Metatarsophalangeal and intermetatarsal angle: different values and interpretation of postoperative results dependent on the technique of measurement.

For measurement of the first metatarsophalangeal angle and intermetatarsal angle I-II, five different methods for drawing the axis of the first metatarsal have been published. This study aimed to evaluate differences in the resulting angles that depend on the method of drawing this axis. Using pre- and postoperative radiographs of 20 patients who had surgery on the hallux (chevron procedure), highly significant differences were found: mean values for the preoperative metatarsophalangeal angle ranged from 27.3 degrees to 31.9 degrees; the mean postoperative values were calculated at 8.6 degrees to 20.3 degrees. The preoperative mean of intermetatarsal angle I-II showed values from 13.0 degrees to 17.6 degrees; the postoperative mean ranged from 5.2 degrees to 16.7 degrees. These differences--especially in the postoperative evaluation--resulted in a postoperative improvement between 11.6 degrees and 20.8 degrees for the metatarsophalangeal angle and between 0.9 degrees and 10.0 degrees for the intermetatarsal angle. These wide differences seem to be unacceptable for angles as a criterion of success in surgery on the hallux. The reason for these discrepancies can be found in the different relations of the points of reference to the anatomical outline of the metatarsal and the site of osteotomy. As a consequence of this study, defining the axis of the first metatarsal as a line connecting the center of the articular surface of the metatarsal head and the center of the proximal articulation can be recommended as the most appropriate method. The resulting angles are independent of the type of surgery performed on the hallux.