CHAPTER 13 Structure and Function of the Ankle and Foot Complex


295 Popliteus


Both the fl exor hallucis longus and the fl exor digito- rum longus provide stability and control during closed chain activities, such as standing, walking, running, and standing on the toes. They contract to provide dynamic support to the medial longitudinal arch. When the body sways forward, the gripping forces of these fl exors on the ground help in maintaining balance.


Action of Plantar Flexors During Ambulation


Tibialis posterior


Flexor


digitorum longus


Flexor hallucis longus


Achilles tendon


Figure 13.23 Muscles of the deep posterior compartment of the leg. (From Starkey C, Brown D. Examination of Orthopedic & Athletic Injuries, 4th ed. Philadelphia, PA: F. A. Davis Company, 2015, p. 245, with permission.)


loads are placed on the leg during standing, walking, or running. As the muscle contracts, it pulls the navicular inferiorly and medially as it stabilizes the bone against the talus. Toward the end of the stance phase of walking, as the weight is being shifted off the weight-bearing leg, the tibialis posterior contracts concentrically to lift the medial longitudinal arch upward, converting the foot into the rigid lever needed to push off the limb and propel the body forward.


Flexor Digitorum Longus and Flexor Hallucis Longus


The fl exor digitorum longus lies in the posterior medial aspect of the calf. As its tendon travels toward the ankle, the tendon is positioned posterior to the tibialis posterior tendon at the medial malleolus. The tendon divides into four sections that attach to the bases of the distal pha- langes of the four lesser toes (Fig. 13.23). The muscle produces fl exion of the MTP and IP joints and assists with plantar fl exion of the ankle. The fl exor hallucis longus is located on the lateral posterior aspect of the calf. The tendon travels downward and crosses to the medial aspect of the leg as it passes behind the medial malleolus and through a groove in the talus before attaching to the base of the distal phalanx of the great toe (Fig. 13.23). In the area near the fi rst MTP joint, the tendon typically contains two sesamoid bones. When activated, the muscle fl exes the fi rst MTP joint and IP joint. It also assists with plantar fl exion.


Once the heel strikes the ground during walking, the anterior ankle dorsifl exors eccentrically lower the foot to the ground. Then the tibialis anterior relaxes, as the foot is fl at on the ground. The plantar fl exors, particularly the soleus, are activated, and they begin to eccentrically control and decelerate the forward rotation of the leg over the foot (Fig. 13.24A). As the leg moves over the foot and the heel begins to rise off the ground, the plantar fl exors concentrically contract to assist with the push-off thrust needed to propel the body forward (Fig. 13.24B). The deep posterior muscle group assists with supi- nation because the muscles resist pronation during the stance phase of the gait cycle. Most notably, the tibialis posterior eccentrically decelerates rearfoot pronation as the entire foot contacts the ground and controls lower- ing of the medial longitudinal arch. Through this action, the tibialis posterior helps absorb some of the impact of loading the foot. As the limb moves into the middle and late portions of stance phase, the tibialis posterior con- centrically guides the foot into supination and heightens the medial longitudinal arch.


LATERAL MUSCLE GROUP: FIBULARIS LONGUS AND FIBULARIS BREVIS


The fi bularis longus and fi bularis brevis make up the lateral muscle group of the ankle. The fi bularis longus attaches to the head of the fi bula close to the distal attach- ment of the biceps femoris muscle. It also attaches to the proximal tibia and fi bular shaft. The muscle fi bers converge into a tendon that travels around the lateral malleolus and then enters the plantar surface of the foot through a groove in the cuboid bone. It inserts on the fi rst tarsometatarsal joint. Because the tibialis anterior also attaches on the plantar surface of the fi rst tarsometa- tarsal joint opposite to the fi bularis longus, they both stabilize the fi rst ray of the foot (Fig. 13.25). The fi bularis brevis attaches lower on the fi bula than the peroneus longus and passes behind the lateral mal- leolus and across the calcaneus and cuboid before attach- ing to the fi fth metatarsal bone. Both the longus and the brevis tendons are anchored around the lateral malleolus by the fi bular retinaculum (Fig. 13.25).


The longus and brevis are the primary evertors of the foot during open chain activities. They also assist with plantar fl exion of the ankle, although they are far more


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