Reverse Hill-Sachs Lesion

1. High-Yield Overview & Pathognomonic Essence

• Morphological Hallmark: An impaction fracture and wedge-shaped osteochondral depression located on the anteromedial aspect of the humeral head, situated at the articular margin immediately adjacent to the lesser tuberosity.
• Pathognomonic Significance: Represents the definitive osseous impaction lesion (McLaughlin defect) resulting from posterior glenohumeral dislocation, produced when the anteromedial humeral articular surface is violently driven against the dense posterior osseous glenoid rim. It is classically precipitated by violent, uncoordinated muscular contractions during epileptic seizures, high-voltage electrocution, or severe vehicular trauma involving adduction, flexion, and internal rotation forces.
• Critical Diagnostic & Surgical Implication: Notoriously overlooked on initial emergency evaluation, with missed diagnosis rates of 50% to 80% on solitary anteroposterior (AP) plain radiographs. Articular defect arc quantification via thin-slice computed tomography (CT) dictates surgical strategy according to the Hawkins classification: defects under 20% of the articular surface are stable following closed reduction and immobilization in external rotation; defects involving 20% to 40% require non-anatomical (modified McLaughlin lesser tuberosity transfer) or anatomical (osteochondral allograft) reconstruction to prevent recurrent engagement; and extensive defects exceeding 40% to 45% necessitate prosthetic arthroplasty.

2. Diagnostic Sign Summary Matrix

3. Clinical Case Imaging & Standardized Figures

4. Pathophysiology & Biomechanical Mechanism

The reverse Hill-Sachs lesion, historically designated the McLaughlin lesion, represents a focal impaction fracture involving the anteromedial articular surface of the humeral head immediately adjacent to the lesser tuberosity. Harrison L. McLaughlin first described this structural depression in 1952 as the diagnostic counterpart to the classic anterior Hill-Sachs lesion, documenting that posterior displacement of the humeral head forces its anterior cartilaginous and subchondral surface violently against the dense, hard posterior osseous glenoid rim.

The biomechanical genesis of this injury is intimately linked to the muscular anatomy and force couples governing the shoulder girdle. The glenohumeral joint is uniquely susceptible to posterior dislocation during episodes of uncoordinated, massive muscular spasm, classically encountered during grand mal epileptic seizures, electroconvulsive therapy, or high-voltage electrical injuries (electrocution). Under these conditions, all muscle groups spanning the shoulder fire simultaneously. The internal rotators and adductors—predominantly the latissimus dorsi, pectoralis major, and subscapularis—possess significantly greater physiological cross-sectional area and mechanical advantage compared to the relatively weaker external rotators (infraspinatus and teres minor). The resulting net muscular force vector violently forces the humeral head into extreme internal rotation, adduction, and flexion.

As the humeral head is driven posteriorly past the posterior labrum and capsule, the dense cortical bone of the posterior glenoid rim acts as an anvil. The softer, cancellous subchondral bone of the anterior humeral head impacts directly against the posterior rim, creating a vertical, wedge-shaped impression defect. The depth and arc of this defect depend upon the magnitude of the impaction force, bone mineral density, and whether the dislocation remains acutely locked.

From a functional standpoint, the geometry of the reverse Hill-Sachs defect determines whether it behaves as an engaging or non-engaging lesion. An engaging defect aligns parallel to the posterior glenoid rim when the arm is brought into functional positions of internal rotation, forward flexion, and adduction. During these motions, the anterior edge of the defect slips over the posterior glenoid rim, dropping into the notch and leveraging the humeral head out of the glenoid cavity. This produces recurrent posterior instability or maintains a chronically locked posterior dislocation. Conversely, non-engaging defects remain clear of the posterior rim throughout physiological motion arcs and do not cause mechanical catching or recurrent subluxation.

5. Modality-Specific Imaging Findings

Plain Radiography

Conventional anteroposterior (AP) radiography of the shoulder is notoriously deceptive in posterior dislocations, frequently appearing deceptively normal or displaying subtle indirect signs that are easily misinterpreted by clinicians:

• The Trough Line Sign: Visualized on frontal AP projections as one or two dense vertical radiopaque lines traversing the anteromedial humeral head, oriented parallel to the medial humeral articular cortex. This vertical line represents the dense, compacted cortical margins of the impaction defect viewed en face on tangent to the radiographic beam.
• The Lightbulb Sign: Because the humeral head is locked in fixed internal rotation, the greater tuberosity is rotated anteriorly toward the midline. The humeral head loses its normal anatomic asymmetrical profile and projects symmetrically and spherically over the glenoid, resembling an incandescent electric lightbulb or an ice cream cone.
• Loss of Normal Glenohumeral Overlap: On a standard AP view, the normal elliptical overlapping shadow between the posterior glenoid rim and the medial humeral head (the half-moon overlap) is obliterated. The joint space may appear falsely widened (>6 mm, known as the positive “rim sign”) or exhibit abnormal medial displacement and overlap depending on the projection angle.
• The Vacant Glenoid Sign: The anterior half of the glenoid fossa appears empty and uncovered because the humeral head has migrated completely into the posterior extrascapular space.

Because solitary AP radiographs result in high missed rates, mandatory orthogonal projections must be performed. The axillary lateral view is the single most critical projection, demonstrating unequivocal posterior displacement of the humeral head relative to the glenoid fossa and displaying the V-shaped anteromedial impaction defect locked onto the posterior glenoid rim. If acute pain and muscular spasm prevent arm abduction, a Velpeau axillary view (obtained with the patient leaning backward 30° over the film cassette with the arm resting in a sling) or a scapular Y view (showing the humeral head centered posterior to the intersection of the spine, acromion, and coracoid) provides definitive orthogonal confirmation.

Computed Tomography

Multi-detector computed tomography (CT) with thin-slice (1 mm or sub-millimeter) axial acquisitions and multiplanar coronal, sagittal, and 3D volume-rendered reformations represents the gold standard imaging modality. Axial CT slices clearly delineate the exact location, morphology, depth, and articular arc percentage of the reverse Hill-Sachs defect along the anteromedial humeral head. The defect appears as a sharp, wedge-shaped corticosubchondral impression defect with compressed trabecular bone adjacent to the bicipital groove and lesser tuberosity.

CT imaging allows precise quantification of articular surface involvement using the arc angle method. The angle subtended by the defect is measured relative to the total 180° circular arc of the normal humeral articular surface on the axial cut exhibiting maximum defect width. Furthermore, CT accurately evaluates concomitant osseous pathology, including posterior glenoid rim fracture (reverse bony Bankart lesion), posterior glenoid retroversion and dysplasia, and lesser tuberosity avulsion fractures. Post-processing 3D volume reconstructions with digital humeral head subtraction allow unobstructed en face evaluation of the glenoid articular surface, essential for comprehensive preoperative planning.

Magnetic Resonance Imaging & Ultrasound

Magnetic resonance imaging (MRI) and MR arthrography provide superior soft-tissue characterization while accurately assessing the osteochondral lesion. On fluid-sensitive sequences (T2-weighted fat-suppressed and STIR), an acute reverse Hill-Sachs lesion demonstrates prominent geographic subchondral bone marrow edema beneath the impacted articular surface, contrasting sharply with the low-signal cortical line. In chronic locked dislocations, marrow edema resolves and is replaced by low T1 and T2 signal corresponding to dense reparative subchondral sclerosis and fibrosis.

MRI is uniquely capable of assessing the integrity of the soft-tissue restraints, specifically the posterior labrocapsular complex and rotator cuff. Associated lesions frequently identified include posterior labral tears (reverse Bankart lesion), incomplete posterior labrocapsular avulsions with concealed retro-labral clefts (Kim lesions), tears of the posterior inferior glenohumeral ligament (PIGHL), and tears or avulsions of the subscapularis tendon from the lesser tuberosity. High-resolution diagnostic ultrasound has limited utility in quantifying deep osseous defects due to acoustic shadow artifact from cortical bone, but dynamic posterior sonography can demonstrate posterior joint subluxation during gentle external rotation maneuvers and can verify subscapularis tendon integrity.

6. Diagnostic Utility, Sensitivity & Specificity

The diagnostic utility of imaging in posterior shoulder dislocation and reverse Hill-Sachs lesions depends fundamentally on obtaining appropriate orthogonal views. Conventional AP plain radiographs exhibit a notorious failure rate: published retrospective series demonstrate that between 50% and 80% of posterior dislocations are missed at initial emergency department presentation when evaluated solely with frontal projections. The subtle nature of the lightbulb and trough line signs often leads clinicians to misdiagnose the condition as frozen shoulder, rotator cuff contusion, or post-ictal paresis.

When orthogonal projections—specifically the axillary lateral or Velpeau view—are included in the radiographic trauma series, the sensitivity of plain radiography for identifying posterior dislocation and the associated anteromedial humeral defect rises to over 90% to 95%. Thin-slice multiplanar CT achieves sensitivity and specificity approaching 100%, serving as the definitive reference standard. CT provides flawless identification of the reverse Hill-Sachs defect, accurate calculation of the articular arc involvement percentage, and precise characterization of posterior glenoid rim integrity. The positive predictive value of a concurrent trough line sign and lightbulb sign on plain radiography is high (exceeding 95%), but the absence of these signs on an isolated AP radiograph can never be used to exclude posterior dislocation.

7. Differential Diagnosis & Radiographic Mimics

8. Clinical Significance & Management Implications

The detection and dimensional quantification of a reverse Hill-Sachs lesion represents the single most critical factor guiding clinical decision-making and surgical reconstruction in posterior shoulder instability. Treatment algorithms are dictated primarily by the size of the articular defect (expressed as a percentage of the total humeral articular arc), the duration of locked dislocation, the age and functional demands of the patient, and the structural integrity of the posterior glenoid:

• Small Defects (<20% of Articular Arc): Acute posterior dislocations associated with small anteromedial defects involving less than 20% of the articular surface are biomechanically stable following closed reduction under adequate sedation or general anesthesia. Once reduced, the arm is immobilized in neutral to 15-20° of external rotation and slight extension using a dedicated external rotation brace for 3 to 4 weeks. Immobilization in internal rotation is strictly avoided, as it places the anteromedial defect directly against the posterior glenoid rim and predisposes to recurrent posterior redislocation.
• Medium Defects (20% to 40% of Articular Arc) — Non-Anatomical Reconstruction: Defects occupying between 20% and 40% of the humeral articular surface are prone to recurrent posterior instability and engagement during activities of daily living. The classic McLaughlin procedure involves open detachment of the subscapularis tendon insertion from the lesser tuberosity and direct transosseous suturing of the tendon into the debrided anteromedial defect, non-anatomically filling the void and preventing engagement. The modified McLaughlin (Neer) procedure mobilizes the lesser tuberosity via an osteotomy with the attached subscapularis tendon and transposes the bone block into the reverse Hill-Sachs defect, securing it with bicortical cancellous lag screws. This provides robust bone-to-bone healing, preserves native subscapularis tendon length, and demonstrates superior long-term union rates compared to soft-tissue transfer alone.
• Medium Defects (20% to 40% of Articular Arc) — Anatomical Reconstruction: In young, active patients desiring joint-preserving anatomical reconstruction, segmental fresh-frozen osteochondral allografting (pioneered by Gerber and Lambert) restores native articular sphericity and cartilage congruity. The graft (typically sculpted from a donor femoral head or humeral head) is press-fit and rigidly fixed with headless compression screws. Alternatively, for acute, uncomminuted impaction defects identified within two to three weeks of injury, disimpaction and humeroplasty (percutaneous or open elevation of the depressed osteochondral fragment combined with structural subchondral bone graft packing) can restore native articular contours.
• Large Defects (>40% to 45% of Articular Arc) — Prosthetic Arthroplasty: Extensive defects involving greater than 40% to 45% of the humeral head articular surface compromise native joint reconstructibility, carrying an unacceptable risk of post-traumatic avascular necrosis, progressive cartilage degeneration, and construct failure if joint preservation is attempted. In physiologically active patients with preserved, healthy glenoid cartilage and an intact posterior glenoid rim, prosthetic hemiarthroplasty restores joint stability, with humeral component retroversion carefully adjusted to neutral (0° to 10° of retroversion rather than standard 30°) to counteract posterior subluxation. In elderly patients, chronic locked dislocations exceeding 6 months duration, or cases complicated by severe posterior glenoid bone loss and cartilage erosion, reverse total shoulder arthroplasty (rTSA) provides reliable pain relief and eliminates the risk of posterior prosthesis dislocation by establishing a semi-constrained, biomechanically stable inverted articulation.
• The Chronicity Factor & Danger of Iatrogenic Fracture: Dislocations chronically locked for more than 3 to 6 weeks undergo severe capsular contraction, soft-tissue fibrosis, and disuse osteopenia. Closed reduction in chronic locked dislocations is strictly contraindicated due to the extreme risk of iatrogenic spiral humeral fracture; open surgical reduction via an extended deltopectoral approach is mandatory.

9. Master Class Pro-Tip

Master Class Pro-Tip: In any patient presenting with severe shoulder pain and an absolute mechanical block to passive external rotation following an epileptic seizure, high-voltage electrical shock, or high-energy trauma, assume a locked posterior glenohumeral dislocation with an engaging reverse Hill-Sachs lesion until proven otherwise. Because standard anteroposterior radiographs fail to detect posterior dislocation in over 50% of cases, an orthogonal axillary lateral or Velpeau view is mandatory, and thin-slice multiplanar CT should be obtained immediately to quantify the anteromedial defect arc. If the dislocation has been locked for more than two to three weeks, never attempt forceful closed reduction or rotational manipulation, as the engaged humeral head acts as a rigid fulcrum against the posterior glenoid rim, producing catastrophic spiral fractures of the proximal humeral shaft; open reduction and anatomical or non-anatomical defect filling is required.

Master Class Radiological Pearl: Reverse Hill-Sachs Lesion and Posterior Shoulder Dislocation

10. Evidence-Based Synthesis

11. References

1. McLaughlin HL. Posterior dislocation of the shoulder. J Bone Joint Surg Am. 1952;34-A(3):584-590. DOI [Level V: Seminal Surgical Technique & Landmark Case Series]
2. Hawkins RJ, Neer CS 2nd, Pianta RM, Mendoza FX. Locked posterior dislocation of the shoulder. J Bone Joint Surg Am. 1987;69(1):9-18. DOI [Level IV: Seminal Case Series & Classification]
3. Gerber C, Lambert SM. Allograft reconstruction of segmental defects of the humeral head for the treatment of chronic locked posterior dislocation of the shoulder. J Bone Joint Surg Am. 1996;78(3):376-382. DOI [Level IV: Landmark Case Series]
4. Longo UG, Ciuffreda M, Locher J, et al. Posterior shoulder instability: a systematic review. Br Med Bull. 2020;134(1):34-53. DOI [Level I: Systematic Review / Meta-Analysis]
5. Prigmore B, Tabbaa S, Crawford DC. Osteochondral Allograft Transplantation in the Shoulder: A Systematic Review of Indications and Outcomes. Cartilage. 2024;15(1):3-15. DOI [Level I: Systematic Review / Meta-Analysis]
6. Al-Mohrej OA, Al-Kenani NS, Al-Hussainan TS, et al. Chronic posterior shoulder dislocation: Current evidence, treatment options, and a decision-making algorithm. J Orthop. 2026;55:102-110. DOI [Level IV: Systematic Review & Clinical Decision Algorithm]
7. Duan D, Zhang L, Li M, et al. Surgical treatment of locked posterior shoulder dislocations with modified McLaughlin procedure: Case series and review of treatment possibilities of reverse Hill-Sachs defect. Chin J Traumatol. 2026;29(4):231-238. DOI [Level IV: Case Series & Systematic Literature Synthesis]
8. De Giorgi S, Carrozzo M, Notarnicola A, et al. From reduction to replacement: a reconstructibility-based framework for chronic locked shoulder dislocations. Int Orthop. 2026;50(10):2541-2550. DOI [Level IV: Multicenter Cohort & Surgical Framework]
9. Wang X, Chen Y, Liu Z, et al. Modified McLaughlin procedure combined with proximal humeral locking plate for proximal humeral fractures with posterior shoulder dislocation and reverse Hill-Sachs lesion: a retrospective case series. Front Surg. 2026;13:1881342. DOI [Level IV: Retrospective Case Series]
10. Moroder P, Ernstbrunner L, Akgun D, et al. Posterior shoulder instability shows a higher, flatter acromion, and increased glenoid retroversion compared with anterior dislocation: A matched computed tomography/magnetic resonance imaging analysis. J ISAKOS. 2026;11(2):125-132. DOI [Level III: Comparative Imaging Cohort Study]