High-grade lumbosacral spondylolisthesis is rare and likely a distinct entity from low-grade spondylolisthesis. Although the etiology of the condition is not completely understood, it is likely the result of a congenitally dysplastic lumbosacral segment with incompetent posterior elements that cannot withstand typical forces associated with maintenance of an upright posture. Unlike low-grade slips, whose manifestations are typically limited to painful segmental instability or neural compromise at the affected level, high-grade slips invariably provoke secondary changes in the regional pelvic anatomy and thus produce global sagittal deformity. It is this global deformity that makes the surgical management of high-grade spondylolisthesis so complex and so challenging.
Although slip reduction was contemplated as early as 1921, the procedure was undeniably associated with an unacceptably high rate of neurologic injury, and most experts agreed that in situ fusion was safer and produced acceptable results. Still, some surgeons continued to pursue reduction, believing that correction of the underlying deformity was supported by sound mechanical principles and—in the right hands—could be safely accomplished. With the advent of modern transpedicular instrumentation, what had once seemed unsafe became possible, and the debate was rekindled between proponents of reduction and advocates of in situ fusion. Unfortunately, no randomized, controlled trials exist to definitively answer the question of which approach is superior. Nevertheless, a close examination of the evidence is warranted and will allow the modern spine surgeon to formulate a cogent approach to the treatment of the patient with high-grade spondylolisthesis.
A 22-year-old woman came for treatment of low back pain that had persisted for the past 8 years; was worse when she was sitting, standing, or walking; and had progressed over the previous year. Nonsteroidal antiinflammatory drugs and physical therapy were initially helpful but no longer provided relief from the pain. In addition, her pain had recently begun to radiate into the buttocks and legs in a nondermatomal distribution.
Exam: On physical examination, the patient was a well-appearing young woman who, when standing erect, showed a subtle sagittal deformity in which the trunk was thrust forward relative to the hips. Motor strength was full throughout, and no sensory deficit was detected. Hamstring tightness was present bilaterally. Deep tendon reflexes were normal throughout. The lumbar paraspinous muscles were moderately tender to manual palpation. The patient reported no bowel or bladder dysfunction.
Imaging: Plain spinal radiographs were obtained, including 36-inch standing posteroanterior and lateral radiographs and flexion-extension views of the lumbar spine. These demonstrated Grade IV lumbosacral spondylolisthesis with the following characteristic findings: retroversion of the pelvis, dysplasia of the posterior elements of L5, including bilateral pars interarticularis defects, rounding of the sacral dome, trapezoidal shape of the L5 vertebral body, and positive sagittal balance. Magnetic resonance imaging of the lumbar spine was obtained to evaluate neural element involvement and confirmed severe, bilateral L5 and S1 neural foraminal narrowing ( Figure 20-1 ).
Among the many decisions to be made when planning a surgery for high-grade spondylolisthesis is whether to reduce the deformity or simply perform fusion in situ ( Table 20-1 ). If reduction is to be performed, will complete anatomic realignment be attempted, or is partial reduction of the slip angle sufficient ( Tips from the Masters 20-1 )? It has become widely accepted that when reduction is to be attempted, wide decompression is essential to minimize the risk of iatrogenic neurologic deficit. Instrumentation, on the other hand, is for most surgeons a must—although in rare cases (such as with severe osteoporosis or renal osteodystrophy) a noninstrumented fusion might be considered, followed by postoperative immobilization in a brace or cast. How, and which levels, to instrument must then be determined.
Partial reduction (particularly of slip angle ) offers significant biomechanical advantages, whereas complete (anatomic) reduction is rarely necessary.
|5.± Extension of instrumentation/fusion to “normal” levels|
|6.± Postoperative immobilization|
Traditional pedicle screw-rod constructs remain the gold standard, but additional options exist, particularly for fixation of the lumbosacral joint; for example, transvertebral screws directed through the S1 pedicle, across the L5-S1 disk space, and into the body of L5 provide excellent fixation across multiple cortices when significant reduction is not desired or achievable, or when significant dysplasia of the L5 pedicles precludes adequate fixation ( Tips from the Masters 20-2 ).
Strong consideration should be given to incorporating supplemental fixation such as iliac screws, S2 pedicle screws, and/or L4 pedicle screws to protect the construct from the powerful shear forces acting at the lumbosacral junction, especially if anatomic reduction is not performed.
Next, the surgeon must decide whether to perform a decompression, which can simply consist of the removal of the loose posterior elements of L5 or may involve wide removal of the pars interarticularis; in addition, osteotomy ( Tips from the Masters 20-3 ) of the sacral dome may in some cases facilitate reduction and increase the safety of the procedure. Options for arthrodesis include posterior (if decompression is not performed), posterolateral, anterior, or a combination of posterior-posterolateral and anterior ( Tips from the Masters 20-4 ). Anterior interbody arthrodesis may be accomplished through an anterior (transperitoneal) approach, or via a transforaminal or posterior approach. Typically, interbody arthrodesis is accomplished using an interbody device (e.g., titanium or carbon fiber cage) or structural bone graft. Alternatively, a metal cage or fibular dowel may be inserted—with either a posterior or anterior trajectory—across the lumbosacral junction.
Wide decompression of the neural elements with particular attention to compressive dysmorphic elements (e.g., fibrocartilaginous pars, sacral dome), in addition to judicious distractive reduction under direct visualization of the neural elements, is essential to avoid iatrogenic neural injury.
Interbody fusion, whether performed from an anterior or posterior approach, is essential to the long-term success of the final construct.
Surgical staging must additionally be considered, particularly in regard to the patient’s ability to tolerate the extended time under anesthesia required by a combined anterior-posterior procedure. Finally, the surgeon must decide whether to extend the arthrodesis and instrumentation beyond the lumbosacral segment. Incorporation of L4 is typical, but the addition of S2 pedicle screws or iliac screws is gaining acceptance for improved construct strength.
Given the severity of the patient’s symptoms, her failure to obtain lasting relief from conservative measures, and her dramatic lumbosacral deformity, she elected to proceed with surgery. She subsequently underwent a single-stage procedure using a posterior midline approach for wide decompression of L5 and pedicle screw fixation at L4, L5, and S1, followed by partial reduction of her lumbosacral slip, lumbosacral interbody fusion, and bilateral L4-S1 inter–transverse process (and interalar) fusion ( Tips from the Masters 20-5 ). There were no intraoperative or postoperative complications and she was able to ambulate without the need for a brace on the second postoperative day. She was discharged home on the third postoperative day and, at latest follow-up, remains pain-free without any need for oral analgesic medicines ( Tips from the Masters 20-6 ). Plain lumbar radiographs obtained postoperatively revealed successful partial slip reduction ( Figure 20-2 ).
Consider transsacral, transvertebral fibular dowel and/or screws when anatomic reduction is not performed.
Consider using the Gaines method when reduction of spondyloptosis is deemed necessary.
The patient is positioned on a radiolucent Jackson table to decompress the abdomen (and thereby decrease intraoperative bleeding) and enable flexion of the pelvis and extension of the lumbar spine via positioning of the anterior superior iliac spine pads. Following wide lateral decompression and exposure of the neural elements, including sacral dome osteotomy when necessary, the reduction maneuver is executed using pedicle screw fixation with extended tab reduction screws from L4 to S1 followed by distraction under direct visualization of the exiting nerve roots. Care is taken not to distract excessively to avoid screw loosening, nerve stretch injury, and iatrogenic instability at adjacent levels. Upon completion of reduction, the nerves are palpated to ensure that they are not under tension, and direct nerve root stimulation is performed.
The recommendation is that continuous neurophysiologic monitoring be performed routinely, including measurement of somatosensory and motor evoked potentials and electromyography, and reduction is terminated if any abnormality is detected with the maneuver. Posterolateral instrumented fusion from L4 to S1 is performed and augmented in essentially all cases by interbody fusion. Use of the anterior approach to the lumbosacral interspace is often impractical, given the limited access to the disk space when slip percentage and angle are severe, and thus the anterior fusion is in almost all cases executed via the transforaminal approach. To reiterate, the many benefits afforded by interbody fusion include (1) availability of increased surface area for fusion, (2) compressive load sharing to increase the stability of posterior instrumentation, (3) indirect neural decompression of the neural foramen via increased intervertebral height, and (4) restoration of segmental lordosis. Iliac fixation is commonly included, particularly when anatomic reduction is not achieved. In cases of spondyloptosis, one of three options is selected, depending on the particular anatomy and clinical presentation: (1) fusion in situ from L4 to the sacrum using fibular dowel grafts, (2) posterior reduction and fusion with iliac fixation, or (3) the Gaines procedure of anterior-posterior L5 spondylectomy and placement of L4 onto the sacrum, supplemented by iliac fixation.
Patients are in most cases mobilized by the second postoperative day. Occasionally, a thoracolumbosacral orthosis (including thigh extensions) is provided to adequately control the pelvis for 3 or 4 months or until radiographic fusion is confirmed.
Discussion of Best Evidence
Due in large part to the rarity of high-grade lumbosacral spondylolisthesis, no prospective studies exist comparing reduction with fusion in situ. The best evidence available to date is limited to retrospective case series with a small number providing a comparison of surgical strategies. Of the several dozen retrospective series reported, more than one third predate modern techniques of transpedicular instrumentation, which makes any conclusions from these publications of limited relevance to contemporary surgical practices.
Further confounding the interpretation of this body of literature is the fact that many series suffer from profound heterogeneity: Study populations frequently included both skeletally mature and immature patients, combined new cases and salvage procedures, and comprised a mixture of patients with spondyloptosis and Grade III/IV slips (many experts posit that spondyloptosis requires a fundamentally different approach). The surgical approach was seldom uniform, with many studies describing a mixture of anterior, posterior, and combined approaches, inconsistent decompression, variable fusion methods, and widely varying degrees of reduction. Finally, the length and quality of follow-up frequently varied significantly both within a given study and between series. Perhaps most problematic of all is the inconstant use of validated outcome measures; moreover, those studies that do use metrics such as the Oswestry Disability Index (ODI) and the Scoliosis Research Society (SRS) questionnaire only rarely report preoperative scores.
In an attempt to draw meaningful conclusions from this heterogeneous body of literature, the available studies have been stratified into three tiers according to the quality of the evidence presented. After exclusion of historical studies that did not use transpedicular instrumentation, each study was evaluated with respect to size, length of follow-up, and use of a validated outcome measure. High-quality studies were of at least moderate size (10+ patients), had at least 2 years of follow-up in all cases, and used a validated outcome measure; intermediate-quality studies were deficient in meeting only one of these criteria; low-quality studies were deficient in meeting two of these criteria.
Of the 19 eligible studies, 3 case series and 1 retrospective comparative study were identified as “high quality” ( Table 20-2 ).
|Ruf et al.|
|Sasso et al.|
|Hanson et al.|
|Poussa et al.|
Following spondylolisthesis reduction in 27 patients, Ruf and colleagues concluded that anatomic reduction and circumferential instrumented fusion from L5 to S1 is feasible and safe, and thus superior to in situ fusion because it accomplishes the ultimate goal of surgery for high-grade spondylolisthesis—restoration of sagittal balance with minimal functional restriction. They note that neurologic injury may largely be avoided by using four key techniques: (1) wide, lateral exposure of the nerve roots; (2) removal of potentially compressive disk material or bony sacral ledge; (3) avoidance of excessive distraction, which is permitted by sufficient resection of the sacral dome and use of small interbody cages; and (4) adequate correction of the sacral retroversion, which thereby relieves tension on the nerve roots.
Sasso and associates reported their results of partial reduction (of slip angle only) in 25 patients and concluded that complete (anatomic) reduction of severe slips is not essential and that partial kyphosis correction followed by fusion from L4 to S1 is safe and results in high satisfaction scores.
Hanson and co-workers reported positive results after partial reduction and circumferential instrumented fusion using a transvertebral fibular dowel in 15 patients. They concluded that partial reduction was safe and effective, noting that use of anterior grafts is critical to the success of the operation.
Poussa and colleagues authored the only comparative series in this group of studies. They reported lengthy follow-up (average, 14.8 years) after in situ fusion or reduction for treatment of high-grade spondylolisthesis. They noted a higher rate of permanent neurologic deficit in the reduction group (9.1% vs. 0%) and found that, although partial correction of slip percentage was achieved and sagittal alignment was improved in the reduction group, outcome (as measured by the SRS questionnaire and ODI) was superior in the in situ fusion group. They concluded that good clinical results are achieved mainly because the slip is stabilized and the neural elements decompressed, and that in situ fusion should therefore be considered the surgical treatment of choice for high-grade spondylolisthesis.
In summary, four studies met the criteria for “highest quality.” Three of the four are case series in which patients were treated with reduction, and these report positive results: high patient satisfaction and function scores (as measured by the SRS questionnaire, ODI, and visual analog scale [VAS]), low rates of permanent neurologic deficit (0% to 3.7%; weighted average, 1.5%), and no loss of correction. The sole comparative study in the group demonstrated inferior results after reduction. This study, however, suffered from significant variability in surgical technique, and although permanent neurologic injury was reported only in the reduction group (one patient), two patients in the in situ group required reoperation to decrease the graft height after emerging from the initial surgery with bilateral peroneal palsies. Furthermore, the poor results after reduction reported by the authors are not consistent with the results reported in the other three studies.
In conclusion, these studies suggest that partial reduction, when accomplished in conjunction with wide neural element decompression and circumferential instrumented arthrodesis, is safe, effective, and durable with low rates of neurologic injury (0% to 9.1%; weighted average, 2.6%), high patient satisfaction, high fusion rates, and infrequent loss of correction at more than 3 years of follow-up.
Eleven studies, consisting of eight case series and three retrospective comparative series, met the criteria for “intermediate quality” ( Table 20-3 ).