HipScreen: a valid mobile app to measure hip migration in children with cerebral palsy in the community setting

Aims: The Reimers migration percentage (MP) is the gold-standard radiological parameter used to aid decision-making regarding surgical management of hip displacement in cerebral palsy (CP). Accurate measurement is important to risk stratify patients and allow timely onward referral from community teams to paediatric orthopaedic services. We performed a study to determine whether experts and novices could use a free smartphone app (HipScreen (HS) app) as a valid method for measuring MP in CP. Methods: Using the HS app, two groups measured MP in 20 pelvis radiographs (40 hips) at weeks 0 and 2. The 'inexperienced' group included four community physiotherapists with no CP experience. The 'experienced' group included four community physiotherapists and two paediatricians with CP experience. All participants watched the tutorial videos on the HS app website. HS app measurements were then compared with gold-standard picture archiving and communication system (PACS) measurements conducted by a senior paediatric orthopaedic surgeon. Modified Pearson correlation (r) was used to determine inter-rater reliability between HS app and PACS measurements. Intraclass correlation coefficient (ICC) was then used to assess intrarater reliability. The mean absolute deviation (MAD) was calculated to compare raters with the gold standard. Results: > 0.86 and p < 0.001. Both inter- and intra-rater reliability were excellent with ICC > 0.9. There was no statistically significant difference in the MAD within individual measurements and compared with the gold standard. Conclusion: The HS app is accurate in measuring MP in CP when used by non-specialists and specialists. Non-specialists do not require additional supplementary training. These findings suggest app efficacy and safety in regional and national hip surveillance programmes for children with CP.