Repeatability and limits of agreement in measurement of hip migration percentage in children with bilateral cerebral palsy

Objective: To determine the repeatability and limits of agreement for X-ray measurement of hip migration percentage in children with cerebral palsy. Design: An inter-rater and intra-rater study. Data: Twenty hip and pelvic X-rays (40 hips) were measured by three health professionals on two separate occasions. Results: Repeatability of the measure was expressed as 95% limits of agreement. Measurements of hip migration were within 7.6% of each other when measured by the same rater on two occasions. When two raters were compared, measurements were within 8.1% of each other. Conclusion: Measurement of hip and pelvic X-rays can be made using the described method within limits of agreement that are acceptable for clinical decision-making. The information thus obtained on the degree and rate of hip subluxation/dislocation can be used to inform therapy and surgical decision-making.