Determining relationship between bone screw insertion torque and insertion speed

Abstract

Abstract Bone screws are used in many orthopaedic procedures. For low-density cancellous and osteoporotic bone, the torque margin for bone screw insertion can be low; over-tightening will strip the threads, while under-tightening may allow screw loosening over time. A model-based system of automatic individualised torque regulation has been proposed, however current efforts assume speed-independence. This publication addresses the lack of knowledge on the speed dependance of insertion torque. Therefore, a bone screw was inserted at various speeds between 2.5 and 25 rpm into 4 different densities of polyurethane foam synthetic bone. A statistically significant upwards trend was found for all materials (p < 0.05). These findings can be used to correct identified bone strength values from previous models, although investigating the physical cause may improve correction schemes.