Scoliosis Research Society (SRS)
An International Organization Dedicated to the Education, Research and Treatment of Spinal Deformity
Our Mission is to Foster Optimal Care for All Patients with Spinal Deformities
Posterior fusion provides permanent stabilization in the corrected position and is achieved by removing the joints between the vertebrae to be fused, usually all the vertebrae which are involved in the curve. Bone graft - either from the pelvis, ribs, or from the bone bank (allograft) - is placed in each joint space which has been removed. Over time (4-6 months), the graft incorporates to the vertebral bone, and the operated portion of the spine heals into a solid block of bone which cannot bend, thus eliminating further progression of the curve. Typically in a child who has reached an appropriate age for definitive fusion, instrumentation will also be placed when the fusion is performed. The instrumentation rigidly fixes the spine internally, so that the corrected position is carefully preserved while the fusion takes place over the 4-6 month period. This rigid fixation is achieved by screws, hooks, and wires ("anchors") attached to the spine, usually at multiple sites along the curve, and then rods are attached to the anchors to stiffen the entire area. Depending on the flexibility of the curve and any preceding treatment (such as traction), there may be additional correction of the deformity achieved by the application of the instrumentation. However, the primary goal of the surgery is to stop the curve from progressing further, and thus be the definitive stabilization - additional correction is an added benefit but not the primary concern. Often the patient does not need any further external immobilization (cast or brace) if the internal fixation device is felt to be adequate at the time of surgery.
Depending on the surgeon's determination of how much growth the patient might have remaining, an anterior (front) fusion of the spine may also be appropriate. This will prevent curve progression after posterior (rear) fusion due to continued growth of the vertebrae. Known as the "crankshaft phenomenon", curves sometimes continue to grow by rotating around the original surgical fusion. This is known to happen when children under the age of ten undergo fusion surgery and can be prevented by performing an anterior fusion at the same time (or shortly before or after) the definitive posterior operation.
Obviously the additional surgery required to prevent crankshaft curve progression is best not done at all if it is not necessary, the decision being dependent on the age of the child at the time surgery is selected. Delaying definitive surgery is the best option if that delay can be accomplished while maintaining control of the curve by non-operative means.