Comparison of HRQL Between Unicompartmental Knee Arthroplasty and Total Knee Arthroplasty for the Treatment of Osteoarthritis

Comparison of HRQL Between Unicompartmental Knee Arthroplasty and Total Knee Arthroplasty for the Treatment of Osteoarthritis

The Journal of Arthroplasty 28 Suppl. 2 (2013) 187–190 Contents lists available at ScienceDirect The Journal of Arthroplasty journal homepage: www.a...

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The Journal of Arthroplasty 28 Suppl. 2 (2013) 187–190

Contents lists available at ScienceDirect

The Journal of Arthroplasty journal homepage:

Comparison of HRQL Between Unicompartmental Knee Arthroplasty and Total Knee Arthroplasty for the Treatment of Osteoarthritis Katie Sweeney, MSc a, Maja Grubisic, MSc a, Carlo A. Marra, PhD a, Richard Kendall, MD b, Linda C. Li, PhD c, Larry D. Lynd, PhD a a b c

Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, BC, Canada Department of Orthopaedic Surgery, University of British Columbia, Richmond, BC, Canada Department of Physical Therapy, University of British Columbia, Vancouver BC, Canada

a r t i c l e

i n f o

Article history: Received 26 November 2012 Accepted 10 May 2013 Keywords: oxford knee arthroplasty HRQL outcomes unicompartmental: total knee

a b s t r a c t This retrospective study evaluates the health related quality of life (HRQL) of patients following unicompartmental knee arthroplasty (UKA) compared to total knee arthroplasty (TKA) for osteoarthritis treatment. The Western Ontario and McMaster Osteoarthritis index (WOMAC) and the Oxford Knee score (OKS) were recorded at baseline, 3 and 6 months. Analysis of 317 UKAs and 425 TKAs showed no significant differences in HRQL between the two groups at baseline, but the TKA group was significantly older and more likely to be male. Both groups showed an overall improvement in the total WOMAC and OKS over time, with males showing significant improvement over females. Adjusting for age and gender, there was no significant difference between UKA and TKA in HRQL over the first 6 months following surgery. © 2013 Published by Elsevier Inc.

Within the last thirty years, advances in technique and design have brought unicompartmental knee replacement (UKA) into the mix as a viable and successful treatment for arthritis affecting only one compartment of the knee [1–3]. However, some surgeons remain skeptical towards the use of UKA due to the lack of randomized controlled trials comparing UKA to total knee arthroplasty (TKA) [4]. To date, there has only been one published well-controlled, randomized control trial directly comparing UKA with TKA [5,6]. Others have compared patients with different preoperative baseline characteristics and varying degrees of disease progression within the two groups making it difficult to directly evaluate differences in outcomes between patients undergoing UKA and TKA given that the patients were inherently different at the time of surgery [7,8]. Outcomes have often been measured by failure of implant with need for revision, cost-effectiveness, time to recovery, patient perception, or using other one-dimensional measures of knee function [9–18]. Binary and one dimensional outcomes such as these tend to exclude relevant data, making self-assessed HRQL, which is being used more frequently for the evaluation of the effectiveness of treatment, potentially more reflective of the patients perceived overall impact of the procedure on overall patient outcomes [19]. Therefore, the

The Conflict of Interest statement associated with this article can be found at http:// Reprint requests: Larry Lynd, PhD, Associate Professor, Faculty of Pharmaceutical Sciences, University of British Columbia, 2405 Wesbrook Mall, Vancouver, BC, Canada V6T 1Z3. 0883-5403/2809-0006$36.00/0 – see front matter © 2013 Published by Elsevier Inc.

objective of this study was to compare the effectiveness of the Biomet Oxford unicompartmental implant (Warsaw, Indiana) to the Wright Advance Medical total implant (Memphis, Tennessee) over the first 6 months post-implantation. For this study, effectiveness was evaluated using two condition-specific questionnaires: the Western Ontario and McMaster Osteoarthritis index (WOMAC) and the Oxford Knee Score (OKS). Patients and Methods A retrospective analysis was conducted to evaluate outcomes following knee arthroplasty on data collected between September 2004 and February 2007 on all patients requiring either UKA or TKA, as determined at the time of consultation by the orthopedic surgeon consulted. All 1110 procedures were performed at Richmond General Hospital in Richmond, British Columbia, Canada by one of five surgeons. Once a decision to perform surgery was made and consent was obtained, the patient completed the WOMAC, OKS and SF-12 preoperatively and then subsequently at 3 and 6 months postsurgery. Of the 1110 procedures, 200 were extracted from a secondary data set, consisting of 317 patients who underwent UKA at the same institution, all of which were performed by one surgeon from July 2000 to February 2007. The patients in both datasets were comparable in terms of baseline characteristics and outcomes, so they were merged and analyzed as one sample. These patients also completed all three outcome questionnaires preoperatively, and at 3 and 6 months postoperatively.


K. Sweeney et al. / The Journal of Arthroplasty 28 Suppl. 2 (2013) 187–190

The WOMAC is a 24-item osteoarthritis (OA) specific instrument that was originally designed for use in clinical trials in patients with OA of the knee or hip [20]. It is comprised of fourteen questions designed to measure quality of life on three arthritis-specific domains: five specific to pain, two to stiffness, and seventeen questions specific to physical function. The Likert 3.1 version was used in this study with the score for each individual domain being calculated by summing the responses corresponding to the domain specific questions, with an overall score of being the sum of the three domain-specific scores. The score for each item ranged from 0 (full health) to 4 (extreme disability) [21]. The OKS is a 12-item questionnaire in which a single score ranging from 12 (full health) to 60 (extreme disability) is derived from a patient’s self-reported responses to questions relating to pain, knee function and day to day tasks and activities. It has been validated and recommended for use in the evaluation of health related quality of life following knee arthroplasty [22,23]. Patients with OA affecting only one compartment of the knee were eligible for UKA in which the Oxford phase III prosthesis was used. It offers a fully congruent mobile bearing that is completely unconstrained and therefore in theory allows for an evenly distributed allocation of weight throughout the joint [24]. Patients were considered candidates for UKA if the following criteria were met: OA of the knee; no inflammatory disease; intact and functional cruciate and collateral ligaments; and, a flexion deformity of less than 15°. The Wright Advance Medical implant utilizing a medial pivot bearing was used for all TKAs [25,26]. Procedures were performed either under regional or general anaesthetic and tourniquets were typically used. The Oxford implant was implanted through an MIS type of approach while TKA was typically done either through a traditional medial parapatellar approach, intravastus or subvastus approach. For both UKA and TKA, femoral and tibial components were cemented with Simplex-P with tobramycin (Stryker Kalamzoo Mi) cement. Patellar resurfacing with TKA was at the surgeon’s discretion, and was performed in > 95% of patients. All patients were mobilized with physiotherapy on the operative day (day 0) with discharge typically between one to three days postoperatively. Upon discharge outpatient physiotherapy was instituted for all patients. Postoperative care and rehabilitation were identical in both groups and followups were performed by the surgeon who performed the knee replacement. Consent was obtained from all patients upon referral for knee replacement. Statistical Analysis Demographic variables and quality of life between the two groups were compared using independent samples t-test for continuous variables and Pearson’s Chi-Square test for categorical variables. Since the measurements that were made at several time points (baseline, 3 months and 6 months) for each patient were not independent, standard linear modeling cannot be used, as it assumes the errors of each observation are independent with a constant variance. Conversely, hierarchical linear models (HLM) estimate the errors for each patient separately; therefore, to investigate the mean longitudinal change, the data were analyzed using a three level hierarchical linear model. In this three level model, the base layer represents time (i.e. baseline, 3 and 6 months follow-up), which is nested within patients who represent level two. Patients are then clustered with surgeon, which represents the third level of the hierarchical model. We used this method to model the total WOMAC scores and OKS as a function of group (either TKA or UKA) and time. Given that all surgeons had the capability of performing both types of procedures at the same institution under identical protocols, using the same indications and instrumentation, we evaluated the heterogeneity in outcomes between physicians and did not find any association between surgeon and patient outcomes. As such, the model intercept was treated as a

fixed effect. To evaluate how differences between treatments change over time, an interaction of time with group was also incorporated into the model. All potential confounding variables for which data were available were initially evaluated in univariate analysis, and then incorporated into a multivariate model using a forward stepwise process based on the p-value (model entry criteria P b 0.20). For patients who had undergone replacement of both knees, only the first procedure was evaluated to ensure that the results reflected the outcome of the index surgery. No patients received simultaneous bilateral replacements. All analyses were performed using SAS 9.1 statistical software (SAS Institute; Cary, NC). Statistical significance was defined as p b 0.05. Results Seven hundred and forty-two patients (67%) of the 1110 UKA or TKA’s performed were included in the analysis of which 317 (43%) were UKAs and 425 (57%) TKA’s. Of the 368 excluded cases, two (0.5%) were revisions, two (0.5%) were missing all baseline HRQL scores, and 26 (7%) had bilateral surgeries in which case only the first procedure was evaluated. The remaining 338 (92%) were missing demographic or surgical data such as surgeon, age, sex or type of procedure. Overall, patients undergoing TKA were significantly older (p = 0.02) and there was a greater proportion of women than men in both groups (P = 0.01 and P b 0.001, respectively). There were no significant differences in preoperative HRQL between the two groups (Table 1); therefore, the groups were deemed comparable at baseline and no potential confounding baseline covariates were included in the final multivariate model. Age and sex were the only two potential confounders included in the multivariate model, with prosthesis type as the primary explanatory variable of interest. Overall, six months post-surgery there was a statistically significant mean change in both the WOMAC (− 33.2; SD 21.5) and OKS (− 18.0; SD 11.1), as would be expected. Table 2 displays the model parameter estimates and 95% confidence intervals for the final adjusted model. While age was not significant in the model, males improved significantly more compared to females on the total WOMAC (i.e. − 3.6; 95% CI − 5.6, −1.2) and the OKS (− 2.0 (95% CI − 3.0, − 1.0) six months following surgery. After adjusting for age and sex, prosthesis type (TKA/UKA) was not a statistically significant predictor of 6-month post-surgery score for either the total WOMAC (P = 0.5) or OKS (P = 0.8) scores. Therefore, based on this cohort, UKA and TKA resulted in similar improvements in HRQL six months following surgery, in similar patients. Furthermore, there was also no significant difference in treatment effect overtime between the two groups as seen through the time and treatment interaction term for both the total WOMAC and OKS (p = 0.2 and p = 0.1, respectively). While the effect of time was significant in the model suggesting a difference in improvement across time, the time x prosthesis interaction was not statistically significant which suggests that there was no difference in improvement over time Table 1 Baseline Characteristics of Unicompartmental and Total Knee Arthroplasty Patients

Variables Female (%) Age Total WOMAC Pain Stiffness Function Oxford Knee Score PCS MCS

Uni Knee N = 317

Total Knee N = 425

179 (56)* Mean (SD) 69.0 (9.5) 54.2 (15.3) 11.5 (3.3) 4.8 (1.6) 37.7 (11.8) 41.3 (7.3) 32.7 (7.3) 48.8 (11.8)

279 (65)** Mean (SD) 70.4 (9.0) 56.2 (16.6) 11.8 (3.5) 5.0 (1.7) 39.5 (12.3) 42.3 (7.9) 31.7 (7.3) 47.5 (11.3)

P Value 0.206 P P P P P P P P

= = = = = = = =

0.03 0.2 0.2 0.2 0.4 0.07 0.4 0.6

K. Sweeney et al. / The Journal of Arthroplasty 28 Suppl. 2 (2013) 187–190 Table 2 Estimated Parameters and 95% CIs of the Mixed Effects Model Comparing HRQL Between UKA and TKA Variables Intercept Group (UKA) Time Time × (UKA) Sex (Male) Age



60.8⁎ (53.0, 68.7) −1.8 (−4.2, 0.7) −6.2⁎ (−7.0, -5.4) 0.5 (−0.2, 1.3) −3.6⁎ (−5.6, -1.5) −0.1 (−0.2, 0.03)

43.2⁎ (39.4, 47.0) −1.1 (−1.9, 0.8) −3.3⁎ (−3.8, -2.8) 0.1 (−0.09, 0.7) −2.0⁎ (−3.0, -1.0) −0.01 (−0.07, 0.04)

between UKA and TKA, at least based on the HRQL measurements at three and six months. The estimated adjusted mean differences in the total WOMAC and OKS between the UKA and TKA groups at each time point are shown in Table 3. Although the differences between the two groups were not significant, at baseline and three months, the mean WOMAC and OKS scores favored the UKA group whereas at 6 months, means scores favored the TKA group. Discussion Many surgeons remain sceptical about the implementation of UKA as a treatment for osteoarthritis affecting one compartment of the knee due to its history of an increased need for revision commonly caused by luxation of the prosthesis, misalignment of the joint translating into progression of the disease into the untreated part of the knee as well as the technically advanced nature of the procedure [27,28]. This is the first study to our knowledge to compare outcomes following UKA and TKA using disease-specific patient self-reported questionnaires with adequate sample size and comparability at baseline between both groups. Using a hierarchical linear model, we were able to account for the correlation within patients over time and the variation within surgeons while adjusting for significant covariates to show that outcomes following UKA do not differ from TKA with respect to pain, function, stiffness and daily knee-specific activities following surgery. Males had greater improvement in HRQL as compared to females and age was not a significant factor in this sample. On average, patients showed significant improvement at 3 and 6 months following both UKA and TKA and there was no significant difference in outcomes between the two groups over time as measured with respect to both WOMAC and OKS. Previous studies have shown equivocal results in outcomes related to UKA and TKA with the exception of one study done by Newman et al [6]. In this study, 102 patients, all of which were suitable for UKA, were randomized to receive either a UKA with the St. Georg Sled (Waldemar Lik, Hamburgh, Germany; n = 50) or a TKA with the Kinematic prosthesis (Howmedica, Rutherford, New Jersey; n = 52). With knee flexion and pain relief measured using the Bristol Knee Score (BKS) as one of the primary outcomes, 68% of patients randomized to receive a UKA had achieved normal flexion (≥120 degrees) after five years versus only 17.8% in the TKA group, and there was no statistically significant difference in mean BKS score ( 91.1 versus 86.7, respectively). Then, after a minimum of 15 years following surgery, 78% of UKA patients had normal flexion versus only 38% in the TKA group [29]. However, the

Table 3 Differences in HRQL Scores Between Unicompartmental and Total Knee Arthroplasty Patients at Each Assessment Time After Adjustment of Covariates


Estimates of Differences at Baseline (95% CI)

Total −1.8 (−4.2, 0.7) WOMAC OKS −1.1 (−2.3, 0.06)

Estimates of Differences at 3 mo (95% CI)

Estimates of Differences at 6 mo (95% CI)

−0.12 (−2.5, 2.2)

1.5 (−2.5, 5.5)

−0.2 (−1.4, 1.0)

0.7 (−1.3, 2.8)


Bristol knee score may not be reflective of the overall improvement in quality of life of the patients given only one dimension of relief and amelioration, bringing to light the importance of proper outcome measures to adequately reflect these changes. Instruments designed to measure multiple health-related quality of life dimensions incorporate an individual’s responses relevant to physical, mental, emotional and daily activities of life and therefore facilitate the consideration of broader implications of both a disease and the associated treatments. It is therefore evident that the assessment of outcomes following knee arthroplasty should include the overall health and quality of life impacts from the patient’s perspective [30]. A recent study by Walton et al. attempted to account for patientperceived change in outcome after either UKA or TKA using the Oxford Knee Score questionnaire (OKS) and the modified Gimby score which assesses levels of patient physical activity as the primary outcomes following surgery along with patient’s levels of sports participation and working status [8]. The UKA group performed better on the OKS and modified Gimby score with mean scores at 1 3+years of 22.2 and 3.9, respectively, compared to 24.5 and 2.8, respectively, in the TKA group. Those undergoing a UKA were also significantly more likely to increase or maintain their level of sporting activity following surgery relative to their preoperative levels compared to TKA patients (P b 0.001). However, the authors do not report preoperative OKS and modified Gimby scores for both groups and therefore it is unclear if the impacts were clinically or statistically significantly different at baseline making it difficult to draw any concrete conclusions from the comparison. For this reason, a comparative analysis as presented in this study that incorporates patient-centered HRQL outcomes between UKA and TKA was needed. Similarly, Anish et al. conducted a five year follow-up study comparing 54 patients who underwent UKA with 54 patients who underwent a TKA.[7] All patients selected for a UKA had anteromedial OA treated with the Oxford Biomet implant [31]. Unicompartmental knee arthroplasty patients were then matched by age, body mass index, preoperative knee score, function score, degree of active range of motion (ROM), and gender to patients undergoing a unilateral TKA that were identified retrospectively by one of the authors. Unicompartmental OA was not a requirement for the entry of TKA patients into the study. The five year survivorship rate based on revision for any reason was 88% for UKA and 100% for TKA, but the mean postoperative ROM was significantly better in the UKA group compared to the TKA group (99° vs 104°; P = 0.001) [7]. Given the uncertainty surrounding the criteria used and the subjectivity inherent in the matching of the two groups by the author, it is unclear how comparable the UKA and TKA groups were at baseline in terms of function and quality of life, as these data are not provided. The present study was a retrospective analysis using data derived from a secondary source and therefore randomization could not be performed. As a result, not all patients were eligible for a UKA, yet we believe the similarity in HRQL at baseline between the UKA and TKA groups suggests that patients in each group were comparable. Another limitation is the lack of long term follow-up in this sample. However, given that the most notable changes in HRQL generally occur within six months post surgery, we are confident that the six month follow-up allows for an adequate amount of time to be representative of the final outcome of the patients [32–34]. Unicompartmental knee arthroplasty appears to be comparable to total knee arthroplasty with respect to HRQL measured by two disease-specific questionnaires in the total WOMAC and OKS. This study therefore lends support for the use of UKA as a therapeutic alternative in patients with the appropriate indications [17,35–37]. Acknowledgments We would like to acknowledge the tireless efforts of Ms. Cindy Roberts of the Vancouver Coastal Health Authority.


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