Exertional compartment syndrome is activity-related pain caused by an increased intermuscular pressure within an anatomic compartment. In the leg, there are four compartments that contain muscle, blood vessels, and nerves. The compartments are enclosed by fascia, which limit muscular expansion during activity and can cause compression of the contents of the compartment. As pressure within the compartment approaches the mean arterial pressure, the blood flow through the microvasculature is diminished and ischemia ensues.

Knowledge of the anatomy of the lower leg is vital to the diagnosis of exertional compartment syndrome (Fig. 65.1). The anterior compartment contains the extensor hallucis longus, extensor digitorum longus, peroneus tertius, and tibialis anterior as well as the deep peroneal nerve. The lateral compartment contains the peroneus longus and brevis as well as the superficial peroneal nerve. The superficial posterior compartment contains the gastrocnemius and soleus muscles and the sural nerve. The deep posterior compartment contains the flexor hallucis longus, flexor digitorum longus, and posterior tibialis muscle as well as the posterior tibial nerve.

The patient is usually asymptomatic upon initiating exercise. The pain will begin at a predictable time during the workout. The pain is described as aching or cramping associated with feelings of swelling, fullness, or tightness. Dysesthesias often accompany the pain along the nerve within the affected compartment. Patients may also complain of altered running style. For example, a runner may state that the foot seems to be slapping the ground when the pain comes on.

Injury to the posterior tibial tendon may occur acutely or as a component of chronic overuse syndrome. The posterior tibial tendon helps invert and plantarflex the foot and has an important role in maintaining the longitudinal arch.

Patients with posterior tibial tendon injury often report pain along the medial aspect of the leg posterior to the medial malleolus. The onset of symptoms is usually gradual with increases in such activities as walking, running, or jumping.

Peroneal tendon pathology is a commonly missed source of chronic lateral-sided ankle pain. The spectrum of peroneal tendon injury includes tenosynovitis, tendon tear, and peroneal tendon instability.

The peroneus longus originates from the proximal aspect of the lateral fibula. Its tendinous portion runs posterior to the lateral malleolus before inserting primarily onto the plantar proximal surface of the first metatarsal. Its function is primarily eversion and plantarflexion of the foot. The peroneus brevis originates from the lateral fibula. Its tendinous portion courses anterior and medial to the peroneus longus tendon at the level of the ankle and inserts onto the base of the fifth metatarsal. Its primary function is to evert the foot.

The patient will often complain of lateral ankle pain that localizes posterior to the lateral malleolus. The patient may also relay a history of pain, “popping,” and transient swelling in this area usually after an inversion injury.

The os trigonum is an ossicle present in 7%-11% of the population as a continuation of the posterior talar process. Painful os trigonum syndrome is one cause of posteromedial ankle pain. This syndrome is most prevalent in athletes who perform frequent or forced plantarflexion. The condition may be misdiagnosed as other conditions such as Achilles tendonitis (14).

Presentation is commonly with pain in the posterior medial ankle that may be worsened with plantarflexion activities (en pointe position in ballet).