Muscles may contribute to shoulder dislocation and stability.

Joint instability is one of the most common human afflictions, affecting not only the hip, knee, and shoulder but all joints of the body. Surgical repair for joint instability is done commonly, yet has not been able to restore function consistently. Pain, recurrence of instability, joint stiffness, muscle injury, and degenerative joint disease are all too common sequelae. Because the glenohumeral joint is most commonly dislocated, efforts have been directed to understanding shoulder instability. Study has included not only the static restraints (capsulolabrum, articular surfaces, intracapsular pressure), but also their important interplay with the dynamic restraints (shoulder muscles). Furthermore, not only were muscles known to stabilize the joint studied but also may have contributed to dislocation. An in vitro, cadaveric model that included relevant shoulder muscles and a mechanism of dislocation similar to an in vivo mechanism was developed. The capsulolabral pathoanatomy that occurred after dislocation was studied. Increased understanding of joint dislocation may improve functional results after rehabilitation and surgical repair, not only at the shoulder, but also at all other joints.