Abstract

Posterior shoulder instability is a relatively rare phenomenon compared to anterior instability, comprising only 5-10% of all shoulder instability. Posterior instability most often occurs either as a result of high force direct trauma to the shoulder such as from a motor vehicle accident or indirect trauma such as from seizures or electrocution. Many cases of posterior shoulder instability are the result of micro-trauma that cause repetitive subluxation of the joint, ultimately compromising the shoulder in certain provocative positions. Surgical treatment of posterior instability is indicated only after an extended trial of rest and physical therapy has failed.

Case Overview

History and physical of the patient with suspected shoulder instability

What injury, trauma or repetitive shoulder motions have contributed to the current problem?
Has the patient dislocated? If so, how many times and what was the mechanism?
What maneuvers provoke pain? What is the patient’s reported pain severity on a scale of 1-10 for each of these maneuvers?
What limitations in activity, if any, have occurred as a result of the instability?
Is pain or instability present at rest? Does it interfere with sleep?
Has the patient had conservative treatments including physical therapy, rest, anti-inflammatory medication, and if so, to what degree did these help?

Physical exam

Palpate the shoulder for tenderness and document range of motion compared to the contralateral, normal extremity.
- Any restriction in motion should be compared to the contralateral shoulder.
- Differences between active and passive motion may indicate pain or capsular contracture.
Impingement signs are tested to determine whether any associated rotator cuff tendinitis is present.
If weakness is present during strength testing, it may be from deconditioning or from underlying rotator cuff or deltoid pathology.
The degree of pathologic subluxation is assessed with a Load and Shift test, as well as any apprehension or pain experienced by the patient during provocative testing.
- Pathologic posterior subluxation is indicated by a positive Jerk Test
- A positive Kim test suggests a posteroinferior labral tear or subluxation.
- Circumduction test. A positive test result is highly suspicious of posterior subluxation or dislocation.
- Sulcus sign evaluation. A positive sulcus sign suggests multidirectional instability.

Imaging

Axial T1 Weighted

Axial Proton-density fat saturation

Coronal Proton-density fat saturation

Preoperative MRI arthrogram

T2 Fat suppressed Axial views show a tear of the posterior labrum and a fluid filled paralabral cyst. No apparent bony defects, such as a reverse Hill Sachs lesion, are identified.

Natural history

Posterior instability can be the result of trauma in the form of a direct blow to the anterior shoulder or may occur as the result of indirect forces acting on the shoulder, causing the combined movements of shoulder flexion, adduction, and internal rotation.¹³ Electrocution and seizures are the most common causes of an indirect mechanism resulting in posterior dislocation. Patients with recurrent posterior subluxation may present with more vague symptoms, with pain being the chief complaint. Athletes may report that velocity with throwing is diminished, and a sharp pain may accompany the follow-through phase of throwing. Associated injuries may include superior labrum anterior posterior (SLAP) lesions, rotator cuff tears, reverse Hill-Sachs defects, and chondral injuries.⁴

Options for treatment

The options for treatment at this time would be a continuation of conservative treatment including physical therapy and NSAIDs, however, the patient has failed extensive conservative treatment (>1 year) and continues to be symptomatic with pain and instability. Another option would be an open surgical repair.

Rationale for this procedure

Advantages of an arthroscopic technique include a shorter recovery and rehabilitation time, less risk of joint infection, less risk of bleeding, the ability to visualize the entire shoulder joint with the arthroscope and address any associated pathology, and decreased pain for the patient during the recovery process.

Special considerations

If there is good reason to believe that the patient would not be compliant with the post operative rehabilitation, this would be a relative contraindication to the procedure. Failure of the patient to comply with the recommended post-operative restrictions and therapy protocols could result in a failure of the repair, necessitating re-operation, infection, a stiff shoulder, or an otherwise sub-optimal result. Patients with large bone defects or developmental abnormalities of the shoulder with dysplasia may require a more extensive, open approach. Normal neurologic function of the upper extremity is a necessity for a successful outcome.

Postoperative Care

The patient leaves the operating room in an abduction sling that can be removed for passive range-of-motion exercises at home.
We allow 90 degrees of forward elevation and external rotation to 0 degrees by 4 weeks after surgery.
The sling is discontinued 6 weeks after surgery and active assisted range-of-motion exercises and gentle passive range of motion exercises are progressed.
Pain-free, gentle internal rotation exercises are instituted at 6 weeks.
At 2 to 3 months after surgery, range of motion is progressed to achieve full passive and active range of motion.
Stretching exercises can be instituted for any deficiency in motion at this point.
After 4 months, the shoulder is often pain-free and eccentric rotator cuff strengthening is begun.
At 5 months, isotonic and isokinetic exercises are advanced.
At 6 months, throwing athletes undergo isokinetic strength testing. If 80% of the strength and endurance of the contralateral extremity is attained, a throwing program is begun.
Full, competitive throwing is typically not attained until 12 months after surgery. Nonthrowing athletes are often released to a sport-specific program by 6 months, when 80% of their strength has returned.

Discussion

Etiology and pathophysiology

The important stabilizing structures of the glenohumeral joint are the articular surfaces and congruity of the humerus and glenoid of the scapula, the capsular structures, the glenoid labrum, the intra-articular portion of the biceps tendon, and the rotator cuff muscles. Histologic evaluation of the posterior capsule shows it to be relatively thin and composed of only radial and circular fibers, with minimal cross-linking. Pathologies of the posterior capsule and labral complex are believed to be the main contributors to posterior instability. With the arm forward-flexed to 90 degrees, the subscapularis provides significant stability against posterior translation, and as the arm is placed in neutral, the coracohumeral ligament resists this force. With internal rotation of the shoulder (follow through phase of throwing), the posterior band of the inferior glenohumeral ligament complex is the main restraint to posterior translation.¹ Patients with a chronically locked posterior dislocation have an increased risk of developing chondral injuries and degenerative osteoarthritis. Static posterior subluxations of the humeral head left untreated have been correlated with the presence of arthritis in young adults.¹⁴

Outcomes

Studies have shown rates of recurrence of 0% to 8% and rates of return to sport of 89% to 100%. ^3,7,15 With the advancement of arthroscopic techniques have come better outcomes for both athletes and non-athletes alike. While open posterior labral repair and reconstructive surgery are still viable options, for the majority of patients, an arthroscopic repair will likely achieve a superior outcome.

Possible complications

Recurrent instability
Stiffness
Infection
Neurovascular injury

Equipment

Arthroscope, Stryker, Kalamazoo, MI
2.3mm Bio-Raptor Suture Anchors loaded with No. 2 Ultrabraid, Smith and Nephew, Andover, MA
Spectrum Hook, Linvatec, Largo, FL
0 PDS Sutures, Ethicon, Somerville, NJ

Disclosures

The author has no financial relationship with any of the companies mentioned in this article.

Statement of Consent

The patient undergoing the filmed procedure gave consent to being filmed for this video article and is aware that it may be published online.