THE INFLUENCE OF SCREW TORQUE, OBJECT RADIUS OF CURVATURE, MODE OF BONE PLATE APPLICATION AND BONE PLATE DESIGN ON BONE-PLATE INTERFACE MECHANICS

Using Fuji Prescale Pressure Sensitive Film we evaluated the influence of screw torque, object radius of curvature, mode of bone plate appli cation (compression or neutral lending) and bone plate design on bone- plate interface mechanics. Testing was performed using 4.5 mm and 3.5 mm dynamic compression (DC) (stainless steel) and limited contact-dyna mic compression (LC-DC) plates (titanium). Plexiglass tubing, having d ifferent radii of curvature, was used to simulate bone but having more uniform geometric and structural properties. With the film interposed between the bone plate and the plexiglass, bone plates were applied a t predetermined levels of screw torque. The resultant image was digiti zed and then underwent computer-assisted analysis to yield the interfa ce contact area (%) and the average force (in Newtons N) between the b one plate and the object to which it wits applied. In any given object , screw torque had the most significant influence on both interface co ntact al ea (P = 0.0001) and average force (P = 0.0002) at the interfa ce. The bone plates responded differently to dynamization. The DC plat e when applied in compression loading mode, was lifted off the object between the two central screws when compared to the same plate applied in neutral loading mode (P = 0.0001). Conversely, in the. LC-DC plate , an increase in the overall interface contact area was observed when applied in compression loading mode (P = 0.0002). At a given level of applied screw torque, the object radius of curvature appeared to be a major determining factor for interface contact area and average force (P = a.0001, P = 0.0001). We conclude that variables other than bone p late design also influence the interface contact area and average forc e between a bone plate and object to which it is applied. (C) 1998 Els evier Science Ltd. All rights reserved.