Influence of preoperative coronal and sagittal tibiofemoral subluxation in knee osteoarthritis on the outcome of primary total knee arthroplasty.

backgroundThe effect of osteoarthritis (OA) with tibiofemoral (TF) subluxation on patients undergoing total knee arthroplasty (TKA) has been less studied, and there have been no studies on sagittal knee subluxation which is a component of a three-dimensional problem. We aim to analyze the influence of preoperative coronal and sagittal knee subluxation with OA on other radiological parameters and the functional outcome in patients undergoing TKA.

methodsWe retrospectively reviewed the 179-consecutive primary TKA in 151 patients from January 2017 to June 2017. The radiological parameters analyzed were the mechanical tibiofemoral angle (HKA), joint line congruence angle (JLCA) and coronal tibiofemoral (CTF) subluxation in long leg films. In the lateral view, posterior tibial slope, the settlement area of the femur over the tibia and the sagittal tibiofemoral (STF) subluxation were calculated. Preoperative and postoperative knee society and knee society functional scores were documented. Multivariate regression analysis was done to determine the association of preoperative radiological parameters with coronal and sagittal TF subluxation.

resultsThe average follow-up was 31 months (2.6 years). 102 knees (57%) had CTF subluxation (< 5 mm) within normal range, and 77 knees (43%) had CTF subluxation. There was a direct correlation between the magnitude of CTF subluxation and poor preoperative functional scores compared with the non-subluxation group (p < 0.05). CTF subluxation was not associated with the magnitude of varus deformity as it is correlated more with mild deformity (odds ratio [OR] 10.07, 95% confidence interval [CI] 3.47-29.25) than with moderate and severe varus deformity. The degree of the joint line convergence angle was positively correlated with the amount of CTF subluxation (p = 0.003). STF subluxation had a significant correlation with the posterior slope (p < 0.001), but not with the magnitude of varus deformity (p = 0.26).

conclusionCoronal and sagittal tibiofemoral subluxation had a significant association with poor preoperative clinical scores. The degree of CTF subluxation reduces with the increasing magnitude of varus deformity and JLCA. STF subluxation was associated with the posterior tibial slope. Patients who underwent posterior stabilized TKA had excellent clinical outcomes irrespective of preoperative knee subluxation.