VALIDITY AND RELIABILITY OF THE 1ST DISTAL METATARSAL ARTICULAR ANGLE

A laboratory study was undertaken to quantify the validity, the intra- and interobserver reliability, and the effect of first metatarsal ori entation on the distal metatarsal articular angle (DMAA). First metata rsals from six cadavers were isolated by sharp disection and attached to a custom-made triplanar protractor. This allowed controlled positio ning of the first metatarsal in the three cardinal planes. Each specim en was moved through a stepwise sequence of first metatarsal orientati on changes. Radiographs were taken at each position. The distal (metat arsophalangeal) articular surface of the first metatarsal was then cir cumscribed with metallic paint and the radiographic series was repeate d. DMAA measurements wer made on each radiograph multiple times by two measurers blinded to the parameters of variation. The difference betw een the standard (clinical) radiographic technique for estimating the DMAA and the metallic paint DMAA averaged -0.9-degrees (SD = 2.4-degre es). Longitudinal rotation (P < .001) and varus deviation (P < .02 at 10-degrees) of the first metatarsal had a significant effect on the ra diographic determination of the DMAA. Although intraobserver reliabili ty for DMAA measurement was high, interobserver reliability for the cl inical technique of measurement was poor (pooled intraclass correlatio n coefficient = 0.14).