Anatomical dissection of the deep posterior compartment and its correlation with clinical reports of chronic compartment syndrome involving the deep posterior compartment

Patients with clinical presentation of deep posterior chronic compartment syndrome (CCS) frequently have symptoms limited to either proximal or distal components of the deep posterior compartment. In this study the posterior aspect of 15 cadaver legs was dissected to document anatomical separations and delineate boundaries, if any, of the deep posterior compartment and to correlate the findings to these patients. Origins of flexor hallucis longus (FHL), flexor digitorum longus (FDL), and tibialis posterior (TP), as well as whether TP existed in its own osseofascial compartment, were noted. Ten specimens had an identifiable distinct layer of tissue separating the deep posterior compartment into two potentially clinically relevant components. Much of this layer was derived from origins of FDL and its anatomical position in relation to the TP muscle. In seven of these cases, FDL had a significant fibular origin in addition to the well-established tibial origin. This essentially compartmentalized the distal third of the tibialis posterior as it descends anterior and medial to FDL in the lower one-third of the leg in five specimens. No cadaver possessed a significant fascial septum encasing TP and separating it from other deep posterior muscles. This study confirms the existence of a proximal and distal sub-compartment of the deep posterior compartment as a variant and supports the most frequent clinical presentation of deep posterior CCS as involving either the distal or proximal deep compartment, rather than the entire deep posterior compartment. The anatomic arrangement of muscles in the deep posterior compartment creates sub-compartments, which may explain the successful outcomes following a deep compartment release limited to symptomatic portion(s) of the deep compartment.