Tendon sheath of tibialis posterior muscle

The tendon sheath of the tibialis posterior muscle is a synovial-lined structure that envelops the tibialis posterior tendon as it courses posterior to the medial malleolus. This sheath facilitates smooth gliding of the tendon and protects it from friction and mechanical stress, especially at the retromalleolar region where the tendon changes direction sharply around the medial malleolus, functioning as a pulley.

The sheath begins proximally near the musculotendinous junction and extends distally to the region just beyond the medial malleolus, terminating before the tendon’s insertion into the navicular and cuneiform bones. Within the sheath, the tendon is surrounded by synovial fluid, which reduces friction during movement. The sheath is composed of two layers: an outer fibrous layer and an inner synovial layer. The synovial layer is responsible for producing lubricating fluid, while the fibrous layer provides structural support.