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Journal of Bone and Joint Surgery - British Volume, Vol 86-B, Issue 3,
434-437.
doi: 10.1302/0301-620X.86B3.14094 Copyright © 2004 by British Editorial Society of Bone and Joint Surgery Inter- and intra-measurer error in the measurement of Reimers’ hip migration percentageS. Faraj, MB ChB, Senior Registrar1; W. G. Atherton, MA, FRCS, Consultant Orthopaedic Surgeon2; and N. S. Stott, PhD, FRACS, Associate Professor of Orthopaedic Surgery1
1 Starship Children’s Hospital, Park Road, Private Bag 92-024, Auckland, New Zealand. Correspondence should be sent to Dr N. S. Stott at the Department of Surgery, Faculty Medicine and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand. Reimers’ hip migration percentage is commonly used to document the extent of subluxation of the hip in children with spasticity. In this study, two measurers, with six months paediatric orthopaedic experience, measured the migration percentage on 44 pelvic radiographs of children with cerebral palsy, aged between two and eight years. Unknown to the measurers, each radiograph was duplicated, giving 22 non-identical radiographs (44 hips) which were measured twice at time 0 and twice six weeks later. The intra-measurer, intra-sessional absolute differences between the first and second measurements ranged from 0% to 23%, with median values of 2.5% to 3.6%. The intra-sessional median absolute differences were not statistically different between the two measurers and measuring sessions (p = 0.42, Kruskal-Wallis test). The inter-sessional absolute differences for measurements made by the same measurers ranged from 0% to 18% with a median absolute difference of 1.7% to 3.2%. Overall, only 5% of the intra-measurer measurement differences, within and between sessions, were above 13%. Repeated measurements by one measurer over time must, therefore, vary by more than 13% in order to be 95% confident of a true change. The inter-measurer error was higher with median absolute differences between the two measurers’ measurements of the same hip of 3.25% to 5% (0% to 26%) and a 95th upper confidence interval of 21% to 23%. Averaging the four separate measurements over the two sessions reduced the inter-measurer error to a median absolute difference of 2.8%, but did not improve the 95th upper confidence interval, which measured 22.4%. Such inter-measurer errors may be clinically unacceptable. This article has been cited by other articles:
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