  Currently available musculoskeletal inverse-dynamics thoracolumbar spine
models are entirely based on data from adults and might therefore not be
applicable for simulations in children and adolescents. In addition, these
models lack lower extremities, which are required for comprehensive evaluations
of functional activities or therapeutic exercises. We therefore created
OpenSim-based musculoskeletal full-body models including a detailed
thoracolumbar spine for children and adolescents aged 6-18 years and validated
by comparing model predictions to in vivo data. After combining our recently
developed adult thoracolumbar spine model with a lower extremity model,
children and adolescent models were created for each year of age by adjusting
segmental length and mass distribution, center of mass positions and moments of
inertia of the major body segments as well as sagittal pelvis and spine
alignment based on literature data. Similarly, muscle strength properties were
adjusted based on CT-derived cross-sectional area measurements. Simulations
were conducted from in vivo studies reported in the literature involving
children and adolescents evaluating maximum trunk muscle strength (MTMS),
lumbar disc compressibility (LDC), intradiscal pressure (IDP) and trunk muscle
activity (MA). Model predictions correlated highly with in vivo data (MTMS:
r>=0.82, p<=0.03; LDC: r=0.77, p<0.001; IDP: r>=0.78, p<0.001; MA: r>=0.90,
p<0.001), indicating suitability for the reasonably accurate prediction of
maximal trunk muscle strength, segmental loading and trunk muscle activity in
children and adolescents. When aiming at investigating children or adolescents
with pathologies such as idiopathic scoliosis, our models can serve as a basis
for the creation of deformed spine models and for comparative purposes.

Medical Physics;Biological Physics;Quantitative Methods