The most superior muscle of the deep posterior compartment of the lower leg is the popliteus muscle. The plantaris muscle allows minor plantar flexion as well. However, the gastrocnemius muscle itself can also facilitate flexion of the knee. The triceps surae muscles provide for plantar flexion of the foot. The plantaris muscle is commonly a source for grafting material. This muscle originates on the lateral supracondylar line of the femur and inserts onto the tuberosity of the calcaneus adjacent to the AT. ĭeep to the triceps surae lies the plantaris muscle. As a unit, the gastrocnemius and soleus muscles form the triceps surae. The soleus muscle originates on the posterior surface of the fibula as well as the soleal line on the tibia. Between the AT and the overlying superficial fascia is a sub-calcaneal bursa that allows for frictionless motion between skin and tendon.Ī deep calcaneal bursa between the tendon and bone facilitates frictionless gliding of the tendon over the bone. The gastrocnemius directly overlies the soleus muscle, and together these two muscles blend into a calcaneal (Achilles) tendon (AT), which inserts into the tuberosity of the calcaneus. The medial is the larger of the two. The medial head originates at the femur and the medial femoral condyle whereas the lateral head originates at the femur and lateral femoral condyle. The gastrocnemius muscle is made up of separate lateral and medial heads. Muscles of the posterior compartment are in two subdivisions: a superficial and deep layer. During midstance and terminal stance, in particular, the plantar flexors of the ankle play a pivotal role as they eccentrically control dorsiflexion, and concentrically allow acceleration of the foot. The stance phase of gait can further divides into a heel strike (where initial contact is made with the ground), a loading response (where the weight of the body is accepted), a midstance (where the knee stabilzation occurs), and a terminal stance (where mass is accelerated forward). Gait is most commonly subdivided into a stance phase and a swing phase (although additional phases can exist depending on clinical scenario). Independent activation, as well as coordination amongst the seven muscles of the posterior leg, is crucial in maintaining balance, facilitating gait, and allowing actions such as stair climbing, jumping, and landing. The popliteus muscle controls weak flexion of the knee and medial rotation of the tibia. The tibialis posterior is primarily involved in ankle plantar flexion as well as inversion of the foot. The flexor digitorum longus is involved in flexion of the other four toes of the foot, plantarflexion of the ankle as well, and also maintains the lateral and medial longitudinal arches of the foot. Additionally, it supports the medial longitudinal arch of the foot. The flexor hallucis longus is primarily involved with flexing the big toe while also having limited contribution to plantar flexion of the ankle. The deep posterior compartment muscles include the flexor hallucis longus, flexor digitorum longus, tibialis posterior and popliteus muscles. The plantaris, a muscle that is thought to be absent in 10% of the population, is also involved in plantar flexion of the ankle but plays a limited compared to the other two superficial posterior muscles. The soleus is involved in plantar flexion of the ankle, irrespective of knee position. The gastrocnemius is involved in plantar flexion of the ankle, while the knee is in extension, and also is involved in flexing the leg at the knee joint. Together these three muscles form the triceps surae. The three muscles within the superficial posterior compartment include the gastrocnemius, soleus, and plantaris muscles. However, current thinking realizes that fascia, such as that of the posterior leg compartment, are not only involved in creating osteofascial compartments for muscles but also provide protective tunnels for neovascular bundles irrespective of limb positions, facilitate venous return, act as protective sheaths, dissipate external pressures, and are clinically significant in the spread or containment of infections. It was traditionally felt that the fascia overlying specialized organs and tissues within the body are irrelevant and only served to hold in place a particular tissue type. Within the posterior compartment of the leg, an additional septum further separates the compartment into two additional layers superficial and deep. The divisions of the lower leg are made up by intermuscular septa that are extensions of the overlying fascia.
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