Lumbar (Low Back) Implants Stabilize the Spine
Lumbar implants are devices surgeons use to decompress and stabilize the spine (low back). Implants used in lumbar fusion surgery can be divided into 2 groups:
1. Those placed within the interbody space
2. Those placed onto the spine to provide stabilization
The purpose of lumbar (low back) stabilization implants is to:
1. Help restore and maintain normal alignment of the lumbar spine
2. Keep the spine fixed (stable) during the fusion process
Stabilization implants are considered temporary devices because their function stops once fusion occurs. They may be removed after solid fusion, if considered necessary. However, in most cases, implants are not removed. These are examples of stabilization implants:
Anterior Lumbar Plates
Wide plates usually placed at the L5-S1 level during an anterior (front) lumbar interbody fusion (ALIF) procedure. The plates are made with screw holes through which screws anchor the plates onto the vertebral body. The plate prevents the interbody space from opening when the patient bends backwards. This reduces loosening of the interbody cages and helps to prevent fusion disruption. Sometimes, anterior places are placed at the L4-L5 level.
Pedicle Screws come in difference diameters and lengths, and are made from metal; either titanium or stainless. These specially designed screws are placed from the back through the hole of the cylinder-shaped pedicle into the vertebral body. Surgeons like pedicle screws because they provide a stable anchor to the spine. Screws are often fit into both pedicles of a vertebra. Then, the pedicle screws are attached to rods or plates, which extend to adjacent vertebrae to provide a stable fixation so fusion occurs.
Lumbar Plates are available in multiple lengths and with many holes for pedicle screw attachment. Nuts lock each plate to the screws. Because lumbar plates are stiff, they provide a stable fixation to the posterior (back) spine. The plates are made from titanium or stainless steel. Newer plate materials are being developed.
Rods connect to pedicle screws to provide stabilization. Rods are more adaptable than plates and provide the surgeon more options when placing pedicle screws. Different types of connectors solidly fix the rod and screws together. Rods are primarily made from metals like titanium, stainless steel and sometimes, cobalt chrome.
Hooks attach over the tops of the lamina and are connected by rods. Today, hooks have largely been replaced by pedicle screws, although hooks are sometimes added to pedicle screw fixation.
Wires and Cables are wrapped around the lamina or spinous processes and tightened to limit motion. Seldom are wires and cables used to surgically treat lumbar degenerative disorders.
One or 2 crosslinks may be used to attach 2 long rods or plates together. Crosslinks provide more stability for long implant constructs. They are made from the same materials as the rods and plates to which they connect.
Role of Bone Graft
Whatever implants the surgeon chooses, the final stability of the spine eventually results from fusion - and fusion is enhanced by bone graft. Autograft is the patient's bone and allograft is donor bone. A genetically engineered protein, recombinant human bone morphogenetic protein (rhBMP-2), stimulates the body to produce natural bone rapidly.
New Lumbar Technology
New implants for treating lumbar (low back) degenerative disease have recently been approved by the U.S. Food and Drug Administration (FDA). These implants address the question of whether it is better to preserve motion at the disease site rather than fuse it. They can be divided into 2 groups:
1. Interbody motion devices (artificial discs)
2. Interspinous process decompression devices
Artificial Lumbar Disc
These devices are implanted from the front of the spine into the interbody space. The procedure is called disc arthroplasty. Arthro is the medical term for a joint and plasty means to shape the anatomy to restore function. Artificial discs are made from different materials. Some designs are all metal and others are plastic and metal composites. There are a many artificial disc clinical trials for safety and efficacy underway in the United States. At least 2 designs are cleared for use by the FDA as a fusion alternative.
Interspinous Process Decompression Device
This implant is placed between the spinous processes at the problem level in the lumbar spine. Interspinous process decompression devices treat low back spinal stenosis. The implant causes a local flexion at the problem level and relieves the patient's symptoms without affecting overall spinal motion. Interspinous devices may be inserted in a minimal access approach under local anesthesia.
Patients who seek treatment for low back pain and degenerative lumbar disorders can be encouraged by the successful outcomes of others from decompression and stabilization procedures. Be sure to discuss all treatment options with the surgeon, who can help you to choose the best care for your particular lumbar disorder.