Postoperative radiographs are used in conjunction with clinical assessment to assess for signs of healing and to monitor for complications [1,2]. With respect to intramedullary nail (IMN) fixation for femoral shaft fractures, radiographs are often obtained at approximately 6 weeks postoperatively. Previous work suggests callus formation should be visible by this time point [3]. Although research has shown that orthopaedic surgeons can accurately predict patients at risk for nonunion at 3 months postoperatively, it is unknown if there is a clinical benefit to these earlier images [4,5].

Radiographs are associated with increased health care expenditure, radiation exposure, increased patient wait times, and prolonged duration of clinic visits [[6], [7], [8]]. Radiographs obtained after open reduction internal fixation (ORIF) of distal radius fractures found no change in alignment based on imaging obtained at 2 weeks, 6 weeks, and final follow-up [9]. Looking at a variety of fractures treated at regional level 1 trauma centers, Ghattas et al. [10] found that no radiographs obtained at the first postoperative visit led to a change in the postoperative course. Given that not enough time had passed for radiographs to demonstrate meaningful healing, the authors suggested that imaging can be delayed to later visits where fracture remodeling could lead to a change in weight bearing or rehabilitation [10]. With respect to intertrochanteric fractures, multiple studies have demonstrated similar findings such that, unless prompted by physical examination or new trauma, early postoperative radiographs have limited clinical value and do not change management [11,12]. Furthermore, avoiding these early radiographs can result in significant health care savings [13]. Assessing IMN fixation after femoral and tibial shaft fractures, Nair et al. [6] found that routine surveillance radiographs obtained before 9 weeks in symptomatic patients or before 14 weeks in asymptomatic patients had limited diagnostic yield.

Whalen et al. [14] found that cortices with bridging callus and the disappearance of fracture lines are reliable radiographic parameters to assess fracture healing. Building on this concept, the Radiographic Union Score for Tibial (RUST) fractures was developed which demonstrated high inter-rater reliability [15]. This scoring system was modified, modified Radiographic Union Score for Tibial (mRUST) fractures, expanding the category of callus progression, and further used to assess metadiaphyseal fractures by Litrenta et al. [16]. Multiple studies have demonstrated high inter- and intra-observer reliability of the mRUST score in assessing fracture healing in a variety of fractures, including femoral shaft fractures [[17], [18], [19], [20], [21]].

The primary goal of this study was to evaluate whether the mRUST score applied to femur fractures 4–8 weeks postoperatively can be used as marker to determine what patients are at risk for nonunion. Furthermore, this study aimed to ascertain if there was a threshold 4–8-week mRUST score that could be used to guide patient follow-up. This study’s hypothesis was that a lower mRUST score calculated at 4–8 weeks postoperatively would be associated with an increased risk of nonunion.