Coronal tibiofemoral subluxation is not an independent risk factor for total knee arthroplasty in patients with moderate to severe varus-osteoarthritis: data from the "Osteoarthritis Initiative".

Purpose: Only few prognostic factors for progression of knee osteoarthritis are well established, including varus malalignment. The purpose of this study was to evaluate whether coronal tibiofemoral subluxation is a predictor for total knee arthroplasty.
Methods: Patients from the progression subcohort of the longitudinal database "Osteoarthritis Initiative" with moderate to severe osteoarthritis and varus malalignment of greater than 3 degrees were included. Patients who underwent total knee arthroplasty were matched with patients treated conservatively. Subluxation was measured on full limb length X-rays. Cox regression analysis was performed to retrospectively evaluate subluxation as a risk factor for total knee arthroplasty and check for a possible association between subluxation and pain at the beginning of the observation period in this study.
Results: A total of 215 patients were included. Cox regression demonstrated that varus malalignment increased the hazard to undergo surgery by 16% (HR 1.158, p = 0.008) while subluxation did not (HR 1.12, p = 0.11). Furthermore, subluxation was neither associated with poor WOMAC (OR 1.13, p = 0.194) nor KOOS (OR 1.11, p = 0.256) knee pain scores at the beginning of the observation period.
Conclusion: The results presented show that subluxation is neither an independent risk factor for total knee arthroplasty, nor for poor pain scores.
Level of Evidence: III.