Anterior Shoulder Instability
Anterior shoulder instability refers to a condition in which the humeral head is displaced from its normal position within the glenoid fossa as a result of injury to soft tissue or bony structures. This can lead to partial loss of joint congruence, as in subluxation, or complete dislocation.[1] The condition is commonly associated with trauma, such as a fall onto an outstretched arm or a direct impact to the shoulder. Anterior shoulder instability is also frequently seen in sports involving overhead movements, including volleyball, swimming and weightlifting.
Anterior shoulder instability may be traumatic or atraumatic. Traumatic instability typically follows a major injury, whereas atraumatic instability may develop gradually as a result of repetitive microtrauma or excessive loading of the stabilizing structures of the shoulder, including the ligaments, capsule and labrum.[1] Treatment depends on severity and activity demands and may range from physiotherapy and rehabilitation to surgery when conservative management is insufficient.
Clinically Relevant Anatomy
The glenohumeral joint (GH joint) is a multiaxial spheroidal joint and one of the largest and most complex joints in the body. It has the greatest range of motion of any joint, but this mobility also creates inherent instability, giving the shoulder the highest risk of dislocation among the body's major joints. The GH joint is formed where the humeral head articulates with the glenoid fossa, an irregular oval surface of the scapula. Although often described as a ball-and-socket joint, only about 25% of the humeral head is in contact with the glenoid at any one time.
The shoulder is surrounded by numerous ligaments and muscles that contribute to stability. The joint capsule also plays an important role, reinforced by the coracohumeral and glenohumeral ligaments. Other important bony structures include:
Acromion: A bony projection of the scapula.
Clavicle: Connects the acromion to the axial skeleton through the acromioclavicular and sternoclavicular joints.
Coracoid process: A hook-shaped bony projection of the scapula.
The shoulder also contains several other important structures:
Rotator cuff: A group of four muscles originating from the scapula: supraspinatus, infraspinatus, subscapularis and teres minor. The rotator cuff stabilizes the GH joint and contributes to its large range of motion.
Bursae: Several bursae are present around the shoulder, but the subacromial bursa is the one most commonly symptomatic in bursitis. It lies between the superior surface of the supraspinatus tendon and the acromion, coracoid process and coracoacromial ligament and extends over the humeral insertion of the supraspinatus tendon.
Labrum: A fibrocartilaginous rim surrounding the glenoid that improves stability by deepening the socket for the humeral head.[2]
Epidemiology
Anterior shoulder dislocations are considerably more common than posterior dislocations.[3] Research shows that recurrent shoulder dislocation is substantially more common in younger patients.[4][5] The consequences of a first-time anterior glenohumeral dislocation in patients over 40 differ from those seen in younger people, mainly because rotator-cuff tears and associated neurovascular injuries are more common in older patients. Both anterior and posterior supporting structures can be injured during an anterior dislocation. In younger patients, failure more often involves the capsuloligamentous structures, whereas in older patients with pre-existing rotator-cuff degeneration, posterior soft-tissue structures may be more vulnerable.[4]
Etiology
The glenohumeral joint is stabilized by both dynamic and static structures.[4]
Rotator-cuff muscles
Dynamic stabilizers: Rotator-cuff muscles, biceps brachii and deltoid.
Static stabilizers: Glenohumeral joint capsule, glenohumeral ligaments, labrum, negative intra-articular pressure and the bony congruence of the joint.[3][5]
Labrum
The concavity-compression mechanism plays an important role in glenohumeral stability by maintaining the humeral head on the glenoid against translational forces. The concavity of the glenoid is created by the shape of the glenoid, glenoid cartilage and glenoid labrum. The labrum increases both the width and depth of the glenoid. Instability increases as the size of a glenoid defect increases.[6]
Glenohumeral Ligaments
Superior glenohumeral ligament: Primarily resists inferior translation and external rotation of the humeral head when the arm is adducted.
Middle glenohumeral ligament: Primarily resists external rotation from 0° to 90° and provides anterior stability when the shoulder is moderately abducted.
Inferior glenohumeral ligament: Consists of anterior and posterior bands with the intervening capsule. The anterior band primarily resists anteroinferior translation.[5][7]
Excessive External Rotation
Excessive external rotation, or over-rotation in the throwing shoulder, is thought to be associated with development of internal impingement syndrome. This occurs when the shoulder is maximally externally rotated and the articular side of the supraspinatus tendon is compressed against the adjacent posterosuperior glenoid and labrum. Internal impingement may contribute to anterior shoulder instability.[7]
Features / Clinical Presentation
Signs and symptoms of anterior shoulder instability include:
Approximately 95% of acute traumatic shoulder dislocations are anterior.[5]
Dead arm syndrome may indicate pathological anterior instability. It often occurs when the arm is abducted and externally rotated. The patient experiences sharp anterior shoulder pain, sometimes with numbness in the hand, and may suddenly drop the arm. It is commonly described in overhead sports such as volleyball, tennis, swimming and water polo.[7]
Rotator-cuff weakness, particularly in external rotation and empty-can abduction, is common among athletes with anterior instability.[7]
Bankart lesions are the most common consequence of traumatic anterior shoulder instability.[5]
Humeral avulsion of the glenohumeral ligaments may also contribute to anterior shoulder instability.[5]
During an anterior dislocation, the posterolateral aspect of the humeral head contacts the anteroinferior rim of the glenoid, often producing a Hill-Sachs defect. This defect has been reported in up to 80% of patients after an initial anterior dislocation and in nearly all patients with recurrent anterior instability.[3][5] If the bony defect engages the anterior glenoid when the arm is abducted to 90° and externally rotated, it is termed an "engaging Hill-Sachs lesion", which carries a higher risk of failure after arthroscopic stabilization.
Shoulder MRI after dislocation may demonstrate a Hill-Sachs defect and a Bankart lesion of the labrum.
Symptoms associated with recurrent anterior instability[7]:
Glenohumeral joint pain
Shoulder stiffness with difficulty warming up before activity.
Rotator-cuff weakness
A sensation of popping, grinding or catching deep within the shoulder joint.
Pain when reaching backward or above shoulder height.
Apprehension when sleeping with the arm overhead in abduction and external rotation.
Neurological symptoms: Numbness or burning in the forearm and hand, or localized numbness over the skin covering the deltoid.
Tenderness over the anterior glenohumeral joint line and posterior rotator cuff.
Differential Diagnoses
Posterior instability: Refers to instability in a posterior direction. It may produce symptoms similar to anterior instability but involves a different mechanism and may require different management.[5]
Frozen shoulder / adhesive capsulitis: Characterized by shoulder pain, stiffness and restricted movement. It can be confused with instability but has a different underlying mechanism, often involving capsular inflammation and fibrosis.[5]
Dead arm syndrome: A specific painful episode that can occur with anterior instability, particularly during overhead movements, and may be accompanied by numbness or a sensation of the arm losing strength.[7]
Rotator-cuff tear: Rotator-cuff injury can cause pain and impaired function and may mimic instability, especially in more advanced cases where the cuff's stabilizing role is reduced.[5]
Subacromial impingement: Compression of rotator-cuff tendons between the humerus and acromion can cause pain and movement limitation and may be difficult to distinguish from instability.[7]
Internal impingement: Occurs when rotator-cuff tendons are compressed within the shoulder joint and may contribute to anterior instability in throwing athletes, particularly in maximal external rotation.[7]
Biceps tendinopathy: Involves pathology of the biceps tendon and may cause shoulder pain resembling anterior instability, particularly when the biceps-labrum complex is involved.[5]
Diagnostic Procedures
Diagnosis of anterior shoulder instability is based on a detailed history, imaging and three specific tests commonly performed in sequence: the apprehension test, relocation test and surprise test (release test). These tests are highly specific and have strong predictive value for traumatic anterior glenohumeral instability. A fourth test, the bony apprehension test, is a variation of the apprehension test and is used when significant osseous pathology is suspected.[8]
History
Glenohumeral instability can be categorized by direction, chronicity and etiology. A detailed history and physical examination are essential. Age, activity level, sports participation and hand dominance should be documented, along with any instability in other joints, especially the contralateral shoulder. If trauma caused the symptoms, the position of the arm and the force involved should be recorded. If this is unknown, identifying the arm position that reproduces the patient's symptoms may be useful.
The presence and frequency of previous shoulder subluxations or dislocations should also be documented. Previous treatment should be reviewed, including periods of immobilization, physiotherapy and prior surgery. Pain characteristics should be recorded, although pain location alone is not specific for glenohumeral instability. It is important to distinguish subluxation, which is partial separation of the humeral head from the glenoid, from complete dislocation. Associated symptoms such as neurological deficits and functional limitations should also be assessed.
Age at first dislocation is an important prognostic factor. Patients younger than 20 years who experience a shoulder dislocation have a very high risk of recurrence, whereas patients over 40 have a much lower recurrence risk but are more susceptible to rotator-cuff injury. Competitive athletes and those participating in contact sports are also at increased risk of recurrence when treated conservatively.[9]
Radiology
Initial imaging for suspected anterior shoulder instability commonly includes anteroposterior (AP) and axillary lateral radiographs. If pain prevents the patient from tolerating an axillary view, a Velpeau view can be obtained with the patient seated in a semi-reclined position. Other useful projections include AP radiographs in internal rotation, the West Point view, Didiee view and Stryker notch view.
Hill-Sachs lesions are best visualized on AP radiographs in internal rotation and with the Stryker notch view. The Stryker notch view is obtained with the patient supine, the arm flexed forward to approximately 100°, and the X-ray beam centered over the coracoid. An apical oblique view is obtained with the patient seated and rotated about 45°, with the beam angled caudally. This can also help assess posterior humeral-head defects.[10]
With bony Bankart lesions, recurrent instability may produce erosive or attritional loss of the glenoid rim, leading to progressively greater instability. Loss of approximately 20% of the glenoid rim has been associated with clinically important recurrent instability and often requires surgical correction of the bony defect. The defect may be visible on an axillary view and may be suggested by disruption of the sclerotic line surrounding the glenoid rim on an AP radiograph. If further imaging is required, Didiee and West Point views may be used. The Didiee view is obtained with the patient prone, the hand on the ipsilateral iliac crest and the beam directed laterally at 45°. The West Point view is obtained in a similar prone position with the shoulder abducted to 90° and the elbow flexed, with the arm hanging from the table while the beam is directed 25° medially and 25° caudally.
Other imaging modalities such as CT and MRI are useful when the diagnosis is unclear. CT can help identify and quantify bony abnormalities including glenoid bone loss or fractures, glenoid version and humeral-head abnormalities. CT arthrography with contrast may also provide information about the labrum, rotator cuff and ligament complex. MRI is particularly useful and is generally preferred for assessment of soft tissues, although it provides less precise characterization of associated bony injury. In the acute phase, hemarthrosis may act as intra-articular contrast. In more chronic cases, gadolinium-enhanced MRI can be useful for evaluating soft-tissue injuries such as labral tears and capsular lesions.[11]
In addition to Bankart lesions, anterior labroligamentous periosteal sleeve avulsion (ALPSA) or humeral avulsion of the glenohumeral ligament (HAGL) may occur with anterior shoulder dislocation. These lesions are associated with higher recurrence rates and, if overlooked, may contribute to failure after surgical stabilization. HAGL and ALPSA lesions are best evaluated with MRI and MR arthrography.
Outcome Measures:
Disabilities of the Arm, Shoulder, and Hand (DASH)
The DASH questionnaire is a widely used outcome measure for physical function and symptoms in people with upper-extremity musculoskeletal disorders. It assesses how a shoulder condition affects daily activities through 30 items covering disability and symptoms. DASH is useful for evaluating functional impairment in anterior shoulder instability. Scores range from 0 to 100, with higher scores indicating greater disability. It is commonly used to monitor changes after interventions such as surgery and physiotherapy.
Visual Analogue Scale (VAS)
The Visual Analogue Scale (VAS) is a simple and widely used method for rating pain intensity. It typically consists of a 10 cm line ranging from "no pain" to "worst imaginable pain." The patient marks the point corresponding to their pain level. In anterior shoulder instability, VAS can be used to quantify pain during provocative activities such as overhead movements or certain sleeping positions, monitor change over time and assess response to treatment.
Examination – Specific Tests
Load and shift test[12][13]
This test can be performed with the patient seated or supine. In sitting, the arm rests on the thigh while the examiner stands beside and slightly behind the patient. One hand stabilizes the scapula while the other controls the shoulder, with the thumb over the posterior humeral head and the fingers over the anterior humeral head. The humerus is first loaded to center the humeral head in the glenoid. While maintaining this position, an anterior force is applied to assess anterior translation. Some movement is normal, but translation should generally not exceed approximately 25% of the humeral-head diameter.
Instability is classified as follows:
Grade 1: Translation between 25% and 50%.
Grade 2: More than 50% translation with spontaneous reduction when the applied force is released.
Grade 3: More than 50% translation without spontaneous reduction, with the humeral head remaining dislocated. The combination of laxity and reproduction of the patient's symptoms determines whether the test is considered positive or negative.
Apprehension, Relocation and Anterior Release Tests[13][14]
The patient lies supine with the shoulder in 90° abduction and maximal external rotation. A positive apprehension test occurs when the patient appears anxious or resists further movement. To distinguish apprehension due to instability from other causes, the relocation test is performed. The starting position is the same, but a posteriorly directed force is applied to the shoulder to relocate the humeral head within the glenoid. Apprehension typically decreases when instability is the cause. The final test is the release test, in which the posterior force used during the relocation test is removed. The result is considered positive if apprehension returns.
Anterior Drawer Test[8][15]
The patient lies supine with the affected shoulder positioned over the edge of the table and the arm relaxed. The arm is placed in a combined mid-range position of abduction, forward flexion and external rotation. The examiner stabilizes the scapula with one hand, securing it around the scapular spine and coracoid process, while the other hand draws the humerus forward to apply an anterior translational force to the glenohumeral joint. An audible or palpable click may suggest a labral tear or sufficient laxity for the humeral head to move over the glenoid rim.
Medical Treatment
Analgesics may be used to reduce pain,[16] while the patient is kept in a comfortable position and the cervical spine is immobilized if clinically indicated. A pillow may be placed between the arm and torso to improve comfort.
Physiotherapy Treatment
A conservative rehabilitation program should be individualized according to the type and degree of instability and the patient's desired level of function. Rehabilitation may combine strengthening, dynamic stabilization, neuromuscular training, proprioceptive training, scapular-muscle strengthening and a gradual return to the desired activity.
Rehabilitation Factors
Seven key factors should be considered when designing a rehabilitation program:
Onset of pathology: Shoulder instability may result from an acute traumatic event or from chronic recurrent instability. Rehabilitation goals can differ substantially depending on onset and mechanism of injury. After a traumatic subluxation or dislocation, the patient typically presents with significant soft-tissue trauma, pain and apprehension. Rehabilitation after a first traumatic episode should progress according to symptoms, with emphasis on early controlled range of motion, reduction of muscle spasm, protection of healing tissues and pain relief.
In contrast, patients with atraumatic instability often have a history of recurrent symptoms. Rehabilitation should emphasize early proprioceptive training, dynamic stabilization, neuromuscular control, scapular-muscle exercises and strengthening to improve dynamic stability, particularly because excessive capsular laxity and redundancy are common in this patient group.
Degree of instability: The second factor is the severity of instability and its functional impact. Rehabilitation progression varies according to the degree of instability and symptom duration. For example, a patient with mild subluxation and limited guarding may tolerate strengthening and neuromuscular-control exercises earlier than a patient with marked protective muscle spasm.
Frequency of dislocation: A primary traumatic dislocation is often managed conservatively with sling immobilization and early controlled passive range-of-motion exercises, particularly after a first-time dislocation. Chronic subluxation associated with atraumatic instability may be treated more aggressively because there is less acute tissue injury, inflammation and guarding. Rotator-cuff and periscapular strengthening can be initiated while range-of-motion exercises progress. Excessive stretching of the capsule should be avoided. The aim is to improve strength, proprioception, dynamic stability and neuromuscular control, particularly in the positions or directions that provoke instability.
Direction of instability: Anterior instability is the most common traumatic direction of shoulder instability seen clinically. The humeral head is typically forced toward the extremes of abduction and external rotation, or horizontal abduction, which may detach or injure the glenolabral complex and capsule at the glenoid rim.
Associated pathology: Other soft-tissue injuries and the pre-injury status of the tissues should be considered. Associated lesions may substantially slow rehabilitation to protect healing structures.
Neuromuscular control: The sixth factor is the patient's level of neuromuscular control, especially near end-range positions.
Activity level: The final factor in conservative rehabilitation is arm dominance and the patient's desired activity level. Patients who frequently perform overhead movements or participate in sports such as tennis, volleyball or throwing sports should progress to sport-specific dynamic-stabilization exercises, neuromuscular-control exercises and overhead plyometric training once full pain-free range of motion and adequate strength have been restored. Patients whose functional demands remain below shoulder height can follow a progressive exercise program aimed at restoring full motion and strength.
Rehabilitation Guidelines
Patients can generally be classified into two common forms of shoulder instability: traumatic and
atraumatic. Specific principles can be used to individualize rehabilitation for each patient.
Traumatic Shoulder Instability[17][18]
The duration of the program varies between patients depending on the seven rehabilitation factors.
Phase I: Acute Motion Phase
Goals:
Protect healing capsular structures.
Restore pain-free range of motion.
Reduce pain, inflammation and muscle spasm.
Limit muscle atrophy and restore voluntary muscle activation.
Restore dynamic stability.
Improve proprioception.
Exercises:
Range of motion: Pendulum exercises, rope-and-pulley exercises and active-assisted ROM for flexion, internal rotation and external rotation.
Strengthening/proprioception: Isometrics for flexion, abduction, external rotation and internal rotation with the arm at the side.
Rhythmic stabilization: External rotation/internal rotation/flexion/extension in the scapular plane, weight shifts with the hands supported on a table, and proprioceptive training using active joint-position reproduction for flexion, internal rotation and external rotation.
During early rehabilitation, care should be taken not to overstress the capsule before dynamic joint stability has been restored. For anterior instability, aggressive external rotation and horizontal abduction should be avoided.
Phase II: Intermediate Phase – Criteria for Progression to Phase II:
Near-full to full passive range of motion, although external rotation may still be limited.
Minimal pain or tenderness.
Good manual muscle-test strength in internal rotation, external rotation, flexion and abduction.
Baseline proprioception and dynamic stability.
Goals:
Restore and improve muscular strength.
Normalize arthrokinematics.
Improve proprioception and kinesthesia.
Improve dynamic stabilization.
Improve neuromuscular control of the shoulder complex.
Exercises:
Progress range-of-motion activities at 90° abduction as tolerated and without pain.
Initiate isotonic strengthening exercises.
Emphasize external-rotation and scapular strengthening: abduction to 90°, side-lying external rotation to 45°, table push-ups, biceps curls, triceps pushdowns and prone rowing.
Improve neuromuscular control with PNF, wall stabilization using a ball and static holds in a push-up position on a ball.
Phase III: Advanced Strengthening Phase – Criteria for Progression to Phase III:
Full, pain-free range of motion.
No tenderness on palpation.
Continued progression of resistance exercises.
Normal muscular strength, dynamic stability and neuromuscular control.
Goals:
Improve strength, power and endurance.
Improve neuromuscular control.
Improve dynamic stabilization.
Prepare the patient or athlete for activity.
Exercises:
Continue isotonic strengthening with progressive resistance: full-ROM strengthening, limited-ROM bench press, and flat and incline chest press.
Emphasize PNF patterns.
Advanced neuromuscular-control exercises: ball throws on a table, push-ups on a ball with rhythmic stabilization, manual scapular neuromuscular-control exercises and initiation of perturbation activities.
Endurance training: timed bouts of 30–60 seconds, increased repetitions and multiple sessions throughout the day.
Initiate plyometric training with two-handed exercises such as chest passes, side throws and overhead football throws, then progress to one-handed exercises such as wall dribbling and 90/90 baseball throws.
Phase IV: Return-to-Activity Phase – Criteria for Progression to Phase IV:
Full range of motion.
No pain or tenderness on palpation.
Satisfactory isokinetic testing.
Satisfactory clinical examination.
Goals:
Maintain optimal strength, power and endurance.
Gradually increase activity level to prepare the patient or athlete for full functional return to activity or sport.
Exercises:
Continue all exercises from Phase III.
Progress isotonic strengthening exercises.
Resume the usual lifting program.
Initiate sport-specific interval training.
Follow-up
Isokinetic testing of external rotation, internal rotation, abduction and adduction.
Progress the interval program.
Maintain the exercise program.
Atraumatic Instability[17][18]
This multiphase program is designed to help the patient or athlete return to their previous level of function as quickly and safely as possible. The duration of each phase varies according to injury severity, deficits in range of motion and strength, and the patient's activity requirements.
Phase I: Acute Phase
Goals:
Reduce pain and inflammation.
Restore functional range of motion.
Establish voluntary muscle activation.
Restore muscular balance.
Improve proprioception.
Reduce pain and inflammation.
Therapeutic modalities such as ice and electrotherapy.
NSAIDs.
Gentle joint mobilizations, Grades I and II, for pain modulation.
Exercises:
Avoid activities and movements at extreme ranges of motion.
Range-of-motion exercises: pendulum and rope-and-pulley exercises.
Strengthening exercises: isometrics for flexion, abduction and external rotation.
Proprioception: active joint-repositioning exercises for external and internal rotation.
Phase II: Intermediate Phase – Criteria for Progression to Phase II:
Full functional range of motion.
Minimal pain or tenderness.
Good manual muscle-test strength.
Goals:
Normalize arthrokinematics of the shoulder complex.
Restore and improve strength of the glenohumeral and scapular musculature.
Improve neuromuscular control of the shoulder complex.
Improve proprioception and kinesthesia.
Exercises:
Initiate isotonic strengthening: internal and external rotation using a side-lying dumbbell and abduction to 90°.
Initiate eccentric strengthening at 0° abduction for internal and external rotation.
Improve neuromuscular control with rhythmic-stabilization drills through inner, middle and outer ranges, proprioceptive training, scapulothoracic and glenohumeral muscle control, PNF, weight shifts with the hand on a ball and wall stabilization.
Phase III: Advanced Strengthening Phase – Criteria for Progression to Phase III:
Full, pain-free range of motion.
No pain or tenderness.
Continued progression of resistance exercises.
Good to normal muscular strength.
Goals:
Improve dynamic stabilization.
Increase strength and endurance.
Improve neuromuscular control.
Prepare the patient for activity.
Exercises:
Continue isotonic strengthening exercises.
Continue eccentric strengthening.
Emphasize PNF exercises with rhythmic stabilization.
Continue progression of neuromuscular-control exercises: push-ups with rhythmic stabilization, progression to unstable surfaces, medicine-ball exercises and rocker-board activities.
Scapular neuromuscular-control program: side-lying manual exercises.
Emphasize endurance training using timed bouts of 30–60 seconds and increased repetitions.
Phase IV: Return-to-Activity Phase – Goals:
Maintain optimal strength, power and endurance.
Gradually increase activity level to prepare the patient or athlete for full functional return to activity or sport.
Exercises:
Continue all exercises from Phase III.
Initiate sport-specific interval training.
Patient education.
Criteria for Progression to Phase IV:
Full range of motion.
No pain or tenderness on palpation.
Satisfactory isokinetic test.
Satisfactory clinical examination.
Clinical Conclusion
Shoulder instability may have either traumatic or atraumatic causes.
Anterior Shoulder Instability: This condition refers to displacement of the humeral head from its normal position in the glenoid, with loss of normal contact between the joint surfaces. It is the most common direction of shoulder instability.
Anterior Shoulder Dislocation: This is far more common than posterior dislocation. Recurrence after a first dislocation is highest in people younger than 20 years, and anterior instability accounts for approximately 95% of acute traumatic shoulder dislocations.
Diagnosis: Diagnosis of anterior shoulder instability is typically based on the patient's history, radiographic imaging and three clinical tests performed in sequence: the apprehension test, relocation test and release or surprise test.
Rehabilitation: Rehabilitation should be individualized according to the patient's pre-injury status, activity level and specific type of instability. The program should focus on restoring strength, stability and proprioception to support recovery and reduce recurrence risk.
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