Biomechanical Evaluation of the Boston Brace System for the Treatment of Adolescent Idiopathic Scoliosis

Relationship between Strap Tension and Brace Interface Forces

Abstract

Study Design.  

Prospective study to evaluate the association between strap tension and brace interface forces in the treatment of adolescent idiopathic scoliosis using the Boston brace system.

Objectives.  

To determine the strap tension associated with optimal brace interface forces.

Summary of Background Data.  

Trim lines, pad placement, and areas of relief for the brace are guided by radiographic studies. However, optimal adjustment of strap tension is unclear and remains mostly empirical.

Methods.  

Brace interface forces in all regions of the trunk were measured for 41 patients with adolescent idiopathic scoliosis at three standardized strap tensions (20 N, 40 N, and 60 N). The brace interface forces were assessed using a mat made of force-sensing transducers. Equivalent interface pressure for each trunk region was also calculated to estimate the distribution of the interface forces.

Results.  

The brace interface forces and the corresponding effective areas increased along with the strap tension for all patients. For patients with a single right thoracic curve, the interface pressure tended to increase with increasing strap tension. This increase was significant in the left axillary, right thoracic, right pelvic, and sternal regions. For double right thoracic–left lumbar curves, the increase in interface pressure was significant in the left axillary, right pelvic, and sternal regions. However, most of this increase occurred between 20 N and 40 N of strap tension, with only slight increase or even a decrease in interface pressures between 40 N and 60 N.

Conclusions.  

The strap tension should be set as high as possible (up to 60 N) for right thoracic curves. For right thoracic–left lumbar curves, the optimal strap tension was ∼40 N. However, clinicians should ensure that the prescribed strap tension does not cause excessive skin pressure or affect the compliance with the brace. A side opening in the right lumbar area may improve the effectiveness of the brace for double right thoracic-left lumbar curves, but care must be taken to avoid skin problems at the opening.

In Brief

Application of adequate corrective forces is required for effective brace treatment in adolescent idiopathic scoliosis. Brace interface forces increased when strap tension was increased. Equivalent pressure improved with increasing strap tension for single right thoracic curves but was optimal at ~40 N for double right thoracic—left lumbar curves.