Three Surgical Principles of MISS: Contralateral Decompression, Minimize Instability, and Indirect Decompression

11 Three Surgical Principles of MISS: Contralateral Decompression, Minimize Instability, and Indirect Decompression

Ibrahim Hussain, Rodrigo Navarro-Ramirez, Sertac Kirnaz, and Roger Härtl

Summary

There are at least three characteristic surgical principles that are relevant for the vast majority of minimally invasive spine surgeries (MISSs) that recur repeatedly in most MISS procedures. These include:

1.The idea that it is possible to achieve a bilateral decompression via a unilateral approac: This is typically done via a tubular or specular retractor or by an endoscope to achieve a bilateral decompression with or without contralateral foraminotomy through a unilateral, minimally invasive approach. This is also frequently called “over the top” decompression. The lumbar tubular decompression procedure has been named “unilateral laminotomy for bilateral decompression” (ULBD). This is a part of several procedures such as MIS transforaminal interbody fusion (TLIF), lumbar stenosis decompression without fusion, contralateral approach for foraminal disc herniation, and synovial cyst resection.

2.The technique of minimizing iatrogenic instability using “over the top” type decompression approaches: This reduces the need for instrumentation and fusion surgery. We use this now routinely in patients with lumbar stenosis and stable grade I spondylolisthesis,1^,² for the contralateral approach for decompression of synovial cysts,¹^,³ contralateral approach for decompression of intraforaminal pathology,³^,⁴^,⁵ and for the treatment of two-level lumbar pathology where one level requires a fusion and the adjacent level with stenosis just a decompression (“one and a half surgery”).⁶

3.The lateral, oblique, or anterior technique of indirect decompression of central and foraminal stenosis: Currently, the challenge is the accurate prediction of successful indirect decompression and to determine which patients should also undergo a direct decompression. This is further covered in Chapter 37 to 40. In addition, these approaches also allow a certain degree of deformity correction depending on the type of implants and techniques used.

Keywords: minimally invasive surgery (MIS) minimally invasive spine surgery (MISS) spine surgery principles spine concepts

11.1 Introduction

Minimally invasive surgery (MIS) has made enormous strides over the past three decades resulting in advanced patient care while minimizing complications associated with traditional open approaches. Most of the workhorse procedures in neurosurgical and orthopaedic spinal surgeries, including laminectomies, discectomies, and interbody fusions, can now be accomplished via MIS strategies. Within these broad categories lie pertinent principles which help provide guidance when assessing patients in the outpatient setting and are the subject of this chapter. Other surgical technique related topics include, for example, the effective and safe integration of two-dimensional/three-dimensional navigation and robotic surgery into the surgical workflow. Also, the use of special anesthetic enhanced recovery approaches (ERAS) falls into this category and will be covered in subsequent chapters.

11.2 Contralateral Decompression

Unilateral laminotomy for bilateral decompression (ULBD) for lumbar stenosis decompression: ULBD technique has evolved since its earliest description in the late 1990s.⁷^,⁸^,⁹ Initially, this was described by McCollough and Spetzger with open surgery but was then modified and combined with tubular surgery by Foley, Fessler, and others.¹⁰^,¹¹^,¹²^,¹³^,¹⁴ A paramedian approach using tubular retractors preserves the posterior tension band, and minimizes muscle cauterization, dissection, and iatrogenic instability. This technique has been shown to significantly improve bilateral symptoms regardless of the side of approach.¹⁵ It can also be used for multi-level decompressions using the “slalom” and “tandem” technique with alternating lateralizing sites of access,¹^,¹⁶ or at levels above a fusion.⁶ Furthermore, a recent meta-analysis demonstrated that patients with lumbar stenosis and degrative spondylolisthesis undergoing ULBD had fewer secondary reoperation rates for fusion, significant decrease in slip progression, and improved clinical outcomes based on pain and disability scoring systems than traditional open laminectomy.²

It is important to review the preoperative magnetic resonance imaging (MRI) in order to understand where the spinal stenosis is in relationship to the disc space. This will determine how far caudally the decompression should be carried (Fig. 11.1). In general, we recommend removing a few millimeters of bone of the upper portion of the lamina below. This will ensure that all the ligament has been removed.

Fig. 11.1 (a-d)Review of preoperative imaging and planning. An image viewer utilizing simultaneous sagittal and axial cuts should be used. The correct level of pathology is identified, and careful attention should be paid to any transitional anatomy. For disc pathology, the size, location, and characteristic of the herniation should be noted. Facet anatomy should be inspected for arthropathy, fluid signal in the joints, and bone spurs which may impair adequate docking of a tubular retractor on the lamina. Spondylolisthesis and ligamentum flavum hypertrophy may cause or exacerbate spinal stenosis. In some situations, the level of stenosis is below the level of the disc space as caudally as the inferior level’s pedicle, which should be accounted for in the decompression intraoperatively. Through minimally invasive surgery (MIS) unilateral laminotomy for bilateral decompression (ULBD) approaches, severe bilateral stenosis can be adequately decompressed.

When performing the minimally invasive ULBD approach, the contralateral lamina and lateral recess of the level of interest are the primary surgical target. Achieving adequate visualization and technical ergonomics is paramount to achieving this goal. After confirming level localization, a 2.5 to 3 cm incision is made about 1 to 1.5 cm from midline on the side of approach. Typically, 18 or 19 mm tubes are adequate to achieve decompression at L4/L5 and L5/S1 levels. At the higher levels (L1/L2, L2/L3, and L3/L4), a smaller diameter tube inserted close to midline minimizes risk of injury to the pars interarticularis. The initial trocar should be used to carefully identify and palpate the inferior edge of the lamina to be operated on. A characteristic “step-off” should be felt when toggling the trocar cranially-caudally. Sequential dilation with the tubular retractors is then performed (Fig. 11.2), taking note to gently rotate the retractors as they are inserted to allow for adequate muscle splitting rather than tearing. At this point, the microscope is brought in; exoscope is also an option.

Fig. 11.2 Instruments and equipment for minimally invasive spine surgery (MISS). (a, b) Retractor arm and table attachment, trocar, serial dilators, and various size tubular retractors. (c, d) 45- and 90-degree bayonetted Kerrison rongeurs, pituitary rongeurs, Frazier suctions, ball-tip probe, nerve hook, 11-blade scalpel on extended handle, and Scanlan tubular dural repair instruments. (e) Monopolar cautery device with bayonetted modification and stabilization with strip bandages.

Video 11.1: Our group prefers the use a 3-mm fluted bit on an extended 15-cm curved handle (Fig. 11.3a). The pinky finger of the dominant hand holding the drill is pressed on the body and used to provide stability, while an extended Frazier suction is held in the nondominant hand (Fig. 11.3b). The drill bit is placed inferior to the edge of the lamina and moved cranially, keeping the tip on the ligament as much as possible. This ensures that the ligamentum flavum is always visualized. Caution should be taken when approaching the cranial insertion of the ligamentum flavum since thecal sac will then be directly underneath the drill bit and is not protected by ligamentum flavum (Fig. 11.4a, b). The cranial insertion of the ligamentum flavum is identified and a ball-tipped dissector can be used to sweep the ligamentum caudally. To bite these superficial tissues away, 3- or 4-mm Kerrison rongeurs can be used (Fig. 11.4c). Along the inner layers of the ligamentum, a ball-tipped dissector or upgoing curette can be used to gently identify a plane in the cranial-caudal direction to identify the underlying epidural fat or thecal sac. To further expose epidural fat or the underlying thecal sac, 2- and 3-mm Kerrison rongeurs are used to slide into this plane and take bites of the ligamentum (Fig. 11.4d). Care should be taken to take bites away from the midline of thecal sac when possible and to ensure constant upwards pressure when biting to prevent iatrogenic dural injury.