An anatomical study of Morton's interdigital neuroma: the relationship between the occurring site and the deep transverse metatarsal ligament (DTML).

BACKGROUND: Using clinical and cadaver studies, we examined the relationship between the location of Morton interdigital neuromas and the surrounding structures, including the deep transverse metatarsal ligament (DTML), which has been suspected as a major causative factor in neuroma formation.

METHODS: Seventeen fresh-frozen cadavers were evaluated to determine the relationship between the location of Morton interdigital neuromas and the DTML at two phases of the gait cycle with 60 degrees of metatarsophalangeal dorsiflexion and with 15 degrees of ankle dorsiflexion. We measured the distance from the bifurcation of the common digital nerve in the foot to the anterior margin of the DTML and also measured the length of the DTML itself. Clinically, we checked the location of the Morton interdigital neuroma and its length during surgery in 32 feet.

RESULTS: In the second and third webspace, the mean distance from the bifurcation of the common digital nerve of the foot to the anterior margin of the DTML was 16.7 mm, 15.1 mm in the mid-stance position, and 15.9 mm and 14.6 mm in the heel-off position. The length of the second and third DTML averaged 12.8 mm and 10.6 mm. Clinically, all of the cases of Morton interdigital neuroma started at the bifurcation area of the common digital nerve, and the mean neuroma length was 7.5 mm (6 to 11).

CONCLUSIONS: Morton interdigital neuromas were located more distally than the DTML in both the mid-stance and the heel-off stage during walking. The main lesion was located between the metatarsal head and the metatarsophalangeal joint and more distal than the DTML, questioning previous studies suggesting that the DTML is the major causative factor in development of Morton interdigital neuroma.