Micro‐Computed Tomography Analysis of Femoral Head Necrosis After Long‐Term Internal Fixation for Femoral Neck Fracture

OBJECTIVE: To analyze necrotic femoral head after long‐term internal fixation for femoral neck fractures using micro‐computed tomography (CT) for bone histomorphometry. METHODS: The experimental group included six patients (two men and four women; mean age 62.00 ± 9.36 years) who underwent hip arthroplasty at 47.67 ± 14.22 months after internal fixation. Surgery was performed because of femoral head necrosis after femoral neck fracture between October 2018 and October 2020. The control group included three patients (two men and one woman; mean age 69.33 ± 4.62 years) who underwent hip arthroplasty for femoral neck fracture. In the experimental group, micro‐CT quantitative analysis of the whole femur, sclerotic region around screws, screw paths, sclerotic region and screw paths, and relatively normal region was performed. The bone volume fraction (BV/TV), number of bone trabeculae (Tb.N), connection density (Conn.D), thickness of bone trabeculae (Tb.Th), separation of bone trabeculae (Tb.SP), structural model index (SMI), and bone mineral density (BMD) of each part were quantitatively analyzed. RESULTS: The BV/TV (0.3180 ± 0.0617), Conn.D (6.9261 ± 2.4715/mm(3)), Tb.Th (0.3262 ± 0.0136 μm), and BMD (298.9241 ± 54.2029 g/cm(3)) of the sclerotic region around the screws were significantly higher in the experimental group than the BV/TV (0.1248 ± 0.0390), Conn.D (2.5708 ± 0.5187/mm(3)), Tb.Th (0.1713 ± 0.0333 μm), and BMD (66.5181 ± 43.0380 g/cm(3)) in the control group (P < 0.05). The BV/TV (0.2222 ± 0.0684), Tb.Th (0.2775 ± 0.0326 μm), and BMD (195.0153 ± 71.8509 g/cm(3)) in the collapsed region were significantly higher in the experimental group than in the control group (P < 0.05). In the experimental group, the volume ratio of the sclerotic region around screws and screw paths to the entire femoral head was 0.4964 ± 0.0950. CONCLUSION: After internal fixation for femoral neck fracture, a large number of sclerotic plate‐like trabeculae were observed around the long‐term retained implant. The screw paths and surrounding sclerotic comprise approximately 50% of the femoral head volume.