Postoperative alignment but not femoral coronal bowing is a significant longevity factor after total knee arthroplasty

Background: Femoral coronal bowing (FCB) has been reported to be a risk factor for mechanical malalignment after total knee arthroplasty (TKA). However, the effects of FCB on the long-term survivorship (when postoperative mechanical alignment (MA) is neutral after TKA) have not been determined.

Hypothesis: The effects of FCB on the cumulative survivorship after TKA may be significantly smaller compared with those of MA.

Patients and methods: Consecutive 328 knees of 211 patients (10 males, 201 females) who underwent TKA between 1995 and 2009 (mean age of 64.2±6.7 years at the time of TKA, mean follow-up period of 11.9±2.5 years) were retrospectively evaluated. FCB and MA were evaluated using preoperative and immediate postoperative whole-leg anteroposterior radiographs, respectively. The patients were grouped according to FCB and postoperative MA, which included group A (FCB≤5°, MA≤3°), B (FCB>5°, MA≤3°), C (FCB>5°, MA>3°), and D (FCB≤5°, MA>3°). Primary end-point was defined as aseptic mechanical failures requiring revision TKA. Survivorship was assessed using the Kaplan-Meier method and compared using log-rank tests. Factors associated with the risk of aseptic mechanical failures were analyzed by Cox regression analysis. Preoperative and final follow-up clinical outcomes were assessed using Hospital for Special Surgery (HSS) scores.

Results: Group A, B, C, and D included 190, 73, 40, and 25 knees, respectively. The 10-year survivorship was similar between group A and B (96.3±1.4% vs. 98.6±1.4%; p=0.733) and group C and D (87.3±5.3 vs. 87.6±6.7%; p=0.974); however, it was significantly higher in group B than in group C (p=0.036) and in group A than in group D (p=0.005). Age (OR=0.991; 95% CI 0.906-1.085; p=0.002) and MA>3° (OR=3.645; 95% CI 1.744-7.604; p=0.001) were associated with the risk of aseptic mechanical failures. The mean preoperative and final HSS scores in the four groups were not significantly different.

Discussion: Marked FCB was not associated with long-term survivorship for knees with neutral alignment after TKA. However, non-neutral postoperative alignment reduced long-term survivorship for knees with marked FCB.

Level of evidence: III, Retrospective comparative cohort study.