Adolescent idiopathic scoliosis (AIS) is a three-dimensional deformity of the spine that can be treated by wearing a correctional rigid brace. The goal of brace treatment is prevention of curve progression, and in some cases the curve even decreases. The current problem concerning treatment of AIS lays in the design decisions made during manufacturing of the brace. Correctional forces are applied through static pressure pads added to the inside of the brace. Evaluation of the correct positioning and size of these forces is done through radiographic imaging which allows limited feedback intervals as cumulative exposure to ionizing radiation increases the risk of cancer development. The design of scoliotic braces is currently suboptimal as the manufacturing remains an inefficient process. Moreover, it was hypothesized that the corrective forces show decreasing time dependant behaviour due to viscoelastic properties of the human body adapting to the load.
The objectives of this study were therefore to increase the effectiveness of brace treatment, by determination of the time dependant behaviour and accurate positioning and sizing of correctional forces.
A dynamic brace was developed containing pressure regulated cuffs creating a three-point-bending system on the spine. A healthy (non-scoliotic) test subject wore the brace with the goal of creating a spinal curvature. The cuffs were tested on stress relaxation behaviour, which was needed to determine if possible changes in pressure were due to viscoelasticity of the cuffs or the body. The tests showed that pressure stayed constant over time, which excludes viscoelasticity of the cuffs. Moreover, compression tests were executed on a cuff to determine the relationship between external loads and internal pressures.
Ultrasound (US) imaging was used to evaluate the effect of the three-point-bending system on the spine. The images showed a curvature, but the results varied too much to draw conclusions from, as this imaging technique works best for large scoliotic curves. BoneMRI has higher imaging accuracy and adds an extra dimension, however supine positioning decreases the spinal curvature. The boneMRI results show a subtle curvature after applying pressure. The cuffs lengthened the spine and caused mechanical torsion. After one hour the lengthening remained equal but the mechanical torsion decreased to its starting value. Lengthening of the spine could be useful in brace treatment to create more space between vertebrae and facilitate vertebral realignment.
This research served as a proof of concept which can be further developed by testing on a scoliotic patient with a moderate spinal curvature. This could result in a dynamic brace used as a method to enhance the positioning and sizing of pressure pads for a static brace, or the dynamic brace design needs adjustment to use it as a daily worn brace which keeps correctional forces constant by adjusting pressures automatically.