RSD’s “The Foot-Drop” A ...
A droopy ankle, with or without significant numbness, can indicate that the peroneal nerve is in trouble. A “Foot-Drop” is a medical term which–thankfully–does not mean that the foot suddenly disconnects from the leg. Rather, it means that when the leg is lifted from the ground, the foot droops downward at the ankle. The muscles that are supposed to prop up the foot have become so weakened that they cannot overcome gravity’s downward pull. When people with this problem try to walk, they have to either hike the leg higher to clear their drooping toes or else risk tripping over them.
What is to blame for this inconvenient symptom? One of the most common culprits is injury to a nerve-bundle in the leg known as the peroneal nerve. To understand how
this nerve-bundle can get in trouble, a quick review of the bones of the leg is helpful. There is just one bone, a big one, that connects the hip to the knee, and that is the femur. There are two bones that connect the knee to the ankle. The tibia is the larger one and lies more to the inside, while the fibula is the thinner one and lies more to the outside.
The nerve-fibers constituting the peroneal nerve travel with the huge sciatic nerve that runs behind the femur from the buttock to the lower thigh. That’s where the “common peroneal nerve” splits out from the pack and runs along the outside of the knee, tucking behind the head of the fibular bone (a knobby protrusion just beyond the knee) and then snaking around the neck of the fibula just below its head. The neck of the fibula forms the floor of the fibular tunnel that the common peroneal nerve must pass through. Within this tunnel the common peroneal nerve is particularly vulnerable to injury.
Also within this tunnel the common peroneal nerve splits into two branches, the “deep peroneal nerve” (farther from the leg’s surface) and the “superficial peroneal nerve” (closer to the leg’s surface). Because the two branches have different connections to muscles and skin, injury to one produces different impairments than are produced by injury to the other. The deep peroneal nerve is responsible for cocking up the ankle and toes, so injury to this branch produces weakness or paralysis of the muscles responsible for these actions. There is just a tiny patch of skin, located between the big toe and the toe next to it, connected to the deep peroneal nerve, so damage to this branch produces numbness limited to this small area.
Impairments due to injury of the common peroneal nerve (the parent of the two branches) are the sum of the impairments associated with each of the branches. So this means that the ankle and toes cannot cock upwards, the outside edge of the foot cannot lift, and there is numbness on the outside of the calf and top of the foot.
“Peroneal neuropathy” means impairment of the peroneal nerve. Peroneal neuropathies are the most common neuropathies (of the kind that affects just one nerve at a time) in the lower extremities. Many were due to physical traumas, which were severe enough to break or dislocate bones, while others involved deep cuts in the soft tissues, and still others involved just a stretch or bruise.
Many cases were due to excessive external pressure being applied to the nerve due to an injury occurring from an accident of any type ranging from something as extreme as a vehicle accident, hit by a 2 wheel hand held delivery cart, or sudden slip and fall. In many cases the nerve recovers from conservative treatments without anything more drastic being done. But if these fail then surgical exploration of the fibular tunnel is often indicated and the risk of evolving into RSD/CRPS increases.
For additional information: Gary E Cordingley, MD, PhD and John Radclffe Hospital, Oxford
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