Correct positioning for hip radiographs allows reliable measurement of hip displacement in cerebral palsy

Abstract

Aim The pelvic radiograph in children with cerebral palsy (CP) can inform the degree of hip displacement by calculation of the migration percentage. However, concerns have arisen about the reliability of this measurement. The present study examined the reliability of radiographic assessment of displacement and the importance of positioning and reporting experience. Method Two pelvic radiographs, taken at least an hour apart, were performed in 20 children (total 40 hips) in the standard position by a trained paediatric radiographer. Children (13 males, seven females) were aged 30 months to 10 years with severe bilateral spastic CP in Gross Motor Function Classification System levels IV (n=10) and V (n=10). The migration percentage of each hip was measured on two occasions 3 months apart by two experienced radiologists independently. Comparisons of migration percentage were made in three ways by (1) the same observer at the same time, (2) the same observer 3 months apart, and (3) different observers 3 months apart. Results Migration percentage (mean [SD]) was (1) 3.2% (3.5), (2) 3.3% (3.2), and (3) 3.7% (3.8) respectively. Interpretation Reliable measures of migration percentage can be obtained with correct positioning and if reported by suitably experienced radiologists, making this a valid surveillance method. Clinical decisions can be made taking into account an expected error in hip displacement measurements.

Validity and reliability of radiological methods to assess proximal hip geometry in children with cerebral palsy: a systematic review

“…The seven other studies examined the reliability of migration percentage, all showing that intra‐ and interrater reliability was good to excellent. Results for standard error of measurement (SEM) × 1.96, mean + 2SD, and 95% confidence intervals were reported to be 5.8%, 10%, and 12.9% respectively, for one measurer and 11%, 11.5%, and 22% respectively, for different measurers depending on the study ( Q‐ scores 74, 74, 71). Using the lateral edge of the acetabular roof was more reliable than using the ‘sourcil’ of the acetabulum, as described by Kim et al …”

“…The hip migration percentage as first proposed by Reimers in 1980 was evaluated in eight studies (mean Q‐ score 67) . Except for the Gose et al .…”

“…The hip migration percentage as first proposed by Reimers in 1980 18 was evaluated in eight studies (mean Q-score 67). 32,[35][36][37][38][39][40][41] Except for the Gose et al 35 study (Q-score 55), the studies found only evaluated the use of anteroposterior X-rays for the assessment of femoral head migration. Gose et al 35 found excellent concurrent validity between…”

Prevention of hip displacement in children with cerebral palsy: a systematic review

“…Migration percentage has been accepted as the most valid and reliable method of monitoring hip displacement from a single anterior–posterior pelvis radiograph . In studies of validity, a threshold for true change between successive radiographs has been defined as 8.3% to 10% when measured by the same rater, and 11% to 11.5% when measured by different raters . When the measurer is inexperienced, this value is increased .…”

“…When the measurer is inexperienced, this value is increased . Changes in migration percentage greater than 10% are therefore considered clinically important . Other radiological measures, including acetabular index and centre‐edge angle, have also been used but found to be less reliable indicators of hip displacement …”