Patellar dislocation has predisposing factors. A roentgenographic study on lateral and tangential views in patients and healthy controls.

One hundred patients with the diagnosis of an acute patellar dislocation treated conservatively and 30 healthy control subjects were studied roentgenographically by lateral and tangential views. The aim of the study was to determine the distribution and incidence of predisposing factors in different study groups. Three study groups were formed as follows: 67 patients (group A) without late problems or operative treatment of redislocation; 33 patients (group B) who underwent a surgical realignment procedure for redislocations or late problems; and 30 healthy control subjects (group C). A statistically significant difference was observed between the patient groups (A, B) and control group (C) when the means, medians and distributions of patellar tendon length (LT), patellar length (LP), tendon to patella length ratio (LT/LP), tendon to patellar articular surface ratio (LT/LAS), sulcus angle (SA), lateral patellar displacement (LPD), lateral patellofemoral angle (LPA) and morphological classification of the patella (1-5, Jägerhut) were compared. In group A, LPD was also significantly greater than in group B. This study demonstrates a considerably high rate of predisposing factors associated with patellar dislocation.