Preoperative lateral x-ray in neutral position of a patient with grade I spondylolisthesis at L4–L5
Preoperative lateral standing scoliosis x-ray of a patient with grade I spondylolisthesis at L4–L5
Meyerding grading system of spondylolisthesis
25 % sagittal translation of vertebral body
50 % sagittal translation of vertebral body
75 % sagittal translation of vertebral body
100 % sagittal translation of vertebral body
Spondyloptosis: >100 % sagittal subluxation
Wiltse classification of spondylolisthesis 
Dysplastic or congenital spondylolisthesis
Isthmic spondylolisthesis (IS): defect in the isthmus or pars interarticularis
Lytic: fatigue fracture of the pars interarticularis
Elongated pars: which may result from pars fracture with subsequent union in the distracted position
Acute fracture: traumatic fracture of the pars
Degenerative spondylolisthesis (DS): resulting from long-standing instability
Traumatic spondylolisthesis: acute fracture of a posterior element (pedicle, lamina, or facets) other than the pars interarticularis
Pathologic spondylolisthesis: structural weakness of the bone secondary to a disease process such as a tumor or other bone disorders
Patients with symptomatic spondylolisthesis typically present with back, leg pain, or neurogenic claudication. Particularly in patients with dynamic instability, the back pain is often described as mechanical – low back pain initiated by axial loading, even with physiologic loads. Leg pain may be radicular and associated either with traversing or exiting nerve root compression. Neurogenic claudication, classically described as bilateral or unilateral calf, buttock, or thigh pain precipitated by walking and prolonged standing, results from central spinal canal stenosis.
Large, multicenter, randomized, prospective clinical trials have consistently reported improved outcomes for patients with symptomatic spondylolisthesis who undergo surgical decompression and fusion . Initially, patients’ symptoms may be managed more conservatively with nonsteroidal anti-inflammatory medications, physical therapy, local injections, weight loss, and exercise. In cases where a reasonable trial of nonsurgical therapy fails, operative intervention has been shown, reproducibly, to offer patients substantial relief of symptoms .
For more than a generation, posterior decompression including bilateral facetectomies was thought to be necessary to treat symptoms related to neuronal compression from spondylolisthesis . More recently, studies have documented that such extensive posterior boney resection and wide muscle dissection predisposed patients to progressive deformity, spinal instability, and symptom recurrence. Spinal fusion with decompression has since become the standard of care for symptomatic spondylolisthesis [8, 14, 20].
Since 2005, several studies have compared the efficacy of various techniques, some of which introduce the placement of lumbar interbody devices. To date, the lack of Level 1 studies proving efficacy has made it difficult to guide standard of care [17, 18]. Minimally invasive surgical techniques have also been employed to address patients with symptomatic spondylolisthesis. One of these techniques, extreme lateral interbody fusion (XLIF) or direct lateral interbody fusion (DLIF), has been demonstrated to be a safe, minimally invasive alternative to traditional open fusion procedures to treat spondylolisthesis [2, 16, 19].
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19.3 Surgical Technique
Lateral lumbar interbody fusion (LLIF), either XLIF or DLIF, is a true lateral retroperitoneal approach to the spinal column that allows for large interbody graft placement and excellent disk height restoration and provides indirect decompression at the stenotic motion segment . The patient is positioned in the right lateral decubitus position with the left side up. Using the left side is preferred to access the spine as the aorta and iliac arteries are sturdier than the vena cava and iliac veins and are more likely to withstand surgical handling without being injured. In patients with scoliosis, the aorta may lie on the lateral aspect of the vertebral bodies and thus would require access from the right side.
The intended surgical level is localized by fluoroscopy. The surgical site is marked, prepped, and draped in sterile fashion. Baseline EMG recordings are performed. Following the skin incision, the abdominal musculature is bluntly divided. Gentle blunt dissection allows one to traverse the retroperitoneal space with minimal disruption of the surround tissues. As the psoas muscle is approached, the lumbosacral plexus is localized by the use of automated electrophysiology. Directional EMG is used to ensure the surgeon docks the retractor anterior to the femoral nerve . Establishing a safe corridor through the psoas muscle requires imaging, real-time EMG, understanding of the regional anatomy with its variations, and surgeon experience. In an approach to the L4–L5 disk space in the well-aligned spinal column, the access corridor is slightly more anterior than that at rostral levels. In a patient with anterolisthesis, however, the regional anatomy may be altered, underscoring the importance of directional EMG as a navigational tool .
Preservation of the anterior and posterior longitudinal ligaments and avoidance of the neural foramen are critical to the success of LLIF for symptomatic spondylolisthesis. Exposure is achieved with an expandable three-bladed retractor, which allows for direct illuminated visualization facilitating diskectomy and complete anterior column stabilization using a large load-bearing implant. After the diskectomy and interbody graft placement, fusion is achieved by either placement of vertebral body screws and plate or from posterior lateral pedicle screw fixation (Figs. 19.3 and 19.4). For high-grade spondylolisthesis, restoration of disk height by the interbody cage often provides only partial reduction of the listhesis; the rest of the correction can be performed using a cantilever maneuver during posterior supplementation .
Postoperative lateral x-ray in neutral position of a patient with grade I spondylolisthesis at L4–L5 after LLIF
Postoperative lateral standing scoliosis x-ray of a patient with grade I spondylolisthesis at L4–L5 after LLIF
Another option is the oblique lumbar interbody fusion (OLIF) procedure, which is an alternative to the traditional anterior lumbar interbody fusion (ALIF) procedure with the convenience of the less-invasive lateral approach. Utilizing an oblique lateral trajectory (Fig. 19.5) away from the posterior nerves within the psoas muscle, this procedure is an alternative to approaches dependent on neuromonitoring to traverse the psoas muscle. By utilizing an oblique lateral approach to the spine, this procedure enables placement of a large interbody graft into the disk space (Fig. 19.6) for anterior column support and segmental sagittal alignment while minimizing the nerve, muscle, and bone obstacles associated with traditional direct lateral approach. At the same time, this approach also avoids the risk of injury to the aorta, iliac vessels, and genitourinary structures that are encountered in a traditional anterior approach .
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