Interphalangeal joints of the foot

Articular surfaces

The interphalangeal joints of the foot are articulations between the phalanges of the toes. In toes 2-5, a proximal and distal set of interphalangeal joints is present. A proximal interphalangeal joint is formed between the convex trochlear surface on the head of a proximal phalanx and the corresponding concave articular surface on the adjacent base of a middle phalanx. The distal interphalangeal joints of toes 2-5 are formed in a similar manner; between the trochlear surfaces on the heads of a middle phalanx and the corresponding concave articular surface on the adjacent bases of a distal phalanx.

As mentioned previously, the big toe has only one interphalangeal joint, formed between the trochlear surface on the head of the proximal phalanx and the concave articular surface of the base of the distal phalanx.

Joint capsule

Each interphalangeal joint is completely enclosed by a joint capsule, lined by synovial membrane. The joint capsule is attached along the articular margins and reinforced by the collateral ligaments, plantar ligament, and the extensor expansions of the extrinsic and intrinsic muscles of the foot.

Ligaments

There are two types of ligaments that support and stabilize both the proximal and distal interphalangeal joints:

• Collateral interphalangeal ligaments: strong ligaments found on the medial and lateral sides of each joint, extending proximally and medially from small tubercles present on each side the head of the proximal phalanx to the base of the next phalanx.
• Plantar interphalangeal ligament: is not a true ligament but a dense fibrocartilaginous plate found on the plantar surface of phalangeal heads in the interphalangeal joints.

Innervation

The interphalangeal joints receive nervous supply from proper plantar branches of the medial and lateral plantar nerves, that arise from the tibial nerve.

Minor contributions to the innervation of the interphalangeal joints of the lateral toes are received from dorsal digital branches, which stem from the deep fibular (peroneal), intermediate dorsal cutaneous and sural nerves. The interphalangeal joint of the big toe receives additional innervation from the medial dorsal cutaneous branch of the superficial fibular nerve.

Blood supply

Interphalangeal joints of the foot receive arterial blood supply from digital branches of the plantar arch, an anastomosis formed by the lateral plantar artery and deep plantar artery.

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Movements

Being uniaxial hinge joints, the only movements permitted in the interphalangeal joints are flexion (plantarflexion) and extension (dorsiflexion), which occur in the sagittal plane around a frontal axis. A considerable amount of flexion is possible, while extension is limited by the collateral and plantar ligaments. The movements are also significantly more pronounced in the proximal interphalangeal joints than in the distal.

In the close packed position, the interphalangeal joints are completely extended, while their loose packed (or resting) position is that of slight flexion. The capsular pattern (or loss of passive range of motion during inflammation) of these joints is flexion more limited than extension.

Muscles acting on the interphalangeal joints

The primary flexor of the proximal interphalangeal joint is flexor digitorum longus, while the main flexor of the distal interphalangeal joint is flexor digitorum brevis. The interphalangeal joint of the big toe is flexed by flexor hallucis longus.

The prime extensors of the interphalangeal joints are extensor digitorum longus, extensor digitorum brevis, lumbricals and interossei.