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ORTHOTICS

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Postoperative Orthoses: 

 The goal for orthotic stabilization of a thoracolumbar injury that has been surgically reduced and instrumented is to protect the surgical construct from large loads that are created from torso motion, until solid biologic fusion occurs. In 1963, Nachemson and Elfstrom reported on inpatients with fusion and Harrington rod instrumentation for idiopathic scoliosis and studied the effect of the Milwaukee brace and body cast on the loads acting on spinal instrumentation. Both the Milwaukee brace and body cast reduced the axial force in the Harrington rod during standing and walking. To date, this is the only study on the effect of post operative immobilization on implant strains.

A postoperative orthosis should protect the surgical construct from the planes of motion in which the construct is vulnerable to failure. 
For Most surgical constructs, these motions are flexion and torsion. The Harrington distraction rod can carry the axial load in the physiologic range. However, it is vulnerable to forward flexion and rotation. Postoperative orthoses are needed to restrict these motions and minimize the chances of hook dislodgment or fracture. Segmental fixation of the Harrington rods using wires improves the failure strength and rigidity of the construct in flexion and rotation, because segmental fixation distributes the load over multiple fixation points, the Luque system benefits from this principle, but it is notable weak in axial loading. The C-D system combines the axial load carrying ability of the Harrington rods with improved torsional rigidity of segmental fixation.

The fixation devices utilizing intrapeduncular screw fixation to the spine result in the most stable construct in all modes of loading and, therefore, can potentially stabilize injury to all three load bearing columns. The improved rigidity of these constructs is derived from the fixation of screws in the pedicles which provides a greater control on the three-dimensional motion of the vertebral body. However, it should be noted that both the strength and rigidity of these constructs will be adversely affected by a loss of bone mineral density such as in osteoporotic bone. A postoperative TLSO should have enough anterior height to resist forward bending at the sternum but it should not induce hyperextension as this will additionally stress the implant. At present, there is no objective data regarding reduction of stresses that other orthosis may provide for these more contemporary implants.
 

Profiles of the Postoperative TLSO

All postoperative TLSO's should provide a stable base of support at the sacrum. This will resist flexion of the lumbar spine and reduce hip flexion range to 90 degrees, thus preventing excessive motion and bending moment at the lower levels of the spine. The cephalad trim line defines the profile of the TLSO and should extend cephalad to or slightly above the most superior point of the spinal fusion or implant. For lumbar fusions (exclusive of fusion for fracture or tumor), the TLSO trimline can terminate at the xyphoid process or just below the breast lien and this will provide immobilization up to T-11. 

For procedures that exceed T-4, or for all fractures and tumors that create large bending loads on the surgical sites, the TLSO should extend to the sternal notch and the clavicles anteriorly. For procedures that include levels T-3 and T-2, the high profile TLSO should come over the shoulder with shoulder straps to reduce upper thoracic motion caused from shoulder rotation, elevation and depression. For procedures that extend to T-1 or into the lower to mid cervical range, a SOMI or Minerva attachment must be used to reduce cervical range of motion. As the procedure that requires postoperative immobilization moves cephalad, motion reduction of bending moments, as there is less axial load on the upper most segments of the spine.

When spinal fusion is performed across the lumbosacral joint a thigh extension must be applied to the TLSO to reduce lumbosacral motion in the orthosis. A TLSO without thigh extension has been shown to either have no effect or actually increase lumbosacral motion.

The primary role of a postoperative orthosis is to protect the surgical spinal implant from undue loads during the process of fusion. The segmental motion limiting requirements of a postoperative orthosis are not as stringent as in the case of non operative treatment since the orthosis is only being used as an adjunct to protect the implant from loads and stresses.
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