Incidence and risk factors for pseudosubluxation of the humeral head following proximal humerus fracture

BACKGROUND: Humeral head pseudosubluxation (HHPS) in relation to the glenohumeral joint is a common finding following fractures of the proximal humerus. The temporary inferior subluxation of the humeral head may be secondary to a transient axillary nerve neuropraxia, pain inhibition of the deltoid, or hemarthrosis or capsular disruption that alters the physiologically negative pressure in the glenohumeral joint. Despite the frequency of this finding, it is not well described in the literature. This study sought to describe the incidence, risk factors, and rate of resolution of HHPS following proximal humerus fracture. METHODS: The practice of two fellowship-trained shoulder and elbow surgeons was queried for proximal humerus fractures. Patient radiographs were reviewed at the time of injury and all subsequent follow-ups through one year after injury. Data collection included the presence of HHPS, type of fracture based on the Neer classification, operative vs. nonoperative management, and resolution of HHPS. Exclusion criteria included skeletally immature patients, fracture-dislocations, patients treated with reverse shoulder arthroplasty, inadequate follow-up, or those patients with incorrect International Classification of Diseases coding. RESULTS: The incidence of HHPS was 20.0% (103 out of 515 patients) overall. Patients who required surgical intervention were more likely to develop pseudosubluxation than those who were treated conservatively (P < .001). There was an increasing incidence of pseudosubluxation based on the Neer classification, with 0-part fractures demonstrating a 2.56% (2/78) rate, whereas 4-part fractures were found to have HHPS in 35.1% (20/57) of cases (P < .001). All patients were found to have resolution of their HHPS at the final follow-up or one year after injury. None of age, sex, obesity, or injury to the dominant arm was associated with the occurrence of HHPS. There was, however, a statistically significant difference in the body mass index of those who developed HHPS (28.4, ± 5.77) vs. those who did not (26.2, ± 5.32, P < .01). CONCLUSION: This retrospective radiographic study is the largest to date investigating the incidence of HHPS following proximal humerus fracture and first to correlate with Neer classification and operative intervention. We found that HHPS occurs in one-fifth of acute proximal humerus fractures and resolves regardless of intervention. More complex fractures, including those with increasing Neer parts or requiring operative intervention, developed HHPS at higher rates than simpler fracture patterns. This study will help both general orthopedists as well as shoulder surgeons understand the epidemiology of HHPS and provide reassurance to patients that PS is a benign finding with expected spontaneous resolution by one year.