Dr. Joseph Zavatsky: 3 Thoughts on Minimally Invasive Spine Research


Joseph Zavatsky, MD, is an orthopedic spine surgeon and section chief of spine in the department of orthopedics at Ochsner Medical Center in New Orleans, where he works collaboratively with other orthopedic spine surgeons, neurosurgeons, pain management and PM&R physicians, anesthesiologists and radiologists at the new Back & Spine Center at Ochsner Baptist Hospital. He was fellowship trained at the New York University Hospital for Joint Diseases. Dr. Zavatsky's research primarily focuses on improving minimally invasive spine surgery. A majority of his patients suffer from adult degenerative deformity conditions so, through research, he strives to find the safest ways to perform these corrective procedures.

Recently, he has been involved with several different minimally invasive spine research studies. Here Dr. Zavatsky details three of those projects and how they may impact the future of spine surgery.

1. Mechanomyography neuromonitoring. Mechanomyography neuromonitoring, or MMG, is a neuromonitoring technology that is an alternative to traditional electromyogram monitoring, or EMG, that can be used during spinal procedures. During Dr. Zavatsky's study, the MMG technology, developed by Sentio, was used to monitor the lumbar plexus in 100 patients undergoing trans-psoas lateral interbody fusion procedures.

"MMG measures the mechanical movement or firing of muscles which is recorded in the leads that are placed on the extremities," he says. "Instead of using needles and measuring the electrical activity through the leads with EMG, you are measuring the acceleration of muscle contraction with MMG. It can be more sensitive and specific since it is not affected by other machines being used simultaneously in the OR like electrocautery or body warmers."

Bear Hugger body warmers and the Bovie cautery used in the operating room can often obscure the surgeons' ability to detect nerve irritation because these machines can produce artifact seen on EMG. But this electrical artifact does not affect MMG monitoring.

"With EMG there are times that you may be operating blind and unable to detect potential nerve injury because of the electrical artifact produced by the Bovie and body warmer devices,” he says. "Using MMG, we found our thigh complication rates including pain, numbness and motor weakness to be less than the reported rates of 30 to 80 percent. Although MMG needs additional investigation, our 20 percent thigh complication rates are promising.

ENT has also been experimenting with MMG technology during surgery to monitor the facial nerve, and Dr. Zavatsky's research showed it can also be successfully used in spinal procedures, particularly those that use the trans-psoas lateral approach, where the lumbar plexus is at risk.

2. Y-wire from Safewire. Dr. Zavatsky conducted a study of 20 patients undergoing minimally invasive L5-S1 transforaminal lumbar interbody fusions. Ten patients had the Y-wire placed through Jamshidi needles to percutaneously place pedicle screws, and 10 patients had standard straight guide wires utilized.

"When you tap the pedicle pilot holes and place the percutaneous pedicle screws over standard guide wires, there is a risk of advancing these wires anterior to the vertebral body especially in osteoporotic bone and at S1 where many surgeons remove the physical anterior block by tapping the distal S1 cortex for bicortical S1 screw purchase," he says. "If you inadvertently advance the guide wire anterior to the vertebral body, you place structures anterior to the spine, including the vessels and bowel, at risk."

However, the Y-wire deploys its Y-shaped tip after it exits the Jamshidi needle and prevents inadvertent advancement of the wire through poor bone and even through the hole of the distal cortex that is made with tapping S1, he says.

Dr. Zavatsky's research showed the Y-wire also increased the safety of the procedure by significantly decreasing the amount of radiation both the patient and surgeon were exposed to when compared with the traditional method of placing percutaneous pedicle screws over standard guide wires. The additional security of the Y-wire means surgeons do not need to use as much fluoroscopy while tapping or placing the pedicle screws to confirm the guide wire did not advance inadvertently. Decreased radiation is important for spine surgeons, especially those who are performing more MIS procedures, as the risk of developing cataracts and thyroid cancer could increase. Dr. Zavatsky currently wears lead-lined glasses in the operating room to decrease the risk of developing cataracts, but even physical precautions are not always enough.

"I used much more X-ray prior to using Y-wire," he says. "I used to constantly check that I wasn't advancing or pulling out the guide wire. With the Y-wire you are able to apply a constant pressure on the guide wire without fear of it advancing, so you don't have to take so many X-rays."

He and other researchers concluded that the Y-wire guide wire makes percutaneous pedicle screw placement significantly safer for everyone in the OR by reducing the amount of radiation exposure.

3. Lateral interbody fusions. This research trial evaluated the effect of optimal cage size and placement on lateral interbody fusion rates. Although previous studies have mentioned the importance of spanning the ring apophysis, the strongest part of the vertebral body endplate, these studies have used various cages without mention of their size or placement, Dr. Zavatsky says. Studies which use thin-cut CT scan, which is the radiographic gold standard to evaluate fusion, for all subjects are also limited. Additionally, some studies have even advocated under-sizing the lateral interbody cage, on the premise that you are placing a rectangular cage on circular endplates, which can result in lateral overhang of the cage.

However, the strongest portion of the endplate is at the very outer edge of vertebral body at the ring apophysis. The researching surgeons oversized the lateral cage by 5mm to ensure the strongest portion of the endplate was spanned. The theory was that there would be less subsidence resulting in increased stability thus affecting fusion rates. After performing lateral fusions on 63 levels, two independent musculoskeletal radiologists confirmed a 100 percent fusion rate by sagittal, coronal and axial thin-cut CT images on all patients.

"Reported fusion rates for laterals are typically high. But by over sizing the lateral cage to ensure ring spanning, further stability may be obtained, mitigating endplate violation by either endplate preparation or poor bone quality and thus improving fusion rates," Dr. Zavatsky says. "Over sizing the lateral cage along with posterior pedicle screw augmentation may be key factors in improving fusion rates."

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