PLIF Surgery: Posterior Lumbar Interbody Fusion

Spine anatomy

The spine, or backbone, is the center of support for the upper body. This column of bones and cartilage extends from the base of our skull to the pelvis, enclosing and protecting the spinal cord. Ligaments and tendons and large muscles connect to the spine, while highly sensitive nerves extend outward from the spinal cord. The spinal cord extends from the base of the brain and enters the spinal canal, a protective space within our bony spine, to carry signals to and from the brain throughout the body.

A healthy spine is both highly flexible and very strong. Its strength holds up our head and shoulders and supports our upper body. It allows us to stand up straight. The flexibility of the spine enables us to bend and twist.

Vertebrae

The spine is not one long rigid bone. It consists of 24 small bones called vertebrae that are stacked in a column from the pelvis to the base of our skull. These bones connect to create a canal that protects the spinal cord.

The vertebrae are divided into four regions. From top to bottom, these are:

The curves of the spine

The spine is not perfectly straight; it has natural curves. If you were looking at the spine from the side, you would see that it is curved like an elongated 'S'. These natural curves are very important. When properly maintained, they give the spine full mobility and provide stability for the backbone and surrounding trunk. Good posture is important to maintain the health of our spine.

Spinal cord and nerves

The spinal cord is a cylinder of nerve tissue. Roughly the thickness of a finger, it extends from the skull to the lower back, traveling through the middle part of each stacked vertebra, called the central canal. Nerves branch out from the spinal cord through openings in the vertebrae and carry messages between the brain and the muscles.

Spinal discs

Structures called intervertebral discs are located between each vertebrae. They are flat and round, and about half an inch thick. Their main purpose is to provide shock absorption and allow mobility between the vertebrae. The structure of a spinal disc can be likened to that of a jelly doughnut. It has an outer ring of firm, spongy, malleable material and an inner core composed of a jelly-like substance.

A herniated disc is a common condition that affects these soft tissues. A disc herniation (sometimes called a "slipped disc") occurs when a portion of a disc's inner core bulges or ruptures through the outer ring, putting pressure on a spinal nerve. This may cause low back pain and/or leg pain – such as that associated with sciatica – leg weakness, leg numbness, cauda equina syndrome and other problems.

Illustrations of the axial (overhead) view of a healthy disc and a herniated disc putting pressure on a spinal nerve.

Spinal musculature

The spine is supported and controlled by several layers of muscles that perform different actions, yet work together in a harmonious fashion to support the spine, hold the body upright and allow the trunk to move, twist and bend.

Long and thick muscles span much of the back and function like guide wires, protecting the spine from excessive and sudden movement.

Deep and thinner muscles connect from the rib cage to the pelvis and hips. Together, these muscle groups act as a natural corset to provide stability and a foundation from which the hips and pelvis can derive power. This is known as core musculature.

Animation: Posterior lumbar interbody fusion (PLIF)

This animation provides illustrates a common PLIF procedure.

How a PLIF spine surgery is performed

Decompression

First, an incision is made in the middle of the low back. The muscles are moved aside and the lamina portion of the vertebrae are exposed. Next a laminectomy and facetectomy are performed to provide a surgical access point: Cutting instruments are used to remove the spinous process, portions of the lamina, and portions of facet joints from the back of the vertebrae.

Removing this bone allows the surgeon to see the spinal disc and the compressed spinal nerves. A grasping instrument is used to remove most of the intervertebral disc, which relieves pressure on the compressed spinal nerve, allowing it to return to the proper position.

Instrumentation

Next, the vertebrae are prepared for instrumentation. A sharp awl is used to make holes in the pedicles for inserting pedicle screws. Screws are placed through a metal plate and then into the pedicle holes, ending with the screw tips in the middle of the vertebral bodies. Screws and plates are placed on both sides of the spine. Two more pedicle screws are then placed through the metal plate and screwed into the lower vertebral body pedicles.

Distraction and graft placement

To prepare for bone graft insertion, the disc space is spread apart (distracted) by moving the vertebral bodies or applying pressure on the pedicle screws. The screws are tightened to hold the disc space in this open position. Two bone grafts are then placed between the vertebral bodies. The bone grafts allow for eventual fusion as bone grows between the vertebral bodies. In variations of this procedure, spacers, cages packed with graft material, or ground bone graft material may also be packed into the disc space to aid with the fusion.

Compression

To provide stability to the spine while the fusion occurs, the lower screws are loosened and the vertebral bodies are squeezed together (compressed). The screws are tightened in the compressed position, which allows for a tight fit of the grafts between the vertebral bodies. Small screws called blockers are placed on the pedicle screws to lock the screws to the metal plate.

Closure and recovery

The incision is closed and dressed to complete the surgery. Patients will typically be hospitalized for two to four days and should avoid strenuous activity for 6 to 12 weeks.

(Find a surgeon who performs lumbar fusion surgery.)

Animation: Minimally invasive PLIF

This animation illustrates a technique known as minimally invasive surgery (MIS), in which a PLIF can be done with a much smaller incision than traditional open spinal surgeries and avoids damaging the low back muscles. The MIS approach can be safely performed with less trauma to the surrounding muscles. MIS procedures can result in less postoperative pain, shorter hospitalizations and quicker patient recovery than traditional open surgical methods.

How a minimally invasive PLIF spine surgery is performed

Incision and dilation

Two short incisions, approximately 2.5 cm. (1 in.) each, are made on either side of the middle of the lower back. A device that projects live X-ray images onto a screen, called a fluoroscope, is typically used to pinpoint the exact position on the spine where the surgery will be performed. Next, a thin wire or needle is inserted through tissues and muscle to the level of the spine on each side. Special dilators are guided down the wire to separate muscle fibers and provide access to the underlying spine without cutting through the muscles. After the initial dilators are docked on the back of the spine, larger dilators are added, gradually increasing the diameter to allow enough room for the surgical procedure on each side.

Retractor and instrument set up

A retractor device that can expand the surgical field and hold back the muscle is placed over the dilators. The dilators are removed and a lighting component is attached to illuminate the surgical field. A hex screwdriver is used to open the retractor blades, holding the soft tissue out of the way. The surgical exposure is now complete. An endoscope or microscope is then added to the edge of the retractor to provide close-up imagery on a screen to help guide the procedure.

Excision

Cutting instruments are used to remove portions of the lamina (laminectomy), and portions of facet joints (facetectomy) from the back of the vertebrae on each side. Removing bone here allows the surgeon to see the degenerating disc. A grasping instrument is used to remove most of the intervertebral disc by entering through the incisions on either side. Removing the abnormal disc relieves the pressure.

Instrumentation

Next, the vertebrae are prepared for instrumentation. A sharp awl is used to make holes in the pedicles for insertion of pedicle screws. Screws are placed through a metal plate and then into the pedicle holes, ending with the screw tips in the middle of the vertebral body. Screws and plates are placed on both sides of the spine. Two more pedicle screws are then placed through the metal plate and screwed into the lower vertebral body pedicles.

Distraction and Graft Placement

To prepare for bone graft insertion, the disc space is spread apart (distracted) by moving the vertebral bodies or applying pressure on the pedicle screws. The screws are tightened to hold the disc space in this open position. Two bone grafts are then placed between the vertebral bodies. The bone grafts allow for eventual fusion as bone grows between the vertebral bodies. In variations of this procedure, spacers, cages packed with graft material, or ground bone graft material may also be packed into the disc space to aid with the fusion.

Compression

To provide stability to the spine while the fusion occurs, the lower screws are loosened and the vertebral bodies are squeezed together (compressed). The screws are tightened in the compressed position, which allows for a tight fit of the grafts in between the vertebral bodies. Small screws called blockers are placed on the pedicle screws to lock the screws to the metal plate.