Eriksen, Thomas

Miles, James Edward

Svalastoga, Eiliv Lars

English

Copenhagen University Research Information System

u n i ve r s i t y  o f  co pe n h ag e n  Københavns UniversitetAgreement and reliability of femoral varus measurements: a comparison of fourtechniquesMiles, James Edward; Svalastoga, Eiliv Lars; Eriksen, ThomasPublication date:2013Document versionEarly version, also known as pre-printCitation for published version (APA):Miles, J. E., Svalastoga, E. L., & Eriksen, T. (2013). Agreement and reliability of femoral varus measurements: acomparison of four techniques. Poster session presented at British Small Animal Veterinary AssociationCongress 2013, Birmingham, United Kingdom.Download date: 02. Feb. 2020       Femoral varus: what's the angle?FACULTY OF HEALTH AND MEDICAL SCIENCESUNIVERSITY OF COPENHAGENJames Miles, Eiliv Svalastoga, Thomas EriksenUniversity Hospital for Companion AnimalsAgreement and reliability of femoral varus measurements: a comparison of four techniquesFurther informationLiterature:1. Jackson and Wendelburg (2012) Evaluation of the effect of distal femoral elevation on radiographic measurement of the     anatomic lateral distal femoral angle. Vet Surg 41:994-10012. Dudley et al (2006) Radiographic and computed tomographic determination of femoral varus and torsion in the dog. Vet Radiol     Ultr 47(6):546-5523. Swiderski et al (2008) Comparison of radiographic and anatomic femoral varus angle measurements in dogs. Vet Surg     37:43-484. Tomlinson et al (2007) Measurement of femoral angles in four dog breeds. Vet Surg 36: 593-5985. Bland and Altman (1996) Statistics notes: measurement error. BMJ 313: 744James Miles (jami@sund.ku.dk)University Hospital for Companion Animals,Dyrlægevej 16,1870 Frederiksberg C,DenmarkContact:Inftroduction heading in 56pt Arial• 'Symax' method is simple to perform• Measured varus does not vary much with femoral angulation, as seen before1• Femoral angulation has least effect on 'Symax' compared to other tested methods• Repeatability for an experienced observer was good for all methods• Observed differences may be clinically irrelevant• Logical next steps: effect of observer experience, interobserver variationConclusions and clinical relevance AbstractThree different techniques have been described for measuring femoral varus radiographically in the dog, but how the measurements from these techniques compare is unknown. Further, measurement reliability has only been assessed for one technique.Seven grossly normal right femora were radiographed with the diaphysis positioned horizontally and inclined at both 12.5° and 25° to the horizontal. Radiographs were blinded, randomised and read twice by one observer using ImageJ. Using coordinate data, varus angles were calculated using Microsoft Excel for the three previously reported techniques and a novel method, which we believed would be more reliable. Reliability between readings was assessed using the within-subject standard deviation and repeatability coefficient, and the effect of angulation on varus measurement was assessed using a mixed model ANOVA.Two of the reported techniques varied significantly (P<.05) with femoral angulation, increasing by approximately 2° from horizontal to 25° angulation. At 25° femoral angulation the novel technique differed significantly (nearly 2°, P<.05) from one of the reported techniques, but otherwise results were similar for all methods. Although we hypothesised that the novel method would be more reliable than the other techniques, all values for the within-subject standard deviation and repeatability coefficient were broadly similar. Graphically, the novel method appeared to vary least with femoral angulation in this population, and its simplicity may offer advantages for clinical use. In the absence of an absolute cut-off for surgical intervention for femoral varus, none of the observed differences are necessarily clinically significant.ResultsVariation with femoral angulation:Methods 'Tomlinson' and 'Swiderski' increased significantly from 0° to 25°, by about 2°.The novel 'Symax' method varied least with femoral angulation. Variation was generally small for all methods, as shown by the ANOVA results and graphically (see chart).Differences between methods:Methods 'Dudley' and 'Symax' were significantly less than 'Tomlinson' at 25°, by about 2°.No other statistically significant differences were observed.Repeatability:Within-subject standard deviations were small (0.5°-0.9°) indicating low variation between readings.Repeatability was similar for all methods with 95% of paired measurements expected to be within 1.4°-2.2° of each other.Introduction heading in 56pt ArialVarus measurement methods and values1 cm1 cmDudley1/21/3TomlinsonddxxSwiderski1/2Symax024680246802468Femoral varus angle (°)25°12.5°0°* ** *Radiographic femoral varus measurements for the four methods and three angulations are shown. Values are arranged in columns according to method, and in rows according to angulation. Error bars represent one standard deviation.Significant differences (P<.05) are marked with a star.Each method's definition of the anatomic proximal femoral axis (aPFA) is illustrated above the chart. Where fractional distances are shown, these refer to the diaphyseal length (unlabelled arrows). The aPFA differs subtly between the four study methods.Femoral angulation was measured between a line joining the lesser trochanter and supracondylar tuberosity, and the horizontal, as shown in the illustrations to the left of the chart.Introduction and objectivesExcessive femoral varus can contribute to medial patellar luxation in dogs, along with other anatomical abnormalities. Varus can be assessed radiographically. Some clinicians insist on radiographs taken with the femora parallel to the radiographic film, whereas others are satisfied with a hip extended view in which it is unlikely that the femora are truly parallel to the film, but instead are angled away from it. A recent report has highlighted small but significant changes in measured varus with femoral angulation.1In addition, three measurement methods have been described,2-4 and there is no consensus on which should be applied or if they produce comparable results.Research questions:Which method's results alter least with femoral angulation?Which method is most repeatable?Does how we measure varus matter?The study objective was to answer these questions.MethodsSeven grossly normal right femoral bone specimens were radiographed with the diaphysis inclined at 0°, 12.5° and 25° relative to the radiographic plane.Varus was measured using three published methods ('Dudley', 'Tomlinson', 'Swiderski')2-4 plus one novel method ('Symax') on two occasions after blinding and randomisation. The freely available software ImageJ was used for all measurements in combination with custom acetate overlays. The same distal femoral reference line was used for all methods, ensuring a true comparison of variability and repeatability.Coordinate data from ImageJ were converted to varus angles using a custom macro in Microsoft Excel. Data were analysed using repeatability coefficients,5 and a mixed model ANOVA in SAS.--

Agreement and reliability of femoral varus measurements: a comparison of four techniques

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Agreement and reliability of femoral varus measurements: a comparison of four techniques

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