Comments on Reito et al.: Assessment of inter- and intra-observer reliability in the determination...
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LETTER TO THE EDITOR Comments on Reito et al.: Assessment of inter- and intra-observer reliability in the determination of radiographic version and inclination of the cup in metal-on-metal hip resurfacing Vikas Bachhal & Sushil Rangdal & Gaurav Saini & Mandeep Dhillon Received: 9 March 2012 / Accepted: 23 April 2012 / Published online: 15 May 2012 # Springer-Verlag 2012 We read the article by Reito et al. [1] which discussed the radiographic method of determining version and inclination in metal-on-metal hip arthroplasty with interest. Although we agree with the validity of the method used by the authors [2], it is not the easiest for measuring anteversion for metal- on-metal arthroplasty. We would like to take the liberty of using the figure used in this article to make our point and describe an alternative method which in our opinion is easier and involves fewer calculations. Instead of measuring value e, an alternative length h, described as the length of a line segment from the point where the major semi axis intersects line p to a point on the same line (extended) where it intersects the circular outline of the cup (assuming it to be a hemisphere), is used (Fig. 1). Now the angle of anteversion can be given by the equation: Anteversion ¼ sin 1 ph = ð Þ Software such as Microsoft excel can be used to make precise calculations for the above equation or a scientific calculator (online, PDAs, etc.) can be used. If one wishes to use ready tables, then it is easy to see that calculation of two fractions (p/e and r/e, Table used in article by Reito et al. [1]) might give values between those provided in the table, thus requiring rounding off of two fractions while a similar table prepared for arcsine function would require rounding off of a single fraction resulting in more accurate calculation of anteversion. We have provided Table 1 for such purposes. To further prove our point, consider an example with the following values: r 0 37, e 0 35, p 0 5, h 0 12. Using Table 1 ( in article by Reito et al. [1]), with p/e 0 0.14 and r/e 0 1.06 (both rounded to 2 decimals), the angle calculated will be 23.5 while using the equation (ours or as given in this article) it is 24.62, and it is 24.83 when using Table 1 for ratio p/h. This clearly shows that our suggested method involves fewer measurements (p and h vs p, r and e), fewer calculations (one ratio vs two) and is more accurate if using a table as it involves approximation of one ratio as compared to two. In our opinion, although this study makes a valid attempt at devising a method for measuring anteversion in MMTHR, their method is not the easiest nor most accurate. Although this method holds true for hemispherical cups, for non-hemispherical cups a second circle can be drawn with major semi axis as its radius and centre at origin of ellipse. Further measurements will be the same as described above. V. Bachhal (*) : S. Rangdal : G. Saini : M. Dhillon Department of Orthopaedics, Postgraduate Institute of Medical Education and Research, Chandigarh, India e-mail: [email protected] International Orthopaedics (SICOT) (2012) 36:1535–1537 DOI 10.1007/s00264-012-1566-x
Transcript of Comments on Reito et al.: Assessment of inter- and intra-observer reliability in the determination...
LETTER TO THE EDITOR
Comments on Reito et al.: Assessment of inter-and intra-observer reliability in the determinationof radiographic version and inclination of the cupin metal-on-metal hip resurfacing
Vikas Bachhal & Sushil Rangdal & Gaurav Saini &Mandeep Dhillon
Received: 9 March 2012 /Accepted: 23 April 2012 /Published online: 15 May 2012# Springer-Verlag 2012
We read the article by Reito et al. [1] which discussed theradiographic method of determining version and inclinationin metal-on-metal hip arthroplasty with interest. Althoughwe agree with the validity of the method used by the authors[2], it is not the easiest for measuring anteversion for metal-on-metal arthroplasty. We would like to take the liberty ofusing the figure used in this article to make our point anddescribe an alternative method which in our opinion is easierand involves fewer calculations.
Instead of measuring value e, an alternative length h,described as the length of a line segment from the pointwhere the major semi axis intersects line p to a point on thesame line (extended) where it intersects the circular outlineof the cup (assuming it to be a hemisphere), is used (Fig. 1).Now the angle of anteversion can be given by the equation:
Anteversion ¼ sin�1 p h=ð Þ
Software such as Microsoft excel can be used to makeprecise calculations for the above equation or a scientific
calculator (online, PDAs, etc.) can be used. If one wishes touse ready tables, then it is easy to see that calculation of twofractions (p/e and r/e, Table used in article by Reito et al.[1]) might give values between those provided in the table,thus requiring rounding off of two fractions while a similartable prepared for arcsine function would require roundingoff of a single fraction resulting in more accurate calculationof anteversion. We have provided Table 1 for such purposes.To further prove our point, consider an example with thefollowing values: r037, e035, p05, h012.
Using Table 1 ( in article by Reito et al. [1]), with p/e00.14 and r/e01.06 (both rounded to 2 decimals), the anglecalculated will be 23.5 while using the equation (ours or asgiven in this article) it is 24.62, and it is 24.83 when usingTable 1 for ratio p/h. This clearly shows that our suggestedmethod involves fewer measurements (p and h vs p, r and e),fewer calculations (one ratio vs two) and is more accurate ifusing a table as it involves approximation of one ratio ascompared to two.
In our opinion, although this study makes a valid attemptat devising a method for measuring anteversion inMMTHR, their method is not the easiest nor most accurate.Although this method holds true for hemispherical cups, fornon-hemispherical cups a second circle can be drawn withmajor semi axis as its radius and centre at origin of ellipse.Further measurements will be the same as described above.
V. Bachhal (*) : S. Rangdal :G. Saini :M. DhillonDepartment of Orthopaedics, Postgraduate Institute of MedicalEducation and Research,Chandigarh, Indiae-mail: [email protected]
International Orthopaedics (SICOT) (2012) 36:1535–1537DOI 10.1007/s00264-012-1566-x
Fig. 1 Modified Fig. 2 fromthe article by Reito et al. withadded measurement of length h
Table 1 Determination of angle of anteversion via fractions
p/h Anteversion p/h Anteversion
0.01 0.57 0.51 30.66
0.02 1.15 0.52 31.33
0.03 1.72 0.53 32.01
0.04 2.29 0.54 32.68
0.05 2.87 0.55 33.37
0.06 3.44 0.56 34.06
0.07 4.01 0.57 34.75
0.08 4.59 0.58 35.45
0.09 5.16 0.59 36.16
0.1 5.74 0.6 36.87
0.11 6.32 0.61 37.59
0.12 6.89 0.62 38.32
0.13 7.47 0.63 39.05
0.14 8.05 0.64 39.79
0.15 8.63 0.65 40.54
0.16 9.21 0.66 41.30
0.17 9.79 0.67 42.07
0.18 10.37 0.68 42.84
0.19 10.95 0.69 43.63
0.2 11.54 0.7 44.43
0.21 12.12 0.71 45.23
0.22 12.71 0.72 46.05
0.23 13.30 0.73 46.89
Table 1 (continued)
p/h Anteversion p/h Anteversion
0.24 13.89 0.74 47.73
0.25 14.48 0.75 48.59
0.26 15.07 0.76 49.46
0.27 15.66 0.77 50.35
0.28 16.26 0.78 51.26
0.29 16.86 0.79 52.19
0.3 17.46 0.8 53.13
0.31 18.06 0.81 54.10
0.32 18.66 0.82 55.08
0.33 19.27 0.83 56.10
0.34 19.88 0.84 57.14
0.35 20.49 0.85 58.21
0.36 21.10 0.86 59.32
0.37 21.72 0.87 60.46
0.38 22.33 0.88 61.64
0.39 22.95 0.89 62.87
0.4 23.58 0.9 64.16
0.41 24.20 0.91 65.51
0.42 24.83 0.92 66.93
0.43 25.47 0.93 68.43
0.44 26.10 0.94 70.05
0.45 26.74 0.95 71.81
0.46 27.39 0.96 73.74
1536 International Orthopaedics (SICOT) (2012) 36:1535–1537
References
1. Reito A, Puolakka T, Paakkala A, Pajamäki J (2012) Assessment ofinter- and intra-observer reliability in the determination of radio-graphic version and inclination of the cup in metal-on-metal hipresurfacing. Int Orthop 36:519–525
2. Hassan DM, Johnston GH, Dust WN, Watson LG, Cassidy D(1995) Radiographic calculation of anteversion in acetabular pros-theses. J Arthroplasty 10:369–37
Table 1 (continued)
p/h Anteversion p/h Anteversion
0.47 28.03 0.97 75.93
0.48 28.69 0.98 78.52
0.49 29.34 0.99 81.89
0.5 30.00 1 90.00
International Orthopaedics (SICOT) (2012) 36:1535–1537 1537
