The Shoulder

instability

Knee Surg Sports Traumatol Arthrosc 1993;1(3-4):152-158

Function of the glenohumeral ligaments in active stabilisation of the shoulder joint.

Jerosch J, Steinbeck J, Clahsen H, Schmitz-Nahrath M, Grosse-Hackmann A

The joint capsules and the glenohumeral ligaments of 12 human shoulder specimens were histologically investigated by light microscopy. Serial sections of 15 microns thickness were cut. The tissue was stained following the haematoxylin-eosin and van Giesson techniques. For specific identification of neural elements we made use of a special silver impregnation technique, described by Novotny, for staining axons in peripheral nerves. Axons of different diameters ranging from 0.2 microns to 70 microns were discovered within the ligaments. Close to the humeral site we found small nerves forming neurovascular bundles. Within their connective tissue sheaths, the axons exhibited a serpentine configuration, which may give extra length and may allow stretching of the nerve during motion. Most of the axons discovered were located in the subsynovial layer of the ligaments. In general the diameter of these subsynovial axons did not exceed 10 microns. In addition to these axonal structures, we detected nerve endings whic h can be classified according to Freeman and Wyke as type II mechanoreceptors (Pacinian corpuscles). These mechanoreceptors had a diameter of approximately 150 microns. They were also positioned directly beneath the synovial membrane and close to the humeral site of insertion of the ligaments. Clinical significance: The described neural structures in the glenohumeral ligaments are of particular clinical importance in the light of the high incidence of recurrent shoulder dislocation and concomitant Bankart lesions. The mechanoreceptors located in the glenohumeral ligaments may control the stabilising shoulder musculature. On this premise, rupture or detachment of these ligaments will lead to a loss of a feedback mechanism.

Clin Orthop 1996 Sep;330:35-39

Role of proprioception in pathoetiology of shoulder instability.

Warner JJ, Lephart S, Fu FH

Proprioception is a specialized sensory modality that gives information about extremity position and direction of movement. This kind of afferent sensory feedback is probably important in mediating muscular control of the shoulder joint. As this articulation is minimally constrained, such a coordinated dynamic control of muscles about the joint is necessary for stability during arm motion. The authors evaluated proprioception in individuals with normal shoulders, unstable shoulders, and after surgical stabilization, by assessing threshold to detection of passive motion and the ability to passively reposition the arm in space. In normal shoulders there is no difference between the dominant and nondominant shoulder, though in unstable shoulders there is a significantly decreased proprioceptive ability. Surgical stabilization normalizes proprioception of the shoulder.

Sportverletz Sportschaden 1995 Mar 9:1 1-8

W�lker M, Rossig S, Korell M, Thren K.

Dynamic stability of the glenohumeral joint. A biomechanical study

Stability of the glenohumeral joint with an anterior, posterior and inferior displacement force of 50 Newton was measured in a dynamic shoulder model. Controlled hydrodynamic actuator forces were applied to the deltoid muscle and to the rotator cuff in seven anatomic specimens. During elevation of the arm, the position of the humerus was measured with a six-degree-of-freedom ultrasonic sensor device. The rotational center of the humeral head was used as reference point for translation. A displacement force of 50N led to significant humeral head displacement anteriorly and posteriorly, but not inferiorly. A 50% reduction of rotator cuff forces increased anterior displacement by 46% and posterior displacement by 31%. Venting of the glenohumeral joint space and of the subacromial bursa resulted in a 50% increase of anterior displacement, a 19% increase of posterior displacement and in significant inferior displacement. This study demonstrates that, in addition to passive stabilizers and negative intraarticular pressure, rotator cuff force significantly contributes to stabilization of the glenohumeral joint during arm motion. Muscle strength and coordination should gain more emphasis in the diagnosis and treatment of shoulder instability.

Clin Orthop 1994 Jul304 84-90

Shoulder instability caused by rotator cuff lesions. An in vitro study.

Loehr JF, Helmig P, Sojbjerg JO, Jung A.

Although many clinical and experimental studies have been published on shoulder instability, little is known about the relationship between degenerative changes of the cranial part of the rotator cuff and shoulder instability. The fact that some cuff lesions cause few symptoms and do not progress, while others are not only incapacitating but also progress to massive ruptures and cuff arthropathy, is still not well understood. In this study the motion patterns of the intact joint, and changes induced by a division of the supraspinatus tendon alone or of the supra- and infraspinatus tendons, were investigated in cadaver specimens. The results demonstrate that a one tendon lesion does not influence the motion pattern, whereas a two tendon lesion induces significant changes compatible with instability of the glenohumeral joint.