Use of a Modified Elmslie-Trillat Procedure to Improve Abnormal Patellar Congruence Angle

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