Q: I'm finding quite a bit on the Internet about anterior shoulder dislocations but not much about posterior dislocations. What are the guidelines for rehab and recovery for this kind of injury?
A: Shoulder dislocations are not uncommon. Most dislocate forward (called an anterior dislocation). Less often are the posterior shoulder dislocations. As the name suggests, a posterior shoulder dislocation occurs when the head of the humerus (upper arm bone) pops backwards out of the shoulder socket.
As you have discovered, there isn't a great deal of information about the results and recovery of these injuries. Most of the published studies are actually individual cases or reports of a handful of patients. But there was a recent study done a group of orthopedic surgeons from The Shoulder Injury Clinic in England.
They took the time to look back at their medical records to find 112 patients with posterior shoulder dislocations. By reviewing the charts, they were able to put together a picture of what those patients looked like (called patient demographics). By analyzing the data collected, they were able to identify predictive factors for high- and low-risk of complications. And they looked at treatment and treatment results for patients with and without complications.
The most common complication following posterior shoulder dislocation was recurrent instability. Recurrent instability means the shoulder dislocated a second time or the shoulder could slip in and out of the joint (called subluxation). They found that when the force of the first dislocation was enough to damage the head of the humerus, the risk of a second dislocation (or recurrent subluxation) went up dramatically.
Other risk factors for recurrent dislocations were age (younger age -- less than 40) and seizure as a cause of the first dislocation. In more than half the cases of recurrence in this group, the second dislocation also occurred during a seizure. Evidently, the force of shoulder muscle contractions during the seizure is enough to pull the shoulder out of joint.
Treatment consisted of wearing a sling for four weeks along with gentle movement exercises. Once the sling was removed, then the patients went to physiotherapy for a 12-week program of joint motion and strengthening exercises. If the shoulder dislocated again, then a longer physiotherapy program was needed. In some cases, surgery to repair the torn soft-tissues and bone lesions was needed to restore shoulder stability.
Even with treatment, all patients still showed loss of normal shoulder movement and function two years after the injury. The authors commented that it may be the case that all posterior shoulder dislocations would do better with surgery rather than conservative care. They are investigating this theory.
For those patients who are not at risk of recurrent dislocation, mild deficits in function may be acceptable. They may be able to get along just fine without surgery to repair damage done to the shoulder as a result of the dislocation. Those individuals who are at risk for another dislocation may do better with early surgical intervention. Future studies are needed to prove or disprove that idea.
Reference: C. Michael Robinson, BMedSci, FRCSEd(Orth), et al. The Epidemiology, Risk of Recurrence, and Functional Outcome After an Acute Traumatic Posterior Dislocation of the Shoulder. In The Journal of Bone and Joint Surgery. September 7, 2011. Vol. 93-A. No. 17. Pp. 1605-1613.
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