![]() 5 Bilateral lower extremity involvement occurs in 85-95% of cases with a predilection for the anterior and deep compartments. LLECS has a median age of onset of 20 years old, and the prevalence decreases with age, though it has been suggested that there is an underdiagnosed population within older adults, plateauing around age 50. 3,4 A vast majority (87%) of patients with LLECS participate in sports, with running accounting for 69%. In fact, this may be under-appreciated secondary to poor awareness among medical providers and the public, as illustrated by an average of 22 months from symptom onset to treatment. The incidence of LLECS in the general population is unknown, although some estimate that it accounts for 14-27% of previously undiagnosed exercise-induced leg pain. Epidemiology including risk factors and primary prevention 2 Functional muscular compression and associated occlusion of vasculature has been proposed to create elevated hydrostatic pressures and fluid accumulation within the compartments, thereby explaining the elevated IMPs and common findings on imaging modalities. ![]() 1 It has been recently suggested that venous outflow occlusion may play a significant role in increased compartment pressures and symptom development. There are several proposed contributing factors, which vary from noncompliant anatomical tissues to deviations of anatomical features and build-up of metabolic byproducts. The exact mechanism by which this occurs remains unclear. The increased intra-compartmental pressures are thought to impede tissue perfusion, create a relative oxygen debt, and result in symptom onset. The exact mechanism that causes exertional compartment syndrome is unknown. Symptoms are absent at rest, occur at a well-defined distance, duration or intensity of exercise, and only subside by discontinuation of provoking activity once elicited. The anterior crural septum divides the muscles in front of and lateral to the two bones into an anterior compartment, which contains four muscles including tibialis anterior, and a more laterally placed peroneal compartment, which contains two of the three peroneal muscles.Lower limb exertional compartment syndrome (LLECS), also known as chronic exertional compartment syndrome (CECS), is an overuse syndrome characterized by exercise-induced elevation of intramuscular pressures (IMP) that results in reproducible transient pain, paresthesias, and neuromuscular dysfunction. These two septa are attached to the fibula here, and here. This is the posterior crural septum, lying just in front of the soleus muscle. To see them, we’ll remove the investing deep fascia down to here, exposing several muscles that we haven’t met yet. The other two septa have cumbersome names: they’re the anterior and the posterior crural intermuscular septa. At the ankle, the transverse septum is continuous with the flexor retinaculum. The transverse septum is thin up here, but toward the ankle it becomes thicker. ![]() To see the transverse septum better, we’ll remove the rest of soleus. Three muscles that we haven’t seen yet lie between the transverse septum and the bones. It runs from here on the tibia, to here on the fibula. In front of soleus, this transverse intermuscular septum crosses the back of the leg. Here’s soleus, divided, here’s the investing deep fascia, divided at a lower level. We’ll remove gastrocnemius and soleus, down to here. Together with the interosseous membrane, they divide the muscles of the leg into four compartments, two on the front of the leg, and two on the back. Now we’ll look at the fibrous septa, the singular of which is septum. Distally the investing deep fascia is continuous with the superficial part of the flexor retinaculum, with the peroneal retinaculum, and with the two parts of the extensor retinaculum. The investing deep fascia wraps around the back of the calcaneal tendon, like a sling. It’s attached to the fibula not directly, but indirectly by two fibrous septa here, and here, that we’ll see in a minute. The investing deep fascia is attached to the tibia here, and here. This outer layer is the investing deep fasica. Before we move on to see the muscles that produce inversion and eversion, we need to digress for two minutes, to look at the layer of deep fascia that surrounds all the muscles of the leg, and the three fibrous partitions, or septa that divide the leg muscles into somewhat distinct compartments.
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