As sports injury therapists we regularly assess and treat patients and athletes with shoulder injury and pain. It has been suggested that shoulder injury and pain can effect up to 2% of the general population. However, we know that posterior shoulder instability is much less common accounting for somewhere between 2 and 10% of these cases. The reason why it is important for use is that these presentations are most common in athletes, secondary to either overuse or a traumatic episode. This makes knowledge of evidence based management and diagnosis of posterior shoulder injury and pain particularly pertinent.
Whilst I never labour the anatomy too much, as it should pretty well be general knowledge, here is a quick run down.
The static stabilizers of the posterior shoulder are:
- Glenoid Surfaces
- Cartilage Surfaces
- shoulder Labrum
- Posterior Shoulder Capsule
- Posterior shoulder Ligaments (with their labral attachments): most importantly the posterior band of the inferior shoulder ligament.
- The anterior stabilizers of the shoulder (including anterior GH ligaments and capsule) will also prevent excessive posterior translation of the humerus.
The dynamic stabilizers of the posterior shoulder are:
- Teres Minor
Dynamic stability is provided through the mechanisms of “scapulohumeral balance” and “concavity compression” (Lippit & Matsen, 1993).
Classification of Posterior Shoulder injury and pain
Hawkins and McCormack (1988) divided patients with posterior shoulder instability into 3 categories:
- Acute Posterior Dislocation
- Chronic Posterior Dislocation (which is fixed or locked)
- Recurrent Posterior Subluxation
The majority of the patients/athletes that you see would likely fit nicely into category 1 or 3. However, we know that posterior shoulder instability can come in many forms. It is usually seen as a component of the following:
- Unidirectional (pure posterior instability)
- Bidirectional (both posterior and inferior)
- Multidirectional (which includes anterior, inferior and posterior: think AMBRI instability).
Assessment of Posterior Shoulder injury and pain
It is important to maintain a high index of clinical suspicion in these cases, as it has been suggested that up to 50% of posterior shoulder dislocations are misdiagnosed on initial medical consultation. There are some sports or athletic pursuits in which posterior shoulder instability is more common. If you work with these athletes, you will encounter posterior shoulder instability in your career. The athletes of the following sports are at risk
- Overhead throwers e.g. pitchers
- Weight Lifting
The athlete will often report:
- Mechanism: similar to that discussed in “Pathogenesis” above
- Pain: aching pain along posterior joint line, superior shoulder, or biceps area
- “Weakness” may be perceived by the athlete
Shoulder injury Physical Examination
- ROM will depend on the extent of damage, chronicity and nature of instability (dislocation vs. subluxation)
- Concomitant rotator cuff tears are uncommon but should be excluded.
- Likely that flexion, adduction and internal rotation will be painful.