For much of the past two decades, the trajectory of minimally invasive spine surgery was easy to understand: Take operations once performed through large exposures and find a way to do them through smaller ones.
Gregory Mundis Jr., MD, helped push that idea into some of spine surgery’s biggest cases. The first successes came in one- and two-level procedures. Then surgeons began applying the same principles to adult spinal deformity, where operations could last eight to 12 hours, involve substantial blood loss and carry high complication and revision rates. They found ways to do more through less disruptive approaches.
Eventually, Dr. Mundis began wondering whether they were asking the wrong question. “If you fuse someone 10 levels, then no matter what, after surgery those patients are super stiff,” he told Becker’s. “The outcome really hasn’t changed much at all.”
Dr. Mundis, co-director of the San Diego Spine Fellowship Program who practices complex adult and pediatric spine surgery at Scripps Green Hospital and Rady Children’s Hospital in San Diego, does not doubt what minimally invasive techniques can accomplish. Surgeons have demonstrated that.
The next advance, he argues, may be less about proving surgeons can perform increasingly large reconstructions through smaller incisions and more about identifying which patients never needed the large reconstruction in the first place. That may prove to be a more consequential form of minimally invasive surgery.
When doing more was the breakthrough
Minimally invasive spine surgery began with comparatively modest ambitions. One-level fusions, decompressions and laminectomies could once mean substantial tissue disruption, blood loss and longer recoveries. New lateral, anterior and posterior approaches began changing that in the early 2000s.
Today, Dr. Mundis estimates roughly 95% of one- and two-level procedures can be performed minimally invasively.
Success there invited a harder experiment. A group of surgeons, including Dr. Mundis, began applying those techniques to adult spinal deformity. They combined anterior and lateral approaches with percutaneous posterior fixation, sometimes splitting the reconstruction across multiple days.
“We felt like there had to be a better way,” he said. Some measures improved. Blood loss fell compared with traditional open surgery.
Other advantages were less clear: Dr. Mundis said complication rates appeared relatively similar, and hospital stays could be comparable because many of the minimally invasive operations were staged. Still, the work pushed the technical limits of what surgeons could accomplish without a conventional open exposure.
Then the field reached what Dr. Mundis describes as a “fork in the road.”
For some of the most complex deformities, he believes open surgery remains the better operation. For another group of patients, the more interesting advance is not performing the same reconstruction differently. It is realizing they may not need the reconstruction at all.
A big deformity does not always require a big operation
That change starts with diagnosis. Dr. Mundis increasingly combines conventional imaging and conversations with patients with tools such as SPECT/CT to better isolate the source of pain.
A patient can have substantial deformity on imaging while symptoms appear to originate from a much smaller part of the spine. When the clinical picture and imaging converge at one or two levels, a targeted operation may be enough.
“I think we’re better at diagnosing and learning which patients are amenable to less invasive techniques than we were before,” he said. That is a different kind of surgical precision.
“If your back pain and nerve symptoms point to the same area, we may be able to treat just one or two levels,” Dr. Mundis said. The benefit is not abstract. Less tissue disruption can mean faster return of muscle function, shorter recovery and, for some patients, discharge without spending a night in the hospital.
For patients, Dr. Mundis said, that early recovery matters enormously. Surgeons and researchers may think in terms of outcomes years later. Someone living with debilitating symptoms is more likely to wonder how soon life will feel normal again.
A 14-level fusion through small incisions is still a 14-level fusion
That is where Dr. Mundis’ definition of minimally invasive surgery becomes more demanding. He considers one- to three-level surgery a sweet spot. Once reconstruction stretches beyond that, incision size tells less of the story.
Dr. Mundis knows how far the technique can be pushed. He has performed three-column osteotomies and vertebral column resections through small incisions. But the experience also clarified something for him. Removing a large amount of bone is still removing a large amount of bone.
“At some point, it’s no longer minimally invasive, just by definition of the work that has to be done,” he said.
A surgeon may be technically capable of performing a 10- or 14-level reconstruction through smaller approaches. Dr. Mundis questions whether that makes the operation itself minimally invasive.
“I don’t think the limit is necessarily the technique,” he said. “I think the limit is how we view surgery.”
For him, minimally invasive should describe more than the route into the spine. It should mean less tissue damage, greater motion preservation and fewer spinal segments being stiffened. “The more you fuse, in my mind, the less minimally invasive it actually is,” he said.
A definition that refuses to stay still
Spine surgeons have been arguing over what “minimally invasive” means for years. Dr. Mundis was barely into practice when he joined a group of minimally invasive spine surgeons in Chicago in 2010 to tackle the question. The group developed a definition that was later published.
More than a decade later, he recently watched that definition appear again during presentations at the Society for Minimally Invasive Spine Surgery meeting.
The debate is still going. He likes that. “It is a moving target, and it should be because we should be becoming less invasive,” Dr. Mundis said.
If the field is progressing, he argues, an operation that represented minimally invasive surgery more than a decade ago should not necessarily qualify as its highest standard today.
That changes the purpose of the debate. Failure to settle permanently on a definition is not necessarily evidence of confusion. It can also mean the threshold keeps rising.
“We should be pushing the limits on it as best we can,” he said.
The surgeon becomes the architect
Doing less surgery does not necessarily mean doing less work. Increasingly, some of the hardest work happens before the patient reaches the operating room.
“I used to say that the artistry of what we do is in the operating room,” Dr. Mundis said. “Right now, I think it’s shifting.” Surgeons can plan alignment before an operation with tools that were unavailable five or 10 years ago. Patient-specific implants and other technologies can then help translate that plan into the operating room.
Dr. Mundis thinks of the surgeon as an architect first and a builder second. “The artistry of what we do is happening before surgery, when we’re planning, designing and creating,” he said. “We’re the architects.”
Once surgery begins, execution follows the blueprint. That places an unusual burden on a field surrounded by increasingly sophisticated technology. Better tools can make the plan easier to execute. They cannot decide what the plan should be.
“Asking an implant, a screw or a cage to do the work is like asking something with an IQ of zero,” he said. “Those implants don’t have an IQ. You do.”
For all the attention paid to surgical approach, Dr. Mundis considers alignment more important. A less disruptive operation that leaves a patient poorly aligned has missed the larger goal.
Technology can help surgeons execute with greater precision. It cannot relieve them of judgment.
What progress would look like in 10 years
When Dr. Mundis imagines adult deformity surgery a decade from now, he does not start with an operation that has yet to become minimally invasive. He starts with an operation he hopes surgeons perform less often.
“My hope is that we see the need for revision spine surgery precipitously drop as our field grows and evolves to realize the importance of alignment,” he said.
That future depends partly on what happens much earlier: better planning, better alignment and better decisions about one-, two- and three-level procedures before patients ever reach the point of needing a major reconstruction.
It also requires a generation of surgeons willing to think beyond the technique in which they were trained. Dr. Mundis has a message for them.
“Be great at your craft of being a spine surgeon more than being a great technician of one particular technique,” he said.
He wants young surgeons to approach every fusion as an intellectual exercise before it becomes a technical one: study the patient, plan the alignment and understand the consequences of what they are changing.
If the field gets better at that work, its biggest achievement in minimally invasive surgery may be difficult to see. There will be no smaller incision to point to. No new approach required to perform an enormous reconstruction. There may simply be fewer patients who need one.
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