The purpose of this study was to clarify some pathogenesis of the cartilage changes of the patellofemoral joint in patellar dislocation knees.
A first arthroscopy was performed in a total of 60 knees, including 30 knees of acute patellar dislocation (APD) and 30 knees of recurrent patellar dislocation (RPD). At the time of the first arthroscopy, 58 knees sustained open medial patellofemoral ligament repair/reconstruction, and 2 knees had only arthroscopy examination. In APD knees, the second-look arthroscopy was performed 16.7 months after the first arthroscopy, and in RPD knees, 25.2 months after the first arthroscopy.
In most APD knees, cracking primarily on the central dome of the patella did not have a remarkable change but in several knees that had a high number of cracking or interlaced cracking, cracking became worse with fibrillation. Osteochondral defect site primarily on the medial facet showed fibrillation and/or ulceration (erosion). In most RPD knees, fissuring primarily on the central dome did not have a remarkable change, and fibrillation and/or erosion mainly on the medial facet also did not have a remarkable change. However, in four knees with the continuation of patellar dislocation, the patellar cartilage changes had definitely worsened. On the other hand, in the first and second-look arthroscopy, most APD and RPD knees had no remarkable cartilage lesions or cartilage changes of the femoro-trochlear aspect.
One of the pathogenesis of fissuring in RPD knees seems to be cracking occurring at the time of APD. Two of the pathogenesis of fibrillation may result from the reparative reaction of the cartilage in osteochondral defect site and the cartilage change due to a high degree of cracking damage mainly on the central dome in APD injury. The continuation of patellar dislocation definitely makes the patellar cartilage lesions worse.