Mechanical effectiveness studies of lumbar spine orthoses.

Intradiscal pressures, intra-gastric pressures and myoelectric trunk muscle activities were measured in four volunteers wearing five different orthoses of three principle types, and performing six tasks. A biomechanical model was used to estimate the load on the spine in the different tasks so as to compare those tasks reliably when done with and without the orthoses. The results indicate that wearing a brace can significantly unload the trunk in some situations, but has no effect in others. Lumbar spine compression was reduced by about one-third in the task involving trunk flexion. The disc pressure values with an orthosis were lower in about two-thirds of the exercises and higher in the remaining one-third. The back muscle activity was in some experiments reduced by one-third by the use of the brace, in others it increased by the same amount. None of the orthoses raised the intra-gastric pressure significantly. No one orthosis was found to be clearly superior in mechanical effectiveness in the tasks studied.