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ex·ten·sor ret·i·nac·u·lum(eks-ten'sŏr ret'i-nak'yū-lŭm) [TA]
extensora muscle, contraction of which tends to straighten or dorsiflex a joint; the antagonist of a flexor
retinaculum (plural: retinacula)restraining band of fibrous tissue
extensor retinaculum bands of thick, fibrous tissue within superficial fascia, at anterior ankle area (subdivided into superior and inferior extensor retinacula) overlying the extensor (dorsiflexor) tendons and synovial sheaths of the extrinsic musculature (i.e. tibialis anterior, extensor hallucis longus, extensor digitorum longus, peroneus tertius)
flexor retinaculum bands of thick fibrous tissue within deep fascia, at posterior ankle area, overlying the plantarflexor tendons and synovial sheaths of the extrinsic musculature (i.e. gastrocnemius, soleus, plantaris, tibialis posterior, flexor hallucis longus, flexor digitorum longus, peroneus longus, peroneus brevis); flexor retinaculum is continuous proximally with deep fascia of leg, and distally with deep fascia of the sole, acting as a point of origin of abductor hallucis