Importância do ligamento femoropatelar medial no deslocamento e na inclinação lateral da patela: estudo radiográfico em cadáveres

OBJECTIVE: Acute Patellar luxation is a complex disease that mainly affects young patients. Its physiopathology is little known and the understanding of it and its therapeutic conduct are controversial. The medial femoropatellar ligament (MFPL) is the main static stabilizer for preventing lateral displacement of the patella. In order to assess the stability of the femoropatellar joint, the authors radiographically assessed the presence, or absence of lateral displacement and inclination of the patella before and after the MFPL section in the knees of cadavers. METHODS: Thirty knees of cadavers were radiographed on the axial incidence of the patella by means of the technique described by Merchant before and after MFPL section. The Merchant angle of congruence and Laurin lateral femoropatellar angle were measured. RESULTS: The medial femoropatellar ligament presented a mean length of 4.8cm, and width of 1.6 cm. In six anatomical pieces there was no change in the Laurin lateral femoropatellar angle (20%), in three anatomical pieces the change was one degree (10%), in 20 (67%) two degrees and in one anatomical piece it was four degrees (3%). Changes occurred between zero and two degrees in 97% of the knees of cadavers. In six anatomical pieces there was no change in the Merchant angle of congruence (17%); in six anatomical pieces the change was one degree (20%), in 17 (57%) two degrees, in one anatomical piece it was three degrees (3%) and in one it was six degrees (3%). These changes occurred between zero and two degrees in 93% of the knees of cadavers. CONCLUSION: Analysis of the results obtained in this study allowed us to conclude that the medial femoropatellar ligament is important in the lateral inclination and displacement of the patella with the knee flexed at 45o.