The Effect of Alignment and BMI on Failure of Total Knee Replacement

Background: The purpose of this study was to determine the effect of tibiofemoral alignment, femoral and tibial com-ponent alignment, and body-mass index (BMI) on implant survival following total knee replacement. Methods: We retrospectively reviewed 6070 knees in 3992 patients with aminimum of two years of follow-up. Each knee was classified on the basis of postoperative alignment (overall tibiofemoral alignment and alignment of the tibial and the femoral component in the coronal plane). Failures (defined as revision for any reason other than infection) were analyzed with use of Cox regression; patient covariates included overall alignment, component alignments, and preoperative BMI. Results: Failure was most likely to occur if the orientation of the tibial component was <90 relative to the tibial axis and the orientation of the femoral component was ‡8 of valgus (failure rate, 8.7%; p < 0.0001). In contrast, failure was least likely to occur if both the tibial and the femoral component were in a neutral orientation (‡90 and <8 of valgus, respectively) (failure rate, 0.2 % [nine of 4633]; p < 0.0001). ‘‘Correction’ ’ of varus or valgus malalignment of the first implanted component by placement of the second component to attain neutral tibiofemoral alignment was associated with a failure rate of 3.2 % (p = 0.4922) for varus tibial malalignment and 7.8 % (p = 0.0082) for valgus femoral mal-alignment. A higher BMIwas associatedwith an increased failure rate. Comparedwith patients with a BMI of 23 to 26 kg/m2, the failure rate in patients with a BMI of ‡41 kg/m2 increased from 0.7 % to 2.6 % (p = 0.0046) in well-aligned knees, from 1.6 % to 2.9 % (p = 0.0180) in varus knees, and from 1.0 % to 7.1 % (p = 0.0260) in valgus knees