Kinematic and dynamic axial computed tomography of the patello-femoral joint in patients with anterior knee pain

Abstract

Thirty-eight knees of 26 patients with anterior knee pain (12 bilateral) were included in the study. There were 22 women and 4 men, and their average age was 29 years. Axial computed tomography (CT) examination of both knees were done at 0°, 10°, 20°, 30°, 40° and 60° of flexion with and without muscle contraction. Images were always taken at the mid-patellar level. Patellar tilt angle (PTA), congruence angle (CA) and sulcus angle (SA) were measured at each knee position. Normal values were also obtained from 14 healthy volunteers (28 knees). Thus, the types of patello-femoral incongruence were determined at each knee position: 1, tilt+lateralisation (TL: 12 knees); 2, lateralisation (L: 4 knees); 3, medialisation (M: 5 knees); 4, lateral to medial instability (LM: 1 knee); 5, tilt (T: 1 knee). Fifteen knees were classified as normal. When the groups were analysed separately, in the TL group the T or L component would have been missed in nine cases if the images were taken only at 30° or only in the first 30° of flexion. In the L group two patellae were reduced at 30°. In three knees in the M group, medialisation began at 10°, 20° and 30°. One patella was reduced at 40°. In the LM case, the patella was lateralised at 0°, 10°, 20° and medialised at 30° and 40°. In the T case, the patella was tilted only at 20°, 40° and 60°. This study showed that axial images taken only at 30° will miss important information. Imaging in the first 30° of flexion will not reveal the correct type of instability, either. Serial imaging over a wider range of flexion is necessary for the correct diagnosis. Determination of the type of incongruence at different knee positions is a new concept. With this methodology, the presence of medial and lateral to medial instabilities is verified. Hence, the classification systems including only lateral instability should be questioned.