Background: Radiographic measurements such as those of the hallux valgus angle and the intermetatarsal angle are essential parameters for assessing the severity of hallux valgus deformities and the extent of surgical correction required. However, to our knowledge, no study has investigated the reliability of the measurements that are made radiographically before and after a proximal crescentic osteotomy of the first metatarsal. The purpose of the present study was to investigate the intraobserver and interobserver reliability of different methods that are used to measure the angles and to determine the most reliable method.

Methods: We selected twenty preoperative and twenty postoperative dorsoplantar weight-bearing radiographs for patients who had undergone a proximal crescentic osteotomy of the first metatarsal. Three foot and ankle surgeons measured the hallux valgus angle and the intermetatarsal angle with use of five different methods. We calculated the intraobserver and interobserver correlation coefficients and agreement to determine the most reliable method.

Results: Significant differences were observed among the methods with regard to the postoperative hallux valgus angle (p < 0.05) and the preoperative and postoperative intermetatarsal angles (p < 0.01 for both). The method in which a line connecting the centers of the first metatarsal head and the proximal articular surface of the first metatarsal was used to define the longitudinal axis of the first metatarsal yielded the highest intraobserver and interobserver correlation coefficients for the preoperative hallux valgus and intermetatarsal angles and the postoperative hallux valgus angle. For this method alone, the intraobserver and interobserver agreements for the angular measurements were found to be >80%.

Conclusions: A line connecting the centers of the first metatarsal head and the proximal articular surface of the first metatarsal to define its longitudinal axis yields the best intraobserver and interobserver reliability for the measurement of the hallux valgus and intermetatarsal angles. Therefore, this method can be recommended for evaluating radiographs before and after a proximal crescentic osteotomy performed for the treatment of hallux valgus.