Improved tibial cutting accuracy in knee arthroplasty

Initial stability and development of long-term fixation for cementless tibial components at the knee both depend on the accuracy of fit between implanted components and prepared bone surfaces. Tibial surfaces prepared for total knee replacement with conventional saw-blades and guides were shown by Toksvig-Larsen to vary by over 2 mm, from a flat surface at the point of maximum variation, and all points varied with a standard deviation of up to 0.4 mm. Surface cutting errors are caused by flexion of the saw-blade and blade angulation from the ideal alignment, due to poor guidance or control by the saw-block or guide. Most conventional knee instrumentation relies on flat surface or slotted cutting blocks, constraining the moving saw-blade against one or two guide surfaces. Improved cutting action was achieved by constraining the saw from the pivot point of the blade, and controlling motion of this constraint with parallel action slides. Using this saw-guide and an improved saw-blade, tibial cuts were made in mock arthroplasty procedures on twenty four cadaveric tibiae in mortuo. Analysis of Variance and Tukey's HSD test showed that the improved saw technique yielded significantly better flatness (p < 0.03) and greatly improved roughness (p < 0.0005).