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Research comment
Understanding why inaccuracies happen when drilling bone
  1. Kinley Smith
  1. Willows Referral and Veterinary Centre, Highlands Road, Solihull, B90 4NH, UK
  1. email: kinley.smith{at}

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Orthopaedic surgery may be reduced to three key factors: knowledge, understanding and accuracy. It is essential that surgeons both know and understand the rules when investigating a problem and when formulating a treatment plan. However, the most perfect plan can fail because of inaccuracies in effecting that plan in theatre. ‘Measure twice, drill once’ is the mantra to improve accuracy. Yet, no matter how careful the surgeon, inaccuracy can arise due to variations in equipment and technique. The more we understand these variations, the more accurate we can be.

Sequential drilling is considered to be the standard approach to creating a large diameter hole in bone, into which a large diameter (more than 3.5 mm) screw may be placed. This involves the creation of a pilot hole with a small diameter drill bit and then, using this as a guide, increasing diameter drill bits in order to reach the desired diameter. Common indications would be the placement of a humeral transcondylar screw to manage humeral condylar fissures or for a sacroiliac lag screw to treat a sacroiliac fracture luxation (Fig 1).

Fig 1: Accurate placement of a humeral transcondylar screw is essential when small errors risk damaging the joint

When compared with direct drilling using a drill bit of the final target diameter, the process of changing drill bits three or four times can be time-consuming. So why has sequential drilling become the norm in veterinary orthopaedics? Among many reasons given, the most commonly cited is improved accuracy.

In human orthopaedic surgery, the accuracy of drill alignment is commonly confirmed by the use of intraoperative fluoroscopy. Techniques include fluoroscopic orientation of a drill guide …

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