INVESTIGATION OF THE AWIJ-DRILLING PROCESS IN CORTICAL BONE

So called “interference screws” are state of the art of bone-tendon-bone fixation in AnteriorCruciate-Ligament (ACL) reconstruction. Theses screws normally consist of materials like different polyactic acids because of their biodegradablility. However, these screws have some disadvantages like frequently reported breakage during insertion and degeneration of bone tissue during the degradation process caused by the chemical reaction products. In contrast, bone material as an implant has the advantage to be fully biocompatible and absorbable by the body. Due to the fact that the AWIJ could already be proven to be a cold cutting process as well in medical aspects, it is possible to machine bone by the AWIJ without any structural damage. Therefore the feasibility to machine a whole bony interference screw by the means of the AWIJ including the bore, the screw thread and the inner contour for the screw drive could be shown in previous works. This study is focused on the AWIJ drilling process in cortical bone. Therefore a reference model in PMMA and a model for cortical bone were established empirically. As a result the drilling depth as well as the bore diameter can be predicted by our model in respect to the parameters abrasive flow rate, pressure and time. Obviously the mean variance of our bone drilling model (depth: σ = 2.87 mm; diameter: σ = 0.20 mm) was much higher than for the model for the PMMA (depth: σ = 0.59 mm; diameter: σ = 0.14 mm) model caused by the inhomogenity of the bone material. Furthermore the quality of bore was investigated in reference to the German Standard DIN ISO 1101 with the value of the cylinder shape tolerance. The minimal cylinder shape tolerance was determined to z = 0.21 mm.