McLaughlin Procedure (Locked Posterior Shoulder Dislocation)

Primary indication. An engaging reverse Hill-Sachs defect involving approximately 20 to 40 percent of the humeral head articular surface after a chronic locked posterior dislocation (greater than 3 weeks duration). The defect is the impaction created on the anteromedial humeral head when the head is locked against the posterior glenoid rim. The transfer blocks re-engagement of the defect on the posterior glenoid rim in functional positions. Classic mechanism triad. The index injury is almost always one of three: - Seizure (ictal phase) - violent contraction of the stronger internal rotators (subscapularis, latissimus, pectoralis) overcomes the external rotators and drives the head posteriorly; the anteromedial head impacts the posterior glenoid rim.

• Electrocution - a similar mechanism, with tetanic internal rotator contraction against a fixed thorax.
• High-energy trauma - a fall on the flexed, adducted, internally-rotated arm, or a motor vehicle accident with an axially-loaded flexed arm. Indications - Absolute: chronic locked posterior dislocation (greater than 3 weeks) with an engaging reverse Hill-Sachs defect; an acute locked posterior dislocation that fails closed reduction (for example, buttonhole engagement of the head through a posterior capsular tear); recurrent posterior instability with a documented engaging reverse Hill-Sachs defect on CT.
• Relative: an acute locked posterior dislocation with a 20 to 40 percent defect addressed as a primary procedure; failed nonoperative management of a smaller defect with persistent symptoms and documented engagement; combined bony (reverse Hill-Sachs) and soft-tissue (posterior Bankart) pathology. Contraindications - Absolute: humeral head avascular necrosis (AVN) with collapse (reverse total shoulder arthroplasty is the answer, not the transfer); established glenohumeral arthritis with loss of joint space (arthroplasty indicated); a defect greater than 40 to 50 percent without sufficient articular surface for transfer (allograft reconstruction or arthroplasty).
• Relative: an acute dislocation with a small defect (less than 20 percent) where nonoperative management should be trialled; a patient unable to comply with the 6-week subscapularis protection protocol; active infection; a neuropathic (Charcot) joint (arthrodesis or reverse total shoulder arthroplasty). Defect size drives the algorithm. The whole management strategy pivots on how much of the articular surface is impacted:

Acute versus chronic. An acute locked posterior dislocation (less than 3 weeks) usually results from high-energy injury and can often be reduced closed under anaesthesia with gentle internal rotation and anterior translation; after reduction, the defect is sized on CT (less than 20 percent: immobilise in slight external rotation for 4 to 6 weeks; 20 to 40 percent engaging: proceed to McLaughlin or modified Neer as a primary procedure; greater than 40 to 50 percent: allograft or arthroplasty). A chronic locked posterior dislocation (greater than 3 weeks) presents weeks to months after the index event, the diagnosis is usually delayed, and open reduction is the rule - closed reduction is rarely successful and risks an iatrogenic humeral shaft fracture. AVN rates rise steeply once the dislocation has been present for greater than 6 months, so warn the patient and obtain CT and MRI before surgery. Why the diagnosis is missed - the post-ictal algorithm. The seizure is the obvious clinical event; the shoulder injury is overlooked. Post-ictal patients may be obtunded, the stiff internally-rotated shoulder is mislabelled a frozen shoulder or rotator cuff tear, and the lightbulb sign is not sought because no axillary view is obtained. - Always obtain an axillary lateral and a scapular Y view in any post-ictal or post-electrocution patient with shoulder pain or stiffness. A normal axillary view rules out posterior dislocation.

• If the lightbulb sign is present on AP and the axillary confirms posterior dislocation, classify by duration: acute (less than 3 weeks), subacute (3 weeks to 3 months), or chronic (greater than 3 months).
• CT to size the reverse Hill-Sachs defect and MRI to assess head viability and exclude AVN, then treat according to the algorithm above. Elderly patients. Osteoporotic bone raises the risk of iatrogenic fracture, rotator cuff disease and glenohumeral arthritis are more prevalent, and functional demand is lower - so the threshold for arthroplasty falls. Consider a reverse total shoulder arthroplasty as the primary procedure when the patient is over 70, the defect is greater than 40 to 50 percent, there is established AVN or arthritis, the rotator cuff is deficient (fatty infiltration grade 3 or 4), a prior McLaughlin has failed, or demand is low. Anaesthesia considerations. Continue the patient's usual anticonvulsants; avoid long-acting paralytics so the surgeon can stimulate and confirm the axillary and musculocutaneous nerves; use bispectral index monitoring for depth; and watch for a post-operative seizure if anticonvulsant levels are subtherapeutic. Consent specifically for the risk of recurrent posterior instability (5 to 15 percent), subscapularis dysfunction or failure (5 to 10 percent), axillary or musculocutaneous nerve injury (1 to 3 percent and less than 1 percent), avascular necrosis of the humeral head (10 to 30 percent in chronic dislocations), and progression to arthritis (20 to 50 percent at 10 to 15 years) requiring conversion to arthroplasty.

The goal: through a deltopectoral approach, reduce the chronic posterior dislocation, fill the engaging anteromedial (reverse Hill-Sachs) defect with the subscapularis tendon (original McLaughlin) or the lesser tuberosity with attached subscapularis (modified Neer / Hawkins), and thereby block re-engagement on the posterior glenoid rim while protecting the axillary nerve throughout. The exposure - the deltopectoral approach to the subscapularis window - is laid out in full as the first steps below.

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Rehabilitation protocol | Phase | Timing | Movement | Precautions | |-------|--------|----------|-------------| | Sling and early protection | 0 to 6 weeks | Pendulum exercises and passive forward flexion in the scapular plane from day 1; hand, wrist and elbow active range of motion from day 1 | Sling in slight abduction (15 to 20 degrees) and neutral rotation; no external rotation past neutral; no active internal rotation against resistance for 6 weeks; cryotherapy | | Intermediate | 6 to 12 weeks | Wean from sling; active-assisted then active forward flexion and abduction in the scapular plane; external rotation stretching toward 30 to 45 degrees in abduction; scapular stabilisation | No resisted internal rotation until 12 weeks; formal physiotherapy 2 to 3 times per week | | Strengthening | 12 to 24 weeks | Progressive rotator cuff and subscapularis strengthening; closed-chain and proprioceptive work; sport- or work-specific conditioning from 16 to 20 weeks | Return to heavy labour at 4 to 6 months; overhead sport at 6 to 9 months; contact sport at 9 to 12 months | | Long-term monitoring | beyond 6 months | Serial Constant or ASES scores; document return to work and sport | MRI at 3 to 6 months and again at 12 to 18 months for AVN surveillance in high-risk patients; annual radiographs for arthritis surveillance | In the short term (less than 2 years), 80 to 90 percent of patients report good-to-excellent results after a McLaughlin or modified Neer for a 20 to 40 percent defect, recurrent instability is 5 to 15 percent, and most activities of daily living resume by 3 to 6 months. Counsel the patient preoperatively that the procedure reliably restores stability and delays arthroplasty for a decade or more in most patients - it is a "buy-time" procedure for the younger patient - but it does not prevent long-term arthritic progression or AVN. Complications

Pathoanatomy - the reverse Hill-Sachs defect. The defect is an impaction fracture of the anteromedial humeral head, created when the head is driven posteriorly against the posterior glenoid rim during a posterior dislocation - the mirror image of the anterolateral (posterolateral head) Hill-Sachs defect of an anterior dislocation. In chronic locked dislocations it usually involves 20 to 50 percent of the articular surface and is best measured on CT (axial cuts) or axillary MRI. The defect engages the posterior glenoid rim in flexion, adduction and internal rotation - functional positions, which is why the joint is unstable in everyday use. Posterior glenohumeral anatomy. The glenoid is a shallow dish-shaped socket; the posterior rim is the third that contacts the anteromedial head during posterior dislocation. The posterior capsule inserts on the posterior rim and labrum (the labrum anchors the posterior band of the inferior glenohumeral ligament, the key static restraint against posterior translation). The posterior capsule is thicker and less compliant than the anterior, which is why posterior dislocations tend to lock rather than reduce. Vascular anatomy of the humeral head and the AVN risk. The arcuate artery, a branch of the anterior circumflex humeral artery, runs along the lateral border of the bicipital groove and enters the head proximally - it is the dominant supply in roughly 80 percent of cadaveric studies. The posteromedial vessels, branches of the posterior circumflex humeral artery, supply the posteromedial head and are the vessels at risk in a chronic posterior dislocation. AVN occurs in 9 to 30 percent of chronic locked posterior dislocations and rises with a duration greater than 6 months and with attempted closed reduction of long-standing dislocations. Subscapularis insertion and the modified Neer osteotomy. The subscapularis inserts on the lesser tuberosity with a footprint roughly 2.5 cm superoinferior by 1.5 cm wide, just lateral to the bicipital groove; the medial border of the lesser tuberosity is the landmark for the medial dissection. The modified Neer osteotomy is a planar cut through the lesser tuberosity just lateral to the groove, freeing a wafer of bone (roughly 2 by 1.5 cm) with the subscapularis attached; this wafer is mobilised medially and transferred into the prepared defect. Original McLaughlin versus modified Neer - the evidence. McLaughlin described the original technique in 1952 - open reduction of the chronic posterior dislocation through a deltopectoral approach followed by transposition of the subscapularis tendon into the reverse Hill-Sachs defect; in his series of 22 patients, 18 had a satisfactory outcome, establishing the principle of addressing the bone defect by filling it with the attached subscapularis rather than relying on capsular repair alone. Hawkins and colleagues (Hughes and Neer 1975; Hawkins 1987) modified the procedure to osteotomise the lesser tuberosity with the attached subscapularis, transferring both bone and tendon; the rationale is a more robust bony block against the posterior rim, cancellous bone-to-bone healing, and stronger fixation (screws versus tendon sutures alone), and the modified Neer has largely superseded the original McLaughlin. Outcomes literature. Hawkins reported 17 of 17 patients with a satisfactory result after open reduction and lesser tuberosity transfer for chronic posterior dislocations, with recurrent instability in one. Smaller series report 80 to 90 percent good-to-excellent results with the modified Neer at mid-term follow-up, with recurrent instability in 5 to 15 percent - lower than soft-tissue-only repairs for engaging defects - and conversion to arthroplasty in 10 to 25 percent at 10 to 15 years, driven by progressive arthritis and AVN. In the long term, arthritic conversion reaches 20 to 50 percent at 10 to 15 years; once arthroplasty is performed, outcomes are similar to primary arthroplasty in matched patients, and the McLaughlin or modified Neer is best understood as a "buy-time" procedure that reliably restores stability and delays arthroplasty for a decade or more in most patients.