Advances in scoliosis surgery have improved correction rates

March 14, 2005

March 14, 2005

Washington, DC - Recent advances in surgery for severe scoliosis have improved the correction rates from 55% in the past to around 80% to 85% in many cases, says Dr Daniel Sucato (Texas Scottish Rite Hospital for Children, Dallas). The surgery, traditionally performed through a large cut in the chest or back, involves the placement of metal rod implants that correct the spine and hold it in position. The implants that are available now are more powerful and can achieve greater correction, Sucato commented at a press briefing at the recent American Academy of Orthopaedic Surgeons meeting.






Another advance has been the development of less invasive surgery. "In cases where surgery is best done through the chest, access is now possible through very small incisions easily hidden along the chest wall," Sucato commented. Thoracoscopy through these portals has resulted in improved cosmesis, shorter hospital stays, and less postoperative pain, and it avoids having to harvest a rib. However, this a new technique that requires advanced training, he noted, as well as new equipment—with disposable items—that increases costs.


Implanting rods was "pretty radical"

Scoliosis, the sideways curvature of the spine, affects about 2% to 3% of adolescents, and while it can occur at any age, it's seen most commonly after the age of 10 during the pubertal growth spurt. A curve with a Cobb angle of more than 45 degrees is usually considered to be an indication for surgical intervention.

The idea of implanting rods and screws into the spine to correct the curvature was "pretty radical" when it was first introduced in the 1970s, Dr Stephen Richards (Texas Scottish Rite Hospital for Children) commented to rheuma wire . Before that, scoliosis was treated with body casts and also with bracing, and bracing is still used for the less severe curvatures of the spine, even though this intervention has never been subjected to a controlled clinical trial, as reported recently by rheuma wire .






"These nonoperative methods such as cast and brace treatments may be ineffective, since the immature rib cage often deforms before significant correction is transmitted to the spine," says Dr BehroozAkbarnia (San Diego Center for Spinal Disorders, La Jolla, CA). He was discussing new developments in scoliosis surgery at a pediatrics symposium during the meeting. Initially, these procedures involved spinal fusion as well as insertion of rods to correct the curvature, but there is increasing use now of "growing rod" instrumentation without fusion to preserve spinal growth. A hook is implanted at each end of the concave side of the deformity and then linked by a rod that is tunneled subcutaneously rather than below the muscle. However, results with this single-rod-distraction technique can be unpredictable, and there are implant-related complications, such as rod breakage and hook dislocation, Akbarnia said.

In an attempt to improve on these results, together with a colleague he developed a dual-rod technique [ 1 ]. In this method, hooks are placed on both sides of the spine in "claw" patterns over 2 to 3 spinal levels to avoid hook crowding. Pedicle screws can be included in the lower formation and appear to add significantly to the stability of the construct, he commented. Rods are inserted subcutaneously on both sides of the spine and are joined together on each side with extended tandem connectors. Initial results from a series of 23 patients, presented at the 2003 meeting of the Scoliosis Research Society, suggested that the dual-rod technique has increased implant stability and fewer complications compared with single-rod systems. Further data on 28 patients, presented at last year's meeting of the same group, compared 3 methods; single rod with fusion (5 patients), single rod without fusion (16 patients), and dual rod (7 patients). The authors (including Akbarnia) concluded that both growing rod methods were effective in controlling severe spinal deformities in young children, but the dual rods offered better initial curve correction as well as maintenance of correction with less implant-related complications.


Research that could revolutionize scoliosis?

Looking further ahead into the future, Dr John Braun (University of Utah, Salt Lake City) described research that has the potential to "revolutionize" the treatment and diagnosis of scoliosis. He likened spinal fusion to putting boards up around a house, pointing out that it eliminates growth, motion, and function and puts the adjacent segments at risk of degeneration. Fusionless surgery is the way forward, he declared, with its goal of "harnessing the scoliosis patient's inherent spinal growth and redirecting it to achieve correction, rather than progression of deformity."

Braun described 2 experimental approaches. One involves the use of a rigid metal staple, implanted at several points on the outside of the curve to provide a "tethering effect": the aim is to slow down the exuberant growth of bone on the outside of the curve and so correct the curvature as the spine grows. The Shape memory alloy staple is already marketed, but only for use in the knee; this use in the spine is off-label and has been tried so far only in 8 patients. Even further back in development is a similar idea, but a more flexible product. Consisting of bone anchor pegs linked up by a flexible "ligament" (which looks like an elastic band), this product has so far been tested only in animal models. Developed by Braun and colleagues, in collaboration with Medtronic, the flexibility of the ligament should overcome the problems caused by the rigidity of the metal staple (which can break under stress). Braun tells rheumawire that he has heard, anecdotally, that 1 staple implanted into a scoliosis patient has broken; about 200 have probably been implanted so far, he estimates—about 2 to 3 staples per level, and some patients have 6 to 7 levels, he explains.

One problem common to all the surgical approaches is the question of who is a good candidate. At the moment, there's no way of predicting whether a curve will progress or whether it will deteriorate only very slightly, Braun comments. He's hopeful that in the near future, maybe 18 months from now, there may be a genetic test that would diagnose idiopathic scoliosis with a high rate of progression. His team has already identified a candidate gene, utilizing linkage analysis and gene-mapping techniques on the very large families who live in Utah, and the researchers are now working with Axial to develop a test.


Source

  1. Akbarnia BA and Marks DS. Instrumentation with limited arthrodesis for the treatment of progressive early-onset scoliosis. Spine: State Art Rev 2000; 14 (1): 181-189.

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