KS43: CORONAL ALIGNMENT IN TOTAL KNEE ARTHROPLASTY: MEASURED VERSUS ARBITRARILY SET DISTAL FEMORAL RESECTION ANGLE.

Abstract

A technical goal in total knee arthroplasty is the production of a neutral coronal plane mechanical axis. Errors may produce large mechanical axis deviations precipitating early implant failure. This study sought to test if measured distal femoral resection produced more accurate and consistent coronal alignment than arbitrarily set distal femoral resection.

Data from a cohort of 255 consecutive unselected primary total knee arthroplasties undertaken by the senior author (PM) was collected prospectively and independently assessed. In the first 167 cases distal femoral resection was arbitrarily set to 5 degrees of valgus. In the remaining 88 cases the distal femoral resection angle was determined on a preoperative long leg standing AP radiograph. Postoperative coronal alignment was measured on long leg standing AP radiograph in all cases.

The measured distal femoral valgus angle was between 4 and 7 degrees. An equal number measured either 5 or 6 degrees and accounted for 85% of the total number. Statistically insignificant improvements in mean axis and standard deviation were observed in the measured group: mean axis deviation −0.31 vs −0.51: p=0.17 (independent samples t test) and standard deviation 0.91 vs 1.09: p=0.055 (Levene test).

Acceptable coronal alignment in total knee arthroplasty can reliably be obtained with conventional instrumentation. Improvement in standard deviation with measured distal femoral valgus angle approaches statistical significance.