The migration percentage measured on EOS® standing full-leg radiographs: equivalent and advantageous in ambulant children with cerebral palsy

BACKGROUND: During ambulatory follow-up of patients with cerebral palsy (CP) systematic radiographic screening is required firstly to evaluate hip migration and development in the prevention of hip dislocation and secondly to analyse lower limb alignment and leg length. The Migration Percentage (MP) is a radiographic measurement used to describe the extent of femoral head lateralisation on conventional supine pelvic radiographs. Our goal was to assess the comparability of the MP measured on low radiation dose EOS® standing full-leg radiographs with that of conventional supine pelvic radiographs. METHODS: Patients presenting with CP were prospectively selected from our outpatient follow-up consultation at our institutions CP reference centre and underwent conventional supine pelvic and EOS® standing full-leg radiographs the same day for diagnostic and screening reasons. RESULTS: Out of 28 prospectively selected patients we included 21 (42 hips), of which 10 were female, with a mean age of 9.25 years and GMFCS levels of I, II and III. Seven out of 28 patients were excluded due to insufficient quality of radiographic images. The absolute differences in MP measured on both conventional supine pelvic and EOS® standing full-leg radiographs ranged between − 8 and 6% with an absolute mean difference of 0% (SD ±3.5) and were not statistically significant (p = 0.99). A Bland-Altman plot showed acceptable agreement between both measurements without proportional bias. CONCLUSION: There is no statistical significant difference between the Migration Percentage measured on conventional supine pelvic radiographs and EOS® standing full-leg radiographs in ambulant patients. These images use lower radiation doses and contain more radiographic information. TRIAL REGISTRATION: Approved by the Medical Research Ethics committee of the University Hospitals Leuven (MP001492).