Tendon sheaths of toes

The tendon sheaths of the toes are specialized synovial structures that envelop the flexor tendons as they traverse the digits, providing lubrication and facilitating smooth tendon gliding. In the toes, the flexor tendons (flexor digitorum longus for the lesser toes and flexor hallucis longus for the hallux) are surrounded by a double-layered synovial sheath, which extends from just proximal to the metatarsophalangeal (MTP) joint to the distal phalanx. This sheath is reinforced by a system of fibrous pulleys.

The annular pulley system in the toes consists of discrete fibrous bands that tether the tendon sheath to the phalanges and adjacent soft tissues, preventing bowstringing during flexion. High-resolution imaging and cadaveric studies have identified four annular pulleys (A1–A5, with A5 less consistently visualized) in the lesser toes and three in the hallux. The A2 and A4 pulleys are the most substantial, located at the proximal and middle phalanges, respectively. Cruciform pulleys, which are thinner and cross-shaped, are interspersed between the annular pulleys and provide additional stabilization.

The sheath itself is composed of an outer fibrous layer and an inner synovial layer, which secretes synovial fluid to reduce friction. The sheath is anchored to the phalanges and the deep transverse metatarsal ligament proximally. The extensor tendons on the dorsal aspect of the toes do not have true synovial sheaths but are stabilized by the extensor apparatus.