A Novel Bone-Screw-Fastener Demonstrates Greater Maximum Compression Force Prior to Failure Compared to a Traditional Buttress Screw.

Abstract

This study compared the maximal compression force prior to thread stripping of the novel bone-screw-fastener (BSF) compared to the traditional-buttress-screw (TBS) in synthetic osteoporotic and cadaveric bone models. Maximum compression force of the plate-bone interface prior to loss of screw purchase during screw tightening was measured between self-tapping 3.5mm BSF and 3.5mm TBS using calibrated load cells. Three synthetic biomechanical models were used: a synthetic osteoporotic diaphysis (model 1); a 3-layer biomechanical polyurethane foam with 50-10-50 pounds-per-cubic-foot (PCF) layering (model 2), and a 3-layer polyurethane foam with 50-15-50 PCF layering (model 3). For the cadaveric metaphyseal model, three sets of cadaveric tibial plafonds and three sets of cadaveric tibial plateaus were used. A plate with sensors between the bone-plate interface was used to measure compression force during screw tightening in the synthetic bone models, while an annular load cell that measured screw compression as it slid through a guide was used to measure compression in the cadaver models. Across all synthetic osteoporotic bone models, the BSF demonstrated greater maximal compression force prior to stripping compared to the TBS (model 1, 155.51N(SD=7.77N) vs 138.78N(SD=12.74N), p=0.036; model 2, 218.14N (SD=14.15N) vs 110.23N(SD=8.00N), p<0.001; model 3, 382.72N(SD=20.15) vs 341.09N(SD=15.57N), p=0.003. The BSF had greater maximal compression force for the overall cadaver trials, the tibial plafond trials, and the tibial plateau trials (overall, 111.27N vs 97.54N(SD 32.32N), p=0.002; plafond, 149.6N vs 132.92N(SD 31.32N), p=0.006; plateau 81.33N vs 69.89N(SD 33.38N), p=0.03. The novel bone-screw-fastener generated 11-65% greater maximal compression force than the traditional-buttress-screw in synthetic osteoporotic and cadaveric metaphyseal bone models. A greater compression force may increase construct stability, facilitate early weight bearing, and reduce construct failure.