First metatarsal bone: An Anatomic Study

Background: The purpose of this study was to establish the range of anatomic variations of the first metatarsal bone, including both the angulations of the articular surfaces and the dimensions of the bone in a large sample. Methods: Four hundred and seventy-eight first metatarsal bones of 239 cadaver specimens were studied. The following parameters were recorded: the distal metatarsal articular angle (DMAA), distal metatarsal articular surface shape, proximal metatarsal articular angle (PMAA), the first metatarsal bone length and width at the mid-region of the shaft, and the existence of a joint between the bases of the first and second metatarsals. These parameters were correlated to the specimen's age, sex, race, height, and weight. The DMAA and PMAA were measured from a digital picture of the first metatarsal bone by a specially designed computer analysis program. Results: Males and African-American race had a longer and wider metatarsal. The joint between the first and second bases was present in 25% of the population. The DMAA ranged from -14 degrees of medial deviation to 30 degrees of lateral deviation with an overall average of 8.21 degrees. The DMAA increased 1 to 3 degrees with every 10 years in age for both right and left bones with a p value of < 0.01 and < 0.001, respectively, and the average increase from 20 to 60 years of age was 4.5 degrees. The PMAA ranged from -13.8 degrees of lateral deviation to 12.7 degrees of medial deviation with an overall average of -1 degrees. PMAA significantly deviated laterally in the presence of a joint between the bases of the first and second metatarsals (p < 0.001). The male and female means for the DMAA and PMAA were nearly equal. Conclusions: The DMAA had a wider range than reported in the literature, and it increased with age. The first-second metatarsal joint was accompanied by lateral deviation of the PMAA. Clinical Relevance: Laterally deviated PMAA could predispose to a varus deformity of the first metatarsal.