Joint Line Obliquity Affects Survivorship Following Total Knee Arthroplasty: 12.7-Year Follow-Up of 800 Cases.

Abstract

The purpose of this study was to evaluate the influence of joint line obliquity (JLO) on survivorship following total knee arthroplasty (TKA) over a mean follow-up of 12.7 years. We reviewed the records for 800 patients who had undergone TKA for primary knee osteoarthritis between January 2004 and December 2010. Based on postoperative alignment, patients were categorized into two groups: the mechanically aligned group (mechanical axis of 0 ± 3°) and the outlier group (mechanical axis beyond 0 ± 3°). In addition, patients were stratified into four groups according to joint line obliquity (JLO), as measured on full-length standing weight-bearing radiographs using both the original classification (sum of lateral distal femoral angle and medial proximal tibial angle) and a modified classification (joint surface angle relative to the hip-knee-ankle axis). Kaplan-Meier survival analysis was utilized to estimate implant survival, with aseptic revision for mechanical failure defined as the endpoint. Mechanical failure occurred in 3.5% of cases (28 of 800) over a mean follow-up of 12.7 years. While the original JLO classification was not associated with aseptic revision, the modified classification revealed significant differences within the outlier group. Notably, lateral joint line inclination was associated with the highest failure rate (5.2% [10 of 193]; P = 0.01). Implant survival was significantly higher in the mechanically aligned group (98.6%) than in the outlier group (92.6%) (P < 0.001, log-rank test). Within the outlier group, the lowest survival rate (87.7%, P < 0.001) was found in knees with non-parallel JLO, particularly those with lateral inclination. Multivariate Cox regression analyses identified postoperative JLO (hazard ratio, 1.58; P = 0.042) as an independent risk factor for mechanical failure. When applying the modified JLO classification, postoperative JLO was associated with high survival rates following TKA at a mean follow-up of 12.7 years. Outlier alignment in combination with non-parallel JLO, particularly lateral inclination, demonstrated the poorest survival rate. Retrospective cohort study; Level III.