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Scientific Articles   |    
Quantitative Measures for Evaluating the Radiographic Outcome of Legg-Calvé-Perthes Disease
Hitesh Shah, MS(Orth)1; N.D. Siddesh, MS(Orth)1; Harish Pai, MS(Orth)1; Stéphane Tercier, MD1; Benjamin Joseph, MS(Orth), MCh(Orth)1
1 Paediatric Orthopaedic Service, Department of Orthopaedics, Kasturba Medical College, Manipal 576 104, Karnataka State, India. E-mail address for B. Joseph: bjosephortho@yahoo.co.in
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Investigation performed at the Paediatric Orthopaedic Service, Department of Orthopaedics, Kasturba Medical College, Manipal, Karnataka State, India



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.

Copyright © 2013 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2013 Feb 20;95(4):354-361. doi: 10.2106/JBJS.L.00172
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Abstract

Background: 

Large sample sizes are needed if discrete outcome measures are used to perform outcome studies, whereas more practicable sample sizes are sufficient if continuous outcome measures are used. Recognizing the need to devise reliable continuous outcome measures for assessing the outcomes of treatment of Legg-Calvé-Perthes disease, we evaluated a method of quantifying the shape and size of the femoral head and the femoral-acetabular relationship from computer images of anteroposterior and lateral radiographs with the help of image-analysis software.

Methods: 

Radiographs of 121 skeletally mature individuals with healed Legg-Calvé-Perthes disease were analyzed, and the sphericity deviation score, femoral head enlargement, femoral neck growth inhibition, and composite femoral congruency arc were calculated.

Results: 

Each of these measurements was reproducible, with distinctly different values for hips in each of the Stulberg classes. Measures of sphericity and congruence (the sphericity deviation score and the composite femoral congruency arc) could very clearly discriminate between spherical and aspherical hips, and there was a strong correlation between these two measurements.

Conclusions: 

The study shows that it is possible to have reliable quantitative measures of the outcome of Legg-Calvé-Perthes disease at skeletal maturity.

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    Benjamin Joseph, Hitesh Shah, ND Siddesh, Stephane Tercier
    Posted on May 06, 2013
    Response to comments by Dr. Nakamura et al
    Paediatric Orthopaedic Service, Department of Orthopaedics, Kasturba Medical College

    We thank Drs. Nakamura, Kamegaya and Saisu for their thoughtful and astute comments regarding our recent paper.

    The suggestion that the value of Ellipsoid Deformation (ED) may be influenced by magnification is very true. However, we overcame the potential inaccuracies on account of differences in magnification of the antero-posterior and lateral views by scaling the x-rays before making measurements. The width of the pelvis at the level of the outer margin of the acetabulum was used for scaling; for both the radiographs this dimension was designated as 1 unit before any further measurements were made. We apologise for not having mentioned this important step in the paper.

    We also acknowledge that changes in positioning could alter the measurements to some extent. This is true of any radiographic measurement used in routine clinical practice such as the Cobb’s angle, the acetabular index, the mechanical axis deviation or the femoral neck-shaft angle. If the degree of error that may result from changes in position is large, the measurement is clearly of little clinical value. Error in the measurement of SDS due to changes in position is likely to be negligible or very small in spherical or near spherical femoral heads (Stulberg Class I and II) while it may be more in the deformed femoral heads. This implies that despite the potential source of error, the measure is likely to be accurate in hips with a good outcome (Stulberg Class I and II), and this measure is primarily meant to distinguish a good outcome from a poor outcome.The SDS values of 1 to 1.5 noted on normal hips could be partly on account of the fact that not all “normal” femoral heads are perfectly spherical and partly on account of error in measurement. This implies that SDS values of affected hips should be compared against these normative values.

    Finally, computing SDS is not time-consuming at all; with a bit of practice both hips can be measured within five minutes. The formulae have already been fed into an Excel spreadsheet and by simply filling in the MIC and MCC values of the AP and lateral x-ray the SDS values are generated instantaneously.

    Junichi Nakamura, MD, Makoto Kamegaya, MD, Takashi Saisu, MD
    Posted on April 22, 2013
    Another option for the expansion of clinical practice
    Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Japan

    We read this article with interest.  Sphericity Deviation Score (SDS), a newly devised continuous measure, reflects Stulberg classes as well as the other parameter for the sequelae of Legg-Calvé-Perthes disease. Although important issues were addressed, the challenging field of quantitative measurement should be considered as another option for the expansion of clinical practice.

    First, roundness error (RE) can be measured with the anteroposterior (AP) and the lateral (Lat) radiograph respectively, but ellipsoid deformation (ED) was calculated by combination of radius AP and radius Lat. Thus ED may be influenced by magnification power, depending on the distance from X-ray tube to the object. Moreover there are several methods of the leg position for taking a lateral radiograph. In a deformed femoral head, the radii of the maximum inscribed circle and the minimum circumscribed circle exist. Theoretically, if both RE AP and RE Lat are zero, the object must be a sphere and then ED is zero. But the results of 1.0 to 1.5 in this study have implications for some error in measurement or calculation. Second, SDS is the sum of RE AP, RE Lat, and ED. It shows high reproducibility and correlation to the other scores, but this measurement might be time-consuming. Automatic imaging analysis software can be helpful for this labor.

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