Accuracy of Low Dose Computed Tomography ...

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using the Bonesetter application. This was a prospective blinded controlled study at a level 1 trauma centre. Sta- tistical analysis was performed, including ...

International Orthopaedics (SICOT) DOI 10.1007/s00264-015-3040-z

ORIGINAL PAPER

Accuracy of Low Dose Computed Tomography Scanogram for Measurement of Femoral Version after Locked Intramedullary Nailing Kristi Lynn Hultman 1 & Rahul Vaidya 1 & Ibraheem Malkawi 2 & Jon Brandon Carlson 1 & Jason Benjamin Wynberg 2

Received: 3 June 2015 / Accepted: 1 November 2015 # SICOT aisbl 2015

Abstract Purpose This prospective study was performed to compare the accuracy of femoral version measurements following repair of femoral shaft fractures using computed tomography (CT) scanograms with 10 % of the standard dose of ionizing radiation versus standard-dose scanograms. Methods CT scanogram protocols that used 90 and 10 % of the usual dose of ionizing radiation were developed. Ten patients with comminuted femoral shaft fractures repaired with either an intramedullary (IM) nail or plate were imaged with both high- and low-dose CT scanograms. Postoperative version of both femurs was measured and compared between the two dose scans using the Bonesetter application. This was a prospective blinded controlled study at a level 1 trauma centre. Statistical analysis was performed, including standard deviation (SD) and paired t test. Significance was set at p15° has been shown to be significant, at which point patients begin to notice an effect on function [5, 7]. Previous studies report the incidence of malrotation from IM nailing of femoral fractures to be up to 28 % [1, 5, 7, 10, 11]. CT scanograms have been shown to be more accurate than clinic evaluation or standard radiographs when evaluating for rotational deformity [5, 12]. Quantitative analysis of postoperative limb length and alignment has been described using a CT scanogram. The scanogram uses the scout view of both lower extremities in conjunction with selected cuts through the bilateral proximal hips and knees. Leg length can be determined by measurements taken from the scout CT. Precise values for rotation of

International Orthopaedics (SICOT)

the lower extremity are obtained by layering axial slices of these areas and measuring relative rotation between each. A significant downside of routine use of CT scanograms following IM fixation of comminuted femoral shaft fractures is the exposure to ionizing radiation, especially in a younger population, which sustains a significant percentage of these injuries secondary to high-energy blunt or penetrating trauma. In this study, the authors demonstrate that the dose of ionizing radiation in the CT scanogram can be reduced to 10 % of the current dose with no significant effect on the accuracy of rotational measurements. This allows for a significant reduction in radiation exposure to the patient while still providing the desired information.

Materials and methods For this prospective study, we developed a CT scanogram protocol that uses 10 % of the usual dose of ionizing radiation and alters the milliampere per second and collimation widths. A 90 % dosing protocol was also developed so that both a low-dose and standard-dose scanogram were performed, with no increase in ionizing radiation to the patient. Initial full-body anteroposterior (AP) and lateral scout images were taken to confirm acceptable positioning of the lower extremities and measure leg lengths. Axial images were then taken only at the femoral neck and condyles using the scouts for alignment. We selected a convenience sample of ten patients from our level 1 trauma centre who had comminuted femoral shaft fractures repaired with either an IM nail or plate between October 2013 and August 2014. All patients who met this criteria were enrolled based on the availability of our radiation technologist trained to do both the 90 and 10 % dosing CT scanograms. The scanograms were taken in succession on the same encounter, typically postoperative day 1, to minimize changes in patient position for optimal image comparison. Average patient age was 24.4±3.8 years, and average body mass index (BMI) was 25.1±5.4, with one outlier having a BMI of 56. One patient was treated with IM femoral nails bilaterally and was thus excluded from comparisons of native vs. repaired measurements. Postoperative version of both femurs at both 90 and 10 % dosing were measured by two orthopaedic surgery residents and a trauma fellowship-trained orthopaedic surgeon using the Bonesetter application for angle measurements, as shown in Fig. 1. Proximal angle measurements were taken in alignment with the femoral neck, while distal angle measurements were taken in alignment with the posterior side of the femoral condyles. CT scans were blinded and randomised. Statistical analysis was performed, including standard deviation (SD) and paired t test. Significance was set at p

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