Posterior shoulder dislocation accounts for roughly 1 to 4 percent of all shoulder dislocations, yet it is misdiagnosed on the first visit somewhere between 50 and 79 percent of the time. That combination of rarity and missed diagnosis makes it one of the most consequential blind spots in emergency orthopedics. Because the humeral head slips behind the glenoid socket rather than in front of it, standard front-to-back X-rays can look deceptively normal, and the injury often gets mistaken for a rotator cuff tear or a frozen shoulder.
Why This Injury Gets Missed So Often
Most shoulder dislocations push the ball of the humerus forward, and that anterior pattern is what clinicians are trained to spot. Posterior dislocations do the opposite, driving the humeral head backward. On a standard anteroposterior (AP) X-ray, the shoulder can still look roughly in place because the displacement is happening in a plane the image does not capture well. The shoulder appears painful and stiff, which leads to a tentative diagnosis of a bruise or soft-tissue strain, particularly in athletes who took a direct blow or fell on an outstretched hand.1PubMed. Posterior shoulder dislocation: avoiding a missed diagnosis
A systematic review of the literature found that the misdiagnosis rate for posterior glenohumeral dislocations sits between roughly 50 and 79 percent at initial presentation.2PubMed. The aetiology of posterior glenohumeral dislocations and occurrence of associated injuries: a systematic review That is an extraordinary failure rate for a structural injury. When the dislocation is not recognized promptly, the humeral head remains locked behind the glenoid, bone and cartilage continue to erode, and the window for a simple closed reduction closes. Cases that are eventually diagnosed weeks or months later often require surgery that would have been avoidable had the injury been caught on day one. More than half of missed cases have later been misdiagnosed as frozen shoulder, which delays appropriate treatment even further.3PubMed. Missed posterior shoulder dislocation and McLaughlin lesion after an electrocution accident
Causes and the Mechanism of Injury
The shoulder dislocates posteriorly when a strong force drives the arm into internal rotation, flexion, and adduction all at once. In athletes, a direct blow to the front of the shoulder or a fall onto an outstretched arm is the most common trigger.4PubMed. Posterior shoulder dislocation: avoiding a missed diagnosis Outside sports, however, two causes dominate the literature: seizures and electrical injuries. During a generalized seizure, the powerful internal rotators of the shoulder overpower the smaller external rotators, snapping the humeral head backward. The same violent muscle contraction happens during an electrical shock.
Bilateral posterior dislocations, where both shoulders dislocate at the same time, are even rarer, making up an estimated 5 to 15 percent of all posterior dislocations. Seizures account for most of those bilateral events, with electrical shock responsible for fewer than 5 percent of posterior dislocations overall.5PubMed Central. Bilateral posterior shoulder dislocation after electrical shock: A case report A bilateral presentation is actually a clinical clue: if both shoulders are locked after a seizure or electrocution, the diagnosis should be high on the list from the start.
What Happens Inside the Joint
When the humeral head lodges behind the glenoid, it crashes into the posterior rim of the socket. That impact creates a constellation of damage whose severity determines the entire treatment plan.
The hallmark injury is the reverse Hill-Sachs lesion, an impression fracture on the front-inner surface of the humeral head where it was crushed against the glenoid rim. Think of it as a dent on the ball of the joint. The size of that dent dictates treatment more than almost any other single factor. Defect size grows with time: one study classifying these lesions found that those from a simple dislocation averaged about 33 degrees of involvement, while locked dislocations that went unrecognized for longer averaged about 49 degrees, and chronic locked dislocations averaged about 64 degrees.6PubMed. Defect Characteristics of Reverse Hill-Sachs Lesions In other words, the longer the shoulder stays dislocated, the larger the crater becomes.
The soft tissues take a beating too. An MRI study of acute posterior dislocations found posterior labral or capsular tears in about 58 percent of patients, and roughly a third had a bony fracture of the posterior glenoid rim, called a reverse osseous Bankart lesion.7PubMed. Acute traumatic posterior shoulder dislocation: MR findings Those labral and bony injuries are important because they compromise the socket’s ability to keep the humeral head centered, making recurrent instability more likely if left unaddressed.
Getting the Imaging Right
The single biggest reason posterior dislocations are missed is reliance on an AP X-ray alone. That view shows the shoulder from front to back, and because the humeral head is displaced directly behind the socket, the overlap can look almost normal. Classic but subtle signs on the AP film exist, such as the “lightbulb sign” where the internally rotated humerus projects as a rounded silhouette, but they are easy to overlook in a busy emergency department.
Adding a lateral view, specifically an axillary or Velpeau view, dramatically improves detection. A Velpeau view can be taken without moving the patient’s arm from a sling, making it practical even when pain limits positioning. In one study evaluating the value of additional views, a Velpeau radiograph caught a posterior dislocation that had been misread as an inferior subluxation on the initial AP film, completely changing the treatment plan and prompting a closed reduction.8PubMed Central. The clinical utility of additional axillary and Velpeau radiographs in the evaluation of suspected shoulder trauma
When posterior dislocation is confirmed or strongly suspected, a CT scan is the next step. CT is the best way to measure how much of the humeral head articular surface is involved by the reverse Hill-Sachs defect, a measurement that drives every downstream treatment decision. MRI adds information about the labrum, capsule, and rotator cuff but is less critical for emergency planning than the CT measurement of bone loss.
Acute Treatment and Closed Reduction
If the dislocation is fresh and the reverse Hill-Sachs defect is small, closed reduction under sedation is usually the first move. The classic DePalma technique involves adducting and internally rotating the arm, applying downward traction, and then pushing the upper arm laterally to lever the humeral head back into the socket.9Turkish Journal of Emergency Medicine. A systematic and technical guide on how to reduce a shoulder dislocation After reduction, the shoulder is typically immobilized in a brace that holds the arm in some degree of external rotation, which keeps the reverse Hill-Sachs defect away from the glenoid rim and lowers the risk of redislocation. The duration and exact position of immobilization remain somewhat debated, but external rotation bracing for several weeks is a common protocol.
Closed reduction works best when the reverse Hill-Sachs lesion involves less than about 25 percent of the humeral head’s articular surface and the joint is stable after the head is seated back in place.10PubMed Central. Posterior shoulder dislocation with associated reverse Hill–Sachs lesion: clinical outcome 10 years after joint-preserving surgery Beyond that threshold, the risk of redislocation climbs steeply because the dent on the humeral head can re-engage on the glenoid rim during normal shoulder movement.
When the Defect Is Too Large for Simple Reduction
Treatment algorithms for posterior shoulder dislocation revolve around defect size. The broad framework used across the literature breaks into three tiers:
- Under 25 percent: Closed reduction and immobilization, usually with good results if the joint is stable afterward.
- 25 to 50 percent: Joint-preserving surgery, most often some variation of the McLaughlin procedure or bone grafting to fill or reconstruct the defect.
- Over 50 percent: Shoulder replacement (arthroplasty), because too little articular surface remains for a reliable reconstruction.
This sizing scheme appears consistently in the literature, though the exact cutoffs shift slightly depending on the source. Some authors set the upper boundary for joint-preserving surgery at 40 percent rather than 50 percent,11Journal of Orthopaedics. Chronic posterior shoulder dislocation: Current evidence, treatment options, and a decision-making algorithm while others have used the modified McLaughlin procedure for defects up to 50 percent of the humeral head.12PubMed Central. Closed Reduction of Bilateral Posterior Shoulder Dislocation with Medium Impression Defect of the Humeral Head: A Case Report and Review of Its Treatment Chronicity matters too: a dislocation that has been locked for weeks or months may be treated more aggressively than a fresh injury with the same defect size because the bone softens and the soft tissues contract over time.
The Modified McLaughlin Procedure
For medium-sized reverse Hill-Sachs defects, the modified McLaughlin procedure has become the workhorse operation. The concept is straightforward: the subscapularis tendon along with a piece of the lesser tuberosity bone is detached from the front of the humerus and transferred into the impression defect on the humeral head. This fills the crater with bone and tendon, preventing it from catching on the glenoid rim during shoulder motion.13PubMed Central. A Case of Modified McLaughlin Procedure in Neglected Posterior Shoulder Fracture Dislocation
A systematic review of the modified McLaughlin procedure for locked posterior dislocations found favorable clinical and radiographic outcomes with low rates of complications and recurrent instability, particularly when the time between injury and surgery was kept short.14JSES Reviews, Reports, and Techniques. Clinical and radiographic outcomes of the modified McLaughlin procedure for locked posterior dislocation of the shoulder: a systematic review Some surgeons have augmented the McLaughlin technique by layering extracellular matrix material into the defect to further fill the void, though this remains a less established variation.15PubMed Central. Posterior Shoulder Instability: The Augmented McLaughlin Procedure
Bone Grafting and Anatomical Reconstruction
An alternative to transferring the subscapularis is to directly rebuild the humeral head’s contour using bone graft. This approach aims to restore normal anatomy rather than plug the defect with a tendon transfer. One series treated patients with an average defect size of about 34 percent by performing open reduction, disimpacting the crushed bone, grafting the defect, and fixing it with internal hardware. All fractures healed by eight weeks, pain scores dropped substantially, and functional scores roughly doubled at final follow-up.16PubMed Central. Management of Locked Posterior Shoulder Dislocation with Reverse Hill–Sachs Lesions via Anatomical Reconstructions
Another series of six patients followed for an average of about five years after anatomical reconstruction with bone grafting reported a mean Constant score of 88 out of 100, reflecting good to excellent function. One patient redislocated at three months and was revised with the same method; at last follow-up, no further redislocations or graft collapse had occurred.17PubMed. Anatomical reconstruction for Reverse Hill-Sachs lesions after posterior locked shoulder dislocation fracture: a case series of six patients A five-year follow-up study comparing various joint-preserving approaches for defects between 25 and 40 percent, including retrograde chondral elevation, cylindrical grafts, and iliac crest grafts, found that all techniques produced fair to good results, with Constant scores in the low 90s by five years.18PubMed Central. Posterior shoulder dislocation with associated reverse Hill-Sachs lesion: treatment options and functional outcome after a 5-year follow up
An emerging option for smaller, acute defects is arthroscopic retrograde disimpaction, where the surgeon pushes the crushed bone back out from inside the humeral head and supports it with bone graft. Early results from one series showed a significant reduction in defect depth from about 8.4 mm to about 1.2 mm on follow-up imaging, and in about a third of patients the defect became undetectable on scans.19Journal of Shoulder and Elbow Surgery. Arthroscopic retrograde disimpaction of reverse Hill-Sachs lesions in acute posterior shoulder dislocation type A2
Shoulder Replacement for Severe or Chronic Cases
When the humeral head is too damaged to save, whether because the impression fracture exceeds roughly 40 to 50 percent of the surface, the bone has become severely soft, or the cartilage has degenerated after months of locked dislocation, shoulder arthroplasty becomes the treatment of choice.20PubMed Central. Chronic locked posterior shoulder dislocation with severe head involvement Depending on the condition of the glenoid, this can be a hemiarthroplasty (replacing only the humeral side) or a total shoulder arthroplasty (replacing both sides).
The largest published series followed 32 patients who received either a hemiarthroplasty or a total shoulder arthroplasty for chronic locked posterior dislocation. Pain improved, and external rotation went from a median of negative 15 degrees (meaning the arm was stuck in internal rotation) to a median of 50 degrees. Results were mixed in the long run, though: instability recurred in three patients, nine required reoperations, and by a modified rating system about 40 percent of outcomes were deemed unsatisfactory.21Journal of Bone and Joint Surgery. Anatomic Shoulder Arthroplasty as Treatment for Locked Posterior Dislocation of the Shoulder That sobering number underscores how much harder the problem becomes once the window for joint preservation has closed.
Arthroscopic Repair for Posterior Instability
Not every posterior shoulder problem involves a large bony defect. Some patients, particularly athletes with repetitive microtrauma, develop recurrent posterior instability driven mainly by labral tears and capsular stretching rather than a massive impression fracture. For these patients, arthroscopic posterior labral repair has become a reliable option.
A study of 200 shoulders treated with arthroscopic posterior stabilization reported improvements in pain, function, and stability scores at three years. About 90 percent of patients returned to sport, with 64 percent returning to the same competitive level. The failure rate was 6 percent.22PubMed Central. Arthroscopic Posterior Labral Repair for Posterior Shoulder Instability A systematic review and meta-analysis looking across multiple studies found similar numbers: return-to-sport rates of about 92 percent, return to the same level of play around 79 percent, and recurrent instability in about 7 percent. Revision surgery was needed in fewer than 4 percent of cases, and the outcomes did not differ significantly between contact and overhead athletes.23PubMed Central. Arthroscopic Repair for Posterior Shoulder Instability Is Associated With Favorable Outcomes and High Return to Sport or Work: A Systematic Review and Meta-Analysis
Long-Term Risk of Arthritis
Even after a successful reduction or surgery, the shoulder that has been posteriorly dislocated carries an elevated long-term risk of developing osteoarthritis. A population-based study found that about 14 percent of patients with posterior instability showed radiographic progression to symptomatic glenohumeral arthritis over follow-up, with five-year survival free of arthritis at roughly 88 percent. Older age at the time of instability diagnosis was a strong predictor: for every additional decade of age, the risk of arthritis progression roughly doubled. Patients who underwent surgery also had a higher rate of radiographic arthritis progression compared to those managed nonoperatively.24PubMed Central. Patient Age and Surgical Intervention as Risk Factors for the Development of Osteoarthritis After Posterior Shoulder Instability: A Population-Based Study That does not necessarily mean surgery causes arthritis; it likely reflects the fact that the patients who need surgery tend to have worse injuries in the first place. Still, it is a reality patients should be aware of going into treatment.
Rehabilitation and Return to Sport
Rehabilitation after posterior shoulder stabilization follows a phased, criteria-based approach rather than a rigid calendar. Early phases focus on protecting the repair while restoring gentle range of motion, gradually progressing to strengthening the rotator cuff and scapular stabilizers. The later phases shift toward sport-specific drills tailored to the individual’s athletic demands.25PubMed Central. Rehabilitation Following Posterior Shoulder Stabilization
There is growing emphasis on passing a structured return-to-sport testing battery before clearing an athlete to compete again, rather than simply counting weeks from surgery. Formal testing has been associated with lower rates of recurrent instability, which makes sense: an objective measure of readiness catches people who feel fine but whose shoulder is not yet strong or coordinated enough to handle contact or overhead loading.26PubMed Central. Return to Sport After Shoulder Stabilization Procedures: A Criteria-Based Testing Continuum to Guide Rehabilitation and Inform Return-to-Play Decision Making In practice, full return after arthroscopic posterior repair typically takes six to nine months, though the exact timeline depends on the sport and the extent of the initial damage.
Posterior Dislocations in Children
Posterior shoulder dislocation is extremely rare in children, and when it does occur, the cause is usually different from what is seen in adults. Congenital abnormalities of the shoulder girdle, obstetric nerve injury, and generalized ligament laxity (leading to voluntary dislocation) account for most pediatric cases. A traumatic posterior dislocation in a child without an accompanying fracture of the growth plate is unusual enough that only isolated case reports exist in the literature.27PubMed Central. Posterior shoulder dislocation in a 10-year-old child: Case report The diagnostic challenges are amplified in children because the growth plates can obscure imaging, and the injury itself is so uncommon in this age group that clinicians may not consider it. As with adults, an axillary or lateral X-ray view is essential to avoid missing the diagnosis.