extensor retinaculum

noun

extensor ret·​i·​nac·​u·​lum -ˌret-ᵊn-ˈa-kyə-ləm 

1

: either of two fibrous bands of fascia crossing the front of the ankle:

a

: a lower band that is attached laterally to the superior aspect of the calcaneus and passes medially to divide in the shape of a Y and that passes over or both over and under the tendons of the extensor muscles at the ankle

called also inferior extensor retinaculum

b

: an upper band passing over and binding down the tendons of the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and peroneus tertius just above the ankle joint

called also superior extensor retinaculum, transverse crural ligament

2

: a fibrous band of fascia crossing the back of the wrist and binding down the tendons of the extensor muscles