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J Bone Joint Surg Am. 2015 Apr 15;97(8):643-50. doi: 10.2106/JBJS.N.00887.

Interobserver and intraobserver reliability of the modified Waldenström classification system for staging of Legg-Calvé-Perthes disease.

Author information

Division of Pediatric Orthopaedic Surgery, New York Presbyterian Morgan Stanley Children's Hospital of New York, 3959 Broadway, CHONY-8N, New York, NY 10032-3784. E-mail address for H. Matsumoto:
Department of Orthopaedic Surgery, Texas Scottish Rite Hospital for Children, 2222 Welborn Street, Dallas, TX 75219.
Department of Orthopaedic Surgery, BC Children's Hospital, Administrative Secretary Room A204, 4480 Oak Street, Vancouver, BC V6H 3V4, Canada.
MedCare Orthopaedics and Spine Hospital, Second Interchange, Sheikh Zayed Road, P.O. Box 215565, Dubai, United Arab Emirates.



The absence of a reliable classification system for Legg-Calvé-Perthes disease has contributed to difficulty in establishing consistent management strategies and in interpreting outcome studies. The purpose of this study was to assess interobserver and intraobserver reliability of the modified Waldenström classification system among a large and diverse group of pediatric orthopaedic surgeons.


Twenty surgeons independently completed the first two rounds of staging: two assessments of forty deidentified radiographs of patients with Legg-Calvé-Perthes disease in various stages. Ten of the twenty surgeons completed another two rounds of staging after the addition of a second pair of radiographs in sequence. Kappa values were calculated within and between each of the rounds.


Interobserver kappa values for the classification for surveys 1, 2, 3, and 4 were 0.81, 0.82, 0.76, and 0.80, respectively (with 0.61 to 0.80 considered substantial agreement and 0.81 to 1.0, nearly perfect agreement). Intraobserver agreement for the classification was an average of 0.88 (range, 0.77 to 0.96) between surveys 1 and 2 and an average of 0.87 (range, 0.81 to 0.94) between surveys 3 and 4.


The modified Waldenström classification system for staging of Legg-Calvé-Perthes disease demonstrated substantial to almost perfect agreement between and within observers across multiple rounds of study. In doing so, the results of this study provide a foundation for future validation studies, in which the classification stage will be associated with clinical outcomes.

[Indexed for MEDLINE]

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