Accuracy of the surgeon’s eye: Use of the tip–apex distance in clinical practice Jonathan Wright *, Steven Kahane, Abdul Moeed, Andrew MacDowell Department of Trauma & Orthopaedics, Broomfield Hospital, Court Road, Broomfield, Chelmsford, Essex CM1 7ET, United Kingdom Introduction Baumgaertner described the measurement of ‘‘Tip–Apex distance’’ in 1995, as a means of assessing the placement of a dynamic hip screw within the femoral head [1]. The measurement is calculated by adding the distance from the tip of the hip screw to that of the apex of the femoral head on the AP and lateral views. Correction is made for magnification by using a known dimension on the radiograph; the diameter of the lag screw shaft. The target maximum distance was set at 25 mm, as the authors reported no failure of fixation due to ‘‘cut out’’ of the hip screw from the femoral head in the patients with measurements of less than this distance. This technique has been repeated by several other authors [2– 5]. A logistic regression of 937 patients showed tip–apex distance to be the most important factor in the risk of cut out of dynamic hip screw fixation in proximal femoral fractures [3]. A twenty-four time increase in risk of screw cut out has been demonstrated in patients with a tip–apex distance exceeding 25 mm, in comparison to those with less than 25 mm [4]. The method has also been described in the use of cephalomedullary screw placement, also demonstrating improvement in failure rates with lower tip–apex distances [5,6]. Instruction of surgeons in the concept of tip–apex distance has been shown to increase the number of patients with satisfactory positioning of the lag screw [7–9], in turn decreasing the frequency of screw cut out [7]. The original description of measurement of the tip–apex distance was by direct measurement from printed hard-copy radiographs [1]. There has been shown to have high inter and intra-observer reliability in direct measurement of tip–apex distance [7,10]. The use of digital picture archive and communication systems has also been shown to be as accurate and reproducible for the purposes of measurement for research and audit purposes [10]. In practice however, the point at which the tip–apex distance would be utilised, is at the time of surgical fixation of the fracture. This would usually require estimation of the distance by eye, from the image intensifier machine, whilst the surgeon is scrubbed. At present, there is no evidence as to the accuracy of such an assessment. We aim to assess how accurately a surgeon can assess adequacy of screw placement by eye, from intra-operative imaging. Materials and methods Intra-operative image intensifier radiographs taken during surgical fixation of proximal femoral fractures are saved onto the in Injury, Int. J. Care Injured 46 (2015) 1346–1348 A R T I C L E I N F O Article history: Accepted 28 April 2015 Keywords: Hip Fracture Dynamic hip screw Tip–apex distance Image intensifier Accuracy A B S T R A C T Tip–apex distance is a well described method for assessment of screw placement in dynamic hip screw fixation of proximal femoral fracture. A distance of <25 mm is associated with a significantly lower rate of cut out of the fixation device. Measurement is frequently performed retrospectively, although there has been no demonstration as to what accuracy the surgeon has of estimating tip–apex distance from image intensifier images, whilst scrubbed in theatre. Thirty-one clinicians working within orthopaedic departments were tested in their ability to identify adequacy of tip–apex distance on a series of image intensifier images. Level of seniority, awareness of the concept of tip–apex distance and use of the concept in clinical practice were each assessed. The accuracy in identifying the correct TAD was 82.5% in consultants, 83.8% in registrars and 71.1% in Senior house officers (SHO). The method was used in clinical practice by 50% of consultants, 89% of registrars and none of the SHOs. ß 2015 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +44 7941672839. E-mail addresses: Jwrightortho@gmail.com, jonathan.wright@nhs.net (J. Wright). Contents lists available at ScienceDirect Injury jo ur n al ho m epag e: ww w.els evier .c om /lo cat e/inju r y http://dx.doi.org/10.1016/j.injury.2015.04.041 0020–1383/ß 2015 Elsevier Ltd. All rights reserved.