Fourth metatarsophalangeal joint

The fourth metatarsophalangeal joint is a synovial condyloid joint formed by the articulation between the head of the fourth metatarsal and the base of the proximal phalanx of the fourth toe. The joint is stabilized by several key structures:

• Capsule: A fibrous capsule surrounds the joint, providing containment and stability.

• Collateral ligaments: Medial and lateral collateral ligaments anchor the sides of the joint, preventing excessive varus and valgus movement.

• Plantar plate: A thick fibrocartilaginous structure on the plantar aspect, which is the primary stabilizer against hyperextension and supports the metatarsal head. The plantar plate is firmly attached proximally to the metatarsal and distally to the base of the proximal phalanx, and it merges with the collateral ligaments and the deep transverse intermetatarsal ligament.

• Deep transverse intermetatarsal ligament: This ligament connects the plantar plates of adjacent lesser MTP joints, contributing to transverse stability.

• Tendons: The flexor digitorum longus and brevis tendons pass plantar to the joint, while the extensor digitorum longus and brevis tendons cross dorsally. The lumbrical tendon inserts medially, and the interossei insert on both sides.

• Articular surfaces: The metatarsal head is convex, and the base of the proximal phalanx is concave, allowing for flexion, extension, and limited abduction/adduction.