A comparison of 4 common methods of hand-measured techniques with a computerized technique to measure the first intermetatarsal angle.

Measurement of the intermetatarsal (IM) angle on plain dorsoplantar radiographs is considered a standard in the surgical evaluation of hallux valgus. The angle formed in this measurement helps determine the selection of surgical procedure. A study was performed to determine the most consistent method to radiographically measure the first IM angle. The IM angle was measured manually with a tractograph by using 4 different techniques on 50 preoperative dorsoplantar radiographs. The techniques used were 1) bisecting the shaft of the first and second metatarsals, 2) bisecting the head and base of the first and second metatarsals (center-of-head method), 3) measuring the angle from the tangent of the medial aspect of the first and the second metatarsal shaft, and 4) measuring the angle formed by the tangent of the lateral aspects of the first and second metatarsal shafts. In addition, the same 50 radiographs were evaluated by a Java software program designed by 1 of the authors to specifically measure the IM angle by bisecting the areas of the first and second metatarsals. A statistical analysis was applied to determine which IM angle of the 4 methods measured by hand was most consistent with the computer-generated IM angle. The median absolute deviation error test was applied to interpret the results. The results showed that the bisection of the shaft of the first and second metatarsals had the smallest mean absolute value of 2.8 degrees (22.37% error), with the other techniques ranging from 3.0 degrees to 3.8 degrees. It appears that the method of bisection of the shafts of the first and second metatarsals provides the most accurate technique compared with the computer-determined technique.