Scoliosis Surgery: Degenerative Conditions and Crankshaft Phenomenon

Adult Scoliosis with Degenerative Disc Disease (below)

Crankshaft Phenomenon
Crankshaft phenomenon occurs when the front part (anterior) of the spine is fused from the back (posterior) and the spine twists as it grows. Despite a solid posterior fusion, the child's spine may continue to curve and rotate. It can occur in children who have much growth remaining and is determined by the patient's age (usually under age 10) and growth status. Therefore, to avoid crankshaft phenomenon, both the front and back of the spine (anterior-posterior surgery) may be fused in patients with large growth potential. Today, with powerful pedicle screw instrumentation, the anterior procedure may be avoided in some patients.

9-year-old female at risk for Crankshaft Phenomenon
because of a large curve and much remaining growth.

Bone Quality
Because osteopenia or osteoporosis is common in adults, bone quality is an important issue. Adult patients are asked to obtain a DEXA (or DXA, Dual Energy X-ray Absorptiometry) or bone density scan before surgery to determine bone quality. Vertebral bone density dictates the strength of spinal fixation (instrumentation and fusion) that can be achieved at surgery. Patients with osteoporosis often need to be braced after surgery and may experience less spinal correction than patients with denser bone.