A new era in spinal fusion: 3 surgeons weigh in on the emergence of osteoimmunology and bone graft technology

In collaboration with Kuros Biosciences -  

Over the past few decades, rates of spinal fusions have steadily risen. However, pseudarthrosis rates— an indicator of unsuccessful spinal fusion — have not improved enough in the past 20 years to reduce the overall non-unions. With a growing number of spinal fusions, a constant pseudarthrosis rate means that each year there are more non-unions, many of which require revision surgery.

The current rate of pseudarthrosis means U.S. patients experience approximately 149,000 non-unions each year. Among these non-unions, about 92,000 require revision surgery, which has negative implications for patients, provider organizations, surgeons and payers. Patients experience longer rehab times, surgeons’ performance metrics decline, and payers and providers have to flip the bill for these additional procedures.

As the number of spinal fusions continue to rise, it’s important for healthcare organizations to ensure these procedures evolve in a way that is clinically beneficial to patients — the status quo is simply not good enough. With a myriad of innovative technology available to help improve spine surgery, surgeons and administrators have to decide which solution is best positioned to improve fusion quality?

To better understand how innovative leaders are answering this question, Becker’s Spine Review recently spoke with three leading spine surgeons:

• Alpesh Patel, MD, Co-Director for Northwestern Center for Spine Health, Professor of Neurosurgery and Orthopedic Surgery at Northwestern Feinberg School of Medicine in Chicago
• Ernest Braxton, MD, Partner at Vail-Summit Orthopaedics & Neurosurgery in Vail Colorado
• Joseph Osorio, MD, PhD, Director of Spinal Oncology and Deformity Surgery and Assistant Professor of Surgery at UC San Diego Health

The following article is based on the experiences of these three surgeons.

The path to better fusions
Currently, spine surgeons who want to improve fusions have several approaches to consider: New methods of patient selection, further surgical education and training, and the integration of emerging technologies and disciplines like osteoimmunology and bone grafts that can modulate human immune response.

All three surgeons interviewed by Becker’s expressed a similar focus on osteoimmunology and bone graft technology. For this reason, each are acutely aware of the FDA-cleared MagnetOsTM, biphasic calcium phosphate bone graft from Kuros and its promising results in spinal fusions. MagnetOs is capable of polarizing macrophages from the M1 pro-inflammatory to the M2 pro-healing phenotype. It stimulates bone growth even in soft tissue due to its NeedleGripTM surface technology.

For years, spine surgeons have been aware the immune system can influence the way a bone heals and the spine fuses. "The immune system can work against you in spine surgery — that is very apparent," Dr. Braxton said. "What we’re discovering now is that the immune system can actually work for you to help with healing and to accelerate a more stable construct."

How spine surgeons view the immune system in relation to their work is changing. The emerging field of osteoimmunology explores the link between the immune and skeletal systems.

Dr. Patel offered several examples of situations where the immune system and skeletal system interact. "Where the immune system is suppressed because of medical issues, like diabetes or patients on chronic steroids for medical issues like rheumatoid arthritis, we know that their skeletal system is pretty severely impacted from those conditions, both at baseline and even more so after surgery. These patients have a high rate of non-union implant failure. These examples paint a pretty good picture of how the immune system and the skeletal system interact with each other."

As an adult spinal deformity surgeon, Dr. Osorio is well aware of the links between the immune and skeletal systems. He said there is evidence that medications such as steroids, nonsteroidal anti-inflammatory drugs and disease-modifying antirheumatic drugs augment patients’ immune response. "All these medications will blunt the immune system, and we know from the literature that patients don’t fuse as well when they are taking these medications," he said. "In my mind, that’s really the reason why we’ve had this explosion in the field of osteoimmunology."

Dr. Braxton offered a succinct summary of the interplay between the immune system and the skeletal system. "We know that the immune system plays a pivotal role in healing. In fact, bone healing is really fusion," he said.

Dr. Patel said the spine surgery field is at an inflection point in terms of integrating biologic products, such as Kuros’ MagnetOs, to help benefit patients.

Harnessing the immune system = more predictable spine fusion healing
Dr. Patel said that early in his training, 15 or so years ago, spine surgeons didn’t spend much time thinking about linkages between the immune and skeletal system. The prevailing view was, "We can overpower the immune system."

The perspective offered by Dr. Osorio was that any linkage between the immune and skeletal systems was viewed as a "negative effect" from the various medications that affected the immune system, because the blunting of the immune system was detrimental to bone formation and healing.

In fact, as part of their preoperative planning in advance of a spine fusion procedure, these surgeons look carefully at a patient’s overall health and prescribed medications. If a patient’s immune system is modulated by chemotherapy or radiation, a fusion is unlikely to be attempted; if a patient has diabetes and their hemoglobin A1C is greater than 7.5, the surgery may be postponed.

However, in addition to paying much more attention to how the immune system could negatively affect spinal fusion, these leading spine surgeons are now leveraging the immune system to aid in the healing process. "Ultimately, I think we can make the immune system our ally to elicit a faster healing response and improve our outcomes in spine fusion," Dr. Braxton said.

Dr. Patel described this mindset shift as moving from a focus on "overpowering the immune system" to "augmenting the biology" and "harnessing the immune system" to help patients heal faster.

The emergence of innovative bone grafts
In the last few years, Dr. Patel has seen increased market adoption of concepts around surface technology and implants where the surface technology can drive a host bone response. "The fact that surface technology can drive a host bone response," Dr. Patel said, "that’s pretty well accepted now." Dr. Osorio concurred. "The field has embraced this concept of surface technology and to the macrophage response that really promotes bone formation."

There is also increased attention paid to the idea of immunomodulation, which is the mechanism by which an agent suppresses or stimulates the immune response.

Dr. Patel continued by raising a question he believes many spine surgeons are now contemplating: "Is there a way to take advantage of that same surface technology effect in bone grafts?"

Dr. Patel sees the moment as "an opportunity to look at a bone graft not just as an osteoconductive scaffold, but as something that can be an active player in the fusion process." 

According to clinical research, bone grafts are a highly effective way to maximize fusion rates, outperforming additional surgical training and improved techniques in the clinical setting. Leveraging the most effective bone grafts, such as those that modulate human immune response, can improve fusion outcomes by up to 60 percent. 

The next evolution in spinal fusion — Biologics
Dr. Braxton sees the role of implants as stabilizing the spine, but noted, "Ultimately there needs to be a biological solution, which is a fusion between spinal elements."

Dr. Osorio agreed. "I’m focusing a lot on surface technology and that goes hand-in-hand with biologics." These surgeons are encouraged by MagnetOs’ proven ability to modulate human immune response. 

According to Dr. Braxton, there is great value in bone graft technologies that are faster, safer and easier to use, improve outcomes and are less costly. They also result in less pain, shorter hospital stays and less use of narcotics. In addition, he sees the potential of Kuros’ MagnetOs to result in fewer revision surgeries, which will save costs.

From Dr. Osorio’s perspective, most spine surgeons already have a fairly good understanding of surface technology, but he sees less knowledge about bone grafts. These surgeons are optimistic about the future of surface technologies and particularly bone grafts. "The science behind this product [MagnetOs] is going to lead us into some really cool places," Dr. Patel said. Getting to these cool places will be aided by use of NeedleGrip, which is Kuros Biosciences’ unique sub- micron needle-shaped surface.

"This concept of osteoimmunology will feel like a new idea, but it’s really the evolution of a number of ideas that have existed in spine surgery for years in terms of the interplay between host biology and bone healing," Dr. Patel said. "These are concepts that already exist and have been well adopted by many surgeons." He concluded, "This is that next natural evolution to marry those concepts together to get better bone healing, better fusion rates for our patients. It seems like a brand-new concept, but it’s really just the next evolution." 

Among all of the steps that spine surgeons can take right now to improve fusions, selecting innovative bone graft technology may be the most important.

Disclaimer: The views, opinions and positions expressed by surgeons in this article are those of the surgeon alone and do not represent those of Kuros Biosciences. In the US, MagnetOs is cleared for standalone use in the extremities and as an autograft extender in posterolateral spine. MagnetOs is not cleared by FDA as an osteoinductive bone graft. Please refer to the product instructions for use for a full list of indications, contraindications, warnings, and precautions.

This article was sponsored by Kuros Biosciences.


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