Elsevier

Injury

Volume 39, Issue 7, July 2008, Pages 734-741
Injury

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

https://doi.org/10.1016/j.injury.2007.11.286Get rights and content

Summary

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 2.8 mm 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° and 30° 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° approach angle with skiving equivalent to that experienced by the 2-fluted drill at 15°. Mechanical testing showed that bending stiffness (N/mm) of the 3-fluted drill (9.5 ± 2.1 N/mm) is more than double that of the 2-fluted drill (3.5 ± 0.6 N/mm) during operation. Computer modeling of the drills supported this finding and demonstrated that bending stiffness (IX) 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 IX of 3-fluted drills may account for the clinical prevalence of rotational bending failure amongst 2-fluted drills.

Introduction

Drilling of bone is routine during fracture fixation and reconstructive surgery in a variety of anatomical sites. Surgical drills are the instruments used to remove a controlled amount of bone prior to the placement of a screw or graft material. They are available in either 2- or 3-fluted configurations, where the flutes are that portion of the drill used to channel debris away from the cutting surface. In reality, a surgeon is often required to drill at non-perpendicular orientations and on a highly curved and irregular surface to achieve the surgical goals. This can be difficult and result in skiving of the drill-tip along (or off) the bone and may result in adjacent soft tissue damage, improper placement of the drill hole or a hole that does not meet the original requirements in geometric terms. Unnecessary removal of bone stock can decrease screw pullout strength and have a negative effect on defect healing.5 Little has been reported on the effects which drill-bit geometry and mechanical properties have on the ability of a surgeon to accurately place a drill hole in bone.

Breakage of orthopaedic drill-bits due to excessive bending rates highly amongst the reported incidences of drill-bit failure.[2], [3], [4] Bending failure of surgical drills is most commonly encountered with 2-fluted drills during bi-cortical drilling of long bones, such as in the placement of a lag screw across a fracture site.1 This can occur due to skiving – or wandering – of the drill-tip along the far cortex prior to purchase which deforms the rotating drill-bit and induces a concentrated moment load causing failure. Where rotational bending failure has previously been reported the broken portion of the drill has been left in situ due to complications associated with removal of the broken portion from the medullary cavity.[2], [3], [4]

This study examined differences in tip geometry (point-angle) and flexural rigidity (EIX) of diameter-matched 2- and 3-fluted surgical drills. We hypothesised that the acute-tip geometry and increased flexural rigidity of 3-fluted drills can – in certain clinical scenarios – equate not only to improved targeting ability for the surgeon, but also account for the clinical prevalence of rotational bending failure amongst 2-fluted drills.

Section snippets

Methods

2.8 mm diameter 2-fluted (Acumed, CA) and 3-fluted (Orthopaedic Innovation, Sydney, Australia) surgical drills were used in this study (Fig. 1). This study consisted of 3 components: (1) examination of accuracy; (2) examination of mechanical properties; (3) mathematical and computer modeling.

Results

Results from the accuracy experiment, shown in Table 1, revealed that the 3-fluted drill outperformed the 2-fluted drill not only in terms of accuracy, but also in the range of allowable approach angles. Our surgeon was unable to drill holes at approach angles beyond 30° using the 2-fluted drill but was able to drill at all angles up to and including 45° using the 3-fluted drill. Mean skiving was contained to within one diameter of the drill (2.8 mm) for both drills at all approach angles.

Discussion

Flexural rigidity (EIX) of a member rotating through a stationary bending moment (such as a surgical drill subjected to a net bending moment) is a function of the principal second (area) moments of inertia (Imax, Imin), Young's modulus (E) of the material, rotation (θ) of the principal axes of the given cross-sectional area relative to the plane of bending according to the following relation:EIX=EAy2dA=EImax+Imin2+ImaxImin2cos2θIxysin2θFor surgical drills – and twist drills in general –

Conflict of interest statement

None.

References (5)

There are more references available in the full text version of this article.

Cited by (25)

  • A novel self-centring drill bit design for low-trauma bone drilling

    2020, International Journal of Machine Tools and Manufacture
    Citation Excerpt :

    Because the working length of a drill bit in orthopaedic surgery is typically longer than 60 mm and the diameter is smaller than 4.2 mm, this frequently causes skidding of the drill tip along the bone surface. This can result in damage to the surrounding soft tissue, tool breakage, and inaccurate positioning of the drill hole, which affect the requirements of position accuracy during implant assembly [10]. Fourth, the cortical bone is a semi-brittle material that exhibits biological activity, so that fracture is easy to generate and propagate inside the bone tissue.

  • Parameters affecting mechanical and thermal responses in bone drilling: A review

    2018, Journal of Biomechanics
    Citation Excerpt :

    Although a U-groove flute is traditionally recommended for twist drill bits, it has been shown that a helical parabolic flute design can be more effective at ejecting bone chips from the cutting zone (Karmani and Lam, 2004; Saha et al., 1982). While two-fluted drill bits are more common, it has been reported that three-fluted drill bits are more resistant to bending of the surgical drill bit, thereby reducing the thrust force (Bertollo et al., 2008). The flute angle refers to the helix angle (Fig. 3(a)), which is defined as that between the end of the flute edge and the vertical axis of the drill bit.

  • Clinical Accuracy of Customized Stereotactic Fixtures for Stereoelectroencephalography

    2018, World Neurosurgery
    Citation Excerpt :

    The automatic segmentation process we use eliminates any subjectivity in the accuracy analysis; however, it may be subject to the limitations of the algorithm.16 Whereas the fixture can support virtually any orientation of the trajectories, it is advised that the approach angle be kept at a minimum to prevent drill skiving17 and minimizing the targeting errors—a precaution that applies to any other stereotactic system. Brain shift is another source of error that is difficult to avoid and equally affects all stereotactic systems.

  • Reducing temperature elevation of robotic bone drilling

    2016, Medical Engineering and Physics
    Citation Excerpt :

    The chisel edge has a negative rake angle which contributes up to 50% of the thrust force and is therefore often optimized with different design techniques (e.g. split-point, s-shaped) [12,13]. Three fluted drill bits have the advantage of a superior bending stiffness, but no temperature reduction was found when comparing to 2-fluted drill bits [14,15]. The drill bit diameter has been shown to increase the temperature elevation in general regardless of the drill bit design [16,17].

  • Drilling of bone: A comprehensive review

    2013, Journal of Clinical Orthopaedics and Trauma
View all citing articles on Scopus
View full text