The Journal of Arthroplasty xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Long-Term Results of Porous-Coated Anatomic Total Hip Arthroplasty for Patients With Osteoarthritis of the Hip Taro Tezuka, MD, Yutaka Inaba, MD, PhD, Naomi Kobayashi, MD, PhD, Masaaki Sato, MD, PhD, Naoto Mitsugi, MD, PhD, Tomoyuki Saito, MD, PhD Department of Orthopaedic Surgery, Yokohama City University, Yokohama, Japan
a r t i c l e
i n f o
Article history: Received 28 July 2013 Accepted 23 November 2013 Available online xxxx Keywords: porous-coated anatomic prosthesis osteoarthritis of the hip total hip arthroplasty long-term results polyethylene wear
a b s t r a c t Between 1986 and 1997, 136 porous-coated anatomic (PCA) total hip arthroplasties were performed for patients with osteoarthritis of the hip, and data were available for 60 hips at final follow-up (mean follow-up, 15.2 years). Of these, 18 hips had undergone revision: 12 for the acetabular component, 10 for the femoral component, and 4 for both components. Survival rate at 23 years postoperatively was 60% for the acetabular component and 82% for the femoral component. Multivariate Cox proportional hazards regression showed that annual polyethylene wear rate, size, and abduction angle of the acetabular component were significantly associated with acetabular component revision surgery, and that annual polyethylene wear rate and filling ratio of the femur were associated with femoral component revision surgery. © 2013 Elsevier Inc. All rights reserved.
The porous-coated anatomic (PCA) total hip system (Stryker Howmedica Osteonics Corp., Allendale, NJ) is a first generation cementless implant introduced in 1983 for primary and revision total hip arthroplasty. The PCA stem has a cobalt–chrome prosthesis that was press-fit for initial fixation and the proximal circumferential one-third of the stem has a porous coating with beads that serve to load the metaphysis, theoretically eliminating the stress shielding associated with diaphyseal fixation. As opposed to the traditional straight stem, the PCA was anatomically designed with a proximal posterior bow and a distal anterior bow to favor maximum fixation in the metaphysis, for which both right and left components were available. The acetabular component is a preassembled, metal-backed, non-modular polyethylene device with metal beads sintered to the metal backing for bony ingrowth; this component was available in 3mm increments from 40 to 64 mm and was implanted after line-toline reaming. Two peripheral fixation plugs were designed for initial fixation, contributing to rotational control and improved stability. The liner was held in place with a central lug at the back and a single peripheral tab to prevent rotation. Wixson et al reported good early results with this implant in a 2- to 4-year study [1], however several authors have reported that this type of implant is associated with a high incidence of aseptic loosening, stress shielding, and osteolysis resulting from the quality of polyethylene or weak liner locking mechanism [2–4]. The purpose of the present study is to assess the long-term clinical and radiographic results with first generation, The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2013.11.015. Reprint requests: Yutaka Inaba, MD, PhD, Department of Orthopaedic Surgery, Yokohama City University, 3-9 Fukuura, Kanazawa-ku, Yokohama 236-0004, Japan.
cementless, anatomically designed femoral component (porous coated anatomic total hip arthroplasty) for patients with osteoarthritis of the hip, as well as to investigate its causes of failure.
Patients and Methods The present study group consisted of 136 hips of 113 patients with osteoarthritis of the hip who underwent PCA total hip arthroplasty between June 1986 and October 1997, at a single institution by 4 different surgeons. The study was approved by the authors' institutional review board. Of these 113 patients (136 hips), 6 (6 hips) died of unrelated causes, and 62 (70 hips) were lost to follow-up less than 10 years postoperatively. All of these patients had well-functioning total hip arthroplasties before they were lost to follow-up or until they died. There were 39 women (52 hips) and 6 men (8 hips) in the available data, with an average follow-up period of 15.2 (10–23) years. The average age at surgery was 60.2 years, with a range of 40–74 years. The preoperative diagnosis of all hips was osteoarthritis, and all patients underwent PCA total hip arthroplasty as the primary procedure. A Morse taper modular 26-mm cobalt–chrome femoral head and a high-density polyethylene liner (1050 GUR sterilized with gamma radiation in air) were used for all patients. In 20 cases of severe acetabular dysplasia of the hip, the isolated femoral head was used for the bulk structural autogenous graft and fixed with 2 ceramic pins. The surviving patients were assessed clinically using the Harris Hip Score [5] preoperatively and at 1, 5, 10, 15, and 20 years postoperatively.
0883-5403/0000-0000$36.00/0 – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2013.11.015
Please cite this article as: Tezuka T, et al, Long-Term Results of Porous-Coated Anatomic Total Hip Arthroplasty for Patients With Osteoarthritis of the Hip, J Arthroplast (2014), http://dx.doi.org/10.1016/j.arth.2013.11.015
2
T. Tezuka et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx
For radiologic analysis, the abduction and anteversion angles of the acetabular component were recorded. We also measured the ratio of the width of the femoral component to that of the femoral canal in the coronal plane at the upper border of the lesser trochanter, according to a previously described procedure [6]. Osteolysis and loosening were recorded as follows: Definite loosening of the femoral component was defined by either progressive axial subsidence N 3 mm or varus or valgus migration, and possible loosening was defined by the presence of a complete radiolucent line surrounding the entire porous-coated surface on both anteroposterior and lateral radiographs [7]. Definite loosening of the acetabular component was defined as a change in abduction angle, N2 mm vertical or horizontal migration, or a continuous radiolucent line N 2 mm wide on both anteroposterior and lateral radiographs [8]. Areas of well-circumscribed, localized, expansile cortical erosion that were at least 5 mm in diameter were considered osteolytic. On the femoral side, osteolytic areas were classified by location using the Gruen zones [9]. On the acetabular side, such areas were recorded using the zones described by DeLee and Charnley [10]. Linear polyethylene wear was measured using Roentgen Monographic Analysis (Roman) Ver. 1.70 (Institute of Orthopaedics, Oswestry, UK). With the Roman method, 8 points on the edge of the cup were chosen and averaged by the software to generate an edge and center. This process was repeated for the femoral head, and the displacement vector between the 2 centers was measured. To rule out deformation immediately after surgery, we measured the difference in the central position of the femoral head between 1 year postoperatively and at the final observation. The polyethylene wear rate after 1 year was determined by fitting a regression line to the data points at 1 year and final observation. The gradient of this line was taken to be the annual polyethylene wear rate in mm/year. The polyethylene wear was measured 2 times after an interval of at least 2 weeks by a single author who was adequately trained in radiographic measurements. The authors assessed the intraobserver reliabilities of the radiographic measurements using intraclass correlation coefficients. The intraclass correlation coefficient for the linear polyethylene wear was 0.92. The data were analyzed using the unpaired Student's t-test and Fisher's exact probability test. The significance level was set as P b 0.05. A Kaplan–Meier survival analysis was performed with revision for any cause as the endpoint [11]. To analyze the factors that affect occurrence of revision surgery, Cox proportional hazards regression was performed. At first, Cox regression analysis was performed univariately with the following factors as explaining variables: bulk bone implantation, abduction angle, anteversion angle, size of the acetabular component and annual polyethylene wear rate. The absolute figure of annual polyethylene wear rate was small, the hazard ratio was represented for a level N 0.1. Furthermore, variables that indicate significant P values b 0.05 were populated for Cox regression analysis as a multivariate assessment. In the same manner, Cox regression analysis was performed for stem revision surgery with the following factors: size of the implanted femoral component, filling ratio of the femur and annual polyethylene wear rate. All statistical analyses were performed using SPSS v.21.0 (IBM Corp., Armonk, NY, USA).
Table 1 Components Used in 60 Porous-Coated Anatomic Total Hip Arthroplasties and Number of Revisions. Femoral Component
Acetabular Component Number
Size
Hips
Revision
0 1 2 3 4 5 6 Total
1 15 13 12 13 3 3 60
0 1 3 1 2 2 1 10
a
Size (mm) 40 43 46 49 52 55 58
Number Hips 3 21 16 13 4 1 2 60
Revisiona 0 7 4 1 0 0 0 12
Including liner exchange.
postoperatively because of polyethylene wear. Table 1 shows the numbers and sizes of components used in the 60 total hip arthroplasties and the numbers of each size component revised during the followup period. Sizes of the revised acetabular components were mainly 43 mm and 46 mm, and the occurrence of cup revision was associated with a cup size b 46 mm (Fisher's exact probability test; P = 0.04). The mean abduction angle of the acetabular component was 41.0° ± 7.1°. The abduction angle was 38.9° ± 6.3° in the survival group and 45.8° ± 6.3° (P b 0.01) in the revision group. The mean anteversion angle of the acetabular component was 14.7° ± 5.9°. The anteversion angle was 15.0° ± 5.5° in the survival group and 14.54° ± 5.7° (N.S.) in the revision group. In total, 10 femoral components were revised after a mean of 13.0 years (range, 10.5–22.5 years). Seven femoral components were revised for aseptic loosening, 2 for osteolysis, and 1 for fracture around the femoral component. No clear tendency was observed between revisions of the femoral component and stem size. The adequacy of the intramedullary stem filling was recorded as satisfactory when the stem filled the proximal canal by N80% in the coronal plane. In 30 of the 60 stems, the stem fill was satisfactory. The average filling ratio of the medullary canal by the stem in the coronal plane was 80.1% ± 6.7% in stem survival cases and 71.5% ± 6.2% in revision cases (P b 0.01). The mean annual linear wear rate of the polyethylene liner was 0.24 ± 0.18 mm/yr. The wear rate was 0.21 ± 0.10 mm/yr in the
Result The mean Harris Hip Score improved from 45 ± 11 points preoperatively to 95 ± 2.4 points 1 year postoperatively but decreased subsequently to 90 ± 6.5 points at 10 years, 85 ± 8.5 points at 15 years, and 78 ± 11 at 20 years postoperatively. A total of 12 acetabular components were revised after a mean of 13.9 years (range, 10.5–22.5 years). Nine acetabular components were revised because of aseptic loosening, and 2 were revised because of periprosthetic osteolysis. One polyethylene liner was revised 11 years
Fig. 1. Femoral and acetabular component survival rates. Kaplan–Meier curves show the survival rate at 23 years with revision of the femoral component, acetabular component, and that of either component as the endpoint. The survival rate at 23 years postoperatively was 60% for the acetabular component and 82% for the femoral component. The overall survival rate was 52%.
Please cite this article as: Tezuka T, et al, Long-Term Results of Porous-Coated Anatomic Total Hip Arthroplasty for Patients With Osteoarthritis of the Hip, J Arthroplast (2014), http://dx.doi.org/10.1016/j.arth.2013.11.015
T. Tezuka et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx Table 2 Result of Cox Proportional Hazards Regression for Revision Surgery of the Acetabular Component. Variables Univariate regression Size of acetabular component Abduction of acetabular component Anteversion of acetabular component Presence of bulk bone implantation Annual polyethylene wear rate Multivariate regression Size of acetabular component Abduction of acetabular component Annual polyethylene wear rate
Hazard Ratio
95% Confidence Interval
P Value
0.742 1.206
0.575–0.958 1.101–1.321
0.022 b0.01
1.072
0.966–1.203
0.182
2.383
0.765–7.382
0.133
3.035
1.715–5.373
0.770 1.128
0.599–0.990 1.005–1.268
0.042 0.041
2.305
1.126–4.756
0.023
b0.01
survival group and 0.32 ± 0.12 mm/yr (P b 0.01) in the revision group. The wear rate was 0.12 ± 0.08 mm/yr in the surviving patients without osteolysis and 0.28 ± 0.02 mm/yr (P b 0.01) in those with osteolysis. The Kaplan–Meier survival characteristics of PCA total hip arthroplasty are outlined in Fig. 1. The survival rate after 10 years was 100% for acetabular and femoral components. The survival rate at 15 years postoperatively was 77% for the acetabular component and 85% for the femoral component. The survival rate at 23 years postoperatively was 60% for the acetabular component and 82% for the femoral component. The overall survival rate at 23 years was 52%. In the 13 patients surviving N20 years, osteolysis was observed around the acetabular component in 6 hips (46%). Of these 6 hips, 3 had osteolysis in zone 1 of the acetabulum, 2 in zones 1 and 2, and 1 in zones 1, 2, and 3. Osteolysis was observed around the femoral component in 7 hips (54%), either in zones 1 and 7 or only in zone 7. There were no cases of femoral osteolysis distal to the porous coating. There were only 6 surviving hips without osteolysis around either the acetabular or femoral components. Table 2 shows the result of Cox proportional hazards regression. Univariate regression showed that acetabular component size and abduction angle and annual polyethylene wear rate were significantly associated with revision surgery. Additionally, multivariate regression showed that acetabular component size and abduction angle and annual polyethylene wear rate were significantly associated with acetabular component revision surgery. Table 3 shows the result of Cox proportional hazards regression for the femoral component. The univariate regression showed that size of the femoral component, filling ratio of the femur, and annual polyethylene wear rate were significantly associated with revision surgery, and multivariate regression showed that filling ratio of the femur and annual polyethylene wear rate were significantly associated with femoral component revision surgery.
Table 3 Results of Cox Proportional Hazards Regression for Revision Surgery of the Femoral Component. Variables Univariate regression Size of femoral component Filling ratio of the femur Annual polyethylene wear rate Multivariate regression Size of femoral component Filling ratio of the femur Annual polyethylene wear rate
Hazard Ratio 95% Confidence Interval P Value 1.687 0.842 1.718
1.062–2.684 0.739–0.959 1.115–2.647
0.027 0.010 0.014
1.578 0.860 2.835
0.906–2.749 0.760–0.973 1.209–6.648
0.107 0.017 0.017
3
Discussion Porous-coated cementless components, designed for bone ingrowth into the prosthesis, were introduced in the early 1980s [12–14]. However, several studies have reported a high incidence of osteolysis around the component, thigh pain, and failure of bone osteointegration; also, the long-term results of PCA total hip arthroplasty have been unsatisfactory [15–19]. In our series, the mean Harris Hip Score improved from 45 points preoperatively to 95 points at 1 year postoperatively but dropped to 78 points at 20 years postoperatively. This finding is similar to those of other studies and in most cases, might be attributed to age-related deterioration in function [20,21]. The survival rate of the acetabular component was 60% over a 23year period. The main cause of revision was loosening or osteolysis around the component because of biological reactions to particulate debris generated from polyethylene wear. As to the cause of failure, Astion et al [19] reported problems with the design of the original PCA acetabular components, including inadequate congruence of the polyethylene liner and the presence of holes in the metal backing that may allow direct access of the debris to the acetabulum. Bartel et al [22] reported that the polyethylene component should have a minimum thickness of 8 mm for reducing the stress that leads to surface damage. In patients who received 43-mm cup and 26-mm femoral head implants, the minimum thickness of the polyethylene liner was 5 mm. In our series, 43-mm acetabular components and 26mm femoral heads were implanted in all patients between 1986 and 1989, regardless of acetabulum size, for preventing bone loss and to obtain an adequate press fit. This was a reason for the relatively high polyethylene wear rate and the poor survival rate of the acetabular components. After 1990, we started to use larger acetabular components. In our series of total hip arthroplasties in which we compared acetabular components of different diameters, we observed a higher revision rate with acetabular components of diameters under 46 mm than that with acetabular components of larger diameters. In cases with acetabular components N 52 mm in diameter, no patients required revision. Patil et al [23] reported that increased abduction angle of the acetabular component leads to increased contact stress on the joint surface, and Little et al [24] reported that abduction angle was associated with polyethylene wear. In our study, multivariate Cox proportional hazards regression showed that annual polyethylene wear rate and acetabular component size and abduction angle were statistically associated with revision surgery. In addition, 20 patients with severe dysplasia of the acetabulum were treated with autogenous bone grafts with screw fixation. In 3 cases, the unstable autogenous bone allowed acetabular component migration. This caused impingement between the acetabular component and the screw, and metallosis led to loosening or osteolysis (Figure 2). Shinar et al reported that 30% of patients who had total hip arthroplasty with autogenous bone implantation required revision surgery within 14 years [25]; however, in this study, there was no significant association between bulk bone implantation and revision occurrence. We experienced 10 hips that needed to be treated with stem revision; however, there was no clear tendency in stem size. The survival rate of the stem was 82% at 23 years postoperatively, which was higher than that of the acetabular component but was lower than that reported by other authors [20,21]. Kim et al reported that 106 of 116 cases were satisfactorily filled by the stem at the proximal area of the femur. The average filling ratio of the medullary canal by the stem was 84%, and the survival rate of the stem at 20 years was 91% [6,20]. In our study, only 50% of cases were satisfactorily filled with the stem, and the survival rate of the stem at 23 years was 82%. Furthermore, there was a significant difference in the filling ratio of the medullary canal between the survival group and the stem
Please cite this article as: Tezuka T, et al, Long-Term Results of Porous-Coated Anatomic Total Hip Arthroplasty for Patients With Osteoarthritis of the Hip, J Arthroplast (2014), http://dx.doi.org/10.1016/j.arth.2013.11.015
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T. Tezuka et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx
revision group, and Cox regression analysis revealed that the stemfilling ratio was significantly associated with femoral component revision surgery. Our poor result for stem survival rate, compared with other studies, was caused by undersized stem implantation. This may cause failure of early rigid bone ingrowth on the porouscoated area of the proximal part of the femoral implants, which limits the spread of polyethylene particulate debris from the socalled effective joint space [26] and leads to component loosening, as Bojescul et al proposed [18]. The present study revealed that the acetabular component was less durable than the femoral component, and annual polyethylene wear rate, size and abduction angle of the acetabular component were responsible for the failure of acetabular component. Failure of the femoral side was associated with filling ratio of the femur and polyethylene wear rate.
Acknowledgments We wish to thank Dr. Kazuo Hirakawa, Dr. Yohei Yukizawa, Dr. Chie Aoki, Dr. Hiroshi Fujimaki, Dr. Hiroyuki Ike, and Dr. Yasuhide Hirata for their valuable contribution to the current study.
References
Fig. 2. Postoperative anteroposterior radiographs of a 49-year-old woman who was treated with autogenous bone grafts and fixation by ceramic screws. (A) Radiograph obtained 1 year postoperatively. The filling ratio by the stem at the level of the upper border of the lesser trochanter was 94%. (B) Radiograph obtained 12 years postoperatively. Cup migration and extensive osteolysis in zones 1 and 7 of the femur were observed, and the femoral head was positioned eccentrically in the acetabular component, indicating linear polyethylene wear. Revision of both cup and stem was performed 13 years after primary total hip arthroplasty following a diagnosis of aseptic loosening of the acetabular component and osteolysis around the femoral component of proximal area. During revision surgery, metallosis, cup loosening, and osteolysis around the proximal area of the femoral component were observed.
1. Wixson RL, Stulberg SD, Mehlhoff M. Total hip replacement with cemented, uncemented, and hybrid prostheses. A comparison of clinical and radiographic results at two to four years. J Bone Joint Surg Am 1991;73:257. 2. Bourne RB, Rorabeck CH, Ghazal ME, et al. Pain in the thigh following total hip replacement with a porous-coated anatomic prosthesis for osteoarthrosis. A fiveyear follow-up study. J Bone Joint Surg Am 1994;76:1464. 3. Maric Z, Karpman RR. Early failure of noncemented porous coated anatomic total hip arthroplasty. Clin Orthop Relat Res 1992:116. 4. Owen TD, Moran CG, Smith SR, et al. Results of uncemented porous-coated anatomic total hip replacement. J Bone Joint Surg Br 1994;76:258. 5. Harris WH. Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. An end-result study using a new method of result evaluation. J Bone Joint Surg Am 1969;51:737. 6. Kim YH, Kim VE. Uncemented porous-coated anatomic total hip replacement. Results at six years in a consecutive series. J Bone Joint Surg Br 1993;75:6. 7. Kim YH, Kim JS, Oh SH, et al. Comparison of porous-coated titanium femoral stems with and without hydroxyapatite coating. J Bone Joint Surg Am 2003;85-A:1682. 8. Dorr LD. Total hip replacement using APR system. Tech Orthop 1986;1:22. 9. Gruen TA, McNeice GM, Amstutz HC. “Modes of failure” of cemented stem-type femoral components: a radiographic analysis of loosening. Clin Orthop Relat Res 1979:17. 10. DeLee JG, Charnley J. Radiological demarcation of cemented sockets in total hip replacement. Clin Orthop Relat Res 1976:20. 11. Kaplan E. Nonparametric estimation from incomplete observations. J Am Stat Assoc 1958;53:457. 12. Callaghan JJ, Dysart SH, Savory CG. The uncemented porous-coated anatomic total hip prosthesis. Two-year results of a prospective consecutive series. J Bone Joint Surg Am 1988;70:337. 13. Burt CF, Garvin KL, Otterberg ET, et al. A femoral component inserted without cement in total hip arthroplasty. A study of the Tri-Lock component with an average ten-year duration of follow-up. J Bone Joint Surg Am 1998;80:952. 14. Engh Jr CA, Culpepper 2nd WJ, Engh CA. Long-term results of use of the anatomic medullary locking prosthesis in total hip arthroplasty. J Bone Joint Surg Am 1997;79:177. 15. Xenos JS, Callaghan JJ, Heekin RD, et al. The porous-coated anatomic total hip prosthesis, inserted without cement. A prospective study with a minimum of ten years of follow-up. J Bone Joint Surg Am 1999;81:74. 16. Kawamura H, Dunbar MJ, Murray P, et al. The porous coated anatomic total hip replacement. A ten to fourteen-year follow-up study of a cementless total hip arthroplasty. J Bone Joint Surg Am 2001;83-A:1333. 17. Healy WL, Casey DJ, Iorio R, et al. Evaluation of the porous-coated anatomic hip at 12 years. J Arthroplasty 2002;17:856. 18. Bojescul JA, Xenos JS, Callaghan JJ, et al. Results of porous-coated anatomic total hip arthroplasty without cement at fifteen years: a concise follow-up of a previous report. J Bone Joint Surg Am 2003;85-A:1079. 19. Astion DJ, Saluan P, Stulberg BN, et al. The porous-coated anatomic total hip prosthesis: failure of the metal-backed acetabular component. J Bone Joint Surg Am 1996;78:755. 20. Kim YH. Long-term results of the cementless porous-coated anatomic total hip prosthesis. J Bone Joint Surg Br 2005;87:623.
Please cite this article as: Tezuka T, et al, Long-Term Results of Porous-Coated Anatomic Total Hip Arthroplasty for Patients With Osteoarthritis of the Hip, J Arthroplast (2014), http://dx.doi.org/10.1016/j.arth.2013.11.015
T. Tezuka et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx 21. Loughead JM, O'Connor PA, Charron K, et al. Twenty-three-year outcome of the porous coated anatomic total hip replacement: a concise follow-up of a previous report. J Bone Joint Surg Am 2012;94:151. 22. Bartel DL, Bicknell VL, Wright TM. The effect of conformity, thickness, and material on stresses in ultra-high molecular weight components for total joint replacement. J Bone Joint Surg Am 1986;68:1041. 23. Patil S, Bergula A, Chen P, et al. Polyethylene wear and acetabular component orientation. J Bone Joint Surg Am 2003;85-A:56.
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24. Little N, Busch C, Gallagher J, et al. Acetabular polyethylene wear and acetabular inclination and femoral offset. Clin Orthop Relat Res 2009;467:2895. 25. Shinar AA, Harris WH. Bulk structural autogenous grafts and allografts for reconstruction of the acetabulum in total hip arthroplasty. Sixteen-year-average follow-up. J Bone Joint Surg Am 1997;79:159. 26. Schmalzried TP, Jasty M, Harris WH. Periprosthetic bone loss in total hip arthroplasty. Polyethylene wear debris and the concept of the effective joint space. J Bone Joint Surg Am 1992;74:849.
Please cite this article as: Tezuka T, et al, Long-Term Results of Porous-Coated Anatomic Total Hip Arthroplasty for Patients With Osteoarthritis of the Hip, J Arthroplast (2014), http://dx.doi.org/10.1016/j.arth.2013.11.015
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Long-Term Results of Porous-Coated Anatomic Total Hip Arthroplasty for Patients With Osteoarthritis of the Hip Taro Tezuka, MD, Yutaka Inaba, MD, PhD, Naomi Kobayashi, MD, PhD, Masaaki Sato, MD, PhD, Naoto Mitsugi, MD, PhD, Tomoyuki Saito, MD, PhD Department of Orthopaedic Surgery, Yokohama City University, Yokohama, Japan
a r t i c l e
i n f o
Article history: Received 28 July 2013 Accepted 23 November 2013 Available online xxxx Keywords: porous-coated anatomic prosthesis osteoarthritis of the hip total hip arthroplasty long-term results polyethylene wear
a b s t r a c t Between 1986 and 1997, 136 porous-coated anatomic (PCA) total hip arthroplasties were performed for patients with osteoarthritis of the hip, and data were available for 60 hips at final follow-up (mean follow-up, 15.2 years). Of these, 18 hips had undergone revision: 12 for the acetabular component, 10 for the femoral component, and 4 for both components. Survival rate at 23 years postoperatively was 60% for the acetabular component and 82% for the femoral component. Multivariate Cox proportional hazards regression showed that annual polyethylene wear rate, size, and abduction angle of the acetabular component were significantly associated with acetabular component revision surgery, and that annual polyethylene wear rate and filling ratio of the femur were associated with femoral component revision surgery. © 2013 Elsevier Inc. All rights reserved.
The porous-coated anatomic (PCA) total hip system (Stryker Howmedica Osteonics Corp., Allendale, NJ) is a first generation cementless implant introduced in 1983 for primary and revision total hip arthroplasty. The PCA stem has a cobalt–chrome prosthesis that was press-fit for initial fixation and the proximal circumferential one-third of the stem has a porous coating with beads that serve to load the metaphysis, theoretically eliminating the stress shielding associated with diaphyseal fixation. As opposed to the traditional straight stem, the PCA was anatomically designed with a proximal posterior bow and a distal anterior bow to favor maximum fixation in the metaphysis, for which both right and left components were available. The acetabular component is a preassembled, metal-backed, non-modular polyethylene device with metal beads sintered to the metal backing for bony ingrowth; this component was available in 3mm increments from 40 to 64 mm and was implanted after line-toline reaming. Two peripheral fixation plugs were designed for initial fixation, contributing to rotational control and improved stability. The liner was held in place with a central lug at the back and a single peripheral tab to prevent rotation. Wixson et al reported good early results with this implant in a 2- to 4-year study [1], however several authors have reported that this type of implant is associated with a high incidence of aseptic loosening, stress shielding, and osteolysis resulting from the quality of polyethylene or weak liner locking mechanism [2–4]. The purpose of the present study is to assess the long-term clinical and radiographic results with first generation, The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2013.11.015. Reprint requests: Yutaka Inaba, MD, PhD, Department of Orthopaedic Surgery, Yokohama City University, 3-9 Fukuura, Kanazawa-ku, Yokohama 236-0004, Japan.
cementless, anatomically designed femoral component (porous coated anatomic total hip arthroplasty) for patients with osteoarthritis of the hip, as well as to investigate its causes of failure.
Patients and Methods The present study group consisted of 136 hips of 113 patients with osteoarthritis of the hip who underwent PCA total hip arthroplasty between June 1986 and October 1997, at a single institution by 4 different surgeons. The study was approved by the authors' institutional review board. Of these 113 patients (136 hips), 6 (6 hips) died of unrelated causes, and 62 (70 hips) were lost to follow-up less than 10 years postoperatively. All of these patients had well-functioning total hip arthroplasties before they were lost to follow-up or until they died. There were 39 women (52 hips) and 6 men (8 hips) in the available data, with an average follow-up period of 15.2 (10–23) years. The average age at surgery was 60.2 years, with a range of 40–74 years. The preoperative diagnosis of all hips was osteoarthritis, and all patients underwent PCA total hip arthroplasty as the primary procedure. A Morse taper modular 26-mm cobalt–chrome femoral head and a high-density polyethylene liner (1050 GUR sterilized with gamma radiation in air) were used for all patients. In 20 cases of severe acetabular dysplasia of the hip, the isolated femoral head was used for the bulk structural autogenous graft and fixed with 2 ceramic pins. The surviving patients were assessed clinically using the Harris Hip Score [5] preoperatively and at 1, 5, 10, 15, and 20 years postoperatively.
0883-5403/0000-0000$36.00/0 – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2013.11.015
Please cite this article as: Tezuka T, et al, Long-Term Results of Porous-Coated Anatomic Total Hip Arthroplasty for Patients With Osteoarthritis of the Hip, J Arthroplast (2014), http://dx.doi.org/10.1016/j.arth.2013.11.015
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T. Tezuka et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx
For radiologic analysis, the abduction and anteversion angles of the acetabular component were recorded. We also measured the ratio of the width of the femoral component to that of the femoral canal in the coronal plane at the upper border of the lesser trochanter, according to a previously described procedure [6]. Osteolysis and loosening were recorded as follows: Definite loosening of the femoral component was defined by either progressive axial subsidence N 3 mm or varus or valgus migration, and possible loosening was defined by the presence of a complete radiolucent line surrounding the entire porous-coated surface on both anteroposterior and lateral radiographs [7]. Definite loosening of the acetabular component was defined as a change in abduction angle, N2 mm vertical or horizontal migration, or a continuous radiolucent line N 2 mm wide on both anteroposterior and lateral radiographs [8]. Areas of well-circumscribed, localized, expansile cortical erosion that were at least 5 mm in diameter were considered osteolytic. On the femoral side, osteolytic areas were classified by location using the Gruen zones [9]. On the acetabular side, such areas were recorded using the zones described by DeLee and Charnley [10]. Linear polyethylene wear was measured using Roentgen Monographic Analysis (Roman) Ver. 1.70 (Institute of Orthopaedics, Oswestry, UK). With the Roman method, 8 points on the edge of the cup were chosen and averaged by the software to generate an edge and center. This process was repeated for the femoral head, and the displacement vector between the 2 centers was measured. To rule out deformation immediately after surgery, we measured the difference in the central position of the femoral head between 1 year postoperatively and at the final observation. The polyethylene wear rate after 1 year was determined by fitting a regression line to the data points at 1 year and final observation. The gradient of this line was taken to be the annual polyethylene wear rate in mm/year. The polyethylene wear was measured 2 times after an interval of at least 2 weeks by a single author who was adequately trained in radiographic measurements. The authors assessed the intraobserver reliabilities of the radiographic measurements using intraclass correlation coefficients. The intraclass correlation coefficient for the linear polyethylene wear was 0.92. The data were analyzed using the unpaired Student's t-test and Fisher's exact probability test. The significance level was set as P b 0.05. A Kaplan–Meier survival analysis was performed with revision for any cause as the endpoint [11]. To analyze the factors that affect occurrence of revision surgery, Cox proportional hazards regression was performed. At first, Cox regression analysis was performed univariately with the following factors as explaining variables: bulk bone implantation, abduction angle, anteversion angle, size of the acetabular component and annual polyethylene wear rate. The absolute figure of annual polyethylene wear rate was small, the hazard ratio was represented for a level N 0.1. Furthermore, variables that indicate significant P values b 0.05 were populated for Cox regression analysis as a multivariate assessment. In the same manner, Cox regression analysis was performed for stem revision surgery with the following factors: size of the implanted femoral component, filling ratio of the femur and annual polyethylene wear rate. All statistical analyses were performed using SPSS v.21.0 (IBM Corp., Armonk, NY, USA).
Table 1 Components Used in 60 Porous-Coated Anatomic Total Hip Arthroplasties and Number of Revisions. Femoral Component
Acetabular Component Number
Size
Hips
Revision
0 1 2 3 4 5 6 Total
1 15 13 12 13 3 3 60
0 1 3 1 2 2 1 10
a
Size (mm) 40 43 46 49 52 55 58
Number Hips 3 21 16 13 4 1 2 60
Revisiona 0 7 4 1 0 0 0 12
Including liner exchange.
postoperatively because of polyethylene wear. Table 1 shows the numbers and sizes of components used in the 60 total hip arthroplasties and the numbers of each size component revised during the followup period. Sizes of the revised acetabular components were mainly 43 mm and 46 mm, and the occurrence of cup revision was associated with a cup size b 46 mm (Fisher's exact probability test; P = 0.04). The mean abduction angle of the acetabular component was 41.0° ± 7.1°. The abduction angle was 38.9° ± 6.3° in the survival group and 45.8° ± 6.3° (P b 0.01) in the revision group. The mean anteversion angle of the acetabular component was 14.7° ± 5.9°. The anteversion angle was 15.0° ± 5.5° in the survival group and 14.54° ± 5.7° (N.S.) in the revision group. In total, 10 femoral components were revised after a mean of 13.0 years (range, 10.5–22.5 years). Seven femoral components were revised for aseptic loosening, 2 for osteolysis, and 1 for fracture around the femoral component. No clear tendency was observed between revisions of the femoral component and stem size. The adequacy of the intramedullary stem filling was recorded as satisfactory when the stem filled the proximal canal by N80% in the coronal plane. In 30 of the 60 stems, the stem fill was satisfactory. The average filling ratio of the medullary canal by the stem in the coronal plane was 80.1% ± 6.7% in stem survival cases and 71.5% ± 6.2% in revision cases (P b 0.01). The mean annual linear wear rate of the polyethylene liner was 0.24 ± 0.18 mm/yr. The wear rate was 0.21 ± 0.10 mm/yr in the
Result The mean Harris Hip Score improved from 45 ± 11 points preoperatively to 95 ± 2.4 points 1 year postoperatively but decreased subsequently to 90 ± 6.5 points at 10 years, 85 ± 8.5 points at 15 years, and 78 ± 11 at 20 years postoperatively. A total of 12 acetabular components were revised after a mean of 13.9 years (range, 10.5–22.5 years). Nine acetabular components were revised because of aseptic loosening, and 2 were revised because of periprosthetic osteolysis. One polyethylene liner was revised 11 years
Fig. 1. Femoral and acetabular component survival rates. Kaplan–Meier curves show the survival rate at 23 years with revision of the femoral component, acetabular component, and that of either component as the endpoint. The survival rate at 23 years postoperatively was 60% for the acetabular component and 82% for the femoral component. The overall survival rate was 52%.
Please cite this article as: Tezuka T, et al, Long-Term Results of Porous-Coated Anatomic Total Hip Arthroplasty for Patients With Osteoarthritis of the Hip, J Arthroplast (2014), http://dx.doi.org/10.1016/j.arth.2013.11.015
T. Tezuka et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx Table 2 Result of Cox Proportional Hazards Regression for Revision Surgery of the Acetabular Component. Variables Univariate regression Size of acetabular component Abduction of acetabular component Anteversion of acetabular component Presence of bulk bone implantation Annual polyethylene wear rate Multivariate regression Size of acetabular component Abduction of acetabular component Annual polyethylene wear rate
Hazard Ratio
95% Confidence Interval
P Value
0.742 1.206
0.575–0.958 1.101–1.321
0.022 b0.01
1.072
0.966–1.203
0.182
2.383
0.765–7.382
0.133
3.035
1.715–5.373
0.770 1.128
0.599–0.990 1.005–1.268
0.042 0.041
2.305
1.126–4.756
0.023
b0.01
survival group and 0.32 ± 0.12 mm/yr (P b 0.01) in the revision group. The wear rate was 0.12 ± 0.08 mm/yr in the surviving patients without osteolysis and 0.28 ± 0.02 mm/yr (P b 0.01) in those with osteolysis. The Kaplan–Meier survival characteristics of PCA total hip arthroplasty are outlined in Fig. 1. The survival rate after 10 years was 100% for acetabular and femoral components. The survival rate at 15 years postoperatively was 77% for the acetabular component and 85% for the femoral component. The survival rate at 23 years postoperatively was 60% for the acetabular component and 82% for the femoral component. The overall survival rate at 23 years was 52%. In the 13 patients surviving N20 years, osteolysis was observed around the acetabular component in 6 hips (46%). Of these 6 hips, 3 had osteolysis in zone 1 of the acetabulum, 2 in zones 1 and 2, and 1 in zones 1, 2, and 3. Osteolysis was observed around the femoral component in 7 hips (54%), either in zones 1 and 7 or only in zone 7. There were no cases of femoral osteolysis distal to the porous coating. There were only 6 surviving hips without osteolysis around either the acetabular or femoral components. Table 2 shows the result of Cox proportional hazards regression. Univariate regression showed that acetabular component size and abduction angle and annual polyethylene wear rate were significantly associated with revision surgery. Additionally, multivariate regression showed that acetabular component size and abduction angle and annual polyethylene wear rate were significantly associated with acetabular component revision surgery. Table 3 shows the result of Cox proportional hazards regression for the femoral component. The univariate regression showed that size of the femoral component, filling ratio of the femur, and annual polyethylene wear rate were significantly associated with revision surgery, and multivariate regression showed that filling ratio of the femur and annual polyethylene wear rate were significantly associated with femoral component revision surgery.
Table 3 Results of Cox Proportional Hazards Regression for Revision Surgery of the Femoral Component. Variables Univariate regression Size of femoral component Filling ratio of the femur Annual polyethylene wear rate Multivariate regression Size of femoral component Filling ratio of the femur Annual polyethylene wear rate
Hazard Ratio 95% Confidence Interval P Value 1.687 0.842 1.718
1.062–2.684 0.739–0.959 1.115–2.647
0.027 0.010 0.014
1.578 0.860 2.835
0.906–2.749 0.760–0.973 1.209–6.648
0.107 0.017 0.017
3
Discussion Porous-coated cementless components, designed for bone ingrowth into the prosthesis, were introduced in the early 1980s [12–14]. However, several studies have reported a high incidence of osteolysis around the component, thigh pain, and failure of bone osteointegration; also, the long-term results of PCA total hip arthroplasty have been unsatisfactory [15–19]. In our series, the mean Harris Hip Score improved from 45 points preoperatively to 95 points at 1 year postoperatively but dropped to 78 points at 20 years postoperatively. This finding is similar to those of other studies and in most cases, might be attributed to age-related deterioration in function [20,21]. The survival rate of the acetabular component was 60% over a 23year period. The main cause of revision was loosening or osteolysis around the component because of biological reactions to particulate debris generated from polyethylene wear. As to the cause of failure, Astion et al [19] reported problems with the design of the original PCA acetabular components, including inadequate congruence of the polyethylene liner and the presence of holes in the metal backing that may allow direct access of the debris to the acetabulum. Bartel et al [22] reported that the polyethylene component should have a minimum thickness of 8 mm for reducing the stress that leads to surface damage. In patients who received 43-mm cup and 26-mm femoral head implants, the minimum thickness of the polyethylene liner was 5 mm. In our series, 43-mm acetabular components and 26mm femoral heads were implanted in all patients between 1986 and 1989, regardless of acetabulum size, for preventing bone loss and to obtain an adequate press fit. This was a reason for the relatively high polyethylene wear rate and the poor survival rate of the acetabular components. After 1990, we started to use larger acetabular components. In our series of total hip arthroplasties in which we compared acetabular components of different diameters, we observed a higher revision rate with acetabular components of diameters under 46 mm than that with acetabular components of larger diameters. In cases with acetabular components N 52 mm in diameter, no patients required revision. Patil et al [23] reported that increased abduction angle of the acetabular component leads to increased contact stress on the joint surface, and Little et al [24] reported that abduction angle was associated with polyethylene wear. In our study, multivariate Cox proportional hazards regression showed that annual polyethylene wear rate and acetabular component size and abduction angle were statistically associated with revision surgery. In addition, 20 patients with severe dysplasia of the acetabulum were treated with autogenous bone grafts with screw fixation. In 3 cases, the unstable autogenous bone allowed acetabular component migration. This caused impingement between the acetabular component and the screw, and metallosis led to loosening or osteolysis (Figure 2). Shinar et al reported that 30% of patients who had total hip arthroplasty with autogenous bone implantation required revision surgery within 14 years [25]; however, in this study, there was no significant association between bulk bone implantation and revision occurrence. We experienced 10 hips that needed to be treated with stem revision; however, there was no clear tendency in stem size. The survival rate of the stem was 82% at 23 years postoperatively, which was higher than that of the acetabular component but was lower than that reported by other authors [20,21]. Kim et al reported that 106 of 116 cases were satisfactorily filled by the stem at the proximal area of the femur. The average filling ratio of the medullary canal by the stem was 84%, and the survival rate of the stem at 20 years was 91% [6,20]. In our study, only 50% of cases were satisfactorily filled with the stem, and the survival rate of the stem at 23 years was 82%. Furthermore, there was a significant difference in the filling ratio of the medullary canal between the survival group and the stem
Please cite this article as: Tezuka T, et al, Long-Term Results of Porous-Coated Anatomic Total Hip Arthroplasty for Patients With Osteoarthritis of the Hip, J Arthroplast (2014), http://dx.doi.org/10.1016/j.arth.2013.11.015
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T. Tezuka et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx
revision group, and Cox regression analysis revealed that the stemfilling ratio was significantly associated with femoral component revision surgery. Our poor result for stem survival rate, compared with other studies, was caused by undersized stem implantation. This may cause failure of early rigid bone ingrowth on the porouscoated area of the proximal part of the femoral implants, which limits the spread of polyethylene particulate debris from the socalled effective joint space [26] and leads to component loosening, as Bojescul et al proposed [18]. The present study revealed that the acetabular component was less durable than the femoral component, and annual polyethylene wear rate, size and abduction angle of the acetabular component were responsible for the failure of acetabular component. Failure of the femoral side was associated with filling ratio of the femur and polyethylene wear rate.
Acknowledgments We wish to thank Dr. Kazuo Hirakawa, Dr. Yohei Yukizawa, Dr. Chie Aoki, Dr. Hiroshi Fujimaki, Dr. Hiroyuki Ike, and Dr. Yasuhide Hirata for their valuable contribution to the current study.
References
Fig. 2. Postoperative anteroposterior radiographs of a 49-year-old woman who was treated with autogenous bone grafts and fixation by ceramic screws. (A) Radiograph obtained 1 year postoperatively. The filling ratio by the stem at the level of the upper border of the lesser trochanter was 94%. (B) Radiograph obtained 12 years postoperatively. Cup migration and extensive osteolysis in zones 1 and 7 of the femur were observed, and the femoral head was positioned eccentrically in the acetabular component, indicating linear polyethylene wear. Revision of both cup and stem was performed 13 years after primary total hip arthroplasty following a diagnosis of aseptic loosening of the acetabular component and osteolysis around the femoral component of proximal area. During revision surgery, metallosis, cup loosening, and osteolysis around the proximal area of the femoral component were observed.
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Please cite this article as: Tezuka T, et al, Long-Term Results of Porous-Coated Anatomic Total Hip Arthroplasty for Patients With Osteoarthritis of the Hip, J Arthroplast (2014), http://dx.doi.org/10.1016/j.arth.2013.11.015
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