Abstract
Introduction
Restoration of a neutral mechanical axis has been a widely held tenet of primary total knee arthroplasty (TKA), however new technologies are recently being marketed which claim correction of alignment deformity is unimportant. This study was undertaken to determine whether the outcome of aseptic loosening was associated with post-operative mal-alignment of the mechanical axis.
Methods
A 1:9 matched case-control analysis was conducted within a cohort of 1,030 consecutive cemented posterior stabilized TKAs with 7 to 11.5 yrs follow-up (average 9 yrs). Aseptic loosening had occurred in 10 knees (1.0%). Nine controls were randomly selected for each case within matching criteria for age and minimum time in situ. Post-operative mechanical alignment was determined using retrieved long leg radiographs. Age-adjusted relative risk was estimated using conditional logistic regression.
Results
Radiographs revealed 8 of the 10 loosened cases had been placed in 3 or more degrees varus mechanical alignment (range, 2? varus to 7? varus), compared to only 4 of the 90 age-matched controls (range, 4? valgus to 4? varus). A single degree change of mechanical alignment in the varus direction was associated with a more than 4-fold increase of risk of loosening (odds ratio 4.6, 95% confidence interval 1.7–12.7; p=0.0035). The relative risk for mechanical alignment >= 3? varus compared to <= 2? varus (dichotomous) was 69.2 (95% confidence interval 8.1–589; p=.0001). BMI, gender, and pre-op deformity were not significant.
Discussion
These results suggest that avoidance of varus postoperative alignment is an extremely important determinant of TKA fixation durability.
