Investigation performed at the Department of Orthopaedic Surgery, Wrightington Hospital, Wigan, United Kingdom

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1 71 COPYRIGHT 2006 BY THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED Long-Term Survival of the Acetabular Component After Total Hip Arthroplasty with Cement in Patients with Developmental Dysplasia of the Hip BY ASLAM CHOUGLE, FRCS, FRCS(TR&ORTH), M.V. HEMMADY, FRCS, FRCS(TR&ORTH), AND J.P. HODGKINSON, FRCS Investigation performed at the Department of Orthopaedic Surgery, Wrightington Hospital, Wigan, United Kingdom Background: Total hip arthroplasty with cement remains a difficult procedure in patients with osteoarthritis secondary to developmental dysplasia of the hip as it is associated with high rates of aseptic loosening of the acetabular component. The purpose of the present study was to evaluate the rate of revision of the acetabular component in this group of patients and the variables that are associated with it. Methods: We retrospectively reviewed the records and radiographs of 292 hips in 206 patients who had undergone total hip arthroplasty with cement for the treatment of osteoarthritis secondary to developmental dysplasia of the hip. The average age of the patients at the time of the index procedure was 42.6 years, and the average duration of follow-up was 15.7 years (range, 2.2 to 31.2 years). Fourteen patients were lost to follow-up, and seven patients died from causes unrelated to surgery. A mm head was used in all cases, and bone-grafting of the acetabulum was performed in forty-eight hips. Survival of the acetabular component was calculated with revision for aseptic loosening as the end point. Individual survival rates based on age, component type, previous surgery, and annual polyethylene wear also were calculated. Results: The most common reason for revision was aseptic loosening of the acetabular component, which led to 87.2% of the revision procedures. The overall rate of survival of the acetabular component was 90.6% at ten years and 63% at twenty years. A higher rate of acetabular revision was noted in association with previous acetabular surgery, the offset-bore cup, younger age, and accelerated polyethylene wear (p < 0.05 for all comparisons). Conclusions: Aseptic loosening of the acetabular component affects the longevity of total hip replacements in patients with osteoarthritis secondary to developmental dysplasia of the hip. The present study identified the risk factors associated with the long-term survival of the acetabular component in this group of patients. Level of Evidence: Prognostic Level II. See Instructions to Authors for a complete description of levels of evidence. Total hip arthroplasty with cement is an effective surgical procedure for the treatment of an arthritic hip. Even though Charnley initially predicted that the operation would be unsuitable for the treatment of arthritis in younger patients, it has been shown to provide good pain relief and improved function in this group 1. However, aseptic loosening can compromise the long-term success of total hip arthroplasty with cement and still remains the leading cause of failure of this procedure. Total hip arthroplasty for the treatment of osteoarthritis secondary to developmental dysplasia of the hip is associated with additional technical problems related to poor bone stock on the acetabular side. Charnley and Feagin suggested that total hip replacement should not be attempted in patients with untreated congenital dislocation of the hip because of the lack of bone stock necessary for acetabular reconstruction 2. High rates of aseptic loosening of the acetabular component, ranging from 24% to 53%, have been reported in this group of patients after 7.5 to sixteen years of follow-up in series ranging in size from twenty-three to eighty arthroplasties 3-5. We previously investigated the rate of survival of the acetabular component in this group of patients by specifically evaluating the influence of the grade of dysplasia on

2 72 aseptic loosening 6. The purpose of the present study was to evaluate the rate of revision of the acetabular component in this group of patients and the variables that affect it. Materials and Methods rom 1969 to 1998, 206 patients (292 hips) underwent total Fhip arthroplasty with cement for the treatment of osteoarthritis secondary to developmental dysplasia of the hip. The study group included 202 women and four men who had an average age of 42.6 years (range, 15.9 to 79.5 years) at the time of the index procedure. Forty-nine patients had the procedure on the right side, seventy-one had the procedure on the left side, and eighty-six had the procedure bilaterally. Fourteen patients were lost to follow-up, and seven patients died from causes unrelated to surgery. The average duration of radiographic followup was 15.7 years (range, 2.2 to 31.2 years). Two hundred and one hips were followed for more than ten years and, of these, sixty-three were followed for more than twenty years. All hips were evaluated annually with standardized anteroposterior radiographs of the pelvis that were made with the patient supine and with the radiographic beam centered over the pubis. The extent of the acetabular deficiency was assessed with use of the Crowe and Hartofilakidis radiographic classification systems 7,8. According to the Crowe system, 161 hips were classified as type 1, seventy-eight were classified as type 2, twenty-seven were classified as type 3, and twenty-six were classified as type 4. According to the Hartofilakidis system, 215 hips were dysplastic, fifty-five had low dislocation, and twenty-two had high dislocation. The groups in both classification systems were similar with regard to gender, age, and duration of follow-up. Two hundred and sixty-two procedures were performed by three surgeons through a transtrochanteric approach, and the remaining thirty procedures were performed by a single surgeon through a direct lateral approach in patients with lower grades of dysplasia. During the early part of the study period, trochanteric reattachment was carried out with use of two stainless steel wires according to the Charnley technique 9. This was later modified with use of the double-spring wiring technique. An attempt was made to insert all cups into the true acetabulum, with use of the teardrop inferiorly as an anatomic reference. Structural bone-grafting of the acetabulum, with use of the patient s own femoral head, was carried out in fortyeight hips. The indication for bone-grafting was uncovering of 25% of the smallest trial cup superolaterally after adequate reaming. To accomplish this, part of the femoral head was denuded of articular cartilage and fixed to the deficient roof of the true acetabulum with one or two cancellous-bone screws. The size of the acetabular component that was used was determined by the anteroposterior diameter of the acetabulum. With use of this technique, placement of the acetabular component in a higher hip center was avoided in all cases. According to the Hartofilakidis classification system 8, acetabular bone-grafting was carried out in twenty-one hips in the dysplastic group, nineteen hips in the low dislocation group, and eight hips in the high dislocation group. According to the Crowe classification system 7, acetabular bone-grafting was carried out in fifteen type-1, fourteen type-2, nine type-3, and ten type-4 hips. In 228 hips, a Charnley monobloc stem (Thackray, Leeds, United Kingdom) was used; seventy-six of these stems were of the CDH variety. In the remaining sixty-four hips, a Wrightington Frusto-Conical (FC) stem (Howmedica, Clare, Ireland) was used. A mm femoral head was used in all cases. A small Charnley cup (outside diameter, 40 mm) was used in 169 hips, an offset-bore cup (outside diameter, 38 mm) was used in seventy hips, and a metal-backed Wrightington Frusto- Conical (FC) cup was used in the remaining fifty-three hips. The Wrightington Frusto-Conical (FC) cup and stem were used instead of the Charnley design during the latter part of the study (from 1985 to 1997) by a single surgeon, who designed the prosthesis. The offset-bore cup was, however, used by all three surgeons for the treatment of hips with higher grades of dysplasia, in which the size of the socket and available bone stock precluded the use of the smallest Charnley cup or the Wrightington Frusto-Conical (FC) cup. Two hundred and four hips had not had any previous surgery. Of the remaining hips, forty-six had had proximal femoral osteotomy, ten had had a shelf procedure, twelve had had manipulation, nine had had open reduction, and eleven had had a Chiari osteotomy. Acetabular loosening was assessed with use of the criteria described by Hodgkinson et al. 10. This system classifies radiographic demarcation at the acetabular cement-bone interface into five groups and is detailed in Table I. Detailed radiographic assessment of the femoral stem was not carried out as a part of the present study. Radiographic measurement of linear polyethylene wear was manually calculated as described by Charnley and Halley 11. With use of this method, the latest radiograph was compared with the immediate postoperative radiograph and magnification was corrected with use of the known diameter of the femoral head (22.25 mm). The hips were divided into three groups on the basis of the annual rate of polyethylene wear: Group 1 (<0.02 mm/yr), Group 2 (0.02 to 0.2 mm/yr), and Group 3 (>0.2 mm/yr). The hips also were grouped into two categories on the basis of the age of the patient at the time of the index procedure (less than or equal to fifty years or more than fifty years). Statistical Methods Statistical analysis was carried out with the SPSS for Windows statistical package (SPSS, Chicago, Illinois). The Kaplan-Meier TABLE I Hodgkinson Classification of Radiographic Demarcation of the Socket 10 Type 0 Type 1 Type 2 Type 3 Type 4 No demarcation Demarcation of outer one-third Demarcation of outer and middle thirds Complete demarcation Socket migration

3 73 method was used to calculate the rate of survival of the acetabular component with revision for aseptic loosening as the end point. The possible predictive variables included the age of the patient at the time of surgery, previous acetabular surgery, the type of acetabular component, and the mean annual rate of polyethylene wear. Individual survival rates for these variables were compared with use of log-rank tests. Multiple logistic regression analysis was carried out to evaluate the predictive variables. Ninety-five percent confidence intervals were calculated, and the level of significance was set at p < Results here were nineteen documented local complications (prev- 7%) related to the index procedure, including six Talence, deep infections, five permanent sciatic nerve palsies, four intraoperative femoral fractures, two recurrent dislocations, and two periprosthetic fractures. Despite the use of first-generation cementing techniques throughout the study, the cementation technique was found to be satisfactory in all hips (with 221 hips being classified as Hodgkinson type 0 and seventy-one classified as Hodgkinson type 1) (Fig. 1). The most common cause of revision was aseptic loosening of the acetabular component, which led to 87.2% of the revision procedures. Sixty-eight hips were revised because of aseptic loosening; of these, fiftythree had an isolated revision of the acetabular component (Fig. 2). Despite the presence of substantial wear in some acetabular components, none of these components were revised because of isolated wear. Sixteen other acetabular components had complete nonprogressive demarcation at the cementbone interface and were classified as Hodgkinson type 3. These patients were clinically asymptomatic and were classified as having radiographic failure. The remaining acetabular components were well fixed at the time of the most recent follow-up. Isolated revision of the femoral stem was performed in six hips; the reasons for revision included aseptic loosening (two hips), stem fracture (three hips), and periprosthetic fracture (one hip). Another four hips had revision of both components because of deep infection. The overall rate of survival of the prosthesis, with revision of either component for any reason as the end point, was 88.3% (95% confidence interval, 84.3% to 92.4%) at ten years and 60.7% (95% confidence interval, 51.7% to 69.6%) at twenty years. The rate of survival of the acetabular component, with revision for aseptic loosening as the end point, was 90.6% (95% confidence interval, 86.8% to 94.4%) at ten years and 63% (95% confidence interval, 53.9% to 72%) at twenty years. The rate of survival of the acetabular component, with radiographic failure as the end point, was 90.5% (95% confidence interval, 86.7% to 94.3%) at ten years and 62.2% (95% confidence in- Fig. 1 Radiograph of the hips of a fifty-four-year-old woman, made ten years after bilateral total hip arthroplasty with cement for the treatment of developmental dysplasia of the hip, showing satisfactory cementing technique.

4 74 terval, 53.1% to 71.3%) at twenty years. Of the forty-eight hips in which the acetabular component had been inserted with bone-grafting, thirty-seven had radiographic evidence of union of the bone graft at the time of the most recent follow-up. Four acetabular components were revised in this group, compared with seven of the eleven acetabular components in the group in which there was no radiographic evidence of union. When the hips were classified according to the Crowe system, there were two nonunions in type-1 hips and three nonunions in each of the remaining three groups of hips. When the groups were classified according to the Hartofilakidis system, there were two nonunions in the dysplastic group, six in the low-dislocation group, and three in the high-dislocation group. Eleven (23%) of the fortyeight acetabular components that had been inserted with bone-grafting were revised because of aseptic loosening, compared with fifty-seven (23.4%) of the 244 that had been inserted without bone-grafting. Twenty-one hips had had previous acetabular surgery; the previous procedure had included ten shelf procedures and eleven Chiari osteotomies. Ten (48%) of these twenty-one acetabular components in these hips were revised, compared with fifty-eight (21.4%) of the 271 acetabular components in hips that had had no previous acetabular surgery. The twenty-year survival rate of the acetabular component was 70.1% for hips without previous acetabular surgery, compared with 22.5% for hips with previous acetabular surgery (p = ) (Fig. 3). The ten-year survival rate was 93.9% for the small Charnley cup, 81.6% for the offset-bore cup, and 88% for the Wrightington metal-backed cup (p < 0.05 for the comparison of the Charnley and offset-bore cups and p > 0.05 for all other comparisons). At twenty years, the survival rate decreased to 73.4% for the small Charnley cup and to 46.9% for the offsetbore cup (p = ) (Fig. 4). The Wrightington metalbacked cup had a maximum duration of follow-up of fifteen years in the present study and therefore could not be included in the latter analysis. The mean annual rate of polyethylene wear was 0.10 mm/yr, and there were no significant differences among the various types of components, with the numbers available. On the basis of annual rate of polyethylene wear, seven of the sixty-seven acetabular components in Group 1 (<0.02 mm/yr) were revised, thirty-eight of the 191 acetabular components in Group 2 (0.02 to 0.2 mm/yr) were revised, and twenty-three of the thirty-four acetabular components in Group 3 (>0.2 mm/yr) were revised. None of the acetabular components in Group 3 survived at twenty years, Fig. 2 Radiograph of the hips of a thirty-four-year-old woman, made seven years after bilateral total hip replacement for the treatment of low dislocation, showing bilateral gross aseptic loosening of the socket.

5 75 Fig. 3 Kaplan-Meier curves illustrating the rates of survival of the acetabular component for hips with and without previous acetabular surgery. The error bars represent 95% confidence intervals. Fig. 4 Kaplan-Meier curves illustrating the rates of survival of the acetabular component according to the type of cup. The error bars represent 95% confidence intervals. compared with 72.3% of those in Group 2 and 84.1% of those in Group 1 (p = ) (Fig. 5). The mean annual rate of polyethylene wear was 0.07 mm/yr in the group of components that were not revised, compared with 0.21 mm/yr in the group of components that were revised. When the patients were classified according to age, the twenty-year survival rate of the acetabular component was 92% for patients who were more than fifty years old and 61.5% for patients who were less than or equal to fifty years old (p = ) (Fig. 6). The mean age was 35.6 years in the group of patients in whom the component was revised, compared with 44.8 years in the group of patients in whom it was not revised. The mean annual rate of polyethylene wear was 0.08 mm/yr for patients who were more than fifty years old, compared with 0.11 mm/yr for

6 76 Fig. 5 Kaplan-Meier curves illustrating the rates of survival of the acetabular component according to the mean annual rate of polyethylene wear. The error bars represent 95% confidence intervals. Fig. 6 Kaplan-Meier curves illustrating the rates of survival of the acetabular component according to the age of the patient at the time of the index procedure. The error bars represent 95% confidence intervals. those who were less than or equal to fifty years old (p > 0.05). Multivariate logistic regression analysis revealed that the offset-bore cup, younger age at the time of surgery, increased polyethylene wear, and previous acetabular surgery were independent predictors of revision of the acetabular component because of aseptic loosening. Factors that did not influence aseptic loosening of the acetabular component included acetabular bone-grafting, stem type, and the operating surgeon. Discussion he purpose of the present study was to document the T long-term results of total hip arthroplasty with cement in

7 77 patients with osteoarthritis secondary to developmental dysplasia of the hip. Two hundred and one hips were followed for more than ten years and, of these, sixty-three hips were followed for more than twenty years. The relatively large number of patients enabled us to identify factors that were associated with both satisfactory and unsatisfactory outcomes. The overall rate of survival of the acetabular component, with revision for aseptic loosening as the end point, was 90.6% at ten years and 63% at twenty years. Even though these rates of loosening are higher than those after primary total hip arthroplasty for the treatment of osteoarthritis, they compare well with the findings of previous studies in which higher rates of aseptic loosening of the acetabular component have been found after total hip arthroplasty for the treatment of osteoarthritis secondary to developmental dysplasia of the hip Although many authors have claimed that a Chiari osteotomy facilitates later component placement and fixation, we agree with others that there are no data to support this claim 15,16. Hashemi-Nejad et al. found no significant difference between two well-matched groups of dysplastic hips with and without previous Chiari osteotomy in terms of the clinical or radiographic outcome after total hip arthroplasty 17. In the present study, survival of the acetabular component was found to be significantly worse after a previous Chiari osteotomy or shelf procedure. The small Charnley cup (outside diameter, 40 mm) was used in hips with all grades of dysplasia and had the best survival rates of the three acetabular components used. However, the deficient, small-sized acetabulum precludes the use of standard acetabular components in hips with severe dysplasia. Polyethylene thickness is important, especially in young patients, and inadequate polyethylene thickness is a major cause of polyethylene debris-mediated osteolysis 18,19. Charnley introduced the offset-bore cup in 1979 to overcome this problem. Its eccentric socket, with an outer diameter of 38 mm, gives the cup a 12-mm polyethylene thickness superiorly and a 4-mm polyethylene thickness inferomedially when used with a mm head. The use of the offset-bore cup for the treatment of previously untreated dislocations has been promising, with excellent wear behavior and low migration and revision rates 20. The present series demonstrated a higher revision rate for the offset-bore cup as compared with the small Charnley cup, despite the finding that there was no significant difference in wear rates. This finding is probably related to the fact that the offset-bore cup was used mainly for hips with higher grades of dysplasia. Second, previous studies have confirmed that, despite low wear rates, socket migration in the offsetbore cup occurs with lower penetration as compared with standard cup designs 21. One possible explanation is impingement of the neck of the stem against the rim of the cup as a result of multiple-vector wear. The metal-backed cup that was introduced by Harris in 1970 was inserted with cement and initially demonstrated excellent clinical and radiographic results 22,23. However, Ritter et al. found a significant increase in the rate of failure of cemented metal-backed cups as compared with all-polyethylene cups when radiolucency (p < ), loosening (p < ), and revision (p < ) were evaluated as the three different modes of failure 24. This finding has been attributed to increased linear and volumetric wear in association with cemented metal-backed cups as compared with all-polyethylene cups 25. Decreased polyethylene thickness remains a problem with metal-backed cups, especially those used with larger femoral heads, and early radiographic failure has been demonstrated in association with both cemented and uncemented cups, although the mean rate of volumetric wear remains higher in association with uncemented metal-backed cups In the present series, the ten-year survival rate of the metal-backed cups was comparable with those of the small Charnley and offset-bore cups. The metal-backed cups were used mainly for hips with lower grades of dysplasia in conjunction with a mm femoral head, which maximizes the polyethylene thickness; this factor may have contributed to the improved survival rate when compared with the offset-bore cup at ten years. However, it should be noted that the metalbacked cup had a maximum duration of follow-up of fifteen years and therefore could not be compared with the offsetbore cup at twenty years, at which time the offset-bore cup clearly had a much poorer survival rate compared with the small Charnley cup. The relationship of acetabular wear to osteolysis and aseptic loosening of the acetabular component following total hip arthroplasty has been well documented 29,30. The mean annual rate of polyethylene wear of 0.10 mm/yr compares favorably with the findings of previous studies, in which it has ranged from 0.07 to 0.14 mm/yr 31,32. The present study also showed that the mean annual rate of polyethylene wear was 0.07 mm/yr for the components that were not revised, compared with 0.21 mm/yr for those that were revised. This finding compares well with the finding of the study by Sochart, in which the mean annual rate of polyethylene wear of revised components was twice that of surviving components 33. Such wear often occurs for many years before radiographic changes and clinical symptoms become apparent 34. This trend was also reflected in the present study, in which the majority of acetabular component failures occurred between ten and twenty years. However, most of the radiographic failures in asymptomatic patients occurred after twenty years, which emphasizes the need for prolonged follow-up in the younger age-group. Higher rates of aseptic loosening of the acetabular component have been reported in young patients These results also may be partly attributable to accelerated polyethylene wear, which has already been reported in other studies 38,39. We could not establish a significant correlation between younger age and increased polyethylene wear, with both of these variables being independent predictors of higher rates of acetabular revision. The lack of correlation may be explained by the fact that the majority of patients in the present series were female as previous studies have suggested that increased polyethylene wear is associated with the male gender and increased postoperative activity involving moderate to heavy manual labor 40,41. The main limitation of the present study is that it was a

8 78 retrospective review. The polyethylene wear was calculated with use of manual methods, which are known to be less accurate than computerized image-analysis methods. We also were unable to compare the metal-backed cup with the small and offset-bore cups at twenty years because of its relatively shortterm follow-up. The present study identified younger age, accelerated polyethylene wear, the offset-bore cup, and previous acetabular surgery as factors that had an adverse effect on the longterm survival of the acetabular component. At the present time, in the absence of long-term follow-up with uncemented components, we still recommend the use of cemented acetabular components in young patients with developmental dysplasia of the hip. However, the risk factors listed above should be identified when total hip arthroplasty is performed for the treatment of a dysplastic hip, and patients should be made aware of the inferior outcomes associated with total hip arthroplasties performed for developmental dysplasia as compared with those performed for primary osteoarthritis. The long period over which the present study was performed indicates that different types of polyethylene and polyethylene sterilization methods have been employed. This factor may well have been one of the reasons for early wear and failure in some cases. Perhaps in the future, total hip arthroplasty with use of newer cross-linked polyethylenes or alternate bearing surfaces such as ceramics and metal may provide improved results for younger patients with developmental dysplasia by reducing the prevalence of wear-mediated loosening. Aslam Chougle, FRCS, FRCS(Tr&Orth) 139 Hallbridge Gardens, Up Holland, Lancashire WN8 0EP, United Kingdom. address for A. 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