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INTRODUCTION: In relatively young patients with end-stage knee OA, TKA comes with the risk of future revision surgery. Knee joint distraction (KJD) is a joint preserving surgery technique, which has been shown to provide sustained clinical and structural improvement for at least five years and postpones the need for TKA. The goal of this study was to evaluate long-term clinical and structural results and identify characteristics predicting survival of the native knee joint after KJD. METHODS: Tibiofemoral OA patients (n=20; age <60 years) indicated for TKA were treated with KJD. Distraction surgery was performed by use of two external fixators with built in springs, placed lateral and medial of the knee joint. The knee was distracted five mm for six weeks and weight-bearing was encouraged. WOMAC questionnaires (100 best) and VAS pain scores (0 best) were used for clinical evaluation at baseline and each consecutive year after treatment, up to nine years. Minimum and mean joint space width (JSW) and mean bone density of the most affected compartment (MAC) were measured using KIDA software on standardized radiographs (baseline and one, two, five and seven years after treatment). The mean cartilage thickness of the MAC was measured on MRI scans using the Eckstein protocol (baseline and one, two and five years after treatment). Survival after treatment was analyzed (failure defined by TKA). Prediction of KJD survival was studied by Cox regression analyses. RESULTS: Three patients withdrew consent. Nine years after treatment, survival was 48%. Survival percentages differed significantly for gender (women 14%, men 72%; p=0.035) and for increase in minimum JSW in the first year (<0.5mm increase 0%, >0.5mm increase 73%; p=0.002). Survivors reported clinical improvement compared to baseline: ΔWOMAC +29.9 points (95%CI +16.9 to +42.9; p=0.001), ΔVAS -46.8mm (95%CI -31.6 to -61.9; p<0.001). In addition, a significant increase of the minimum JSW (+0.62mm; 95%CI +0.13 to +1.11; p=0.020) was found after seven years. No significant changes were found for the mean JSW (+0.36mm; 95%CI -0.85 to +1.57; p=0.505). In patients whose treatment failed over time, last reported clinical scores were still improved compared to baseline: ΔWOMAC +20.5 points (95%CI -1.8 to +42.8; p=0.067), ΔVAS - 25.4mm (95%CI -3.2 to -47.7; p=0.030). In contrast, the minimum JSW (+0.22mm; 95%CI -0.15 to 0.58; p=0.205) and mean JSW (+0.21mm; 95%CI -1.08 to 1.51) at the last reported time points were no longer increased. First-year minimum JSW on radiographs and cartilage thickness increase on MRI predict nine-year survival (HR 0.05 and 0.12, respectively; both p<0.026). Male gender was associated with survival (HR 0.24; p=0.050). DISCUSSION: Joint distraction for end-stage knee OA shows long-lasting clinical and structural improvement with a survival of 48% at nine years. Clinical scores in patients failing treatment were still improved compared to baseline and cannot fully explain the subsequent TKA surgery. In addition to a greater survival rate for males (>two out of three), the initial cartilage repair activity is important for long-term clinical success. While these conclusions are currently demonstrated in only a small number of patients, this is thus far the only cohort of KJD patients followed for such a long period of time and promising long-term survival of joint distraction in knee OA is shown, especially in those with a better initial structural response after KJD. SIGNIFICANCE/CLINICAL RELEVANCE: This is the first time long-lasting clinical and structural benefit of knee joint distraction as a treatment for end- stage knee osteoarthritis is shown and characteristics predicting treatment success are identified.
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