Early displacement of two part proximal humerus fractures treated with intramedullary proximal humeral nail

Introduction: Proximal humerus nails (PHN) are commonly used for the treatment of simple proximal humerus fractures, and have a reported malunion rate of about 10%. The surgeons who used PHN in one medical institution have noticed a high rate of fracture re-displacement in the early post-operative period. This study's aim is to evaluate the rate of secondary displacement and malunion of patients treated for two part proximal humerus fractures with an angle-stable PHN (MultiLoc), and to assess possible risk factors for this secondary displacement. Methods: A retrospective study comprised of 25 consecutive patients with 2 part surgical neck or metaphysis displaced proximal humerus fracture, treated with PHN between the years 2014-2017. Results assessed included radiographic measures (neck-shaft angle) and clinical data: range of motion (ROM) and functional scores (Constant, DASH, SSV). A univariate regression analysis was used to assess possible risk factors for secondary displacement. Results: Mean age was 66.6 (range 17-93), and mean follow up was 20 months (range 6-40). Mean neck shaft angle (NSA) changed from 139.1 degrees post operatively to 122.6 degrees at last follow up, with 6 patients (24%) having a NSA change larger than 20 degrees. Two patients (8%) ended up with NSA less than 90 degrees, defined as malunion. The deltoid tuberosity index was found to correlate with the degree of displacement (-0.41, p = 0.04). Conclusions: PHN for simple displaced proximal humerus fractures was associated with fair clinical results but an unacceptable rate secondary displacement. The deltoid tuberosity index was found to correlate with the degree of this secondary displacement.