The common plantar digital nerves arise from the medial and lateral plantar nerves and run in the intermetatarsal spaces deep to the deep transverse metatarsal ligament. The third common digital nerve (in the third web space, between the third and fourth metatarsal heads) receives a communicating branch from both the medial and lateral plantar nerves, making it the largest and most frequently affected by Morton neuroma. Each common digital nerve divides at the web space into two proper plantar digital nerves supplying the adjacent toe surfaces.
Morton's neuroma is perineural fibrosis of the common plantar digital nerve in the third web space (80%) or second web space (15%), producing burning forefoot pain and paresthesiae in the third and fourth (or second and third) toes. The Mulder click test (transverse metatarsal compression with simultaneous web space pressure) and Tinel's sign in the web space are the clinical tests. Ultrasound demonstrates the hypoechoic nerve enlargement. Corticosteroid injection, orthotic padding, and wide footwear are first-line treatments; neurectomy for resistant cases removes 2-3 cm of the nerve with the neuroma.
Perineural fibrosis and entrapment of the third common plantar digital nerve between the third and fourth metatarsal heads produces burning forefoot pain in the third web space radiating to the adjacent toe tips, reproduced by the Mulder click test; corticosteroid injection reduces perineural inflammation in 60% of cases and surgical neurectomy is reserved for persistent symptoms.
