Robinson Andrew H N, Cullen Nicholas P, Chhaya Neal C, Sri-Ram K, Lynch Andy
Addenbrooke's Hospital, Department of Trauma and Orthopaedics, Box 37, Hill's Road, Cambridge, CB2 2QQ, United Kingdom.
Foot Ankle Int. 2006 Dec;27(12):1036-40. doi: 10.1177/107110070602701207.
The distal metatarsal articular angle (DMAA) is a radiographic measure of the orientation of the first metatarsal articular surface. There is debate with regards to the accuracy, reproducibility, and validity of measurement of the DMAA in the literature. This study aimed to test the validity of the measurement of the DMAA from standard radiographs, to explore the trigonometric relationship of the first metatarsal rotation and the DMAA, and to assess interobserver reliability.
Thirty-four separate dry cadaver first metatarsal bones were mounted onto a customized light-box-protractor, allowing controlled incremental changes in rotation and inclination. A series of 39 digital photographs were taken of each metatarsal in 5-degree increments of rotation between 30 degrees supination and 30 degrees pronation at 10, 20 and 30 degrees of inclination. Three reviewers performed blinded DMAA measurements from each photographic image; the data were collated for statistical analysis. The data were analysed using a mixed effects linear model comparing the DMAA with rotation of the first metatarsal.
A strong statistically significant trend of increasing score with increasing pronation of the metatarsal was observed, the relationship was approximately linear. There was a strong effect of inclination, but the strength of this varied with rotation and was amplified at higher inclinations. Interobserver error was noted in line with other studies, but even allowing for this interobserver error, the linear relationship was maintained.
This study showed that the DMAA varies significantly in a linear pattern with axial rotation of the first metatarsal. Inclination of the first metatarsal also affects the magnitude of the angle. This study does not refute the DMAA as an entity but does confirm the inaccuracy of extrapolating the DMAA from plain anteroposterior radiographs.
跖骨远端关节角（DMAA）是第一跖骨关节面方向的影像学测量指标。关于文献中DMAA测量的准确性、可重复性和有效性存在争议。本研究旨在检验标准X线片测量DMAA的有效性，探讨第一跖骨旋转与DMAA的三角关系，并评估观察者间的可靠性。
将34块单独的干燥尸体第一跖骨安装在定制的灯箱量角器上，以控制旋转和倾斜的增量变化。在10°、20°和30°倾斜度下，以30°旋前至30°旋后的5°旋转增量对每根跖骨拍摄一系列39张数码照片。三名观察者对每张照片进行盲法DMAA测量；整理数据进行统计分析。使用混合效应线性模型分析数据，将DMAA与第一跖骨的旋转进行比较。
观察到随着跖骨旋前增加得分有很强的统计学显著趋势，关系近似线性。倾斜有很强的影响，但这种影响的强度随旋转而变化，在较高倾斜度时放大。与其他研究一致，观察到观察者间误差，但即使考虑到这种观察者间误差，线性关系仍得以维持。
本研究表明，DMAA随第一跖骨的轴向旋转呈线性显著变化。第一跖骨的倾斜也会影响角度的大小。本研究并未否定DMAA这一实体，但确实证实了从普通前后位X线片推断DMAA的不准确性。
