Background: Complex posterior fracture-dislocations of the shoulder are rare and often associated with poor long-term function regardless of the choice of treatment. The purposes of this study were to evaluate the epidemiology and pathological anatomy of posterior fracture-dislocations of the shoulder and to assess the clinical and radiographic outcomes of a specific treatment protocol of open reduction and internal fixation.

Methods: We studied the demographic details of a consecutive series of twenty-six patients (twenty-eight shoulders in nineteen men and seven women with a mean age of fifty-three years) who sustained acute posterior dislocation of the humeral head with an associated Neer two, three, or four-part fracture. We used age and gender-specific local census data to assess the incidence of injury in our local population. All patients were treated by open relocation of the humeral head, bone-grafting of humeral head defects if they were causing residual shoulder instability, and internal fixation of the fracture. We recorded the prevalence of fracture complications that were clinically and radiographically apparent and assessed the functional outcome using three validated scoring systems (the Short Form-36 general health measure, the Disabilities of the Arm, Shoulder and Hand score, and the Constant score).

Results: The overall incidence of posterior fracture-dislocations was 0.6 per 100,000 population per year. The peak incidence was in middle-aged men, and most injuries were sustained during a seizure or a fall from a height. In all patients, there was a displaced primary fracture of the anatomic neck of the humerus, propagating from the area of an osteochondral fracture of the anterior aspect of the humeral head (a reverse Hill-Sachs lesion). We recognized three subtypes determined by the extent of the secondary fracture lines. At two years after surgery, the median Constant score was 83.5 points and the median Disabilities of the Arm, Shoulder and Hand score was 17.5 points. The eight components of the Short Form-36 score were not significantly different from those of age and sex-matched controls at two years.

Conclusions: Acute complex posterior fracture-dislocations of the shoulder are rare, but they occur in patients who are younger than the majority of other patients who sustain a proximal humeral fracture. The use of open reduction and internal fixation to treat these fractures is associated with a relatively low risk of postoperative complications, and the functional outcome is generally favorable.

Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.