The Compartments of the Lower Leg
Anatomist’s Corner

By Thomas Myers

Originally published in Massage Bodywork magazine, December/January 2001.
Copyright 2003. Associated Bodywork and Massage Professionals. All rights reserved.

FIG. 1 - In modern anatomies, the mechanical action of individual muscles are emphasized, and we rarely see this type of view where the fascial compartments themselves are visible.
Author's note: When we consider the lower leg, we tend to think of it either as a simple whole, as in, "Your calf is tight," or, when we are learning it, as individual muscles -- the tibialis anterior, the gastrocnemius, the flexor hallucis longus, etc. In this column, we are going to explore the lower leg in terms of its fascial compartments, and see how they connect to the rest of the body's myofasciae.

With the usual caveat that dividing the body into pieces is at best a convenient device for learning, and never an end in itself, let us look at the arrangement of parts in the lower leg. There are two bones, the tibia and fibula. The tibia is clearly designed for bearing weight, cupping the femoral condyles at the knee with the semilunar cartilages on the tibial shelf, sending the weight down its shaft to the talus, the top of the foot's tripod. The fibula is more problematic -- it does not 'sit' on anything, it hangs, forming the outside of the ankle and tucking its head up under the tibial condyle.

FIG. 2 - It's clear from the body's design that the tibia bears the body's weight. So what is the fibula doing?
The way the tibia curves in provides a space between the two bones, and this space is filled in with the interossous membrane, which joins the two bones. Actually, it is a bit more complex than that -- the bones touch at the top and bottom, and are held together in both places by fibrous joints. At the bottom, it must be tightly held together to maintain the integrity of the ankle, so the joint is a syndemosis -- a simple fibrous joint almost like a suture or the joints that hold your teeth to your jaw. At the top, where the fibula tucks under the tibia, more movement is sometimes necessary. Consider the amount of torque going through the lower leg when Stefi Graf or Venus Williams plants a foot and whips her body around on top of it to smash a backhand across the tennis court. As such, the tibio-fibular joint can take different forms -- from fibrous through cartilaginous to synovial, with corresponding variability in the amount of movement possible -- depending on the demands a person puts on the body in general, and the leg in particular.

If you stand your client's lower leg on the table, and place both hands just under the knee, your outside hand can find the head of the fibula. Being careful of the peroneal nerve that runs behind it, wiggle the fibular head forward and back to determine how much "play" there is. Do this with a few different clients and see for yourself how variable the amount of movement is in this joint.

Fig. 3 - The deepest layer of fascia in the lower leg is the periosteum/ interosseous membrane wrapped around the bones.
Between this lower tight joint and upper variable joint lies the interosseous membrane. Again, it's a little more complex than that -- the interosseous membrane is not separate from the bones, it is an extension of the periosteum of each bone. A simple way of understanding this is to imagine that one of God's elves has been assigned the job of wrapping each bone in a kind of Saran Wrap(R) coating. One elf got tired of wrapping the tibia and fibula separately, and just took both bones, wrapped a piece of plastic around them both, and then ran a thumb and forefinger up between them to seal the two layers together. Instead of rapping this elf's knuckles, God looked and saw that this was good, and now everybody comes built this way. The periosteum of the front of the tibia continues onto the front of the interosseous membrane, and onto the front of the fibular periosteum, and on around back of them all in a circle (Fig. 3). The interosseous membrane is dissectably bi-laminar, and functions 1) to bind the bones together tightly right to left, 2) to allow limited movement in rotations (and in dorsiflexion, but we'll save that story for another time when we consider the foot), and 3) to provide additional area for muscle attachment.

Fig. 4 - Between the outer sleeve and the inner core, the lower leg is divided into four fascial compartments by intermuscular septa.
So the deepest level of fascia -- aside from the bone itself which is a variable combination of collagen and calcium salts -- is this periosteum-interosseous membrane complex. The most superficial level of fascia (below the skin's dermis and the subcutaneous fat) is the body stocking, which is called the fascia lata in the thigh, but termed the crural (leg) fascia in the lower leg (Fig. 4).

The crural fascia is quite tough. It has to be in order to provide a good foundation for the muscles going to the foot which frequently have to carry the entire body weight, and in order to resist the tendency for too much fluid to gather at the gravitational bottom of the organism. This system fails sometimes during pregnancy, for instance, when the veins for returning blood are somewhat blocked by the weight of the baby, and in other conditions of lower leg edema.

fig. 5 - The two intermuscular septa lie on either side of the peroneal muscles.
Between the circumference of the crural fascia and the center point (more or less) of the bones lie three more fascial divisions, the intermuscular septa. One radiates out from the front of the fibula, one radiates out from the back of the fibula, and the third runs along behind the two bones. These fascial divisions create four compartments, the anterior compartment in front of the two bones, the lateral compartment outside the fibula, and two compartments behind the bones: the superficial and deep posterior compartments. The rest of this column addresses two subjects related to these compartments: how to find the fascial division between the compartments, and how the compartments connect to the myofascia above and below them.

The Intermuscular Septa
You can do all the following palpatory explorations with yourself or with a client model. Turning first to the anterior intermuscular septum, we find it divides the anterior compartment from the lateral compartment. The anterior compartment contains the tibialis anterior muscle, plus the two long extensors -- extensor hallucis and extensor digitorum. All of these muscles go down under the retinaculum and across the top of the foot to where they attach. The lateral compartment contains the peroneal muscles -- longus and brevis, which both go behind the lateral malleolus on their way to their attachments. This gives us a clue as to where to start at the bottom: the lateral malleolus. If you start at this easily-found bony prominence and walk your fingers up, you will soon feel, within a couple of inches, where the peroneals start attaching from behind and the toe extensors (including peroneus tertius, if your model happens to have one) attach from the front. The fascial division can be felt here, either as a slight valley palpable between the two muscle groups, or, in cases where this tissue is storing some calcium lactate crystals or other toxicity, as a string of very small pearls. (These "beads" can be worked out through assiduous and repeated self-massage.)

Let your fingers walk up this anterior septum, seeing if you can keep in contact with it. At the top, you should end up just in front of the fibular head, about an inch below the knee. If you wander directly onto the fibular head itself, or behind it, you lost contact with the septum. To check whether you are in the right place, have your model dorsiflex and plantarflex the foot. Because the peroneus longus is a plantarflexor, and the tibialis anterior is a dorsiflexor, you can feel the muscles contracting and being stretched alternately -- the fascial septum is right between them. Put your fingers into this valley and your other finger on the lateral malleolus. This septum runs a straight line between the two; fascial release here can help ease lower leg strain, free up movement, and help with folks who have a chronically anterior shifted pelvis (forward lean to the legs).

Fig. 6A - The extensions of these compartments along the tissues of the knee provides the key to how the fascial compartments link to the tissues above.
The septum behind the peroneals, the posterior intermuscular septum, runs between the peroneals and the soleus. This one is sometimes a little harder to pinpoint. We know where the peroneals run (just behind the lateral malleolus), and we know where the soleus goes (into the Achilles tendon), so we know where to start at the bottom -- in that little open space just in front of the Achilles tendon. Walk your fingers up a few inches in this space, and the tissues of the soleus and peroneus will come together, meeting in this septum. See if you can follow the septum up to where it ends behind the head of the fibula. This time it is a little harder to separate the two muscles, as they are both plantarflexors. Plantarflex strongly and the soleus will stand out in most people, and are mistaken by some students for the peroneals. But since the peroneus is an everter of the foot and the soleus is, if anything, a mild inverter, you can get your model to evert the foot (turn the sole toward the outside), and the peroneals should strongly tighten, allowing you to find the valley of the septum behind them. This septum can be extra-tight in those with hyperextended knees, and once again, release of these tissues can make more room in these compartments.

The third septum runs between the two posterior compartments, separating the more superficial gastrocnemius/soleus/plantaris compartment from the deeper tibialis posterior/long toe flexor compartment behind the tibia-fibula complex. This septum runs from just behind the medial edge of the tibia over to the posterior intermuscular septum. This septum and the muscles associated with it are quite hard to palpate -- or at least it is hard to talk you through it on a printed page. The tendons can be felt just above and behind the ankle on the medial side, though take care with the tibial nerve. Besides, there is not much you can do with those tendons.

You can approach the muscles from the inside of the leg: put your model on the side, with the upper knee and hip flexed so that you have access to the inner aspect of the lower leg lying on the table. Place your fingertips just on the border between the tibia and the muscle behind it and let your fingers "swim" into the leg. You may be surprised at how tight the myofascia under your fingers is, and your model may be surprised too. The pain here is stored pain, from tightness, which can be melted through gentle but persistent work.

Fig. 6B - The extensions of these compartments along tissues of the knee provides the key to how the fascial compartments link to the tissues above.
Another way to approach the compartment involves lying your model supine and placing one set of fingers just behind the tibia as before, with the other set on the posterior intermuscular septum (see Fig. 4). Get close to your model's leg and let your elbows go wide, so that it is shoulder-power and not finger-power in your hands. Bring the fingertips of your two hands slowly toward each other, essentially "pinching" the lower leg between your two hands. Have your model move slowly through the range from dorsiflexion to plantarflexion and back again. This will bring fluid and dawning awareness into this often-forgotten area. Be sure you are right behind the bone on the inside, and on the posterior intermuscular septum with the outside hand. If you are on muscle instead of between the fascial planes, the pain caused is greater and the effectiveness decreases.

Connections Above and Below
Now that we have delineated the compartments of the lower leg and identified the fascial walls that separate and create those compartments, let's look at the fascial connections that proceed in both directions from the compartments.

Looking down, the anterior compartment, as we noted, runs under the retinacula at the ankle, splitting into six or seven tendons (depending on whether you have a peronius tertius or not) that span the top of the foot from inside to outside. The lateral compartment runs behind the malleolus to the outside and inside of the metatarsals. The deep posterior compartment runs down the inside of the ankle to the toes and the underside of the metatarsals. The superficial posterior compartment runs down the heel and is continuous with the plantar fascia, the sheet that lines the bottom of the foot -- so this connection also ends more or less at the underside of the toes, though at a more superficial level than the deep compartment.

Fig. 6C - The lateral compartment of the lower leg has a natural affinity for the lateral tissues of the thigh - the iliotibial tract. But it als has a clear connection with the lateral hamstring. Your body works out these choices automatically, depending on the second-by-second response to the physical forces occassioned by your movement, gravity and the environment.
Looking upward gets us into more interesting territory. The superficial posterior compartment -- gastrocs, etc. -- clearly interlinks with the hamstrings to continue up the back of the leg and into the back (Fig. 6A). The deep posterior compartment goes over the back of the knee, but then moves medial in the thigh to link with the adductor group, which is then fascially linked to the pelvic floor and psoas group. The lateral and anterior compartments present us with choices. The top of the anterior compartment contains the tibialis anterior. If we look at the fascial connections that run up from here, we can see we have a choice. There is a very clear connection to the anterior part of the iliotibial tract (ITT) to the outside, to the sartorius on the inside, or a direct route straight up with the rectus femoris and quadriceps group (Fig. 6B). The lateral connection goes up through the ITT and on around the body in a spiral (see "Anatomy Trains," Massage Bodywork, April/May 2000 for a full discussion of these connections). The straight-up connection onto the quadriceps is obviously more in use during straightforward flexion and extension, movements in the sagittal plane.

The lateral compartment likewise has a dual connection, which you can see if you refer back to Fig. 5. From the top of the peroneus longus and the head of the fibula, a fascial link -- sometimes labeled the anterior ligament of the head of the fibula -- runs up and forward onto the middle and posterior part of the ITT. Another clear link runs from the head of the fibula up and back onto the lateral hamstring, the biceps femoris. The connection onto the ITT is used for steadying lateral motions through the leg. The connection onto the hamstring connects the heel with the sacroiliac joint, and the back of the body in general.

So, working the lower leg is not merely an end in itself, but a doorway into many of the body's fascial planes. This can be useful in understanding why freeing the leg can have such distant effects on the upper body. Everything's connected, but some things are more connected than others.

Thomas Myers, Certified Advanced Rolfer(R), LMT, NCTMB, studied directly with Drs. Ida Rolf and Moshe Feldenkrais, and has practiced integrative bodywork for more than 25 years in a variety of cultural and clinical settings. Myers directs Kinesis, Inc. that develops and runs training courses internationally for manual and movement therapists. He served as a founding member of the NCBTMB, and as chair of the Rolf Institute's Anatomy faculty. His articles have appeared in a number of magazines and journals, and a book is now underway on his "Anatomy Trains" Myofascial Meridians approach. Myers retains a strong interest in perinatal and developmental issues around movement. His practice in Boston combines structural integration, physiological rhythmic sensitivity and movement. He lives, writes and sails on the coast of Maine.

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