How Does Position of Immobilization Affect Stability Following Shoulder Dislocation?
Abstract & Commentary
Synopsis: Immobilizing the arm in a position of external rotation improved approximation of a Bankart lesion and capsule to the glenoid in the desired position following both initial and recurrent shoulder dislocation.
Source: Itoi E, et al. Position of immobilization after dislocation of the glenohumeral joint. J Bone Joint Surg Am. 2001; 83-A(5):661-667.
Historically, we have treated patients with the assumption that the method and duration of immobilization following anterior, traumatic shoulder dislocation did not influence outcome. Itoi and colleagues now challenge that notion with a study using MRI to assess the position of the labrum and capsule with varying positions of arm rotation. They studied 19 shoulders including 6 with an initial anterior dislocation and 13 with recurrent dislocation. Patients were scanned with the arm in an internally rotated position that corresponded to the use of a sling with the forearm against the abdomen. Next, they externally rotated the arm as far as comfortably possible (mean, 35°) and a repeat MRI was performed. If the MRI was performed more than 2 weeks out from initial injury, then intra-articular dye to improve the MR resolution was used. The labrum and Bankart lesion position relative to the glenoid neck, including the amount of displacement, separation, and lift-off were all assessed. The actual amount of shoulder rotation was also assessed quantitatively by MRI. Patients with bony Bankart lesions or no Bankart lesion were excluded.
In a position of external rotation, the shoulders had significantly less separation and displacement of the labrum and Bankart lesion. The capsule was found to be better opposed along the anterior aspect of the glenoid with a shorter, detached length. Basically, the labrum and the capsule were closer to the normal anatomic position. These results were statistically significant for both acute and recurrent shoulder dislocations.
Comment by David R. Diduch, MS, MD
Although young patients have a high likelihood of recurrent anterior shoulder instability following dislocation, not everyone develops further dislocations. Also, some patients with chronic instability can spontaneously stabilize. It is possible that some patients with either a fresh or chronic Bankart lesion can somehow heal this in a position that is functional, preventing further instability. Itoi and colleagues in Japan have used the MRI to document for the first time the position of these anterior shoulder stabilizers as they relate to the rotation of the arm following dislocation. They found that when the shoulders were rotated an average of 35° externally, which is where patients were able to maximally rotate it within their degree of comfort, that the labrum and the anterior capsule were much closer to their original anatomic position. The external rotation tightened the anterior capsule as well as the subscapularis, squeezing any hematoma posteriorly in the joint and producing improved coaptation against the glenoid neck. Also, the Bankart lesion was less retracted medially along the neck of the scapular as can be seen when it heals there with an ALPSA lesion.
If we carefully look at the numbers, there is a lot of variability, and the standard deviations are sizeable. However, all of their measurements did reach statistical significance. I think we can conclude from this that not all patients will respond the same, but there seems to be a measurable benefit to immobilize patients with the arm in an externally rotated position if you look at the population as a whole. How this is practically done is another matter. Whether this produces a clinically measurable decrease in the rate of recurrent dislocation is also another matter. These are 2 shortcomings of the study that definitely need to be addressed as we try to apply this information to our patient population. Nevertheless, this paper does provide meaningful information, and if supported by other studies may well change the way shoulder dislocations are treated by all members of the sports medicine team.