What's New in Spinal Deformity Surgery

The Scoliosis Research Society (SRS) Annual Meeting was held in Salt Lake City, Utah, September 10 to 13, 2008. The Harrington lecturer was Marc Asher, MD, who spoke on Dr. Paul Harrington's contributions and perspective. Lifetime Achievement awards were given to John E. Hall, MD, and to Jacquelin Perry, MD, DSc, and George Thompson, MD, completed a two-year term as President. SRS globalization efforts have expanded over the last five years. The SRS Global Outreach Program currently represents a service initiative with nine endorsed sites on four continents, and the development of worldwide regional courses has focused on international educational activities and the building of professional relationships.

Adolescent Idiopathic Scoliosis
Work continues on the genetic profiling of teenagers with idiopathic scoliosis. Ward and Ogilvie presented evidence suggesting that it may now be possible to predict which curves will progress into the surgical range and which will be resistant to bracing. This may have a profound impact on the nonoperative treatment of idiopathic scoliosis.

Scoliosis surgeons continue to debate the surgical treatment of double-major curves and "false" double-major curves with regard to fusion of the lumbar curve. A multicenter study by the Harms Study Group concluded that patients with preserved lumbar motion had greater function and satisfaction at two years after surgery in comparison with those who had a lumbar curve that was fused. A group of authors from Turkey concluded that selective thoracic fusion may be considered if the lumbar curve is <50 and demonstrates >50% flexibility.

The topic of thoracic pedicle screws for the treatment of adolescent idiopathic scoliosis remains controversial. One report by the Spinal Deformity Study Group suggested that the correction of a thoracic deformity was related to the number of fixation points rather than which specific type of bone anchor was implemented. Several studies have suggested that sublaminar wires are kyphogenic in the thoracic spine and that thoracic pedicle screws have a lordosing tendency, especially if a direct apical derotation maneuver is performed. Researchers at Cincinnati Children's Hospital documented an 80% increase in surgical costs for idiopathic scoliosis treatment over a seven-year time frame, attributed mostly to the increased use of pedicle screws.

Researchers from Texas Scottish Rite Hospital for Children in Dallas and Washington University in St. Louis independently assessed the benefits of halo traction for the treatment of severe deformities. Both groups of researchers concluded that halo traction had a high benefit-to-risk ratio, with improved overall correction and a reduced risk of neurologic deficit in association with the ultimate surgery.

Adult Spinal Deformity
It is generally accepted that the surgical treatment of adult spinal deformity demands a solid fusion, and a long construct from the thoracic spine to the sacrum is often needed. The annual meeting of the SRS highlighted much of the ongoing research in this difficult treatment group. Contrasting views on the role of anterior surgery in this patient subset were presented. Regardless of which approach is utilized, patient outcomes at a minimum of two years of follow-up were good if a solid fusion was achieved and complications were minimized. The results supported sagittal plane balance (not coronal plane correction/balance) as the primary radiographic factor in determining the outcome. Some of the trends gleaned from recent presentations include decreased use of circumferential fusion; increased use of bilateral pedicle screw fixation and multiple fixation points in the sacropelvic unit, usually with use of iliac screws; and frequent off-label use of BMP to enhance fusion rates in both anterior and posterior fusions. To date, we are not aware of any reports of local or systemic complications related to the use of BMP during adult spinal deformity surgery in contrast to its use during anterior cervical spine fusion. Nonetheless, the use of BMP for the treatment of adult spinal deformity will remain highly controversial until it is approved by the FDA for multilevel posterior fusion and more than one vendor distributes it.

Complications of adult spinal deformity surgery were the focus of many presentations. Additional data on catastrophic failures of the proximal adjacent segment in pedicle screw constructs were presented. The patients who were found to be at greatest risk were women over the age of sixty years with sagittal imbalance, obesity, osteopenia, and a substantial sagittal plane correction. Alternative methods of fixing the cephalad level with something other than pedicle screw implants are being evaluated.

Age appears to be a primary determinant of complication rates after spinal deformity surgery. Patients over the age of sixty years are more likely to experience complications than those in the forty-to-sixty-year-old age group. Nonetheless, data suggest that the postoperative incremental improvement in outcome according to SRS and Oswestry Disability Index measures is identical for patients in the forty-to-sixty-year-old age group and those in the more-than-sixty-year-old age group. It appears that complications reduce the likelihood of benefit from surgery, but they do not preclude benefit as long as the complications are not catastrophic (major paralysis, blindness, death).

Neuromuscular Scoliosis
There is a strong trend away from performing anterior and posterior surgery for fusions to the sacrum in patients with cerebral palsy. The current preferred method is intraoperative traction and a long posterior procedure extending from the upper thoracic spine to the sacrum and pelvis. In most cases, halo traction and posterior techniques will suffice. The crankshaft phenomenon is a substantial concern for juvenile patients with neuromuscular scoliosis who require a long fusion. One study suggested that anterior surgery did not preclude the crankshaft phenomenon and that those at greater risk were the particularly young patients (eight years of age or younger) and those who did not have a long fusion, defined as one extending from above T5 and down to the sacrum as opposed to stopping at L4 or L5. Pedicle screw fixation may improve the correction, especially in patients with Duchenne muscular dystrophy.

Infections are a substantial problem in juvenile patients with neuromuscular scoliosis. A study from the Shriners Hospital-Chicago demonstrated an 11.2% infection rate in patients with cerebral palsy and a 19.2% rate in patients with a myelomeningocele. The majority of patients with deep infections ultimately required implant removal.

Early-Onset Scoliosis
The term "early onset" refers to scoliosis that presents before the age of six years. Etiologies include congenital, infantile, and early juvenile idiopathic scoliosis; chromosomal syndromes; and genetic connective-tissue disorders. These are all circumstances in which traditional bracing does not control the spinal deformity. There usually is substantial risk of either pulmonary compromise or a neurologic deficit if the disorder is not treated. Spinal fusion is not a good alternative because there is much growth remaining. Strategies include dual growing rods, the Vertical Expandable Prosthetic Titanium Rib technique, vertebral body stapling, and the use of multiple corrective casts. No one technique is completely effective. Although there is no statistical proof that neuromonitoring reduces the prevalence of neurologic deficit, there is a consensus that it is highly advisable.

High-Grade Developmental Spondylolisthesis
Sacral doming is thought to be an early sign of progressive high-grade spondylolisthesis and "impaired spinopelvic alignment." Thus, this finding is considered by many to signal an indication for early intervention and surgery. The classic high-grade developmental spondylolisthesis, which benefits from a reduction with instrumentation, is one with lumbosacral kyphosis, retroversion of the sacrum and pelvis, compensatory proximal lumbar hyperlordosis, and positive sagittal balance. Surgical treatment should be aimed at reducing the lumbosacral kyphosis and correcting the pelvic retroversion so that the anterior spinal gravity line falls through the sacrum and the lumbar segments above can spontaneously adjust to a more normal segmental sagittal alignment.