Posterior Approaches to the Lumbar Spine: Minimally Invasive Decompression

Posterior Minimally Invasive Approaches to the Lumbar Spine

Posterior lumbar decompressive procedures are fundamental tools in the surgical treatment of symptomatic lumbar degenerative disease. Lumbar spinal stenosis is one of the most common pathologies resulting in leg and back pain, claudication, and disability. After conservative measures have been exhausted, surgical decompression is an option. Lumbar discectomy has been shown to provide good to excellent outcomes in 70% to 94% of patients with radiculopathy and back pain ^{. ,} Similarly, selective lumbar foraminotomy has been demonstrated to provide excellent results in up to 95% of patients.

Open laminectomy is the most common method used to treat lumbar spinal stenosis and has been shown to be safe and effective for the treatment of lumbar spinal stenosis in 62% to 70% of patients. ^, However, open posterior approaches to the lumbar spine require extensive muscle retraction, leading to spinal muscle atrophy and persistent paraspinal nerve damage. ^, Muscle and soft tissue manipulation leads to increased postoperative pain, spasm, and dysfunction, which can be persistently disabling. Furthermore, wide laminectomies and long segment decompressions disrupting osteoligamentous structures that stabilize the lumbar spine may exacerbate preexisting spondylolisthesis and increase the risk for postoperative sagittal plane deformity.

Less invasive methods of lumbar discectomies were first reported by Caspar and colleagues in the early 1990s. ^, In 1997, Foley and Smith detailed the first endoscopic tubular approach in a case of a far lateral herniated disc. This was followed by a larger series with our senior author and Foley and colleagues. ^, The METRx (Medtronic, Sofamor Danek, USA) tubular retractor system was developed in 2003, providing a method of minimal muscular disruption. Tubular retractors facilitate the fundamentals of minimally invasive surgery (MIS) techniques, which involve minimal muscle dissection and soft tissue trauma, and avoid detachment of the osteoligamentous structures, which may help preserve stabilizing structures; while reducing operative time, blood loss, and hospitalization times and improving clinical outcomes. Tubular retractor systems and the use of endoscopic technology or the microscope have allowed for the application of MIS techniques for decompression of the lumbar spine.

The surgical techniques to follow will build upon each other as we “unroof” the lumbar spine. We will start with the MIS posterior lumbar foraminotomy, followed by the MIS lumbar discectomy, and concluding with the MIS lumbar laminectomy ( Fig. 127.1 ). The MIS posterior lumbar unilateral approach for bilateral decompression of stenosis is the most technically challenging. The indications, preoperative evaluation, general operative setup, positioning, general surgical technique, and nuances of MIS posterior lumbar techniques will be discussed.

Indications

Patients who are candidates for MIS lumbar procedures are those that have failed conservative treatment whose symptoms consist of lumbar radiculopathy, claudication, and neurological sensory or motor changes, with or without lower back pain. Clinical symptoms should correlate with magnetic resonance imaging (MRI) findings, which may include an osteophyte, LF hypertrophy, facet arthropathy, loss of intervertebral disc height, bulging annulus fibrosus, static grade I spondylolisthesis central or foraminal stenosis, or disc herniation ( Fig. 127.2 ). These approaches can be used in patients with recurrent disc herniations or in need of a revision foraminotomy. MIS techniques can also be used in patients requiring multilevel decompression with symptomatic lumbar degenerative disease. MIS posterior lumbar decompression techniques can be used in patients with degenerative scoliosis; however, tubular anatomy can be disorienting, and the degree of scoliosis can create an even greater challenge. Surgical experience is a major contributor to successful results. Reoperation using an MIS laminectomy technique (especially an “over-the-top” technique) is not advised for less experienced surgeons. The protective plane between the dura and LF is lost, given the scar tissue. Finally, patients with a dynamic component of their pain (improved when lying down vs. when standing) should be evaluated with flexion/extension films. Contraindications to MIS laminectomy alone include mobile grade I spondylolisthesis or more static spondylolisthesis of higher grade. Further details will be discussed later in this chapter.

Preoperative Evaluation

The preoperative radiographic evaluation follows a detailed history and physical examination and should include MRI or postmyelographic computed tomography, in addition to anteroposterior (AP), lateral, and dynamic lumbar radiographs. Electromyography (EMG) and nerve conduction studies (NCS) may also assist to confirm the localization of radicular compression. Selective nerve root blocks can also be a useful additional therapeutic and diagnostic tool. All patients with pure radiculopathy who go on to surgery have failed a trial of conservative therapy, which includes oral medications, physical therapy, or steroid injections. All patients are carefully counseled regarding the risks and benefits of and the alternatives to surgery.