Proximal fracture line extension in humeral shaft fractures.

Introduction: Humeral shaft fractures are common injuries treated by orthopaedic surgeons. The purpose of this study is to evaluate displaced diaphyseal humerus fractures and describe the incidence and characteristics associated with non or minimally displaced fracture line extension into the proximal metadiaphyseal region of the humerus. Methods and materials: All adult patients with diaphyseal humeral shaft fractures located within the distal two-thirds of the humeral shaft, treated at a single level I trauma institution between 2007 and 2020, were retrospectively identified. 202 patients with 203 fractures of the humeral shaft were included. Fracture patterns were classified according to AO/OTA classification and fracture line extension into the proximal metadiaphyseal region was evaluated on radiographs. Patient demographics, management details, and radiographic outcomes were obtained from review of the electronic medical record. Results: Of 203 diaphyseal humerus fractures, 11.8 % (n = 24) had non or minimally displaced proximal extension of their main fracture line. This included 43.7 % (n = 7) of all proximal third junction diaphyseal fractures, 10.7 % (n = 16) of all middle third diaphyseal fractures, and 2.6 % (n = 1) of all distal third diaphyseal fractures. Patients with proximal fracture extension were, on average, older (61.7 versus 44.4 years, p < 0.001), and a higher percentage were female (75 % versus 45.5 %, p < 0.01) compared to patients without fracture proximal extension. Fractures with proximal extension were all closed fractures (n = 24), were more often sustained from low-energy fall (87.5 % versus 35.2 %, p < 0.001), and were more often spiral type fractures (62.5 % versus 17.2 %). Fractures with proximal extension were more often treated non-operatively (58.3 % versus 42.1 %, p < 0.01), but were found to have a higher rate of nonunion after non-operative treatment (17.6 % versus 8.1 %) compared to fractures without proximal extension. All operatively treated fractures that had proximal metaphyseal extension were secured with a fixation construct to achieve fixation proximal to the extent of the fracture line, most often into the humeral head and neck. Operative management with proximal fixation into the humeral head was also pursued for a patient with nonunion, including persistent lucency of the proximal extension line, after failed non-operative treatment. Mean follow-up was 35.5 weeks (range: 0-607 weeks). Conclusions: Proximal fracture line extension in the setting of diaphyseal humerus fractures is not uncommon. Detection and consideration of this sometimes subtle finding is important when planning to treat these injuries operatively.