Development and clinical application of screw remover for the skidded screws / 中华创伤杂志

ABSTRACT

ObjectiveTo develop an EZ screw remover for screwing out the skidded screws,discuss its design features and biomechanical characteristics and verify its extracting effect by clinical applications.MethodsFresh skeleton specimens were used in the study,including the femur (n =3),tibia ( n =3 ),radius and ulna ( n =3 ).The screws were fixed to the specimens according to clinical requirements and bone cement was filled into the medullary cavity.The specimens were randomized into three biomechanical test model groups,ie,Group A (measuring the skidded screws with the biggest torsion when the screws were taken out by screwdriver),Group B (measuring the skidded screws with the biggest torsion when the screws were taken out by one handle of EZ screw remover) and Group C ( measuring the skidded screws with the biggest torsion when the screws were taken out by two handles).The fixed screws were divided into two types of φ4.5 mm and φ3.5 mm.The experimental specimens were tested on the universal testing machines to measure the maximum torque,torsion angle,power consumption value and efficiency when drawing out the screws. The experimental data were compared between groups.The skidded screws encountered in clinical were taken out with EZ screw remover to verify the extracting effect.ResultsThe pullout torque in Groups A,B and C was 2.87-3.27 N · m,3.06-4.83N · m and 4.12-8.36 N · m respectively ( P ＜ 0.05 ).The average torsion angle value in each corresponding group was 0.77°,0.28°,0.16° respectively (P ＜ 0.05 ).When the screws were screwed out,the average power consumption was 21 J,32 J and 45 J in Groups A,B and C respectively and power ( mechanical efficiency) was 0.35 J/s,0.53 J/s and 0.75J/s in Groups A,B and C respectively,with significant differences ( P ＜ 0.05 ).Seventeen pieces of the cannulated skidded screws of φ7.3 mm in seven patients were successfully taken out by using the EZ screw remover.ConclusionEZ screw removerhas enough resistance strength and rigidity to torsion as well as powerful clamping force and hence is an ideal tool for screwing out the skidded screw in orthopedics.