Rotational malalignment of the femoral component in total knee arthroplasty

Ligamentous balancing is a crucial part of total knee arthroplasty. To ensure proper kinematics, balance must be achieved in flexion and extension. Failure to do so may result in limited range of motion, premature polyethylene wear, or patellofemoral tracking problems. Balancing in extension is dependent on the type and extent of correctional ligamentous release. Flexion balance is dependent on proper femoral rotation. There are two methods to determine femoral rotation. In the classic method, the knee is tensed in flexion after ligamentous release in extension. The anteroposterior cut then is made parallel to the cut tibial surface. Alternatively, the anteroposterior cut can be based off fixed femoral landmarks. The purpose of the current study was to determine the variance between balancing the flexion gap with the classic method versus the technique of using fixed femoral landmarks to determine rotation. One hundred consecutive posterior stabilized knee arthroplasties were performed using the classic method. The resected posterior condyles in each case were measured. The actual difference between the resected condyles using the classic method was compared with the calculated difference of resected bone using bony landmarks to determine rotation. A variance analysis then was performed. Compared with classically balanced knees, rotational errors of at least 3 degrees occurred in 45 % of patients when rotation was determined from fixed bony landmarks. These patients had trapezoidal rather than rectangular flexion gaps. Such errors may have implications regarding polyethylene wear, range of motion, and long-term clinical results.