| A "foot-drop" is a medical term | | | | recently collected a series of 318 patients |
| which--thankfully--does not mean that the | | | | with peroneal neuropathy who required |
| foot suddenly disconnects from the leg. | | | | surgery, while Italian researchers collected |
| Rather, it means that when the leg is lifted | | | | another 69 cases that included those who |
| from the ground, the foot droops downward at | | | | didn't need surgery. From these two |
| the ankle. The muscles that are supposed to | | | | tabulations of cases a good picture emerges |
| prop up the foot have become so weakened that | | | | of the more common causes of peroneal |
| they cannot overcome gravity's downward pull. | | | | neuropathy.Many were due to physical traumas. |
| When people with this problem try to walk, | | | | Some of the traumas were severe enough to |
| they have to either hike the leg higher to | | | | break or dislocate bones, while others |
| clear their drooping toes or else risk | | | | involved deep cuts in the soft tissues, and |
| tripping over them.What is to blame for this | | | | still others involved just a stretch or |
| inconvenient symptom? In truth, there are | | | | bruise. Another common cause was surgical |
| multiple possible causes, but one of the most | | | | operations. Some of the surgeries were to the |
| common culprits is injury to a nerve-bundle | | | | nearby knee, but others were performed on |
| in the leg known as the peroneal nerve. To | | | | more distant structures, like the hip, the |
| understand how this nerve-bundle can get in | | | | abdomen or even the chest.Many cases were due |
| trouble, a quick review of the bones of the | | | | to excessive external pressure being applied |
| leg is helpful. There is just one bone, a big | | | | to the nerve. This occurred in different |
| one, that connects the hip to the knee, and | | | | ways. For example, in prolonged leg-crossing |
| that is the femur. There are two bones that | | | | the knee of the bottom leg pushes steadily |
| connect the knee to the ankle. The tibia is | | | | against the peroneal nerve of the crossing |
| the larger one and lies more to the inside, | | | | leg. Peroneal neuropathies seen in bedridden |
| while the fibula is the thinner one and lies | | | | patients were presumably due to lying on the |
| more to the outside. That's the extent of the | | | | fibular tunnel for too long without a shift |
| bony anatomy we need to know.The nerve-fibers | | | | in position. Other patients had entrapment or |
| constituting the peroneal nerve travel with | | | | pinching of the nerve within the fibular |
| the huge sciatic nerve that runs behind the | | | | tunnel unrelated to external pressure.A |
| femur from the buttock to the lower thigh. | | | | surprisingly large group of patients had |
| That's where the "common peroneal nerve" | | | | peroneal neuropathy due to weight loss, also |
| splits out from the pack and runs along the | | | | known as "slimmer's paralysis." More than one |
| outside of the knee, tucking behind the head | | | | factor might have been at play in these |
| of the fibular bone (a knobby protrusion just | | | | cases, including lack of nutrients, pressure |
| beyond the knee) and then snaking around the | | | | on the nerve, or both.Researchers and |
| neck of the fibula just below its head. The | | | | clinicians find that in some people an |
| neck of the fibula forms the floor of the | | | | apparently isolated peroneal neuropathy is |
| fibular tunnel that the common peroneal nerve | | | | actually the leading edge of a more |
| must pass through. Within this tunnel the | | | | widespread polyneuropathy. "Polyneuropathy" |
| common peroneal nerve is particularly | | | | means that peripheral nerves are impaired in |
| vulnerable to injury.Also within this tunnel | | | | a more diffuse pattern--not just single |
| the common peroneal nerve splits into two | | | | nerves in single places. So in some cases of |
| branches, the "deep peroneal nerve" (farther | | | | apparent peroneal neuropathy further |
| from the leg's surface) and the "superficial | | | | investigations turn up polyneuropathy due to |
| peroneal nerve" (closer to the leg's | | | | other causes, for example, diabetes, |
| surface). Because the two branches have | | | | excessive alcohol consumption or genetic |
| different connections to muscles and skin, | | | | factors.How are cases evaluated? The |
| injury to one produces different impairments | | | | physician's evaluation starts with the |
| than are produced by injury to the other.The | | | | time-honored methods of history-taking and |
| deep peroneal nerve is responsible for | | | | physical examination. As part of the physical |
| cocking up the ankle and toes, so injury to | | | | examination the doctor inventories which |
| this branch produces weakness or paralysis of | | | | muscles are weak (and which are not) and maps |
| the muscles responsible for these actions. | | | | out areas of numbness affecting the skin. |
| There is just a tiny patch of skin, located | | | | Additional testing with electromyography and |
| between the big toe and the toe next to it, | | | | nerve conduction studies, which check on |
| connected to the deep peroneal nerve, so | | | | electrical functions of the muscles and |
| damage to this branch produces numbness | | | | nerves, often provides valuable information, |
| limited to this small area.The superficial | | | | including whether additional nerves are |
| peroneal nerve, by contrast, is responsible | | | | affected and how bad the impairments are.How |
| for skin sensation on most of the outside of | | | | about treatment? Treatment varies according |
| the calf and top of the foot, so these areas | | | | to what caused the peroneal neuropathy in the |
| can become numb when the superficial peroneal | | | | first place, but let's consider a typical |
| nerve is injured. This branch is also | | | | case unrelated to severe trauma. Nonsurgical |
| responsible for lifting the outside edge of | | | | approaches are usually tried first, including |
| the foot, so this action is gone when the | | | | avoidance of further pressure on the peroneal |
| superficial peroneal nerve is not functioning | | | | nerve, improved nutrition and supplementation |
| properly.Impairments due to injury of the | | | | of the diet with vitamins. A simple brace |
| common peroneal nerve (the parent of the two | | | | applied to the ankle improves walking. In |
| branches) are the sum of the impairments | | | | many cases the nerve recovers without |
| associated with each of the branches. So this | | | | anything more drastic being done. But if |
| means that the ankle and toes cannot cock | | | | these conservative treatments fail (and the |
| upwards, the outside edge of the foot cannot | | | | peroneal neuropathy is not part of a more |
| lift, and there is numbness on the outside of | | | | widespread polyneuropathy) then surgical |
| the calf and top of the foot."Peroneal | | | | exploration of the fibular tunnel is often |
| neuropathy" means impairment of the peroneal | | | | indicated. If the nerve is pinched, then the |
| nerve. Peroneal neuropathies are the most | | | | surgeon frees up the nerve from whatever was |
| common neuropathies (of the kind that affects | | | | pinching it.(C) 2005 by Gary CordingleyGary |
| just one nerve at a time) in the lower | | | | Cordingley, MD, PhD, is a clinical |
| extremities. Investigators at the Louisiana | | | | neurologist, teacher and researcher who works |
| State University Health Sciences Center | | | | in Athens, Ohio. |