Abstract
Bone autograft contains living cells that participate in the healing process. Fragmentation and heat production during cutting will kill cells. We have investigated how excessive graft fragmentation and heating can be avoided.
Two prototype cutters were fabricated. Each had a single cutting edge at the front end of a 12 mm diameter collection barrel. The principal difference between the cutters was the rake angle (at the cutting edge): 23° on cutter #1 and 45° on cutter #2.
Thrust load, feed-rate, and torque were measured using an instrumented drill press. A total of 58 tests on specimens of fresh bovine cancellous bone (distal femur, ex-abattoir) and medium density polyurethane foam (Sawbones, WA. USA) (density 252 kg/m3) were conducted: twenty-four at 100 rpm and thirty-four at 200 rpm.
Small flake-like fragmented bone chips were encountered at low thrust loads. As thrust load was increased the chips became thicker. The average cutting energy for bone was 43.7 Nm (s.d. 48.2 Nm) for cutter 1 and 37 Nm (s.d. 27 Nm) for cutter 2. The average cutting energy for the foam was 13.9 Nm (s.d. 6.0 Nm) for cutter 1 and 8.1 Nm (s.d. 3.0 Nm) for cutter 2. Polyurethane results showed a similar trend.
A higher rake angle on a bone graft tool is associated with a lower cutting energy. In turn, a lower cutting energy will generate a lower temperature in the graft, a result that is beneficial for cell survival. Graft tool design can also influence bone chip size. These experimental results are being used for the development of cell-friendly tooling.
The abstracts were prepared by Jean-Claude Theis. Correspondence should be addressed to him at Department of Orthopaedic Surgery, Dunedin Hospital, Private Bag 1921, Dunedin, New Zealand.
