The incidence of the intermetatarsal facet of the first metatarsal and its relationship to metatarsus primus varus: a cadaveric study.

The purpose of this study was to determine the incidence of the intermetatarsal facet on the lateral aspect of the base of the first metatarsal and its role in the medial angulation of the proximal metatarsal base as it relates to metatarsus primus varus. A total of 77 human first metatarsals were examined for the presence of the intermetatarsal facet. The intermetatarsal facet was seen on the lateral aspect of the first metatarsal base, superior to the tuberous attachment of the peroneus longus tendon. The obliquity of the first metatarsal base was measured on metatarsals with and without the intermetatarsal facet. The intermetatarsal facet was present on 22 of 77 first metatarsals, or 29% of specimens. The proximal obliquity angle was 2.92 degrees in metatarsals without the facet and 4.63 degrees when the facet was present. This increase in the medial obliquity of the proximal first metatarsal base in the presence of an intermetatarsal facet was statistically significant (P < .002). The intermetatarsal facet between the first and second metatarsals may have a role in an increased medial obliquity of the first metatarsal base and is present in approximately 30% of the population.