First metatarsocuneiform joint mobility: radiographic, anatomic, and clinical characteristics of the articular surface.

BACKGROUND: The first metatarsocuneiform joint is involved in first ray biomechanics and related forefoot pathology. The purpose of this study was to evaluate the first metatarsocuneiform joint radiographic findings in relation to angular position of the radiographic beam, and to assess the joint mobility as it relates to the anatomic orientation of the facets on both radiographic imaging and gross anatomic dissection.

METHODS: Thirty-nine cadaveric lower extremity limbs were stratified as normal, mild, moderate, or severe hallux valgus deformity. Mobility of the first metatarsocuneiform joint for each specimen was assessed using the Klaue device. The medial inclination angle (obliquity) of the first metatarsocuneiform joint was determined on both 10-degree and 20-degree anteroposterior radiographs. The lateral inclination angle of both the dorsal and plantar facets was determined on lateral radiographs. Each specimen was then dissected to directly inspect the metatarsocuneiform joint.

RESULTS: The metatarsocuneiform joint mean height was 28.3 mm and the mean width was 13.1 mm. Twenty-three feet demonstrated a continuous cartilaginous surface, 15 feet demonstrated a bilobed cartilaginous surface, and 1 foot demonstrated completely separated facets. Dorsal facets were curved in 37 specimens and flat 2 specimens. Plantar facets were flat in 30 specimens and curved in 9 specimens. The medial inclination angle measured 15.8 degrees on the 10-degree radiograph and 2.6 degrees on the 20-degree radiograph. We were unable to establish any correlations of metatarsocuneiform joint angles or facet contour with mobility measured by the Klaue device.

CONCLUSIONS: The metatarsocuneiform joint has a height to width ratio of nearly 2:1. Continuous and bilobed facets are both very common anatomic variants. The contour of the dorsal facet was predominantly curved and the contour of the plantar facet was predominantly flat. First metatarsocuneiform joint mobility does not appear to be dependent on the contour of the facets or the degree of medial inclination of the joint.

CLINICAL RELEVANCE: Anatomic and radiographic findings with regard to mobility of the first metatarsocuneiform joint may assist the surgeon in interpreting the joint's relationship to hallux valgus deformity and to aid in clinical decision making. Our findings suggest that radiographic interpretation of medial inclination is unreliable and should not be used to determine the appropriateness of specific operative procedures.