Bone Abstracts

Objective: Mobility is an important endpoint in patient care with implications for activities of daily living, community participation, and quality of life. We adapted the performance-oriented mobility assessment (POMA-G),¹ a widely used and validated clinical gait assessment tool for adults, to use in children with hypophosphatasia (HPP). HPP is the rare metabolic disease caused by loss-of-function mutation(s) in the gene encoding tissue non-specific alkaline phosphatase. HPP manifests a broad spectrum of complications in children, which may include rickets and proximal muscle weakness.

Methods: The 12-point POMA-G (12, no impairment and 0, greatest impairment) was chosen as a potential measure of clinically meaningful musculoskeletal impairments in children with HPP because the majority of components (including trunk sway, walking stance, and step and gait assessments) directly or indirectly measure defects seen in HPP. The POMA-G was modified (modified performance-oriented mobility assessment (MPOMA-G)) to focus on its components most relevant to HPP while increasing utility in video analysis. Three trained physical therapists scored archival videos of walking from an HPP natural history database² using MPOMA-G. Intraclass correlation coefficients (ICCs) were calculated to assess inter-rater agreement. The relationship between MPOMA-G scores and other clinical outcome measures available in these patients (Childhood Health Assessment Questionnaire (CHAQ) Disability Index, Pediatric Outcomes Data Collection Instrument (PODCI) Transfer and Mobility Scale, 6-Minute Walk Test (6MWT)) was determined through linear regression.

Results: Modifications to the POMA-G included: removal of gait initiation (less sensitive for children with musculoskeletal disorders) and path assessment (limited utility in single point-of-view video); increasing step length and step continuity from two- to three-point scales to improve sensitivity to detect change; and, clarifying descriptions of components such as Trunk sway to increase sensitivity and consistency amongst raters. Inter-rater agreement across all patient-visits was strong (ICC=0.76, P<0.0001). Linear regressions between MPOMA-G and other clinical endpoints resulted in r² values of 0.73 (CHAQ; 21 datapoints), 0.53 (PODCI; 21 datapoints), and 0.70 (6MWT; 28 datapoints).

Conclusions: The MPOMA-G is a reliable and valid measure for detecting clinically significant impairments in gait in videos of children with hypophosphatasia. This tool should be evaluated further for direct implementation in the clinical setting.

Disclosure: D Phillips received consulting fees from Alexion Pharmaceuticals, Inc. M Vallée and K P Fujita are the employees of Alexion Pharmaceuticals, Inc. K L Madson has received honoraria from Alexion Pharmaceuticals, Inc. M P Whyte has received honoraria, research grants, and travel support from Alexion Pharmaceuticals, Inc.

References: 1. Tinetti Am J Med 1986.

2. Whyte JMBR 2014 29 (Suppl 1).