Interbody cages are angled boxes with retentive teeth on the upper and lower surfaces to improve bone fixation reducing the possibility of dislocation and optimizing anchorage to vertebral bodies. They are used in lumbar fusion.
When is lumbar fusion indicated?
A doctor may recommend a lumbar fusion in those circumstances in which it is assumed that the main cause of back pain lies in a severely degenerated disc between two vertebrae or in a “slippage” of the vertebral bones (which is called spondylolisthesis). The sliding of the bones results in a misalignment of the spine and possible entrapment of the vertebral nerves.
There are other circumstances in which fusion may be the best treatment for back and leg pain. When referring to which discs are involved, a doctor will speak in medical jargon of the “levels involved.” A one-level fusion joins or merges the two vertebrae on each side of the affected disc. A merger of two levels unites or merges three vertebrae with the two disks involved.
Fusion is a true solid bone bridge created through surgery that joins the bones together to maintain alignment and provide stability and strength. By eliminating movement at the damaged level, pain can be calmed. A solid bone bridge eliminates the movement that would normally take place in the disc space and in the joints of the spine.
A lumbar fusion may be recommended for diagnoses such as recurrent disc herniation, spondylolisthesis, scoliosis or curvature of the spine, severe degeneration of the disc or for a traumatic spinal injury such as a fracture.
The surgical procedure
A lumbar fusion can be achieved in several ways and through different approaches to the spine. What this means for the patient is that an incision will be made in their abdominal wall, side, back, or a combination of these approaches. The surgeon will study your x-rays and determine which approach you require.
Pedicle screws versus interbody cages
The specialist will also decide whether the use of titanium screws would be beneficial. Usually, they are placed through the pedicle bone of the spine and thus allow traction of the back, middle, and frontal parts of your vertebral bones. These screws adhere to a rod or plate that follows the shape of your spine. This type of spinal instrumentation provides immediate strength to your spine during the bone fusion process.
You might also want to read: What are pedicle screws?
In other cases, a titanium cage or a bone cylinder that is screwed into the disc space can be used. This is called fusion between bodies because it is done between the bodies of the vertebrae and is done through the affected disk space. It can be performed from the front (anterior) or from the back (posterior). An approach through the abdomen can be done in a laparoscopic way through small incisions or open through a single incision.
Your surgeon can discuss with you the advantages and disadvantages of both techniques, as well as what worked best according to his own experience. Usually, these cages or metal or bone cylinders are filled with bone grafts taken from your pelvis (ileum) or coccyx (spiny processes and laminar bone). The bone graft serves as a source for bone cells to help them begin the fusion process at the surgery site. In some cases, the cages can be used along with pedicle screws.