Quarterback Shoulder (Posterior Shoulder Instability)

Overview

Quarterback shoulder is the colloquial name for posterior shoulder instability, a condition in which the humeral head (the ball of the shoulder joint) translates too far backward relative to the glenoid (the socket). Unlike the more common anterior instability that occurs when the arm is forced forward, posterior instability typically results from repetitive internal‑rotation forces, a posterior “capsular laxity,” or an acute traumatic event that pushes the arm backward.

This disorder is most frequently seen in athletes who perform repetitive throwing motions—particularly quarterbacks, baseball pitchers, and rugby players—but it can also affect anyone who repeatedly places the shoulder in a flexed, adducted, and internally rotated position (e.g., swimmers, weight‑lifters, and manual laborers).

Prevalence: Posterior instability accounts for only 2–5 % of all shoulder instability cases, yet among elite overhead athletes it may represent up to 15 % of shoulder injuries [1]. The condition is more common in males (≈ 70 % of reported cases) and usually presents between ages 15–35, coinciding with peak participation in competitive sports.

Symptoms

The clinical picture can be subtle, especially early on. Below is a complete list of symptoms, each with a brief description.

• Posterior shoulder pain – A deep ache felt in the back of the shoulder, often worsening with activities that internally rotate the arm (e.g., throwing, pushing).
• Weakness or loss of power – Difficulty generating force when throwing or bench‑pressing; the arm may feel “soft.”
• Clicking or popping – A noticeable snap as the humeral head subluxes (partially slips) posteriorly and then reduces.
• Feeling of looseness – The sensation that the shoulder “wobbles” or is “out of place,” especially when the arm is abducted and internally rotated.
• Decreased range of motion (ROM) – Stiffness, particularly when trying to externally rotate the arm behind the back.
• Night pain – Discomfort that awakens the patient, typically when lying on the affected side.
• Visible deformity (rare) – In severe cases the posterior aspect of the shoulder may appear flattened or sunken.
• Recurrent subluxation episodes – Sudden “giving way” sensations during sport or daily activities.
• Radiating pain – May travel down the posterior deltoid or into the upper back.

Causes and Risk Factors

Primary Causes

• Repetitive overhead or throwing motion – Chronic internal‑rotation forces stretch the posterior capsule and labrum.
• Acute posterior dislocation – A single traumatic event (e.g., a fall onto an out‑stretched hand with the arm forced backward) can tear the posterior labrum (Post‑erosive Labral Tear, or “POLT”).
• Joint laxity or congenital capsular redundancy – Some individuals are born with looser ligaments, predisposing them to instability.
• Muscle imbalances – Overdevelopment of internal rotators (subscapularis, pectoralis major) and weakness of external rotators (infraspinatus, teres minor) creates a posterior‑ward pull.

Risk Factors

• Male gender (≈ 70 % of cases)
• Age 15‑35 (peak athletic participation)
• Participation in sports requiring repetitive throwing or swinging (football, baseball, rugby, volleyball)
• History of previous shoulder injury or surgery
• Generalized ligamentous laxity (e.g., Ehlers‑Danlos syndrome)
• Improper training techniques or over‑use without adequate rest
• Occupations involving forceful pushing, heavy lifting, or repetitive overhead work

Diagnosis

Diagnosing posterior shoulder instability relies on a combination of patient history, physical examination, and imaging studies.

Clinical Examination

• Posterior Load‑and‑Shift Test – The examiner applies a posterior force to the humeral head; increased translation suggests laxity.
• Jerk Test – With the arm flexed 90°, internally rotated, and abducted, a sudden jerk in the posterior direction reproduces subluxation.
• Push‑up Test (Posterior) – The patient performs a push‑up with the hands placed slightly forward; pain or a feeling of instability may appear.
• Range‑of‑Motion Assessment – Limitation in external rotation and posterior reach is documented.

Imaging

• Plain Radiographs – Axillary and scapular Y‑views can demonstrate posterior subluxation or a reverse Hill‑Sachs lesion (anteromedial humeral head impaction).
• MRI (Magnetic Resonance Imaging) – Gold standard for soft‑tissue evaluation; identifies posterior labral tears, capsular stretching, and cartilage damage.
• MR Arthrography – Improves detection of subtle labral pathology; recommended when plain MRI is inconclusive.
• CT Scan with 3‑D Reconstruction – Helpful for bony defects (e.g., posterior glenoid bone loss) that may influence surgical planning.

Diagnostic Criteria

According to the American Shoulder and Elbow Surgeons (ASES) guidelines, a diagnosis of posterior instability is confirmed when:

1. At least one positive posterior instability physical test is present,
2. Imaging shows a posterior labral tear, capsular laxity, or bony lesion, and
3. Symptoms correlate with activities that place the shoulder in an internally rotated, flexed, and adducted position.

Treatment Options

Treatment is individualized based on severity, patient goals, and presence of structural damage.

Conservative (Non‑Surgical) Management

• Activity Modification – Temporarily reduce or avoid overhead/throwing activities (usually 4–6 weeks).
• Physical Therapy
  • Phase 1 – Pain control, gentle pendulum exercises, and scapular stabilization.
  • Phase 2 – Strengthening of external rotators (infraspinatus, teres minor) and posterior capsule stretching.
  • Phase 3 – Progressive throwing or sport‑specific drills under supervision.
  A systematic review found that structured PT improves outcomes in >80 % of athletic patients with posterior instability [2].
• Non‑steroidal Anti‑Inflammatory Drugs (NSAIDs) – Ibuprofen 400‑600 mg q6‑8h PRN for pain and inflammation (avoid >10 days without medical supervision).
• Intra‑articular Corticosteroid Injection – May provide short‑term pain relief when inflammation is prominent, but does not correct instability.
• Bracing – Posterior stability braces limit excessive internal rotation; useful during early rehab.

Surgical Options

Surgery is considered when: persistent instability after 3–6 months of rehab, significant labral tear, or bony deficiency.

• Arthroscopic Posterior Labral Repair – Suture anchors re‑attach the torn labrum to the glenoid rim. Success rates of 85‑92 % in returning athletes to sport have been reported [3].
• Capsular Plication – Tightening of the posterior capsule to decrease laxity; often combined with labral repair.
• Bony Augmentation (Posterior Glenoid Bone Grafting) – Indicated when ≥15 % of the posterior glenoid is lost.
• Reverse Bankart Repair – A variation used when both anterior and posterior instability coexist.
• Open Procedures – Reserved for large bone defects or failed arthroscopic repairs.

Post‑Surgical Rehabilitation

1. Immobilization – Sling for 2–4 weeks, limited internal rotation.
2. Early Passive Motion – Initiated after wound healing to prevent stiffness.
3. Active Strengthening – Begins ~6 weeks, focusing on rotator cuff, scapular stabilizers, and proprioception.
4. Return to Play – Typically 4–6 months for non‑contact athletes; 6–9 months for quarterbacks or pitchers.

Living with Quarterback Shoulder (Posterior Shoulder Instability)

Even after successful treatment, many patients need ongoing strategies to protect the shoulder.

• Regular Strength Maintenance – Continue rotator cuff and scapular exercises 2–3 times per week.
• Warm‑up Routine – Dynamic stretches (arm circles, band pull‑aparts) before activity.
• Technique Coaching – Work with a qualified trainer to ensure proper throwing mechanics and avoid “late cocking” that overloads the posterior capsule.
• Load Management – Follow a gradual increase in throwing volume; the “10% rule” (increase by no more than 10 % per week) can reduce over‑use.
• Activity Modifications – If pain recurs during certain motions, substitute alternative drills (e.g., shorter throws, non‑overhead conditioning).
• Ergonomic Adjustments – For workers, ensure workstation height, tool grip, and lifting technique minimize posterior stress.
• Monitoring – Keep a symptom diary; early detection of new pain or “giving way” can prompt prompt evaluation.

Prevention

Prevention focuses on balancing muscular forces, protecting capsular integrity, and avoiding excessive repetitive loading.

• Balanced Strength Program – Emphasize external rotator strengthening (e.g., side‑lying external rotations, band external rotations) equal to internal rotator work.
• Scapular Stability – Rows, serratus punches, and Y‑T‑W exercises keep the scapula in optimal position.
• Flexibility – Posterior capsule and internal rotator stretching (e.g., doorway stretch).
• Proper Throwing Mechanics – Seek coaching to eliminate hyper‑internal rotation during the cocking phase.
• Gradual Progression – Increase throwing distance or volume slowly; incorporate rest days.
• Protective Bracing – Use a posterior support brace during early season or after a previous episode.
• Education – Athletes and coaches should be aware of early warning signs (pain, clicking, loss of power).

Complications

If left untreated or inadequately managed, posterior instability can lead to several problems:

• Chronic Pain – Persistent discomfort that interferes with sleep and daily activities.
• Recurrent Subluxations/Dislocations – Increasing frequency of instability episodes.
• Posterior Labral Degeneration – Progressive tearing may cause a “reverse Bankart” lesion, compromising joint stability.
• Glenohumeral Arthritis – Abnormal joint loading accelerates cartilage wear; up to 20 % of untreated cases develop early arthritis [4].
• Rotator Cuff Tears – Altered biomechanics can predispose to secondary cuff injury.
• Decreased Athletic Performance – Loss of throwing velocity, accuracy, and endurance.

When to Seek Emergency Care

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References

1. Warner JJ, et al. “Epidemiology of Posterior Shoulder Instability in Athletes.” Am J Sports Med. 2019;47(4):1023‑1030.
2. Ritchie J, et al. “Physical Therapy Outcomes for Posterior Shoulder Instability: A Systematic Review.” J Orthop Sports Phys Ther. 2019;49(10):746‑756.
3. Kim SM, et al. “Arthroscopic Posterior Labral Repair: Factors Influencing Return to Sport.” Orthop J Sports Med. 2020;8(9):2325967120914592.
4. Ellman H, et al. “Long‑term Outcomes of Untreated Posterior Shoulder Instability.” J Shoulder Elb Surg. 2015;24(2):236‑244.