Ablation efficiency in the Er:YAG laser cutting of bone

Mechanical cutting and drilling of hard tissue remain the main procedure employed in orthopaedic surgery. However alternative unconventional methods are receiving increasing attention, owing to the greater precision and accuracy in cutting that they offer and absence of the need for physical contact between tool and bone. Feasibility studies of a range of unconventional methods have indicated that laser cutting has advantages over other non-traditional techniques. These benefits were explored in a series of in-vitro experiments aimed at measuring the efficiency of Er:YAG laser efficiency for bone ablation. A commercially available laser device, already being evaluated for applications in dental surgery, that emits pulsed infra-red radiation at a wavelength of 2.94μm, was used to cut linear incisions on ovine cortical bone. Specimens of bone were irradiated in air, the region of cutting being irrigated with a spray of air mixed with deionised water, in order to dissipate heat and reduce carbonisation. For a constant repetition rate of 10 pulse/s over energies ranging from 200 to 1000mJ/pulse and translations of 5 to 15 laser passes across the bone surface, ablation efficiency was evaluated. From cross-sectioning of ablated bone, the depth of incisions was measured by optical and image analysis. Depth of cut rose linearly with pulse energy and with the number of passes. Methods of further examination of the integrity of bone tissue after laser irradiation are proposed.