About the Procedure
Surgery time is approximately 15-30 minutes per disc. A small ¼ inch incision is made on the back to the side of the spine. Entry point is precisely calculated by fluoroscopic intraoperative measurements using a technique designed by Dr. Yeung. Sedation and local anesthesia is provided. The anesthetic will allow the patient to be comfortable during the procedure but will leave enough feeling in the nerves so the patient can actually tell when the nerve is being stimulated or when pressure is taken away from the nerve. The nerves may also be monitored during the procedure with continuous EMG and nerve conduction measurements so that changes are carefully monitored.
The instrument placement is performed under fluoroscopic guidance. A conical probe (obturator) with a side hole for palpating structures and for anesthetizing painful structures is used to dilate a path to the disc. After determining that the probe is in the safe triangular zone between the traversing and exiting spinal nerves, the disc is entered either by bluntly fenestrating the annular fibers with the probe or cutting the annulus with a trephine.
If there is an unusual amount of pain with the docking of the blunt probe on the annulus, the surgeon can opt to visualize the outer aspect of the disc before entering the disc. Anomalous nerves and branches of spinal and automonic nerves have been visualized and documented as contributing causes of back and leg pain that are currently not recognized by traditional surgeons. This area in the foraminal and extra-foraminal zone has been termed the “hidden zone” by surgeons Ian MacNab and John McCullouch. The presence of these anomalous nerves, and the ingrowth of nerves from an inflammatory membrane that forms over the sensitive disc annulus is responsible for pain that is out of proportion to what the MRI shows. This phenomenon is not yet completely understood, but good results have been obtained by identification and ablation of these nerves, and by elimination of the condition causing the inflammation.
The procedure proceeds by a cannula being passed over the blunt obturator followed by insertion of the endoscope and operating instruments. The two spinal nerves are protected by the cannula and only thepart of the disc needing surgery will be exposed to the operating instruments. The endoscope is inserted into the cannula and degenerated nucleus pulposus is visualized and selectively removed from the herniation site in the posterior portion of the disc. When treating annular tears a small amount of nuclear tissue is removed from underneath the tear. Often, some of this nuclear tissue is seen interposed within the tear preventing it from healing.
The advanced endoscope has integrated multichannel irrigation channels allowing for continuous cool saline irrigation similar to knee arthroscopy. A radio frequency electrode is used to help control bleeding, shrink the disc tissue or shrink the annulus, and ablate ingrown inflammatory/granulation tissue. Heat from the radio frequency probe may also help depopulate and ablate the pain fibers in the annulus.
Occasionally chymopapain may be recommended to assist in the removal of disc tissue when the fragment is large and narrow, has migrated beyond the reach of instruments, or to decrease the chance of recurrence. Using Chymopapain is similar to using a solvent to help remove rubbery and hardened pieces of gum. Chymopapain can also alter the remaining nucleus pulposus by making it less chemically or mechanically irritating to the adjacent sensitized spinal nerves.
A “biportal” approach is needed which adds one small incision on both sides of the spine. This allows the surgeon to visualize his instruments inside the disc when the size of the instrument is too large to use within the operating scope.
Sometimes disc fragments are identified outside the confines of the annulus. If the fragment cannot be completely extracted with the endoscopic instruments, a subsequent surgical procedure using the traditional posterior approach may be necessary. Occasionally, a second endoscopic procedure is recommended when a missed fragment is left behind. This happens about 10% of the time if there is a sequestered fragment. Advanced endoscopic techniques will also allow the experienced endoscopic spine surgeon the ability to routinely visualize the exiting nerve root, a nerve that is rarely visualized by traditional spine surgeons when they remove herniated discs. Lateral or foraminal stenosis contributing to back pain and can also be documented and surgically treated at the same time.
The procedure is performed in an outpatient setting. No hospitalization is needed.