2016-02-23, Schmoelz, Werner, Mayr, Raul, Schlottig, Falko, Ivanovic, Nikola, Hörmann, Romed, Goldhahn, Jörg

Background: Screw anchorage in osteoporotic bone is still limited and makes treatment of osteoporotic fractures challenging for surgeons. Conventional screws fail in poor bone quality due to loosening at the screw-bone interface. A new technology should help to improve this interface. In a novel constant amelioration process technique, a polymer sleeve is melted by ultrasound in the predrilled screw hole prior to screw insertion. The purpose of this study was to investigate in vitro the effect of the constant amelioration process platform technology on primary screw anchorage. Methods: Fresh frozen femoral heads (n=6) and vertebrae (n=6) were used to measure the maximum screw insertion torque of reference and constant amelioration process augmented screws. Specimens were cut in cranio-caudal direction, and the screws (reference and constant amelioration process) were implanted in predrilled holes in the trabecular structure on both sides of the cross section. This allowed the pairwise comparison of insertion torque for constant amelioration process and reference screws (femoral heads n=18, vertebrae n=12). Prior to screw insertion, a micro-CT scan was made to ensure comparable bone quality at the screw placement location. Findings: The mean insertion torque for the constant amelioration process augmented screws in both, the femoral heads (44.2Ncm, SD 14.7) and the vertebral bodies (13.5Ncm, SD 6.3) was significantly higher than for the reference screws of the femoral heads (31.7Ncm, SD 9.6, p<0.001) and the vertebral bodies (7.1Ncm, SD 4.5, p<0.001). Interpretation: The interconnection of the melted polymer sleeve with the surrounding trabecular bone in the constant amelioration process technique resulted in a higher screw insertion torque and can improve screw anchorage in osteoporotic trabecular bone.