Development And Biomechanical Study Of Absorbable Scaphoid Screw

ObjectiveTo develop a new internal fixator absorbable scaphoid screw (ASS) for fracture of the scaphoid waist and to test the biomechanical characteristics of ASS so as to provide the biomechanical proofs for clinical application.MethodsAccording to the acquired measurements and anatomic features of the scaphoid in Chinese population, a special internal fixator——ASS was designed. The biomechanical fatigue experiment: The 20 fresh specimens of fractures of the waist of scaphoid were divided randomly into 2 groups(n=10). Reduction and internal xation were carried out in each specimen,with Kirschner wires, and with ASS. Wrist joint was pressured load of palmar exion by Moving Target Simnlater(MTS) and dorsal extension motion was simulated ; the range of movement was from palmar exion 5°to dorsal extension 25°and the frequency was 2 000 cycles. Displace data offragment were measured with Materialise's Interactive Medical Image Control System (MIMICS)and Vernier Caliper. The biomechanical intensity experiment:Scaphoids were taken out from the 20 fresh specimens of fractures of the waist and divided into with Kirschner, and with ASS groups. The 10 corrosion spec-imens of fractures of the waist of scaphoid were carried out with ASS. Scaphoids was vertically pressured and pulled load of palmar exion by MTS. Their inflect strength was tested by a hydrolic pressure biomechanical system.Results1. Examination model instauration: The groups ASS and groups Kirschner displacement of the fracture lines were (0±0)mm,(0±0)mm by vernier calipers measurement;The displacement of the fracture lines were(0.16±0.02)mm,(0.22±0.02)mm by MIMICS measurement;Experiment showed that there were not differences between Group ASS and groups Kirschner (P>0.05). 2. The biomechanical fatigue experiment:The biomechanical fatigue experiment showed that The groups ASS and groups Kirschner displacement of the fracture lines were(0±0)mm,(0.23±0.03)mm,(0±0)mm,(0.49±0.1)mm,(0±0)mm,(1.38±0.1)mm by vernier calipers measurement;The displacement of the fracture lines were(0.21±0.03)mm,(1.52±0.07)mm by MIMICS measurement;Experiment showed that there were significant differences between Group ASS and groups Kirschner (P<0.01) according to the measured results of the displacements of the fracture lines.3. The biomechanical intensity experiment : The groups ASS and groups Kirschner traction intension were (0.95±0.02)Mpa,(0.63±0.02)Mpa;Experiment showed that there were significant differences between Group ASS and groups Kirschner (P<0.01) according to the measured results of the traction intension;The groups ASS bend intension were(2.71±0.20)Mpa.ConclusionThe design of ASS is in accordance with the anatomic features of the scaphoid.The fixed strength can meet the demand of the biomechanics and the range of fatigue strength can meet the demand of bony union.