Issue: June 2011
June 01, 2011
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Internal rotator and external rotator weakness associated with recurrent anterior instability

Edouard P, et al. J Bone Joint Surg Am. 2011;93:759-765. doi:10.2106/JBJS.I.01791

Issue: June 2011
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Recurrent anterior instability may lead to weakness in the internal and external rotator, with side-to-side differences depending on the side of hand dominance, according to French investigators.

The investigators performed a controlled study of 37 patients with unilateral recurrent anterior post-traumatic shoulder dislocation and 11 healthy, nonathletic subjects. Side-to-side comparisons, as well as comparisons with the control group were used to investigate the association between internal rotator and external rotator strength with regard to shoulder instability.

A dynamometer was used to evaluate internal rotator and external rotator strength, with patients seated and the shoulder abducted 45° in the scapular plane. According to the study abstract, tests were performed at 180°/s, 120°/s, and 60°/s in concentric mode on both sides.

“The association between shoulder instability and internal rotator and external rotator strength was associated with side-to-side differences,” the authors wrote. “Compared with a control group, strength values were lower on the pathological shoulder side of the patients with shoulder instability than on the healthy contralateral shoulder of control subjects at 180°/s and 120°/s.”

The investigators added that side-to-side differences were increased upon involvement of the nondominant upper extremity side, with a decrease occurring upon the involvement of the dominant side. No association was found between glenohumeral joint instability and external rotator to internal rotator ratio.

The investigators noted further prospective studies are needed in the effort to determine whether the weakness is a cause or effect of instability.

Perspective

I read the article in J Bone Joint Surg Am by Edouard et al on rotator cuff strength in recurrent anterior shoulder instability with great interest. This is a well-designed, level III observation-controlled study trying to answer the question of whether there is an association between isokinetic internal rotator and external rotator muscle strength and glenohumeral joint instability in patients with nonoperatively treated recurrent anterior instability.

The methods utilized in this study were appropriate for the question the authors were trying to answer. The findings of the study showed that internal rotator and external rotator weakness was associated with recurrent anterior instability, and side-to-side differences depended on the side of hand dominance. The authors concluded that the use of a control group which they utilized in this study rather than the contralateral limb was most appropriate in the analysis of the influence of constraints on shoulder strength.

In conclusion, this study successfully further evaluated the question of rotator cuff strength deficits in unstable shoulders. It adds to our understanding of traumatic anterior shoulder instability and stimulates further discussion and questions. The authors raise a valid question as to whether the notable internal and external rotator muscle strength differences were prevalent before or after the index shoulder instability. This study raised several questions in my mind for possible future related studies:

  • Does rotator cuff rehab after instability help to return the rotator cuff muscle strength mismatches closer to baseline?
  • Is there any correlation between rotator cuff strength deficits and relative risk of recurrent instability?

— Joseph A. Abboud, MD
Clinical assistant professor of orthopaedic surgery
University of Pennsylvania Health System