Ankle Movements During Supine Kicking in Infants Born Preterm.

BACKGROUND: Knowledge of musculoskeletal factors that influence supine kicking of infants born preterm has implications for early intervention. HYPOTHESES: Differences exist between infants born preterm and full-term in ankle kinematics during supine kicking, which are attributable to passive measures of the gastrocnemius/soleus (g/s) muscle tendon unit (MTU). SUBJECTS: Twenty infants born full-term and 22 born preterm were measured at term, 6 weeks, and 12 weeks of age. OUTCOME MEASURES: Ankle kinematics during supine kicking and g/s MTU length. RESULTS: Infants born preterm demonstrated less dorsiflexion, more plantar flexion, and more total ankle range during supine kicking. Gestational age explained 69% to 85% of the variability in MTU length from term to 12 weeks of age. MTU lengths explained 0% to 42% of the variance in ankle kinematics. CONCLUSIONS: Passive measures of the g/s MTU may inform clinicians about ankle kinematics in newborns to 12-week infants during supine kicking.

Gastrocnemius-soleus muscle tendon unit changes over the first 12 weeks of adjusted age in infants born preterm.

BACKGROUND AND PURPOSE: Differences in the gastrocnemius-soleus muscle and tendon have been documented shortly after birth in infants born preterm compared with infants born at term. Knowledge of muscle tendon unit lengths at term age to 12 weeks of age in infants born preterm may be useful in understanding motor development. PARTICIPANTS AND METHOD: Gastrocnemius-soleus muscle tendon unit lengths were compared at term age, at 6 weeks of age, and at 12 weeks of age (preterm adjusted age) in 20 infants born full term and 22 infants born preterm. RESULTS: Significant differences were found between the 2 groups on taut tendon, relaxed muscle length (A(O)); taut tendon, stretched muscle length (A(Max)); and muscle stretch (A(O) to A(Max)). Infants born preterm demonstrated measures of A(O) and A(Max) in positions of greater plantar flexion compared with infants born full term. Significant differences in measurements of A(O) were found between term age and 12 weeks of age, indicating that the tendon lengthens during this period for both groups. DISCUSSION AND CONCLUSION: These results provide knowledge of musculoskeletal development of the gastrocnemius-soleus muscle and tendon. Differences in musculoskeletal measurements are consistent with uterine confinement in the last weeks of full-term gestation. These findings have implications when examining the musculoskeletal system in infants born preterm who are demonstrating functional changes.