Use of a modified Elmslie-Trillat procedure to improve abnormal patellar congruence angle.

Forty patients underwent 45 modified Elmslie-Trillat realignment procedures (mean followup, 2 years) for refractory patellar instability (34 knees) or painful patellofemoral syndrome with malalignment (11 knees). The postoperative congruence angle (mean, +3.4 degrees) was significantly improved compared with the preoperative value (mean, +21.5 degrees). We considered the "normal" congruence angle average as -8 degrees (range, -20 degrees to +4 degrees). Over time postoperatively, we detected no statistical difference in the congruence angle (5 months, 3.4 degrees; 24 months, 6.3 degrees). There were no patellar dislocations postoperatively. Nine knees (20%) had some postoperative subluxation. Ninety-four percent of the patients without subluxation had congruence angles less than 15 degrees, whereas 54% of patients with postoperative subluxation had postoperative congruence angles greater than 15 degrees. The evidence in this study population indicates that the modified Elmslie-Trillat procedure can predictably improve the patellar congruence angle. Adequate correction may eliminate patellar dislocation. Correction of the congruence angle to less than +15 degrees will result in a decreased incidence of postoperative patellar instability. Early full activity postoperatively did not affect the modified Elmslie-Trillat correction of the congruence angle being maintained over time.