Relationship between joint structure of the first tarsometatarsal joint and its degeneration.

This study aimed to elucidate the relationship between joint structures of the first tarsometatarsal and articular facet degeneration. A total of 100 feet from 50 cadavers were examined. The articular facets of the first metatarsal and medial cuneiform were categorized into four types based on the superior and inferior facets' separation, and the formation of the inferior lateral facet on the lateral plantar prominence: Type I, a single facet with no separation or inferior lateral facet; Type II-a, two facets with separation but no inferior lateral facet; Type II-b, two facets, no separation, but with an inferior lateral facet; Type III, three facets with separation and an inferior lateral facet. When both bone types matched, they were defined as Type I, Type II-a, Type II-b, and Type III joints, respectively; unmatched types were classified as Unpair joints. The severity of articular cartilage degeneration on both bones was assessed using a 5-point scale. The degeneration grade was compared among joint types. Type III joints exhibited significantly milder articular cartilage degeneration in medial cuneiform compared to Type II-a, II-b, Unpair joints. The formation of inferior lateral facet and separation of the superior and inferior facets might be crucial for the joint's stability.