Success rates for conventional open discectomy for lumbar disc herniation range from 75 to 100%.[2
] The outcomes of lumbar discectomy do not seem to be affected by the introduction of the microscope and depend on patient selection rather than surgical technique.[21
] From the point of avoidance or reduction of traumatic injury to spinal canal structures, endoscopic surgery may be an option for treating lumbar disc herniation. A patient's preoperative functioning is attained to a high extent and rehabilitative programs are not needed after surgery.[7
] Additionally, there is no surgery related deterioration of existing symptoms in the epidural and intra-disc procedure.[28
] Associated medical diseases do not increase the morbidity.
Yeung and Tsou[39
] have improved the percutaneous transforaminal endoscopic technique by using the principles of targeted fragmentectomy under LA with the introduction of high-resolution working channel endoscopes, lasers, and RF bipolar flexible probes. The technique is now more versatile after improvements have been made in the endoscopic system and surgical technique. There are several anatomical peculiarities at the L5–S1 level that hinder the transforaminal approach to the L5–S1 disc space, including facet joints overlapping the disc space cephalocaudally and laterally. The transverse process at the L5 level is larger than in the upper lumbar spine. Ebraheim et al
] have found that the intertransverse space was the narrowest at the L5–S1 level (average, 13.4 mm ± 4.1 mm), compared with an average of 24 mm ± 3 mm at all the other lumbar intertransverse spaces in cadaveric dissection. All the above-described anatomical peculiarities with high iliac wing hinder transforaminal access to the L5–S1 disc space. Although many different techniques have evolved to overcome these problems,[1
] it is still difficult to access the migrated disc and centrally located disc herniation.
Ebraheim et al
] found the interlaminar distance to be the greatest at L5–S1 level and the width of the interlaminar space was also a maximum of 31 mm (range, 21–40 mm). In the coronal plane, the L5 lamina is not directed vertically as the upper lumbar lamina, and it has a backward and downward angulation. This anatomical peculiarity helps to access the interlaminar space of the spinal canal at the L5–S1 level if the trajectory of the endoscope is 5°–10° in the craniocaudal direction. The spinal canal at the L5–S1 level contains the thecal sac with only the sacral roots, and the proportion of free space at the L5–S1 level is also greater. The S1 root exits at the L5–S1 disc space with an average 22° (range, 18°–26°) of take-off angle, and it is possible to access the herniation in the axilla of the S1 root within this angle.[5
] In cases of a posterolateral herniated L5–S1 disc, the nerve root is displaced and this creates more space for entry because of the mass effect. Irrespective of the location in the shoulder or axilla areas, the mass effect of a herniated disc always has the same displaced vector to the nerve root.
The ligamentum flavum forms a tented recess with the apex in the midline and just inferior to the inferior edge of the cephalic lamina. The depth of this recess up to the dura measures 3–4 mm and is usually occupied by epidural fat.[24
] This depth may be partly obliterated in cases of a disc prolapsed in the canal. This recess forms the working space for the entry of the endoscopic in an interlaminar lumbar discectomy. Peridural fibrosis is the direct consequence of intrusion into the spinal canal with a break of this effective barrier.[4
] The epidural fat, which acts as a lubricant, is largely preserved. Postoperative MRI revealed no scar in the access area and only slight scarring in the spinal canal. The revision procedures, unlike those following conventional procedures, were no more difficult and did not require a longer operative time.[4
In cases with a large annular defect, the posterior third of the intra-disc nucleus should be cleaned to prevent recurrence. Because of the difference in level between the interlaminar window and the intervetebral disc space, resection of the intra-discal nucleus is frequently limited.[14
] This might explain the shorter time period of recurrent disc herniation. The new endoscope with its 4.1 mm working channel and corresponding instruments has largely overcome the technical problems associated with previous devices.[30
] The following advantages are gained from this surgical technique and endoscopic system: 1) good illumination and expanded field of vision with 25° optics; 2) cost effectiveness due to shorter hospital stay and reduced anatomical trauma; 3) reduced bleeding; 4) facilitation of revision surgery; 5) no need for postoperative rehabilitation; and 6) a high degree of patient satisfaction. The disadvantages of this technique are the steep learning curve and the expense of the equipment.
The clinical results of this prospective study are comparable to those obtained with conventional procedures. Although a case of injury to the dura and nerve root occurred in GA group, we have not shown a definite difference in outcomes for VAS and ODI scores between LA and GA . Both the anesthetic techniques applied in endoscopic interlaminar lumbar discectomy at L5–S1 level achieved good outcomes and high patient satisfaction, but LA was associated with significantly shorter hospital stay. The patients in the LA group usually felt discomfort in the low back and leg during intraoperative manipulation of the dural sac and nerve root, but they tolerated the procedure well under mild conscious sedation with pethidine (25–50 mg intramuscularly) and fentanyl (1–2 ml intravenously) . To prevent over irritation of dural sac and nerve root, we sometimes kept the working sheath out of the incision window of ligamentum flavum and extracted the protruding disc with disc forceps. Fewer transient postoperative dysesthesia occurred in the LA group (13.7%) than in the GA group (24%). The most important contribution of using LA is that we can get continuous feedback from the patient to prevent excessive neural manipulation or damage and help to monitor clinical improvement during the operation.
We compared performing the surgery with LA and GA because of the different problems that would potentially be encountered during surgery. The avoidance of intraoperative nerve injury might be easier due to intraoperative feedback from patients under LA, but it is relatively difficult to use the working sheath as a nerve hook and the joystick principle to search for and remove the protruding disc due to patient's feeling discomfort. However, the technique can be mastered by an experienced surgeon. In contrast, GA affords freedom from discomfort, and allows manipulation of the instruments and retraction of the dural sac and nerve root in the spinal canal, but does not allow patient's feedback. The majority of protruded disc was through the axilla area in the LA group and it was usually approached via the shoulder area in the GA group.
We conclude that endoscopic interlaminar discectomy at the L5–S1 level is an effective operation, regardless of which method of anesthesia is used. Both the anesthetic methods achieved good outcomes and high patient satisfaction. LA is associated with significantly shorter hospital stay and fewer transient postoperative dysesthesia due to continuous patient's feedback and helps to monitor clinical improvement during surgery. In our opinion, the LA is preferred than the GA in percutaneous endoscopic lumbar discectomysurgery.