Muscle anatomy and dynamic muscle function in osteogenesis imperfecta type I.

CONTEXT: Results of previous studies suggested that children and adolescents with osteogenesis imperfecta (OI) type I have a muscle force deficit. However, muscle function has only been assessed by static isometric force tests and not in more natural conditions such as dynamic force and power tests.
OBJECTIVE: The purpose of this study was to assess lower extremity dynamic muscle function and muscle anatomy in OI type I.
SETTING: The study was performed in the outpatient department of a pediatric orthopedic hospital. PATIENTS AND OTHER PARTICIPANTS: A total of 54 individuals with OI type I (6-21 years; 20 male) and 54 age- and sex-matched controls took part in this study. MAIN OUTCOME MEASURES: Calf muscle cross-sectional area and density were measured by peripheral quantitative computed tomography. Lower extremity muscle function (peak force per body weight and peak power per body mass) was measured by jumping mechanography through 5 tests: multiple two-legged hopping, multiple one-legged hopping, single two-legged jump, chair-rise test, and heel-rise test.
RESULTS: Compared with age- and sex-matched controls, patients with OI type I had smaller muscle size (P = .04) but normal muscle density (P = .21). They also had lower average peak force and lower specific force (peak force/muscle cross-sectional area; all P < .008). Average peak power was lower in patients with OI type I but not significantly so (all P > .054).
CONCLUSIONS: Children and adolescents with OI type I have, on average, a significant force deficit in the lower limb as measured by dynamic force tests. Nonetheless, these data also show that OI type I is compatible with normal muscle performance in some individuals.