Posterior Shoulder Instability

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Original Editors

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Search Strategy

Sarch Datebases: CINAHL, Cochrane Library, EBSCO, Elseivier, Health Source Medline with full text, Pubmed, Google Scholar 

Search dates: 11/1/10-11/21/10. 

Search terms: Posterior Shoulder Instability, Rehabilitation, Physical Therapy, Surgical Techniques, Protocols 

Definition/Description

A continuum of shoulder instability exists with laxity at one end and complete dislocation of the joint at the other. Defining posterior shoulder instability (PSI) is therefore difficult, not only definin it within this continuum but differentiating it from other shoulder pathologies. PSI is described as posterior glenohumeral translation that reproduces symptoms outside the normal physiologic translation in an individual which only accounts for about 5% of all patients with shoulder instabilities. (Robinson, safran, Fritz) Translation that is not symptomatic is considered laxity.

Epidemiology /Etiology

The etiology of posterior shoulder instability is very complex, multidirectional, and the paucity of research leaves it challenging to accurately diagnose, classify, and treat. (Robinson Provencher) The majority of the patient population consists of active men 20-30 years of age engaging in high contact sports. Approximately 50% of patients report a distinct injury that brought on the instability or symptoms they have, yet only 17% according to a new instability report stated having a dislocation requiring reduction. (Robinson, Fritsch) Posterior shoulder instability is generally uncommon and rarely occurs alone.  Contributing existing/coexisting factors include microtrauma or macrotrauma injuries to the shoulder, previous dislocations, soft-tissue and/or boney structural abnormalities, scapulothoracic dysfunction, or be described as volitional through psychogenic, positional and muscular instabilities.

Trauma

Microtrauma is important factor in the development of instability due to the repetitive shearing forces and loads to the posterior shoulder in the flexed, adducted, and interally rotated position. It can lead to degeneration of anatomical structures stabilizing the joint. This population usually consists of weight lifters doing bench-presses, overhead sports, swimming, and commonly military patients. (Robinson Provencher) Macrotrauma is a mechanism from a substantial injury such as a blow to the anterior shoulder or axial load while the shoulder is flexed. This population commonly consists of patients involved in high contact sports such as football.

Pathoanatomy

Structural abnormalities are shown to attribute to posterior instability of the shoulder. Important structures that stabilize the shoulder posteriorly and that are important to be aware of dysfunction include the posterior band of the inferior gleno-humeral ligament, glenoid, coracohumeral ligament, posterior capsule, the rotator cuff muscles and the biceps tendon. Soft-Tissue etiologies attribute to structural abnormalities and include, but are not limited to, a reverse-bankart lesion involving tearing of the posterioinferior region of the capsulolabral complex, Kim lesion or avulsion to the posteroinferior labrum, osseous avulsion of the posterior aspect of the glenoid rim from a reverse osseous Bankart lesion, reverse Hills-sachs lesion, capsular laxity, chondrolabral erosion of the glenoid rim, tear of rotator cuff and/or tendons, and avulsion of the glenohumeral ligaments. (Robinson, Provencher, Fritsch) According to Hundza et. al, avulsion of the glenohumeral ligament in an under diagnosed, yet highly important, cause in traumatic or macrotrauma mechanisms of posterior shoulder instability. (Hundza) Recurrent subluxation can cause the capsule to increase in volume through plastic deformation resulting in capsular laxity. Boney abnormalities that are associated with posterior instability of the shoulder are glenoid retroversion, anterior humeral head defects, glenoid erosion. (Robinson)

Scapulothoracic Dysfunction

Scapulothoracic dysfunction in the importance of posterior instability is poorly understood. Winging of the scapula often occurs as the shoulder subluxates during a provocative position and dynamic anatomical movement. It is unclear whether it is due to a compensatory motion or a contributor to instability. Also, weakness of the serratus muscle may attribute to instability. (Robinson)

Volitional

Volitional subluxation from an instable shoulder can be pshycogenic. This is where the patient voluntarily subluxes their shoulder for some secondary gain, such as attention, and can evolve into being symptomatic. Some patients can subluxate by placing their shoulder in an unstable position of flexion, adduction and internal rotation. Other volitional subluxers includes a muscular group usually physically active and have involvement of involuntary subluxation and instability that interferes with their sports. (Robinson, Fritsch)

Characteristics/Clinical Presentation

Patients will commonly present with pain or general, poorly localized aching of their involved shoulder at the posterior aspect, generally after a dislocation or repeated use/fatigue, more so than instability itself. (provencher, Harish, Robinson, Vidal) The involved arm may be internally rotated revealing the humeral head more prominently on the posterior shoulder, and they may complain that external rotation or the throwing motion causes symptoms. (dang) The patient may also report a feeling of looseness when the arm is placed is provocative positions such as adduction, internal rotation and flexion. (Harish, Robinson) Therefore, a good history taken from the patient is also important in diagnosing posterior instability because of all the coinciding conditions and no confirmed etiology. A pt will often report a pre-symptomatic injury, volitional subluxation, dislocation and/or reduction,clicking, interference with sports/physical activities, and involvement in overhead sports or weightlifting. (Vidal, Robinson)

Differential Diagnosis

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Examination

Physical Exam

As with any injury it is important to rule out the joints above and below for possible involvement, and therefore a complete upper quarter exam is recommended.

The shoulder exam should include observation, palpation and manual testing that includes motion, strength, and laxity tests of both the involved shoulder and the uninvolved shoulder for comparisons (Williams, Provencher). Upon observation the therapist should be looking for any obvious dislocation or asymmetry of the shoulders, abnormal motion, muscle hypertrophy or atrophy, swelling, and at altered scapulothoracic movement (Provencher). The patient may have tenderness with palpation at the posterior glenohumeral joint line (Provencher). They may also present with weakness of the rotator cuff muscles and scapular stabilizers. Diagnostic tests for posterior instability include: the Posterior Apprehension Sign, the Posterior Stress Test, the Jerk Test, the Kim Test, the Load-and-Shift, and Posterior Drawer Test (Kim, Engle, Williams, Van Tongel, Vidal, Provencher). During these tests the clinician is trying to reproduce the subluxation or the patient’s symptoms of pain and instability.

Jerk Test                                                                                Posterior Apprehension Test

Posterior Drawer Test

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Imaging 

It is important to determine the cause, degree and direction in order to properly treat PSI and prevent recurrent instability. Plain radiographs are often interpreted to be normal in patients with PSI, but may reveal any possible damage to the Glenoid (Vidal, Von Tongel, Provencher). In addition to the routine anterior-posterior and lateral radiographs, it is recommended that patients also get an Axillary view, as it reveals the most diagnostic information for a posterior dislocation or subluxation (Provencher, Zabel, Williams). However, Magnetic Resonance (MR) Imaging, especially MR arthrography, is the radiological tool of choice and an important diagnostic tool to identify any possible soft tissue lesions that may be contributing to or associated with the instability (Fritsch, Harish, Provencher, Williams, Van Tongel, Vidal). MR imaging may also be used to help determine if the patient would benefit from an open surgical approach or an arthroscopic approach (Harish). If a plain radiograph reveals there may be bony abnormalities then Computerized Tomography (CT) scans are recommended for their ability to better delineate bone quality and glenoid morphology (Williams, Zabel, Van Tongel).

Medical Management (current best evidence)

Operative stabilization should be considered in patients who fail to return to activity or continue to experience pain or instability, are psychologically stable, and have failed a trial of physical therapy (Provencher, Robinson). The success of surgical intervention depends on the ability to correct the underlying impairment. Therefore, operative treatment may involve more than one procedure to address the factors contributing to the instability (Robinson). Factors that influence the choice of operative intervention include volitional instability, injury to the shoulder, degree of instability, structural abnormalities, and direction of instabilities (Robinson).

Volitional Instability

Operative treatment is contraindicated for patients with voluntary instability due to psychological problems. Patients without psychological problems usually respond well to a trial of physical therapy that includes pain management, activity modification, and strengthening of the scapulothoracic and rotator cuff muscles (Robinson). Operative treatment is usually recommended if conservative treatment fails after a trial of 6 months (Robinson).

Shoulder Injury

In patients with posterior instability with a traumatic etiology, operative treatment is recommended because conservative treatment is usually unsuccessful (Robinson, Fritsch). Bottoni et al. found good results in patients with posterior instability secondary to trauma after an open or arthroscopic procedure (Fritsch).

Degree of Instability

Patients with recurrent dislocation often have anterior defects of the humeral head and posterior defects of the glenoid rim. In these patients, operative treatment may include bone-grafting of defects of the humeral head and glenoid rim, and soft-tissue reconstruction. In cases of recurrent subluxation, posterior-soft tissue stabilization is often performed (Robinson).

Structural Abnormalities

In cases of soft-tissue injury, stabilization typically involves the reattachment of the posteror capsulolabral complex and retensioning of the redundant posteroinferior aspect of the capsule (Robinson, Fritsch).

• Open procedures for posterior instability secondary to soft-tissue abnormalities include the posterior capsular shift, scapularis tendon transfer, posterior-capsular plication with infraspinatous advancement, reverse Putti-Platt plication, reverse Bankart repair, Boyd-Sisk procedure, and biceps tendon transposition (Provencher, Robinson). The open technique is usually performed posteriorly with an incision of the infraspinatous tendon or the development of a plane between the infraspinatous and teres minor tendons (Robinson, Bottoni). Complications include infection, neurovascular injury, pain, stiffness, and weakness. Recurrent instability following an open soft-tissue stabilization has been reported to be 24% (Robinson).
• Arthroscopic procedures for posterior instability secondary to soft-tissue abnormalities include posterior-labral repair, plication, superior shift, thermal shrinkage of the posterinferior aspect of the capsule, subacromial decompression and rotator cuff repair (Robinson). Patients that undergo arthroscopic treatment report higher overall outcome scores, less postoperative pain, and shorter hospital stays (Robinson, Provecher). Similar outcomes were observed between throwers and nonthrowers following an arthroscopic posterior capsulolabral repair (Radowski). Arthroscopic stabilization has had good results with 5% overall recurrence rate (Robinson, Servien, Fritsch).

In patients with distortion of the osseous anatomy, posterior glenoplasty or bone-block can be used. A posterior glenoplasty is used to treat patients with glenoid retroversion greater than 15 degrees (Robinson, Servien). A posterior bone-block operation has been used in patients with a deficiency of the posterior wall of the glenoid or with attenuation of the posterior capsule (Robinson). Typically, a posterior bone-block is used in patients with recurrent posterior dislocation (Servien). These procedures have a high risk of severe complications and are not commonly used. There is a 25% recurrence rate of instability following an open glenoid osteotomy or bone-block procedure (Robinson).

Directions of Instability

Patients with bidirectional or multidirectional instability typically respond to physical therapy consisting of pain management, activity modification, and strengthening of the scapulothoracic and rotator cuff muscles. If conservative treatment is unsuccessful, open or arthroscopic surgery may be indicated. Operative treatment should treat all directions of instability. (Robinson)

Physical Therapy Management (current best evidence)

Although there are articles describing the following physical therapy treatment and this treatment is commonly accepted as best practice, a systematic review by Gibson et al found little “definitive, empiric evidence to substantiate their effectiveness,” (p 230) but concludes that conservative physical therapy treatment should be the first line treatment especially for those patients with isolated dislocations. (Gibson, Engle) The treatment parameters described are mostly based on biological evidence rather than clinical trials.

Immobilization

Immobilization for three weeks may be indicated for patients with primary dislocation to help prevent recurrence of dislocation and instability in the joint. (Kiviluoto) This “low quality RCT” (Gibson) reported 17% recurrence at one year with immobilization at three weeks compared to 26% recurrence with immobilization at one week for patients less than 50 years of age. A limitation of the study was that it was not differentiate what kind of dislocation had occurred.

Strengthening

Rehabilitative treatment of posterior shoulder instability includes strengthening of external rotators and the rotator cuff (supraspinatus, infraspinatus, teres minor, subscapularis) (Hurley, Engle, Provencher), most importantly the infraspinatus muscle. (Van Tongle, Vidal, Engle, Fritsch) Scapular stabilizers (Williams, Vidal, Engle, Fritsch, Provencher), and posterior deltoid (Vidal, Young) strengthening is also important. Strengthening exercises engage the muscular stabilizers of the shoulder joint to compensate for the stretched capsule that often occurs with shoulder instability and to promote proprioception of the joint. (Fritsch) Isometric, concentric and eccentric strengthening is indicated with focus on correct muscle firing and position before moving to more advanced strengthening of glenohumeral muscles. (Engle) Resistance can be given through manual techniques, resistive tubing, free weights, or machines (Provencher). An upper body ergometer may be used to improve dynamic stabilization by demanding coordinated and consistent muscle activity across both arms without moving the arm through painful or unstable motions (Hundza)

Biofeedback and EMG

Simply strengthening the rotator cuff muscles may not be enough because of the underlying lack of muscle firing synergy and abnormal recruitment pattern of muscles commonly seen in posterior instability patients. (Fritsch, Provencher) These deficits have been documented through EMG studies. (Young, Williams, Vidal) To help focus muscular activity on dynamic stabilizers biofeedback can be useful. (Vidal, willimas, Gibson) A case study using EMG biofeedback on the posterior deltoid for neuromuscular reeducation was shown to help the patient activate the posterior deltoid to prevent voluntary dislocations. (Young)

Neuromuscular reeducation

Neuromuscular reeducation is an important part of activating scapular and glenohumeral muscles during functional movements. Strengthening should progress to include full range and diagonal and spiral patterns including PNF patterns. (Engle) Further study is needed to determine if UBE training will normalize muscle activation patterns (Hundza).

Activity modification

Avoiding activities that encourage instability or symptoms such as the forward flexed, adducted, internally rotated position is recommended. (Vidal) Often the instability is only present during sport and activity modification is not realistic unless the person is willing to retire from sport. (Vidal, Hurley)

Effectiveness

Physical therapy usually cannot eliminate the instability but reports of 70%(vidal) to 80% (Williams, burkhead) of patients note improvement and an ability to return to sport after a physical therapy program. (Vidal, Burkhead) A majority of patients in a retrospective study were satisfied with their results from rehabilitative strengthening (Hurley). The effectiveness of physical therapy depends on the type of instability and the demands the patient places on their shoulder. After an extended period of 12 weeks (Gibson, Engle) to 6 months (Robinson) of rehabilitation without improvement and persistent disability surgery should be considered as long as the instability can be attributed to an anatomical problem. (Vidal, Hurley)

Post-surgical Physical Therapy

Post-surgical rehabilitation does not differ significantly from conservative treatment without surgery. The goals of treatment are the same and treatment includes ROM, neuromuscular reeducation/function, and strengthening.

Strengthening

Again, the rotator cuff and periscapular muscles are important dynamic stabilizers of the joint and much of the rehabilitation is focused on these muscles (Perez, Vidal) Gentle isometric contraction is suggested as the first active muscle contraction progressing to AROM and resisted exercises. (Perez)

Range of Motion

The need to restore normal ROM is an important outcome for the success of posterior shoulder instability post-surgical rehabilitation. The anatomy of the repair, tissue involved, patient motivation, and complications are factors that play a large role in the success and progression of a rehabilitation program. (Perez)

Neuromuscular Function

Supporting musculature of the scapula need to function properly to decrease the stress on the static stabilizers of the joint such as ligamentous and capsular structures that may have been compromised with surgery. (Perez) This includes strength, muscle firing timing, endurance, and coordination. (Perez) Rhythmic stabilization can be used to promote proper muscle firing and enhance stability (Perez) EMG biofeedback has also been used successfully post surgically to reeducate muscle patterns, specifically the posterior deltoid. (Beall)

Treatment Timeline for post-surgical rehabilitation                                    

Vidal, Perez, Provencher, Robinson

Timeline	Treatment
Weeks 1-4	Abduction sling Limited PROM:     -Forward flexion to 90° in scapular plane     -ER to 0°-30° Limited IR and adduction Control swelling and pain Patient education Pendulums Soft tissue mobilization
Weeks 4-6	Abduction sling Control swelling and pain Patient education AAROM:      -With periscapular strengthening Limited IR and adduction Pulleys UBE
Weeks 6-8	AROM with resistance:     -ER and limited forward flexion Joint mobilizations if not achieving ROM
Months 2-3	Full PROM and AROM Isotonic strengthening Proprioception training in end ranges Increased speed and volume of strength training
Month 4	Pain free shoulder Resisted strengthening with free weights General conditioning Avoid resisted activities with posterior force placed on shoulder such as push-ups
Month 6	Isokinetic testing If strength and endurance at least 80% of uninvolved side progress to throwing program or sport specific rehab Push-ups and pull-ups can be attempted
Months 6-9	Recreational athletes return to sport once acheive full ROM, strength and report no pain
Months 8-12	Non-contact athletes (golfers, swimmers) usually return to play
Months 9-12	Contact athletes and power athletes usually return to play

Key Research

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Resources

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Clinical Bottom Line

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Recent Related Research (from Pubmed)

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References

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