Errors in knee alignment using fixed femoral resection angles

This study describes the variance within a representative population of total knee arthroplasty (TKA) patients to provide guidance in improving coronal alignment. The authors retrospectively reviewed 250 preoperative full-length standing radiographs in a consecutive series of TKAs performed by one surgeon. The distal femoral resection was templated on each radiograph to establish a femoral mechanical anatomical (FMA) angle to guide resection. Mean FMA angle was 5.35°, with a wide variation in FMA angle ranging from 1° to 10°. Slightly more than half (56%) of patients had either a 5° or 6° FMA angle, which is concerning for surgeons using a fixed resection angle. Ninety percent of patients measured within the 5°±2° window. Similarly, 90.7% of patients measured within the 6°±2° window. However, nearly 10% of patients (9.75%) had measurements greater than 7° or less than 3°. This study reports a wide variance in the angle of resection required to establish proper femoral mechanical alignment in TKA. Surgeons should be cognizant of the numerous variables that play a role in TKA and influence overall coronal alignment. Many of these variables can be fully assessed by evaluating full-length standing leg radiographs preoperatively. With experience, templating long-leg films can be reproducible and informative in preparing for each surgical procedure. Routine reliance on a single fixed resection angle could result in malalignment in 10% of patients.