Friday, August 8, 2008

Swimmers and Unstable Shoulders

The 2008 Summer Olympics are coming up, and one of the main events will be swimming. Many eyes will be on Michael Phelps, who won eight medals at the 2004 Summer Olympics:

Swimmers like Michael Phelps are athletes who repeatedly stretch the shoulder girdle, and the capsular attachments of the glenohumeral joint. This can lead to ligamentous laxity, particularly in patients predisposed to this condition on a genetic basis. Ligamentous laxity can lead to shoulder instability, with repeated subluxations and dislocations.

Shoulder instability can be in one direction (anterior or posterior), or be multidirectional. Most cases of multidirectional instability are atraumatic in nature, and are related to increased joint volume and capsular laxity.

22 year-old male with history of multidirectional instability. An MR arthrogram was requested to evaluate the capsule and labrum. Axial image reveals a markedly capacious posterior joint:

For comparison, here is a patient without a history of posterior instability; note that the posterior capular volume is markedly smaller:

Sagittal image from the patient with multidirectional instability confirms the patulous nature of the posterior joint, particularly posteroinferiorly (yellow arrows). Green arrow= coracoid process, an anterior structure:

Dewing et al. published an analysis of this issue recently (AJSM 36:515-522, 2008). They analyzed capsular area in patients with anterior, posterior, and multidirectional instability. They found that capsular area is increased in the setting of posterior and multidirectional instability, but not in patients with anterior instability. They pointed out that it may be difficult to reproducibly measure joint volume, due to variability in the amount of contrast injected between patients. In addition, they also noted that gravity might play a role in the relative size of the anterior aspect of the joint. (Patients are scanned in the supine position, and it is unclear what would happen to the relative volume of the anterior and posterior aspect of the joint in the prone position).

My own experience suggests that one should examine the capacity of the glenohumeral joint when analyzing an MR arthrogram, particularly in patients with a history of multidirectional instability. Some of these patients will have no labral abnormality whatsoever, but will have clear evidence of increased posterior or posteroinferior joint capacity. I will comment on this in my report, noting the absence of a labral tear, but the presence of an abnormally increased joint volume. In addition, my anecdotal observations of increased anterior joint volume in the setting of repeated anterior dislocations are consonant with the observations of Urayama et. al, (
AJSM 31:64-67, 2003) who reported capsular elongation in patients with recurrent anterior dislocation.

Vic David MD

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