Bone mineral density and functional measures in patients with arthrogryposis

Patients with arthrogryposis often report decreased ambulation and physical activity. Given that skeletal mineralisation is responsive to force, we identified the need to characterize bone mineral density and functional measures in this population, and conducted a cross-sectional study to establish a reference for future investigations.

Thirty consecutive patients aged 5 to 18 years with either the diagnosis of amyoplasia or nonsyndromic arthrogryposis with predominantly lower extremity involvement underwent bone densitometry testing, and lumbar spine Z-scores were calculated against an age and sex-matched control population as is customary in children. Pediatric outcomes data collection instrument (PODCI) and functional independence measure for Children (WeeFIM) assessment forms were completed. Mean Z-scores, PODCI, and WeeFIM scores were calculated. Statistical analysis was performed to compare lumbar spine Z-scores between patients divided by ambulatory status and to correlate WeeFIM and PODCI scores.

Mean lumbar spine Z-score was -0.47, with 73% of Z-scores being <0. Mean Z-score among nonambulators or home ambulators was -1.05, as compared to a mean Z-score among limited and unlimited community ambulators of -0.14 with a trend toward significance (P=0.10), and a dose-response relationship between higher bone density and increasing ambulatory function. Mean WeeFIM self-care and mobility quotient scores were 67.5/100 and 70.9/100, respectively. PODCI normative scores were decreased for upper extremity (10/50), transfer/basic mobility (-17/50), and sports/physical function (4/50), but normal in pain/comfort (45/50) and happiness (49/50). A linear relationship was noted between functional ambulation level and WeeFIM quotient and PODCI normative scores. There was good correlation between WeeFIM mobility and PODCI transfers and basic mobility standardised scores (R=0.86).

This is the first study to measure bone mineral density in children with arthrogryposis, and shows it to be lower than age-matched means, especially in patients with limited ambulation. Objective measures of functional ability (WeeFIM and PODCI) are decreased and demonstrate a linear relationship with ambulatory level. Further investigation is needed to quantify long-term effects of entering adulthood with below average bone mineral density in patients with arthrogryposis.

Level II.