Unstable isolated ulnar shaft fractures are rare injuries that need to be surgically treated. The purpose of this study was to compare the functional and radiographic outcomes of two types of surgeries: closed reduction and intramedullary fixation (IMF) by pinning and open reduction and internal fixation (ORIF).

Our hypothesis was that IMF obtained similar outcomes to ORIF.

All patients treated for an isolated distal or middle third ulnar shaft fracture between 2016 and 2019 were enrolled into two groups: ORIF and IMF. The technique performed depended on the surgeon's preference and not the type of fracture or patient. Demographic and clinical data (QuickDASH) and complications were retrospectively collected. X-rays were also examined to classify the fracture, assess postoperative reduction quality, and determine the amount of shortening and angulation.

A total of 81 patients with a mean age of 34 years were divided into two groups: 34 in ORIF and 47 in IMF. The two groups had similar demographics, mechanisms of injury, and preoperative fracture characteristics. The only difference was smoking (p<0.001). Despite a greater mean ulnar shortening of 0.4 mm in the IMF group (p=0.048), there were no significant differences regarding the functional score (QuickDASH) and rate of pseudarthrosis. However, the operative time (p<0.001) was shorter in the IMF group.

In the treatment of unstable isolated ulnar shaft fractures, IMF and ORIF had similar clinical and radiographic outcomes in terms of bone healing. The mean ulnar shortening reported in the IMF group was small and was not at risk of developing posttraumatic osteoarthritis.

IMF is a feasible therapeutic alternative to ORIF for isolated fractures of the distal two-thirds of the ulnar shaft. Further studies with a higher level of evidence need to be conducted to confirm the equivalence of these two fixation techniques.

IV, retrospective study.