Minimally Invasive Surgical Method

Minimally Invasive Surgical Method


James B. Macon



Abstract


Minimally invasive surgery (MIS), as applied to the lumbar spine, includes many techniques for both decompression and fusion as alternatives to the open spine procedures described elsewhere in this text. Although decompression can be performed with smaller access than fusion, MIS means the minimal access that can safely accomplish the individual surgical goal. Each MIS approach is designed to reduce unnecessary tissue trauma and thereby reduce postoperative pain, blood loss, infection rate and length of stay relative to the open surgery counterparts and thereby optimize value for patients. This chapter provides in some detail a step-by-step guide for performance of some commonly employed approaches for MIS decompression for lumbar disc herniations and spinal stenosis as well as three approaches to perform MIS fusion for lumbar segmental instability including TLIF, PLIF and XLIF. The risks and benefits of each procedure are described as they should be presented to patients prior to surgery by the operating surgeon. The relative benefits of lumbar MIS versus open techniques are discussed as well as the opportunities for future advancement of the MIS method.


Keywords: MIS, minimally invasive lumbar decompression, fusion, discectomy, herniation, stenosis, foraminotomy, laminectomy, TLIF, PLIF, XLIF



Everything should be made as simple as possible, but not simpler.


Albert Einstein


8.1 Introduction


The concept of minimally invasive surgery (MIS) originated in the 1980s, but its application to the lumbar spine has been credited to the 1997 publication by Foley and Smith, 1 who introduced the minimally invasive endoscopic lumbar microdiscectomy. MIS is defined as the minimal access that allows accomplishment of the surgical goal. MIS is not defined by incision size since that will vary depending on the type of procedure performed (i.e., discectomy or fusion). The minimally invasive discectomy involves inserting a tubular port directly through the paraspinal muscles by splitting the muscles using concentric dilators, then passing the working port over the final dilator. This muscle-splitting approach of Wiltse 2 minimizes muscle trauma and pain without damaging subsequent muscle function. 3 The tube trajectory is monitored and adjusted using biplane fluoroscopy in order that placement will be required only once and be precisely where the surgical pathology is accessible. Multiple attempts to place the tube must be avoided to prevent unnecessary muscle trauma.


This “simple” method allows the surgery to be performed through the smallest access that will allow the procedure to be accomplished safely and successfully. 4 The goal of the MIS approach is to minimize tissue trauma, thereby reducing postoperative pain, blood loss, infection rates, operative time, and hospital length of stay. All of these advantages would appear to be cost-effective in favor of the MIS approach. The disadvantage and constraint of working the limited space at the bottom of the tube has been countered by introducing fiberoptic light sources from the endoscope and using bayonet-handled instruments that do not impair the line of sight when looking down the tube. Now the operating microscope, that is ubiquitous in the neurosurgical operating suite, is used instead of the endoscope to preserve binocular vision and depth perception. The parameters that define the transtubular approach must be optimized including tube length and diameter with each procedure in order that the surgical goal can be accomplished successfully. Naturally a tube that is too small or positioned with the wrong trajectory will not allow a successful procedure. Attempting to perform surgery through too narrow a tube preventing adequate visualization or placement of instruments is dangerous and would be an example of “simpler than possible.” There is a balancing act between minimally invasive access and safety that will be determined by each spine surgeon based on individual patience and skill with the goal of providing the best outcome for patients. Attempting to reduce the exposure to a size that is too small to safely achieve the surgical goal with an optimal outcome would be “simpler than possible” and should be avoided by all MIS spine surgeons. However, the safe exposure size needed to accomplish the surgical goals will vary with the patience, skill, training, and experience of each surgeon.


When performed properly, this method is brilliant in its simplicity and as a consequence increases value for patients. In order to perform MIS surgery, there are many new factors and technical details that must be considered and consequently only surgeons well trained in open procedures should attempt the MIS approach. Although the procedure is conceptually simple, it is technically different from the open technique. It is important to stress that experience with open surgery is essential before attempting the MIS approach.


When it comes to comparing MIS relative to open surgery, it is accurate to say that “less is more” when lumbar MIS procedures are performed correctly and safely and all the surgical goals are accomplished. Comparison studies have shown that MIS techniques have results and complication rates comparable to open procedures. 5 Considering the added advantages of less surgical tissue trauma, the MIS method optimizes value for patients and at the same time may prove to be cost-effective. The following descriptions of MIS are intended for comparison with the previously described open surgeries in prior chapters of this text.


8.2 Surgical Decision: Open or MIS of the Lumbar Spine


8.2.1 Patient–Surgeon Interaction in Surgical Decision–Making




  • When the decision has been made by the surgeon and patient that surgery is indicated, the patient must be informed of the alternatives available for treatment.



  • The risks and possible complications of the open versus MIS methods should be explained in detail.



  • Together the patient and surgeon should choose the procedure that is most likely to safely provide the optimal outcome.



  • To avoid unnecessary surgery, the pathology seen on imaging must adequately account for the patient’s clinical presentation.


8.2.2 Operative Plan for MIS the Approach




  • The choice of procedure will provide direct minimally invasive access to the symptomatic pathology with no unnecessary components to avoid collateral damage (i.e., no fusion without instability on imaging and no extra levels without indication).



  • Procedures designed for treatment of pain alone will only be performed if the pain generator has been confidently identified with preoperative objective radicular neurological deficits, relief with nerve root blocks, or provocative and block discography. The pain must be confined to the distribution of the decompressed nerve root with correctable pathology identified on imaging.



  • Imaging abnormalities without correlating pain distribution should not be treated by the MIS approach to optimize outcomes and prevent unnecessary operative exposure. MIS is not appropriate for exploration due to high failure rates. Attempting MIS decompressions for nonradicular or diffuse nonlocalized axial low back pain alone without radiculopathy is doomed to failure.


8.3 Minimally Invasive Surgery Fundamentals


8.3.1 Opening and Closure of Surgical Incision




  • The length of the skin incision to accommodate the tube diameter is only relevant if it is too small and thus hindering visualization and/or manipulation of instruments through the working tube. In addition, the incision length must be at least 2 mm longer than the tube diameter; otherwise, prolonged skin stretch may result in necrosis of incision margins and subsequent wound dehiscence.



  • The deep fascia is opened to the same length as the skin incision to allow uninhibited passage by the tubular dilation system



  • After working tube removal at closure, the fascia is exposed with a self-retaining retractor and sutured with resorbable interrupted sutures. For easier anatomic closure, it is recommended that all fascial sutures be placed before tying them down.



  • Closure of subcutaneous adipose tissue reduces dead space resulting in fluid accumulation and adds some resistance to wound dehiscence, especially in obese patients.



  • Superficial subcuticular closure (inverted absorbable suture) of the dermis is imperative for establishing an adequate well-apposed skin closure.



  • No drainage catheter should be required for most MIS procedures except for a complete multilevel laminectomy.


8.3.2 Decompression with Nonoperated Anatomy




  • After placement of the working tube, verification of the proper level and approach trajectory, and removal of soft tissue to expose the lamina and facet bone, a long shaft angled high-speed 3-mm cutting burr is used to thin the lamina. The residual bone can then be removed with a 2-mm Kerrison rongeur.



  • The ligamentum flavum is preserved as much as possible during primary bone removal with high-speed drills, thus serving as a barrier of safety preventing durotomy.



  • The ligamentum flavum is always removed by detaching it laterally (with 2-mm Kerrison rongeurs) beginning at either its upper (cephalad) or its lower (caudal) edge. It will thus be separated from underlying dura in a lateral to medial fashion. Complete removal requires its medial incision (near midline) before or after lateral detachment.



  • Early nerve root visualization is done, whenever possible, before attention to its compressive pathology. With intracanalicular pathology, this visualization is almost always distal to the pathology (i.e., at the foraminal entrance).



  • Bayoneted instruments are utilized for discectomy in order to allow direct visualization through the tube. Straight instruments will block visualization and are not utilized after tubular access is achieved.


8.4 Minimally Invasive Surgery Decompression Techniques


8.4.1 Unilateral Decompression of Nerve Root with MIS Medial Discectomy and/or Foraminotomy


Clinical Presentation




  • Painful radiculopathy.



  • One-level pain generator.


Image Pathology




  • Lateral or paramedian herniated lumbar disc.



  • Foraminal stenosis due to disc or facet hypertrophy.



  • Subarticular (lateral recess) stenosis on symptomatic side.



  • Small/moderate synovial cyst.


Contraindications (Relative)




  • Large central disc herniation.



  • Far lateral or extraforaminal disc herniation.



  • Bilateral foraminal stenosis or nerve root compression.


Operative Technique


The operative technique (▶ Fig. 8.1, ▶ Fig. 8.2a) 6 is paramedian incision (~1.0–1.5 cm lateral to the midline) with tubular diameter (18–22 mm).




  • After induction of general endotracheal anesthesia, the patient is placed prone on a spinal frame and the back prepped and draped in the standard manner. The incision size should be 2 mm greater than the anticipated working tube diameter. Be certain to verify the side to be operated by checking the preoperative imaging study.



  • Place a 22-gauge spinal needle in the center of the anticipated incision site to the depth of the lamina. Note the level of needle insertion to assure it correlates with the imaging and pathological condition. Use biplane fluoroscopy to accurately determine the required tube length and trajectory. Measure the final depth of the needle to confirm the tube length.



  • Make the skin incision (20–24 mm) only after absolute certainty that the proper level, trajectory, and position with respect to the surgical pathology have been determined (▶ Fig. 8.1a).



  • Place the guidewire to the level of the facet and dock in bone, making certain that the docking site is not too near the interlaminar space, and confirm its position with biplane fluoroscopy. Pass the inner dilator over the guidewire rotating the dilator until it hits the lamina and facet, then “wanding” the dilator to clear soft tissue (▶ Fig. 8.1b). Next, again confirm that the guidewire and dilator are properly positioned using biplane fluoroscopy (anteroposterior [AP] and lateral) before proceeding with dilation. Pass additional dilators until the desired working diameter (18–22 mm, depending on the pathology) is achieved (▶ Fig. 8.1c).



  • Pass the working tube over the dilators. Remove the guidewire and dilators keeping the working tube steady to prevent migration and secure to the flex arm attached to the operating table. Do not release the working channel until a firm attachment is secured. The working tube must be firmly compressed against the lamina and facet and secured to prevent posterior movement of the tube that allows muscle to creep into the work space. Final confirmation of the tube position is then made with biplane fluoroscopy before beginning any surgery. Since localization is not dependent on visualization of anatomical structures, accurate radiological localization is essential.



  • The operating microscope will then be positioned to allow illumination and visualization of the operative site at the bottom of the tube. The operating microscope must be moved out of the field in order to rotate the C-arm into position from this point forward in the procedure. There will usually be soft tissue consisting of muscle and ligament obscuring the bone surface. After palpation with instruments (Penfield 4), the soft tissue is removed with monopolar cautery to expose and allow identification of the bony margins of the lamina and facet. (Only bipolar cautery is used for the remainder of the procedure.) If the expected appearance of the bone is not what is seen, repeat biplane fluoroscopy as necessary to determine if the trajectory requires adjustment. This can be performed by loosening the flex arm and tilting the tube (“wanding”) in the required direction.



  • The laminotomy, foraminotomy, and discectomy are then performed through the access tube using bayonet-angled instruments in a manner identical to the open surgery (▶ Fig. 8.1d). The illumination and visualization obtained with the operating microscope is superior to loupes or an endoscope. A two-level unilateral decompression can be performed through a single approach by making the incision midway between the two disc spaces and wanding the tube to each level with final position determined by fluoroscopy (▶ Fig. 8.2a).



  • After the decompression is complete, the working tube is removed, hemostasis achieved, and sutures are placed in the fascia and subcutaneous and subcuticular tissues, followed by a small dressing.



    Fig. 8.1 (a) MIS decompression tube trajectory and paramedian skin incision site 1.5 cm lateral to midline. (b) Placement of initial inner dilator for tube placement trajectory confirmation and wanding to prepare lamina for working tube contact. (c) Placement of dilators in preparation for insertion of the working tube. (d) Removal of herniated disc with nerve root retractor protecting the dura.


    9781626238077_c008_f001.tif



    Fig. 8.2 (a) Two adjacent level ipsilateral decompression tubular approaches. (b) Same level bilateral decompression tubular approach angles.


    9781626238077_c008_f002.tif



Complications of Minimally Invasive Surgery Decompression


The complications of MIS decompression 7 surgery are similar to those encountered during open surgery, including infection, bleeding, dural tear with cerebrospinal fluid (CSF) leak, and nerve root injury. There are certain issues specific to the MIS decompression technique that must be considered to prevent complications.




  • Bleeding must be meticulously controlled as encountered in order to allow visualization in the working tube. Since bleeding must be controlled at each step to perform the operation, significant postoperative hematomas are very rare.



  • Infection prophylaxis with broad spectrum perioperative antibiotics combined with meticulous sterile technique will reduce the incidence of infection to a minimum. Infection rates should be less than 1%. 8



  • During discectomy or foraminotomy, when operating around the thecal sac, the dura must be retracted with a right-angled suction retractor since conventional retractors will block visualization, especially when there is significant epidural bleeding. If a dural tear occurs, the narrow tube diameter makes conventional primary suture of the dura technically difficult requiring microvascular clips, so the repair method usually consists of application of a synthetic collagen or fascial patch covered by fibrin sealant and reinforced by muscle or fat. A significant or persistent CSF leak will require a lumbar subarachnoid drain for CSF diversion. Failure to adequately stop a CSF leak should not be ignored since the leak increases the risk of infection and meningitis. A persistent leak may require a direct suture repair via conversion to open technique or another open surgery. Dural tear risk is 2 to 10% depending on the surgeon’s experience and skill.



  • The risk of dural tear is significant during the dilation process that requires docking the guidewire under biplane fluoroscopy (AP and lateral), then passing small-diameter inner dilators blindly over the guidewire. It is essential to monitor this process with lateral fluoroscopy so the guidewire does not bind to the inner dilator and get pushed blindly through the interlaminar space, puncturing the dura and potentially injuring one or more nerve roots.



  • Wrong side surgery is possible with MIS decompressions. Be certain to verify the side to be operated on by checking the preoperative imaging study before the skin incision is made. Wrong level surgery is no more likely than open surgery as long as the level is confirmed with intraoperative fluoroscopy (or computed tomography [CT]).


8.4.2 Bilateral Decompression (MIS Dual-Tube Medial Foraminotomy)


Clinical Presentation




  • Painful bilateral lower extremity radiculopathy.



  • One-level bilateral pain generator.


Image Pathology




  • Bilateral medial foraminal stenosis due to disc protrusion or facet hypertrophy.



  • Bilateral subarticular (lateral recess) stenosis with nerve root compression.



  • Bilateral disc protrusions with nerve root compression in the lateral recess.


Contraindications (Relative)




  • Large central disc herniation.



  • Far lateral or extraforaminal disc herniation.



  • Central canal stenosis due to facet/ligament hypertrophy.



  • Lumbar spondylolisthesis.


Operative Technique


The operative technique (▶ Fig. 8.2b) is midline incision (20–24 mm length) and two fascial incisions (1 cm lateral to spinous process) with tubular diameter (18–22 mm).




  • After induction of general endotracheal anesthesia, the patient is placed prone on a spinal frame and the back prepped and draped in the standard manner. The incision size should be 2 mm greater than the anticipated working tube diameter to prevent skin necrosis due to stretch. Be certain to verify the side and level to be operated on by checking the preoperative imaging study before the skin incision is made.



  • Place a 22-gauge spinal needle in the midline at the center of the anticipated incision site to the depth of the lamina. The needle is directed from the midline laterally 20 to 30 degrees passing paramedian 1 to 2 cm lateral to the spinous process toward the medial facet and lateral lamina (▶ Fig. 8.2b). Note the level of needle insertion to assure it correlates with the imaging and pathological condition in the lateral spinal canal. Use biplane fluoroscopy to accurately determine the required tube length and trajectory. Measure the final depth of the needle to confirm the tube length.



  • Make the skin incision (20–24 mm) only after absolute certainty that the proper level, trajectory, and position with respect to the surgical pathology have been determined.



  • A fascial incision (20–24 mm) is made 1 cm lateral to the edge of the spinous process. Pass the guidewire through the fascial incision to the level of the facet and dock in bone, making certain that the docking site is not too near the interlaminar space, and confirm its position with biplane fluoroscopy. Pass the inner dilator over the guidewire rotating the dilator until it hits the facet. Then again confirm that the guidewire and dilator are properly positioned using biplane fluoroscopy before proceeding with dilation. Pass additional dilators until the desired working diameter (18–22 mm, depending on the pathology) is achieved.



  • Pass the working tube over the dilators. Remove the guidewire and dilators keeping the working tube steady to prevent migration and secure to the flex arm attached to the operating table. Do not release the working channel until a firm attachment is secured. The working tube must be firmly compressed against the lamina and facet and secured to prevent posterior movement of the tube that allows the muscle to creep into the work space. Final confirmation of the tube position is then made with biplane fluoroscopy before beginning any surgery. Since localization is not dependent on visualization of anatomical structures, accurate radiological localization is essential.



  • The operating microscope will then be positioned to allow illumination and visualization of the operative site at the bottom of the tube. The surgeon will stand on the contralateral side to the pathology. The operating microscope must be moved out of the field in order to rotate the C-arm into position from this point forward in the procedure. There will be soft tissue consisting of muscle and ligament obscuring the bone surface. After palpation with instruments (Penfield 4), the soft tissue is removed with monopolar cautery to expose and allow identification of the bony margins of the lamina and facet. (Only bipolar cautery is used for the remainder of the procedure.) If the expected appearance of the bone is not what is seen, repeat biplane fluoroscopy is necessary to determine if the trajectory requires adjustment. This can be performed by loosening the flex arm and tilting the tube (“wanding”) in the required direction.



  • The lateral laminectomy and medial foraminotomy are then performed through the access tube using bayonet-angled instruments in a manner identical to the unilateral decompression. The main difference is that the tube is angled about 10 degrees laterally (▶ Fig. 8.2b). The illumination and visualization obtained with the operating microscope is superior to loupes or endoscope. After the pathology is removed on one side, the tube is removed, hemostasis achieved, and sutures are placed in the fascia; then, attention is turned to the contralateral side.



  • Once the decompression is completed on one side working from the opposite side of the operating table, repeat the process to decompress the contralateral lateral recess and medial foramen to accomplish the bilateral decompression as necessary (▶ Fig. 8.2b).



  • After the second decompression, the tube is removed, hemostasis is achieved, and sutures are placed in the fascia and subcutaneous and subcuticular tissues, followed by a small dressing.



  • The advantage of this approach is that bilateral decompressions can be performed through a single midline vertical skin incision without disrupting the stabilizing midline spinous processes or ligaments constituting the posterior lumbar tension band. This method is only to be used when there is no significant central stenosis or pre-existing instability.


Complications




  • Bleeding.



  • Infection.



  • Nerve root injury.



  • Dural tear with CSF leak.



  • Instability due to excessive bilateral facetectomy.


8.4.3 Laminectomy (MIS Unilateral Single-Tube Bilateral Decompression)


Clinical Presentation




  • Neurogenic claudication (bilateral).



  • Single-level stenotic radiculopathy.



  • Central stenosis and bilateral foraminal or lateral recess stenosis.


Image Pathology




  • Single-level severe/moderate central stenosis with significant ligamentum flavum hypertrophy.



  • Bilateral focal (<2cm length) lateral recess and central canal stenosis.


Contraindications




  • Large central disc herniation with cauda equina decompression.


Operative Technique


The operative technique (▶ Fig. 8.3) 9,​ 10,​ 11,​ 12,​ 13 is paramedian incision (between 1.5 and 3 cm lateral to midline) with tubular diameter (22 mm).



Fig. 8.3 (a) Tube trajectories required for bilateral decompression from unilateral approach: ipsilateral (1) and contralateral (2). (b) Step 1 ipsilateral laminotomy with preservation of ligamentum flavum. (c) Step 2 contralateral decompression with medial facetectomy using the rongeur with adjacent retractor protecting the dura. (d) Step 3 ipsilateral decompression after resection of ligament and medial facetectomy with the rongeur. (e) Step 4 completed bilateral decompression from a unilateral approach.


9781626238077_c008_f003.tif



Ipsilateral nerve root decompression is performed via a more lateral trajectory (1) and tube placement (as previously described for unilateral decompression) with modifications as detailed below. Contralateral decompression is performed via the more medial trajectory (2) as described below (▶ Fig. 8.3a).




  1. After induction of general endotracheal anesthesia, the patient is placed prone on a spinal frame and the back prepped and draped in the standard manner. The incision size should be 2 mm greater than the anticipated working tube diameter. Be certain to verify the side and level to be operated on by checking the preoperative imaging study before the skin incision is made.



  2. Place a 22-gauge spinal needle in the center of the anticipated skin incision site 2.5 cm lateral to the midline (▶ Fig. 8.3a) to the depth of the ipsilateral lamina. Note the level of needle insertion to assure it correlates with the imaging and pathological condition. Use biplane fluoroscopy to accurately determine the required tube length and trajectory. Measure the final depth of the needle to confirm the tube length.



  3. Make the skin incision (24 mm) only after absolute certainty that the proper level, trajectory, and position with respect to the surgical pathology have been determined. After the skin incision, retract subcutaneous tissues to the fascial level and sharply open horizontally to allow required medial to lateral tube trajectory adjustments.



  4. Place the guidewire through the fascial incision to the level of the facet and dock on bone, making certain that the docking site is not too near the interlaminar space, and confirm its position with biplane fluoroscopy. Pass the inner dilator over the guidewire rotating the dilator until it hits the facet. Then again confirm that the guidewire and dilator are properly positioned using biplane fluoroscopy before proceeding with dilation. Pass additional dilators until the desired working diameter (18–22 mm, depending on the pathology) is achieved.



  5. Pass the working tube over the dilators. Remove the guidewire and dilators keeping the working tube steady to prevent migration and secure to the flex arm attached to the operating table. Do not release the working channel until a firm attachment is secured. The working tube must be firmly compressed against the lamina and facet and secured to prevent posterior movement of the tube that allows the muscle to creep into the work space. Final confirmation of the tube position is then made with biplane fluoroscopy before beginning any surgery. Since localization is not dependent on visualization of anatomical structures, accurate radiological localization is essential.



  6. The operating microscope will then be positioned to allow illumination and visualization of the operative site at the bottom of the tube. The operating microscope must be moved out of the field in order to rotate the C-arm into position from this point forward in the procedure. There will be soft tissue consisting of muscle and ligament obscuring the bone surface. After palpation with instruments (Penfield 4), the soft tissue is removed with monopolar cautery to expose and allow identification of the bony margins of the lamina and facet. (Only bipolar cautery is used for the remainder of the procedure.) If the expected appearance of the bone is not what is seen, repeat biplane fluoroscopy is necessary to determine if the trajectory requires adjustment. This can be performed by loosening the flex arm and tilting the tube (“wanding”) in the required direction.



  7. Initial ipsilateral exposure (step 1) is performed with the tube at the skin level positioned 1 cm from the midline (trajectory 1) by separating the ligamentum flavum from the lamina with a curved curette and then performing a laminectomy with the drill and Kerrison rongeurs to the cranial margin of the ligament wide enough to decompress the stenotic spinal canal. The ligament is left in place to protect the dura during the contralateral decompression (▶ Fig. 8.3b).



  8. Then the tube is released and wanded medially with the tube at the skin level 3 cm lateral to the midline to expose the base of the spinous process and achieve the exposure (trajectory 2) required for the contralateral decompression (▶ Fig. 8.3c). The tube is then secured to the operating table with the flex arm. The table is turned away from the surgeon to allow a direct approach to the contralateral lamina (step 2). The Kerrison rongeur and high-speed drill are then used to remove the base of the spinous process and resect the inner cortex of the contralateral lamina (▶ Fig. 8.3c). The dura is protected by leaving the ligament intact and gently retracting with a multiperforated no. 7 suction tube during the drilling. Bleeding is controlled with bone wax applied on the back of a Penfield no. 4 instrument. The laminar resection is continued until the contralateral facet is encountered. Care is taken to preserve the outer cortex of the lamina to insure stability of the spinous process. It is essential to control bone bleeding from the residual laminar and facet surface with bone wax to prevent postoperative hematoma.



  9. The contralateral decompression is completed by drilling the medial facet and performing a contralateral foraminotomy with a 40-degree angled 2-mm Kerrison rongeur (▶ Fig. 8.3c). After all drilling is completed, the contralateral ligamentum flavum is removed to expose the dura and a ball tip probe is utilized to confirm adequate decompression of the nerve roots of the cauda equina. After completion of the contralateral decompression, the tube is removed to the original position for completion of the ipsilateral decompression (step 3).



  10. The ipsilateral laminectomy, foraminotomy, and discectomy are then performed through the access tube using bayonet- or right-angled instruments in a manner identical to unilateral decompression surgery. The residual ligament is removed to expose the dura and then a medial facetectomy and foraminotomy are performed with the Kerrison rongeur (▶ Fig. 8.3d). If discectomy is required for central canal decompression, it is performed from the ipsilateral approach. The adequacy of the bilateral decompression is checked with a ball-tipped probe or angled flat dural separator (▶ Fig. 8.3e). The illumination and visualization obtained with the operating microscope is superior to loupes or endoscope especially for the contralateral decompression.



  11. After the ipsilateral pathology is resected and the decompression completed, the working tube is removed (▶ Fig. 8.3e), hemostasis achieved, and the sutures are placed in the fascial incisions and subcutaneous and subcuticular tissues; then, a small dressing is applied.



  12. The advantage of this procedure is the reduction of risk of iatrogenic instability by preserving the midline tension band composed of the spinous process and midline ligaments and minimizing the extent of facetectomy especially on the contralateral side. This method has been proposed as superior to open decompression and fusion for stable grade I or II spondylolisthesis with no motion on pre-op flexion–extension X-rays, thereby avoiding the risks of fixation and fusion. 14


Complications




  • Bleeding from drilled contralateral lamina.



  • Infection.



  • Dural tear with CSF leak.



  • Residual contralateral stenosis.



  • Cauda equina compression due to retraction or hematoma.


8.4.4 Far Lateral Nerve Root Decompression (MIS Lateral Discectomy)


Clinical Presentation




  • Painful single-level radiculopathy: discogenic and/or stenotic.


Image Pathology




  • Lateral foraminal or extraforaminal far-lateral HNP (herniated nucleus pulposus) best seen on magnetic resonance (MR) scan (▶ Fig. 8.4a).



  • Lateral foraminal stenosis best seen on CT scan.



    Fig. 8.4 (a) Axial scan demonstrates nerve root compression at the level of a lateral foraminal disc herniation (open arrow). (b) MIS decompression tube positioned for lateral discectomy with proper trajectory passing through a paramedian skin incision centered 4.5 cm lateral to the midline. (c) View through MIS decompression tube with drill performing lateral foraminotomy to expose the nerve root compressed in the foramen by a lateral disc herniation. (d) Lateral discectomy performed through the MIS decompression tube.


    9781626238077_c008_f004.tif

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