Lumbar spinal stenosis is one of the common diseases causing back and leg pain, which seriously affects the patient’s daily life and ability to work. Lumbar spinal stenosis includes central spinal stenosis and lateral saphenous stenosis and lateral saphenous stenosis, and complete decompression and release of the compressed nerve roots is the main goal of treatment. The most commonly used traditional surgical method is posterior open spinal canal decompression-plasty. Although the decompression is adequate, it is highly traumatic, with extensive muscle and soft tissue stripping and bleeding, and the destruction of the posterior spinal column structure is prone to postoperative secondary spinal instability, while postoperative hematoma scar formation will lead to poor efficacy, resulting in unsatisfactory medium- and long-term outcomes. With the development of minimally invasive surgery, the use of endoscopic surgery in spine surgery is increasing, and minimally invasive decompression surgery is increasingly valued by spine surgeons at home and abroad because of its ability to meet the need for adequate decompression while minimizing the damage caused by surgery and maximizing postoperative spinal biomechanical stability. Microendoscopic discectomy (MED) has been successfully applied in the treatment of LDH, which has the advantages of less trauma, less tissue damage, faster recovery, clearer field, and the same efficacy as conventional open surgery, and then the METRx surgical system has been extended for the treatment of lumbar spinal stenosis. The purpose of the METRx system is to ensure the effectiveness of the decompression procedure while minimizing the trauma of the operation, maintaining the postoperative mechanical stability of the lumbar spine, and reducing the postoperative complications associated with the procedure, especially through unilateral access for bilateral decompression of the spinal canal.
Case selection and preoperative preparation for unilateral approach to MEDL
The rational choice of surgical indications is very important for achieving satisfactory postoperative results. To perform bilateral spinal canal decompression by unilateral approach, the operator must first have good MED surgical skills and rich experience, and must judge whether bilateral decompression can be achieved by unilateral approach only through clinical manifestations and imaging data before surgery, especially whether it can meet the needs of the counsellor for decompression of the contralateral saphenous fossa and nerve root canal. Otherwise, a bilateral approach or even open surgical decompression should be considered. In addition, preoperative assessment of the presence of segmental instability and possible post-decompression medical instability is required, although endoscopic decompression is less damaging than conventional surgery, and if interbody fusion is required, appropriate tools and plants for microscopic interbody fusion (e.g., B-twin, etc.) and possibly percutaneous pedicle nail fixation techniques and equipment are required, otherwise Otherwise, conventional open surgery or PLIF or TLIF surgery with small incisions and dilated canals should be performed instead.
I. Indications and contraindications for surgery
(A) Indications
It is mainly indicated for single- or double-segment lumbar spinal stenosis with clinical manifestations of nerve root pain, numbness and intermittent claudication in the lower extremities, mainly on one side, and with or without segmental instability if there is significant back pain or mechanical back pain closely related to activity. Since it is a microscopic operation, its operating time is increased compared with conventional surgery, and such cases are mostly middle-aged and elderly patients, often combined with other visceral diseases; therefore, while choosing minimally invasive surgery, the impact of prolonged surgical anesthesia on them must be weighed, so microscopic decompression is generally chosen for single-segment stenosis cases, and open conventional surgery is recommended for those with three or more segmental stenosis. Specific inclusion criteria include the following.
(1) Low back pain with or without lower extremity radiating pain.
(2) Intermittent neurologic claudication, primarily due to limited ambulation due to low back pain and/or inability to tolerate sustained standing.
(3) Those who cannot tolerate exercise.
(4) Imaging confirmed presence of degenerative lumbar spinal stenosis that is clinically consistent.
(5) Those who have failed conservative treatment for at least 6 months.
(6) Those with lumbar instability may be considered in combination with other minimally invasive spinal stabilization or fusion procedures.
(B) Contraindications
The main contraindications to surgery are as follows:
(1) Clinical and imaging inconsistencies.
(2) Congenital lumbar spinal stenosis.
(3) Degenerative lumbar spondylolisthesis and isthmic cleft lumbar spondylolisthesis exceeding I°, or significant preoperative lumbar instability that is not amenable to minimally invasive spinal stabilization or fusion.
(4) Degenerative lumbar scoliosis with a Cobb angle of more than 20° or the presence of severe lumbar deformity.
(5) History of lumbar spine surgery at the same segment.
(6) Presence of acute infectious or neoplastic disease.
(7) Cauda equina syndrome, or a combination of giant central disc herniation with calcification.
(8) More than 3 segments of lumbar spinal stenosis.
Preoperative treatment and preparation
CT is a good indicator of ligamentous calcification, arthroplasia and the direction of the synovial joint; MRI sagittal images show the nerve roots as well; spinal canal imaging and CTM can show the degree of lateral saphenous fossa stenosis and nerve root compression better than CT and MRI, which can reflect the degree of stenosis more visually.
Unilateral approach to endoscopic decompression surgery
The key to successful endoscopic decompression is the establishment of a working channel and the unilateral access to the lateral saphenous fossa and surgical decompression. The operator needs to have a good foundation in open spinal canal decompression and MED surgery, be familiar with the knowledge of pathological anatomy, and need to undergo a certain amount of skill training and be proficient in using various equipment and instruments of the MED system, and also need to have some special equipment such as microdynamic grinding drills with protective cuffs and gun-like biting forceps of various angles. Intraoperative bleeding from the intradural epidural plexus is often a major factor affecting the operation and progress. The operator needs to have experience in microscopic surgery in the stone room, operate gently, and stop bleeding in a timely and reasonable manner to ensure a clear operative field, otherwise it is easy to cause hard tears or nerve root fusion injuries, especially when performing decompression of the contralateral spinal canal. It is very important to determine whether the decompression is adequate, especially for the unilateral approach, because the contralateral part of the spinal canal cannot be revealed through the unilateral approach in conventional open surgery, and it is possible to clearly reveal the contralateral part through the endoscopic single approach by tilting the working channel and increasing the field of view with a 30° angle lens. If the adequacy of decompression cannot be determined by probing or intraoperative spinal canal imaging, a bilateral approach is recommended, i.e., re-establishing access to the contralateral side and performing microscopic decompression.
Position and working channel establishment
The side with lower extremity nerve root symptoms or heavy symptoms is selected and punctured with a fine positioning needle from the paraspinal process to the lower edge of the lumbar 4 plate on that side, and the discoscopic dilatation tube is inserted incrementally for muscle and soft tissue expansion, and finally a working channel of 18 mm in diameter is placed and the free arm is attached to fix the anterior, which clearly shows the vertebral plate, its gap and the medial part of the small articular eminence on one side and establishes the working channel.
Third, ipsilateral spinal canal decompression
Remove the residual soft tissue outside the vertebral plate in the field of view, stop the bleeding by bipolar electrocoagulation, bite off the intervertebral ligament, bite off the upper and lower vertebral plate with the vertebral plate biting forceps to remove the attachment of the yellow ligament and the medial part of the lesser articular eminence, peel off the adhesion between the yellow ligament and the dura with the right-angle stripper, and bite off the yellow ligament. The scope of decompression is expanded according to the spinal stenosis, including the lower 2/3 of the vertebral plate, the upper 1/2 of the vertebral plate of the inferior lumbar body or the hemi-vertebral plate decompression, the medial non-articular surface part of the articular eminence of hyperplasia, with emphasis on decompression of the lateral saphenous fossa and the nerve root canal. For those who also have disc herniation, the nucleus pulposus is removed after protecting the nerve roots, and the hyperplastic part of the articular eminence is further occluded to enlarge the nerve root canal and decompress to the ipsilateral nerve root.
IV. Decompression of the contralateral spinal canal
The ligamentum flavum is occluded medially to the junction of the spinous process lamina, the working channel tube is tilted to the contralateral side, and the base of the interspinous process ligament is removed microscopically to enlarge the central canal, so that the decompression of the space at the level of the contralateral spinal canal row can be performed under direct endoscopic vision at an angle of 30°.
The angle of the working channel can be adjusted as needed to subconsciously bite off the deep layer of the contralateral vertebral plate. V. Intraoperative judgment of decompression effect
V. Intraoperative determination of decompression effect and the application of vertebral canalography
Intraoperative spinal canal imaging is used to determine the decompression of the operated segment and bilateral nerve roots. The adjacent segment is punctured with a lumbar puncture needle, and contrast Onyx is injected. After successful decompression, the lateral edge of the contralateral dural sac and the nerve root cuff are visible under direct vision, and the contralateral vertebral nerve root can be explored with a nerve probe. If the contralateral nerve root is explored and intraoperative imaging suggests that stenosis compression still exists, a skin incision can be used to create a contralateral working channel by pulling it to the contralateral spinous process. Contralateral spinal canaloscopic decompression is achieved through this channel.
VI. Sutured incision for drainage
Intraoperative bleeding can be stopped by cotton pad compression or double-plate electrocoagulation of the venous plexus, large amounts of saline to flush the operative field, remove the working channel, routinely rotate the drainage tube outside the vertebral plate, such as bilateral access can be bilaterally drained, suture the fascia and skin incision, and close the operation.
VII. Complications and their preventive measures
The incidence of complications associated with the surgical access operation is not high. Dural tears are the most common complication, and their occurrence is related to the unilateral approach requiring excessive retraction of the dural sac to expose the contralateral spinal canal and learning curve, but is still lower than the incidence of dural tears in conventional open laminectomy. In addition, the nerve roots must be exposed and protected intraoperatively, and the epidural adhesions must be carefully peeled away, otherwise they are prone to dural tears, but even if this occurs intraoperatively, it is not likely to have serious long-term consequences, as long as the small rupture is detected and treated in a timely manner, and the small rupture can be compressed with brain cotton, while the large rupture needs to be treated accordingly. If the operation is continued without timely intraoperative detection, further damage to the cauda equina and nerve roots may occur, along with serious cerebrospinal fluid leakage. After decompression is completed, careful hemostasis should be performed, otherwise postoperative epidural hematoma formation may occur despite postoperative drainage, which may lead to recurrence of symptoms in severe cases. At the same time, strict aseptic operation, strict sterilization of the endoscope, and routine use of antibiotics before and after surgery should be used to prevent intervertebral space infection and skin incision infection.
VIII. Complications and their preventive measures
The incidence of complications associated with the surgical access operation is not high. Dural tears are the most common complication, and their occurrence is related to the unilateral approach requiring excessive retraction of the dural sac to expose the contralateral spinal canal and learning curve, but is still lower than the incidence of dural tears in conventional open laminectomy. In addition, the nerve roots must be exposed and protected intraoperatively, and the epidural adhesions must be carefully peeled off, otherwise they are prone to dural tears, but even if this occurs intraoperatively, it is not likely to have serious long-term consequences, as long as the small rupture is detected and treated in a timely manner, and the small rupture can be compressed with brain cotton, while the large rupture needs to be treated accordingly. If the operation is continued without timely intraoperative detection, further damage to the cauda equina and nerve roots may occur, along with severe cerebrospinal fluid leakage. Careful hemostasis should be completed after decompression, otherwise postoperative epidural hematoma formation may occur despite postoperative drainage, which may lead to recurrence of symptoms in severe cases. At the same time, strict aseptic operation, strict sterilization of the endoscope, routine use of antibiotics before and after surgery, and prevention of intervertebral space infection and skin incision infection should be performed.
IX. Postoperative treatment, efficacy evaluation and follow-up
Antibiotics and methylprednisolone 80mg, 2/day, were routinely administered within 3 days after surgery. The drainage tube was removed on the 1st day after surgery, and the lumbar brace was taken out of bed on the 3rd day after surgery, and functional exercise of the lumbar back muscle was started after 5-7 days.
Analysis of unilateral access endoscopic bilateral spinal canal decompression technique
The pathological basis of degenerative lumbar spinal stenosis is the reduction of nerve root or cauda equina due to the reduction of the spinal canal volume caused by the coalescence of the joint protrusions, hypertrophy of the ligamentum flavum and calcification of the herniated intervertebral disc, as well as the compression of the venous plexus causing blood flow obstruction, thus causing a series of symptoms. Although the traditional surgical approach of open laminoplasty provides extensive decompression, a large body of retrospective or prospective research literature has been meta-analysed to show that its intermediate efficacy rate is only 64%, and its long-term rate is even lower. These surgical operations further aggravate the already existing reduced stability of the degenerative lesion, resulting in postoperative medically induced lumbar instability, and often require both prophylactic internal fixation with an arch nail and fusion with an implant. The implantation of pedicle screws implies greater muscle dissection and exposure, which further aggravates the damage to the paravertebral muscles and soft tissues, resulting in muscle atrophy, muscle weakness and muscle denervation, which are the main causes of postoperative low back pain, as well as the problems associated with integration. Therefore, the ideal surgical approach is one that restores the spinal canal volume, satisfies adequate nerve root decompression, and maximally maintains the biomechanical stability of the spine.
I. Significance and efficacy of unilateral access endoscopic bilateral spinal canal decompression
The unilateral access bilateral lumbar spinal canal decompression technique was first proposed by Young in 1988 and has been successfully used in clinical practice since then, and its effectiveness has been confirmed by various basic and clinical studies. Khoo et al. have been using the microscope since 1999 to perform unilateral bilateral decompression of the spinal canal for lumbar stenosis, with results similar to those of conventional open surgery. The average operative time per segment was 124 min and the bleeding volume was 68 ml, and the postoperative MRI showed a significant overturning of the spinal canal and a 72% improvement in the postoperative JOA score compared with the preoperative one.
Previous reports on unilateral access bilateral lumbar spinal canal decompression were mostly few cases with short follow-up time, until Oertel et al. reported in 2006 that in 102 cases of lumbar spinal stenosis using unilateral access microscopic endoscopic bilateral decompression, 97.7% of the patients had immediate postoperative symptomatic improvement, and the average 5.6-year interim follow-up had an excellent efficacy rate of 85.3%. Postoperative pain and intermittent claudication in the lower extremities of the patients were relieved, and postoperative follow-up CT showed enlarged nerve root canals. Postoperative complications included membranous tears and cerebrospinal fluid leakage.
The efficacy was evaluated according to Nakai criteria (excellent: disappearance of pain, no limitation of motor function, return to normal work and activity; good: occasional pain, able to do light work; acceptable: some improvement, still painful, unable to work; poor: manifestation of nerve root compression, requiring further surgical treatment).
This shows that it is feasible to extend the MED technique to spinal decompression (MEDL) for the treatment of lumbar spinal stenosis, which has the superiority of small incision, less tissue stripping damage, less bleeding, fewer complications, and faster postoperative recovery, and its efficacy is similar to or even better than that of conventional open surgery. Specific reasons for the good outcomes obtained by bilateral decompression with unilateral access include the following.
(1) The dilated canal expansion technique is used to establish a working channel without extensive stripping of the sacrospinous muscle and injury to its innervated nerve branches, and the function of the sacrospinous muscle, especially the multifidus muscle, is well preserved after surgery; the unilateral approach also directly avoids damage to the contralateral soft tissue.
(2) Most of the pathological changes of lumbar stenosis appear at the level of the intervertebral space, with the most serious at the level of the joint complex, which is the area where the working channel is exposed, facilitating the operation of microscopic decompression.
(3) Due to the 6.4-fold magnification of the operative field, the extent of occlusion of the lamina and articular processes can be precisely determined, and most of the articular processes can be retained to the maximum extent, which better preserves the stable bony structures of the spine; the microscopic operation is more accurate, and the adhesion release can be more delicate, which can effectively avoid nerve root or dural sac injury.
(4) The contralateral vertebral canal was subconsciously decompressed, preserving the outer layer of the contralateral vertebral plate and most of the articular processes, as well as the spinous process and supraspinous ligaments, and the preservation of these posterior column bones and ligamentous structures is conducive to maintaining postoperative spinal stability.
(5) By reorienting the access up and down, it is possible to operate on the ipsilateral spinal canal of two adjacent segments through a small incision of 1.8-2.0 cm and preserve part of the laminae bridge to block edema compression and adhesions outside the spinal canal.
The unilateral approach with the METRx surgical system clearly shows the ipsilateral dural sac, nerve roots and nerve root exit holes, and by adjusting the working canal and direction also shows the contralateral posterior part of the spinal canal, thus decompressing the lateral spinal canal, revealing the contralateral pedicle is extremely critical for bilateral decompression, and decompressing the contralateral nerve root hole under direct vision is safe enough.
Second, the technical essentials
(A) Basic requirements
Endoscopic decompression of the spinal canal must have rich experience in open surgery and skilled endoscopic operation skills, and strictly grasp the indications. If it is difficult to enter the spinal canal, bleeding, difficult to stop bleeding, unsatisfactory visual field, unsatisfactory decompression and difficult to deal with nerve or dural injury, it should be converted to conventional open surgery.
(B) Surgical segmental localization
The segment that causes symptoms and requires decompression should be clearly identified. Usually, the segment with the most severe stenosis on imaging is the most likely to cause the patient’s symptoms, and attention should be paid to the presence of migrating vertebrae or anatomical abnormalities leading to wrong diagnosis and positioning.
(iii) Incision selection
For single-segment stenosis with calcification of the ligamentum flavum or intervertebral disc on one side, the approach to the intervertebral space on the calcified side is chosen; for those without calcification, the approach to the intervertebral space on the side with heavy clinical symptoms is chosen. For bipartite stenosis, an incision is made between the two interspaces, and the upper and lower segmental approaches are established by skin traction. Although endoscopic surgery affects the field of view by excising too much muscle tissue, increasing the damage to the paravertebral muscles and causing postoperative pain, open surgery should still be chosen for extensive multisegmental stenosis.
(iv) Ideal location of the access tube placement
The best approach is from the junction of the inferior edge of the superior vertebral plate and the medial edge of the inferior articular eminence, because there is a potential posterior space in this area, far from the dural sac nerve roots, which is a safer area. In the lumbar 4/5 segment, the intervertebral space is generally located on the upper side of the vertebral plate gap, so the upper 2/3 of the channel is the inferior edge of the lumbar 4 plate and the lower 1/3 is the ligamentum flavum; in the lumbar 5/sacral 1 segment, the intervertebral space is generally located below the vertebral plate, so the upper 1/3 of the channel is the inferior edge of the lumbar 5 plate and the lower 2/3 is the ligamentum flavum.
(E) Decompression order
The nucleus pulposus should be removed in case of disc herniation, and the nerve root-centered decompression principle should be adhered to by enlarging the narrow lateral saphenous fossa, exposing the nerve root and expanding the nerve root canal along the nerve root, until the nerve root is completely decompressed. Before removing the ligamentum flavum of the posterior wall of the lateral saphenous fossa, a decompressive blunt separation operation should be performed on its superficial surface to avoid damaging the deep nerve roots, and then remove the ligamentum flavum after decompression, so that the operation can complete the effective decompression of the dorsal ventral side of the ipsilateral nerve roots including the dorsal side of the contralateral spinal canal, but it is difficult to decompress the ventral central part of the spinal canal and the contralateral ventral side of the spinal canal.
(F) Treatment of intravertebral canal hemorrhage
The adhesions between the ligamentum flavum and the dural sac can be separated with a right-angle stripper before biting off the ligamentum flavum, which can reduce the bleeding of small and medium vessels in the fat outside the dural sac, and if bleeding can be stopped by bipolar electrocoagulation; the venous plexus behind the vertebral body is prone to rupture and bleeding due to the high pressure of the local spinal stenosis, which is sometimes difficult to handle, and the repeated pushing of the stripper on the nerve root or dural sac should be minimized to avoid its rupture; the ruptured venous plexus should be stopped by bipolar If it is ineffective, small pieces of gelatin sponge and brain cotton should be used to stop bleeding; adequate decompression including removal of the herniated disc nucleus pulposus can help to reduce the pressure of the venous plexus and stop bleeding; bleeding of each operation should be stopped in time, and the operator should not be impatient and operate blindly when there is more bleeding.
Third, the scope of decompression, decompression standards and the significance of intraoperative imaging
(A) Decompression range
The width of decompression usually reaches the medial 1/3 of the superior articular eminence, fully exposing and decompressing along the nerve root until the nerve root compression is released, and bilateral nerve root compression must be decompressed bilaterally.
(ii) Decompression criteria
After complete decompression, the excessive tension of the nerve root disappears and becomes relaxed, and it can be moved laterally by 5 mm; the color of the nerve root which is flattened or curved under the microscope due to compression changes from gray to white and can be seen to be shiny, and its shape returns to normal; the accompanying nuchal vein is well restored, and the dural sac is no longer indented and inflated.
(iii) The significance of intraoperative angiography
The main purpose is to understand the effect of decompression of the contralateral nerve root and to guide the scope of decompression. If the contralateral nerve root is poorly visualized or not visualized through comparison with the preoperative imaging, it suggests that the decompression is not sufficient and the bilateral approach should be changed.
IV. Reoperation rate and postoperative instability
The natural course of lumbar degeneration itself, bone regeneration of the vertebral plate gradually causing restenosis, and postoperative instability due to compromised lumbar spine integrity are related. The literature reports that bone regeneration in the surgical region after posterior decompression of lumbar stenosis can occur in 44% to 94% of patients, so bone regeneration is considered a manifestation of spinal instability. Because surgery does not only affect the local area, but often affects the spine including adjacent segments, postoperative lumbar degenerative disease can continue to develop, and the incidence of reoperation due to disc herniation or spinal stenosis in adjacent segments has been reported to be 9.8% in the literature.
The use of unilateral access for bilateral spinal canal decompression preserves the posterior lumbar column structure better and reduces postoperative bone regeneration due to less injury, so the postoperative rate of distant restenosis, segmental instability, and the resulting need for reoperation is reported to be 6.9% in the literature, which is lower than after total laminectomy and open bilateral decompression. Lumbar spondylolisthesis may occur after conventional open decompression, with a maximum incidence of 31% in those without preoperative spondylolisthesis and a higher incidence of postoperative spondylolisthesis exacerbation in those with preoperative spondylolisthesis, thus requiring fusion for these conditions such as open surgical decompression. For preoperative stable slippage using unilateral access microscopic decompression does not necessarily aggravate instability, so the presence of slippage is not an absolute indication for the need of fusion.
In conclusion, the use of microendoscopic spinal decompression for lumbar spinal stenosis fully reflects the superiority of minimally invasive surgery, with small surgical incisions and minimal interference with the paravertebral muscles, which maximally maintains the stability of the lumbar spine; its high surgical accuracy, minimal trauma, and few postoperative complications allow patients to get out of bed early and return to work sooner, and can achieve comparable or even better results than conventional surgical treatment.