Transforaminal and posterior decompressions of the lumbar spine. A comparative study of stability and intervertebral foramen area.

STUDY DESIGN: Ten fresh, cadaveric, two-vertebrae, functional spinal units were used to study the pathoanatomy, intervertebral foraminal area, and flexibility changes after posterior and transforaminal decompression. OBJECTIVES: To determine the feasibility of an endoscopic transforaminal approach as an alternative to conventional approaches, to establish the adequacy of transforaminal decompression without destabilizing the spine, and to study the structural changes in the spine after decompressions. SUMMARY OF THE BACKGROUND DATA: Posterior decompression entails major dissection and excision of bone and ligaments to access the spinal canal. Posterior decompression may be complicated by acute or chronic spinal instability, and the adequacy of lateral decompression is highly subjective. METHODS: The functional spinal units were mounted in quick-setting epoxy blocks. Pre- and postoperative computed tomography scans were taken to study changes in the foraminal area. Pre- and postoperative flexibility and anatomic studies were performed to compare the results. RESULTS: A 45.5% increase in the intervertebral foraminal area was possible, there was no flexibility change, and minimal anatomic damage to the spine was noted after transforaminal decompression. A 34.2% increase in the intervertebral foraminal area and a significant increase in extension and axial rotation flexibility were noted after the posterior decompression. CONCLUSION: Transforaminal decompression produced a significantly larger increase in the intervertebral foraminal area than posterior decompression, without increasing the range of motion or neutral zone in any direction. Because there was no violation of the anatomic integrity of the spine in the transforaminal approach, the risk of surgically induced instability was minimized. Endoscopic transforaminal decompression is a feasible alternative to current approaches.

Endoscopic transiliac approach to L5-S1 disc and foramen. A cadaver study.

STUDY DESIGN: The toros of fresh cadavers were used to create endoscopic channels through the iliac wings to gain access to the L5-S1 disc and foramen. The spine and pelvis then were dissected out en bloc, and the anatomic relationships were studied. OBJECTIVES: To determine the feasibility of a transiliac approach to the L5-S1 disc and foramen and to assess the safety of this approach by studying the anatomic relationships of the transiliac track. SUMMARY OF BACKGROUND DATA: Because of its location deep in the pelvis, the L5-S1 disc and foramen are not easily accessible via a supra-iliac portal. A laparoscopic approach violates the abdominal cavity, and makes major vessels and viscera at risk for injury. METHODS: A core drill was inserted over a guide wire into the iliac wing under fluoroscopy to obtain a core of bone, which then was removed to create a transiliac channel. An arthroscope was inserted through the channel to perform discoscopy or foraminoscopy. The spine was dissected out en bloc to study the relationships of the track. RESULTS: It was possible to use a transiliac approach to L5-S1 in all the experiments. There was no damage of neural structures in any of the experiments. CONCLUSIONS: The results of this study suggest that it is possible to access the L5-S1 disc and foramen through the ilium without injuring important structures. It would be necessary to conduct a study based on an animal model and to evaluate the results before using this procedure in a clinical situation.

Endoscopic electrode implantation. A new technique in an animal model.

The purpose of this study was 2-fold: (1) to describe a technique of creating an endoscopic interstitial working space; and (2) to describe the technique of implanting the modified double helix and the Huntington cuff electrode in the space created. Two cannulated balloons were inserted on either side of a standard arthroscope, which had been inserted to identify the target branch of the sciatic nerve. Traction was applied on each cannula after inflating the balloons with 3 to 5 cc of saline, to create a cylindrical operating space between them. After mobilizing a segment of the nerve, either of the 2 electrodes was implanted with the aid of special instruments. The results indicate that (a) it is possible to create interstitial operating spaces reliably and consistently; (b) satisfactory hemostasis can be achieved through the tamponade effect of the balloons and endoscopic cautery units; (c) excellent visualization is achievable; and (d) it is possible to implant electrodes in a reproducible manner. The interstitial spaces are portable and can be used for various procedures in most anatomic locations. Modification of the cuff electrode will be necessary to make it easier for endoscopic implantation.

Posterolateral arthroscopic discectomies of the thoracic and lumbar spine.

Posterolateral arthroscopic discoscopies were performed on the lumbar and thoracic spine of the cadaver of a 6-foot-tall man. The purpose of this study was to determine the anatomic relationships of the discotomies and to examine the feasibility of the procedure for thoracic discectomies. At most levels in the thoracic spine, the rib neck acted as a guide to the posterolateral disc and as a safeguard against penetration of the pleural cavity. The average distance from the dura to the discotomy was 0.79 cm, with this distance increasing caudally. The thoracic nerve roots were found, in general, to be at less risk of damage because of their initial posterolateral course as they entered the subcostal groove. In the lumbar spine, the average distance from discostomy to the dura was 11.5 mm. Access to the triangular working zone could be gained with angles of insertion ranging from 38 degrees to 65 degrees. At angles less than 35 degrees, there was a significant risk of nerve injury. It is concluded that some thoracic discs can be safely removed through this approach and that the lumbar ventral ramii are very vulnerable to injury because of their proximity to the annulotomy.

Endoscopic electrode implantation for enhanced stimulation of the hamstring branches of the sciatic nerve in paralyzed subjects.

Seven hamstring branches of the sciatic nerves in eight posterior thighs of four paraplegics were implanted with electrodes endoscopically. Strong initial responses were obtained in each case on continuous electrical stimulation. Three of the implants were removed immediately due to rapid decay in the response to stimulation; two had muscle power reduced to grade IV and two to grade III over 2-week period postoperatively. We believe the reduction in strength was partly due to hematoma surrounding the electrode and partly due to migration of the electrode away from the target nerves. Further work needs to be done to improve the technique and implant designs to improve results. Due to the excellent visual control it offers, this technique has the potential for accurate implantation of electrodes without massive exposures and its attendant morbidity.