The most appropriate method for measuring the first MTP angle remains a matter of debate. No previous method measures this angle without relying on reference points within the first metatarsal. Miller’s method was recently reported to be the most reproducible of the current five methods of measurement and was originally described to measure hallux valgus by using the intermetatarsal angle (3). His method was not originally described with the use of a distal chevron osteotomy, as all referenced studies have tested. Reproducibility of all five methods of measurement against a variety of surgical osteotomies has not been studied.
Schneider’s team in 1998 published a study that showed significant preoperative and postoperative differences in MTP angle measurements among the five methods (2). They deemed the wide ranges unacceptable and speculated that the discrepancies could be found in the different relations of the points of reference to the anatomic outline of the metatarsal and the site of osteotomy. This led them to recommend a line connecting the center of the articular head of the metatarsal and the center of the proximal articulation, a method published by Mitchell et al. (6), as the most appropriate method for measurement of the first MTP angle. Since the proximal point of reference will always be proximal to the osteotomy and the distal point of reference will always be distal to the osteotomy site, the line connecting these two points should remain unaltered by surgery (2). Subsequently, Schneider’s team compared the five methods and concluded that Miller’s yielded the greatest reproducibility, especially postoperatively (3). The findings of these two studies suggested that the use of reference points in the metatarsal shaft for determining the first metatarsal axis is not appropriate for precise calculation of the MTP angle, as their use resulted in poorer reproducibility and they were most likely to be affected by surgical intervention and anatomic variations involving the first metatarsal.
The aim of our study was to assess the precision of a method that did not use any aspect of the first metatarsal as a reference in calculating the MTP angle, specifically in the context of a distal chevron osteotomy. To do this, we compared interobserver variances both preoperatively and postoperatively using Miller’s method and Elliot and Saxby’s method adapted by us for calculating the MTP angle. Our study’s finding of higher interobserver variances in MTP angles determined by Miller’s method suggest its lesser reproducibility compared with the new method.
There are several factors that may account for the findings in our study. When Miller’s method is used, the reference point within the first metatarsal must be placed based on the observer’s estimation of the point that bisects the head. The method adopted in this study uses a delineated articular surface on the base of the metatarsal, which eliminates the need for estimation during determination of the first metatarsal axis.
Furthermore, the effects of anatomic variations and surgical interventions in the first metatarsal have been cited in the literature as potential factors affecting the reproducibility in MTP angle measurement among different methods used (2). Using points of reference that are not located in any portion of the first metatarsal eliminates the possibility of these influences.
The method used in our study is shown here to be applicable in distal chevron osteotomy. There is a need to assess it in the contexts of other types of osteotomy. Additionally, no standard was created during this study for patients who have no hallux valgus deformity.
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