If you're considering having a spine fusion, you will want to know about the results of these 2 recent studies.
A fusion surgery is pretty unique, because the fusion has to grow after the surgery is complete. For this to happen, over time new bone needs to grow across the fusion site—replacing the joint complex with one solid bony bridge—in order to stop the motion at that level.
Learn more: Elements of a Spine Fusion
So the question is, how can the type of implant used in the spine help—or hinder—this bone fusion? Or, more urgently, can the implant material itself cause new problems in your body?
2 new studies indicate that implant choice is vital
The following studies reveal the unique risks and benefits of specific implant materials and how they're incorporated into the body:
- Titanium has been shown to help with bone growth.
In a study that compared titanium implants versus plastic (PEEK) implants, the titanium implants created a response in the surrounding bone cells that helped stimulate the bone growth needed for a fusion. The titanium implants used in the study were the Endoskeleton brand, made entirely of titanium with surface etching.
In the same study, the plastic, or PEEK, implant was shown to create an inflammatory environment around the fusion site that was thought to actually hinder the fusion process.1
- Surface-etched solid titanium does not come off; titanium sprayed onto an implant does.
This study investigated the use of PEEK implants coated with titanium, called titanium plasma spray, or TPS for short, compared with implants made entirely of titanium with a surface etching.2
The goal of spraying titanium to coat a plastic implant is based on the idea (described above) that titanium enhances bone growth, which in turn improves the fusion. However, this study showed that titanium plasma spray delaminates, or comes off, when the surgeon hammers it into place in the spine. In the study, titanium that is solid and surface etched does not delaminate.
The study was small (N=6), but simulated the amount of force typically used by a surgeon when hammering the implant into the disc space between the vertebrae.
There are significant potential risks of small titanium particles coming off inside the body. In the study, more than half of all particles that came off were of a size range that allows phagocytosis. Simply put, phagocytosis is a process whereby the body's cells try to eat, or digest, a foreign object to get rid of it. The way the cells digest things is by producing acid, but because they are unable to digest the titanium, the cells actually end up digesting themselves. When this happens, the acid from the cells is released into the body and—over time—causes the bone in the area to deteriorate (called osteolysis).
This process of bone deterioration is very slow and evolves over a number of years, but the risks are significant: The implant may come loose, and/or a second surgery may be needed to remove the titanium particles from the body to stop the process of bone loss.
The bottom line from these 2 studies is that titanium as a material produces a cellular reaction that results in a firm anchorage of bone cells to a medical device, which makes for a better fusion success rate; however, if the titanium is sprayed on to a plastic device some of the particles may come off and cause additional risks.
If you're considering a spine fusion, what does this mean for you?
For a fusion to successfully set up, new bone needs to grow across the fusion site—replacing the joint complex with one solid bony bridge—in order to stop the motion at that level. So what does this mean for patients?
Anyone planning on having a spine fusion would be well-served to talk with the surgeon about the type of implant that will be used, and to ask how the implant will help promote a solid, robust fusion.
Examples of questions you might consider asking your surgeon:
- What type of implant will be used if I have a fusion?
- What is the rate of nonunion (lack of a solid fusion) with that implant?
- What is the rate of re-operation with that implant—how often does a patient have to have a new surgery to revise the fusion?
- If you or someone in your family were to have a fusion, would you recommend this implant?
- May I see the "Indications for Use" labeling that comes with the device you are recommending? Is there a warning that the device could be damaged if it is inserted under excessive force? This type of labeling may reflect a concern that some of the titanium coating could come off.
These studies provide new knowledge about the role of the implant material used in a spine fusion. If you want, you can also print up these studies (links given in the references below) to discuss them with your surgeon.
- Olivares-Navarrete, R., Hyzy, S.L., Slosar, P.J., Schneider, J.M., Schwartz, Z., and Boyan, B.D. (2015). Implant materials generate different peri-implant inflammatory factors: PEEK promotes fibrosis and micro-textured titanium promotes osteogenic factors. Spine, Volume 40, Issue 6, 399–404. http://journals.lww.com/spinejournal/Abstract/2015/03150/Implant_Materials_Generate_Different_Peri_implant.12.aspx. Accessed April 7, 2015.
- Kienle, A., Graf, N., Wilke, H. Does impaction of titanium-coated interbody fusion cages into the disc space cause wear debris and/or delamination? Spine J. [In Press]. http://www.ncbi.nlm.nih.gov/pubmed/26409208. Accessed November 18, 2015.