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Outcome After Isolated Polyethylene Tibial Insert Exchange in Revision Total Knee Arthroplasty
The Journal of Arthroplasty Vol. 28 No. 1 2013
Outcome After Isolated Polyethylene Tibial Insert Exchange in Revision Total Knee Arthroplasty Richard P. Baker, MSc, MBChB, FRCS, Bassam A. Masri, MD, FRCSC, Nelson V. Greidanus, MD, FRCSC, and Donald S. Garbuz, MD, FRCSC
Abstract: We identified 45 knees in 42 patients who had an isolated tibial insert exchange for a failed primary knee arthroplasty with a minimum of 2 years of follow-up. The mean age at revision was 68 years, and the mean time to revision was 80 months. Thirty patients completed follow-up questionnaires (Oxford Knee Score, University Of California Activity Index score, Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC], and Short Form 12) with a mean follow-up of 58 months. Patients' current scores were compared with preoperative scores in 14 knees. Four patients (9%) were subsequently revised. Significant improvement was seen in the Oxford Knee Score, Short Form 12 physical component, and all WOMAC domains, but only 58% of patients had a clinically successful result by global WOMAC score. When patients are selected appropriately, an isolated liner exchange can significantly improve the function of the knee. Keywords: tibial insert exchange, total knee arthroplasty, revision, osteolysis. © 2013 Elsevier Inc. All rights reserved.
this study was to assess the effectiveness of isolated tibial insert exchange in the salvage of malfunctioning total knee replacements in which all components were well fixed with no evidence of loosening at the host-prosthesis interface.
Infection followed by mechanical loosening is the most common cause of failure of total knee arthroplasty (TKA) [1]. Polyethylene wear is a causative factor in osteolysis and loosening of prosthetic components. The modularity of modern TKA prostheses allows for tibial insert exchange in cases of isolated polyethylene wear when the components are well fixed. Tibial insert exchange when indicated is a simple operation with relatively little morbidity. Conversely, the removal of femoral and/or tibial components at revision can often lead to the removal of host bone and increases the magnitude of the procedure. Conflicting reports exist as to the efficacy of tibial insert exchange, recommended by some [2,3] and used with caution by others [4,5]. However, we have continued to offer patients tibial insert exchange as we feel it can be a successful procedure, when indicated, and in highly selected patients. The aim of
Materials and Methods All patients who had undergone an isolated tibial polyethylene insert exchange were identified from our institutional database. Patients were only included if they were 2 years or more after the procedure and had had no revisions before liner exchange. A prerequisite for a tibial insert exchange was the absence of infection on preoperative workup, well-aligned implants in a knee that is well balanced or could be rendered well balanced as a result of surgery. Components that appeared well fixed on preoperative radiographs were confirmed with rigorous intraoperative examination. The tibial and femoral components are also examined intraoperatively to ensure that they were well rotated. Ethical approval was obtained from our institutional review board, and accordingly, all initial patient contact had to be by mail. Patients were interviewed by telephone if they failed to respond to the postal questionnaire on 2 occasions. The self-reported outcomes used were the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) [6], Oxford Knee Score (OKS) [7], Short Form 12 item score (SF-12) [8], and
From the Department of Orthopaedics, University of British Columbia and Vancouver Acute Health Services, Vancouver, British Columbia, Canada. Submitted September 9, 2011; accepted May 30, 2012. The Conflict of Interest statement associated with this article can be found at http://dx.doi.org/10.1016/j.arth.2012.05.030. Reprint requests: Dr Donald Garbuz, MD, FRCSC, Complex Joint Clinic—3rd Floor, Gordon and Leslie Diamond Health Centre, 2775 Laurel St, Vancouver, V5Z 1M9, British Columbia, Canada. © 2013 Elsevier Inc. All rights reserved. 0883-5403/2801-0001$36.00/0 http://dx.doi.org/10.1016/j.arth.2012.05.030
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2 The Journal of Arthroplasty Vol. 28 No. 1 January 2013 the University Of California Activity Index (UCLA) [9]. Satisfaction with the procedure was measured using the Mahomed questionnaire [10]. The Mahomed questionnaire is a scale designed to assess satisfaction with joint arthroplasty. Patients answer 4 questions: patients' overall satisfaction with surgery, the extent of pain relief, the ability to perform home or yard work, and the ability to perform recreational activities. Items are scored on a 4-point Likert scale with response categories consisting of very satisfied (100 points), somewhat satisfied (75 points), somewhat dissatisfied (50 points), and very dissatisfied (25 points). The scale score is the unweighted mean of the scores from the individual items, ranging from 25 to 100 per item (with 100 being most satisfied) [10]. Preoperative radiographs were evaluated using the Knee Society Radiographic Grading system [11]. This allowed for uniform grading of any osteolysis and loosening at the bone component interfaces. Evidence of polyethylene wear was analyzed via measurement of loss of joint space height and asymmetric wear of the polyethylene liner. In addition, the alignment of the prostheses was assessed by measuring the anatomical axis of the TKA. Where patients had undergone a later procedure after liner exchange, they were considered a failure, and the incidence of further surgery was calculated. Statistical Analysis Statistical analysis was performed using SAS version 9.2 (SAS Institute, Inc, Cary, NC). The OKS and WOMAC scores were normalized out of 100, with larger values signifying better outcomes. Univariate t test analysis was used to compare preoperative and postoperative scores for OKS, SF-12, WOMAC, and UCLA. Multivariate analysis of variance was used to identify if indication for tibial insert exchange affected the outcome scores. As multiple comparisons were made between groups, probability values were subjected to the Bonferroni correction. Kaplan-Meier analysis was used to document survival after liner exchange with logrank analysis to identify if osteolysis affected survival.
Results Forty-five isolated tibial insert exchanges were identified from the institutional database. There were 42 patients, 3 patients underwent bilateral surgery, and 23 were female. Thirty-seven patients were alive and available for review. Five patients were deceased, and all had been between 3 and 7 years post-revision at the time of their death. None had experienced failure of their tibial insert revision or required any further knee intervention. Of the total cohort of 42 patients (45 knees), 4 knees were subsequently revised (9%) and were excluded from questionnaire analysis. Twentynine patients completed questionnaires of the remaining 33 (88%). One patient refused to complete the
questionnaire, and 3 patients were unable to complete the questionnaires as English was not their native language. None of these patients had undergone further surgery. An additional 4 patients were identified who had an isolated tibial insert exchange but were excluded, as they had a prior full revision TKA, which was considered an exclusion criterion for the study. The mean time to revision after the primary TKA was 80 months (range, 12-152 months). Their mean age at revision was 68 years (range, 43-90 years). The mean follow-up time from tibial insert exchange was 58 months (range, 24-123 months). The mean body mass index was 33 (20-45). Thirty-six patients had a primary PFC (Depuy, Warsaw, IN); 3, an Advance Duramer (Wright Medical, Arlington, TN); 2, a PCA (Stryker [Howmedica], Mawah, NJ); 2, a Kinematic (Stryker [Howmedica], Mawah, NJ); 1, an Osteonics (Stryker [Howmedica], Mawah, NJ); 1, a Scorpio (Stryker [Howmedica], Kalamazoo, MI); and 1, a MG2 (Zimmer, Warsaw, IN) primary total knee replacement. Twenty-four knees were cruciate-retaining designs, and 21, posterior stabilized. Indication for Liner Exchange The main clinical indication for tibial insert exchange was polyethylene wear in 34 (76%) of 45 knees, stiffness in 5 (11%) of 45 knees, instability in 3 (7%) of 45 knees, and pain in 3 (7%) of 45 knees. In this latter group, the tibial insert exchange was a part of a synovectomy and intraoperative examination of the components. Preoperatively, the patient's main presenting complaints were pain and swelling in the case of polyethylene wear. Intraoperative Findings Seven patients had no evidence of polyethylene wear. Five of these patients were revised for stiffness, and 2, for pain. Severe polyethylene wear was noted in all knees that underwent surgery for a preoperative diagnosis of polyethylene wear or for instability. Twenty-four patients had a like-for-like liner exchange. Twelve patients had their liners increased in size, the median increase being 2 mm (range, 2-7.5 mm); 11 were in cases revised for polyethylene wear; and 1 patient, for instability. Six patients had their liners downsized, the median decrease being 2.5 mm (range, 2-5 mm), the indications were stiffness in 3 patients; pain, in 2; and polyethylene wear, in 1 case. In 3 patients, the primary liner thickness was not available from the original operative records and unobtainable at the time of surgery due to wear of the liner itself. Of the 38 patients who had intraoperative evidence of polyethylene wear, there was delamination and/or fracture of the polyethylene in 10 cases (26%): 4 were posteriorly stabilized, and 6, cruciate-retaining designs. In the others, there was evidence of both backside and bearing surface wear. A large proportion (36/45) of our patients had a PFC modular (Depuy) liner sterilized
Isolated Polyethylene Tibial Insert Exchange in Revision TKA Baker et al
initially in air. This liner has been shown to have a high prevalence of accelerated wear and early failure. Nineteen patients had a synovectomy performed alongside their isolated tibial insert exchange. All patients who had a preoperative diagnosis of stiffness required a synovectomy. Three patients had a loose patellar button removed during the tibial insert exchange procedure—no patient had their patella resurfaced. Thirteen patients had intraoperative evidence of periarticular osteolysis, of whom 2 required bone grafting; the remaining defects were too small to consider grafting. Both were bone grafted with freezedried croutons into the defects, and all components were stable. Two patients had evidence of scratching to the femoral condylar surface. This was minimal, and careful assessment revealed that the risk of damage to the host bone for component removal outweighed the disadvantage of leaving the imperfect implant in situ. Clinical Outcome Preoperative scores were available in 14 patients, as this is a retrospective study and not all patients had completed routine preoperative questionnaires. After tibial insert exchange, 30 patients completed questionnaires at a minimum of 2 years postoperatively. There was a significant improvement in patient-reported OKS, SF-12 physical, and WOMAC (across all WOMAC domains) (Table 1). The mean satisfaction score across all patients was 79.5 (range, 0-100), indicating the majority of patients were highly satisfied with the tibial insert exchange procedure (Table 2). Fig. 1 highlights the improvements in quality-of-life measures. Patients with stiffness as the indication for tibial insert exchange showed a greater improvement in postoperative scores when compared with baseline—although this effect did not reach significance once Bonferroni correction was applied. Clinical Failures Analysis of the postoperative scores (Table 2) revealed that most patients were satisfied with the liner exchange procedure. Previously, a WOMAC score of less than 65 has been used to indicate failure and greater
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Table 2. Distribution of Postoperative Scores Variable OKS UCLA (6) SF-12 mental SF-12 physical WOMAC function WOMAC stiffness WOMAC pain WOMAC global Satisfaction All Pain Function Recreation Results
Lowest Quartile
Median
Top Quartile
12-15 1-4 27-53 18-27 4-57 0-63 20-65 15-60
22 5 58 39 81 78 87 82
26-57 7-10 62-69 51-58 94-100 88-100 100-100 94-100
0-67 0-67 0-67 0-67 0-67
93 86 86 80 86
100-100 100-100 100-100 100-100 100-100
than 75 success [12]. In this series, 8 patients (26%) had a global WOMAC score less than 65, and 18 (58%) had a score greater than 75; the remainder (16%) had an intermediate WOMAC score (66-74). These 8 patients also had the lowest OKS scores (range, 24-57), indicating clinical failure of the procedure to relieve the patient's symptoms. Radiographic Findings Three patients had no radiographs available for analysis. The mean anatomical axis was 7º (range, 2º13º). Radiographic evidence of osteolysis was present in 16 patients, of whom 12 were confirmed intraoperatively. Most radiographic lucencies occurred in tibial zones 1 and 2 [11]. There was 1 case with femoral lysis present radiographically. Liner Exchange Survival Two survival curves were produced, those for patients with evidence of osteolysis and those with none (Fig. 2). Analysis of the curves showed that those with osteolysis had a greater chance of failure (log rank, P = .0259). Failures Four patients required revision after isolated tibial insert exchange. They failed between 1 and 12 years postoperatively. All failed due to osteolysis and
Table 1. Clinical Outcomes Variable OKS UCLA (6) SF-12 mental SF-12 physical WOMAC function WOMAC stiffness WOMAC pain WOMAC global
Preoperative Score
Postoperative Score
No. Patients Compared
Mean Difference
95% CI
P
45 (13-75) 4 (2-5) 49 (24-68) 29 (20-47) 50 (9-84) 43 (0-100) 49 (25-85) 50 (13-84)
75 (6-100) 6 (1-10) 56 (27-69) 39 (18-58) 74 (4-100) 73 (0-100) 81 (20-100) 75 (15-100)
14 6 13 13 14 13 14 14
31.2 0.7 5.2 8.7 26.1 34.6 33.4 28
19.6-42.7 −1.1 to 2.4 −1.7 to 12.2 3.5-13.9 13.4-38.8 19.6-49.6 21.8-44.9 16-40
b.001 .484 .164 .007 .001 .001 b.001 .001
Abbreviation: CI, confidence interval.
4 The Journal of Arthroplasty Vol. 28 No. 1 January 2013 significant wear and had fractured. At the time of the femoral revision 7 years later, it was apparent that progressive osteolysis contributed to aseptic loosening of the femoral component. A fourth patient was revised 16 months after tibial insert exchange for progressive and severe tibial osteolysis under the medial tibia with associated collapse into the lytic defect. At tibial insert exchange, delamination of the polyethylene was present, but minimal osteolysis was present radiographically preoperatively.
Discussion
Fig. 1. Preoperative and postoperative quality-of-life scores.
Isolated tibial insert exchange is an infrequent operation, and few large studies exist analysing its outcome. This is in part due to the fact that infection and component loosening are the 2 main reasons for revision knee arthroplasty and these failures are usually associated with major component revision procedures [1]. It has been shown that when isolated tibial insert exchange for polyethylene wear was contemplated preoperatively, 89% actually required revision of one or more of the tibial or femoral components due to macroscopic damage to their surfaces [13]. Babis et al [4] reported a high rate of failures in their series of isolated tibial insert revisions. When tibial insert exchange alone was used for instability, 44% failed, and 33% failed for polyethylene wear. The total failure rate was reported to be 25% within 3 years. The same group of authors also reported on a cohort of patients that underwent isolated tibial insert exchange for stiff TKAs with poor outcomes and advise against the procedure due to the poor outcomes [14]. Engh et al [5] reviewed their series of tibial insert exchange and reported that, if severe wear and delamination are present within 10 years of primary surgery, isolated exchange should not be attempted as the accelerated wear likely indicated an
loosening of the implants; 2 femoral and 2 tibial components were loose. The details of these 4 patients are as follows: One patient who failed the earliest (at 1 year) was bone grafted at his isolated tibial insert exchange on both the medial tibial and femoral sides. Preoperatively, the lysis was only present radiographically in tibial zone 1 [11]. His osteolysis progressed, and his femoral component became loose requiring a subsequent stemmed revision. The polyethylene liner in this case had significant backside wear only. A second patient, with rheumatoid arthritis, had her liner exchange because the knee was stiff post primary TKA. A synovectomy and liner downsizing were performed, both tibial and femoral components were not loose, and there was no polyethylene wear present. At 12 years, the femoral component had become loose, and a stemmed revision was performed. A third patient had her femoral component revised 7 years post tibial insert exchange. At liner exchange, the femoral component had been well fixed despite preoperative radiographs displaying lysis in femoral zones 1 and 2. The polyethylene liner had
Kaplan Meier survival curves for Months to Revision by Osteolysis
Survival Distribution Function
1.0
0.8
0.6
0.4
0.2
0.0 0
25
50
75
100
Months PLOT
No Osteolysis Intra–operative Osteolysis
Censored Censored
Fig. 2. Kaplan-Meier liner exchange survival.
125
150
Isolated Polyethylene Tibial Insert Exchange in Revision TKA Baker et al
overall problem with the joint itself, which would not be addressed by modular component exchange. A small proportion (10/38; 26%) of our patients had actual delamination of the polyethylene. However, in our series, we are unable to make the same conclusions as Engh et al [5], as we believe that a contributing cause for tibial insert wear and need for tibial insert exchange was the fact that the primary knee tibial insert was subjected to sterilization in air [15]. All subsequent tibial inserts, which we used for our revision procedures, were sterilized in an inert environment, as the manufacturer had changed the sterilization procedure for the PFC Modular liners after 1999. For this reason, we felt that an isolated tibial insert exchange was not necessarily contraindicated, as the polyethylene had improved. Our results support this premise. Our series is not the first to report good results from tibial insert exchange procedures, as Jensen et al [2] reported good results with tibial insert exchange in 27 patients. It is important to note that, in the Jensen series, 22 of the patients also received a patellar resurfacing and, therefore, it becomes difficult to attribute success solely to tibial insert exchange. No patients in our series had a patella resurfaced, but 3 patients had a loose patella button removed at the same time as tibial insert exchange. Interpreting preoperative knee radiographs for osteolysis is difficult, as often, the implant may obscure the defect. However, in 75% (12/16) of cases, a preoperative suspicion of osteolysis was confirmed intraoperatively, and 4 were simple cementing defects. Of our 4 failures, 3 had evidence of radiographic osteolysis preoperatively, which was confirmed in 2 intraoperatively; therefore, 2 (17%) of 12 patients with intraoperative lysis went onto subsequent revision. As such, the failure rate for tibial insert exchange when radiographically visible osteolysis is present is 3 (25%) of 12. Although this is a substantial failure rate, it should be kept in mind that, for the duration of our study, 75% of such patients did well, and an isolated tibial insert exchange was a good operation, but patients need to be counselled that they have a 1:4 chance of needing a subsequent revision if osteolysis is present. In our series, there was only 1 case of femoral osteolysis, and this went on to fail. With only 1 case, it is impossible to tell whether the presence of femoral osteolysis is a harbinger of impending failure. Despite 27% (12/45) of cases having osteolysis, only 9% (4/45) of tibial insert exchanges failed. This is likely due to the fact that all cases had good alignment and the components were well fixed and well rotated. In a multicenter study, Griffin et al [3] reported a revision rate of 16.2% (11 of 68) of knees undergoing an isolated tibial insert exchange at an average of 44 months of follow-up, despite the presence of osteolytic lesions. In that study, 97% of patients did not show progression of osteolytic
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defects, and the authors did not feel that an isolated tibial insert exchange was contraindicated in the presence of osteolysis. Although our results were not as good, we are in agreement with this recommendation. In our series, most patients also had a concomitant synovectomy as part of the procedure. We do not believe that this is a confounding factor in our series as this is a standard part of all of our revision operations. Routine synovectomy facilitates exposure and provides safe access to the tibial insert mechanism, as well as it permits the removal of polyethylene-induced synovitis or hypertrophic tissue in the stiff knee. Although it is possible that the synovectomy may provide some symptomatic relief to the patient, it is unlikely that it could provide the magnitude of improvement reported by our patients over a minimum of 2 years of follow-up from the procedure. Clinical failure as indicated by low WOMAC and OKS scores was seen in 8 of our patients who completed postoperative questionnaires. This is similar to Willson et al [16] who reported a similar finding of 30% of patients having persistent pain in a liner exchange series similar in size to our own. In the series of Willson et al, isolated liner exchange was more likely to fail if performed within 3 years of primary TKA, and 29% of their patients have required a subsequent revision. In our series, our time from primary TKA to liner exchange was longer, and we revised a greater proportion of our patients for polyethylene wear, whereas Willson et al [16] had a greater proportion revised for instability. It is interesting that we both report similar rates of pain after isolated liner exchange and probably represent the effect of multiple operations on the knee regardless of indication for revision. Our study is among the first to report a significant patient-reported benefit to isolated revision tibial insert exchange across a comprehensive array of generic, disease-specific, and joint-specific quality-of-life outcomes. In addition, our study includes many patients with preoperative baseline quality-of-life scores; we are able to evaluate the change in quality of life arising from the liner exchange procedure. We believe these data will assist surgeons and patients with regard to anticipating the potential improvement from such a procedure. However, our study has some limitations including that of sample size and the fact that we have included multiple indications for tibial insert exchange in the analyses. Although this may contribute to the generalizability of our results, our sample size is not sufficient to permit detailed analyses of outcomes for each indication for the tibial insert exchange procedure. However, we performed exploratory subgroup analyses and intergroup comparisons to evaluate the potential for differences among patient groupings. Interestingly, no group displayed superiority over another after Bonferonni adjustments for multiple comparisons (P N .05).
6 The Journal of Arthroplasty Vol. 28 No. 1 January 2013 Although our sample size may be inadequate to permit detailed subgroup analyses and intergroup comparisons, several trends were observed. We have shown success in isolated tibial insert exchange in a significant proportion of our patients as demonstrated by the high satisfaction rates, improved outcomes reported by the patients, and low failure rate. Although this was observed across our patient population, regardless of the indication for the procedure, further research is necessary to evaluate any differences that may arise as a result of the preoperative diagnosis (ie, tibial insert wear vs instability vs stiffness). This may explain why a large minority (26%) of patients had persisting pain/dysfunction after this procedure despite the absence of a readily apparent explanation at this time. The primary determinants of success in our cohort appear to be related to patient selection and careful evaluation of the implant to document fixation, alignment, and rotation of the existing knee system. If these criteria are met, isolated tibial insert exchange may provide improved knee function, a significant improvement in quality of life, and a high level of patientreported satisfaction.
Acknowledgments The authors thank Ms Daphne Savoy for her help with data acquisition and Dr Eric Sayre for his statistical analysis.
References 1. Bozic KJ, Kurtz SM, Lau E, et al. The epidemiology of revision total knee arthroplasty in the United States. Clin Orthop Relat Res 2010;468:45. 2. Jensen CL, Petersen MM, Jensen KE, et al. Outcome of isolated tibial polyethylene insert exchange after uncemented total knee arthroplasty. Acta Othop Scand 2006; 77:917. 3. Griffin WL, Scott RD, Dalury DF, et al. Modular insert exchange in knee arthroplasty for treatment of wear and osteolysis. Clin Orthop Rel Res 2007;464:132.
4. Babis GC, Trousdale RT, Morrey BF. The effectiveness of isolated tibial liner exchange in revision total knee arthroplasty. J Bone Joint Surg Am 2002;84-A:64. 5. Engh GA, Koralewicz LM, Pereles TR. Clinical results of modular polyethylene insert exchange with retention of total knee arthroplasty components. J Bone Joint Surg Am 2000;82-A:516. 6. Bellamy N, Buchanan W, Goldsmith CH, et al. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or the knee. J Rheumatol 1988; 15:1833. 7. Murray DW, Fitzpatrick R, Rogers K, et al. The use of the Oxford hip and knee scores. J Bone Joint Surg Br 2007 Aug;89:1010. 8. Ware Jr JE, Sherbourne CD. The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Med Care 1992;30:473. 9. Amstutz HC, Thomas BJ, Jinnah R, et al. Treatment of primary osteoarthritis of the hip. A comparison of total joint and surface replacement arthroplasty. J Bone Joint Surg Am 1984;66-2:228. 10. Mahomed N, Gandhi R, Daltroy L, et al. The selfadministered patient satisfaction scale for primary hip and knee arthroplasty. Arthritis 2011;2011:591253. 11. Ewald FC. The knee society total knee arthroplasty roentgenographic evaluation and scoring system. Clin Orthop Rel Res 1989;248:9. 12. Garbuz DG, Awwad MA, Duncan CP. Periacetabular osteotomy and total hip arthroplasty in patients older than 40 years. J Arthroplasty 2008;23:960. 13. Bert JM, Reuben J, Kelly F, et al. The incidence of modular tibial polyethylene insert exchange in total knee arthroplasty when polyethylene failure occurs. J Arthroplasty 1998;13:609. 14. Babis GC, Trousdale RT, Pagnano MW, et al. Poor outcomes of isolated tibial insert exchange and arthrolysis for the management of stiffness following total knee arthroplasty. J Bone Joint Surg Am 2001;83-A:1534. 15. Griffin WL, Fehring TK, Pomeroy DL, et al. Sterilisation and wear-related failure in first- and second-generation press-fit condylar total knee arthroplasty. Clin Orthop Relat Res 2007;464:16. 16. Willson SE, Munro ML, Sandwell JC, et al. Isolated tibial polyethylene insert exchange outcomes after total knee arthroplasty. Clin Orthop Relat Res 2010;468:96.
Outcome After Isolated Polyethylene Tibial Insert Exchange in Revision Total Knee Arthroplasty Richard P. Baker, MSc, MBChB, FRCS, Bassam A. Masri, MD, FRCSC, Nelson V. Greidanus, MD, FRCSC, and Donald S. Garbuz, MD, FRCSC
Abstract: We identified 45 knees in 42 patients who had an isolated tibial insert exchange for a failed primary knee arthroplasty with a minimum of 2 years of follow-up. The mean age at revision was 68 years, and the mean time to revision was 80 months. Thirty patients completed follow-up questionnaires (Oxford Knee Score, University Of California Activity Index score, Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC], and Short Form 12) with a mean follow-up of 58 months. Patients' current scores were compared with preoperative scores in 14 knees. Four patients (9%) were subsequently revised. Significant improvement was seen in the Oxford Knee Score, Short Form 12 physical component, and all WOMAC domains, but only 58% of patients had a clinically successful result by global WOMAC score. When patients are selected appropriately, an isolated liner exchange can significantly improve the function of the knee. Keywords: tibial insert exchange, total knee arthroplasty, revision, osteolysis. © 2013 Elsevier Inc. All rights reserved.
this study was to assess the effectiveness of isolated tibial insert exchange in the salvage of malfunctioning total knee replacements in which all components were well fixed with no evidence of loosening at the host-prosthesis interface.
Infection followed by mechanical loosening is the most common cause of failure of total knee arthroplasty (TKA) [1]. Polyethylene wear is a causative factor in osteolysis and loosening of prosthetic components. The modularity of modern TKA prostheses allows for tibial insert exchange in cases of isolated polyethylene wear when the components are well fixed. Tibial insert exchange when indicated is a simple operation with relatively little morbidity. Conversely, the removal of femoral and/or tibial components at revision can often lead to the removal of host bone and increases the magnitude of the procedure. Conflicting reports exist as to the efficacy of tibial insert exchange, recommended by some [2,3] and used with caution by others [4,5]. However, we have continued to offer patients tibial insert exchange as we feel it can be a successful procedure, when indicated, and in highly selected patients. The aim of
Materials and Methods All patients who had undergone an isolated tibial polyethylene insert exchange were identified from our institutional database. Patients were only included if they were 2 years or more after the procedure and had had no revisions before liner exchange. A prerequisite for a tibial insert exchange was the absence of infection on preoperative workup, well-aligned implants in a knee that is well balanced or could be rendered well balanced as a result of surgery. Components that appeared well fixed on preoperative radiographs were confirmed with rigorous intraoperative examination. The tibial and femoral components are also examined intraoperatively to ensure that they were well rotated. Ethical approval was obtained from our institutional review board, and accordingly, all initial patient contact had to be by mail. Patients were interviewed by telephone if they failed to respond to the postal questionnaire on 2 occasions. The self-reported outcomes used were the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) [6], Oxford Knee Score (OKS) [7], Short Form 12 item score (SF-12) [8], and
From the Department of Orthopaedics, University of British Columbia and Vancouver Acute Health Services, Vancouver, British Columbia, Canada. Submitted September 9, 2011; accepted May 30, 2012. The Conflict of Interest statement associated with this article can be found at http://dx.doi.org/10.1016/j.arth.2012.05.030. Reprint requests: Dr Donald Garbuz, MD, FRCSC, Complex Joint Clinic—3rd Floor, Gordon and Leslie Diamond Health Centre, 2775 Laurel St, Vancouver, V5Z 1M9, British Columbia, Canada. © 2013 Elsevier Inc. All rights reserved. 0883-5403/2801-0001$36.00/0 http://dx.doi.org/10.1016/j.arth.2012.05.030
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2 The Journal of Arthroplasty Vol. 28 No. 1 January 2013 the University Of California Activity Index (UCLA) [9]. Satisfaction with the procedure was measured using the Mahomed questionnaire [10]. The Mahomed questionnaire is a scale designed to assess satisfaction with joint arthroplasty. Patients answer 4 questions: patients' overall satisfaction with surgery, the extent of pain relief, the ability to perform home or yard work, and the ability to perform recreational activities. Items are scored on a 4-point Likert scale with response categories consisting of very satisfied (100 points), somewhat satisfied (75 points), somewhat dissatisfied (50 points), and very dissatisfied (25 points). The scale score is the unweighted mean of the scores from the individual items, ranging from 25 to 100 per item (with 100 being most satisfied) [10]. Preoperative radiographs were evaluated using the Knee Society Radiographic Grading system [11]. This allowed for uniform grading of any osteolysis and loosening at the bone component interfaces. Evidence of polyethylene wear was analyzed via measurement of loss of joint space height and asymmetric wear of the polyethylene liner. In addition, the alignment of the prostheses was assessed by measuring the anatomical axis of the TKA. Where patients had undergone a later procedure after liner exchange, they were considered a failure, and the incidence of further surgery was calculated. Statistical Analysis Statistical analysis was performed using SAS version 9.2 (SAS Institute, Inc, Cary, NC). The OKS and WOMAC scores were normalized out of 100, with larger values signifying better outcomes. Univariate t test analysis was used to compare preoperative and postoperative scores for OKS, SF-12, WOMAC, and UCLA. Multivariate analysis of variance was used to identify if indication for tibial insert exchange affected the outcome scores. As multiple comparisons were made between groups, probability values were subjected to the Bonferroni correction. Kaplan-Meier analysis was used to document survival after liner exchange with logrank analysis to identify if osteolysis affected survival.
Results Forty-five isolated tibial insert exchanges were identified from the institutional database. There were 42 patients, 3 patients underwent bilateral surgery, and 23 were female. Thirty-seven patients were alive and available for review. Five patients were deceased, and all had been between 3 and 7 years post-revision at the time of their death. None had experienced failure of their tibial insert revision or required any further knee intervention. Of the total cohort of 42 patients (45 knees), 4 knees were subsequently revised (9%) and were excluded from questionnaire analysis. Twentynine patients completed questionnaires of the remaining 33 (88%). One patient refused to complete the
questionnaire, and 3 patients were unable to complete the questionnaires as English was not their native language. None of these patients had undergone further surgery. An additional 4 patients were identified who had an isolated tibial insert exchange but were excluded, as they had a prior full revision TKA, which was considered an exclusion criterion for the study. The mean time to revision after the primary TKA was 80 months (range, 12-152 months). Their mean age at revision was 68 years (range, 43-90 years). The mean follow-up time from tibial insert exchange was 58 months (range, 24-123 months). The mean body mass index was 33 (20-45). Thirty-six patients had a primary PFC (Depuy, Warsaw, IN); 3, an Advance Duramer (Wright Medical, Arlington, TN); 2, a PCA (Stryker [Howmedica], Mawah, NJ); 2, a Kinematic (Stryker [Howmedica], Mawah, NJ); 1, an Osteonics (Stryker [Howmedica], Mawah, NJ); 1, a Scorpio (Stryker [Howmedica], Kalamazoo, MI); and 1, a MG2 (Zimmer, Warsaw, IN) primary total knee replacement. Twenty-four knees were cruciate-retaining designs, and 21, posterior stabilized. Indication for Liner Exchange The main clinical indication for tibial insert exchange was polyethylene wear in 34 (76%) of 45 knees, stiffness in 5 (11%) of 45 knees, instability in 3 (7%) of 45 knees, and pain in 3 (7%) of 45 knees. In this latter group, the tibial insert exchange was a part of a synovectomy and intraoperative examination of the components. Preoperatively, the patient's main presenting complaints were pain and swelling in the case of polyethylene wear. Intraoperative Findings Seven patients had no evidence of polyethylene wear. Five of these patients were revised for stiffness, and 2, for pain. Severe polyethylene wear was noted in all knees that underwent surgery for a preoperative diagnosis of polyethylene wear or for instability. Twenty-four patients had a like-for-like liner exchange. Twelve patients had their liners increased in size, the median increase being 2 mm (range, 2-7.5 mm); 11 were in cases revised for polyethylene wear; and 1 patient, for instability. Six patients had their liners downsized, the median decrease being 2.5 mm (range, 2-5 mm), the indications were stiffness in 3 patients; pain, in 2; and polyethylene wear, in 1 case. In 3 patients, the primary liner thickness was not available from the original operative records and unobtainable at the time of surgery due to wear of the liner itself. Of the 38 patients who had intraoperative evidence of polyethylene wear, there was delamination and/or fracture of the polyethylene in 10 cases (26%): 4 were posteriorly stabilized, and 6, cruciate-retaining designs. In the others, there was evidence of both backside and bearing surface wear. A large proportion (36/45) of our patients had a PFC modular (Depuy) liner sterilized
Isolated Polyethylene Tibial Insert Exchange in Revision TKA Baker et al
initially in air. This liner has been shown to have a high prevalence of accelerated wear and early failure. Nineteen patients had a synovectomy performed alongside their isolated tibial insert exchange. All patients who had a preoperative diagnosis of stiffness required a synovectomy. Three patients had a loose patellar button removed during the tibial insert exchange procedure—no patient had their patella resurfaced. Thirteen patients had intraoperative evidence of periarticular osteolysis, of whom 2 required bone grafting; the remaining defects were too small to consider grafting. Both were bone grafted with freezedried croutons into the defects, and all components were stable. Two patients had evidence of scratching to the femoral condylar surface. This was minimal, and careful assessment revealed that the risk of damage to the host bone for component removal outweighed the disadvantage of leaving the imperfect implant in situ. Clinical Outcome Preoperative scores were available in 14 patients, as this is a retrospective study and not all patients had completed routine preoperative questionnaires. After tibial insert exchange, 30 patients completed questionnaires at a minimum of 2 years postoperatively. There was a significant improvement in patient-reported OKS, SF-12 physical, and WOMAC (across all WOMAC domains) (Table 1). The mean satisfaction score across all patients was 79.5 (range, 0-100), indicating the majority of patients were highly satisfied with the tibial insert exchange procedure (Table 2). Fig. 1 highlights the improvements in quality-of-life measures. Patients with stiffness as the indication for tibial insert exchange showed a greater improvement in postoperative scores when compared with baseline—although this effect did not reach significance once Bonferroni correction was applied. Clinical Failures Analysis of the postoperative scores (Table 2) revealed that most patients were satisfied with the liner exchange procedure. Previously, a WOMAC score of less than 65 has been used to indicate failure and greater
3
Table 2. Distribution of Postoperative Scores Variable OKS UCLA (6) SF-12 mental SF-12 physical WOMAC function WOMAC stiffness WOMAC pain WOMAC global Satisfaction All Pain Function Recreation Results
Lowest Quartile
Median
Top Quartile
12-15 1-4 27-53 18-27 4-57 0-63 20-65 15-60
22 5 58 39 81 78 87 82
26-57 7-10 62-69 51-58 94-100 88-100 100-100 94-100
0-67 0-67 0-67 0-67 0-67
93 86 86 80 86
100-100 100-100 100-100 100-100 100-100
than 75 success [12]. In this series, 8 patients (26%) had a global WOMAC score less than 65, and 18 (58%) had a score greater than 75; the remainder (16%) had an intermediate WOMAC score (66-74). These 8 patients also had the lowest OKS scores (range, 24-57), indicating clinical failure of the procedure to relieve the patient's symptoms. Radiographic Findings Three patients had no radiographs available for analysis. The mean anatomical axis was 7º (range, 2º13º). Radiographic evidence of osteolysis was present in 16 patients, of whom 12 were confirmed intraoperatively. Most radiographic lucencies occurred in tibial zones 1 and 2 [11]. There was 1 case with femoral lysis present radiographically. Liner Exchange Survival Two survival curves were produced, those for patients with evidence of osteolysis and those with none (Fig. 2). Analysis of the curves showed that those with osteolysis had a greater chance of failure (log rank, P = .0259). Failures Four patients required revision after isolated tibial insert exchange. They failed between 1 and 12 years postoperatively. All failed due to osteolysis and
Table 1. Clinical Outcomes Variable OKS UCLA (6) SF-12 mental SF-12 physical WOMAC function WOMAC stiffness WOMAC pain WOMAC global
Preoperative Score
Postoperative Score
No. Patients Compared
Mean Difference
95% CI
P
45 (13-75) 4 (2-5) 49 (24-68) 29 (20-47) 50 (9-84) 43 (0-100) 49 (25-85) 50 (13-84)
75 (6-100) 6 (1-10) 56 (27-69) 39 (18-58) 74 (4-100) 73 (0-100) 81 (20-100) 75 (15-100)
14 6 13 13 14 13 14 14
31.2 0.7 5.2 8.7 26.1 34.6 33.4 28
19.6-42.7 −1.1 to 2.4 −1.7 to 12.2 3.5-13.9 13.4-38.8 19.6-49.6 21.8-44.9 16-40
b.001 .484 .164 .007 .001 .001 b.001 .001
Abbreviation: CI, confidence interval.
4 The Journal of Arthroplasty Vol. 28 No. 1 January 2013 significant wear and had fractured. At the time of the femoral revision 7 years later, it was apparent that progressive osteolysis contributed to aseptic loosening of the femoral component. A fourth patient was revised 16 months after tibial insert exchange for progressive and severe tibial osteolysis under the medial tibia with associated collapse into the lytic defect. At tibial insert exchange, delamination of the polyethylene was present, but minimal osteolysis was present radiographically preoperatively.
Discussion
Fig. 1. Preoperative and postoperative quality-of-life scores.
Isolated tibial insert exchange is an infrequent operation, and few large studies exist analysing its outcome. This is in part due to the fact that infection and component loosening are the 2 main reasons for revision knee arthroplasty and these failures are usually associated with major component revision procedures [1]. It has been shown that when isolated tibial insert exchange for polyethylene wear was contemplated preoperatively, 89% actually required revision of one or more of the tibial or femoral components due to macroscopic damage to their surfaces [13]. Babis et al [4] reported a high rate of failures in their series of isolated tibial insert revisions. When tibial insert exchange alone was used for instability, 44% failed, and 33% failed for polyethylene wear. The total failure rate was reported to be 25% within 3 years. The same group of authors also reported on a cohort of patients that underwent isolated tibial insert exchange for stiff TKAs with poor outcomes and advise against the procedure due to the poor outcomes [14]. Engh et al [5] reviewed their series of tibial insert exchange and reported that, if severe wear and delamination are present within 10 years of primary surgery, isolated exchange should not be attempted as the accelerated wear likely indicated an
loosening of the implants; 2 femoral and 2 tibial components were loose. The details of these 4 patients are as follows: One patient who failed the earliest (at 1 year) was bone grafted at his isolated tibial insert exchange on both the medial tibial and femoral sides. Preoperatively, the lysis was only present radiographically in tibial zone 1 [11]. His osteolysis progressed, and his femoral component became loose requiring a subsequent stemmed revision. The polyethylene liner in this case had significant backside wear only. A second patient, with rheumatoid arthritis, had her liner exchange because the knee was stiff post primary TKA. A synovectomy and liner downsizing were performed, both tibial and femoral components were not loose, and there was no polyethylene wear present. At 12 years, the femoral component had become loose, and a stemmed revision was performed. A third patient had her femoral component revised 7 years post tibial insert exchange. At liner exchange, the femoral component had been well fixed despite preoperative radiographs displaying lysis in femoral zones 1 and 2. The polyethylene liner had
Kaplan Meier survival curves for Months to Revision by Osteolysis
Survival Distribution Function
1.0
0.8
0.6
0.4
0.2
0.0 0
25
50
75
100
Months PLOT
No Osteolysis Intra–operative Osteolysis
Censored Censored
Fig. 2. Kaplan-Meier liner exchange survival.
125
150
Isolated Polyethylene Tibial Insert Exchange in Revision TKA Baker et al
overall problem with the joint itself, which would not be addressed by modular component exchange. A small proportion (10/38; 26%) of our patients had actual delamination of the polyethylene. However, in our series, we are unable to make the same conclusions as Engh et al [5], as we believe that a contributing cause for tibial insert wear and need for tibial insert exchange was the fact that the primary knee tibial insert was subjected to sterilization in air [15]. All subsequent tibial inserts, which we used for our revision procedures, were sterilized in an inert environment, as the manufacturer had changed the sterilization procedure for the PFC Modular liners after 1999. For this reason, we felt that an isolated tibial insert exchange was not necessarily contraindicated, as the polyethylene had improved. Our results support this premise. Our series is not the first to report good results from tibial insert exchange procedures, as Jensen et al [2] reported good results with tibial insert exchange in 27 patients. It is important to note that, in the Jensen series, 22 of the patients also received a patellar resurfacing and, therefore, it becomes difficult to attribute success solely to tibial insert exchange. No patients in our series had a patella resurfaced, but 3 patients had a loose patella button removed at the same time as tibial insert exchange. Interpreting preoperative knee radiographs for osteolysis is difficult, as often, the implant may obscure the defect. However, in 75% (12/16) of cases, a preoperative suspicion of osteolysis was confirmed intraoperatively, and 4 were simple cementing defects. Of our 4 failures, 3 had evidence of radiographic osteolysis preoperatively, which was confirmed in 2 intraoperatively; therefore, 2 (17%) of 12 patients with intraoperative lysis went onto subsequent revision. As such, the failure rate for tibial insert exchange when radiographically visible osteolysis is present is 3 (25%) of 12. Although this is a substantial failure rate, it should be kept in mind that, for the duration of our study, 75% of such patients did well, and an isolated tibial insert exchange was a good operation, but patients need to be counselled that they have a 1:4 chance of needing a subsequent revision if osteolysis is present. In our series, there was only 1 case of femoral osteolysis, and this went on to fail. With only 1 case, it is impossible to tell whether the presence of femoral osteolysis is a harbinger of impending failure. Despite 27% (12/45) of cases having osteolysis, only 9% (4/45) of tibial insert exchanges failed. This is likely due to the fact that all cases had good alignment and the components were well fixed and well rotated. In a multicenter study, Griffin et al [3] reported a revision rate of 16.2% (11 of 68) of knees undergoing an isolated tibial insert exchange at an average of 44 months of follow-up, despite the presence of osteolytic lesions. In that study, 97% of patients did not show progression of osteolytic
5
defects, and the authors did not feel that an isolated tibial insert exchange was contraindicated in the presence of osteolysis. Although our results were not as good, we are in agreement with this recommendation. In our series, most patients also had a concomitant synovectomy as part of the procedure. We do not believe that this is a confounding factor in our series as this is a standard part of all of our revision operations. Routine synovectomy facilitates exposure and provides safe access to the tibial insert mechanism, as well as it permits the removal of polyethylene-induced synovitis or hypertrophic tissue in the stiff knee. Although it is possible that the synovectomy may provide some symptomatic relief to the patient, it is unlikely that it could provide the magnitude of improvement reported by our patients over a minimum of 2 years of follow-up from the procedure. Clinical failure as indicated by low WOMAC and OKS scores was seen in 8 of our patients who completed postoperative questionnaires. This is similar to Willson et al [16] who reported a similar finding of 30% of patients having persistent pain in a liner exchange series similar in size to our own. In the series of Willson et al, isolated liner exchange was more likely to fail if performed within 3 years of primary TKA, and 29% of their patients have required a subsequent revision. In our series, our time from primary TKA to liner exchange was longer, and we revised a greater proportion of our patients for polyethylene wear, whereas Willson et al [16] had a greater proportion revised for instability. It is interesting that we both report similar rates of pain after isolated liner exchange and probably represent the effect of multiple operations on the knee regardless of indication for revision. Our study is among the first to report a significant patient-reported benefit to isolated revision tibial insert exchange across a comprehensive array of generic, disease-specific, and joint-specific quality-of-life outcomes. In addition, our study includes many patients with preoperative baseline quality-of-life scores; we are able to evaluate the change in quality of life arising from the liner exchange procedure. We believe these data will assist surgeons and patients with regard to anticipating the potential improvement from such a procedure. However, our study has some limitations including that of sample size and the fact that we have included multiple indications for tibial insert exchange in the analyses. Although this may contribute to the generalizability of our results, our sample size is not sufficient to permit detailed analyses of outcomes for each indication for the tibial insert exchange procedure. However, we performed exploratory subgroup analyses and intergroup comparisons to evaluate the potential for differences among patient groupings. Interestingly, no group displayed superiority over another after Bonferonni adjustments for multiple comparisons (P N .05).
6 The Journal of Arthroplasty Vol. 28 No. 1 January 2013 Although our sample size may be inadequate to permit detailed subgroup analyses and intergroup comparisons, several trends were observed. We have shown success in isolated tibial insert exchange in a significant proportion of our patients as demonstrated by the high satisfaction rates, improved outcomes reported by the patients, and low failure rate. Although this was observed across our patient population, regardless of the indication for the procedure, further research is necessary to evaluate any differences that may arise as a result of the preoperative diagnosis (ie, tibial insert wear vs instability vs stiffness). This may explain why a large minority (26%) of patients had persisting pain/dysfunction after this procedure despite the absence of a readily apparent explanation at this time. The primary determinants of success in our cohort appear to be related to patient selection and careful evaluation of the implant to document fixation, alignment, and rotation of the existing knee system. If these criteria are met, isolated tibial insert exchange may provide improved knee function, a significant improvement in quality of life, and a high level of patientreported satisfaction.
Acknowledgments The authors thank Ms Daphne Savoy for her help with data acquisition and Dr Eric Sayre for his statistical analysis.
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