Connective tissues of muscle and muscle compartments

There are at least three different connective tissues that surround the muscle and connect the muscle cells to each other and to other structures (such as bones), these tissues are important for the structure/shape of the muscle and for conducting the force of contraction to other structures (usually bones).  These connective tissues include endomysium, perimysium, epimysium, tendon, and fascia.

Here is a brief description of each of the connective tissues of muscle….

Endomysium:  This connective tissue surrounds individual muscle fibers (muscle cells).   Endomysium is made mostly of elastic fibers and it contains capillary blood vessels and lymphatic vessels, and also nerves.  Endomysium considered wispy and delicate, but I suspect that this is simply because it is so thin, for it’s size it has to be tough.

Perimysium:  This connective tissue surrounds groups of muscle cells called fascicles.  The arrangement of these fascicles has an effect on the strength and coordination capabilities of each given muscle.

Epimysium:  This connective tissue surrounds the outside of the entire muscle.  Epimysium is made of dense irregular connective tissue, producing a tough outer covering for the muscle.  Epimysium functions to contain the muscle and to separates muscles from each other so that they can contract independently.

Tendon:  All of the above connective tissues come together and connect to the tendon at the end of a muscle (muscles don’t always have tendons by the way).  Tendons are made of dense regular connective tissue (all of the collagen fibers are running in the same direction) giving them very high tensile strength (so they can conduct a lot of pulling force without getting damaged).  The end of a tendon is connected to a bone (connected deeply to the periosteum layer of the bone), and this bone will be pulled on when the muscle contracts.

Fascia:  Dense connective tissue sheets that surround multiple muscles creating muscle compartments.

Fascia and Muscle Compartments:

Groups of skeletal muscles are surrounded by fascia creating muscle compartments, within these compartments are specific muscles and the blood vessels and nerves that service those muscles (for simplicity I tend to think of these fascial compartments like a plastic bag that snugly surrounds the muscles and has holes for the blood vessels and nerves–  the bag does not stretch much, it is a snug compartment) .  Example fascial compartment:  The front of your thigh contains the anterior compartment of the thigh, this compartment is surrounded by a layer of dense connective tissue and it contains the quadriceps group along with a few other muscles (the sartorius and the articularis genus).  This anterior compartment of the thigh is one of three in the thigh.  There are also compartments in the lower legs, and in your arms.  So, why do we care?  Compartment syndrome!!!

Compartment Syndrome:

Acute Compartment syndrome is a very painful and dangerous medical emergency that can occur after trauma to a compartment (I have seen two cases of acute compartment syndrome, one was a vehicle accident where the person’s thigh was hit by his steering wheel and the other was the result of a horse kicking a woman in her thigh).  The trauma to the muscles in the compartment can cause them to swell due to inflammation and may cause bleeding into the compartment.  Again, these are very snug compartments so there is little room for bleeding or swelling and they can quickly become pressurized, if the pressure in the compartment is too high blood flow into the compartment decreases and all of the muscles and nerves in the compartment experience ischemia (low blood flow).  This quickly becomes very painful (a lot more painful that we might expect from the visible injuries), and the person also often experiences parasthesia (pins and needles, similar to what we feel when a limb is returning from “falling asleep”).  If this goes untreated the muscles in the compartment can die from lack of blood flow.  The treatment is to surgically cut open the compartment and relieve the pressure.

Chronic compartment syndrome is not emergent and is caused usually by repeated excessive exercise (most commonly seen in runners).  Basically, whenever we exercise a muscle it swells due to the dilation of blood vessels inside the muscle, add that to the normal swelling due to low grade inflammation that occurs when we push a muscle to its limits and the pressure can become high enough to cause ischemia inside a compartment and a lot of pain.  Usually when this happens the person stops exercising and the pain decreases.  Prevention and treatment are to allow the muscles to completely recover after pushing them to their limits before pushing them to their limits again (if you have really pushed them give them a couple of days to recover before pushing them again).

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