Radiologic measures of migration percentage (MP) and acetabular index (AI) taken from plain radiographs of the pelvis are the most commonly used tools for determining hip displacement and management options in children with cerebral palsy and spastic hip disease. This study determined interrater and intrarater reliability of MP and AI on pelvic radiographs chosen to represent a wide range of age (11 months to 8 years 5 months), MP (0%–56%), and AI (9°–33°). The study demonstrated that an experienced rater would be expected to measure MP on a single radiograph to within ±5.8% of the true value and a change in MP between two radiographs taken at different times to within ±8.3% of the true value. Similarly for AI, the measurement error for a typical rater would be within ±2.6°on a single reading and ±3.7° if recording change between two occasions. The authors believe that the results indicating true change are acceptable in clinical practice, provided treatment decisions are based on a series of radiographs taken at 6-month intervals, methods and training are standardized, and consistent raters are used.
Study conducted at the Royal Children's Hospital, Melbourne, Australia
From *Hugh Williamson Gait Laboratory and Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Australia; †Sydney Children's Hospital, New South Wales, Australia; ‡Princess Margaret Hospital, Western Australia, Australia; §St. John's Private Rehabilitation, Tasmania, Australia; ∥Clinical Epidemiology and Biostatistics Unit, Department of Pediatrics, University of Melbourne, Victoria, Australia; ¶Orthopaedic Department and Hugh Williamson Gait Laboratory, Royal Children's Hospital, Melbourne, Australia; and #Orthopaedic Department and Hugh Williamson Gait Laboratory, Royal Children's Hospital, Melbourne, Australia and University of Melbourne, Victoria, Australia.
Address correspondence and reprint requests to H. Kerr Graham, M.D., F.R.C.S.(Ed), F.R.A.C.S., Professor of Orthopaedic Surgery, University of Melbourne and Royal Children's Hospital, Flemington Road, Parkville 3052, Victoria, Australia (email: firstname.lastname@example.org).
This study is supported by the National Health and Medical Research Council of Australia (NHMRC) through grant No. 980753 and the Murdoch Children's Research Institute (C. P. Theme grant), The Royal Hobart Hospital Research Foundation, Tascare Society for Children, and the St. John's Rehabilitation Services. Roslyn N. Boyd is in receipt of a part-time salary grant from the Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Australia.