Aims. This study aimed to evaluate the relationship between hip shape and mid-term function in Perthes’ disease. It also explored whether the modified three-group Stulberg classification can offer similar prognostic information to the five-group system. Methods. A total of 136 individuals aged 12 years or older who had Perthes’ disease in childhood completed the Patient-Reported Outcomes Measurement Information System (PROMIS) Mobility score (function), Nonarthritic Hip Score (NAHS) (function), EuroQol five-dimension five-level questionnaire (EQ-5D-5L) score (quality of life), and the numeric rating scale for pain (NRS). The Stulberg class of the participants’ hip radiographs were evaluated by three fellowship-trained paediatric orthopaedic surgeons. Hip shape and Stulberg class were compared to PROM scores. Results. A spherical hip was associated with the highest function and quality of life, and lowest pain. Conversely, aspherical hips exhibited the lowest functional scores and highest pain. The association between worsening Stulberg class (i.e. greater deviation from sphericity) and worse outcome persisted after adjustment for age and sex in relation to PROMIS (predicted mean difference -1.77 (95% confidence interval (CI) -2.70 to -0.83)), NAHS (-5.68 (95% CI -8.45 to -2.90)), and NRS (0.61 (95% CI 0.14 to 1.08)), but not EQ-5D-5L (-0.03 (95% CI -0.72 to 0.11)). Conclusion. Patient-reported outcomes identify lower function, quality of life, and higher pain in aspherical hips. The magnitude of symptoms deteriorated with time. Hip sphericity (i.e. the modified three-group classification of spherical, oval, and aspherical) appeared to offer similar levels of detail to the five-group Stulberg classification. Cite this article: Bone Joint J 2023;105-B(6):711–716

Aims. The reduction in mobility due to hip diseases in children is likely to affect their physical activity (PA) levels. Physical inactivity negatively influences quality of life and health. Our aim was to objectively measure PA in children with hip disease, and correlate it with the Patient-Reported Outcomes Measurement Information System (PROMIS) Mobility Score. Methods. A total of 28 children (12 boys and 16 girls) with hip disease aged between 8and 17 years (mean 12 (SD 3)) were studied between December 2018 and July 2019. Children completed the PROMIS Paediatric Item Bank v. 2.0 – Mobility Short Form 8a and wore a hip accelerometer (ActiGraph) for seven consecutive days. Sedentary time (ST), light PA (LPA), moderate to vigorous PA (MVPA), and vigorous PA were calculated from the accelerometers' data. The PROMIS Mobility score was classified as normal, mild, and moderate functions, based on the PROMIS cut scores on the physical function metric. A one-way analysis of covariance (ANCOVA) was used to assess differences among mobility (normal; mild; moderate) and measured PA and relationships between these variables were assessed using bivariate Pearson correlations. Results. Children classified as normally functioning on the PROMIS had less ST (p = 0.002), higher MVPA, (p = 0.002) and VPA (p = 0.004) compared to those classified as mild or moderate function. A moderate correlation was evident between the overall PROMIS score and daily LPA (r = 0.462, n = 28; p = 0.013), moderate-to-vigorous PA (r = 0.689, n = 28; p = 0.013) and vigorous PA (VPA) (r = 0.535, n = 28; p = 0.013). No correlation was evident between the mean daily ST and overall PROMIS score (r = -0.282, n = 28; p = 0.146). Conclusion. PROMIS Pediatric Mobility tool correlates well with experimentally measured levels of physical activity in children with hip disease. We provide external validity for the use of this tool as a measure of physical activity in children. Cite this article: Bone Joint J 2021;103-B(2):405–410