Short Leg Film Is Sufficient for Postoperative Follow-Up in Total Knee Arthroplasty

Abstract

The gold standard for evaluating postoperative alignment after total knee arthroplasty (TKA) has been standing AP hip to ankle radiograph. The objective of this study was to determine if the angle between the anatomic axis of the tibia and femur measured on short standard radiographs accu-rately reflected overall coronal and mechanical alignment from full length knee films. Both full length and short length knee films were retrospectively compared measurements made on from 188 knees in 129 consecutive patients after primary TKA between July 1990 and January 1991. The tibiofemoral angle, distal femur and proximal tibia resection angles, and mechanical align-ment were evaluated on the long leg by a blinded observer. The difference in the tibiofemoral an-gle measured on short and long leg films, 4.4 (+/−2.9) vs 5.2 (+/−3.0) degrees of valgus, respec-tively, was statistically significant (p <0.01). The correlation coefficient between the tibiofemoral angle and mechanical axis was 0.9 (p <0.01). There was no difference in the distal femur or prox-imal tibia resection angle measured on short length knee vs long leg films. In conclusion, the tibi-ofemoral angle measured on short length knee radiographs accurately reflects postoperative alignment. The differences between tibiofemoral angle and the mechanical alignment are highly correlated and equivalent measures of overall alignment.