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Reliability of Predictors for Screw Cutout in Intertrochanteric Hip Fractures
Kirstin De Bruijn, MD1; Dennis den Hartog, MD, PhD1; Wim Tuinebreijer, MD, PhD, MSc, MA1; Gert Roukema, MD2
1 Department of Surgery (K.D.B.) and Department of Surgery-Traumatology (D.d.H., W.T.), Erasmus MC, University Medical Center Rotterdam, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands. E-mail address for K. De Bruijn: k.debruijn@erasmusmc.nl. E-mail address for D. den Hartog: d.denhartog@erasmusmc.nl. E-mail address for W. Tuinebreijer: w.tuinebreijer@erasmusmc.nl
2 Maasstad Ziekenhuis, Groene Hilledijk 315, 3075EA Rotterdam, The Netherlands. E-mail address: roukemag@maasstadziekenhuis.nl
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Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

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Investigation performed at Maasstad Hospital, Rotterdam, The Netherlands, and Erasmus MC, University Medical Center, Rotterdam, The Netherlands

Copyright © 2012 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2012 Jul 18;94(14):1266-1272. doi: 10.2106/JBJS.K.00357
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Following internal fixation of intertrochanteric hip fractures, tip apex distance, fracture classification, position of the screw in the femoral head, and fracture reduction are known predictors for screw cutout, but the reliability of these measurements is unknown. We investigated the reliability of the tip apex distance measurement, the Cleveland femoral head dividing system, the three-grade classification system of Baumgaertner for fracture reduction, and the AO classification system as predictors for screw cutout.


All patients with an intertrochanteric hip fracture who were managed with either a dynamic hip screw or a gamma nail between January 2007 and June 2010 were evaluated from our hip trauma database.


The tip apex distance measurement was reliable and patients with device cutout had a significantly higher tip apex distance. The agreement between observers with regard to screw position and fracture reduction was moderately reliable. After adjustment for tip apex distance and screw position, A3 fractures were at more risk of cutout compared with A1 fractures. Poor fracture reduction was significantly related with a higher incidence of cutout in univariate analysis, but not in multivariate analysis. Central-inferior and anterior-inferior positions, after adjustment for tip apex distance and screw position, were significantly protective against cutout.


To decrease probable risks of cutout, the tip apex distance needs to stay small or the screw needs to be placed central-inferiorly or anterior-inferiorly.

Level of Evidence: 

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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    Geert Meermans
    Posted on July 22, 2012
    Trigonometry and Tip Apex Distance
    Lievensberg Hospital, Bergen Op Zoom, The Netherlands

    I do agree with the comment of Dr. Pottorff that the Tip-Apex Distance described by Baumgaertner et al. (TADort) is not the actual distance between the tip of the screw and the apex of the femoral head (this point was also made by the authors in their original paper). However, the lines drawn from the screw tip and the apex in the lateral (Xlat) and AP projection (Xap) are not the two sides of a right triangle and therefore the sum of their squares does not equal the square of the actual TAD. The actual relation between the true TAD (TADtrue) is TADtrue²= Xlat² + Xap².sin²α where a is the angle between the axis and Xap on the AP view or TADtrue²= Xap² + Xlat².sin²β where β is the angle between the axis and Xlat on the lateral view. The equation proposed by Dr. Pottorff is only true when angle α or β equals 90°. Since the femoral head is a sphere this would mean that the tip of the screw is at the apex or has penetrated the femoral head. I do think we should use the TADtrue because the sum of Xlat and Xap can differ a lot from the TADtrue. If we take the first equation for TADtrue and the screw is placed at the apex (α = 90° and Xlat=0) then TADort=TADtrue. If the screw is placed along the axis (α = 0° and β = 0°; Xlat=(Xap.cosα)/cosβ ⇒ Xlat=Xap) the sum of Xlat and Xap would be twice that of the TADtrue (TADort/TADtrue = (Xlat+Xap)/Xlat ⇒ (Xlat+Xlat)/Xlat=2). In the paper by Baumgaertner et al. the ratio TADort/TADtrue=(Xap+Xap.cosα/cosβ)/√(Xap².cos²α/cos²β+Xap².sin²α) varied from 1.22 to 2.04 (mean 1.70). This means that we overestimate TADtrue with an average of 70% and a range from 22 to 104%. This seems quite a lot when taking into account that all you need is one angle to make it mathematically correct or you can use the formula for a diagonal of a right-angled parallelepiped as described by the authors in their original paper.

    Gregg Pottorff
    Posted on July 18, 2012
    Tip-Apex Distance (TAD) Reliability
    Associated Orthopedic Surgeons, Castro Valley, CA

    Perhaps this comment should be more appropriately levied at the authors of the 1995 article ((Baumgartner et al) but the ACTUAL measurement that should be used for the Tip-Apex Distance (TAD) is not the simple sum of the two X's (one measured on AP, one on Lat X-Ray) as reported here. Those two measurements are simply the two-dimensional orthogonal projections in the AP and Lateral planes of the true TAD and if summed the result is the same as if adding the two sides of a right triangle were intended to give a true representation of the length of the corresponding hypotenuse of said right triangle. As such the ACTUAL measurement for TAD should not be the sum of these two X's but instead the square root of the sum of the SQUARES of the two X's. I know this is a small point but when trying to determine reliability and using descriptive terms like "true" we should at least be precise to the level of our high school trigonometry classes.

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