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Crankshaft Phenomenon

- Discussion:
    - 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;
          - in the study by Noordeen MHH, et al (1999), it was found that there was significant growth plate activity in patients in Risser stage 4, 
                which makes it unlikely that the crankshaft phenomenon is caused soley by end plate activity;
    - risk factors:
          - open triradiate cartilages:
                - w/ a closed triradiate cartilage, there should be less than a 5% chance of developing crankshaft syndrome;
          - physiologic youth:
                - girls younger than 11 years;
                - boys younger than 13 years;
                - Risser grade 0 or 1;
    - potential risk of crankshaft phenomena appears highest in children w/ normal growth potential of anterior vertebral body growth plates, 
          such as may be in children w/ juvenile scoliosis;
          - patients w/ congential scoliosis may have a reduced risk for the crankshaft phenomena due to abnormal anterior growth plates;

- Radiographs:
    - crankshaft phenomenon is evident w/ more than 10 deg of progression of the Cobb angle or the rib-vertebral angle (assuming that 
          other causes of curve progression such as pseudoarthrosis is not present);
          - rib-vertebral angle difference is most sensitive;

- Prevention:
    - to prevent occurance of this deformity, anterior and posterior arthrodesis should be performed in physiologically young patients w/ 
          progressive congenital scoliosis > 50 deg

The crankshaft phenomenon

Posterior Arthrodesis and Instrumentation in the Immature (Risser-Grade-0) Spine in Idiopathic Scoliosis.

Spinal growth and a histologic evaluation of the Risser grade in idiopathic scoliosis.