Preoperative malalignment increases risk of failure after total knee arthroplasty.

BACKGROUND: Implant survival after total knee arthroplasty has historically been dependent on postoperative knee alignment, although failure may occur when alignment is correct. Preoperative knee alignment has not been thoroughly evaluated as a possible risk factor for implant failure after arthroplasty. The purpose of this study was to analyze the effect of preoperative knee alignment on implant survival after total knee arthroplasty.

METHODS: We performed a retrospective review of 5342 total knee arthroplasties performed with use of cemented Anatomic Graduated Component implants from 1983 to 2006. Each knee was independently measured preoperatively and postoperatively for overall coronal alignment. Neutral ranges for preoperative and postoperative alignment were defined by means of Cox proportional hazards regression.

RESULTS: The overall failure rate was 1.0% (fifty-four of 5342 prostheses); failure was defined as aseptic loosening of the femoral and/or tibial component. The average preoperative anatomical alignment (and standard deviation) was 0.1° ± 7.7° of varus (range, 25° of varus to 35° of valgus), and the average postoperative anatomical alignment (and standard deviation) was 4.7° ± 2.5° of valgus (range, 12° of varus to 20° of valgus). The failure rate in knees in >8° of varus preoperatively (2.2%; p = 0.0005) or >11° of valgus preoperatively (2.4%; p = 0.0081) was elevated when compared with knees in neutral preoperatively (0.71%). Knees with preoperative deformities corrected to postoperative neutral alignment (2.5° through 7.4°) had a lower failure rate (1.9%) than undercorrected or overcorrected knees (3.0%) (p = 0.0103). Knees with postoperative neutral alignment, regardless of preoperative alignment, had a lower failure rate (0.74%) than knees with postoperative alignment of <2.5° or >7.4° of anatomic valgus (1.7%) (p < 0.0001).

CONCLUSIONS: Patients with excessive preoperative alignment (>8° of varus or >11° of valgus) have a greater risk of failure (2.3%). Neutral postoperative alignment (2.5° through 7.4° of valgus) improves (1.9% for preoperatively deformed knees) but does not completely eliminate the risk of failure (0.5% for knees that were neutral both preoperatively and postoperatively). Careful attention should be paid to knee alignment during total knee arthroplasty, especially for patients with severe preoperative deformities.