Part I Posterior Approach

Benjamin Khechen, Brittany E. Haws, Ankur Narain, Fady Hijji, Jordan A. Guntin, Kaitlyn L. Cardinal, and Kern Singh

2 Introduction to MIS Posterior Approach

2.1 Introduction

The minimally invasive spine (MIS) posterior approach for decompression and fusion of the lumbar spine utilizes the Harms modification of the original Wiltse approach, described in 1968. ¹ ^, ² The posterior parasagittal technique was designed to reduce the morbidity associated with the traditional open midline approach. ³ This approach minimizes muscular trauma by dissecting the natural plane of two separate muscle groups and allowed for the preservation of midline structures. ³ The MIS posterior approach can be utilized for the treatment of a variety of pathologies of the thoracic and lumbar spine. ⁴ ^, ⁵ These treatment options can include decompression, diskectomy, posterior instrumentation, and interbody fusion. ⁴ ^, ⁶ This approach allows for the direct decompression of neural elements and direct access to the disk space. ⁴ ^, ⁶ ^, ⁷ ^, ⁸

2.2 Surgical Anatomy

The lumbar spinous processes and iliac crests are easily palpable for orientation prior to performing the MIS posterior approach. This approach utilizes the internervous plane between the paraspinal muscles, minimizing any requirement for muscle dissection. However, multiple structures of the posterior vertebrae are encountered with this approach. The lamina and facet joints are directly involved with this approach, and their removal will lead to exposure of the traversing nerve root and underlying dura mater.

Due to the posterior orientation of this approach, some structures are at risk for injury. ⁴ Primarily, the traversing and exiting nerve roots can be iatrogenically injured as it passes the surgical corridor. Additionally, the dura is within the proximity of the approach and may be inadvertently disrupted while decompressing the overlying structures.

2.3 Surgical Technique

2.3.1 Positioning

Patients undergoing a posterior MIS approach are placed in the prone position on a radiolucent table following anesthesia induction (▶ Fig. 2.1). Pads are placed under the manubrium and anterior superior iliac spine to maintain lumbar lordosis. The patient’s legs are left extended, while the arms are placed in 90 degrees of shoulder and elbow flexion. A foam pad is placed underneath the flexed arms to reduce the risk of ulnar nerve compression. Prior to surgical preparation and draping, fluoroscopic images are obtained of the lumbar spine to confirm visibility of the pedicles and other spinal anatomy.

2.3.2 Approach (Exposure) for MIS Transforaminal Lumbar Interbody Fusion

A 22-gauge needle is oriented toward the facet joint at the disk level of interest and inserted. A fluoroscopic image is then obtained to confirm the correct surgical level. The side of the operation to be performed is determined by the location of neurologic symptoms. Following confirmation, an incision is made paramedially, 4 to 5 cm lateral to the midline. The incision is made to be approximately 2.0 cm in length in order to fit the final tubular retractor. Bovie cautery is used to incise the underlying fascia. The smallest tubular dilator is inserted through the muscle down to the level of the facet joint or lamina in a lateral to medial direction. Once appropriate positioning of the initial dilator is determined using fluoroscopy, serial dilators are inserted, gradually increasing the size of the surgical corridor. Finally, the tubular retractor is then placed over the last dilator and the dilators are subsequently removed (▶ Fig. 2.2). The tubular retractor is then fixed to the table after being docked over the area of interest. Fluoroscopy is then utilized to confirm adequate positioning and orientation of the retractor.

**Fig. 2.1** Demonstration of prone surgical positioning. (Reproduced, with permission, from Singh K, Vaccaro A, eds. Pocket Atlas of Spine Surgery. 2nd ed. New York, NY: Thieme; 2018.)

The following aspects of the procedure are performed under illumination with loupe magnification or with the use of an operating microscope. Residual soft tissue overlying the lamina and facet is removed with electrocautery followed by pituitary instruments. Following laminar exposure, a high-speed drill is used to perform a complete bilateral laminectomy. Bone removed from the laminectomy can be used as graft material within the interbody cage. Once the ligamentum flavum is identified, the laminectomy is extended cranially until the flavum insertion is visualized; however, the flavum is left intact to protect underlying neural structures. Following complete laminectomy, a facetectomy is performed. To facilitate the facetectomy, the inferior articular process and pars interarticularis are removed first. Caution must be taken to avoid drilling into the pedicle. Once the facet joint is removed, the ligamentum is removed to expose the underlying nerve roots. The working zone for MIS transforaminal lumbar interbody fusion (TLIF) is defined medially by the traversing nerve root and laterally by the exiting nerve root (▶ Fig. 2.3). The venous plexus surrounding the epidural space can cause significant bleeding; therefore, adequate hemostasis using bipolar electrocautery is crucial to maintain appropriate visualization of the disk space.

2.3.3 Disk Space Preparation

A complete diskectomy is performed through the tubular retractor. Pituitaries and curettes can be utilized to perform the annulotomy and remove disk material. Once all disk material is removed, the intervertebral space is distracted with paddle distractors and the endplates are prepared utilizing end plate shavers.