Phalanges of the Foot
The phalanges are long bones in the foot located distal to the metatarsals. Like in the hand, each of the toes consists of three phalanges, which are named the proximal, middle and distal phalanges. However, the hallux (great toe) only has two phalanges, a proximal and a distal one. Occasionally, there are only two phalanges in the little toe. The phalanges consist of a proximal base, a shaft and a distal head. This article will cover the anatomy of the phalanges of the foot, including muscle attachments, supply and ossification followed by any relevant clinical pathology.
The phalanges in the foot are much shorter than those in the hand, and their total length is also much shorter than the metatarsals. The bases of the proximal phalanges articulate with the heads of the associated metatarsal bones to form the metatarsophalangeal joints. The heads of the proximal phalanges articulate with the bases of the middle phalanges to form the proximal interphalangeal joints. The distal interphalangeal joints are formed by the articulations between the heads of the middle phalanges and the bases of the distal phalanges. These hinge joints allow flexion and extension and are reinforced by plantar ligaments as well as by medial and lateral collateral ligaments.
The bases of the proximal phalanges are concave to allow for articulation with the metatarsal heads, whilst the heads are trochlear, or pulley shaped. Like the metatarsals, the shafts of the proximal phalanges are convex dorsally but concave on their plantar aspect. The small, middle phalanges are broader than their proximal counterparts.
The distal phalanges are flatter and smaller than the ones in the hand. They consist of a broad base for articulation with the middle phalanges as well as a non-articular head. A rough, crescent shaped tuberosity is present on the plantar surface of the heads, which supports the pads or pulps of the toes.
Muscle Attachments, Blood Supply And Innervation
Many muscles of the foot attach to the phalanges. The muscles that attach to the proximal phalanges include:
- Lumbricals – medial aspect of the four lateral phalanges
- Interossei – both sides of the second, third and fourth proximal phalanges
Muscles that attach to the middle phalanges include:
- Flexor digitorum brevis – plantar aspect of the base
- Extensor digitorum brevis – dorsal aspect of the base
Two muscles attach to the distal phalange of the hallux:
- Flexor hallucis longus – plantar aspect of the base
- Extensor hallucis longus – plantar aspect of the base
Muscles that attach to the four lateral distal phalanges include:
- Flexor digitorum longus – plantar aspect of the base
- Extensor digitorum longus – plantar aspect of the base
The dorsal digital arteries supply the proximal and middle phalanges. The middle phalanges also receive blood supply from the plantar digital arteries. These arteries also supply the distal phalanges. The dorsal and plantar digital nerves innervate all of the phalangeal bones.
Ossification is a bone remodelling process where new bone is laid down by osteoblasts, cells involved in synthesising bone. It is an important process in bone development and involves transforming cartilage into bone. The location where ossification begins is referred to as the ossification centre.
The ossification centres for the distal phalanges are the first to appear, between the 9th and 12th week of development. This is followed by appearance of the ossification centres for the proximal phalanges between the 11th and 15th weeks of development. The development of the middle phalanges usually occurs soon after their proximal counterparts.