Metaphyseal fracture stabilization in osteoporotic bone

Introduction Locked plate osteosynthesis is an alternative to intramedullary nailing (IMN) especially in the metaphyseal region. Some studies are available reporting on the mechanical properties of IMN and locking plates but data are rare and results are conflicting. To date, no studies are available reporting on mechanical properties of angle-stable IMN in proximal and distal tibia fractures in osteoporotic bone compared to locked plate osteosynthesis. Therefore, the aim of the present study is to evaluate the mechanical properties of new angle-stable IMN compared to locked plating. The innovative approach is the development of proximal and distal metaphyseal fracture models in osteoporotic bone. Material and methods To compare angle-stable IMN (Expert Nailing System, Synthes, Switzerland) with the Locking Compression Plate (LCP, Synthes, Switzerland) a proximal and distal metaphyseal fracture model is created using 24 paired fresh- frozen cadaveric tibiae. After randomisation and fracture stabilization with the angle stable nail or with the LCP, samples are embedded in PMMA and then tested axially and in torsion with a servohydraulic material testing machine (Instron 8874; High Wycombe, UK). Compression of 100N and tension of 50N are applied for 3 cycles at 0.1mm/min. Torsion of the tibial shaft is applied in both directions with an amplitude of 5Nm for 3 cycles at 0.1 degrees/min. Shear testing across the osteotomy and the 4-point bending test are performed with an electromechanical material testing machine (Z010; Zwick, Germany). Shear loading is applied across the site of the osteotomy with an amplitude of 100N. Four-point bending moments are applied with an amplitude of 20Nm. The span width is 70mm for the inner and 200mm for the outer supports. An ultrasound based 3D motion system is used to detect micromotions between the fragments (CMS20BI; Zebris, Isny, Germany). Load, linear deformations, and angular rotations within the principal loading directions are measured at a sampling rate of 50Hz with the machine system. The stiffness of the nail/plate-bone-construct is assessed. Magnitudes of movement in different directions are presented in boxplots (minimum, 25% quartile, median, 75% quartile, maximum), and differences are assessed for statistical significance using the nonparametric U-test with a significance level of 0.05. Aim of the study The principle aim of the study is to provide assess the optimal treatment option for osteoporotic metaphyseal fractures of the tibia. Further, we investigate the mechanical properties of angle stable intramedullary nailing in this proximal and distal metaphyseal tibia fracture model.