Three-dimensional computed tomography mapping and clinical predictive factors for morphologic characterization of displaced femoral neck fractures.

Background: This study aimed to define the distribution and frequency of fracture lines and bone defects in displaced femoral neck fractures (DFNFs) using a three-dimensional (3D) mapping technique, and to investigate the factors associated with the area of bone defects in patients with DFNFs. Methods: The data of 256 adult patients with DFNFs were retrospectively reviewed. Multiplanar reconstructions of the DFNFs were made using computed tomography (CT) images, and the DFNF fragments were virtually reduced to match a 3D model of the femoral neck. Subsequently, 3D mapping was performed by graphically superimposing all of the fracture lines and bone defects onto a femoral neck template. The 3D mappings were independently examined by two orthopedic surgeons, and the interobserver agreement was analyzed. For intraobserver analysis, one of the surgeons measured the mappings twice more, and the intraclass correlation coefficients (ICCs) were calculated. A linear regression analysis was conducted to explore bone defect area-related factors. Results: The cohort comprised 141 (55%) patients with left hip injuries and 115 (45%) patients with right hip injuries. On the 3D maps, the dense zones of the fracture lines were largely observed from the superior to the posterior part of the femoral neck, while the dense zone of the bone defect was primarily concentrated in the posterior part of the femoral neck. Only a few dense zones were located in the anterior and inferior parts of the femoral neck. An overlapping region between the fracture line and the bone defect was located in the 2.5th to 4.5th (5th) part of the 1/10 of the superior (posterior) femoral neck length. Both the fracture line and bone defect mapping techniques had good intra- and inter-observer reliability, with ICCs of 0.879 (0.977) and 0.780 (0.974), respectively. Garden type and age were positively correlated with bone defects, while simplified AO Foundation/Orthopaedic Trauma Association (AO/OTA) classification was negatively associated with bone defects. Conclusions: The fracture lines and bone defects of the DFNFs were mainly located in the superior and posterior parts of the femoral neck, while an overlapping region was observed in the subcapital area of the femoral neck. 3D mapping is a reliable method for searching for DFNF features, and separately studying fracture lines and bone defects can further elucidate the morphology of these fractures. Bone defects in patients with DFNFs were associated with Garden type, simplified AO/OTA classification, and age.