The human locomotor apparatus consists of an active motor system (muscles) and a passive system of transmission (bones and joints) connected by an intermediate formation, the muscular and tendinous insertions. The insertions must be differentiated from the other two systems both anatomically and functionally. These insertions are effected in three principal manners: (1) inlaid piercing into the bony substance through periosteum (tendinous insertion), (2) reinforcing fibrous bundles extending from tendon to ligaments, joint capsule, or other tendons (aponeurosis), and (3) direct adhesion to periosteum of the bone (muscular or tendinomuscular attachment).
The locations of these attachments are therefore spots where tissues of common mesenchymal origin, but often poorly differentiated, meet. Possibly for this reason, insertions show a peculiar reaction to irritative stimuli, often characterized by metaplastic phenomena. Most frequently these stimuli are of traumatic, particularly microtraumatic, origin. The continually recurring concentration of muscle stress at these points provokes a reaction