Tibial tubercle malposition in patellar joint instability: a computed tomograpy study in full extension and at 30 degree flexion.

We evaluated the tibial tubercle position in knees with patellar instability. CT in full extension and at 30 degree flexion was used in 18 knees with instability and 18 control knees. Scans were taken at the level of the femoral epicondyles, tibial tubercle and distal tibia. We found that in full extension, the tibial tubercle was in a more lateral position in the unstable than in the control knees. At 30 degree flexion, the tibial tubercle in the unstable knees rotated internally, but it was never within the normal range. CT scans taken in full extension and at 30 degree flexion seem to be of value for ascertaining the degree of tibial tubercle malposition during knee flexion in patellar instability.