![]() Two common design elements of all orthoses are similar in principle to internal fixation constructs and include end-stabilizing elements (e.g., thoracic bands, pelvic bands) and longitudinal members or uprights that interconnect the end elements. Passive mechanisms for motion control are important in three-point bending mechanisms and are derived from intrinsic properties of the orthosis itself such as design, size, and material composition. 3,4 However, brace discomfort may also contribute to higher levels of noncompliance. Sypert and others noted that the effectiveness of an appliance is directly related to the level of its discomfort. Stiffer, more securely worn appliances are more effective at limiting motion because of the heightened sensation of resistance that the stiffer appliance produces. 4,12-15 The patient therefore is able to prevent undesirable motion of the spine using only intrinsic muscular support guided by the orthosis. Pressure at the orthosis-skin contact site produces a reminder to maintain a specific position and limit unwanted gross body motion. Orthoses promote muscular stabilization through tactile feedback, guiding the patient to maintain proper positioning of the body. 2 In terms of a column model, muscular action directly affects the modulus of elasticity and relative cross-sectional area of the composite spinal column. ![]() 8 If isolated from its muscular support, the osseous and ligamentous spinal column holds only 2 kg of axial load before failure by buckling. It has been demonstrated experimentally that opposing muscular forces significantly stiffen the spinal column, increasing its load-bearing capacity. Dynamic control describes the significant role of intrinsic musculature in actively stabilizing the spine and is a major component in the effect of most orthoses. Benzel, in Benzel's Spine Surgery, 2-Volume Set (Fourth Edition), 2017 Dynamic and Passive ControlĪll orthoses control spinal motion by a combination of dynamic and passive mechanisms. ![]()
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