Malrotation causing patellofemoral complications after total knee arthroplasty

Thirty patients with isolated patellofemoral complications after total knee arthroplasty were compared with 20 patients with well functioning total kn ee replacements without patellofemoral complications. The epicondylar axis and tibial tubercle were used as references on computed tomography scans to measure quantitatively rotational alignment of the femoral and tibial comp onents. The group with patellofemoral complications had excessive combined (tibial plus femoral) internal component rotation. This excessive combined internal rotation was directly proportional to the severity of the patellof emoral complication. Small amounts of combined internal rotation (1 degrees -4 degrees) correlated with lateral tracking and patellar tilting. Moderate combined internal rotation (3 degrees-8 degrees) correlated with patellar subluxation. Large amounts of combined internal rotational (7 degrees-17 de grees) correlated with early patellar dislocation or late patellar prosthes is failure. The control group was in combined external rotation (10 degrees -0 degrees). The direct correlation of combined (femoral and tibial) intern al component rotation to the severity of the patellofemoral complication su ggests that internal component rotation may be the predominant cause of pat ellofemoral complications in patients with normal axial alignment. The epic ondylar axis and tibial tubercle are reproducible landmarks which are visib le on computed tomography scans and can be used intraoperatively. Using thi s computed tomography study can determine whether rotational malalignment i s present and thus, whether revision of one or both components may be indic ated.