A preference-based single-item measure of quality of life following medial opening wedge high tibial osteotomy: Large improvements similar to arthroplasty

Abstract

Background

Improvements in generic and disease specific scores have been reported with medial opening wedge high tibial osteotomy (MOW HTO). However, meaningful comparisons between competing surgical interventions have been hampered by the lack of a preference based single index of health related quality of life (HRQoL). The primary aim of this study was to derive and report a single index measure of HRQoL for patients undergoing MOW HTO, preoperatively and at 12 and 24  postoperatively. Secondary aims were to evaluate changes in various additional measures of quality of life at these time points.

Methods

The impact of MOW HTO was evaluated using generic and disease specific instruments. One hundred thirty eight patients completed the Medical Outcomes Study short form health survey (SF-12) and Knee Osteoarthritis Outcomes Score (KOOS) before, 12 and 24 months after surgery. A preference-based single index measure of HRQoL was calculated and changes were evaluated.

Results

The mean change in the HRQoL suggested large, clinically significant improvements from 0.69 preoperatively to 0.82 (p < 0.001) and 0.8 at 12 and 24 months postoperatively respectively. All dimensions of the SF-12, except role mental health, and all dimensions of the KOOS also demonstrated statistically significant improvements between pre and postoperative measurements.

Conclusions

The preoperative HRQoL of young patients with mechanical varus alignment and medial compartment knee osteoarthritis is similar to older patients with knee osteoarthritis. Medial opening wedge high tibial osteomoty results in significant improvements in HRQoL, the magnitude of which is comparable to other surgical interventions for knee osteoarthristis.

Introduction

There has been a substantial increase in the prevalence and burden of knee osteoarthritis (OA) [1], [2]. One surgical treatment option for knee OA located primarily in the medial compartment of the tibiofemoral joint is high tibial osteotomy (HTO) [3], [4], [5]. There has been a recent increase in the number of publications on HTO, which may be due to the confirmed importance of lower limb malalignment to compartment-specific disease [6], [7], the proposed joint preserving nature of the procedure and the possible disease modifying outcomes of surgery [8].

Alignment of the lower limb has a major influence on the proportion of load shared between the compartments of the tibiofemoral joint, with varus alignment resulting in substantially greater load on the medial side [9]. The reported interaction between body mass and lower limb alignment on dynamic knee joint load emphasizes the important role that varus deformity has on patients with knee OA [10], [11], [12]. Moreover, in the presence of medial compartment knee OA, medial articular cartilage degeneration is proposed to lead to a perpetuating cycle of reduced medial joint space, further shift in lower limb alignment toward varus, and an even greater load on the medial compartment [13], [14].

The goals of HTO are to improve alignment of the weight bearing axis of the lower limb, to lessen the load on the medial tibiofemoral compartment and consequently to decrease these important risk factors for disease progression [15]. When coupled with concerns regarding longevity of unicompartmental and total knee replacement in younger, more demanding patients, surgeons may be increasingly re-looking at HTO as a viable treatment option to improve knee function, and delay or even prevent the eventual need for arthroplasty.

A generic instrument of health related quality of life (HRQoL) measures general health status including physical symptoms, ability to function, and emotional health, and is useful when measuring the impact of a specific illness or injury across different diseases, severities, interventions, and patient populations. The Medical Outcomes Study Short Form health survey-36 (SF-36) [16] and the reduced form, the Medical Outcomes Study Short Form health survey-12 (SF-12) [16], [17] are among the most commonly used generic HRQoL scores. Both scores have well-established psychometric properties across a wide variety of populations and contexts, including patients with OA [18], [19], [20], [21], [22].

Previous authors have reported large clinically significant improvements in radiographic measures and in knee specific and generic patient-reported outcomes following HTO, including the Knee Injury and Osteoarthritis Outcome Score (KOOS) and the SF-36 [15], [23], [24], [25], [26], [27], [28], [29], [30]. Although those instruments continue to be of utmost importance, the addition of a preference-based single index measure of HRQoL would aid in the comparison of competing interventions, particularly those that include an economic analysis [31]. A preference-based single index measure of HRQoL can be used to calculate the quality-adjusted life year (QALY) [32]. QALYs incorporate both length of life and quality of life into a single metric, and are calculated by multiplying the length of time an individual spends in a health state, by the quality weight (utility score) of that health state. Similar to generic HRQoL measures, they can be used to compare dissimilar interventions. However, QALYs can also be used to calculate the cost utility of an intervention (cost per QALY) to enable economic comparisons.

Although the changes in QALYs for patients with knee OA undergoing total knee replacement (TKR) have been reported [33], [34], [35], patients undergoing HTO for OA could be considered a different group as they are typically younger and make higher demands upon their knees. It would therefore be expected that these patients would have different utility scores to older patients undergoing TKR. Not only would the estimation of QALYs for patients undergoing HTO allow the comparison with different surgical options for knee OA, such as unicompartmental knee replacement (UKR) and TKR, but it would also allow subsequent economic comparison of the various treatments.

We are unaware of previous research investigating a preference-based single index measure of HRQoL following HTO. As the incidence of knee OA and the resultant economic burden to the health care system continue to rise, we believe that the publication of such data is important and can ultimately be used to inform the most cost-effective interventions. Given the proposed importance of comparing HTO to other treatments for knee OA, the primary aim of this study was to derive and evaluate a preference-based single index measure of HRQoL (hereafter referred to as the utility score) from the SF-12 scores of patients undergoing medial opening wedge HTO, preoperatively and at 12 and 24 months postoperatively. The secondary aim was to evaluate changes in other frequently used patient-reported measures (SF-12 and KOOS) and radiographic measurement of mechanical axis angle at the same time points. We hypothesized that significant changes in all measures would exist at 12 and 24 months.