21.1) Mean ± SD 22.5 ± 2.5 Items All patients Patients (%) 76 Sex Male 14 (18.4) Female 62 (81.6) Age (years) 40–49 5 (6.6) 50–59 30 (39.5) 60–69 22 (28.9) 70–75 19 (25.0) Diagnosis Osteoarthritis 73 (96.1) Osteonecrosis 3 (3.9) Charnley Category A 40 (52.6) B 36 (47.4) Side Right 42 (55.3) Left 34 (44.7) Body Height (cm) > 140 to ≦ 150 17 (22.4) > 150 to ≦ 160 40 (52.6) > 160 to ≦ 170 18 (23.7) > 170 to ≦ 180 1 (1.3) Mean ± SD 155.5 ± 6.5 Body Weight (kg) > 30 to ≦ 40 4 (5.3) > 40 to ≦ 50 17 (22.4) > 50 to ≦ 60 41 (53.9) > 60 to ≦ 70 13 (17.1) > 70 to ≦ 80 1 (1.3) Mean ± SD 54.4 ± 7.4 Body Mass Index > 15 to ≦ 20 11 (14.5) > 20 to ≦ 25 49 (64.5) > 25 to ≦ 30 16 (21.1) Mean ± SD 22.5 ± 2.5 Open in new tab Table 1. Preoperative demographic data. Items All patients Patients (%) 76 Sex Male 14 (18.4) Female 62 (81.6) Age (years) 40–49 5 (6.6) 50–59 30 (39.5) 60–69 22 (28.9) 70–75 19 (25.0) Diagnosis Osteoarthritis 73 (96.1) Osteonecrosis 3 (3.9) Charnley Category A 40 (52.6) B 36 (47.4) Side Right 42 (55.3) Left 34 (44.7) Body Height (cm) > 140 to ≦ 150 17 (22.4) > 150 to ≦ 160 40 (52.6) > 160 to ≦ 170 18 (23.7) > 170 to ≦ 180 1 (1.3) Mean ± SD 155.5 ± 6.5 Body Weight (kg) > 30 to ≦ 40 4 (5.3) > 40 to ≦ 50 17 (22.4) > 50 to ≦ 60 41 (53.9) > 60 to ≦ 70 13 (17.1) > 70 to ≦ 80 1 (1.3) Mean ± SD 54.4 ± 7.4 Body Mass Index > 15 to ≦ 20 11 (14.5) > 20 to ≦ 25 49 (64.5) > 25 to ≦ 30 16 (21.1) Mean ± SD 22.5 ± 2.5 Items All patients Patients (%) 76 Sex Male 14 (18.4) Female 62 (81.6) Age (years) 40–49 5 (6.6) 50–59 30 (39.5) 60–69 22 (28.9) 70–75 19 (25.0) Diagnosis Osteoarthritis 73 (96.1) Osteonecrosis 3 (3.9) Charnley Category A 40 (52.6) B 36 (47.4) Side Right 42 (55.3) Left 34 (44.7) Body Height (cm) > 140 to ≦ 150 17 (22.4) > 150 to ≦ 160 40 (52.6) > 160 to ≦ 170 18 (23.7) > 170 to ≦ 180 1 (1.3) Mean ± SD 155.5 ± 6.5 Body Weight (kg) > 30 to ≦ 40 4 (5.3) > 40 to ≦ 50 17 (22.4) > 50 to ≦ 60 41 (53.9) > 60 to ≦ 70 13 (17.1) > 70 to ≦ 80 1 (1.3) Mean ± SD 54.4 ± 7.4 Body Mass Index > 15 to ≦ 20 11 (14.5) > 20 to ≦ 25 49 (64.5) > 25 to ≦ 30 16 (21.1) Mean ± SD 22.5 ± 2.5 Open in new tab No adverse events suspected to correlate with the implanted PMPC-grafted HXLPE liner were recorded, and no revision operations were performed during the follow-up period. Three patients had deep vein thrombosis, which was treated successfully with anticoagulants in each case. Two patients had dislocation, which was treated nonoperatively and no deep infection occurred. The mean JOA score improved at 3 years postoperatively (p < 0.01; Figure 1). According to Fujisawa's regression formula [16], the mean JOA score immediately after THR and at 3 years after THR corresponded with Harris hip scores of 46.7 and 95.6, respectively. Therefore, the clinical outcomes of the present cohort were similar to those of other contemporary cementless THRs [22,24]. Figure 1. Open in new tabDownload slide Average Japanese Orthopaedic Association hip score before surgery and at 1 and 3 years after surgery. The change was most apparent in the pain category. Figure 1. Open in new tabDownload slide Average Japanese Orthopaedic Association hip score before surgery and at 1 and 3 years after surgery. The change was most apparent in the pain category. On radiographic analysis, neither periprosthetic osteolysis nor femoral component migration was detected in all 76 patients (Figure 2). Seventy-four patients had a stable acetabular component and two had a suboptimally stable component. In the two patients with a suboptimally stable acetabular component, the component had changed its position up to 6 months after the index surgery and was stable afterwards. Similar observations have been reported in other cementless acetabular components and are not compatible with the predictive radiographic findings for the early diagnosis of loosening [19,26]. We attributed this limited migration to insufficient initial seating of the component. Figure 2. Open in new tabDownload slide Radiographs of a representative case (Case 66). Radiographs obtained 3 weeks, 1 year, and 3 years after surgery, showing no findings related to implant migration or periprosthetic osteolysis. Figure 2. Open in new tabDownload slide Radiographs of a representative case (Case 66). Radiographs obtained 3 weeks, 1 year, and 3 years after surgery, showing no findings related to implant migration or periprosthetic osteolysis. Penetration during the first year was regarded as bedding-in and that after 1 year as steady-state wear [21,25]. Among all patients, 38 (50%) had negative wear between 1 and 3 years. The mean femoral head penetration rate between 1 and 3 years was 0.002 mm/year (Figure 3), representing marked reduction compared with the mean wear rate of other HXLPE liners [19,21–25]. The mean femoral head penetration rate correlated weakly with patient age (R = 0.331), but it did not correlate with sex, preoperative diagnosis, body weight, or BMI. Figure 3. Open in new tabDownload slide Femoral head penetration at 6 months, 1 year, and 3 years after surgery. The amount of femoral head penetration is calculated using the position at 3 weeks as the original position. Penetration during the first year is larger than that in the subsequent 2 years. Standard deviation bars are displayed. Figure 3. Open in new tabDownload slide Femoral head penetration at 6 months, 1 year, and 3 years after surgery. The amount of femoral head penetration is calculated using the position at 3 weeks as the original position. Penetration during the first year is larger than that in the subsequent 2 years. Standard deviation bars are displayed. In the present cohort, the mean penetration at 1 year was 0.210 mm, and was slightly greater in male patients than that in female patients (p = 0.021). Although men were heavier than women (p = 0.014), the mean penetration did not correlate with body weight. We also found no correlation between mean penetration at 1 year and patient age, preoperative diagnosis, and BMI. Mean penetration at 3 years correlated weakly with BMI (Figure 4), but it did not correlate with sex, age, preoperative diagnosis, or body weight. Figure 4. Open in new tabDownload slide Relationship between amount of femoral head penetration at 3 years after surgery and body mass index. y = 0.0065x + 0.077; R = 0.215. Figure 4. Open in new tabDownload slide Relationship between amount of femoral head penetration at 3 years after surgery and body mass index. y = 0.0065x + 0.077; R = 0.215. We compared the data of the 2 patients with a suboptimally stable acetabular component with those of the 74 patients with a stable component (Table 2). In one patient (Case 33), a large amount of penetration was observed at 6 months, and the value decreased up to 3 years after surgery. In the other patient (Case 36), the amount of penetration was relatively small at 1 year and relatively large at 3 years. As a result, this patient showed a high wear rate between 1 and 3 years. The cause of these unusual observations is unclear and continued follow-up is required to determine their relevance to the clinical outcome. Table 2. Summary of the results of measurement of the penetration of the femoral heads. All hips (76 hips)* Stable (74 hips)* Suboptimally stable (2 hips) Case 33 Case 36 6 months (mm) 0.210 ± 0.050 0.196 ± 0.050 1.050 0.170 1 year (mm) 0.223 ± 0.100 0.214 ± 0.069 0.863 0.137 3 years (mm) 0.226 ± 0.090 0.218 ± 0.065 0.765 0.302 Wear rate (mm/year) 0.002 ± 0.043 0.002 ± 0.041 − 0.049 0.083 All hips (76 hips)* Stable (74 hips)* Suboptimally stable (2 hips) Case 33 Case 36 6 months (mm) 0.210 ± 0.050 0.196 ± 0.050 1.050 0.170 1 year (mm) 0.223 ± 0.100 0.214 ± 0.069 0.863 0.137 3 years (mm) 0.226 ± 0.090 0.218 ± 0.065 0.765 0.302 Wear rate (mm/year) 0.002 ± 0.043 0.002 ± 0.041 − 0.049 0.083 *Values are expressed as mean and standard deviation. Open in new tab Table 2. Summary of the results of measurement of the penetration of the femoral heads. All hips (76 hips)* Stable (74 hips)* Suboptimally stable (2 hips) Case 33 Case 36 6 months (mm) 0.210 ± 0.050 0.196 ± 0.050 1.050 0.170 1 year (mm) 0.223 ± 0.100 0.214 ± 0.069 0.863 0.137 3 years (mm) 0.226 ± 0.090 0.218 ± 0.065 0.765 0.302 Wear rate (mm/year) 0.002 ± 0.043 0.002 ± 0.041 − 0.049 0.083 All hips (76 hips)* Stable (74 hips)* Suboptimally stable (2 hips) Case 33 Case 36 6 months (mm) 0.210 ± 0.050 0.196 ± 0.050 1.050 0.170 1 year (mm) 0.223 ± 0.100 0.214 ± 0.069 0.863 0.137 3 years (mm) 0.226 ± 0.090 0.218 ± 0.065 0.765 0.302 Wear rate (mm/year) 0.002 ± 0.043 0.002 ± 0.041 − 0.049 0.083 *Values are expressed as mean and standard deviation. Open in new tab Discussion To support the continued use of a new implant, updated clinical data should be available on the safety and efficacy. PMPC-grafted HXLPE liners were introduced to address concerns of wear and osteolysis in hip replacement. Regarding the safety of these implants, this study demonstrated that THR using this liner provided good clinical results, and no adverse events associated with the liner occurred during the 3 years after implantation. Therefore, this liner should be considered as a safe option in hip replacement. Regarding the efficacy of PMPC-grafting in reducing wear, the mean amount of bedding-in was 0.210 mm and the steady-state wear rate was 0.002 mm/year in the present study. We found no osteolysis on serial radiographs. For comparison, the results of six other prospective studies are summarized in Table 3 [19,21–25]. In these studies, a 26- or 28-mm-diameter Co–Cr–Mo alloy femoral head and HXLPE liner secured in a cementless shell were used for the bearing coupling, and the patients were followed for at least 3 years. Among these studies, three reported detailed data on bedding-in: it occurred from 6 months to 1 year after surgery, and the mean amount of penetration ranged from 0.123 to 0.260 mm. Thus, in the first year, the behavior of the PMPC-grafted HXLPE liner is quite similar to that of other liners. Because PMPC grafting is nanometer-scaled surface modification, this technique does not affect the physical or mechanical properties of the HXLPE substrate [27]. Hence, we attributed the differences in the amount of penetration to the characteristics of the HXLPE liners. They can vary in terms of resin type, radiation technique used for cross-linking, post-irradiation stabilization process, and sterilization modality, any of which can influence the mechanical properties, crystallinity, and pre-aging and post-aging oxidation levels of the components [28]. For instance, Medel et al. reported that annealing preserves the mechanical properties better than remelting with regard to both fatigue and fracture resistance [29]. Meanwhile, all six studies reported steady-state penetration rates: they varied from 0.01 to 0.06 mm/year. Although PE wear is a multifactorial process [18], the results of the present study seem to compare favorably with those of the other six studies in terms of marked reduction. Among patient characteristics, the body weight of the patients was significantly lesser in the present study than in the other studies. Therefore, we believe that PMPC grafting is a promising method for reducing HXLPE wear, and the results of the present study support the continued use of these liners. We plan to conduct a longer follow-up to elucidate the true clinical benefit of PMPC-grafted HXLPE liners in hip replacement surgery. Table 3. Summary of six prospective studies using a 26- or 28-mm cobalt–chromium–molybdenum alloy femoral head with highly cross-linked polyethylene liner. Authors HXLPE Head size (mm) n Body weight (kg) BMI Follow-up (year)* Measurement technique Bedding-in duration (year) Amount of Bedding-in (mm)† Steady-state penetration rate (mm/y)‡ Engh et al. (2006) [19] Marathon® 28 76 84.4 ± 21.3 (51.3–149.4) 28.6 ± 5.5 (19.9–47.3) 5.5 (4.1–7.0) Hip Analysis Suite 0.75 ≦ 0.22 ± 0.31 0.01 ± 0.07 Calvert et al. (2009) [22] Marathon® 28 59 NA NA 4 PolyWare Auto 0.5 NA 0.0239 (–0.008–0.0558) Glyn-Jones et al. (2008) [21] Longevity® 28 26 79 (49–117) NA 3 RSA 1 0.26 ± 0.17 0.03 ± 0.06 Lachiewicz et al. (2009) [23] Longevity® 26 14 NA 29 (18.9–46.4) 5.7 (5–8) Hip Analysis Suite NA NA 0.060 ± 0.042 Lachiewicz et al. (2009) [23] Longevity® 28 33 NA 29 (18.9–46.4) 5.7 (5–8) Hip Analysis Suite NA NA 0.032 ± 0.019 Whittaker et al. (2010) [24] Longevity® 28 36 78.9 ± 13.8 29.3 ± 3.9 7.64 (6.60–8.53) Hip Analysis Suite NA NA 0.025 (0.009–0.042) Whittaker et al. (2010) [24] XLPE® 28 47 88.7 ± 23.4 31.1 ± 6.3 6.42 (5.0–8.01) Hip Analysis Suite NA NA 0.026 (0.004–0.047) Capello et al. (2011) [25] Crossfire® 28 42 79.2 ± 19.6 27.4 ± 4.5 8.6 (7.0–10.3) Livermore 1 0.123 0.031 ± 0.014 Present study Poly(MPC)- grafted 26 76 55.1 ± 8.2 (37.0–77.9) 22.9 ± 3.0 (17.3–31.6) 3 PolyWare 1 0.223 ± 0.100 0.002 ± 0.043 Authors HXLPE Head size (mm) n Body weight (kg) BMI Follow-up (year)* Measurement technique Bedding-in duration (year) Amount of Bedding-in (mm)† Steady-state penetration rate (mm/y)‡ Engh et al. (2006) [19] Marathon® 28 76 84.4 ± 21.3 (51.3–149.4) 28.6 ± 5.5 (19.9–47.3) 5.5 (4.1–7.0) Hip Analysis Suite 0.75 ≦ 0.22 ± 0.31 0.01 ± 0.07 Calvert et al. (2009) [22] Marathon® 28 59 NA NA 4 PolyWare Auto 0.5 NA 0.0239 (–0.008–0.0558) Glyn-Jones et al. (2008) [21] Longevity® 28 26 79 (49–117) NA 3 RSA 1 0.26 ± 0.17 0.03 ± 0.06 Lachiewicz et al. (2009) [23] Longevity® 26 14 NA 29 (18.9–46.4) 5.7 (5–8) Hip Analysis Suite NA NA 0.060 ± 0.042 Lachiewicz et al. (2009) [23] Longevity® 28 33 NA 29 (18.9–46.4) 5.7 (5–8) Hip Analysis Suite NA NA 0.032 ± 0.019 Whittaker et al. (2010) [24] Longevity® 28 36 78.9 ± 13.8 29.3 ± 3.9 7.64 (6.60–8.53) Hip Analysis Suite NA NA 0.025 (0.009–0.042) Whittaker et al. (2010) [24] XLPE® 28 47 88.7 ± 23.4 31.1 ± 6.3 6.42 (5.0–8.01) Hip Analysis Suite NA NA 0.026 (0.004–0.047) Capello et al. (2011) [25] Crossfire® 28 42 79.2 ± 19.6 27.4 ± 4.5 8.6 (7.0–10.3) Livermore 1 0.123 0.031 ± 0.014 Present study Poly(MPC)- grafted 26 76 55.1 ± 8.2 (37.0–77.9) 22.9 ± 3.0 (17.3–31.6) 3 PolyWare 1 0.223 ± 0.100 0.002 ± 0.043 HXLPE highly cross-linked polyethylene, NA not available *Values are expressed as the mean, with the range in parentheses. †Values are expressed as the mean and standard deviation. ‡Values are expressed as the mean and standard deviation, or 95% confidence limit in parentheses. Open in new tab Table 3. Summary of six prospective studies using a 26- or 28-mm cobalt–chromium–molybdenum alloy femoral head with highly cross-linked polyethylene liner. Authors HXLPE Head size (mm) n Body weight (kg) BMI Follow-up (year)* Measurement technique Bedding-in duration (year) Amount of Bedding-in (mm)† Steady-state penetration rate (mm/y)‡ Engh et al. (2006) [19] Marathon® 28 76 84.4 ± 21.3 (51.3–149.4) 28.6 ± 5.5 (19.9–47.3) 5.5 (4.1–7.0) Hip Analysis Suite 0.75 ≦ 0.22 ± 0.31 0.01 ± 0.07 Calvert et al. (2009) [22] Marathon® 28 59 NA NA 4 PolyWare Auto 0.5 NA 0.0239 (–0.008–0.0558) Glyn-Jones et al. (2008) [21] Longevity® 28 26 79 (49–117) NA 3 RSA 1 0.26 ± 0.17 0.03 ± 0.06 Lachiewicz et al. (2009) [23] Longevity® 26 14 NA 29 (18.9–46.4) 5.7 (5–8) Hip Analysis Suite NA NA 0.060 ± 0.042 Lachiewicz et al. (2009) [23] Longevity® 28 33 NA 29 (18.9–46.4) 5.7 (5–8) Hip Analysis Suite NA NA 0.032 ± 0.019 Whittaker et al. (2010) [24] Longevity® 28 36 78.9 ± 13.8 29.3 ± 3.9 7.64 (6.60–8.53) Hip Analysis Suite NA NA 0.025 (0.009–0.042) Whittaker et al. (2010) [24] XLPE® 28 47 88.7 ± 23.4 31.1 ± 6.3 6.42 (5.0–8.01) Hip Analysis Suite NA NA 0.026 (0.004–0.047) Capello et al. (2011) [25] Crossfire® 28 42 79.2 ± 19.6 27.4 ± 4.5 8.6 (7.0–10.3) Livermore 1 0.123 0.031 ± 0.014 Present study Poly(MPC)- grafted 26 76 55.1 ± 8.2 (37.0–77.9) 22.9 ± 3.0 (17.3–31.6) 3 PolyWare 1 0.223 ± 0.100 0.002 ± 0.043 Authors HXLPE Head size (mm) n Body weight (kg) BMI Follow-up (year)* Measurement technique Bedding-in duration (year) Amount of Bedding-in (mm)† Steady-state penetration rate (mm/y)‡ Engh et al. (2006) [19] Marathon® 28 76 84.4 ± 21.3 (51.3–149.4) 28.6 ± 5.5 (19.9–47.3) 5.5 (4.1–7.0) Hip Analysis Suite 0.75 ≦ 0.22 ± 0.31 0.01 ± 0.07 Calvert et al. (2009) [22] Marathon® 28 59 NA NA 4 PolyWare Auto 0.5 NA 0.0239 (–0.008–0.0558) Glyn-Jones et al. (2008) [21] Longevity® 28 26 79 (49–117) NA 3 RSA 1 0.26 ± 0.17 0.03 ± 0.06 Lachiewicz et al. (2009) [23] Longevity® 26 14 NA 29 (18.9–46.4) 5.7 (5–8) Hip Analysis Suite NA NA 0.060 ± 0.042 Lachiewicz et al. (2009) [23] Longevity® 28 33 NA 29 (18.9–46.4) 5.7 (5–8) Hip Analysis Suite NA NA 0.032 ± 0.019 Whittaker et al. (2010) [24] Longevity® 28 36 78.9 ± 13.8 29.3 ± 3.9 7.64 (6.60–8.53) Hip Analysis Suite NA NA 0.025 (0.009–0.042) Whittaker et al. (2010) [24] XLPE® 28 47 88.7 ± 23.4 31.1 ± 6.3 6.42 (5.0–8.01) Hip Analysis Suite NA NA 0.026 (0.004–0.047) Capello et al. (2011) [25] Crossfire® 28 42 79.2 ± 19.6 27.4 ± 4.5 8.6 (7.0–10.3) Livermore 1 0.123 0.031 ± 0.014 Present study Poly(MPC)- grafted 26 76 55.1 ± 8.2 (37.0–77.9) 22.9 ± 3.0 (17.3–31.6) 3 PolyWare 1 0.223 ± 0.100 0.002 ± 0.043 HXLPE highly cross-linked polyethylene, NA not available *Values are expressed as the mean, with the range in parentheses. †Values are expressed as the mean and standard deviation. ‡Values are expressed as the mean and standard deviation, or 95% confidence limit in parentheses. Open in new tab This study has several limitations. First, it was not a randomized controlled trial. A randomized controlled trial comparing HXLPE liners and PMPC-grafted HXLPE liners would be the best scientific method to evaluate the efficacy of PMPC grafting. However, most candidates reported that they preferred the new liner and did not want to join a clinical trial in which their liner was chosen by a chance mechanism. Therefore, we performed a prospective cohort study to address this issue. Second, 76 individuals and a 3-year follow-up may not be sufficient to deny the possibility of rare adverse reactions related to these new bearings. Thus, a long-term follow-up study (UMIN000003681) is underway for an extended investigation. Third, the radiostereometric analysis (RSA) method, which has been reported to be the most accurate tool for in vivo assessment of PE wear [30], was not used in this study because of the need for the placement of marker balls. Many potential candidates believed that these metals provided no benefit. Therefore, we employed the PolyWare technique instead. As reported by Stilling et al., mean PE wear measured with PolyWare tends to be greater than that measured using the RSA method [31]. Consequently, the present study possibly overestimated the amount of penetration. Fourth, among all patients, 38 (50%) had negative wear between 1 and 3 years. Such results are common in short-term studies of HXLPE liners [19,23,24]. Engh et al. reported a negative wear rate in 32% of the patients in their study [19]. As Lachiewicz et al. pointed out, these paradoxical observations should be attributed to the detection limits of the measurement technique [23]. Fifth, we used 26-mm-diameter Co–Cr–Mo alloy heads on the femoral side. However, in the clinical setting, various femoral heads of larger sizes and materials are available. Although we confirmed that improvements due to PMPC grafting surpassed those due to changes in the femoral head sizes or materials in the hip joint simulator studies [32], the outcome of THR using other femoral heads should be evaluated to determine the clinical utility of PMPC-grafted HXLPE liners. A multicenter study (UMIN000008730) is currently underway for the evaluation of other femoral heads, including zirconia-toughened alumina ceramic femoral heads and femoral heads with a larger diameter [33]. In conclusion, this study demonstrated that use of a PMPC-grafted HXLPE liner in THR appears to provide good clinical and radiographic results at 3 years after the index surgery. Further follow-up is needed to determine whether PMPC-grafted HXLPE liners improve long-term clinical outcomes. Acknowledgments The authors would like to thank the late Dr. Shuhei Morimoto for his invaluable contribution and participation in the present study since 2006. 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TI - Clinical and radiographic outcomes of total hip replacement with poly(2-methacryloyloxyethyl phosphorylcholine)-grafted highly cross-linked polyethylene liners: Three-year results of a prospective consecutive series
JF - Modern Rheumatology
DO - 10.3109/14397595.2014.941438
DA - 2015-03-04
UR - https://www.deepdyve.com/lp/oxford-university-press/clinical-and-radiographic-outcomes-of-total-hip-replacement-with-poly-jXMU4oBsGC
SP - 286
EP - 291
VL - 25
IS - 2
DP - DeepDyve
ER -