Glenohumeral instability

Definition

Glenohumeral shoulder instability is the sympotmatic inability to actively centre the humeral head in relation to the glenoid. Hyperlaxity on the other hand is a translation of the humeral head greater than can be expected physiologically [1].

Often instability is referred to, when speaking about symptomatic translations of the shoulder joint with loss of performance or pain, whereas hyperlaxity is seen as an asymptomatic, however not necessarily non-pathological, condition [1].

It should be noted that hyperlaxity may predispose for instability in the glenohumeral joint or might favour traumatic incidences. However, hyperlaxity may also be a separate entity which does not create instability. In other words shoulder instability can be present with or without hyperlaxity.

Aetiology

Several mechanisms may lead to instability of the shoulder. They can be generally divided into two different groups:

Traumatic

• • • The instability is typically unidirectional and unilateral

    • Mechanisms leading to instability

• • • • Anterior dislocation or subluxation

      • Posterior dislocation or subluxation

      • Inferior dislocation or subluxation

    • Observed lesions in the glenohumeral joint:

      • Labral tears

      • Ligament injuries (typically inferior glenohumeral ligament)

      • Bone defects at the glenoid (bony Bankart lesion, bone deficiency at the rim of the glenoid)

      • Bone defects at the humeral head (Hill Sachs lesion)

Atraumatic

• • The instability is often multidirectional and bilateral. Unilateral, unidirectional instability may however exist

  • Mechanisms leading to instability:

• • • Joint hyperlaxity, with or without congenital disorders

    • Overuse, resulting in a weakness of stabilisers of the glenohumeral joint

    • Muscular dysbalance

  • Observed lesions in the glenohumeral joint:

    • • Dysplasia of the glenoid with a deficient posterior glenoid rim may be present in patients with unidirectional posterior instability

      • Most often, MRI shows a wide joint capsule, but no other lesion of the glenohumeral joint

Epidemiology

Sports are the main cause of instability events in young patients as injuries during activities account for 75% of dislocations or subluxations [3]. Anterior instability represents more than 70% followed by posterior instability with more than 20% [3]. These numbers do correlate with the direction of dislocation. The majority of patients presenting with any type of instability are below 30 years old, male and active, since this population is most susceptible to dislocation events [3].

History

Anamnesis is the most vital tool in diagnosing shoulder instability, where different course of events might indicate certain aetiologies. There are several points, which should be addressed if shoulder instability is suspected in a patient [4]:

• Age

  • • Patients are usually young (<40) compared to other pathologies of the shoulder; Patients in their teenage years or 20s often describe a traumatic event [1]

• Unilateral or bilateral involvement

  • • Bilateral involvement is usually observed in atraumatic aetiologies

• Family history of instability

  • • Could be an indicator for genetic disorders affecting tissue matrix proteins leading to hypermobility

• Initial or recurrent event

• Arm position during event

  • • Suggesting anterior dislocation and instability:

      • • • Abduction, extension an external rotation

    • Suggesting posterior dislocation and instability:

      • • • Adduction, flexion, and internal rotation (e.g. rugby players)

• Number of previous events

• Degree of force (initial and recurrent)

• Can the patient voluntarily recreate the event?

• Was a reduction manoeuvre required?

• Presence and location of pain or sensory disturbance

• Presence of mechanical symptoms

• Previous shoulder surgeries

Disease specific diagnosis

Physical examination is the next step in diagnosing shoulder instability. First and foremost, the patient’s shoulder should be inspected thoroughly. Asymmetries in form of atrophy in the deltoid, supraspinatus or infraspinatus may indicate damage to nerves or rotator-cuff tears and should be further assessed [4]. Also, scapular position at rest and during elevation should be closely inspected to detect any scapular dyskinesia [4]. Testing both shoulders for range of motion as well as strength may indicate direction of instability and course of disease. Neurovascular testing is important since patients with recurrent dislocations are at risk of experiencing lesions of the axillary nerve as well as surrounding vessels [4].

Several clinical tests allow for the diagnosis of instability and/or (hyper-)laxity of the affected shoulder

Tests for shoulder instability (videos can be found at the end of the page):

• Apprehension Test (anterior unidirectional instability)

  • • • • The Patient either is sitting or lying supine at the edge of the examiner-bed, additionally supporting the scapula. In 90° abduction, the examiner slowly externally rotates to 90°. Apprehension or pain in this position already indicates anterior instability. The test can be enhanced by applying an anterior directed force to the proximal humerus.

• Relocation test (anterior unidirectional instability)

  • • • • The relocation test can be viewed as a variant of the apprehension test since patient and patients’ arm are in the same position. However, instead of anterior-directed force, posterior-directed force is applied, which will alleviate the patient’s apprehension and/or pain. At last, a release test can be executed, where the examiner releases the posterior directed force, which should result in reproducing the apprehension and/or pain.

• Jerk Test (posterior unidirectional instability)

  • • • • The patient lays supine on the edge of the examiners bed, who takes the patients arm and puts it in 90° forward flexion and maximal adduction and internal rotation. The examiner then pushes down on the elbow, generating a posterior directed force (posterior load) while keeping close watch for subluxation or dislocation. While maintaining posterior load, the arm is slowly and gently abducted and felt for a jerk when the humeral head relocates into the glenoid.

Tests for (hyper-)laxity:

• Drawer Test (anterior/posterior unidirectional (hyper-)laxity)

  • • • • Anterior: Patient sits upright, examiner stabilizes scapula by placing index finger on coracoid and thumb on the scapular spine. The examiner then places his/her other index finger and thumb around the humerus and pushes it gently forward. The amount of translation is estimated as the percentage of the humeral head that can be subluxated anterior to the glenoid rim.

        • Posterior: Very similar to the anterior drawer test, the examiner stabilizes the scapula while patient sits upright. He/she then proceeds by gently pushing the humeral head in posterior direction to the glenoid rim. Just as in the anterior drawer test, translation is measured as the percentage of the humeral head that can be subluxated.

    • NOTE: Up to 50% can be considered physiological emphasizing the relevance of comparing both sides

• Load and shift test (anterior/posterior unidirectional (hyper-)laxity)

  • • • • With the patient supine on the edge of the examiners bed, the examiner abducts the arm gently, proceeded by applying an axial load to the patient’s arm. With one hand around the patients proximal humerus, the humeral head is than translated in posterior and anterior direction (shift). According to the classification by Gerber and Ganz, the amount of translation can be divided into three grades:

          • • Grade I: Minimal translation of the humeral head

            • Grade II: Translation of the humeral head to the glenoid rim

            • Grade III: Translation of the humeral head over the glenoid rim

• Sulcus-Test (inferior (hyper-)laxity)

  • • • • Patient is sitting in upright position with the arm to be examined loosely to his side. The examiner fixates scapula and acromion by placing his/her index finger on the coracoid and the thumb on the scapular spine. The arm is then pulled downwards by the elbow. The sulcus test is positive if an indentation below the acromion becomes visible.

If previous findings indicate a generalized laxity or instability in multiple directions existed in previous testing, hyperlaxity should be assessed according to the Beighton score [5]. Patients are scored in different tests from 0 to 9 including:

• hyperextension of the small finger metacarpophalangeal joint past 90 degrees (2P)

• ability to place the thumb on the volar forearm (2P)

• hyperextension of the elbow joint beyond 10 degrees (2P)

• hyperextension of the knee joint >10 degrees (2P)

• the ability to place both palms flat on the floor with the knees extended (1P)

One point is given for a positive finding on either side. A score of 4 or more is associated with generalized ligamentous laxity [5].

In case of instability, x-ray, CT, or MRI should be performed in order to rule in or out possible lesions of the glenoid or humeral head as these might have implications for treatment [1].

Differential Diagnosis

• Rotator cuff tear

• Impingement syndrome (posterior instability)

• Osteoarthritis

• Glenohumeral synovitis due to a systemic disease

Risk factors for recurrent instability are: age below 30 years, male sex and participating in contact sports or sports involving high levels of upper body activity [2]. Overall, prognosis is favourable if treated sufficiently early. Yet there are long-term problems associated with instability of the glenohumeral joint. These include damage to the joint capsule, glenoid and humeral head bone loss and glenohumeral osteoarthritis [2]. A study suggests that 31.2% of joints showed radiographic signs of glenohumeral osteoarthritis before initial stabilisation surgery and that the quantity of dislocations correlates with the degree of degenerative changes [2].