Capsular Elongation in Recurrent Anterior Shoulder Instability

Abstract & Commentary

Synopsis: Using a new, MRA-based method in live patients, this study was able to demonstrate capsular stretch with traumatic shoulder dislocations.

Source: Urayama M, et al. Capsular elongation in shoulders with recurrent anterior dislocation. Am J Sports Med. 2003; 31(1):64-67.

Although capsulolabral detachment from the glenoid (Bankart lesion) is well recognized as the "essential" lesion in anterior shoulder instability, permanent deformation (stretch) of the capsule has also been well characterized. The purpose of the present study was to attempt to quantify the amount of capsular deformation with magnetic resonance arthrography.

Twelve patients (11 men and 1 woman) with recurrent traumatic anterior dislocations of the shoulder were studied. The patients studied had an average of 2 previous dislocations (range, 1-4). Both shoulders were studied with the uninvolved shoulder serving as a control. Urayama and colleagues injected 10 cc of gadolinium into the subjects’ shoulders and studied selected axial and coronal MRI views. Using special image analyzing software, the capsular length was measured and recorded for those views and compared to the opposite shoulder. The values were normalized based on the size of the humeral head and were statistically evaluated.

All 12 patients had a Bankart lesion. The anteroinferior capsule was elongated an average of 16-19% more than the opposite (control) side. The inferior capsule was elongated an average of 12-29%. Urayama et al suggest that the capsule should be addressed (capsular shift, plication, shrinkage, etc) at the time of Bankart repair. Urayama et al note several limitations of their study, including not considering the possible effect of different volumes of gadolinium, technical issues regarding the plane of imaging, the effect of scar tissue, the effect of dominant vs nondominant shoulders, and the relatively small numbers of dislocations in their patients.

Comment by Mark D. Miller, MD

Biomechanical studies have demonstrated that capsular deformation does occur with anterior shoulder dislocations. Other studies have shown that stretching of the capsule is progressive—that is, the more dislocations, the more stretching. That is why Urayama et al were correct to point this out as a limitation of their study: Their subjects only had an average of 2 dislocations each. I believe that they are correct, however, in their recommendation to address this capsular laxity at the time of surgery. This can be done with open techniques (capsular shift) or arthroscopic techniques (plication or possibly thermal shrinkage). It would be interesting to perform these procedures in their study population and repeat their measurements.

Although attempts to measure capsular laxity by measuring volume in vivo have demonstrated reduction in these volumes following capsular shift procedures, the technique used to measure volume (injection and aspiration of saline) was variable, and only a small percentage of the fluid injected was recovered.1 We have studied capsular volume reduction in vitro in a cadaver model and found that humeral-based capsular shifts result in more volume reduction than glenoid-based shifts.2 The next phase of this research will compare these results with arthroscopic techniques.

The technique that Urayama et al described may be of benefit to future clinical studies. It would be interesting to use this technique to study patients with atraumatic shoulder instability. Capsular laxity is the only factor in that group. As noted above, the technique could also be used to compare the outcomes of various surgical procedures. Additional studies with more patients (and more dislocation episodes) may lead to further credibility for the use of magnetic resonance arthrography to study capsular laxity associated with shoulder instability.

Dr. Miller is Associate Professor, UVA Health System, Department of Orthopaedic Surgery, Charlottesville,VA.

References

1. Lubowitz J, Bartolozzi A, Rubenstein D. How much does inferior capsular shift reduce shoulder volume? Clin Orthop. 1996;328:86-90.

2. Miller MD, et al. Anterior capsular shift volume reduction: An in vitro comparison of three techniques. J Shoulder Elbow Surg. In Press 2003.