CHAPTER 13 Structure and Function of the Ankle and Foot Complex Clinical Connection 13.2


An abnormally raised medial longitudinal arch with excessive rearfoot inversion is known as pes cavus. The most obvious features of pes cavus include a combined rearfoot inversion, forefoot eversion, and excessively plantar-fl exed fi rst metatarsal. Pes cavus can be congenital (occurring at birth) or develop progressively over a lifetime. Many mild forms of pes cavus are idiopathic and tend to be inherited. More severe cases can arise from trauma injuries or have a neurological origin, such as Charcot-Marie- Tooth disease, poliomyelitis, cerebral palsy, or brain or peripheral nerve injuries. This condition often produces spasticity, weaknesses, and muscle imbal- ances that result in deformities. The excessively high arch alters the weight-bearing of the foot as the metatarsal heads experience a greater amount of contact pressure. This additional pressure on the metatarsals can result in pain and discomfort. The pes cavus foot is very rigid and has diffi culty absorb- ing forces during walking and running. Complete or near-complete loss of the medial longitudinal arch is called pes planus.


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Plantar aponeurosis


Calcaneus Figure 13.18 Plantar aponeurosis.


tension is placed on the plantar fascia when the joints extend. This tension pulls the metatarsal and tarsal bones together, converting the foot into a rigid structure. This tension provides the main passive support of the medial longitudinal arch. During higher loading activities, such as walking, running, and jumping, muscles provide addi- tional dynamic support to the medial longitudinal arch.


is in plantar fl exion. The foot moves into a mobile pro- nated position that allows it to absorb the impact of weight-bearing and the forces of the leg as it moves over the foot and to conform to the ground surface. This acceptance of weight with the foot fl at on the ground is referred to as the stance phase of ambulation. Once the foot is fl at on the ground during walking, the body moves forward over the leg, and then the heel begins to rise off the ground. As the foot begins to push off to propel the body forward, the subtalar and trans- verse tarsal joints begin to supinate. The forefoot moves into plantar fl exion of the fi rst metatarsal and dorsifl exion of the fi fth metatarsal. This reversal of motions in the foot increases the arch, and the foot assumes a stable position. The foot becomes a rigid lever that is able to propel the body forward during the push-off phase of ambulation.


The fat pads on the plantar surface of the foot, the sesamoid bones at the base of the great toe, the spring ligament, and the plantar aponeurosis (plantar fascia) all are connective tissue structures that help the arch absorb loads during low-stress positions and activities. The plantar aponeurosis consists of extensive strong, thick bands of fascia that attach posteriorly to the medial cal- caneal tuberosity and extend to attach at the MTP joints and sheaths of the fl exor tendons of the toes (Fig. 13.18). Because these attachments are distal to the MTP joints,


MUSCLES


This discussion of the muscles of the ankle and foot includes the extrinsic and intrinsic muscles and their indi- vidual functions. The extrinsic muscles originate outside of the foot and occupy four separate compartments in the lower leg: an anterior, posterior superfi cial, poste- rior deep, and lateral compartment (Fig. 13.19). A thick fascial membrane called a septum contains each compart- ment of muscle bellies. The intrinsic muscles have both attachments within the structures of the foot. Appendix C, which follows chapter 14, lists the attachment sites and innervations of the extrinsic and intrinsic muscles of the ankle and foot.


ANTERIOR MUSCLE GROUP


The muscles of the anterior group include the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fi bularis tertius (also known as peroneus tertius). The group is located on the lateral side of the anterior tibial shaft, the adjacent fi bula, and the inter- osseous membrane. The tendons of these muscles are restrained by the superior and inferior extensor retinacu- lum as they cross the ankle before attaching to their distal insertions (Fig. 13.20).


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