Shoulder Subluxation – Causes, Symptoms, Treatment

Shoulder subluxation is defined as partial or incomplete dislocation of the glenohumeral joint or translation between the humeral head and glenoid fossa while the humeral head is in contact with the glenoid fossa.[rx][rx] The weakness of rotator cuff muscles or laxity of the glenohumeral ligaments causes the humeral head to easily slip out of the glenoid fossa and results in glenohumeral subluxation.

Causes of Shoulder Subluxation

The etiology can be classified as traumatic, non-traumatic and neuromuscular causes. For the traumatic cause, it is more frequent in active young individuals[rx]. Shoulder subluxation is prevalent in boxers.[rx] However, a non-contact sport with repetitive shoulder movements and a hand in the outstretched position can also cause subluxation. For the non-traumatic cause, the etiology could be multifactorial. The patients may have suboptimal shoulder muscle control or tendon/ligament injury in the rotator cuff interval.[rx][rx] These 2 patterns of shoulder instability can be defined as TUBS syndrome (traumatic, unilateral dislocations with a Bankart lesion, often requiring surgery) and AMBRI syndrome (atraumatic, multidirectional, bilateral shoulder subluxation/dislocations, often treated with rehabilitation, and sometimes requiring inferior capsular shift), respectively.[rx] The neuromuscular causes, such as stroke, cerebral palsy, and brachial plexus injury can also lead to shoulder subluxation.[rx][rx]

Pathophysiology

The anterior labral detachment is the most common traumatic cause leading to anterior shoulder instability.[rx] In the non-traumatic population, the loose and redundant inferior capsule, ligamentous laxity, and injury around the rotator cuff interval affect shoulder movement and lead to subsequent glenohumeral instability.[rx] For neuromuscular cases, weakness of rotator cuff and shoulder girdle muscles results in shoulder inferior subluxation. Spasticity of internal rotation muscles (latissimus dorsi, pectoralis major, and subscapularis muscles) results in a backward tendency of the humeral head and causes the posterior shoulder subluxation.[rx]

The adolescents frequently experience recurrent subluxations. There is a higher amount of collagen type III (more elastic than type I collagen) in ligaments and tendons. With the increase in age, the collagen-producing cells produce more collagen type I which is less insoluble and more stable.[rx]

For the atraumatic cause, the cysteine contents which are abundant in collagen type III are higher in shoulder joint capsule when compare with the normal population. In addition, the adaptation and remodeling of collagen in the joint capsules of unstable shoulders show higher stable and reducible collagen cross-links, collagen fibril diameters, and elastin content to provide the strength for the shoulder capsule. The collagen study in the skin tissue shows smaller collagen fibril diameters correlate with the increases in glenohumeral joint laxity.[rx]

Diagnosis of Shoulder Subluxation

History and Physical

The patients present with the symptoms of feeling stiffness, mild pain, and instability of the shoulder girdle. A history of previous dislocation, mechanism of injury (direction of shoulder movements during the traumatic event), and family history of shoulder instability are also important.[rx]

For stroke patients with hemiplegia, although there is no clear association between shoulder subluxation and pain, both medical conditions can exist simultaneously. Furthermore, some patients have a limited range of motions on the hemiplegic shoulder after shoulder subluxation.

During physical examinations, subluxation is detected by palpation of the glenohumeral joint. The extent of shoulder subluxation can be quantified by the distance from the acromion to the humeral head, using fingerbreadth, caliper, or tape.[rx] However, the physical examination should be performed bilaterally, and comparison between both sides is important for establishing a correct diagnosis. Inspection of shoulder contours, the examination of the active and passive range of motion, and motor and sensory testing are suggested to perform for finding out the causes of shoulder subluxation.

The tests to examine shoulder laxity include the load and shift, drawer, sulcus, hyperabduction, and push-and-pull tests.[rx][]rx The apprehension and relocation test is specific for examining anterior shoulder instability.[rx]

For patients with a history of stroke, if they present with concomitant subluxation and shoulder pain, the physical examination for the rotator cuff tendinopathy, acromioclavicular arthropathy, and subacromial impingement helps identify the cause of shoulder pain.[rx]

Evaluation

Patients with traumatic shoulder subluxations should have plain radiographs of anteroposterior, scapular-Y, and axilla views done to evaluate the severity of shoulder subluxation and collateral injuries to the bones and joints. The diagnostic ultrasound and magnetic resonance imaging (MRI) can provide the details of soft tissue injuries such as the labral tear. Computerized tomography (CT) scan is mainly indicated for traumatic shoulder dislocation to rule out subtle fractures not visible on radiographs or to assess the severity of associated fractures already noticed on the radiographs.[rx][rx]

In atraumatic shoulder subluxations, shoulder radiographs can be arranged to evaluate the translation of the humeral head with respect to the glenoid. It may be helpful to detect some bony factors leading to shoulder instability, such as a hypoplastic/dysplastic glenoid with a flat glenoid fossa. The stress radiographs arthrography, MRI, or arthroscopy, are not mandatory for diagnosis unless some underlying pathology is suspected.[rx]

For hemiplegic shoulder subluxation, the shoulder radiographic can be arranged to follow up on the treatment effectiveness or development of glenohumeral subluxation over time. However, palpation of the subacromial gap for grading the extent of shoulder dislocation seems to be reliable and unnecessary radiographs should be avoided. Also, diagnostic ultrasound can help to investigate the causes of shoulder pain with subluxation, such as bicipital or supraspinatus tendinosis and impingement.[rx]

Treatment of Shoulder Subluxation

Non-Surgical Treatment

In traumatic shoulder subluxation, the immediate treatments include ice packing to reduce soft tissue swelling, avoiding postures leading to recurrent subluxation, and wearing a protective arm sling. Narcotics or non-steroid anti-inflammatory drugs can be used for pain control. The passive or active assistive range of motion exercise of upper limb and scapular stabilization exercise can start as early as possible, followed by strengthening of shoulder girdles muscles, and glenohumeral joint proprioceptive training to improve dynamic shoulder stability.[rx][rx]

In the atraumatic group, the goal of treatment is to restore the shoulder function. The rehabilitation should emphasize the progressive strengthening of the rotator cuff, deltoid, and scapular stabilization muscles. Exercises to improve shoulder coordination with lifestyle modification is also recommended.[rx]

The hemiplegic shoulder subluxation, functional electrical stimulation (FES) is effective in reducing subluxation in the acute stage. Shoulder support or orthosis such as Bobath, Rolyan humeral cuff, or standard hemi sling may reduce the subluxation. To prevent further subluxation in stroke patients, supporting the hemiplegic limb in the proper position is crucial.[rx][rx]

The modalities for pain control, including ice in an acute phase, ultrasound therapy, transcutaneous electrical nerve stimulation (TENS), electrical stimulation (ES), and moist heat.[rx][rx]

Surgical Treatment

Surgical management is considered in younger patients or active individuals with chronic shoulder subluxations. The indications for the operation include failed non-operative treatment, recurrent dislocation in younger age, irreducible dislocation, open dislocation, unstable reduction, the first time in the young adults with traumatic unilateral dislocations, high work demand and bony Bankart lesion.[rx]

The surgical procedure classified into arthroscopic and open surgeries. The open shoulder stabilization surgery is needed if there is a contraindication for arthroscopic management like Hill-Sachs lesions, glenoid defects more than 30%, humeral avulsion glenohumeral ligament (HAGL) injury, shoulder instability with the bony fragment, shoulder deformity and previous surgery of shoulder stabilization. The operations commonly performed are the capsular-shift procedure to tighten the shoulder capsule, Bankart repair for labral tears, the Remplissage procedure for the Hill-Sach lesion, and Latarjet procedure for the glenoid bone loss more than 30%. The capsular-shift, Bankart repair, and Rempissage procedure can be done with open or arthroscopic technique. The Latarjet procedure should be performed openly.[rx]

When comparing the results of open and arthroscopic surgeries, arthroscopic management is as effective as open repair in improving shoulder stability. The advantages of arthroscopic surgery include shorter operative time and hospital stay, decreased morbidities, and complications and lower cost, and less surgical scar.[rx] However, this arthroscopic technique highly depends on surgeons’ experiences and is not able to correct the bony defect.