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Optimizing Curve Correction With A Three-Dimensional Approach

The CD HORIZON® LEGACY™ Spinal System and Vertebral Column Manipulation (VCM) Instrument Set give surgeons an effective means for addressing all three dimensions of spinal curve correction.

When you think of scoliosis, what is the first thing that comes to mind? Probably the lateral, side-to-side curves that are the hallmark of the condition, and that have the potential to affect the body's overall balance and alignment. But did you know that the bones of the spine (vertebrae) along the curve also actually rotate, or turn out of position, potentially leading to more severe physical deformities and health problems? Rotated vertebrae in the thoracic spine (chest area), for example, can turn the rib cage out of position, creating a "rib hump" and possibly impairing the function of the lungs.

Effectively realigning vertebrae that have rotated out of position — a process called derotation — is an area of great interest in scoliosis correction surgery. In recent years, surgeons have sought new ways to maximize curve correction three-dimensionally. This means addressing the curve in all three "planes" of the deformity: the coronal (front and back), sagittal (left and right) and axial (upper and lower). Correcting vertebral rotation requires considering the axial aspect of the spine, or the cross-sectional view from the top of the spine down.


Three-dimensional scoliosis correction involves addressing a spinal curve in all three planes of the deformity.

"The rotational malalignment manifested by the rib hump/prominence in scoliosis has been the most difficult part of the three-dimensional deformity to correct," says orthopaedic surgeon Dr. Lawrence Lenke, co-chief of adult/pediatric scoliosis and reconstructive spinal surgery at the Washington University School of Medicine in St. Louis, Missouri. "Previous spinal instrumentation and correction techniques have done very well with frontal and sagittal plane correction, but not axial or rotational plane correction."

In the 1980s, the release of groundbreaking technology designed by two orthopaedic research pioneers in France, Dr. Jean Dubousset, professor of pediatric orthopaedics at the University Rene Descartes in Paris, and Dr. Yves Cotrel, formerly with the renowned French hospital Institute Calot, launched what many consider to be a revolution in scoliosis correction surgery, both in terms of improving spinal realignment and the recovery process for patients. The technology they developed, originally called Universal Instrumentation but later renamed CD® Instrumentation in honor of its two developers, has served as the basis for a variety of spine surgery applications, for the benefit of patients of all ages.

Today, one of the latest versions of this technology, the CD HORIZON® LEGACY™ Spinal System and Vertebral Column Manipulation (VCM) Instrument Set, gives surgeons an effective means for addressing all three dimensions of spinal curve correction, including axial rotation. "The CD HORIZON® LEGACY™ Spinal System and VCM Instrument Set allow us to securely attach to the apical vertebrae (the vertebrae at the tip, or apex, of the curve) that are most twisted, and place a strong, derotational force on this part of the curve," Lenke explains. "This in turn allows us to not only untwist the vertebrae, but at the same time reduce the rib hump, since the ribs associated with the deformity are attached to the vertebrae being derotated."

Scoliosis: Dimensions In Treatment

A certain degree of curvature is normal in the human spine. When you look at your body from the side, you can see the gentle inward and outward curves of the neck, upper back and lower back, which are necessary for keeping the body properly balanced and aligned over the pelvis. But when viewed from the back, the vertebrae of a healthy spine should form a straight line. In someone with scoliosis, the spine looks more like an "S" or a "C" than an "I." Vertebral rotation can further contribute to the severity of spinal deformity, both in terms of appearance and health. A rib hump results from the rib cage rotating along with the spine, altering the contour of the ribs. When the patient is observed bending over from the back, the ribs on one side of the spine appear higher than those on the other side, hence the "hump."

Treatment of scoliosis depends on the severity of the curve, along with other factors such as the patient's age and physical condition. Non-surgical treatment, such as observation and bracing, is always the first line of defense, and many scoliosis curves never progress to the point where surgery is necessary. Surgery — specifically, spinal fusion — is recommended for severe curves and for curves that have not responded to non-surgical intervention. Spinal fusion involves placing graft material between the affected vertebrae to encourage them to fuse, or join together. Instrumentation, such as screws, rods, plates and cages, is implanted along the treated area and is a key element because it creates an "internal cast" to support the vertebral structures and redirect stress properly along the spine during the healing process. Ultimately, the goal is to halt the progression of the curve and reduce spinal deformity, to the extent possible, restoring proper spinal stability and alignment.

If the patient has a significant rib hump that's expected to remain even after fusion surgery because axial derotation was not addressed, a procedure called a thoracoplasty also may be performed, either along with the fusion or at a later date. In a thoracoplasty, sections of the ribs that form the hump are surgically removed, or resected, to shorten the ribs and reduce their prominence. The benefits can include an improved appearance and pain relief.

Since the mid-20th century, rods have been a mainstay in scoliosis correction technology. Until the advent of CD® technology in the 1980s, hooks were the primary means of fixation to the vertebrae; by the early 1990s, more surgeons were discovering the benefits of using pedicle screws in skeletally mature patients. These are very small bone screws designed to be implanted into the two bony protrusions — the pedicles — that project from the back, or posterior, of each vertebra, and connect to other spinal structures such as the lamina and vertebral arch. Pedicle screws can be used to affix rods and plates to the spine, and to stabilize the spine to promote fusion. "What once seemed impossible has now become commonplace¬ — placing pedicle screws into the individual vertebrae involved in the deformity, thereby obtaining strong, three-column purchase of these vertebral segments," Lenke says.

CD® Technology And Axial Derotation: How It Works

The CD HORIZON® LEGACY™ Spinal System and VCM Instrument Set enables surgeons to correct scoliosis-related spinal curves with a powerful yet controlled derotation technique referred to as bilateral apical vertebral derotation (BAVD). The CD HORIZON® Spinal System consists of a variety of shapes and sizes of rods, hooks, screws, plates, staples and other connection components. The VCM Instrument Set includes a derotator implant holder that attaches to the side wall of a CD HORIZON® LEGACY™ pedicle screw, a derotator bridge that connects to the implant holder with a bridge nut, and derotator bridge handles that can be joined together. During surgery, the components of the system are assembled into a framework attached to the vertebrae at the apex, or highest point, of the curve to be corrected. The technology differs from previous scoliosis correction systems in that it allows surgeons to manipulate the "apical" vertebrae of the curve as a single unit, rather than separately.

How the system works is:

  • Two pedicle screws are implanted into each vertebra along the curve to be corrected
  • An implant holder is attached to each of the two pedicle screws on the vertebra
  • The pedicle screws on the vertebra are joined by attaching the bridge nut to the top of each of the two implant holders on the vertebra
  • The bridge nuts are tightened to secure the attachment
  • Using interlink devices, the pairs of implant holders on each vertebrae are joined together to form a quadrilateral (four-sided) frame attached to the apical vertebrae
  • Using handles attached to the implant holders, the entire assembly is manipulated as a unit to rotate the vertebrae into alignment, to the greatest extent possible
  • The pedicle screws on each of the derotated vertebrae are secured to rods that extend along both sides of the vertebrae to be fused

The CD HORIZON® LEGACY™ Spinal System and VCM Instrument Set allows a stronger derotational force to be applied to the spine.

"By attaching to a group (typically two to three) vertebrae simultaneously with the VCM device, a much stronger derotational force can be applied," Lenke explains. "The unique attachment of the VCM device allows the placement of the rod into the saddle of the screws while the derotational force is actively being applied. When the rod is secured, the spine and rib hump are then fixed into the derotated position."

Potential benefits to the patient include reduction of both their spinal curve and rib prominence, as well as restored breathing ability in those whose uncorrected deformities interfered with lung function. "The patient benefits from a markedly improved appearance, with the normal anatomy of the rib cage preserved," Lenke says.

As with any spine surgery, however, there is some risk involved, and the CD HORIZON® LEGACY™ Spinal System and VCM Instrument Set may not be the most suitable treatment option for every case. Talk with your surgeon about the technology, and rely on his or her judgment as to whether it's the right surgical technology for you.

Dr. Lenke says that in his clinical experience, performing fusion surgery to correct scoliosis using the BAVD technique with the CD HORIZON® LEGACY™ Spinal System and VCM Instrument Set has significantly reduced the need for rib resection in many of his patients.

A Milestone On The Journey, But Not The Final Destination

Through their collaboration, Drs. Cotrel and Dubousset transformed an original idea into a truly innovative new approach to spinal correction. Out of an earnest desire to improve the lives of scoliosis patients emerged an instrumentation system on which a variety of applications — such as the CD HORIZON® LEGACY™ Spinal System and VCM Instrument Set — are based. CD® Instrumentation was patented in February 1987, and in December cleared by the U.S. Food and Drug Administration (FDA) for marketing. Since then, more than 450,000 surgeries have been performed worldwide using CD® technology and technology derived from the "CD" design.

Since the introduction of CD® technology, the quest for optimal three-dimensional scoliosis correction continues. Addressing curve correction and axial vertebral derotation along all three planes of the deformity using the BAVD technique with the CD HORIZON® LEGACY™ Spinal System and VCM Instrument Set, released in 2006, marks a milestone on the journey, but certainly not its end. In the words of Dr. Cotrel: "On the staircase of our knowledge in the treatment of this disease, we have reached a certain level thanks to the work of people who have come before us. Let's try to climb one step higher. There still will be many steps left for those who come after us."

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It is important that you discuss the potential risks, complications, and benefits of spinal surgery with your doctor prior to receiving treatment, and that you rely on your physician's judgment. Only your doctor can determine whether you are a suitable candidate for this treatment.

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  • Published: April 17, 2009
  • Updated: April 17, 2009