To understand lumbar spine surgery, it is important to know about low back conditions, treatment goals, and surgical techniques. But first, a basic lumbar spine anatomy lesson will help you understand the problems in your spine that are causing your lower back pain.
The lumbar spine, or low back, consists of 5 vertebrae (spinal bones) numbered L1 through L5. These vertebrae (vertebral bodies) are the largest in the spine and support the head and trunk. For example, the L5 vertebra transfers upper body weight through the sacrum and pelvis into the legs. The sacrum consists of 5 naturally fused vertebrae and provides a stable platform for the spinal column. Although the bones of sacrum are fused, they are numbered S1 through S5. The pelvis is often referred to as the hip.
Each lumbar vertebra shares a basic structure:
Between each vertebral body is an intervertebral disc. Discs are numbered according to their spinal position. For example, the L4-L5 disc is found between the fourth and fifth lumbar vertebrae. The low back discs are the spine's largest and match the kidney-shape of the vertebrae.
There are 2 parts to each disc: The outer layer consists of rings of tough, yet flexible cartilage called the annulus fibrosus. Inside the annulus is a jelly-like substance called the nucleus pulposus. The nucleus contains mostly water to help maintain hydrostatic disc pressure (balance).
Discs perform 2 important functions:
Spinal cord, cauda equina and nerves
The spinal cord is a firm, yet delicate structure of nerve tissue. It cannot be easily moved without the potential for serious neurological injury. The spinal cord ends at L1 (first lumbar vertebra).
Below L1 are nerves that make up the cauda equina, which are encased in a thick sack of fluid similar to a water balloon. Cauda equina is Latin meaning horse's tail, which is what the human cauda equina resembles. The cauda equina is somewhat flexible and may be moved slightly to gain access to the intervertebral discs during posterior (back) low back spine surgery. Spinal nerves exit the cauda equina through small holes called lateral foramina, and they control leg function and sensation.
Associated anatomical structures
The abdominal cavity sits directly in front of the lumbar spine. The intestines, major organs, and large blood vessels are positioned near the lumbar spine. These soft structures can make an anterior (front) surgical approach to the lumbar spine challenging.
The lumbar discs are tough structures, but wear and tear from normal life can cause discs to break down and lead to low back osteoarthritis (spondylosis). The degenerative process can lead to significant changes in the lumbar spine anatomy. These changes can cause low back pain or leg symptoms because of:
The degenerative process in the lumbar spine includes distinct characteristics. Some or all characteristics may be present.
Characteristic: desiccation (disc dehydration)
The first stage of degeneration occurs when the nucleus pulposus begins to lose water. This early stage is not painful and is called desiccation, which essentially means dehydration. Eventually, the affected disc loses height and hydrostatic pressure (balance) because of water loss.
Characteristic: discogenic pain
Fibers in the annulus fibrous may tear and rupture causing the onset of sudden, but persistent low back pain. Some doctors call this discogenic pain because pain originates from within the disc. Discogenic pain is also referred to as mechanical axial back pain because pain occurs when the patient is active.
Characteristic: abnormal motion
Abnormal motion occurs between vertebral bodies when a disc no longer functions as an effective shock absorber. Too much motion can make discogenic pain worse. Too much motion can also cause facet joint pain as cartilage-coated joint surfaces wear down.
Characteristic: bulging disc or ruptured disc
Remnants of an annulus fibrosus may bulge backward into the spinal canal and cause cauda equina or nerve compression. Compression of nerve structures can cause leg pain, numbness, and tingling. This is called lumbar radiculopathy. Sometimes, a disc completely ruptures (herniates) and the nucleus pulposus comes into direct contact with nerve structures.
Characteristic: bone spurs
Bone spurs (osteophytes) can develop anywhere on the vertebrae. Osteophytes can protrude into the spinal canal and foramina (nerve passageways) causing cauda equina or nerve root compression.
The purpose of low back surgery is to reduce or relieve pain and restore lumbar spine stability. Two general surgical techniques help to achieve these goals:
Lumbar decompression procedures are generally performed from the posterior (back) and include the techniques below.
Foraminotomy: When disc material and/or bone spurs press against a nerve exiting the foramen (nerve passageway), a foraminotomy may be performed. Otomy is the medical term for making an opening. A foraminotomy makes the opening of the foramen larger and relieves nerve compression.
Laminotomy and Laminectomy: To access disc material invading the spinal canal, a small opening is made in the lamina. During a laminectomy, all or part of the lamina is removed (ectomy is the medical term for removal of). A laminectomy is performed to relieve spinal cord compression or to gain access to a disc from the back. Laminectomy is often used to treat lumbar spinal stenosis, a narrowing of the spinal canal sometimes caused by arthritis.
Facetectomy: Involves a complete or partial removal of the facet joint. A facetectomy is performed to reduce nerve root compression or to gain access to disc space.
Discectomy: Surgical removal of all or part of a disc. Discectomy can be performed from the posterior (back) or front (anterior) through the abdominal cavity to reach the spine.
All the above procedures are decompression techniques. Foraminotomy and laminotomy usually do not disturb spinal stability. However, because laminectomy, facetectomy, and discectomy techniques remove something from the spine, the lumbar spine may need to be surgically stabilized. Spondylolisthesis (when a vertebra slips over the one below) often requires stabilization. The main stabilization techniques are below.
Fusion: Bonds (fuses) bones together often using bone graft or a biological substance. Fusion stops motion between 2 or more vertebrae and provides long-term spinal stabilization. During a low back fusion, adjacent vertebral bodies, facet joints, and/or lamina may be fused together.
When fusion is performed from behind (posterior), the surgeon may lay strips of bone graft from one vertebra to the one below. This is termed a posterior fusion. Sometimes, when the lamina has been removed, bone graft is placed from one transverse process to the one below. This is called a posterolateral fusion.
Surgeons have many bone graft choices including autograft, allograft, and biological substances. The use of bone substitutes reduces problems associated when taking the patient's own bone for bone graft (autograft). A bone growth stimulator may be prescribed to help spinal bone heal after a fusion procedure.
Instrumentation: Spine specific implants, called instrumentation, are regularly combined with fusion. Instrumentation includes such devices as plates, rods, screws, and interbody devices. These devices hold the spine stable until the fusion heals solid. Certain types of non-fusion devices may be utilized to treat lumbar spinal stenosis.
Sometimes a spinal decompression and fusion are performed during the same surgery. However, these procedures require evaluation on a patient-by-patient basis. Below are common low back procedures that combine spinal decompression and stabilization with fusion and instrumentation.
Anterior lumbar interbody fusion (ALIF): An ALIF is performed through the front of the spine, or around the abdominal cavity. A complete discectomy (removal of the disc) is performed. Then, interbody devices surrounded with bone graft, are implanted into the empty disc space. The devices and bone graft provide spinal stability. An anterior lumbar plate may be fixed at L5-S1 for added stability.
Sometimes additional posterior instrumentation, such as screws connected to rods or a plate, supplement an ALIF. This is called a 360 procedure because the spine is approached from the front and back.
Posterior lumbar interbody fusion (PLIF): A PLIF is performed through the back of the spine. Decompression is performed by laminectomy and discectomy. The spine is stabilized using cages or interbody spacers and bone graft. Pedicle screws connected to rods or plates are fixed to the vertebral pedicles above and below the fusion site to supplement spinal stabilization.
Transforaminal lumbar interbody fusion (TLIF): A TLIF is performed through the side of the body in which the patient has pain. A facetectomy allows access to a disc space from beneath the pedicle. Facetectomy and discectomy decompress the affected nerve, and an interbody device and bone graft fuses the spine. Pedicle screws with rods or plates provide supplemental stabilization.
Extreme lateral lumbar interbody fusion (XLIF): XLIF is a minimally invasive procedure performed through the side of the body. After discectomy, an interbody device is inserted into the empty disc space to provide spinal stabilization. Pedicle screws may be used for added stabilization.
Lumbar artificial discs: Some surgeons implant lumbar artificial discs. Careful patient selection is important because an artificial disc is not always an appropriate alternative to low back fusion. An artificial disc allows motion to continue, whereas spinal fusion stops motion.
Lumbar spine procedures are some of the most successful operations spine surgeons perform today. However, spine surgery to treat lumbar degeneration is performed only if all non-surgical treatments fail. Patients who are well selected and have the appropriate surgical procedure generally recover rapidly and return to the activities they enjoy.