Spondylolisthesis Reduction

Overview

Spondylolisthesis, a slippage or displacement of one vertebra on another, is a common spinal condition that affects children and adults. Spinal pathology may vary for the slip severity, but the clinical presentation can be quite similar. Often, patients come to medical attention with severe back and leg pain, and a cosmetic or postural component may be apparent. Cauda equina symptoms are an uncommon feature in the vast majority of patients with low-grade spondylolisthesis, and they may occur in only a small percentage of high-grade spondylolisthesis.

Classification

A widely used classification, as described by Meyerding, is useful in understanding the amount of listhesis. The Meyerding grade is shown in Table 48-1 .

Table 48-1

Meyerding Classification

Meyerding Grade	Slip (%)
I	0-25
II	25-50
III	50-75
IV	75-100

The percentage of slippage is calculated by measuring the distance between the posterior borders for the cephalad vertebral body and the caudad vertebral body, and then dividing that distance by the length on the inferior end plate ( Fig. 48-1 ). Most authors agree that grade three and four slips are considered high-grade and are generally associated with higher incidence of progression and disabling symptomatology.

In addition to the translational deformity, high-grade slips can have angular deformity as well. The degree of angulation can be expressed as a slip angle ( Fig. 48-2 ). This slip angle or lumbosacral kyphosis can have a profound impact on the entire lumbar spine, because the patient often compensates with hyperlordosis, which leads to facet joint changes, stenosis, and potential retrolisthesis proximal to the more obvious deformity at L5–S1.

Evidence-based Decision Making

Unfortunately, no prospective randomized studies compare the radiographic and clinical outcomes of reduction and fusion versus in situ fusion. Current studies of high-grade spondylolisthesis are of limited number, and only level III studies exist. Using this available literature, short- and long-term outcomes of patients undergoing these procedures suggest that both reduction and in situ fusion can be performed safely and can provide reliable radiographic and clinical outcomes in terms of patient success and pain improvement. Comparable adverse outcomes and risks occur with both procedures. The literature also suggests that patients with high-grade developmental spondylolisthesis may benefit from having a reduction of the deformity to improve global spinal alignment and perhaps enhance the biomechanical environment for fusion. Strong consideration for reduction should be given to pediatric patients with a significant lumbosacral kyphosis. Ultimately, it is up to the surgeon to treat each patient in an individualized plan that best suits the clinical scenario.

Treatment Options

Surgical procedures for spondylolisthesis in this chapter will focus on three primary techniques. In the setting of low-grade slips, we recommend in situ fusion with posterior instrumentation. In the setting of high-grade slips, in situ fusion or a reduction and fusion may be done. The indications for reduction of a high-grade slip include 1) progression of a high-grade slip; 2) inability to stand upright, with significant lumbrosacral kyphosis; 3) unacceptable clinical appearance; or 4) a high slip angle that is not reduced, which is more likely to develop a progression after fusion.

Low- and High-Grade Slip Treated with Fusion

A midline incision is made over the lumbar spine. The incision is taken down through the lumbodorsal fascia, and the spinous processes of the involved lumbar spine and sacrum are subperiosteally dissected ( Fig. 48-3 ). Intraoperative radiographs can be used to confirm the levels. Exposure of the transverse processes of L5 and S1 follow. Typically, the goal is just to fuse L5–S1, but sometimes the L4–L5 facet is so deteriorated and adherent to the old pars fracture, it may require fusion up to L4. Low-grade slips can be managed with fusion of only the L5–S1 segment; however, higher grade slips will often need fusions extending to the L4 level.

A Gill laminectomy is performed, and typically the lamina is quite unstable as a result of the chronic pars fractures. A central laminectomy is performed by resection of the medial articular facets, because these are grossly unstable ( Fig. 48-4 ). The next step is to inspect the spinal canal, looking at each nerve root and decompressing each root in the subarticular region, as well as within the foramen, with angled Kerrison rongeurs and curettes. In particular, the L5 roots typically get severely pinched in the caudal-cranial direction because of the pedicle abutting the sacrum. Often a posterior lumbar interbody fusion (PLIF) can be used to regain the foraminal height, thereby indirectly decompressing the L5 nerve root.

The S1 nerve root is retracted medially ( Fig. 48-5, A ), then bipolar cautery is used to cauterize all the epidural veins. A window into the annulus is made by resecting a small portion of the posterior superior lip of the remodeled sacrum with an osteotome and pituitary rongeurs (see Fig. 48-5, B ). This allows for good access to the intervertebral disk space. Serial dilators are then inserted from 6 to 10 mm bilaterally. The disk space is then reamed out, including the disk and cartilage end plate. Often a 22- to 32-mm by 10- to 12-mm intervertebral cage device is used. This is placed into the L5–S1 interval bilaterally to get good anterior column support, and after doing this, the L5 nerve root will be completely mobile and free as a result of the caudal and cranial decompression ( Fig. 48-6 ).

The transverse process of L4, L5, and the sacrum are carefully decorticated. The autologous bone graft is then packed into posterolateral gutters, fusing the L4 through sacral segments. Two pedicle screws are inserted into L4, L5, and the sacrum. The sacral screws are placed bicortically to maximize stability of the construct, and two 5.5-mm rods are cut to the appropriate length and contoured; the rods are placed into the screw heads, and the nuts are tightened according to the manufacturer’s specifications. Intraoperative anteroposterior (AP) and lateral radiographs can be used to confirm good positioning of the hardware and proper alignment of the spine. Compression between the L5–S1 screws can be performed to get further lordosis and compression of the anterior cages to prevent these cages from backing out inadvertently before final tightening of the nuts. The wound is then irrigated and closed over a drain.

Formal Reduction Maneuver

For higher grade slips, the first step is to place the pedicle screws in the sacrum. The sacral fixation must be solid, because it serves as the base for the reduction maneuver. To this end, we recommend bicortical fixation into the sacrum. Some authors recommend an S2, iliac, or sacral plate bolster. The plate allows for fixation into the promontory and the ala. Once the stable sacral base is established, a reduction can be performed. Screws should then be placed into the L4 vertebra and into the L5 vertebra, if it is accessible. The distractor is applied to L4 and the sacrum to help disengage the L5 vertebra ( Fig. 48-7 ).