Introduction: Braces are the most generally accepted form of non surgical treatment for adolescent idiopathic scoliosis (AIS). Despite decades of usage controversy still exists regarding the efficacy of this treatment. We believe this controversy continues in part because there are few studies describing the mechanical effect of bracing and linking mechanically effective bracing to changes in the natural history of AIS. If braces are effective, is it because they apply significant mechanical support to a collapsing spine or are they effective for other reasons? A first step towards answering this question is to document the mechanical action of braces during activities of daily living. This would enable researchers to examine the effect of mechanical support on progression of the scoliosis. The objective of this study was to determine the temporal pattern of forces exerted by the pressure pad in Boston braces prescribed for the treatment of AIS.

Methods and results: A force transducer and a programmable data logger were designed to measure loads exerted by the pressure pad over extended periods of time. The loads were recorded at one minute intervals. Braces were adjusted to a prescribed load level and the patients were asked to set the brace tightness to match this target any time the brace was donned. Brace wear data were stratified into: not worn, worn at less than 80% of target, 80–120% of target and greater than 120% of target. Bracing was considered mechanically effective if the load was at least 80% of the prescribed level. Patients were aware of the study and consented to participate.

Thirteen patients were followed from 1 to 16 days, average was 9±5 days. Nine patients were asked to wear their braces 23 hours per day, two for 20 and two for 16 hours per day. Braces were not worn 34±27% of the time logged. When they were worn, patients adjusted the tightness of the brace such that it was < 80% of the target 29±20% of the time, within 20% of target 19±19% and over 120% of target 18±13% of the time. Patients wore their braces at or above the target levels 33% of the time logged or 8 hours in a typical day. Subjects had no difficulties using the data logger and none complained that it interfered with brace wear. Reviewing individual histories suggested that subjects did not alter their brace wear pattern because of the data logger.

Conclusion: The mechanical effectiveness of the brace varies considerably over the normal course of wear but seldom does it provide the support intended. While patients wear their braces for about 16 hours per day, it is mechanically effective for 8 hours only.