What Is M6 Revision Surgery? When and Why Is It Needed?

Prof. Dr. Bertagnoli is now offering revision surgery specifically for M6-C and M6-L patients. This is a rare opportunity. The vast majority of spine surgeons will not take on M6 revision cases, the procedure is technically demanding, requires specific implant expertise, and carries complexity that most surgical teams are not equipped to manage. This article explains exactly what M6 revision surgery involves, why it has become urgently necessary for many patients, and how to determine whether you need it.

What Went Wrong With the M6 Artificial Disc?

To understand why revision is necessary, you first need to understand what is happening inside the body of patients who received an M6 implant, and why no one told them sooner.

How the M6 Was Designed, and Why That Design Is Now Failing

The Spinal Kinetics M6 was marketed as the most biomechanically advanced artificial disc available. Unlike conventional hard-endplate disc implants, the M6 used a soft polymer core made of polyurethane, surrounded by a woven polyethylene fiber annulus, a design intended to replicate the viscoelastic behavior of a natural spinal disc. In the short term, many patients did well. The device moved naturally. Symptoms improved. Surgeons were impressed.

The problem emerged over time. The polyurethane core and polyethylene fiber components are subject to mechanical wear. As the implant degrades, it sheds microscopic debris into the surrounding tissue. Polyurethane, when exposed to bone, triggers a biological response that causes osteolysis, progressive bone destruction around the implant. In some patients this is initially asymptomatic. In others, it presents as returning pain or neurological symptoms. In severe cases, it has led to implant failure, vertebral collapse, and the need for emergency surgery.

Prof. Dr. Bertagnoli long warned against elastomeric disc designs for precisely this reason. The concern was not theoretical, it was based on a deep understanding of implant biomechanics and long-term biological response. The clinical data has since confirmed those concerns at a scale no one could ignore.

The Regulatory Response

The M6-C and M6-L artificial discs are no longer being manufactured. Spinal Kinetics, which originally developed the device, was acquired by Orthofix. The manufacturer discontinued the M6-C in February 2025. Australia formally banned the use of the M6-C based on its documented failure rates. Regulatory agencies including the UK MHRA and the Australian TGA have issued hazard alerts. The manufacturer's own instructions for use have been updated multiple times to add osteolysis warnings, updates that in many markets were delayed or not communicated to patients who had already received the device.

If you have an M6-C or M6-L implant, there is no longer a manufacturer standing behind it. There are no replacement devices. The only path forward, if your implant is failing or at risk of failure, is revision surgery, and finding a surgeon who is both willing and qualified to perform it.

What Is Happening Inside a Failing M6 Implant?

The most important thing M6 patients need to understand is this: you can have significant implant breakdown occurring right now with no symptoms at all. The failure mode that is driving revision in the majority of M6 patients, osteolysis, is frequently asymptomatic until it has caused substantial damage.

Osteolysis:

Osteolysis is the central failure mechanism in M6 patients requiring revision. As the polyurethane core and polyethylene fibers of the M6 wear down over time, they release debris particles into the surrounding tissue. The body recognizes these particles as foreign material and mounts an inflammatory response. That response activates osteoclasts, the cells responsible for breaking down bone, and the result is progressive loss of the bone surrounding the implant. This is osteolysis.

In the vertebral bodies of the cervical or lumbar spine, bone loss around an implant is not a minor issue. It can destabilize the entire segment. It can cause the implant to migrate or collapse. It can create a situation where the structural integrity of the spinal column itself is compromised. In severe cases, the resulting instability can compress the spinal cord or nerve roots in ways that cannot wait for a scheduled appointment, they require emergency intervention.

Critically: MRI is unreliable for detecting osteolysis.
A CT scan with 3-dimensional reformats is the only imaging modality that accurately reveals the extent of bone loss around an M6 implant. If you have had only MRI follow-up since your M6 surgery, you may have bone loss that has never been properly evaluated.

Disc Breakdown and Core Herniation

Beyond osteolysis, the physical structure of the M6 can fail. Case reports have documented herniation of the polyurethane core through the outer sheath, a mechanical failure in which the inner material of the implant ruptures outward. In the cervical spine, this can directly compress the spinal cord or nerve roots. These events are not predictable from symptoms alone and can manifest rapidly.

Why Osteolysis Is Often Silent Until It Isn't

Multiple studies have now confirmed that osteolysis in M6 patients can be completely asymptomatic at moderate grades, and that pain scores in patients with documented bone loss are often similar to those in patients without it. This is the most dangerous aspect of M6 failure: patients feel relatively well, decline follow-up imaging, and present for the first time with a surgical emergency.

This is not a reason for alarm, it is a reason to act proactively. A CT scan will tell you what your implant looks like today. That information, reviewed by a surgeon with specific M6 revision experience, will determine whether you need monitoring, prompt revision, or urgent intervention.

What Is M6 Revision Surgery?

M6 revision surgery refers to any surgical procedure performed at the same spinal level as your M6 implant, whether that means removing the device and converting to fusion, removing and replacing with a different motion-preserving implant if anatomy allows, or surgically addressing complications that have developed around the device. It is a clinical decision driven by specific findings, not just symptoms.

Why Most Surgeons Will Not Perform M6 Revision

This needs to be stated directly: the vast majority of spine surgeons will decline to perform M6 revision surgery. This is not because it cannot be done, it is because the procedure is substantially more demanding than the original implantation, carries significant risk if performed without adequate experience, and most surgeons have little to no familiarity with M6 explantation specifically.

The anterior cervical and lumbar corridors, once operated on, are surrounded by scar tissue. The polyurethane and polyethylene components of the M6 integrate with surrounding bone in ways that differ from hard-endplate implants. The explantation technique requires specific familiarity. And in cases where osteolysis has caused significant bone loss, the reconstruction decisions, what to do once the implant is out, require intraoperative judgment that only comes from having performed this procedure repeatedly.

Prof. Dr. Bertagnoli is among a very small number of surgeons worldwide offering M6 revision to current patients. His experience with ADR surgery, implant biomechanics, and complex spinal reconstruction makes him uniquely positioned to evaluate and manage these cases.

Revision vs. Conversion to Fusion, What Is the Difference?

When patients hear "revision," many assume it means a repeat of the original surgery. In practice, it means something more specific: whatever surgical approach is required to address the failing implant and restore spinal stability.

In some patients, those where the endplates remain structurally sound, alignment is adequate, and arthroplasty candidacy criteria are still met, it may be possible to remove the M6 and replace it with a different, proven motion-preserving disc. This would be true revision to re-arthroplasty. However, given that osteolysis damages bone by definition, this option is frequently not available to patients who have delayed evaluation. In those cases, the appropriate intervention is conversion to anterior cervical discectomy and fusion (ACDF) or, in severe cases, vertebrectomy (removal of the vertebral body itself) followed by a more complex reconstruction. The choice is made based on what the anatomy reveals, both on pre-operative CT and intraoperatively once the implant is removed.

How Is the M6 Implant Removed?

Explantation of the M6 is more complex than removal of a conventional hard-endplate implant. The polyurethane core and woven fiber annulus integrate differently with surrounding bone, and in cases involving osteolysis, the surrounding anatomy is already compromised. The procedure is performed through the same anterior approach used for the original surgery, through a previously scarred surgical corridor, requiring meticulous tissue management to protect the carotid artery, jugular vein, vertebral arteries, esophagus, and trachea.

Once the implant is removed, the surgeon assesses the endplates directly. The extent of bone loss, the quality of remaining endplate bone, and the overall alignment of the spine all determine what reconstruction is performed. This assessment cannot be made with certainty from imaging alone, it requires intraoperative judgment from a surgeon who has done this before.

When Is M6 Revision Surgery Needed?

Not every M6 patient requires immediate revision. But every M6 patient requires evaluation. The indications for revision range from urgent to scheduled, depending on findings. Here is what drives the decision.

Confirmed Osteolysis on CT Imaging

Osteolysis is currently the primary driver of M6 revision. It is graded radiographically from mild bone changes to severe structural bone loss. Grades 1 and 2 may allow for monitoring with close follow-up. Grades 3 and 4, involving significant cystic bone loss or structural compromise, typically require surgical intervention. The grade is determined by CT scan, not X-ray or MRI, which is why routine CT surveillance is now mandated for all M6 patients.

Implant Subsidence

Subsidence refers to the M6 implant sinking or migrating into the adjacent vertebral bone, a consequence of the bone being unable to support the load through the implant, particularly when endplate integrity has been compromised by osteolysis or insufficient bone density. Even mild subsidence can alter spinal alignment and accelerate adjacent level degeneration. Severe subsidence can recompress neural structures and requires surgical correction.

Disc Breakdown and Core Herniation

If the outer sheath of the M6 fails and the polyurethane core herniates outward, the resulting compression of neural structures can be rapid and severe. This presentation may require urgent intervention rather than a scheduled revision. Any sudden change in neurological symptoms, rapid worsening of arm or leg function, new signs of spinal cord compression, in an M6 patient should be treated as a potential emergency and evaluated immediately.

Loss of Segmental Motion Due to Heterotopic Ossification

Heterotopic ossification (HO), abnormal bone formation around the implant, is common in M6 patients and is often concurrent with osteolysis. At lower grades, HO restricts motion progressively. At higher grades, it can create a functional fusion at the operated level while the failing implant remains in place. When HO is grade III or IV, surgical intervention to remove the abnormal bone and address the implant becomes indicated.

Return of Neurological Symptoms

Returning radiculopathy (arm or leg pain, numbness, weakness), new myelopathic symptoms (difficulty with balance, hand clumsiness, fine motor loss), or new axial pain at the operated level are all clinical reasons to pursue urgent imaging and surgical evaluation. In the context of an M6 implant, these symptoms should not be assumed to be a new, unrelated problem, they should be assumed to be implant-related until proven otherwise by a surgeon with M6 experience.

Warning Signs That Require Immediate Evaluation:

What Happens If M6 Revision Surgery Is Delayed?

The instinct to wait, to hope symptoms settle or that the problem is minor, is the most dangerous thing an M6 patient can do at this stage. Delay in the setting of a failing M6 implant carries consequences that are not recoverable.

Bone Loss That Cannot Be Rebuilt

Osteolysis is a progressive process. Bone that has been destroyed by polyurethane debris cannot be regrown. As bone loss advances, the structural options for reconstruction narrow: what begins as a straightforward conversion to ACDF becomes a vertebrectomy; what might have been a two-hour procedure becomes a five-hour one with a much longer recovery and significantly higher complication risk. Every month of delay in the setting of confirmed or suspected osteolysis represents bone loss that cannot be recovered.

Permanent Nerve and Spinal Cord Damage

When a failing implant compresses nerve roots or the spinal cord, whether from subsidence, core herniation, or osteolysis-related instability, the neurological damage that accumulates is not always reversible after surgery. Nerve roots have some capacity for recovery after decompression. The spinal cord does not. A patient who reaches revision with established myelopathic cord changes may never fully recover those functions, even after a technically perfect procedure. The window for complete neurological recovery is not indefinite, it is open now, and delay closes it.

Losing the Option to Avoid Fusion

For patients where re-arthroplasty is still possible, where the bone is intact enough to support a new motion-preserving disc, that option disappears as osteolysis advances. Once bone loss reaches Grade 3 or 4, fusion becomes the only structurally viable option. Patients who act early preserve the choice. Patients who delay lose it.

Escalating Surgical Complexity

A revision performed today, while the implant is failing but the anatomy is still manageable, is a fundamentally different procedure than a revision performed after the implant has collapsed, the vertebra has fractured, and the neural structures are acutely compromised. Surgical complexity affects not just the procedure itself but recovery time, risk of complications, and long-term functional outcome. Revision surgery is always more demanding than primary surgery, but the gap between a manageable revision and a catastrophic reconstruction widens every month of delay.

What to Expect at an M6 Revision Consultation with Prof. Dr. Bertagnoli

Prof. Dr. Bertagnoli has performed more than 10,000 artificial disc replacement procedures, holds 36 patents and co-patents in spinal devices, has trained over 3,000 surgeons from 55 countries, and is the founder of the International Society for the Advancement of Spine Surgery (ISASS). He has consulted at Mayo Clinic and Cedars-Sinai and manages the world's largest ADR database. He has long-standing expertise in exactly the kind of complex implant failure analysis and revision surgery that M6 patients now need.

A revision consultation begins with a thorough review of your original operative report, your current CT scan (with 3D reformats if not already obtained), and any available MRI and X-ray imaging. A detailed neurological examination is performed. The goal is to determine: what is the current state of the implant and surrounding bone, what are your neurological findings, and what reconstruction options exist given your specific anatomy.

The consultation results in a clear, honest assessment: whether revision is indicated now, how urgently, and what the surgical approach will look like, whether that means conversion to fusion, vertebrectomy and reconstruction, or in appropriate cases, re-arthroplasty with a proven alternative implant. You will not leave that consultation with unanswered questions.

Frequently Asked Questions

Q. I have an M6 implant and feel fine. Do I still need to be evaluated?

Ans. Yes, and this is critically important. Osteolysis is frequently asymptomatic at moderate grades. Multiple studies have shown that patients with significant bone loss around their M6 implant have pain scores similar to those without bone loss. Feeling well does not mean your implant is stable. If you have not had a CT scan since your surgery, you should arrange one immediately and have it reviewed by a surgeon with M6 revision experience.

Q. What imaging do I need before a consultation?

Ans. A CT scan with 3-dimensional reformats of the operated level is the most important study. MRI is unreliable for detecting osteolysis, it will often look normal even when significant bone loss is present. If you have only had MRI follow-up, you need a CT. Bring whatever imaging you have to the consultation; Prof. Dr. Bertagnoli's team will advise on any additional studies needed.

Q. Will I definitely need fusion, or is there a chance of keeping a disc replacement?

Ans. It depends on the state of your bone. If CT imaging shows that the endplates remain structurally intact and alignment is preserved, re-arthroplasty with a different implant may still be possible. However, if osteolysis has caused significant bone loss, fusion, including in some cases vertebrectomy, becomes the appropriate reconstruction. The final determination is made intraoperatively once the failed implant is removed and the actual bone quality is assessed directly.

Q. The M6 is no longer made, can it be replaced with another disc?

Ans. Not with another M6, the device has been discontinued. However, revision to a different, proven motion-preserving implant is a possibility for patients whose anatomy supports it. Prof. Dr. Bertagnoli works with over 31 different ADR models and will select the most appropriate device for your specific anatomy and clinical situation, if re-arthroplasty is indicated.

Q. How soon do I need to act?

Ans. That depends on your current status. If you are having progressive neurological symptoms, worsening weakness, balance problems, myelopathic signs, you should seek evaluation urgently, within days. If you are currently asymptomatic but have not had CT follow-up, you should arrange imaging within weeks, not months. If you have already had CT imaging showing osteolysis, the grade of that finding will determine urgency. Do not wait for symptoms to escalate, act now while your options are greatest.

Q. Is this surgery covered by insurance?

Ans. Prof. Dr. Bertagnoli operates as a private clinic and does not accept insurance unless the insurance company pays ahead of time. However, the clinic can provide documentation to support insurance claims and pre-approval requests. Many patients travel internationally to receive care at the clinic, and the cost, even when not covered by insurance, is frequently significantly lower than equivalent care in the United States. Please refer to the Insurance and Travel pages on the website for details.

Conclusion

If you received an M6-C or M6-L artificial disc, you are in a group of patients that requires active, informed management, regardless of how you feel today. The implant you received is no longer manufactured. Its failure mechanism, osteolysis caused by polyurethane debris, is progressive, frequently silent, and can lead to outcomes ranging from complex surgery to emergency spinal reconstruction.

Prof. Dr. Bertagnoli warned against elastomeric discs for years. His concern was clinical, not commercial. Now, as the consequences of that design are being realized in patients across the world, he is offering revision surgery to M6 patients who need it, bringing to these complex cases the rarest combination of willingness and capability.

If you have an M6 implant: get a CT scan. Have it reviewed by a surgeon who understands M6 revision surgery. Do not assume that feeling well means you are safe. The patients who recover most completely are those who acted before their anatomy forced a more difficult path. That window is open now. For M6 revision surgery performed by one of the few ADR surgeons in the world equipped to manage it, contact Prof. Dr. Bertagnoli today.