In a Carl Zeiss Meditec, Inc.-sponsored webinar titled, "The role of microsurgery and navigation in minimally invasive spinal surgery," Roger Härtl, MD, of New York City Presbyterian Hospital – Weill Cornell Medicine, discussed how to combine microsurgical techniques, navigation and instrumentation technology to successfully perform MIS. He serves as a neurological surgery professor and director of spinal surgery and neurotrauma at Weill Cornell Brain & Spine Center.
The four pillars of minimally invasive surgical technique include:
1. Access strategies: percutaneous and mini-open approaches
2. Microsurgery: residents train to operate under microscope, endoscope
3. Instrumentation: collaboration with engineers for instrumentation techniques
4. Navigation: visualization of the anatomy in two-dimensional and three-dimensional views
"When we talk about minimally invasive spinal surgery, what we talk about is really an evolution of surgery that has occurred over the last decade," said Dr. Härtl.
The microscopic surgery technique involves tubular retractors, microscopes, endoscopes, three-dimensional navigation systems and implants. Carl Zeiss developed the first surgical microscope with a coaxial light system in 1953. By 1978, microsurgical discectomy gained popularity in the United States.
MIS offers various advantages over a traditional approach:
- Smaller incision
- Decreased soft-tissue damage
- Less blood loss
- Lower complication rates
- Reduced scarring
- Less post-operative pain
- Faster recovery
- Decreased length of hospital stay
The goal of MIS involves improving patient outcomes by decreasing collateral tissue damage, reducing morbidity and accelerating a functional recovery. "The basic idea of MIS surgery, especially in the lumbar spine, is to protect those muscle groups that are so important for our patients' recovery and postoperative activity," said Dr. Härtl.
Surgeons avoid muscle injury during MIS by utilizing muscle splitting self-retaining retractors, limiting the surgical corridor width and using known anatomic neurovascular and muscle planes. Dr. Härtl emphasized surgeons should avoid detaching tendons of key muscles.
MIS spinal surgery principles
Dr. Härtl believes the most important principles of spinal MIS to be contralateral decompression achieved through tubular retractors; instability minimization; and indirect decompression achieved by cages.
Contralateral decompression
Via a unilateral MIS approach, a surgeon may perform a bilateral decompression and a contralateral foraminotomy. When operating contralaterally, Dr. Härtl said the key is to rotate the table and angle the tubular retractor, keeping the ligaments and flavum in place on the contralteral side to protect the dura.
"The advantages are obvious. Instead of doing a big open laminectomy, you can do this now with a small opening unilateral approach for contralateral decompression," said Dr. Härtl. Class III evidence suggests that MIS tubular laminectomy patients experience faster recovery; enhanced perioperative clinical outcomes; and reduced hospital costs.
Dr. Härtl believes the percutaneously-inserted endoscope may find its place where the tubular retractors and microscopes fall short.
"I'm personally very excited about endoscopy and how we can integrate that," Dr. Härtl said. "It will not totally replace what we're doing now with the microscope, but I think it will add to our ability to decompress certain parts of the anatomy where we just can't get to, currently."
Minimize instability
MIS decompression has the ability to decrease iatrogenic instability and reduce the need for instrumentation and fusion.
"I think that we can avoid fusion surgery if, instead of doing an open laminectomy, we do a tubular decompression, because we leave all those ligament structures intact," said Dr. Härtl. He believes routine fusion is not indicated in all lumbar spinal stenosis patients and spondylolisthesis patients if they don't have mechanical back pain, abnormal motion inflexion or extension problems.
Dr. Härtl recommended a contralateral approach for patients with foraminal stenosis with radiculopathy as well as patients with synovial cysts. For patients with central stenosis with neurogenic claudication, Dr. Härtl recommended a right-sided approach for right-handed surgeons and a left-handed approach for left-handed surgeons. He teaches his fellows to treat unilateral disc herniation with an ipsilateral approach.
Indirect decompression
MIS permits indirect decompression of central and foraminal stenosis in some patients. Cage width impacts the success of indirect decompression in terms of foramen decompression and disc height elevation. Dr. Härtl explained lower facet tropism is associated with a greater foramen extension.
Mastering navigation
Navigation is just as critical in MIS as microsurgery techniques, as it enhances implant accuracy.
Dr. Härtl utilizes navigation during the entire surgery, including pedicle screw placement; skin incision; tubular reactor placement; decompression; cage placement; rod measurement; and final CT check.
The new generation navigation systems assist MIS goals by reducing fluoroscopy and X-ray exposure and eliminating K-wires. "I think as microsurgeons, as important as it is to master these microsurgical decompression techniques under the microscope, it is also important to navigate," said Dr. Härtl.
Listen to the webinar recording here and view the webinar slides here.