A careful review of the preoperative studies (plain radiographs, magnetic resonance imaging or computed tomography myelography) to precisely localize pathology and facilitate focal decompression. After the induction of anesthesia, the patient is placed prone on a radiolucent operating table to facilitate the use of fluoroscopic imaging of the lumbar spine. The authors prefer a Jackson table with a sling as this prevents excessive flexion as with the Wilson frame. Without excessive flexion, it is easier to visualize the laminae of both inferior and superior laminae through the tube, and adequate decompression is more reliable. A standard sterile prep and drape of the low back is utilized. The authors prefer to place the clamp for the tubular retractor on the contralateral side of the surgical approach. The C-arm should be brought in on the opposite side of the surgeon while the microscope (optional) should be used on the same side as the surgeon (Fig. 23.1).

Before the surgical incision, palpable landmarks including the spinous processes should be marked on the back as reference. Obtain proper anterior/posterior (AP) and lateral fluoroscopic views of the spine to localize the level for the surgical incision and the trajectory of tubular retractor (Fig. 23.2). An incision equal in length to the diameter of the tubular retractor is then made one to two fingerbreadths lateral to the midline. The multifidus muscle compartment is then opened by incising the overlying fascia. A more lateral incision may be necessary to better access pathology on the contralateral side, and also in more obese patients. The initial dilator is placed through the multifidus muscle and docked on the inferior edge of the superior lamina, at the spinolaminar junction. Docking can be done in the AP or lateral views. The dilator is “walked” from medial to lateral to feel for the inflection point of the spinous process and the lamina, and also to feel for the inferior edge of the superior lamina. The dilator is also “wanded” back and forth to bluntly dissect the soft tissue from the underlying lamina. This step creates the docking site needed for the tubular retractor and thus will minimize the soft tissue resection required to perform the procedure. The use of a K-wire as the initial step, prior to dilation, carries a high risk of inadvertent dural puncture and should be avoided. Sequential tubular dilators are then used to gently dilate and create the working surgical corridor. At this point, a tubular retractor of appropriate length is placed and secured to the table-mounted holder, and the dilators are removed. The tubular retractor should have a slightly medial trajectory and be in line with the disk space (Fig. 23.3). A 18 to 22 mm diameter tubular retractor is typically used, depending on surgeon preference. Confirmation of the position of the tubular retractor should then be obtained using C-arm fluoroscopy (Fig. 23.4). Any necessary adjustments should be made prior to the commencement of the procedure to ensure optimal access to the pathology. An operative microscope may be used for visualization of the surgical field. Any residual soft tissue should be cleared away with electrocautery to ensure good visualization of the bony landmarks. These include the inferior laminar edge, ligamentum flavum, and the medial portion of the facet complex (Fig. 23.5).

Once the tubular surgical portal is achieved, the decompressive technique is similar to that used with the standard open surgical exposure. A laminotomy is performed on the ipsilateral side, leaving the ligamentum flavum intact³ (Fig. 23.6). If needed, the tubular retractor is “wanded”

medially and the spinous process region is undercutted. When the tubular retractor has been properly positioned, the surgeon should be able to see the junction of the base of the spinous process and ipsilateral lamina. It is helpful to tilt the operating table away from the surgeon during this maneuver to decrease the angle of the microscope. This will improve the surgeon’s visibility across the midline. Next, the undersurface of the contralateral spinous process and lamina is drilled away using a high-speed drill/burr. Initially, cancellous bone will be encountered at the base of the spinous process and bone bleeding will be encountered. This should be controlled with bone wax or hemostatic agents. Next, cortical bone of the contralateral lamina will be encountered and bone bleeding is generally minimal. As the surgeon begins to drill into the bone of the contralateral articular processes, a more cancellous-type bone will be encountered. The contralateral facet joint must be thinned until a Kerrison rongeur can remove the remaining medial portion of the facet to complete the decompression. After all the necessary bone drilling has been completed, the ligamentum flavum is removed by releasing the attachments of the ligament from the bone edges using a curved curette (Fig. 23.7). After removal of the ligamentum flavum, direct visualization of the dural structures is then available and complete decompression of the contralateral lateral recess and foramen can be achieved. Once the contralateral decompression has been completed, decompression of the ipsilateral side can be performed as described above (Fig. 23.8). At the conclusion of the decompression, a ball-tipped probe is used to confirm that an adequate decompression of the nerve roots has been achieved throughout. Adequate hemostasis is achieved, followed by removal of the tubular retractor and closure of the incision.

The thoracolumbar fascia can be closed using interrupted sutures. However, if this is not possible to reach the fascia in an obese patient, the deep subcutaneous tissues are reapproximated followed by skin closure. The subcutaneous tissues along the incision are infiltrated with a long-acting local anesthetic to minimize pain in the early postoperative period. A surgical
dressing can be used according to surgeon preference. Early mobilization of the patient should be the goal following an MIS decompression. Most patients can be discharged from the hospital on the day of surgery. Patients are encouraged to walk a few times a day following surgery. Strenuous activity is allowed at the 4 to 6 week postoperative time point.

Minimize “wanding” if possible because this can lead to muscle creep making visualization more difficult. Therefore, take the necessary time initially to dock in the best position using fluoroscopy. If “wanding” or redirection is needed, this may be facilitated by inserting the largest dilators into the tube to gain more leverage and reduce muscle creep. The surgeon should be careful to avoid excessive thinning of the pars intra-articularis and the inferior articular process because of the risk of iatrogenic fracture. Palpation of the bone in the region of the pars interarticularis with a #4 Penfield instrument is useful to ensure adequate bone is left in this region. The ligamentum flavum should be left intact until the end of drilling, to reduce the risk of a dural or nerve root injury. We prefer to use a 3 mm matchstick burr. After the ligamentum flavum has been removed, frequent palpation of the plane between the dura and the overlying tissue should be undertaken to reduce the risk of dural tear. Bleeding can be controlled with a combination of bone wax on bony edges and flowable hemostatic agents into the lateral gutters of the decompression. Palpation of the bone in the region of the pars interarticularis with a #4 Penfield instrument is useful to ensure adequate bone is left in this region. The ligamentum flavum should be left intact until the end of drilling, to reduce the risk of a dural or nerve root injury. We prefer to use a 3 mm matchstick burr. After the ligamentum flavum has been removed, frequent palpation of the plane between the dura and the overlying tissue should be undertaken to reduce the risk of dural tear. Bleeding can be controlled with a combination of bone wax on bony edges and flowable hemostatic agents into the lateral gutters of the decompression.

The potential benefits of MIS may include avoidance of the morbidity inherent to open procedures, as well as minimization of epidural scar formation and postoperative low back pain. Weiner et al.¹³ completed a prospective evaluation of patients treated with MIS decompression and found 87% high satisfaction rates. Multiple series have reported success rates approaching 90%, with no increase in postoperative subluxation, even in patients with degenerative spondylolisthesis.¹⁴,¹⁵ Costa et al.¹⁶ retrospectively reviewed 374 patients treated with MIS decompression for LSS and found 87.9% of patients experienced clinical benefit, with only 0.8% incidence of postoperative instability. Khoo and Fessler¹ compared MIS decompression to open laminectomy and found the short-term outcomes to be equivalent, but with less morbidity in the MIS group. Similarly, Thome et al.¹⁷ did a prospective, randomized study comparing
MIS decompression to standard laminectomy and found the greatest improvement and lowest complication rate in patients who received MIS decompression. In another study, Rahman et al.¹⁸ compared MIS decompression to open laminectomy and observed less operative blood loss, shorter operative times/hospital stays, and fewer complications with the MIS technique.