ALS is a progressive neurological disease causing the degeneration of nerve cells in the brain and spinal cord. This loss of motor neurons leads to increasing muscle weakness throughout the body. Foot drop, a common symptom of ALS, is the inability to lift the front part of the foot, a movement called dorsiflexion. This difficulty significantly impacts mobility and is a frequent concern for individuals living with the disease.
Understanding the Neurological Cause
Foot drop in ALS originates from the destruction of specialized nerve cells that control voluntary muscle movement. Both the upper motor neurons in the brain and the lower motor neurons in the spinal cord and brainstem progressively die off. Lower motor neurons are directly responsible for transmitting signals from the spinal cord to the muscles in the limbs.
The loss of these neurons starves the muscles of nerve signals, leading to weakness and eventual atrophy. The dorsiflexor muscles that lift the foot, primarily the tibialis anterior, are particularly affected. These muscles receive instruction via the common peroneal nerve. When the motor neurons supplying this pathway fail, the message to lift the foot is lost, causing the ankle to remain in a dropped position.
Identifying the Physical Manifestation
The lack of control over the foot’s position during walking creates distinct changes in a person’s gait. To compensate for the inability to clear the ground, an observable abnormality known as “steppage gait” develops. This involves lifting the thigh and knee higher than normal, similar to climbing stairs, to prevent the toes from dragging.
The weakened dorsiflexor muscles cannot control the descent of the forefoot, causing the foot to strike the ground suddenly, heel first. This uncontrolled landing is called “foot slap” and is characterized by a distinct noise as the foot hits the floor. This impaired movement greatly increases the risk of tripping and stumbling, even over small obstacles like carpet edges or uneven pavement.
Management Strategies and Assistive Devices
The primary intervention for managing foot drop is the use of an Ankle-Foot Orthosis (AFO). This lightweight brace supports the ankle and foot by holding it at a neutral, 90-degree angle, mechanically preventing the toe from dropping and dragging. AFOs come in different materials, such as rigid plastic for maximum support or lighter carbon fiber for a more dynamic effect.
Physical therapy (PT) focuses on maintaining the available range of motion. Therapists guide individuals through stretching exercises to prevent the calf muscles and Achilles tendon from tightening, which can worsen the foot drop. PT also helps improve overall gait and stability when used in conjunction with assistive devices.
Functional Electrical Stimulation (FES) is an alternative or supplement to an AFO. FES devices apply small electrical impulses to the peroneal nerve during the swing phase of walking. This electrical signal causes the muscles to contract, actively lifting the foot and promoting a more natural walking pattern. FES offers advantages like less restriction of movement and a lighter feel compared to a traditional AFO.
Addressing Daily Mobility and Fall Risk
Reducing the risk of falls is paramount in managing foot drop, requiring both device use and environmental adjustments. Footwear must be supportive and secure, often recommending shoes with high tops and firm, non-slip soles. Footwear must also comfortably accommodate the AFO and have secure closures to prevent the foot from sliding.
Environmental Modifications
Within the home, simple modifications can enhance safety and mobility. Removing throw rugs and securing loose cords eliminates common tripping hazards. Improving lighting, especially near stairs or in hallways, helps the person see obstacles and navigate their surroundings. General mobility aids, such as canes and walkers, are often used alongside AFOs to provide additional balance and stability during ambulation.
Education and Safety Protocols
Education for the individual and caregivers is a continuous process to reinforce safety protocols and fall prevention strategies. This includes advice like avoiding rushing, not carrying heavy items while walking, and consistently using all prescribed assistive devices. These practical adjustments maximize independence and reduce the daily challenges associated with foot drop.