Fascias of the leg and foot
Like fasciae of most parts of the limbs, the fasciae of the leg and foot form closed spaces which end proximally and distally at the joints. Inflammations within such closed spaces or compartments spread chiefly in a distal direction.
However, formation of pus (suppuration) from pus-forming (purulent) infections in the lateral compartment of the leg can ascend proximally into the popliteal fossa (a fat-filled diamond shaped space relatively confined posterior to the knee and is traversed by all neurovascular structures passing between the thigh and the leg).
Fascia and septa divide other soft and bony tissues of the leg into three fascial compartments, namely, anterior, lateral, and posterior compartments. On the foot, there are superficial (subcutaneous) and deep fasciae. The subcutaneous tissue lying deep to the dorsal skin is loose and prone to oedema. On the plantar surface, the subcutaneous tissue is tough and fibrous than in other areas of the foot.
Fasciae of the leg
The deep fascia of the leg covers only muscles, being attached to the periosteum at all places where bone is subcutaneous.
Thus at the anterior part of the leg, there is only subcutaneous tissue of the tibia on the medial side. This superficial fascia of the tibia has subcutaneous fat attached to its periosteum.
On the anterolateral side of the leg, there is a deep fascia of the leg. The fascia is dense superiorly, providing part of the proximally attachment of the muscle immediately deep to it.
Inferiorly, two band-like thickenings of the deep fascia form retinacula that bind the tendons of the anterior compartment muscles before and after they cross the ankle joint, preventing them from bowstringing anteriorly during dorsiflexion of the joint. These retinacula are:
- The superior extensor retinaculum: this is a strong, broad band of deep fascia which passes from the fibula to the tibia, proximal to the malleoli.
- The inferior extensor retinaculum: this is a Y-shaped band of deep fascia, which attaches laterally to the anterosuperior surface of the calcaneus bone. It forms a strong loop around the tendons of the fibularis tertius and the extensor digitorum longus muscles.
Fasciae of the foot
The superficial fasciae of the foot are both fibrous and loose, and vary in thickness (strength) and texture. On the dorsal aspect of the foot, the superficial fascia is loose and lies deep to the skin. In the sole of the foot (plantar aspects), it is fibrous. The skin of the foot is also anchored by underlying deep fascia or plantar aponeurosis, which functions to promote the grip of the sole.
The deep fasciae of the foot divide the sole into three compartments, which are:
- Medial compartment of the sole - covered by the medial plantar fascia
- Central compartment of the sole – invests, superficially by the dense plantar aponeurosis
- The lateral compartment of the sole – covered by the thinner lateral plantar fascia.
In the forefoot only, a 4th compartment called the interosseous compartment of the foot exists, and it is surrounded by the plantar and dorsal interosseous fasciae. Also, there is a 5th compartment, the dorsal compartment of the foot, which lies between the dorsal fascia of the foot and the tarsal bones and the dorsal interosseous fascia of the mid-foot and forefoot.
The deep fascia is continuous proximally with the inferior extensor retinaculum and it is thin on the dorsum of the foot. Over the lateral and posterior aspects of the foot, the deep fascia is continuous with the plantar fascia – the deep fascia of the sole.
The plantar fascia has a thick central part and weaker medial and lateral parts. The thick central part forms the dense plantar aponeurosis mentioned above. This plantar aponeurosis resembles the palmar aponeurosis of the palm of the hand, but it is tougher, denser, and elongated.
Plantar fasciitis is a condition in which the plantar aponeurosis is strained and inflamed. This may result from running and high impact aerobics, especially when an inappropriate foot-wear is worn. It causes severe pain in the plantar surface of the heel and on the medial aspect of the foot.