Proximal interphalangeal joints of foot

The proximal interphalangeal joints of the foot are synovial hinge joints located between the proximal and middle phalanges of the lesser toes (second through fifth) and, in the hallux, between the proximal and distal phalanges. Each joint consists of the head of the proximal phalanx, which is bicondylar, articulating with the base of the middle phalanx, which is concave and also bicondylar. The articular surfaces are covered by hyaline cartilage and are non-conforming, with the base of the middle phalanx having a greater radius of curvature than the head of the proximal phalanx, resulting in two distinct contact points at the condyles and a small central joint cavity.

The joint capsule surrounds the articulation and is reinforced medially and laterally by the proper collateral ligaments, which originate dorsal and proximal to the fovea on the side of the proximal phalanx head and insert along the side of the base of the middle phalanx. These ligaments are stout and oriented parallel to the middle phalanx in all joint positions.

The plantar plate is a fibrocartilaginous structure attached distally to the base of the middle phalanx and proximally to the joint capsule, providing resistance to hyperextension and serving as an attachment for the flexor tendons. The flexor digitorum longus tendon runs plantar to the joint, while the extensor digitorum longus and brevis tendons cross dorsally. The joint is stabilized by these ligaments and the surrounding musculotendinous structures.