If you’re like most of my patients, the idea of undergoing spinal implant surgery brings up a lot of questions:
- What types of spinal implants are there?
- How do they work?
- What are they made of?
- Are they safe?
Many people have heard of various types of lumbar implants but don’t have a good-enough understanding about them to feel comfortable heading into surgery. It’s also easy to get overwhelmed by the amount of information available online, and hard to know what’s important and what’s not.
This article covers the types of spinal implants and reasons why they are used. We’ll also talk briefly about safety issues with regard to lumbar implants.
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Spinal implant surgery: What is it & why would you need it?
What is a spinal implant?
A spinal implant is a medical device manufactured to help maintain stability of the spine, either by replacing a damaged component of the spine or by providing support in place of a non-functioning component.
For example, if a severely degenerating disc and facet joints have prompted a doctor to recommend back surgery, an implant will have to be used in place of these elements should they need to be removed. A BalancedBack Total Joint Replacement is one type of implant that could potentially replace those damaged components and take over their function, enabling the spine to move normally.
Why would you need spinal implant surgery?
Your spine has 24 vertebrae, each made up of a disc in the front and two facet joints in the back. All your vertebrae move together as a unit. If any part of that unit is removed or becomes dysfunctional for one reason or another, it will create spinal instability.
Common conditions that may require back surgery and an implant are:
- Severe spinal stenosis—The narrowing of the passages of the spinal cord and exiting nerves constricts these structures, which sometimes requires decompression to remove the offending material. Often, removing the bone or disc material creates spinal instability.
- Degenerative disc disease—Discs naturally wear out over time and sometimes need to be removed. Very often, however, a degenerated disc is accompanied by degenerating facet joints, which cause back and leg pain. In that case, both the disc and facet joints will have to be removed and an implant used in their place.
- Multiple recurrent herniated discs—Patients suffering from multiple recurrent herniated discs will eventually lose too much of the disc as a result of repeated microdiscectomies. A typical microdiscectomy removes approximately 15 percent of your disc; once you have lost more than 25% or 30%, you’re at risk of spinal instability and will likely need a spinal implant.
- Spondylolisthesis—The translation of one vertebral body over another is known as spondylolisthesis, a condition often associated with a high degree of instability. Patients suffering from this condition will need an implant.
- Severe facet arthropathy—Similar to degenerative disc disease, arthritic joints are sometimes accompanied by worn-out discs. The removal of one or both elements will require a spinal implant.
Types Of Spinal Implants
There are two categories of spinal implants: motion devices and fusion devices.
Motion devices are implants that replace the function of the non-working element of your spine, such as the disc, or the disc and facet joints together. These types of spinal implants preserve the natural range of movement in the spine.
A motion device is an ideal solution if you’ve already tried conservative therapies and/or a minimally invasive surgery (such as a laminectomy).
Why is preserving natural range of movement so important? Because a healthy spine moves freely. Studies have shown that when your spine loses its ability to move naturally (such as when a level of your spine is removed during a fusion), it puts greater stress on the remaining levels.1 Both of the motion devices in this category allow your spine to move as it normally would after surgery, which means your spine is more likely to be healthier, longer.
The two types of motion devices are:
In artificial disc replacement surgery, a surgeon replaces a degenerated or worn disc in the spine with a new, artificial one. The facet joints are left alone, and only the disc itself is replaced. While continued motion is a benefit of this device, it only works for a very small percentage of people.2 It’s important to understand that this procedure addresses only a degenerating disc. If you have leg pain, the beginnings of arthritis in the facet joints, pinched nerves, or spinal stenosis, you may still be in pain after the procedure. Replacing a worn disc alone won’t address any of the other factors that are contributing to your pain. Lastly, if your facets can’t move normally because of degeneration, the new ADR won’t be able to either.
The BalancedBack procedure uses a spinal implant that replaces the function of both the disc and facet joints. By replacing the function of all three structures at each level, patients continue to move naturally after surgery while fully addressing a wide range of pathologies. In fact, the BalancedBack procedure is appropriate for more than 50% of all fusion patients, compared to just 5% for ADR. BalancedBack surgeons use a posterior approach to implant the device, which allows them to address pain from the posterior structures, like arthritic facet joints and pinched nerves from spinal stenosis.
Fusion is, unfortunately, often recommended as the first course of treatment for many conditions. In reality, fusion should be a last resort.
However, in a small percentage of severe cases (such as cancer resection, a major trauma, or severe deformity), fusion is the only option. Sometimes this option is presented as a “minimally invasive fusion,” but there is only one type of fusion: that in which your vertebrae are fused together permanently, eliminating the motion segments and altering the biomechanics of the spine.
Fusion devices almost always include some sort of screw and rod fixation. During fusion, a surgeon removes the disc material and all or part of the facet joints, packs the space with bone graft, and then inserts spacers, screws, and rods into the bones to temporarily hold everything in place. Eventually the bone graft fuses, the body heals, and what were once two separate vertebrae are now joined as one solid mass of bone.
A fusion may be done using different techniques, and therefore different types of spinal implants.
- A non-instrumented in situ fusion, more commonly done in older patients, uses bone graft as a type of implant; it replaces the joint that’s being removed.
- An instrumented fusion uses bone graft and surgical implants such as screws and rods to hold the bone graft construction in place internally.
- An instrumented fusion with a cage uses a hollow spacer to provide added strength in holding the two vertebrae and bone graft in the correct position until fusion has occurred.
- Flexible spinal implants are rarely but occasionally used for spinal fusion. These spinal rods work on the theory that using hardware with less rigidity (a couple of degrees of flexibility) in the fused segment will provide stability but might also relieve some of the additional mechanical stress placed on the levels above and below it, potentially slowing down adjacent segment degeneration.3
Which spinal implant surgery is right for you?
Before delving into the details of spinal implants—titanium or stainless steel, cage or no cage, MIS or open—it’s important to make sure you’re choosing the right type of spinal implant surgery to begin with. Our Knowledge Center includes numerous resources about a variety of conditions that cause back and leg pain, many of which may be helpful to you as you research your treatment options.
1 Ren, C., Song, Y., Liu, L., & Xue, Y. (2014). Adjacent segment degeneration and disease after lumbar fusion compared with motion-preserving procedures: a meta-analysis. European Journal of Orthopaedic Surgery & Traumatology, 24(1), 245-253.
2 Gelalis, I. D., Papadopoulos, D. V., Giannoulis, D. K., Tsantes, A. G., & Korompilias, A. V. (2018). Spinal motion preservation surgery: indications and applications. European Journal of Orthopaedic Surgery & Traumatology, 28(3), 335-342.
3 Etebar, S., & Cahill, D. W. (1999). Risk factors for adjacent-segment failure following lumbar fixation with rigid instrumentation for degenerative instability. Journal of Neurosurgery: Spine, 90(2), 163-169.