As the tendons of the muscles of the leg cross the tinkle-joint on their way to the foot, they are bound down by localized thickenings in the deep fascia which constitute retinacular bands comparable, both in mode of formation and in function, to the flexor and extensor retinacula, of the wrist. They comprise the superior and inferior extensor retinacula (transverse and cruciate crural ligaments), the flexor retinaculum (laciniate ligament), and the superior and inferior peroneal retinacula.
The superior extensor retinaculum (transverse crural ligament) (figs. 655, 662) binds down the tendons of the Tibialis anterior, Extensor hallucis longus, Extensor digitorum longus and Peroneus tertius, as they descend on the front of the ankle-joint, the anterior tibial vessels and nerve also pass under cover of it. It is attached laterally to the lower end of the anterior border of the fibula, and medially to the anterior border of the tibia; above, it is continuous with the deep fascia of the leg.
The inferior extensor retinaculum (cruciate crural ligament) (figs. 661, 662) is a Y-shaped band placed in front of the ankle-joint. The stem of the Y is attached to the upper surface of the calcaneum, in front of the sulcus calcanei, and passes medially, forming a strong loop which encloses the tendons of the Peroneus tertius and the Extensor digitorum longus. From the extremity of this loop two diverging bands pass medially to complete the Y. The upper band consists of two distinct lamellae. The deep lamella passes behind the tendons of the Extensor hallucis longus and the Tibialis anterior, but in front of the anterior tibial vessels and nerve, to reach the tibial malleolus. The superficial lamella crosses in front of the tendon of the Extensor hallucis longus and is then firmly connected to the deep lamella; it may or may .not be continued in front of the tendon of the Tibialis anterior to reach the tibia. The lower band, extends downwards and medially to be attached to the plantar aponeurosis; it crosses the tendons of the Extensor hallucis longus and Tibialis anterior, the arteries dorsalis pedis and the terminal branches of the anterior tibial (deep peroneal) nerve. From the deep surface of the loop which encloses the tendons of the Peroneus tertius and the Extensor digitorum longus, a distinct, band of fibers passes medially between the constituent layers of the interosseous talocalcaneal ligament to gain attachment to the upper surface of the calcaneum and the under surface of the neck of the talus.
The flexor retinaculum (laciniate ligament) extends from the tibial malleolus above to the margin of the calcaneum below; its upper border is continuous with the deep transverse fascia of the leg, its lower with the plantar aponeurosis and the fibers of origin of the Abductor hallucis muscle. It converts a series of bony grooves in this situation into canals for the passage of the tendons of the flexor muscles into the sole of the foot, and also affords protection to the posterior tibial vessels and nerve as they enter the sole of the foot. From the medial to the lateral side these structures lie in the following order: tendon of the Tibialis posterior, tendon of the Flexor digitorum longus, Posterior tibial vessels and nerve, and tendon of the Flexor hallucis longus (fig. 661).
The synovial sheaths of the tendons round the ankle.-The tendons crossing the ankle-joint are enclosed in synovial sheaths. On the front of the ankle (fig.662) the sheath for the Tibialis anterior extends from the upper margin of the upper extensor retinaculum to the interval between the diverging limbs of the lower retinaculum; those for the Extensor digitorum longus and Extensor hallucis longus reach upwards to just above the level of the malleoli the former being the higher. The sheath of the Extensor hallucis longus is prolonged on to the base of the first metatarsal bone, while that of the Extensor digitorum longus reaches only to the level of the base of the fifth metatarsal bone. On the medial side of the ankle (fig. 663) the sheath for the Tibialis posterior extends for about 4 cm, above the malleolus; below, it ends just short of the insertion of the tendon into the tuberosity of the navicular bone. The sheath for the Flexor hallucis longus reaches up to the level of the malleolus, while that for the Flexor digitorum longus goes slightly higher; the former is continued to the base of the first metatarsal bone, but the latter ends opposite the navicular bone. On the lateral side of the ankle (fig. 662) a sheath, the upper part of which is single, and the lower part double, encloses the Peroneus longus and brevis. It extends upwards for about 4 cm. above the tip of the malleolus, and downwards and forwards for about the same distance.
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