Shoulder Dislocations — Acute, Recurrent, and Habitual

Introduction

The glenohumeral joint is the most commonly dislocated major joint in the body, accounting for approximately 50 percent of all major joint dislocations. The combination of anatomical features that produce the extraordinary range of motion of the shoulder — a shallow, slightly tilted glenoid relative to a large humeral head, a primary reliance on capsuloligamentous and muscular stabilizers rather than bony congruity, and the dynamic dependence on the rotator cuff — also predispose the joint to instability. The clinical spectrum of shoulder instability ranges from the single traumatic dislocation in the young athlete with subsequent recurrence to the multidirectional instability of the joint-lax adolescent and the voluntary “habitual” dislocator. The treatment options span from closed reduction and a brief period of immobilization to arthroscopic and open capsulolabral repair, bone-block procedures for glenoid deficiency, and, in the elderly, hemiarthroplasty or reverse arthroplasty for fracture-dislocations. This chapter, drawing on Rockwood and Green’s Fractures in Adults, AO Principles, Miller’s Review of Orthopaedics, and Apley & Solomon’s, addresses the spectrum of shoulder instability.

Anatomy and Pathomechanics

The glenohumeral joint is a ball-and-socket articulation with a marked size mismatch — the humeral articular surface area is approximately three to four times that of the glenoid. The static stabilizers include the glenoid labrum (which deepens the glenoid by approximately 50 percent), the glenohumeral ligaments (superior, middle, and inferior — the inferior glenohumeral ligament complex with its anterior and posterior bands and intervening axillary pouch is the principal restraint to anterior translation in abduction and external rotation), the capsule, and the negative intra-articular pressure that produces a “suction” effect. The dynamic stabilizers include the rotator cuff (subscapularis, supraspinatus, infraspinatus, teres minor) which produces compressive force into the glenoid, the long head of the biceps, the scapular rotators (trapezius, serratus anterior, rhomboids), and the deltoid. The classical mechanism of anterior dislocation is forced abduction and external rotation, producing failure of the inferior glenohumeral ligament complex with avulsion of the anteroinferior labrum from the glenoid (the Bankart lesion, described by A.S. Blundell Bankart in 1923 and 1938). Concurrent injuries include the Hill-Sachs lesion — a posterolateral humeral head impression fracture produced as the head dislocates over the anterior glenoid rim, described by Hill and Sachs in 1940 — and bony involvement of the anterior glenoid rim (the bony Bankart, or, when associated with substantial bone loss producing an “inverted pear” glenoid, the anteroinferior glenoid rim defect).

Acute Anterior Dislocation

Anterior dislocation accounts for 95 to 97 percent of glenohumeral dislocations. The patient presents with the affected arm held in slight abduction and external rotation, with loss of the normal rounded deltoid contour (“squared off” shoulder), prominence of the acromion, and a palpable humeral head anteriorly in the deltopectoral groove. The patient is typically unable to bring the hand to the opposite shoulder. Neurovascular examination is mandatory before reduction and must be documented — the axillary nerve is the most commonly injured structure (clinically tested by sensation over the lateral deltoid; motor testing in the acutely dislocated shoulder is unreliable because of pain), but the musculocutaneous nerve, the radial nerve, and the brachial plexus can all be injured. Vascular injury (axillary artery) is rare but is more common in elderly patients with calcified atherosclerotic vessels. Radiographic assessment before reduction is standard practice in adult patients with first-time dislocations or those without an established history. The minimum series is an AP, scapular Y (lateral), and axillary view; the axillary view is the most reliable confirmation of joint congruity. In the patient who cannot tolerate axillary positioning, a Velpeau axillary view or a trans-thoracic lateral may be substituted. CT is reserved for the evaluation of bony injury after the first dislocation in selected patients, particularly those with suspected glenoid bone loss or Hill-Sachs lesion of significant size. Closed reduction is performed with appropriate analgesia and muscle relaxation. Multiple techniques exist; the most commonly used include: • Traction-countertraction with axial traction on the abducted arm and countertraction by an assistant with a sheet around the chest. • Stimson technique, with the patient prone and the arm hanging over the side of the bed with a 5- to 10-pound weight providing traction over 15 to 30 minutes. • Kocher technique — adduction of the arm to the side, external rotation, then internal rotation and adduction — historically popular but with higher risk of neurovascular injury and humeral fracture in the unrelaxed patient. • Milch technique — abduction and external rotation with overhead positioning, followed by gentle longitudinal traction. • Scapular manipulation — with the patient seated and gentle traction on the arm, the inferior pole of the scapula is rotated medially while the superior pole is rotated laterally; among the most gentle and successful techniques. • FARES (Fast, Reliable, and Safe) method, a more recent technique with gentle oscillating movements through gradual elevation of the abducted arm. Post-reduction radiographs confirm successful reduction, and a repeat neurovascular examination is mandatory. The arm is placed in a sling (or, in some protocols, in an external rotation brace following a 2007 trial by Itoi et al. that suggested improved capsular healing position) for 3 to 6 weeks, followed by progressive rehabilitation.

The Question of Recurrence and Surgical Intervention After First Dislocation

The risk of recurrence after a first-time anterior shoulder dislocation correlates most strongly with age at first dislocation. The classical figure from the Hovelius series and confirmed by multiple subsequent studies is that patients under 20 years have a recurrence rate exceeding 60 percent (approaching 80 to 90 percent in active populations of military or contact-sport athletes), while patients over 40 have recurrence rates below 20 percent. Other predictive factors include male sex, high-demand sport or occupation, the presence of bony defects (Hill-Sachs lesion, glenoid bone loss), and the duration of immobilization (which has little proven effect on recurrence). The traditional teaching that all first-time dislocations should be treated non-operatively has been challenged by the arthroscopic Bankart repair after first dislocation literature. Trials including those by Kirkley (2005) and Robinson (2006) have shown that early arthroscopic stabilization in young athletes substantially reduces recurrence rate (approximately 10 to 15 percent) compared with non-operative management (60 to 80 percent), with associated improvements in function and return to sport. The current treatment paradigm in young active patients (under 25 to 30, depending on the source) is increasingly to offer early arthroscopic Bankart repair after the first dislocation, particularly in collision and overhead athletes; in older or less active patients, non- operative management with selective stabilization for recurrence remains standard.

Posterior Dislocation

Posterior dislocation accounts for 2 to 4 percent of shoulder dislocations and is notoriously easy to miss. The classical mechanisms are seizure, electric shock, and posteriorly directed force on the flexed and adducted arm. The clinical picture is subtle — the arm is held in adduction and internal rotation (typically across the body), the shoulder appears flat, there is a posterior prominence, and external rotation is markedly limited (the most useful clinical sign). Plain AP radiographs may appear nearly normal — the classical “lightbulb sign” of internal rotation of the humeral head, or the “rim sign” with widened glenohumeral space, may be subtle. The axillary view is essential and diagnostic. CT defines associated bony injury, particularly the reverse Hill-Sachs lesion (anteromedial humeral head impression fracture) and any posterior glenoid rim fracture. Closed reduction is performed by axial traction with the arm adducted, combined with gentle anteriorly directed pressure on the posterior humeral head. The reduction should be performed gently to avoid converting a posterior dislocation with a small reverse Hill- Sachs into a humeral head fracture. Post-reduction, the arm is immobilized in slight external rotation (or in a gunslinger brace) for 4 to 6 weeks. The patient with chronic locked posterior dislocation (missed and presenting weeks to months after injury) requires individualized management. A reverse Hill-Sachs lesion involving less than 25 percent of the humeral head can be addressed by open reduction with subscapularis transfer into the defect (McLaughlin procedure, 1952; or its bone- block modification, the modified McLaughlin). Defects of 25 to 50 percent require osteochondral allograft or rotational osteotomy. Defects greater than 50 percent, or in the

elderly with osteoarthritic changes, are addressed by hemiarthroplasty or reverse total shoulder arthroplasty.

Inferior Dislocation (Luxatio Erecta)

Luxatio erecta is a rare (<1 percent of shoulder dislocations) dislocation in which the humeral head dislocates inferiorly into the subglenoid position, with the arm fixed in marked abduction (typically 110 to 160 degrees) and the forearm draped over the head — a striking and unmistakable clinical presentation. The mechanism is a hyperabduction force, typically a fall with the arm raised overhead. Neurovascular injury is more common than in anterior dislocation (axillary artery injury in 3 percent, axillary nerve injury in approximately 60 percent), and most patients have associated rotator cuff tears. Reduction is by axial traction along the line of the humerus combined with anteriorly directed countertraction, with conversion of the dislocation into an anterior dislocation pattern as the arm is brought down to the side. Open reduction is required for irreducible cases.

Recurrent Anterior Instability — Evaluation

The patient with recurrent anterior shoulder instability requires careful evaluation directed at the structural and functional contributors. History establishes the number, frequency, and circumstances of dislocations; whether the patient requires assisted reduction or self-reduces; the energy required to produce dislocation (high-energy dislocations imply more severe pathology than low-energy events that occur in mid-range positions). Physical examination includes specific instability tests: the apprehension test (anterior instability — pain or sensation of impending dislocation with the arm in abduction and external rotation), the Jobe relocation test (relief of apprehension with posterior pressure on the humeral head), the anterior load-and-shift test, the sulcus sign (inferior translation of the humeral head with traction — a positive sulcus suggests inferior instability or multidirectional instability), and the posterior jerk test. The Beighton score evaluates generalized joint laxity (one point each for elbow hyperextension >10°, knee hyperextension >10°, thumb-to-forearm apposition, fifth MCP hyperextension >90°, palms- to-floor on forward bending; total out of 9 with scores ≥4 indicating generalized hypermobility). Imaging evaluates bony involvement. The best radiographs are the Stryker notch view (for Hill-Sachs), the West Point view (for anterior glenoid bone loss), and the Bernageau profile view (for glenoid bone loss). CT with 3D reconstruction has largely replaced specialized radiographs for bone-loss assessment and is the standard for surgical planning. MR arthrography delineates labral and capsular pathology, including the Bankart lesion (anteroinferior labral avulsion), the bony Bankart (labral avulsion with attached bone fragment), the Perthes lesion (labral avulsion with intact periosteum, undisplaced), the ALPSA lesion (anterior labroligamentous periosteal sleeve avulsion — labrum displaced medially down the scapular neck), the GLAD lesion (glenolabral articular disruption — labral injury with adjacent cartilage damage), and the HAGL lesion (humeral avulsion of the glenohumeral ligaments).

Recurrent Instability — Treatment

The choice of treatment for recurrent anterior instability is structured around the bony anatomy. The critical concept is glenoid bone loss, quantified on the en-face glenoid view of 3D CT. Glenoid bone loss less than 13 to 15 percent (depending on series) of the inferior glenoid diameter is considered amenable to arthroscopic soft-tissue Bankart repair alone; bone loss greater than 20 to 25 percent (the “critical bone loss” of Burkhart and De Beer, 2000) requires bony augmentation. The intermediate range (15 to 20 percent, the “subcritical” zone of Shaha) is currently debated, with increasing recognition that bony procedures may produce better outcomes than soft-tissue repair alone even in this range. Arthroscopic Bankart Repair The standard procedure for recurrent anterior instability without significant bone loss is arthroscopic Bankart repair with suture anchor fixation of the labrum to the glenoid rim. Outcomes are generally good (90 percent or more return to sport), with the most important risk factors for recurrence being unrecognized bone loss, contact sport participation, and prior failed instability surgery. The Latarjet Procedure For significant glenoid bone loss, the Latarjet procedure, described by Michel Latarjet in 1954, transfers the coracoid process with the conjoint tendon (short head of biceps and coracobrachialis) to the anterior glenoid neck, where it is fixed with screws. The procedure provides stability by three mechanisms (“triple effect” or “sling effect”): the bony block restoration of the anterior glenoid arc, the dynamic “sling” effect of the conjoint tendon across the anterior shoulder as the arm is abducted and externally rotated, and the capsular reinforcement provided by suturing the coracoacromial ligament stump back to the capsule. The Bristow procedure is a similar but smaller bone-block procedure (transferring only the coracoid tip with a single screw). The Latarjet has substantially lower recurrence rates than soft-tissue repair in the bone-loss patient and has the additional advantage of preserved external rotation; complications include screw or fixation failure, nerve injury (musculocutaneous, axillary), graft fracture, and progression to glenohumeral arthritis (the “Latarjet arthropathy”). Arthroscopic Latarjet has been developed but remains technically demanding. Glenoid Reconstruction with Bone Graft Alternatives to the Latarjet for glenoid bone reconstruction include iliac crest autograft (the Eden-Hybinette procedure, historically), distal tibial allograft (Provencher’s contribution, with excellent cartilage match and lower donor-site morbidity), and distal clavicle autograft. Each restores the bony anatomy without the dynamic sling effect of the Latarjet.

Humeral Bone Loss Significant Hill-Sachs lesions, particularly engaging Hill-Sachs (where the defect engages the anterior glenoid rim in abduction and external rotation, identified by the “glenoid

track” concept of Yamamoto et al., 2007), may require dedicated treatment. Remplissage is an arthroscopic procedure in which the infraspinatus tendon is sutured into the Hill- Sachs defect, converting it into an extra-articular defect and tethering the humeral head against re-engagement. The procedure is commonly added to Bankart repair when an engaging Hill-Sachs is identified. Larger humeral defects may require allograft reconstruction or partial humeral head resurfacing.

Multidirectional Instability and Habitual Dislocation

Multidirectional instability (MDI), characterized by symptomatic instability in more than one direction (anterior, inferior, or posterior) typically in the patient with constitutional ligamentous laxity, presents a different challenge. The pathology is generally not a discrete labral tear but a globally lax, redundant capsule. The patient is typically young, with bilateral involvement common, and often has features of generalized joint laxity (positive sulcus sign, high Beighton score). The mainstay of treatment is dedicated physiotherapy to strengthen the dynamic stabilizers (the Rockwood protocol of progressive rotator cuff and periscapular strengthening), continued for at least six months. Surgical management is reserved for those failing conservative treatment and consists of arthroscopic capsular plication (or, historically, open capsular shift) to reduce capsular volume. The treatment of voluntary or habitual dislocation in the patient with psychogenic features is virtually always non-operative — surgical fixation in this population has uniformly poor outcomes. Habitual posterior dislocation, the rare condition in which the patient voluntarily dislocates the shoulder posteriorly through selective muscle contraction, requires careful psychological evaluation and is typically managed by physiotherapy and behavioral approaches. The historical Boyd-Sisk procedure of biceps tendon transfer for habitual posterior instability is now rarely performed.

Summary and Take-Home Points

Shoulder dislocation is most commonly anterior, with the classical mechanism of forced abduction and external rotation producing the Bankart lesion of the anteroinferior labrum and the Hill-Sachs impression of the posterior humeral head. Neurovascular evaluation (axillary nerve in particular) is mandatory before and after reduction. Closed reduction by traction-countertraction, scapular manipulation, or FARES technique is generally successful; post-reduction immobilization for 3 to 6 weeks followed by progressive rehabilitation is standard. Recurrence is age-dependent, with patients under 20 facing rates of 60 to 90 percent; early arthroscopic Bankart repair is increasingly offered to young high-demand patients after the first dislocation. Recurrent anterior instability is evaluated for bony involvement on CT. Soft-tissue Bankart repair is appropriate for cases without significant glenoid bone loss; the Latarjet coracoid transfer provides reliable stability with its bony, sling, and capsular components for cases with significant glenoid bone loss. The remplissage procedure addresses engaging Hill- Sachs lesions. Posterior dislocations, often missed at first presentation, require attention to the lightbulb sign and the axillary view, with reduction performed gently to avoid

converting reverse Hill-Sachs into humeral head fracture. Luxatio erecta presents in unmistakable fashion and is reduced by traction with conversion to anterior dislocation. Multidirectional instability and habitual dislocation are largely non-operative entities responding to dedicated rotator cuff and periscapular strengthening, with surgical management reserved for treatment failures and explicitly avoided in voluntary dislocators with psychogenic features. The chapter that follows turns to proximal humerus fractures, which often coexist with dislocation as “fracture-dislocations” and which represent another major orthopedic decision-point at the shoulder.