The muscular anatomy of the leg is divided into four compartments. The anterior compartment consists of the tibialis anterior, extensor hallicus longus, extensor digitorum longus, and peroneus tertius muscles as well as the deep peroneal nerve and anterior tibial artery. The peroneus longus, peroneus brevis muscles, and superficial peroneal nerve make up the contents of the lateral compartment. The superficial posterior compartment contains the gastrocnemius, soleus, plantaris muscles, and the sural nerve. Tibialis posterior, flexor digitorum longus, flexor hallicus longus muscles, the posterior tibial artery, and the tibial nerve are all found in the deep posterior compartment. The various compartments serve to control motion at the ankle and in the foot based on their anatomical location. Each specific muscle has its own function but generally speaking, muscles located in the anterior compartment provide dorsiflexion, muscles in the lateral
compartment provide eversion, muscles in the deep posterior compartment provide plantar flexion and inversion in the foot, and muscles located in the superficial posterior compartment provide plantar flexion at the ankle. All muscles originate in the leg itself with the exception of the gastrocnemius, which originates on the posterior aspect of the femoral condyles, and the plantaris, which originates on the lateral femoral condyle. Muscles that cross multiple joints, the hamstrings, rectus femoris, gastrocnemius, and adductor magnus, are more susceptible to strain injury (1). The gastrocnemius crosses the knee, ankle, and subtalar joint before inserting on the posterior aspect of the calcaneus, making it more susceptible to injury than the other muscles of the leg (2).

Strain or rupture of the medial head of the gastrocnemius is often referred as “Tennis Leg.” Initially this clinical entity was believed to be a strain of the plantaris muscle. The plantaris has a similar anatomical course to the gastrocnemius in the leg, but a review of the literature did not support rupture or strain of the plantaris as a clinical entity. Miller (3) reported on his surgical experience with tennis leg and found the gastrocnemius to be torn in every case while the plantaris was found to be intact. Although the overwhelming majority of muscular injuries to the leg are of the gastrocnemius, two surgically documented cases of plantaris rupture have been reported (4,5). Additionally, tear of the peroneus longus is a rare injury that has also been reported in the literature and should be kept in consideration when evaluating these injuries (6,7,8).

Muscle strains usually occur as a result of stretch. A muscle strain occurs when the tissue is only partially torn; rupture involves a tear of all the fibers of the muscle–tendon unit. The two terms represent a continuum of the same injury. Muscles are more prone to injury during eccentric contraction than during passive stretching alone (9). In eccentric contraction the length of the muscles increases over the course of contraction. Higher muscle forces can be seen during lengthening (10), which can be additive to forces due to the connective tissues (11). Muscle strain often occurs while the muscle is controlling, or decelerating, joint range of motion during activity. This is often the case in many higher speed sports including soccer, basketball, and football. The gastrocnemius muscle has the capability to restrict range of motion at the ankle, specifically dorsiflexion, if it is intrinsically tight. Most muscular injuries to the leg are isolated to the gastrocnemius muscle. They can either be acute sprains or rupture of the muscle itself. Most ruptures occur at the musculotendinous junction. The medial head is most commonly torn. The muscle belly of the medial head is larger than that of the lateral head. Additionally, the muscle fibers are fast twitch. Both are believed to contribute to the frequency of injury to the medial head of the gastrocnemius (12).

Muscle contusion is another frequently seen injury to the muscular structures of the leg. The injury is a result of direct blunt trauma. Contusion can occur to any muscular structure in the leg but is most commonly seen in the muscles of the anterior compartment. Local pain and swelling of the tissues are characteristic of this form of injury.