Inferior subluxation of humeral head after plate surgery for proximal humerus fracture isn't always benign.

Background: Inferior subluxation of humeral head following shoulder trauma, osteosynthesis or rotator cuff repair has been considered as a benign or temporary phenomenon due to muscle fatigue or capsular injury. However, the clinical impact is still unclear as to their occurrence after plating for proximal humerus fractures. This study aims to investigate their patterns and identify associated risk factors as well as clinical outcomes.

Methods: The research included patients who received locking plate surgery following an acute proximal humerus fracture with a minimum follow-up of 12 months. Pathologic fractures, history of previous shoulder surgery or associated with neuromuscular diseases were excluded. Patients were grouped based on the onset and duration of subluxation. Differences between groups regarding patient characteristics, fracture patterns, reduction quality and clinical outcomes were analyzed.

Results: There are 303 patients included in this study, with 28 patients (9.2%) in the pseudo subluxation group, showing subluxation in the first month and self-recovered before 6 months after surgery, 18 patients (5.9%) in the delay subluxation group, showing normal radiograph in first month but presented subluxation 3 or 6 months after surgery, 12 patients (3.9%) in the sustained subluxation group, showing persistent subluxation throughout the 6-month follow-up. Older age significantly correlated with delayed subluxation; greater BMI correlated with sustained subluxation. Male sex and Neer 3-part fracture correlated with lower incidence of all types of subluxations. Besides, female, smaller neck-shaft angle, and screw perforation correlated with subluxation 6 months after surgery. Moreover, patients with delayed onset of subluxation showed higher rate of loss of reduction (16.7%) and requiring reverse shoulder arthroplasty (22.2%).

Conclusion: Presence of subluxation after plate surgery for proximal humerus fracture is not always benign. Delayed presentation may indicate migration of greater tuberosity, loss of reduction and screw perforation. Secondary procedure may be required. Female patients or those with a decreased neck-shaft angle may experience a longer duration of inferior subluxation which would not spontaneously recover. Closer follow-up would be recommended beyond 6 months for these patients regarding the necessity of secondary interventions.