Saturday, January 05, 2008

Proprioception of the shoulder can be a real issue!

Proprioception of the Shoulder.

Far too often we see people with their shoulders and arms situated incorrectly while on their bikes! Could this be from a lack of detection of internal rotation? A loss of the feedback mechanism seems to be from the loss of control or someone not teaching them. You just don't jump on the bike and ride! There are many things to learn.

Insights into the role of joint proprioception on muscular stabilization of the shoulder was investigated by [ Blasier et al.,1994]who provided information on the central nervous system in the management of muscular activity. Shoulder joint proprioception was measured in a population of persons without known shoulder abnormalities, and it was found that individuals who have clinically determined generalized joint laxity are significantly less sensitive in proprioception. The detection of external rotation is significantly more sensitive than the detection of internal rotation, and it becomes significantly more sensitive as a limit of external rotation is approached. Blasier et al. suggested capsular tightening as one possible mechanism for shoulder proprioception.

Further investigation into joint proprioception was performed by [ Jerosch et al., 1995 ] who harvested the joint capsule, the glenohumeral and coracohumeral ligaments, and used the van Gieson technique coupled with a special silver impregnation for staining peripheral neurons. Axons, of the type II mechanical receptors (Pacini receptors), were discovered in all the ligaments with no detectable relationship to vessels or vessel walls. The significance of the finding is that neural structures discovered in the glenohumeral capsule are of clinical importance, particularly in recurrent subluxation and/or dislocation of the shoulder as they may control stabilization of the shoulder musculature causing a loss of the feedback mechanism.

[ Itoi et al., 1998 ] studied supero-inferior stabilizing functions of the coracohumeral ligament and the rotator interval capsule with the aid of a material testing machine. They found actual translation of the humerus in three instances: with the capsule intact and vented, with the coracohumeral ligament sectioned, and with the rotator interval capsule incised. Moreover, they discovered that with the arm in internal or neutral rotation, venting the capsule significantly increased supero-inferior translation that was unaffected by further sectioning of the coracohumeral ligament or the rotator interval capsule. With the arm in external rotation, only the coracohumeral ligament contributed significantly to inferior instability. Both this ligament and the rotator interval capsule contributed to superior instability to a lesser degree. Thus the coracohumeral ligament is a stabilizer in a superior and inferior direction with the arm in external rotation. Intra-articular pressure that is maintained by the rotator interval capsule is a stabilizer in supero-inferior direction with the arm in internal rotation.

Think of this information the next time you ride. Comfort is good!

No comments: