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I am now the proud "owner" of an artificial disc. It's in my low back around L4. I've been told not to jump (or fall) from tall buildings or use a jackhammer 24/7. All joking aside, I understand the reason for caution. But just how durable are these devices? Could it really break if I fell on my back, for example or stepped in a hole unexpectedly and went down?
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Artificial disc replacements are gaining in popularity as studies show how well they are working. They are still used primarily for patients with degenerative disc disease, but the number and types of patients with this diagnosis who have benefited continues to expand. For example, younger patients (less than 65 years old) and younger adults with early disc degeneration from trauma or work-related repetitive motions are now getting artificial implants of this type.
Artificial disc replacements do have their own problems. Sometimes they break or migrate (move). In some cases, malposition of the implant results in uneven wear and eventual hardware failure. Bone growth around the implant is expected and helps hold the implant in place. But in some patients, ossification occurs -- so much bone growth that the implant is buried and nonfunctional.
But these complications are fairly rare and short-to-medium term studies report good-to-excellent results with patient satisfaction described by a majority of patients. What we don't know is how well would an artificial disc replacement hold up under significant trauma? This idea can be tested in the laboratory using cadavers (spinal segments preserved from humans after death). But without the dynamic effects of muscles, ligaments, and other connective or soft tissues, it's impossible to know how a traumatic force might affect the implant.
Right now, we are relying on individual patient cases to gather information on how durable these implants are under compressive or traumatic forces. There are only a handful of reports so far but here's what has been said about the effects of impact and trauma on disc replacements.
First, most fractures of the vertebra (spinal bone) have occurred because of failure of the disc, not the other way around. Improper or unbalanced placement of the implant causing uneven force on the endplate (cartilage between the disc and the vertebral body) can result in damage to the implant and fracture of the adjacent bone. Dislocation of the implant can have the same effect.
Only one case of traumatic injury in a patient with an artificial disc replacement has been reported. A 31-year-old manual laborer with an L4-5 Charité artificial disc fell off a roof and fractured his spine at the L3 level (third vertebral bone in the lumbar spine). The compressive load through the spine was powerful enough to cause the L3 vertebra to burst into tiny pieces. This injury is called a burst fracture. The fracture was unstable meaning that pieces of the fractured bone shifted, pushing into the spinal canal and pressing on the nerves. The accident occurred 10 months after the implant was put in the spine and while the patient was back to work full-time.
Fortunately, there was no evidence of damage to the artificial disc between the fourth and fifth lumbar vertebrae. The L4 and L5 vertebrae were also undamaged. In fact, the authors think that maybe the artificial disc actually protected the vertebrae above and below it. The surgeons involved in that case hope to follow this patient long-term to see how well the implant holds up and what effects the fusion the patient had above and below the implant might have on motion, biomechanics, and spinal stability.
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