Slap gait is a heel gait abnormality that can be diagnosed by hearing the patient walk. With a normal walking gait (Figure 1), the heel strikes the ground first, followed by controlled relaxation of the foot and ankle dorsiflexors in order to allow the forefoot to come in contact with the ground. Slap gait occurs due to weakness of the foot and ankle dorsiflexors which causes the foot to slap down on the floor with each step.
Steppage gait occurs due to total paralysis of the ankle and foot dorsiflexors (tibialis anterior muscle). Steppage gait (Figure 2) is sometimes called “foot drop gait” or “neuropathic gait”. A common symptom of foot drop is a high steppage gait that is often characterized by raising the thigh up in an exaggerated fashion while walking.
The patient will have difficulty in clearing the toes during the swing phase. The patient must externally rotate the leg or flex the hip or knee to raise the foot high enough to avoid dragging the toes along the ground. The leg is brought high off the ground by flexing the ipsilateral hip and knee so the toes will not drag on the ground during the swing phase. If the patient has foot drop (Figure 3), then they must have a high steppage gait. Otherwise, they will trip on their feet and fall forward.
The ankle and foot dorsiflexors are supplied by the peroneal nerve which is part of the sciatic nerve (Figure 4). The sciatic nerve starts in the lower back and runs through the buttock and lower limb. In the lower thigh just above the back of the knee, the sciatic nerve divides into two nerves, the tibial and peroneal nerves, which innervate different parts of the lower leg. The common peroneal nerve then travels anterior around the fibular neck dividing into superficial and deep peroneal nerves. The deep peroneal nerve gives innervation to the tibialis anterior muscle of the lower leg which is responsible for dorsiflexion of the ankle.
There are several conditions that may cause foot drop, for example: a herniated disc (L4-L5) compressing the L5 nerve root may cause foot drop; a lumbosacral plexus injury or pelvis fracture; a sciatic nerve injury or hip dislocation may cause foot drop due to the common peroneal division of the sciatic nerve being injured during a fracture dislocation injury involving the hip. A knee dislocation can injure the common peroneal nerve and/ or the popliteal artery (Figure 5).
In established compartment syndrome, foot drop is a late finding and ischemia for more than 6-8 hours may cause irreversible changes to the muscles (Figure 6). A fasciotomy should be performed early as ischemia may be tolerated, but by 8 hours the damage is often irreversible.
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