The Chevron bunionectomy: a trigonometric analysis to predict correction.

A trigonometric analysis was developed in an attempt to predict the postoperative hallux valgus angles and intermetatarsal angles after Chevron bunionectomy. This analysis was used in 20 feet to predict postoperative angles, and these predicted values were compared with actual measured roentgenographic values. The postoperative intermetatarsal angles were evaluated to determine their correction to postoperative hallux valgus angles of 20 degrees or less. Using the trigonometric analysis, the postoperative intermetatarsal angles were highly predictable, but the hallux valgus angle could not be reliably predicted for individual patients. The intermetatarsal angle obtained at surgery, however, was indicative of the final hallux valgus angle: 75% of feet with intermetatarsal angles of more than 11 degrees had postoperative hallux valgus angles of more than 20 degrees. Thus, when an intermetatarsal angle of 11 degrees or less can be obtained surgically, the hallux valgus angle can be corrected to 20 degrees or less in most patients.