Shoulder Instability, Dysfunction and Scapular Dyskinesis

Disease/Disorder

Definition

Shoulder instability refers to the inability of the shoulder joint to remain stable within its socket (glenoid fossa). This instability can range from laxity to subluxation to dislocation of the humeral head from the glenoid.¹ Shoulder instability events are characterized in terms of type (subluxation, dislocation), laterality (right, left), and direction (anterior, posterior, inferior, multidirectional) based on history, physical examination, and medical imaging. Subluxations are instability events that do not require a reduction maneuver, while dislocations are instability events that typically necessitate manual reduction.

Shoulder dysfunction is a broad term that includes any impairment or loss of function in the shoulder joint, such as pain, restricted motion, weakness, or instability.⁶

Scapular dyskinesis refers to abnormal positioning or movement of the scapula during shoulder movements. It is often associated with shoulder pain and other shoulder pathologies.⁶ This may be secondary to a painful condition of the shoulder; however, it does not necessarily indicate a pathological condition,² but, rather, a previously asymptomatic condition in the shoulder girdle or muscle imbalance.³ Scapular dyskinesias can be subdivided into a posterior displacement from the posterior thorax of the inferior medial angle (type I), a posterior displacement from the posterior thorax of the entire medial border of the scapula (type II) and an early scapular elevation or excessive/insufficient scapular upward rotation (dysrhythmia) during dynamic observation (type III).¹²

Etiology

Shoulder Instability

Unidirectional instability (UDI) typically results from shoulder subluxation/dislocation. Multidirectional instability (MDI) results from atraumatic laxity of the anterior capsule and glenohumeral (GH) ligaments.⁹ In MDI the ratio of elastin in capsular tissues is increased,¹⁰ leading to a redundant capsule and increasing glenohumeral joint volume.¹¹

• Traumatic Instability: Often due to a sudden injury, such as a fall or direct blow, causing the shoulder to dislocate.⁴
• Atraumatic Instability: Results from repetitive microtrauma, especially in overhead athletes (e.g., baseball pitchers, volleyball players).⁸
• Congenital Instability: Occurs in individuals with connective tissue disorders such as Ehlers-Danlos syndrome or Marfan syndrome, leading to lax ligaments.⁷

Shoulder Dysfunction

• Trauma: Acute injuries, including fractures, dislocations, and muscle tears, can lead to shoulder dysfunction.⁷
• Overuse: Repetitive overhead motions can cause tendinitis, bursitis, or impingement syndrome.⁸
• Degenerative Changes: Age-related wear and tear, including osteoarthritis and degenerative rotator cuff tears, can impair shoulder function.⁵
• Postural Imbalances: Poor posture, especially rounded shoulders or forward head positioning can lead to muscular imbalances and shoulder dysfunction.⁶

Scapular Dyskinesis

• Muscle Imbalances: Weakness or fatigue in scapular stabilizers, such as the serratus anterior and lower trapezius, glenohumeral internal rotation deficit (GIRD), or tightness in muscles like the pectoralis minor can lead to dyskinesis.^6,13,14
• Nerve Injuries: Injury to the long thoracic or spinal accessory nerves can impair scapular control.⁷
• Previous Shoulder Injuries: Dyskinesis can occur as a compensatory mechanism following shoulder trauma or surgery.⁸
• Postural Deficits: Poor posture, especially rounded shoulders or a forward head, can disrupt scapular mechanics and lead to dyskinesis.⁶
• Joint Factors: acromioclavicular separation or arthritis, GH instability (capsular laxity), biceps tendinitis and labral damage.^13,14
• Kinetic Chain Problems: weakness of hip/leg and core muscles.^13,14

Epidemiology including risk factors and primary prevention

Shoulder Instability

• Athletes: Primarily affects young athletes, especially those in sports requiring extensive overhead activity (e.g., swimming, baseball).⁸ More than 90% of unidirectional instability results from anterior dislocations. MDI reportedly occurs more often in gymnasts and swimmers but is also seen in other overhead athletes such as throwers and volleyball players.¹⁵
• Gender: Highest incidence is in males aged 18-25, participating in contact sports.^4,41,42

Shoulder Dysfunction

• Age: Most common in middle-aged and older adults, especially those with degenerative conditions like arthritis or rotator cuff tears.⁵
• Risk Groups: Overhead athletes and individuals in occupations that require repetitive shoulder use (e.g., painters, manual laborers) are at higher risk.⁸

Scapular Dyskinesis

• Athletes: Common in athletes involved in repetitive overhead activities, such as throwing or swimming.⁸ Scapular dyskinesis is associated with posterior capsular tightness, GIRD, and serratus anterior/lower trapezius weakness.¹³ The majority of volleyball players are considered tall. In this population, the prevalence of Marfan’s syndrome may be higher than a general population (1:5000).¹⁶ The connective tissue disorder related to Marfan’s syndrome might be a risk factor of shoulder instability in the tall athlete population.
• General Population: Scapular dyskinesis is also seen in individuals with poor postural habits or those recovering from shoulder injuries.⁶

Patho-anatomy/physiology

The GH joint has little inherent bony stability. During shoulder abduction, the humeral head rolls superiorly, simultaneously sliding inferiorly to prevent impingement.¹⁴ GH joint stability depends on both static and dynamic restraints. Static restraints include the interface of the humeral head, glenoid fossa, GH ligaments, and glenoid labrum.^14,15 Dynamic stability is achieved primarily through the eccentric action of the rotator cuff, keeping the humeral head “seated” within the glenoid fossa during motion.^14,15

Scapulohumeral rhythm is the coordinated movement of the scapulothoracic and GH joints. Below 30 degrees of abduction, most of the motion occurs at the GH joint. Beyond 30 degrees of abduction, the ratio of glenohumeral to scapulothoracic movement generally occurs at a ratio of 5:4.¹⁹ Scapular movement includes upward/downward rotation, anterior/posterior tilt, and internal/external rotation. Scapular retraction is the coupling of external rotation, posterior tilt, upward rotation, and medial translation.

The normal kinematic pattern of the scapula during arm elevation is upward rotation, posterior tilt, and external rotation. This allows the humeral head to clear the acromion during upward rotation. The scapula has an important function in the proximal-to-distal sequencing of shoulder movements. The body segments and muscles are coordinated to transfer forces to the terminal link (i.e., hand) through the shoulder, which is known as kinetic chain.¹⁷

Shoulder Instability                                 

• Capsulolabral Complex: Damage to the labrum, especially in the form of a Bankart lesion, is common in shoulder instability.⁴
• Glenohumeral Ligaments: Injury or laxity of the inferior glenohumeral ligament is common in anterior instability.⁸
• Rotator Cuff and Muscles: Overuse or injury to the rotator cuff muscles (supraspinatus, infraspinatus, subscapularis, teres minor) often occurs, leading to dysfunction.⁵
• Bony Lesions: Repeated dislocations may lead to Hill-Sachs lesions (compression fractures of the humeral head) or glenoid bone loss.⁸

Shoulder Dysfunction

• Rotator Cuff: Dysfunction typically involves the supraspinatus tendon, which is vulnerable to degeneration and tears.⁵
• Subacromial Space: Impingement of structures, such as the rotator cuff tendons or subacromial bursa, can result in pain and reduced motion.⁷
• Scapulothoracic Articulation: Poor scapular mechanics can contribute to shoulder dysfunction, leading to muscle imbalances and pain.⁶
• Glenohumeral Joint: Degeneration of cartilage in this joint can lead to osteoarthritis, stiffness, and reduced function.⁵

Scapular Dyskinesis

• Scapulohumeral Rhythm: Scapulohumeral rhythm, which refers to the coordinated movement between the scapula and humerus, becomes altered, leading to compensatory or abnormal movements.⁷
• Muscle Weakness and Tightness: Weakness in the scapular stabilizers (serratus anterior, lower trapezius) or tightness in the pectoralis minor may cause scapular winging or anterior tilting.⁶
• Impingement: Dyskinesis can decrease the subacromial space, leading to impingement of the rotator cuff tendons or bursa.⁸

Specific secondary or associated conditions and complications

MDI and scapular dyskinesis are often associated with external/internal impingement, rotator cuff tendinopathy, subacromial bursitis, biceps tendinopathy, acromioclavicular joint arthropathy, scapulothoracic bursitis and, rarely, scapular tumors.

Shoulder Instability

• Recurrent Instability: Increased risk of future dislocations following an initial dislocation.⁸
• Labral Tears: A torn labrum (e.g., SLAP lesions) can worsen shoulder instability.⁴
• Rotator Cuff Injuries: Instability can lead to rotator cuff tears, particularly in older individuals.⁵
• Post-Traumatic Osteoarthritis: Repeated dislocations may contribute to the development of early-onset osteoarthritis.⁴

Traumatic UDI is often associated with a soft tissue or bony Bankart lesion, Hill-Sachs lesion, rotator cuff tears, and proximal humerus fractures.

Shoulder Dysfunction

• Chronic Pain: Persistent dysfunction may result in long-term pain and disability.⁷
• Loss of Function: Ongoing damage can result in reduced ROM, strength, and difficulty with daily activities.⁶
• Adhesive Capsulitis: Often referred to as frozen shoulder, this condition is characterized by painful stiffness and restricted motion.⁵
• Nerve Compression: Shoulder dysfunction can lead to nerve impingement, such as suprascapular nerve compression.⁸

Scapular Dyskinesis

• Rotator Cuff Impingement: Dyskinesis can cause impingement of the rotator cuff tendons, leading to pain and tears.⁸
• Labral Tears: Scapular dyskinesis may contribute to labral tears, particularly in athletes who perform overhead movements.⁴
• Chronic Shoulder Pain: Dyskinesis is a common cause of ongoing shoulder pain, even after other pathologies are treated.⁷
• Instability: Dyskinesis can exacerbate shoulder instability, particularly in individuals with ligamentous laxity or rotator cuff weakness.⁶

Essentials of Assessment

History

UDI is often associated with trauma. Anterior/inferior instability is commonly caused by a single event where the shoulder is placed in an unstable position, typically 90 degrees of abduction and 90 degrees of external rotation. Posterior instability may be caused by a single event (car accident) or chronic microtrauma (football offensive lineman). The clinician must determine the mechanism of injury, associated neurologic symptoms, and if manual or spontaneous reduction occurred. MDI generally presents atraumatically, bilaterally, and with reports of weakness and/or poor athletic performance. Any inciting activities, prior history, pain, paresthesia, and history of hypermobility should be identified.

Physical examination

To rule out referred pathology, evaluate the cervical spine and peripheral nerves.

Inspection

• Look for atrophy, resting scapular position, bilateral symmetry, and prominence of the inferior and medial scapular border.^2,10
• A rounded shoulder posture suggests anterior chest wall tightness.²
• Dynamic observation of scapular motion during flexion and abduction may display prominence of the medial scapular border and dyskinetic patterns, part of a dynamic scapular dyskinesis test.^2,10

Palpation

• Examine the entire shoulder girdle for areas of tenderness. Tenderness over the coracoid process suggests pectoralis minor tightness associated with scapular dyskinesis.^2,10
• Assess both active and passive ROM in multiple planes. Patients with increased laxity of the glenohumeral joint may be able to voluntarily subluxate or dislocate and relocate their shoulders.²¹
• Test for glenohumeral internal rotation deficit (GIRD) which suggests posterior capsular tightness.^2,13

Special tests

• Load and Shift: Increased anterior or posterior motion of humeral head upon the glenoid suggests laxity.²²
• Drawer test: Suggests humeral head subluxation.¹⁰
• Sulcus Sign: Inferior instability may be indicative of multidirectional instability/congenital laxity.^18,22
• Relocation Test: Suggests anterior instability.^1,2
• Scapular Assistance Test: With active arm elevation apply gentle pressure on the inferior medial scapular border in upward rotation and posterior tilt. A positive test results in an increased arc of motion and relief of impingement symptoms.^8,15,20
• Scapular Retraction Test: Stabilize the scapula in a retracted position. A positive test results in relief of impingement symptoms.^13,18,23
• Gagey hyper-abduction test: Above 105 degrees of passive abduction is associated with laxity of glenohumeral ligaments.¹³
• Scapular Dyskinesis test: Observe scapular motion with weighted shoulder flexion and abduction movements. A positive test consists of characterizing scapular dyskinesis as absent or present, rating each side separately.²⁴
• Lateral Scapular slide test: Measure the distance between the scapular medial-inferior border and adjacent thoracic vertebrae in different positions (standing, hands on waist, and shoulder abduction to 90 degrees while maintaining arm in full medial rotation).²⁵

Imaging

• Radiography (orthogonal view): Identify traumatic lesions (i.e. bony Bankart lesions, Hill-Sachs defects, or other fractures) at pre- and post-reduction stage.²⁶ Assess underlying atraumatic diseases (i.e. bony pathology and humeral head position).
• MRI: Assess capsular laxity, glenoid labral tears or potential rotator cuff tears in patients over 40.²⁶ If labral pathology is suspected, then MRI Arthrography may be preferred.
• CT: Identify subtle fractures not recognized on plain radiographs and glenoid bone loss after a subluxation event.
• Ultrasound: Evaluate instabilities dynamically as well as soft tissue lesions (GH ligament or capsular thickening, rotator cuff injuries, joint effusions) in a cost-effective manner.

Other modalities

Nerve conduction tests and electromyography: Identify traumatic long thoracic nerve, dorsal scapular nerve or spinal accessory nerve damage as a cause of periscapular muscle weakness leading to dyskinesis.¹⁷ Most cases are due to muscular imbalances and other factors and not due to true nerve injuries, however.

Rehabilitation Management and Treatments

Available or current treatment guidelines

In MDI, current treatment guidelines recommend an initial course of non-operative management with a structured rehabilitation program. A surgical referral may be considered for an identified anatomic lesion and failure of the rehabilitation program. According to a 2017 review article, the surgical intervention revealed 14% of unsatisfactory result due to persistent instability or pain.²⁷

In order to decrease the failure rate, a well-designed and structured rehabilitation program should be provided to the patients. Focus should be on kinetic chain deficits, scapular stabilizer strengthening, appropriate shoulder girdle flexibility, and scapulothoracic mechanics. Maximal rotator cuff strengthening requires a stabilized, retracted scapula and should occur only after scapular control is achieved.^2,13,14

For traumatic first-time dislocations, non-operative treatment is often recommended. Operative treatment is usually indicated for persistent pain, recurrent dislocations, Bankart lesions involving greater than 20% of the glenoid fossa, and significantly displaced proximal humerus fractures.

Conservative treatment in scapular dyskinesis cases aims to restore scapular retraction, posterior tilt, and external rotation. Specific exercises for scapular rehabilitation include flexibility exercises to decrease scapular traction, and scapular stabilization exercises focusing on strengthening the serratus anterior, rhomboids and lower trapezius to optimize scapular kinematics.¹²

For patients with traumatic causes of instability, bracing of the shoulder to limit abduction and external rotation has been frequently used to attempt to return them to sport and prevent further instability events. Athletes have reported that they experience a greater sense of stability with bracing however evidence is limited to assess the ability of bracing to prevent further instability events or improve functional outcomes and there have been studies that have failed to show a significant difference in outcomes between bracing and no bracing.²⁸

It is unclear currently what role, if any, bracing has in the management of MDI. The decision to pursue a trial of bracing is an individualized decision and several factors including the patient’s sport, compliance, and ability to perform with a brace should be considered.³⁷

Prior to return to sport or occupation, the patient should be symptom-free, functionally prepared for return, and without persistent biomechanical abnormalities.³⁸

At different disease stages

Phase I – Soft Tissue Flexibility

• Increase the length of pectoralis minor and stretch short head of the biceps (i.e. “unilateral stretch,” “sitting manual stretch,” and “supine manual stretch).^14,29
• Address posterior capsular tightness and glenohumeral internal rotation deficit (i.e., “sleeper stretch,” and “cross body stretch”).^14,29

Phase II – Muscle Performance

• Stage 1-Kinetic Chain
  • Focus on hip extensor deficits, core stability, and pelvic control. Initial strengthening should involve static exercise with progression to dynamic multiplanar exercises involving trunk rotation.¹⁴
• Stage 2-Scapular Orientation
  • Achieve a neutral position of lumbopelvic, scapulothoracic, and cervical posture (i.e. “occipital lift maneuver”).²⁹
• Stage 3-Muscle Control
  • Open chain exercise
    • Improve the stability of scapular control.^10,26 Focus on rehabilitation of the lower trapezius and serratus anterior (i.e. “low row,” “inferior girdle,” “lawnmower,” and “robbery” exercise).²⁹
  • Closed chain exercise
    • Improve the dynamic stability of glenohumeral joint after achieving joint mobility and scapular stability.^14,29
    • Enhance fixation of scapula on thoracic wall by activating rotator cuff muscles (i.e. “wall sliding exercise,” and “push-ups”).²⁹
• Stage 4- Sports-specific Exercise
  • Power and endurance training for the upper extremities.
  • Perform multiplanar exercise for neuromuscular control.
  • Also include sport- and job-specific exercise.

Scapular Dyskinesis Treatment

Anterior Instability Protocol

Anterior shoulder instability rehabilitation primarily focuses on subscapularis muscle strengthening and coordination to dynamically hold the anterior portion of the glenohumeral joint in place.³⁹ It is recommended to do isometric contractions for the subscapularis and isolate this muscle from latissimus dorsi and pectoralis major muscles to better stabilize the anterior scapula.³⁹ This is done via “drawing the shoulder into its socket” or internally rotating the shoulder without activating other internal rotators (latissimus dorsi and pectoralis major). Rehabilitation is more on strengthening the internal rotation of the shoulder.³⁹ Later, patients work on concentric and eccentric exercises which involve weights, towels, or band work. More advanced training involves sports/job specific training and then higher neuro-muscular training.

Posterior Instability Protocol

Posterior shoulder instability protocol focuses on strengthening the infraspinatus muscle.³⁹ The rest of protocol is similar to the anterior instability protocol but focuses on external rotator strengthening.

Coordination of care

The physiatrist’s role is to coordinate care and ensure a patient-centered approach. Members of the team may include the physiatrist, patient, surgeon, primary care physician, physical therapist, athletic trainer, and coach. If symptoms do not resolve with a rehabilitation program, the patient should be reevaluated to ensure accurate diagnosis, consider further imaging, and/or consider surgical intervention.

Patient & family education

Patient and family understanding of the injury, risk factors, future prevention, and the treatment plan is key to patient “buy in” and subsequent recovery. The patient and family must play an active role in the rehabilitation process. In athletes, it is important to involve coaches and athletic trainers as early as possible.

Emerging/unique interventions

Multiple standardized metrics are used to measure shoulder dysfunction. No one test has been identified as the gold standard. Condition-specific measures such as the Melbourne Instability Shoulder Score (MISS) and Western Ontario Shoulder Instability Index (WOSI) have been utilized. A recent review of more than ten standardized metrics was completed and recommended the use of these tests because they have been shown to be reliable, valid, and responsive in patients with shoulder instability.³⁰ Other outcome measures provide general assessments such as: Oxford Shoulder Instability Questionnaires, Disability of the Arm, Shoulder and Hand (DASH), and Constant Shoulder Outcome Score.

Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills

Patients with MDI are more likely to experience subluxations than dislocations (84.6% vs. 15.4).^11,31 A majority of them are recurrent compared to primary subluxations (54.5% vs. 45.5%).²² Asymptomatic shoulder laxity must be distinguished from laxity associated with symptomatic instability.¹¹

No single diagnostic test can confirm the presence of multidirectional instability or scapular dyskinesis.¹¹ All causative factors mentioned above should be tested to properly evaluate scapular dyskinesia.

Always consider scapular dyskinesis when evaluating a patient with symptoms of shoulder impingement.

Cutting Edge/Emerging and Unique Concepts and Practice

In the last two decades, scapular stabilization has become a key component of shoulder rehabilitation. Inclusion of scapular exercises as part of a rehabilitation program achieves better results and higher patient-rated outcomes.³² The systemic review of MDI indicates arthroscopic capsular plication and open capsular shift as the best surgical procedures after rehabilitative treatment failure.³³ Short term rigid or Kinesio taping was shown to improve scapular dyskinesis in a study examining 72 asymptomatic athletes,³⁴ however high level evidence from clinical trials is still needed. Scapular dyskinesis was also noted to improve based on the scapular dyskinesis test with a combination of dry needling and manual therapy.³⁵

Gaps in the Evidence-Based Knowledge

The effects of scapular-focused programs have not been studied across all relevant shoulder diagnoses and, thus, more information is needed.³² In addition, there is a lack of studies focusing on chronic neck problems followed by shoulder dyskinesis. The validity and reliability of the aforementioned physical examinations are yet unanswered.³⁶ The role of regenerative and biologic treatments such as PRP, stem cell, prolotherapy, and ozone has not yet been identified in the medical literature for treatment of shoulder instability.

There remains controversy regarding the role of immediate surgical intervention for first time dislocation. Labral injury, internal impingement, rotator cuff injury, clavicle fractures and AC separations can cause muscle inhibition, which eventually results in scapular dyskinesis. In these cases, the surgical intervention such as arthroscopic plication should be considered primarily.¹⁷ Recurrent shoulder instability events increases after primary traumatic instability events. According to the traumatic shoulder instability study, 54.5% of subluxation and 33.3% of dislocation cases were secondary instability events.³¹ In one recent retrospective review, it was noted that moist patients under 40 years old with a first time traumatic anterior shoulder dislocation did well with 6 months of nonoperative management, but over one-third went on to have further shoulder instability and 20% later underwent shoulder surgery.⁴⁰

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Original Version of the Topic

A. Michael Henrie, DO, Robert Engelen, DO. Shoulder instability, dysfunction and scapular dyskinesis. 9/20/2013.

Previous Revision(s) of the Topic

Soo Yeon Kim, MD and Keonhee Kim, BS. Shoulder instability, dysfunction and scapular dyskinesis. 8/3/2017.

Sol Abreu-Sosa, MD, Joseph C Brutzkus, MD, Lane M Lagattuta, DO. Shoulder Instability, Dysfunction and Scapular Dyskinesis. 11/8/2021.

Author Disclosure

Lawrence Chang, DO, MPH
Nothing to Disclose

Michael Lem, MD
Nothing to Disclose

Tracie Dang, DO
Nothing to Disclose