title: 3-Fluted orthopaedic drills exhibit superior bending stiffness to their 2-fluted rivals: clinical implications for targeting ability and the incidence of drill-bit failure.
abstract: Non-perpendicular drilling of bone is commonplace in orthopaedic surgery. In the absence of drill-jigs and guides, the drill-tip is prone to skiving along the bone. Skiving can alter the position of the intended hole or result in damage to surrounding tissues. We hypothesised that the acute point-angle and increased flexural rigidity of 3-fluted drills - in certain clinical scenarios - can increase a surgeons' ability to accurately position a hole. This study examined differences in drill-tip geometry (point-angle) and mechanical properties (flexural rigidity) between 2.8mm diameter 2-fluted and 3-fluted surgical drills. Our results show that the 3-fluted design offers a significant improvement over the 2-fluted design not only in terms of accuracy; at 15 degrees and 30 degrees approach angles the 3-fluted drill skived significantly less than the 2-fluted drill in the hands of our surgeon, but also in the range of permissible approach angles; the 3-fluted drill was able to drill at a 45 degrees approach angle with skiving equivalent to that experienced by the 2-fluted drill at 15 degrees . Mechanical testing showed that bending stiffness (N/mm) of the 3-fluted drill (9.5+/-2.1N/mm) is more than double that of the 2-fluted drill (3.5+/-0.6N/mm) during operation. Computer modeling of the drills supported this finding and demonstrated that bending stiffness (I X) for the 2-fluted drill varies dynamically during operation whilst remaining constant for the 3-fluted drill. Our study confirms a correlation between mechanical properties, point-geometry and targeting capability for surgical drills. Increased I X of 3-fluted drills may account for the clinical prevalence of rotational bending failure amongst 2-fluted drills.
authors.affiliation: Surgical & Orthopaedic Research Laboratories, University of New South Wales, Prince of Wales Hospital, Sydney, Australia. nickyb@student.unsw.edu.au
authors.forename: N
authors.initials: N
authors.lastname: Bertollo
authors.forename: T K
authors.initials: TK
authors.lastname: Gothelf
authors.forename: W R
authors.initials: WR
authors.lastname: Walsh
mesh_terms: D003198:Computer Simulation; D004548:Elasticity; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008422:Materials Testing / Q000379:methods; D008962:Models, Theoretical; D019637:Orthopedic Procedures / Q000295:instrumentation*