Segmental Spinal Stabilization using a Low-Profile Crosslinking Device

Early Beginnings of Spinal Stabilization
One of the most common techniques used by spine surgeons to correct spinal problems is spinal fusion. Fusion is a technique that works to 'weld' specific bony segments of the spine together to enhance bone growth into a solid and stable construct.

During recent years, many different types of instrumentation have been developed to help facilitate spinal fusion. Instrumentation includes such devices as special plates, rods, hooks, and screws to join bony parts of the spine together.

The evolution of spinal instrumentation systems started during the late 1950's with the Harrington rod and hook system. By today's standards, the Harrington system was very basic although considered a major advance at that time. In the 1980's, a new standard was established for treating spinal deformity three-dimensionally using the Cotrel-Dubousset (CD) Instrumentation system. The CD Instrumentation system considered the coronal, sagittal and axial planes of the spine during surgical procedures to reconstruct the spine (Fig. 1). Significant advancement in spinal technology and surgical techniques continued through the 1990's.

anatomical planes

Figure 1.
Anatomical Planes

Advances continued with the development of spinal instrumentation systems that enable the spine to be fixed segmentally at two or more levels. To better understand this concept, consider the example of two lumbar herniated discs so damaged that surgical removal is necessary (e.g., discectomy). The damaged discs are located between the third and fourth (L3-L4) and fourth and fifth lumbar vertebrae (L4-L5). After the discs are removed, a spinal instrumentation and fusion procedure is performed to (1) restore lost disc height as a result of the disc removal, and (2) to join L3-L5 together to stabilize those segments of the spine.

The latest trend is low-profile segmental spinal instrumentation systems. Low-profile means the instrumentation has been designed to lay flatter against the surface of the bone. This is an advantage to patients who are young and slim, and also to avoid muscle irritation. Other types of instrumentation may be bulky and felt beneath the patient's skin.

The X10 CROSSLINK® Plate Spinal System is one such low-profile spinal instrumentation system spine surgeons are using to segmentally stabilize spinal instability and deformity.

Crosslinking Devices and Low-Profile Design
In general, crosslinking devices are simple transverse/placed implants that connect the implants (rod) on one side of the spine to the implants (rod) on the other side. The use of crosslinking devices to provide additional stability to posterior spinal instrumentation constructs is universally accepted.

Traditionally, crosslinking devices have been added to the top and bottom ends of rod constructs to increase biomechanical strength. A drawback to particular crosslinking implants is size - some are bulky. However, low-profile instrumentation is designed to be implanted flatter against a spinal structure - a definite advantage in thinner patients.

A problem this author has experienced with typical 'flat' crosslinking devices is that unless a fair amount of bone is removed from the spinal segment, there is not enough room underneath the device to implant bone graft. Bone graft (e.g. autograft, allograft, BMP) application to the back of the spine is essential for a successful spinal fusion and a good surgical outcome. The X10 CROSSLINK® system helps to eliminate this problem by means of an arch that is built into the product's design to provide room underneath for the bone graft. Additionally, the small expandable limbs of the X10 CROSSLINK® (Fig. 2) are slimmer and sleeker, and versatile to ease application to the spinal rods.

crosslink plate spinal system
Figure 2.
X10 CROSSLINK® Plate Spinal System

From the image below (Fig. 3), it can be seen that the low-profile X10 CROSSLINK® device is simply one-piece that connects to a rod from the top. Top loading makes it easier to insert the device and tighten it into place. In addition, the device is adjustable and the transverse rods are pre-contoured to fit the patient's anatomy.

crosslink plate variety configurations

Figure 3.
X10 CROSSLINK® Plates rigidly lock into a variety of configurations

Overcoming Failed Fusion
Certain areas of the spine are at higher risk for pseudarthrosis (non-union, failed fusion) than others. Particularly troublesome in adult scoliosis surgery are the thoracolumbar (T11-L1) and lumbosacral (L5-S1) junctions. Some types of crosslinking devices at these levels will restrict the spine's ability to form a healthy fusion mass underneath the crosslink.

Another potential problem in treating these levels is the placement of pedicle screws. The lordotic curve (swayback) of the lumbar spine may require pedicle screws to be implanted closely together. This leaves little room for crosslink devices with wider attachments to the rod. Thus, the design of the X10 CROSSLINK® overcomes these difficulties. Small "feet" that attach to the rod are able to fit between the screw heads that are relatively close together.

Patient Case
Our example is a 58-year-old female patient who was surgically treated for degenerative lumbar scoliosis two years ago. Her original surgical procedure involved posterior lumbar interbody fusion (PLIF) and instrumentation from L1 to the sacrum. A non-union or failed fusion (pseudarthrosis) developed at L5-S1 (lumbosacral junction) and an angular kyphotic deformity (humpback) occurred at T12-L1, which made it necessary for her to undergo a revision procedure.

The revision procedure included fixing the spine using instrumentation and fusion from T10 to the sacrum to add stability and correct spinal imbalance. Further, her revision procedure made use of the X10 CROSSLINK® Plate system, which helped stabilize the construct while maximizing the underlying surface area for placement of bone grafting material. Her postoperative x-rays (Fig. 4, far right) reflect a good radiographic (x-ray) outcome.

pre post op x-rays

Figure 4.
Preoperative (1, 3) and postoperative (2, 4) anterior-posterior and lateral x-rays.

In summary, crosslinking devices are extremely important to the ultimate success of reconstructive procedures to treat spinal instability and deformity. The development of the X10 CROSSLINK® Plate System is one way spine specialists are working to improve the lives of patients with spinal instability and deformity.

Updated on: 02/01/10