The human leg contains several distinct muscle groups, each requiring specific signals from the nervous system to function. This communication between nerves and muscles or skin is known as innervation. The lower leg is anatomically organized into three primary sections: the anterior, lateral, and posterior compartments. Each compartment houses different muscles and is supplied by a unique nerve. This organization ensures complex movements like walking and balancing are executed smoothly, and the integrity of the nerve supply is necessary for full mobility and sensation.
Identifying the Primary Nerve
The nerve that supplies the muscles of the anterior lower leg is the Deep Fibular Nerve (also known as the Deep Peroneal Nerve). This nerve is a terminal branch of the Common Fibular Nerve, which originates from the larger Sciatic Nerve (L4 through S2). The Common Fibular Nerve descends near the head of the fibula bone, where it divides into its deep and superficial branches. The Deep Fibular Nerve then enters the anterior compartment of the leg, traveling alongside the anterior tibial artery. It is the sole source of motor input for all the muscles in this compartment, supplying the specific muscle fibers responsible for lifting the foot.
Controlling Movement and Sensation
The Deep Fibular Nerve’s main function is to enable dorsiflexion, which is the upward movement or lifting of the foot at the ankle joint. It supplies the muscles responsible for this action, including:
- The Tibialis Anterior muscle, the largest muscle in the anterior compartment and the chief dorsiflexor.
- The Extensor Digitorum Longus, which straightens the four lesser toes.
- The Extensor Hallucis Longus, which straightens the great toe.
- The Fibularis Tertius, which aids in lifting and everting the foot.
These actions are necessary during the swing phase of walking, ensuring the foot is lifted high enough to clear the ground and allowing for a smooth gait cycle. Beyond its motor role, the Deep Fibular Nerve provides sensory function to the skin located in the web space between the first and second toes on the top of the foot.
Understanding Foot Drop
Damage to the Deep Fibular Nerve or the Common Fibular Nerve can result in foot drop, which is the inability to actively dorsiflex the foot. This condition leads to a dragging of the toes during movement. Because the Common Fibular Nerve wraps closely around the neck of the fibula, it is susceptible to compression injuries from tight casts, habitual leg crossing, or trauma to the knee area. Foot drop can also be caused by nerve root compression in the lower spine or systemic conditions like diabetes. Individuals with this condition often develop a compensatory walking pattern known as steppage gait. To prevent tripping, the person must lift the thigh higher than normal, causing the foot to slap down onto the floor with each step.