JBJS | Retention of All-Polyethylene Acetabular Components After Femoral Revision of a Cemented Total Hip Replacement

The Journal of Bone & Joint Surgery, Volume 83, Issue 11

Scientific Article | November 01, 2001

Retention of All-Polyethylene Acetabular Components After Femoral Revision of a Cemented Total Hip Replacement

Brian R. Hamlin, MD; Charles Rowland, MS; Bernard F. Morrey, MD

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The Journal of Bone & Joint Surgery. 2001; 83:1700-1705

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Abstract

Background: This study was undertaken to provide a basis for decision-making when a well-fixed cemented cup is encountered at the time of a revision of a femoral component of a total hip replacement. It may be beneficial to retain the cup in some instances and thus reduce morbidity, complications, blood loss, operative time, and cost.

Methods: All patients who had a revision of the femoral component and retention of an all-polyethylene acetabular component from 1971 to 1996 were identified. Three hundred and seventy-four patients with a total of 395 cemented total hip replacements fit the inclusion criteria. The gender, date of and age at the index surgery, type of acetabular implant, and time of and reason for the revision of the femoral component were reviewed. The time to subsequent cup revision or latest surveillance was noted. The average age (and standard deviation) was 66.5 ± 11.8 years at the time of the femoral revision, which was performed at an average of 8.0 ± 4.4 years after the primary arthroplasty. For the purposes of this study, the end point for survival of the acetabular component was cup revision for any reason.

Results: At the time of the latest follow-up, at an average of nine years after the femoral revision and 17.3 years after the primary arthroplasty, 342 (86.6%) of the 395 cups remained in situ. Fifty-three cups (13.4%) in fifty-two patients had been revised, at an average of 10.0 ± 5.7 years after the femoral revision and 16.7 ± 5.3 years after the primary arthroplasty. The rate of survival of the retained acetabular components was 96.9% at five years, 89.3% at ten years, and 78.7% at fifteen years after the femoral revision and was 95.1% at fifteen years and 87.1% at twenty years after the primary arthroplasty. Increased age (p < 0.0001) and a shorter time-interval (less than 7.5 years) between the primary arthroplasty and the femoral revision (p = 0.05) were significantly associated with an increased likelihood of survival free of cup revision. Femoral head size, acetabular component design, gender, and primary diagnosis did not affect prosthetic survival in this sample of patients.

Conclusions: The likelihood of survival of the unrevised cup was associated with patient age and duration of implantation, with the age of the patient being the more dominant factor predicting failure of the acetabular component.

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Introduction

Introduction | Materials and Methods | Results | Discussion | References

Patients with a cemented total hip replacement that requires femoral revision may have a well-fixed acetabular component. Surgeons are thus faced with the question of whether these well-fixed devices should be replaced routinely when the femoral implant is exchanged. In some instances, retention of the cup may be beneficial as it may result in reduced morbidity, complications, blood loss, operative time, and cost. Recently, there have been reports of good results following the retention of well-fixed femoral components at the time of acetabular revision^1,2, supporting the notion that isolated revision of one of the components does not affect the survival of the other. However, this position has been justified in part by the fact that the femoral head does not undergo wear changes over time.

There is little information regarding the results of isolated femoral revision in cases in which a well-fixed acetabular implant is left in place. It has been our belief that revision of the femoral component does not alter the survival of the cup. However, because the cup is subject to wear, this observation is not necessarily correct. The purpose of this study was, therefore, to determine the success of retaining a well-fixed acetabular component at the time of isolated femoral revision and to identify any variables that may influence clinical decision-making.

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Fig. 1:: Survival of the cup after the primary procedure, according to the age at the time of the primary procedure, calculated with use of the Kaplan-Meier method.

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Fig. 2:: Survival of the cup after the femoral revision, according to the age at the time of the femoral revision, calculated with use of the Kaplan-Meier method.

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Fig. 3:: Survival of the cup after the femoral revision, according to both the age at the time of the femoral revision (older or younger than sixty-eight years) and the interval (int) between the primary arthroplasty and the femoral revision (more or less than 7.5 years), calculated with use of the Kaplan-Meier method.

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

We identified all patients, at the Mayo Clinic, who had a cemented total hip replacement with an all-polyethylene cup and subsequently underwent revision of only the femoral component. The clinical characteristics that were analyzed included patient age at both the primary and the revision arthroplasty, gender, acetabular design, diagnosis, and duration from the primary arthroplasty to the revision procedure. Subsequent revision of the cup was defined as the end point of the analysis. Patients were followed for a minimum of two years.

We identified 374 patients, with a total of 395 total hip arthroplasties, who had isolated revision of the femoral component from 1971 to 1996. Two hundred and eighty-one (71.1%) of the procedures were performed in men, and 114 (28.9%) were done in women. The average age (and standard deviation) at the time of the primary arthroplasty was 58.5 ± 11.9 years (range, eighteen to eighty-eight years). Two hundred and seventy-five (69.6%) of the primary arthroplasties were performed for the treatment of degenerative arthritis; forty-six (11.6%), for avascular necrosis; twenty-five (6.3%), for developmental dysplasia; fourteen (3.5%), for rheumatoid arthritis; ten (2.5%), for a fracture; five (1.3%), for a nonunion; four (1.0%), for a tumor; four (1.0%), for ankylosing spondylitis; and twelve (3.0%), for another diagnosis. The acetabular components consisted of 225 Charnley implants (57%) (Thackray, Leeds, England), seventy T-28 (Trapezoidal-28) implants (17.7%) (Zimmer), fifty-eight Aufranc-Turner implants (14.7%) (Howmedica, Rutherford, New Jersey), twenty-three Müller implants (5.8%) (Howmedica), and nineteen other all-polyethylene designs (4.8%). There were 234 22-mm femoral heads (59.2%), eighty-one 32-mm heads (20.5%), seventy-five 28-mm heads (19.0%), and five 26-mm heads (1.3%).

The age at femoral revision averaged 66.5 ± 11.8 years (range, twenty-five to ninety-three years). The patients were stratified by decade as follows: less than forty-five years of age (nineteen hips), forty-five to fifty-four years of age (thirty-seven), fifty-five to sixty-four years of age (ninety-nine), sixty-five to seventy-four years of age (135), and seventy-five years of age or more (105). Two hundred and forty-five (62.0%) of the femoral components were revised because of aseptic loosening; seventy-four (18.7%), because of a fractured component; thirty-six (9.1%), because of a fractured component with aseptic loosening; twenty-one (5.3%), because of aseptic loosening and a femoral fracture; ten (2.5%), because of a femoral fracture; six (1.5%), because of a fractured component and a femoral fracture; and three (0.8%), because of a dislocation. The time from the primary arthroplasty to the femoral revision averaged 8.0 4.4 years (range, ten days to twenty-two years). Three hundred and eighteen (80.5%) of the revision stems were cemented, and seventy-seven (19.5%) were uncemented.

Statistical Analysis

Survival estimates were calculated with use of the method of Kaplan and Meier³. The Cox proportional-hazards model was used to determine the significance of the association between survival and various risk factors: age at the primary arthroplasty, age at the femoral revision, time-interval from the primary arthroplasty to the revision, femoral head size, acetabular component design, gender, and primary diagnosis⁴. Age was used as a continuous variable in all significance tests, although it was divided into groups for graph purposes in Figures 1, 2, and3. The time-interval from the primary arthroplasty to the femoral revision was discretized at the median value of 7.5 years for all significance tests.

Results

Introduction | Materials and Methods | Results | Discussion | References

At the latest follow-up examination, at an average of 9.0 ± 4.75 years after the femoral revision and 17.3 ± 5.2 years after the primary arthroplasty, 342 (86.6%) of the 395 cups remained in place. The rate of survival of the retained acetabular components was 96.6% at five years, 89.3% at ten years, and 78.7% at fifteen years after the femoral revision and was 95.1% at fifteen years and 87.1% at twenty years after the primary arthroplasty. Fifty-three cups (13.4%) in fifty-two patients had been revised, at an average of 10.0 ± 5.7 years after the femoral revision and 16.7 ± 5.3 years after the primary arthroplasty. The reasons for these revisions included aseptic loosening (forty-two hips), infection (eight hips), and dislocation (three hips).

With use of age as a continuous variable in Cox proportional-hazards regression models, poorer cup survival after the primary arthroplasty was found to be significantly associated with a younger age at the time of the primary arthroplasty (p < 0.0001) (Fig. 1), poorer cup survival after the femoral revision was found to be significantly associated with a younger age at the time of the primary arthroplasty (p < 0.0001), and poorer cup survival after the femoral revision was found to be significantly associated with a younger age at the time of the femoral revision (p < 0.0001) (Fig. 2). A longer time-interval (more than 7.5 years) between the primary arthroplasty and the femoral revision was associated with an increased risk of revision (p = 0.05). The time-interval remained a significant factor after adjustment for age at the femoral revision in a Cox proportional-hazards model (p = 0.05). The time-interval did not have a significant effect on cup survival among patients who were older than sixty-eight years of age (p = 0.35), but it was significantly associated with an increased risk of revision among patients younger than sixty-eight years of age (p = 0.002) (Fig. 3).

A femoral head size of 22 mm was associated with a significant improvement in cup survival (p = 0.035), but, when this factor was cross-correlated for age, head size became an insignificant parameter. Gender (p = 0.172), cup type (p = 0.158), and primary diagnosis (p = 0.217) had no significant effect on cup survival, probably because of the small sample sizes that resulted from stratifying the data into these subsets.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

The decision to retain a well-fixed acetabular component at the time of femoral revision has, to date, been a matter of judgment, with little information in the literature to direct the thought process. At our institution, cups that are loose or show increased wear or roughening at the interface are replaced. When these findings are absent, the decision must be based on the ability to predict the survival of the well-fixed cup. It would be helpful to know the variables that affect the survival of the cup or to be able to predict whether, and under what circumstances, it should be revised, even if well fixed^5,6.

Our results with regard to survival of a cemented all-polyethylene cup compare favorably with those in other reports in the literature. Wroblewski and Siney⁷ reported on 193 hips with a 7% rate of revision of the cup at twenty-five years. Studies with sample sizes ranging from 293 to 1041 did show radiographic loosening rates that ranged from 16% to 42% after fifteen to twenty years of follow-up^8-10. However, the radiographic status of cemented all-polyethylene cups is not necessarily associated with the clinical results. Ranawat et al.¹¹ studied the results of 236 procedures and noted a discrepancy between the rates of clinical success (98%) and radiographic success (92%). Wroblewski and Siney assessed the results of more than a thousand procedures and also found no relationship between the radiographic appearance of the bone-cement interface of the socket and the clinical results; both radiographically loose and well-fixed components were equally successful clinically.

We chose not to use the radiographic appearance of the cup as evidence of cup failure because, as noted above, this is a less discrete end point than reoperation. Hence, cup survival without revision, rather than without subsequent radiographic changes, was selected as the criterion of success.

We found that certain variables do influence cup survival. In this study, patients who were younger than sixty-eight years of age at the time of both the primary arthroplasty and the femoral revision did not fare as well with regard to long-term cup survival. Kavanagh et al.⁹ examined the twenty-year results of 333 so-called first-generation Charnley arthroplasties and found that age at the time of the arthroplasty affected survival of the cup, with the probability of revision substantially increased in patients less than fifty-nine years of age. Kobayashi et al.¹², in a study of cemented total hip replacements, compared patients who were less than fifty years of age (fifty-five cups) with those older than fifty years of age (273 cups) at the time of the arthroplasty. At ten to twenty years (average, fourteen years), the rate of revision of the acetabular component was 20% for the younger patients and only 4% for the older group.

We also found that components that had been in place for a shorter period of time had a better survival rate after the femoral revision. Although this finding may be intuitive, it does support the hypothesis that the femoral revision itself does not affect the survival of the acetabular component. The simplest interpretation of our finding is that the expected survival of the cup is predicated on the duration of its use and the age of the patient. Furthermore, as shown in Figure 3, the age at the time of the revision is clearly more important than the length of time that the implant has been in place. Better cup survival was observed in patients more than sixty-eight years of age, regardless of the time until the index revision. The worst survival curve was for patients less than sixty-eight years of age, regardless of the time until the index revision. This finding is in contrast to the experience of Peters et al.¹, who studied the results of thirty-seven isolated acetabular revisions in which the femoral component was left in place. They found no association between the time that the femoral component had been left in situ at the time of the cup revision (p = 0.58) and the ultimate survival of the stem.

We believe that our data support the practice of retaining a well-fixed cemented all-polyethylene cup at the time of femoral revision in selected patients. Consideration of the implant survival curve by age allows prediction of future cup survival, and the data reflected in this curve now influence our decision to retain cemented all-polyethylene cups.

References

Introduction | Materials and Methods | Results | Discussion | References

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Ranawat CS, Deshmukh RG, Peters LE,Umlas ME. Prediction of the long-term durability of all-polyethylene cemented sockets. Clin Orthop,1995;317: 89-105. 31789 1995 [PubMed]

Kobayashi S, Takaoka K, Saito N,Hisa K. Factors affecting aseptic failure of fixation after primary Charnley total hip arthroplasty. Multivariate survival analysis. J Bone Joint Surg Am,1997;79: 1618-27. 791618 1997 [PubMed]

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