Muscle Compartments, What could go wrong?

Frederick Ilgenfritz, MD
Bitterroot General & Vascular Surgery

During normal life we are not aware of the coordinated movement of the muscles of our arms and legs as they alternately contract and relax to allow us to go about our activities. There is actually a very complex interaction of the muscles to finely control our movements. This includes both complex tasks such as typing and large muscle tasks such as running or just getting out of bed. The muscles connect to our bones and cross various joints, and in some cases they connect to fibrous tissue called fascia.

This fascia forms an envelope around the various muscle groups. We call the area enclosed by the fascia a muscular compartment. These compartments are found in the lower leg, thigh and arms primarily. The lower leg, or calf, has 4 compartments: anterior, lateral, posterior and deep posterior. The muscles in the anterior compartment primarily function to pull the foot upward, whereas the posterior compartments point the toes down. In general, these muscle groups work together in harmony so the anterior group relaxes as the posterior contracts, allowing just enough counterbalancing strength to keep your balance. Injuries to one or another group of muscles can result in significant difficulty with tasks that require coordinated muscular movement.

An example of such an injury is peroneal nerve damage. The peroneal nerve is located in the upper calf on the outside of the leg just below the knee. It passes around the fibula (the outer of the two bones in the lower leg), and is susceptible to damage at that place. A fracture of the fibula near the knee, or a blunt or penetrating (knife, bullet, etc) injury to the upper outer leg can cause the nerve to be injured and stop sending signals to the muscles of the lateral and anterior compartments of the leg. This results in a condition known as "foot drop". What this really means is that the muscles of these two compartments no longer are working. Normally they would work together with the posterior compartments to maintain balance to the movement of the leg. With the loss of the anterior and lateral muscles, the posterior muscle become dominant and they pull the foot and toes downward, and inward- hence the term "foot drop". If the injury is temporary, the nerve function returns and the normal actions resume. If there is a permanent injury to the nerve, the leg may need to be braced to resist the posterior muscles and allow some protection against foot drop.

Compartment syndrome is another condition that can result in this same kind of problem. Compartment syndrome develops when there is injury to the muscle in a fascial compartment and it begins to swell. This can happen from blunt, penetrating or crush injuries to the muscle compartment, some rare drug reactions, and even more rarely over-exertion of the muscles. The fascia envelope allows only a limited space for swelling. Once that compartment is full from swelling, the compartment pressure starts to rise and the compartment becomes very tight. Our venous pressure is normally relatively low and so the next thing that happens is that the veins in the compartment collapse. When this happens there is no room for new arterial blood and so the muscles and nerves in the compartment stop receiving their oxygen and nutrients. While this is happening, there is increasing severe pain in the area and medical assistance is sought. The problem is diagnosed by tests that look for signs of muscle injury in the blood, and by direct measuring the pressure in the fascial compartments. Other causes of leg pain are also excluded. Other than the pain, the appearance of the leg may be pretty normal. The pulses are often still felt. The muscles will be very sore to stretch.

The treatment for compartment syndrome is twofold. First, if possible, to stop what ever the process was that caused the muscle swelling in the first place, and second a surgical procedure is performed to slit open the fascia envelope and release the pressure allowing the blood flow back to the muscle. If the problem is identified in the first 6-12 hours there is generally full recovery. The muscle swelling returns to normal over several days and then the incisions can be closed and slow resumption of normal activity can begin. If the diagnosis is delayed, there can be muscle death and long-term disability similar to when the nerves are damaged.

Questions or comments can be addressed to Frederick M. Ilgenfritz, MD, FACS, c/o Bitterroot General & Vascular Surgery, 1150 Westwood Drive, Suite C, Hamilton, MT 59840 or visit www.bgvs.us

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