A Novel Cannulated Compression Screw with Coating-capable and Reverse Self-tapping for Femoral Neck Fractures: Finite Element Analysis and Preliminary Feasibility Tests

In the treatment of femoral neck fractures with closed reduction and internal fixation, implanting bone repair materials at the fracture site is challenging. To address this problem, this study developed a novel cannulated compression screw (N-CCS) with coating compatibility and a reverse self-tapping function. Six N-CCS prototypes with different transition section lengths were designed for finite element analysis. Under gradient loading conditions, the Von Mises stress and equivalent elastic strain of the screws were compared to determine the optimal structural parameters. A tap based on the reverse self-tapping structure was fabricated to verify the N-CCS?s extraction performance. Three-point bending tests were performed to compare the flexural strength of N-CCS and Conventional cannulated compression screw (C-CCS). A composite coating with calcium phosphate cement (CPC) as the matrix was prepared, and its adhesive stability during implantation was evaluated. The results indicated that the N-CCS with an 8.5 mm transition section exhibited superior mechanical performance and a more uniform stress distribution. The reverse self-tapping structure enabled efficient bone cutting and smooth implant removal. Although the N-CCS yielded a lower bending load than the C-CCS of the same length, its mechanical strength fully met clinical requirements. The CPC coating maintained stable adhesion throughout the implantation process. In conclusion, the N-CCS demonstrates satisfactory mechanical properties, a reliable reverse self-tapping design, and stable coating adhesion.