The Crankshaft Phenomenon
The crankshaft phenomenon, a progressive rotational and angular spinal deformity that can occur after posterior spinal surgery, has been reported in pediatric patients with idiopathic, congenital, and neuromuscular scoliosis. In the skeletally immature patient, the crankshaft phenomenon is thought to occur secondary to continued growth of the anterior elements of the spine after solid posterior spinal fusion. The condition has also been reported in the setting of newer, so-called growth-friendly posterior distraction-based spinal instrumentation. The clinical evidence of crankshaft phenomenon is often subtle, whereas radiographic findings are usually more apparent. However, objective measurement of radiographic signs may be complicated by instrumentation and postoperative changes. Treatment options for patients with the crankshaft phenomenon are limited; in those with problematic deformity and/or risk of progression, additional surgery may be indicated.