Full Endoscopic Trans-Kambin Trans-SAP Lumber Interbody Fusion with Expandable Cage: Our Technique with Rectangular Dilator and Experience with 32 Cases

Abstract

Techniques in spine surgery have changed, with Endoscopic spine surgery (ESS) becoming a major surgical technique. ESS has advantages such as less soft tissue dissection and no collateral tissue damage, reduced blood loss, less epidural scarring, reduced hospital stay, and earlier functional recovery, Despite these advantages, endoscopic procedures have been a steep learning curve and  is   constantly evolving . Endoscopic interbody fusion is a highly effective technique for treating a variety of disorders of lumbar spine. Because the technique involves disc removal, cage placement, interbody height restoration, and intersegmental fusion, numerous pathologies can be treated, including segmental instability, mild deformity, and vertical foraminal stenosis. However, certain modifications are necessary when using endoscopic approach. Most critically, since the access is through Kambin’s triangle, care must be taken to avoid injury to the exiting nerve root. In addition, because  the facet removal is incomplete, the use of expandable interbody cage is generally necessary. The operating room setup typically involves a single fluoroscopic machine. An Anteroposterior (AP) endplate view of the caudal index-level vertebral body is obtained showing the endplate as a single line on fluoroscopy, and the spinous process precisely centered. For Transforaminal endoscopic lumbar interbody Fusion, the approach corridor is typically in the plane of the disc in order to reach the contralateral side as well as to place the cage appropriately. The skin incision is planned 8 to 10 cms off midline along the projection of the index-level disc space. The distance to the midline is influenced by several factors including the size of the patient, size of the facet joint, and the spinal segment treated. A 12mm transverse skin incision using a no.11 blade is made and an 12-G Tomshidi needle is advanced into the Kambin’s triangle. In cases of overgrown facet joints or small foramen, a trans-superior articular process (trans-SAP) corridor may be utilized to gain access to the foraminal annular window. Advancing successive dilators over the needle/guidewire system allows for final port of 8-10 mm in diameter. Ports of larger diameter can also be used, but it increases the risk of impingement of the dorsal root ganglion of the exiting nerve root.In the setting of an interbody fusion, the patient benefits from the effects of indirect decompression. Restoring interbody disc space height can achieve both central canal decompression and bilateral neuroforaminal decompression in select cases. This beneficial effect is particularly seen in patients with spondylolisthesis. Because one of the major goals of the procedure is achieving a successful arthrodesis, the preparation of the graft site is critical. To assist with adequate disc clearance, we utilize specialized tools like disc shaver, curettes and steel brushes. We typically restore the disc height using a specially designed rectangular dilator. The endplate preparation can be inspected directly using the endoscope. After preparation of the disc space, we insert osteobilogics and intervertebral expandable cage device. The use of expandable cages can also enhance interbody height restoration and allow for the most efficient indirect decompression. Percutaneous screw placement is followed by sub-muscular rod passage to create a screw-rod construct to enhance stabilization and facilitate arthrodesis. 32 followed-up patients is given in table-1. There were 20 males and 12 females. The average age of the patients is 51 years and the mean duration of symptoms was 25.22 months. 14 patients had degenerative Grade-1 spondylolisthesis and 18 had prolapsed disc with segment instability or severe narrowing of disc space, 2 out of which had 2 level involvement. The pre-operative VAS of 6.78 decreased to 0.83 at 2 years follow-up which is statistically significant (P<0.05). The mean pre-operative ODI score decreased from 42.27 to 10.66 at 2 years follow-up which again is statistically significant (P<0.05) .Our study shows that when combined with posterior stabilization using percutaneous pedicle screws and rods, it is stable enough in avoiding intervertebral collapse and screw failure. Limitation of our study can be the smaller study group size, no control group. The rectangular dilator further facilitates the cage insertion safely without enlarging the skin incision. This technique has several advantages over the standard open or MIS techniques including paraspinal muscle trauma, better intra-operative visualization and end plate preparation, lower risk of nerve root injury, decreased blood loss, shorter ambulatory time and hospital stay and better patient acceptance. Because of constantly evolving and steep learning curve, endoscopic- Fusion is still a challenging procedure. Further scope in improvements and development of instrumentation and cage design is definitely there in future.

Keywords: Endoscopic, Trans-SAP, Lumber Interbody Fusion