Kinematic CT of the patellofemoral joint.

OBJECTIVE: The purpose of this study was to determine if kinematic CT can be applied to the patellofemoral joint using current slip-ring CT scanner design in patients with anterior knee pain and thus a suspected patellar tracking disorder. SUBJECTS AND METHODS: Twenty knees in 18 patients with anterior knee pain were evaluated with kinematic CT. A single 10-sec exposure of the patellofemoral joint was obtained during active flexion and extension. Static nonkinematic and loaded kinematic examinations were compared with unloaded kinematic studies in a subset of patients. The changes in lateral patellofemoral angle and lateral shift were measured. Video cine viewing of patellofemoral motion was used to subjectively grade image quality and patellofemoral abnormalities by consensus.
RESULTS: Kinematic CT was successfully used in all 20 knees. In nine knees studied with static nonkinematic and unloaded kinematic images, the lateral patellofemoral angle improved an average of 4" on the kinematic images. In addition, lateral shift improved by an average of 3%, an improvement that was statistically significant (p = .01). In 10 knees studied with and without loading, the lateral patellofemoral angle decreased an average of 3% with loading. No significant change was seen in lateral shift. In all patients, cine viewing was thought to be more useful than single images. Cine viewing was of good or diagnostic quality in all 20 knees studied. Lateral patellar translation during extension was detected in eight of 20 kinematic studies. Lateral patellar tilting also was detected in eight of 20 kinematic studies. Narrowing of the articular space was detected in 12 of 20 knees. Six knees were determined to be normal.
CONCLUSION: Kinematic CT with slip-ring technology is a new technique that can be easily performed on the patellofemoral joint. This technique shows promise as a tool for determining the cause of anterior knee pain.