Congruous versus incongruous patellar tilt--a preliminary study.

UNLABELLED Although the presence of patellar tilt usually implies a tight lateral retinaculum and unhealthy pressure distributions within the patellar cartilage, it is possible for the bony portion of the patella to appear tilted while the articular cartilage is in fact fully congruous in a medial-lateral direction. We call this "congruous tilt." In such cases, a patient may not suffer from an excessive lateral pressure phenomenon, despite the presence of tilt. MATERIALS AND METHODS One hundred and forty-nine knee MRIs were evaluated with respect to patellar tilt and Wiberg morphology. RESULTS Thirty-one patellae were tilted (tilt angle > 10°). Twenty-five of 31 patellae demonstrated normal morphology in the axial plane (Wiberg 2). One of these 25 tilted patellae demonstrated congruous tilt. Three of 31 patellae were of the Wiberg type 3(a long lateral facet, a very short medial facet). In two out three of these, the tilt was deemed to be congruous. CONCLUSION Based on this preliminary study, a tilted patella of the Wiberg 3 variety is likely to demonstrate congruous tilt. It remains to be determined whether patients with congruous tilt are less prone to pain but more prone to instability than their incongruous counterparts.