The surgical participants recruited from the pediatric orthopaedic clinic and have severe scoliosis curves requiring posterior spinal fusion. Physical activity measured using Tri-axial accelerometers and paraspinal muscle stiffness measured by Shear Wave Elastography (SWUE) ultrasound will be quantified before and one year after spinal fusion surgery.

The bracing participants have scoliosis curves that require treatment with a spinal brace for at least the next year. All braces will have monitors to record hours of brace wear, as is current standard of care. Physical activity measured using Tri-axial accelerometers and paraspinal muscle stiffness measured by Shear Wave Elastography (SWUE) ultrasound will be quantified before bracing and after one year.

The control group are participants who do not have scoliosis. Physical activity measured using Tri-axial accelerometers and paraspinal muscle stiffness measured by Shear Wave Elastography (SWUE) ultrasound will be quantified at baseline and one year after enrollment.

Participants with severe scoliosis curves requiring spinal fusion surgery.

Physical activity is measured by 4 wearable Tri-axial Accelerometers, worn for a 4 day period at baseline (prior to surgery or brace placement) and at one year after surgery of brace placement. Each second of data will be classified as static or dynamic. Among static postures, lying, standing and sitting are determined based on the orientation of the waist and thigh accelerometers in relation to the line of gravity. Accelerometer data from the 4 activity monitors are combined to provide a total percentage of time with static activities.

Physical activity is measured by 4 wearable Tri-axial Accelerometers worn for a 4 day period at baseline (prior to surgery or brace placement) and at one year after surgery of brace placement. Each second of data will be classified as static or dynamic. Dynamic movements will be classified as walking, jogging or stair climbing based activity that exceeds the pre-defined accelerometer amplitude threshold. Step counts will be calculated based on detection of peak accelerations of the bilateral ankles using adaptive thresholds during the longest period of walking. Accelerometer data from the 4 activity monitors are combined to provide a total measure of dynamic physical activity.

Muscle stiffness is measured by Shear Wave Elastography (SWUE). This measurement evaluates normal muscle's passive and active properties at a variety of angles and tensions, resulting in a shear modulus reading, measured in average kilo Pascal units from 10 images of each muscle region of interest. A transducer is used with ultrasound to produce shear waves in tissue. The wave speed relates to the tissue's mechanical properties and is used to create a quantitative 2D elastogram of the tissue. Multiple shear modulus measurements will be averaged, and obtained:

• on control subjects at the left and right sides of the T12 spine segment level
• on the scoliosis patients, at the periapical area (apex of curve, where it is most tilted)
• at the concave and convex sides as well as at an area remote from the curvature