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Adult Low-Grade Acquired Spondylolytic Spondylolisthesis: Evaluation and Management

Kwon, Brian K., MD, PhD, FRCSC*; Albert, Todd J., MD

doi: 10.1097/01.brs.0000155561.70727.20
Evaluation and Management
Free

Study Design. Literature review.

Objective. To discuss the presentation and evaluation of adult patients with acquired spondylolytic spondylolisthesis of low-grade severity and to review surgical treatment options.

Summary of Background Data. Low-grade adult acquired spondylolytic spondylolisthesis is one of the most common forms of spondylolisthesis.

Methods. Literature review.

Results. Adults with symptomatic low-grade spondylolytic spondylolisthesis are treated predominantly nonoperatively, with activity modification, physiotherapy, nonsteroidal anti-inflammatory agents, and local injections. Surgical treatment is reserved for individuals with intractable back pain and/or radicular symptoms. A number of surgical options exist, including direct pars repair, and fusion with or without decompression. Fusion can be achieved by providing anterior column support alone, posterior support alone, or a combined circumferential approach; the optimal method by which fusion should be achieved has not been established.

Conclusions. The management of low-grade acquired spondylolytic spondylolisthesis requires a thoughtful and individualized approach, recognizing the frequently benign natural history of the deformity and the potentially good clinical outcomes from surgery in those select patients with intolerable back and leg pain. While fusion is the mainstay of surgical management, a prospective randomized study would be extremely useful to delineate the optimal fusion technique.

Low-grade acquired spondylolytic spondylolisthesis in adults is a frequently benign condition. This paper reviews the natural history, clinical evaluation, surgical options for such patients. The optimal fusion technique has not been established, although a systematic review of the literature favors procedures that provide circumferential stability

From the *Combined Neurosurgical and Orthopaedic Spine Program, Department of Orthopaedics and Gowan and Michele Guest Neuroscience Canada Foundation/CIHR Research Fellow, International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia; and †Department of Orthopaedic Surgery, Thomas Jefferson University and the Rothman Institute, Philadelphia, PA.

Acknowledgment date: May 25, 2004. Acceptance date: December 21, 2004.

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Level of Evidence: Therapeutic Studies, Level III.

Address correspondence and reprint requests to Todd J. Albert, MD, Department of Orthopaedic Surgery, Thomas Jefferson University and the Rothman Institute, 925 Chestnut St., Philadelphia, PA 19107; E-mail: Tjsurg@aol.com

Lumbosacral spondylolisthesis was initially classified in 1963 by Newman and Stone in their radiographic review of more than 300 patients.1 Approximately half of these patients were described as having a “spondylolytic” form of spondylolisthesis, in which the anterior translation was related to a lytic defect in the pars interarticularis. Subsequent classification systems by Wiltse et al2 and by Marchetti and Bartolozzi3 have been proposed and are discussed in greater detail elsewhere within this Focus Issue. In terms of describing the actual severity of spondylolisthesis, the Meyerding scale is the most widely recognized method. In this scale, the severity is graded according to the relative extent of anterior translation of the cephalad vertebral body over its distal counterpart. Anterior translation of less than 25%, 25% to 49%, 50% to 74%, 75% to 99%, or 100% or greater are defined as Grades I, II, III, IV, or V, respectively. This review addresses the topic of adult patients who present with an acquired spondylolytic spondylolisthesis, and specifically those with a “low-grade” (Meyerding Grade 0, I, and II) severity.

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Presentation and Clinical Evaluation

For those adults with low-grade spondylolisthesis who seek a medical opinion, the typical complaints are that of low back pain and/or radicular symptoms.4,5 A thorough clinical history and physical examination should be performed to characterize the back pain, distinguish referred from radicular symptoms, document sagittal alignment and spinal mobility, and establish the presence of any neurologic deficit, paying particular attention to the function of the nerve roots exiting at the level of the olisthetic vertebrae. Neuroforaminal compression may be related to hypermobility of the olisthetic segment, fibrocartilaginous scar around the pars defect, and ventro-inferior compression from the disc.

The imaging analysis begins with conventional radiology, with anteroposterior, lateral, and flexion–extension radiographs providing the most useful information (Figures 1 and 2). If an obvious pars defect is not visualized on the lateral views, an oblique radiograph may be helpful in demonstrating the defect as the collar of the “Scottie dog.” A number of radiographic indices can be made from the standing lateral radiograph, including the degree of slippage, slip angle, sacral inclination, sacrohorizontal angle, and lumbar index. The slip angle is conceptually appealing to consider as a representation of the local kyphosis across the L5–S1 motion segment; its correction during surgical management is a desirable goal in an effort to restore physiologic lumbosacral lordosis.

Figure 1

Figure 1

Figure 2

Figure 2

CT and MRI are useful advanced imaging methods, particularly in the preoperative planning stage, for better defining both the bony and soft tissue anatomy, respectively. The axial CT scans can demonstrate the actual pars defect, facet hypertrophy, and the pedicular anatomy (i.e., size and trajectory) in anticipation of internal fixation. Sagittal reconstructions are useful for looking at the adaptive changes within the olisthetic vertebrae and its subjacent vertebrae such as the erosion and rounding off of the sacral dome in an L5–S1 spondylolisthesis. The MRI is helpful for evaluating the neural foramen on the sagittal views, particularly on T1-weighted images in which the dark-appearing nerve root is typically surrounded by bright-appearing fat within the foramen (Figure 3). The extent of disc hydration and height can be determined on the MRI, both at the olisthetic and adjacent levels (Figure 4). Provocative discography may be useful to determine if adjacent level is contributing to the low back pain, although one should recognize that there are limitations to the interpretation and predictive value of this examination.6

Figure 3

Figure 3

Figure 4

Figure 4

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Treatment Decisions: Nonoperative Versus Operative Management

Not unlike other spinal disorders, management decisions for adults with low-grade acquired spondylolytic spondylolisthesis need to take into account the natural history of the deformity, the severity and duration of symptoms, and patient comorbidities. The long-term follow-up studies by Frederickson et al7 and Beutler et al8 have shown that the natural history of this condition is typically a benign one, and that while progressive deformity might occur as the result of disc degeneration at the olisthetic level, the incidence and magnitude of such progression is small. For those patients with intolerable back and/or leg pain recalcitrant to a prolonged conservative treatment program, the prospective randomized trial reported by Moller and Hedlund in July 2000 indicated that in situ posterolateral fusion (PLF) can provide favorable clinical outcomes compared with a supervised exercise program.9 Given that there is no consensus as to what constitutes the optimal surgical treatment (see below) or, for that matter, what constitutes an acceptable nonoperative regimen, the decision to recommend surgical treatment to an adult patient with low-grade spondylolytic spondylolisthesis must be carefully individualized.

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Treatment Decisions: Operative Management

The mainstay of surgical treatment for adult patients with low-grade acquired spondylolytic spondylolisthesis is fusion, with or without decompression. Direct pars repair in adult patients or decompression alone (i.e., Gill procedure) are procedures that are not typically recommended and will not be discussed.

The fusion techniques available for this deformity can be conceptually divided into those techniques that achieve posterior column stability (i.e., posterolateral intertransverse fusion [PLF]), those that achieve anterior column stability (i.e., anterior lumbar interbody fusion [ALIF]), and combined approaches that achieve both (i.e., ALIF + PLF, or posterior/transforaminal lumbar interbody fusion).

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Posterior Approach: Posterolateral Intertransverse Fusion With or Without Decompression

Techniques that achieve posterior column stability are the most straightforward and historically the most popular means of performing fusion. Posterior surgical techniques allow for direct decompression of the neural elements, deformity correction if desired, and the achievement of stability with pedicle screw instrumentation. The posterior exposure and obligatory stripping of paraspinal musculature, however, have been postulated to contribute to ongoing low back pain in what has been described as “fusion disease.”10 In addition, the PLF does not biomechanically address the anterior column and is recognized to have a less optimal fusion rate. Even in the face of a solidly healed PLF, persistent strain anteriorly may cause ongoing discogenic low back pain. This was suggested by Barrick et al in their report of patients who continued to suffer low back pain despite solid PLF, but then went on to be successfully treated with ALIF.11 Along the same lines, L’Heureux et al12 and La Rosa et al13 have reported that, in adult low-grade spondylolisthesis patients treated with PLF, the correction in slip angle that was achieved intraoperatively was lost over time as the result of progressive disc space degeneration anteriorly. This again suggests that the rigidity of a solid PLF does not necessarily protect the disc from the biomechanical loading that can induce further degenerative changes.

Nevertheless, the preponderance of literature on the surgical management of spondylolytic spondylolisthesis describes the results of patients undergoing PLF. Fusion rates in as high as 100%14–16 and as low as 33% to 50%17–19 have been described for adult patients undergoing PLF for low-grade spondylolytic spondylolisthesis. This wide spectrum in fusion rate is likely indicative of the wide variation in the radiographic criteria that are used to define fusion among different authors. While pedicle screw fixation is commonly added to provide immediate stabilization, it is interesting to note that improved fusion rates have not been demonstrated in the studies that actually randomized lytic spondylolisthesis patients to PLF with or without pedicle screw instrumentation. McGuire and Admundson reported fusion in 10 of 13 (78%) patients with and in 10 of 14 (72%) patients without pedicle screw instrumentation (P > 0.05),20 while Moller and Hedlund reported definite fusion in 24 of 37 (65%) patients with and 29 of 37 (78%) patients without pedicle screw instrumentation (P > 0.05).21 Moller and Hedlund also reported no difference in functional clinical outcome between those patients with or without pedicle screw fixation,21 while Bjark et al found that the lytic spondylolisthesis patients randomized to pedicle screw fixation actually fared significantly worse on the Dallas Pain Questionnaire at their 5-year follow-up compared to uninstrumented patients.22 These results serve as a reminder that pedicle screw fixation must be performed with great caution, and in no way does it supplant the need for meticulous fusion technique.

Whether or not a posterior decompression is also warranted when performing PLF is subject to some controversy as well. While one may feel compelled to perform a direct decompression in the face of significant radicular symptoms and MRI evidence of exiting root entrapment, the provision of stability alone may suffice to relieve the dynamic component of foraminal compression and resolve the radicular symptoms. The argument against decompression relates to the potential instability that the removal of the posterior elements may exacerbate, thus impeding successful fusion. This phenomenon was illustrated in a retrospective study by Garreau de Loubresse et al45 who described a pseudarthrosis rate of 7 of 23 patients (30%) undergoing PLF with decompression, compared to 2 of 25 patients (8%) undergoing PLF alone. Carragee43 then reported an important prospective randomized study in which more than 40 adult patients with lytic spondylolisthesis were randomized to PLF with or without posterior decompression (even in the presence of radicular lower extremity symptoms). In general, patients randomized to PLF with decompression fared significantly worse, with four of four radiographic nonunions and six of seven fair to poor clinical results occurring in patients having a decompression. These findings speak to the role that the posterior elements play in providing tension-band stability to the olisthetic motion segment (despite the fact that a pars defect already exists), and the importance of dynamic compression to the nerve root symptomatology.

If significant kyphosis exists at the level of the spondylolisthesis, an attempt to correct the slip angle to make the olisthetic and adjacent disc space more horizontal and place the posterolateral bone graft in less tension is intuitively desirable. While it is uncertain whether an attempt to reduce the anterior slip is actually necessary or desirable, some degree of slip reduction is often accomplished with the prone positioning and subsequent exposure and resection of the posterior elements.23 Naderi et al24 reported on 30 patients with low-grade spondylolisthesis who underwent single-level instrumented PLFs without any attempt to surgically reduce the slip. Twenty-nine of the 30 patients achieved a modest reduction of the slip, a correction that amounted to typically 20% of the original displacement.24 The greatest amount of correction was achieved in spondylolisthesis at L4–L5, in patients younger than 50 years of age, and in patients with increased facet joint angles. While the results of Naderi et al describe what is achievable with a single-level instrumented fusion with no effort to reduce the slip, a more complete reduction may be accomplished by pulling the pedicle screw within the olisthetic vertebrae posteriorly (either with systems that allow one to lever against the rod, or by instrumenting an additional level above and using a pedicle screw with an extended head) (Figure 4C).24 Alternatively, the reduction of the slip can be facilitated by performing a complete discectomy (i.e., posterior lumbar interbody fusion [PLIF], transforaminal lumbar interbody fusion [TLIF], or ALIF), particularly in the face of significant degeneration and collapse25–27 (Figure 4).

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Anterior Approach: Anterior Lumbar Interbody Fusion

The ALIF allows for the most complete discectomy and permits the placement of a large interbody graft which can facilitate the correction of slip angle and the reconstitution of disc space height. The anterior position of the ALIF graft places it into a biomechanically compressive environment that is optimal for fusion. The anterior transperitoneal or retroperitoneal exposure used to access the anterior L4–L5 and L5–S1 disc spaces avoids the stripping of the lumbar paraspinal muscles thought to contribute to “fusion disease.” Nevertheless, such anterior exposures do carry some risk of catastrophic injury to major vessels and other retroperitoneal and intraperitoneal structures.28 For young males in particular, the risk of damaging the sympathetic plexus and causing retrograde ejaculation needs to be carefully considered before recommending this approach. Also, direct decompression of the nerve roots is not possible with ALIF, although the restoration of disc space height and correction of kyphosis achieved with the interbody graft may open the foramen and indirectly decompress the nerve root. As mentioned previously, the provision of stability may be sufficient for alleviating root symptomatology.

In general, there are only a handful of reports on adult patients with stand-alone ALIFs for spondylolytic spondylolisthesis. Long-term results, however, have been published by a number of authors. Cheng et al reported on 20 patients with an average 10.5 years of follow-up, in whom 15 had fused and 19 were deemed to have a successful (excellent or satisfactory) clinical result.44 Ishihara et al29 and van Rens and van Horn30 reviewed patients with a minimum 10-year follow-up and reported fusion rates of 83% and 90%, respectively. These long-term studies provide interesting insight into the behavior of the disc space adjacent to the fused olisthetic segment. Ishihara et al reported finding degenerative changes on plain radiographs at the upper adjacent level in 52% of cases and at the lower adjacent level in 70% of cases; using MRI, these rates were 73% and 100%, respectively.29 In contrast, van Rens and van Horn found only 3 of 24 patients with instability or disc space narrowing at the disc space above the fused segment.30 Other than the fact that the patients in the Ishihara series were slightly older than those of van Rens and van Horn at the time of surgery, the reasons for this discrepancy are not entirely clear; most likely, they relate to the methods by which the authors defined degenerative changes, or also, differences in the overall sagittal balance of the lumbar spine after fusion.

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Combined Approach: Transforaminal or Posterior Lumbar Interbody Fusion, Anterior Lumbar Interbody Fusion With Posterolateral Intertransverse Fusion

Approaches that achieve both anterior and posterior/posterolateral stabilization include combined ALIF and PLF or TLIF/PLIF. In essence, these techniques are associated with all the aforementioned risks and benefits of anterior or posterior procedures alone. The provision of circumferential stability obviously promotes a high fusion rate. Reconstruction of the anterior column can reconstitute disc height, reduce the slip angle, reduce the anterolisthesis, and provide an optimal graft environment for fusion, while the posterior approach allows for direct decompression, stabilization with pedicle screw fixation, and PLF. An explosion of interest in interbody devices such as titanium and carbon-fiber cages, machined allograft, and plastics and a rapidly increasing sophistication in the instrumentation to implant them via a posterior approach has popularized PLIF and TLIF techniques. Nonetheless, these techniques are more technically demanding than ALIF alone or PLF alone and are thus associated with longer operating times and higher complication rates.

Many authors that have described their experiences with ALIF/PLF or PLIF/TLIF have reported a fusion rate of 100%, confirming that, indeed, reliable fusion can be achieved with circumferential stabilization.13,25,26,31–34 Given that an increase in surgical effort to circumferentially stabilize the spine can promote an increase in fusion rate, it is only natural to question whether this ultimately leads to a better clinical outcome, recognizing that solid fusion and clinical success have not always enjoyed a decisively correlative association in other degenerative disorders of the lumbar spine.35,36 A number of retrospective studies have reported a close association between achieving a solid fusion and a successful clinical outcome in adults with acquired lytic spondylolisthesis, which would suggest that for this particular condition (in essence, a form of chronic instability) the extra time and effort to obtain circumferential stability are worthwhile for the patient.16,20,37–40 Having said that, retrospective studies that actually compare PLF against PLIF have arrived at conflicting results. Madan and Boeree,26 Suk et al,25 and La Rosa et al13 all performed comparative studies and found that many radiographic parameters such as fusion, slip reduction, correction of slip angle, and maintenance of deformity correction to be superior with PLIF compared with PLF. Nevertheless, in none of these studies were the clinical outcomes reported to be better in the patients undergoing PLIF compared with PLF. Indeed, in the Madan and Boeree study,26 patients undergoing PLIF had significantly worse Oswestry scores than patients undergoing PLF. Unsatisfactory outcomes were reported in 7 of 23 patients (30.4%) undergoing PLIF and only 3 of 21 patients (14.3%) undergoing PLF, despite the fact that there were no nonunions in the PLIF group and 2 in the PLF group. Thus, one must carefully weigh the radiologic (and possibly clinical) benefits engendered by performing a combined approach against the risks associated with a longer and more technically demanding procedure.

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Posterior, Anterior, or Combined Approach? Is There a Clear Choice?

Taking all of these aforementioned considerations into account, the choice of which approach to take can be quite difficult. Certainly, surgeon preference, familiarity, and resources can weigh heavily in this decision. For example, a spine surgeon who does not have an access surgeon readily available for anterior approaches may prefer to stay posteriorly. In reviewing the literature on the surgical management of adult spondylolytic spondylolisthesis, we found a striking paucity of prospective studies and even retrospective comparative studies among a multitude of retrospective case series, most of which reported on small numbers of patients. No prospective randomized studies have been published to date that compare one surgical approach against another; i.e., PLF (posterior alone) versus ALIF (anterior alone), or PLF (posterior alone) versus TLIF (combined posterior/anterior approach). To establish if recommendations regarding the optimal surgical approach could be made from the literature, we consolidated the results of those studies describing adult patients with low-grade lytic spondylolisthesis in which the radiographic fusion and pseudarthrosis rates were reported and the clinical outcome results (usually a 3- or 4-point Odom’s scale) could be interpreted into being either “successful” or “unsuccessful.” This review was presented initially at the annual North American Spine Society Meeting in 200041 and updated recently to include papers published up to December 2003.42

Thirty-five studies were identified that met these criteria.13–22,25,26,30–34,37–40,43–56 This cohort of studies had some striking limitations. Only four were prospective randomized studies, three of which compared noninstrumented PLF against the use of pedicle screw instrumentation for adults with lytic spondylolisthesis,20–22 and one of which compared the performance of a fusion with laminectomy against fusion without laminectomy.43 Of the retrospective studies, only six compared the results of two different forms of treatment.13,25,26,33,49,54 The remainder consisted of single-institution case series describing one technique. Only five retrospective studies had both a minimum 2-year follow-up with an independent assessment of radiographic and clinical outcome.26,34,37,39,52 Most importantly, the methods by which radiographic fusion and clinical outcome were determined varied quite substantially among the various reports.

With this being said, combining the results of these 35 studies produced approximately 900 patients treated with a posterior approach alone (PLF), 100 treated with an anterior approach alone (ALIF), and 170 treated with a combined procedure, either ALIF plus PLF or PLIF/TLIF. Overall, patients who underwent a combined procedure experienced the highest fusion rate (98.2%), which was significantly higher than that of patients undergoing an anterior or posterior procedure alone (75.3% and 83.3% respectively, P < 0.0001 for both, Fisher’s exact test). Interestingly, culling the clinical outcomes data into either “successful” or “unsuccessful” revealed the highest rate of successful clinical outcome in those patients undergoing a combined procedure: 86.4% versus 74.8% for posterior procedures alone (P = 0.0045) and 79.3% for anterior procedures alone (P = 0.19).

Pertinent to the prior discussion regarding pedicle screw instrumentation and the performance of a laminectomy for PLF, we pooled the radiographic and clinical outcome results of those studies of PLF that described these techniques and outcomes. Pooling these results revealed radiographic fusion in 333 of 369 patients (90.2%) with spinal fixation and in 254 of 328 patients (77.4%) with uninstrumented fusions (P < 0.0001, Fisher’s exact test). With regards to the clinical results, 304 of 358 patients (84.9%) with spinal fixation were described as having a successful outcome compared with 192 of 298 patients (64.4%) without (P < 0.0001). These would suggest a strong correlation between the accomplishment of fusion and clinical success. With regards to the issue of performing a laminectomy, 284 of 342 patients (83%) with a laminectomy and 157 of 177 patients (88.7%) without a laminectomy achieved fusion (P = 0.093). Clinical success was described in 267 of 361 patients (74%) with a laminectomy and 186 of 233 patients (79.8%) without a laminectomy (P = 0.11). This would suggest that the performance of a laminectomy did not significantly influence rates of fusion or clinical success. While the results of this evaluation provide an interesting perspective on the different surgical approaches to spondylolytic spondylolisthesis in adults, the reader is reminded that the studies included in the analysis are predominantly retrospective and most certainly describe a wide variety of surgical indications, surgical techniques, methods for determining fusion, and methods for evaluating clinical outcome. As such, the reader is cautioned against making overly strong conclusions from such an analysis. Clearly, this is an area in dire need for a well-designed prospective randomized surgical trial.

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Conclusion

The management of adult patients with spondylolytic spondylolisthesis requires a thoughtful and evidence-based approach. While the majority of patients will likely enjoy a fairly benign course requiring nothing more than physical methods and oral non-narcotic analgesics or anti-inflammatories, surgical management appears to have a role for those patients with intractable back and/or leg symptoms. The contemporary surgical treatment is fusion, which can be achieved via a number of different approaches. No clearly optimal approach has been established to date, however, and as such, a prospective randomized comparison would be highly desirable.

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Key Points

  • Isthmic spondylolisthesis is a relatively common disorder and is frequently either asymptomatic or associated with minimal symptoms.
  • Slip progression is unusual in adults, and when occurs is typically the result of disc degeneration.
  • Combined surgical approaches that provide both anterior and posterior stability appear to be associated with the highest rates of fusion and successful clinical outcomes, although prospective randomized trials to establish the optimal surgical treatment are lacking.
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References

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Keywords:

spondylolytic spondylolisthesis; natural history; fusion; systematic review

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