The evaluation of patellofemoral pain using computerized tomography. A preliminary study.

There are well-recognized limitations of conventional axial radiographs of the patellofemoral joint in assessing patients with peripatellar pain, particularly in the first 20 degrees of knee flexion. Computerized tomography (CT) was used, therefore, to evaluate 20 patients with persistent patellofemoral pain and ten asymptomatic volunteers. Multiple midpatellar images were obtained between zero degrees and 30 degrees -40 degrees (sometimes 40 degrees) of flexion, with and without maximal quadriceps contraction. Three distinct patterns of malalignment were identified. When compared to controls, 11 patients had lateralized patellae based on high-congruence angles in extension. With progressive flexion to 30 degrees, all but one reduced into the trochlea. This group was subdivided into those lateralized with or without associated patellar tilting. There were seven patients whose patellae progressively tilted between zero degrees and 30 degrees of flexion while remaining centered in the trochlea. Anatomic differences demonstrated by CT appear to be a factor in distinguishing these groups. Computerized tomography may be the optimal method of radiographically evaluating the patellofemoral joint. Patients have been identified with lateralized patellae in extension that subsequently become congruent by 30 degrees of flexion and therefore may not be appreciated on traditional radiographs. An awareness of different patterns of malalignment is a significant advantage of computerized tomography when planning selective surgical realignment for these patients.