Compartmentalization in the pig latissimus dorsi muscle

Portions of the latissimus dorsi (LD) muscle are frequently employed as free muscle or myocutaneous grafts. The functional consequences for both the graft and the remaining donor tissue must depend in part on the neural organization of the muscle. Previous anatomical and clinical reports have suggested that the LD is organized into independently innervated segments, but experimental documentation has been lacking. This study investigated the neural organization of the LD in pigs using (1) synchronous electromyography (EMG) of several sites within the LD and motion analysis of the shoulder and forelimb, and (2) dissection and stimulation of the primary branches of the thoracodorsal nerve, followed by histochemical analysis, to delineate the areas innervated by each. The findings indicated that while there is minor overlap between adjacent segments, the LD can be considered as consisting of three semi-independent compartments. Further, the teres major is linked to the LD functionally as well as anatomically, so that the two muscles can be considered as a four-part complex.