As sports physiotherapists we regularly assess and treat patients and athletes with shoulder instability. It has been suggested that glenohumeral instabllity affects up to 2% of the general population (Ahlgren et al., 1978). However, we know that posterior instability is much less common accounting for somewhere between 2 and 10% of these cases (Tannenbaum & Sekiya, 2011). 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 instability 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 stabilisers of the posterior shoulder are:
- Glenoid Surfaces
- Cartilage Surfaces
- Glenoid Labrum
- Posterior Shoulder Capsule
- Posterior Glenohumeral Ligaments (with their labral attachments): most importantly the posterior band of the inferior glenohumeral ligament.
- The anterior stabilisers of the shoulder (including anterior GH ligaments and capsule) will also prevent excessive posterior translation of the humerus.
The dynamic stabilisers 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 Instability
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).
Pathogenesis of Posterior Shoulder Instability
Posterior shoulder instability is generally caused by one of the following three mechanisms (Tannenbaum & Sekiya, 2011). The shoulder can be:
1. Torn Loose: through a single event of macrotrauma. The mechanism is an axial load to a slightly flexed shoulder. It is worth noting that a subluxation will likely only injure the posterior capsulolabral structures, however, with a dislocation the anterior structures will be injured also.
2. Worn Loose: through repeated events of microtrauma. The mechanism is small axial loads to the posterior capsulolabral structures such as bench press or a “don’t argue” fend.
3. Born Loose: this is when congenital or developmental issues are at play. These may include:
- Soft-tisse abnormalities: such as those in Marfans or Ehlers-Danlos Syndrome
- Glenohumeral Dyslpasia
- Glenoid Retroversion (Weishaupt et al., 2000)
Assessment of Posterior Shoulder Instability
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 (Robinson & Aderint, 2005). 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 (Tibone et al., 1993):
- 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
- ROM and RIMT 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 (Steinitz et al., 2003)
- Likely that flexion, adduction and internal rotation will be painful
Special Tests For Posterior Shoulder Instability
Posterior Stress/Apprehension Test
The diagnostic accuracy of these tests is not well established.
Imaging for Posterior Shoulder Instability
X-Rays: may be normal. Standard views are essential. To identify a Reverse Hill-Sachs Lesion you will require an axillary-lateral view.
CT: useful for identifying the size and orientation of:
- Reverse Hill-Sachs Lesion
- Posterior Glenoid Bone Loss
- Bony Bankart Lesion
MRI: ideal for the examination of the posterior capsulolabral complex; including reverse bankart lesions. When correlated with the physical examination MRI has shown accuracy for labral pathology of greater than 90% (Gusmer & Potter, 1995).
Conservative Physiotherapy Management for Posterior Shoulder Instability
The consensus in the literature is that conservative physiotherapy management is the optimal first line of treatment (Tannenbaum & Sekiya, 2011). This is not true in the following cases:
- Significant Bony Pathology
- Functional Instability remains following closed reduction i.e. internal rotation re-dislocates shoulder.
- Greater than 6 months failed conservative management
However, the optimal physiotherapy rehabilitation for posterior shoulder instability has not been determined or widely studied. The following information is loosely based on various rehabilitation programs for both posterior and multi-directional shoulder instability (Tibone & Bradley, 1993; Moseley et al., 1992). The time-frames for each “Phase” will be very individualised for each patient.
NB: This rehabilitation program will follow a period of sling immobilisation (preferably in neutral or external rotation), timeframes are condition dependent but may be up to 4 weeks (Gerber, 1997).
Phase 1 (Acute)
- Modalities for pain
- PROM and AAROM exercises (avoiding end range adduction, internal rotation, flexion)
- Isometric to isotonic rotator cuff strengthening (DB’s or Theraband)
- Scapular and Shoulder Girdle strengthening as tolerated (Traps, Delts, Serratus Anterior etc)
- Progress mobilisations and ROM as required
- Increase RC challenges (resistance and position i.e. 45 degrees to 90/90)
- PNF Patterns
- Heavier shoulder girdle strengthening
- Wall push-ups plus (recruiting serratus anterior) to challenge posterior restraints. Careful.
- Where appropriate commence of a “Return to Throwing Program”
- Advanced strengthening
- Advanced “Return to Throwing Program”
- Challenging shoulder strength exercises, including overhead work (military press, curl and press)
- Floor push ups eventually progress to bench press
- Required skill work with progressive return to full training
- Graduated return to play
Surgical Management for Posterior Shoulder Instability
Inevitably there will be cases that you will have to refer the patient to their orthopaedic specialist. When they get there they will have a number of surgical options. These are selected on an individual case basis (Tannenbaum & Sekiya, 2011; Robinson & Aderint, 2005). There is not enough evidence to distinguish between the success rates of any, and the surgeon’s preference often guides decision making. As you know, we don’t make the surgical decisions, so I rarely labour the point of surgical options. Regardless, here is a list of the options frequently utilised for posterior instability/dislocations:
- Reverse bankart repair: obvious indications
- Arthroscopic capsular plication: unidirectional posterior instability
- Open postero-inferior capsular shift: bidirectional instability
- Posterior bone block or posterior wedge osteotomy: glenoid osseous lesions
- McLaughlin’s procedure or Neer’s modification of McLaughlin’s: smaller reverse Hill-Sachs lesions
- Humeral head allograft: large reverse Hill-Sachs lesions
- Open reduction internal fixation: significant fracture-dislocations
- Shoulder replacement: when underlying osteoarthritic changes are evident
Given the fact that posterior dislocation or instability is relatively rare there is a dearth of quality evidence. It is challenging to make accurate judgements about most effective form of therapy or surgery and the prognoses of either. We do know the following are correlated with less favourable outcomes (Robinson & Aderint, 2005):
- Late diagnosis of dislocation
- Large humeral head defect
- Secondary humeral head deformity
- Concomitant proximal humeral fracture
Take Home Messages
- Posterior shoulder instability is more commonly seen in certain sports.
- Shoulders can be born loose, torn loose, or worn loose.
- Accurate diagnosis requires a combination of subjective, objective and imaging information.
- Physiotherapy is (in most cases) the first line of treatment: the best rehabilitation program is not well established.
- Surgical options are many: the most effective is not well established.
- There are some established indicators of less favourable outcomes.
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