LETTER TO THE EDITOR: Assessment of Coolant Delivery Techniques for Irrigation During Bone Drilling: A Cadaveric Observation

We would like to share an unexpected finding related to a common orthopaedic procedure. Erickson et al reported that temperature above 47o C for one minute is the critical threshold for bone necrosis1 . Modification of drill bits designs (cutting surface, flutes/helix angle), drilling techniques (drilling speed, drilling time, pre-drilling) and use of coolant has been recommended to lower this risk2 . Although many orthopaedic and trauma surgeons are faithfully irrigating the drill bit / drill sleeve with saline during bone drilling for this purpose, we do not even know whether the coolant ever reach the bone / drill bit interface, especially during minimally invasive percutaneous procedures. Benington et al and Sener et al showed that external saline irrigation was effective to prevent bone necrosis for dental procedures, but there was no similar study on clinical orthopaedic models3,4. We decided to investigate whether saline sprayed over the incision wounds or outer end of drill sleeves wound reach the interface between bone and drill bit during bone drilling (Fig. 1). We chose different sites corresponding to safe zones of external fixator for the femur and tibia, and introduce a new 3.5mm drill bit / corresponding drill sleeve at angles of 0°, 45° and 90° to the vertical line (Fig. 2) through a 1cm incision wound. Drilling were performed for about 5 seconds, irrigated with 10ml of saline (with blue dye). The drilling path were then dissected down to the bone for examination.