The new shank construct of lag screw improves the maximum compression force for internal fixations: preliminary results

D.-Q. Xu, P.-D. Sun, J. Wang, H.-L. Yang, X.-J. Liu, W.-D. Zhao

Department of Orthopedics, Affiliated Jianhu Hospital of Nantong University Jianhu, Jiangsu, P.R. China. daqiangxu@yeah.net

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• Orthopedics

OBJECTIVE: The treatment of osteoporotic intra-articular fractures with AO lag screws remained challenging due to insufficient compression. Several strategies to improve the compressive ability of lag screws have been evaluated. However, the effect of the shank construct on the compressive ability of lag screw has never been explored. The aim of this study was to determine the effect of a shank construction the compressive ability of lag screw for different bone mineral densities (BMDs).

MATERIALS AND METHODS: Three synthetic cancellous bone blocks were used for this study, including 0.12 g/cc, 0.16 g/cc, and 0.20 g/cc. 24 pilot holes with 3.2 mm diameters were drilled equably in each block. An AO lag screw and a combined lag screw with the newly designed compound shank construct were inserted through the custom-designed measuring device into a pilot hole by hand until failure, and the maximum compressive force (CMAX) was determined.

RESULTS: Among three densities specimens CMAX of the combined lag screw was significantly higher than that of the AO lag screw (p < 0.001), and the mean CMAX difference value of the two screws in a specimen increased as the BMD increased. The CMAX of two screws increased as the BMD increased (p < 0.001), and the amplification of the CMAX generated by the combined lag screw was higher than that generated by the AO lag screw when the BMD increased.

CONCLUSIONS: The newly designed compound shank construct improves the compressive ability of lag screws independent of the BMD.

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