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Posterior Fusion



- See: Crankshaft Phenomenon:

- Progressive Congenital Scoliosis:
    - fundemental procedure for congenital scoliosis is posterior spine fusion w/o instrumentation;
    - in young children correction of congenital scoliosis w/ instrumentation carries a higher risk of neurologic injury;
    - in older children w/ congenital scoliosis, instrumentation & correction of deformity may be done if tethering of spinal cord has been ruled 
           out;
    - posterior fusion is performed on both convex & concave sides of curve because arthrodesis performed only on convex side only tend to 
           bend with time;
           - the exception to this, however, is when a convex fusion is combined with hemi-epiphysiodesis;
    - anterior and posterior spinal arthrodesis:
           - indicated for deformities with known high risk of progression (such as concave bar with convex hemivertebrae);
           - curve correction occurs through the angulated vertebrae adjacent to actual congenital bar or hemivertebrae, & not through congenital 
                   deformity;


- Surgical Considerations:
    - Harrington distraction rods may be dangerous in congenital scoliosis, because of dysraphic problems;
          - distracting a tethered cord is likely to produce paralysis;
          - shortening of a long (convex) side of the curve can be preferable to lengthening of a short (concave) side;
          - use of subQ Harrington rod, which involves exposure of spine at ends of rod for hook insertion, has been successful when vertebrae 
                  adjacent to hooks are fused;
                  - rod must be distracted periodically (every six months) & spine must be braced until arthrodesis of the remainder of curve is 
                         performed when child is older (10 years of age or older);
    - crankshaft phenomenon
          - in skeletally immature pt, isolated posterior arthrodesis w/ instrumentation of a lordotic curve may act as a posterior tethering bar, 
                  producing lordosis & bending of the fusion mass as the unfused anterior vertebral bodies continue to grow