Accelerated degeneration in the motion segments adjacent to a lumbar procedure occurs as a result of pre-existing degenerative and neuromuscular conditions. This degeneration is likely potentiated by biomechanical changes from stabilizing a motion segment coupled with iatrogenic bony, muscular, and neural changes that occur as a result of the surgical exposure and implant placement. There is a lack of precision regarding the terminology used to describe the pathologies of what is often called adjacent segment disease. The term adjacent segment pathology (ASP) is proposed as an umbrella term to refer to the breadth of clinical and/or radiographical changes at adjacent motion segments that develop subsequent to a spinal intervention. Under this umbrella term, radiological ASP and clinical ASP (CASP) are then used to categorize radiographical features (e.g., degenerative changes on magnetic resonance imaging) and clinical manifestations (e.g., new radiculopathy), respectively. The rates of radiographical and clinical changes are widely reported. Although the overall lumbar ASP reoperation rates may approximate 3% per year, the great breadth of reported rates seem to implicate procedural factors more than pure biomechanics. Surgeons have postulated that partial disruption of the adjacent facet during placement of pedicle screws or disruption of the supraspinous and interspinous ligaments may play a role in the rate of occurrence. In addition, it has been debated how much of the degeneration is actually related to the fused segment and how much is related to the natural history of the aging spine. Moreover, in some circumstances, ASP occurs, yet not to the point that the patient's quality of life is compromised to the point that surgery is warranted.
Knowledge of the natural history of a given condition and nonoperative treatment options are essential for evidence-based discussions and informed patient choice. In this article, we wish to evaluate the treatment of ASP with an interest in how nonoperative care compares with operative care and how various types of surgery compare with another based upon the best available literature.
Shared decision making in the treatment of CASP requires a balanced application of evidence-based knowledge, surgeon experience, and patient preference. These factors play out directly in surgical decision making, for example, if surgery is elected, especially when it is unclear which surgical intervention is superior. For example, anterior surgery avoids facet disruption, may be superior in restoring disc height and inducing lordosis, and may have a higher arthrodesis rate. However, anterior surgery relies on indirect decompression of stenosis, and it may prove inferior to posterior surgery in cases of severe central stenosis. For patients who mainly present with stenosis without instability or kyphosis, there is no consensus on how to treat such patients. Some surgeons think that decompression of the adjacent segment alone has a significant likelihood of development of instability with potential reoperation, whereas other surgeons think that the smaller scope of a simple decompression operation justifies that risk. Again, it is unclear if 1 mode of treatment is superior to the other.
Finally, we wished to report outcomes in the literature resulting from the treatment of ASP. Although surgery is undertaken to improve function and pain, we wish to assess the literature to determine if there is evidence to support the treatment of ASP.
The primary goal of this review is to perform an evidence synthesis of the literature to identify and compare lumbar CASP treatment options and outcomes. The following key questions were addressed: (1) What is the comparative effectiveness and safety of operative versus nonoperative treatments for lumbar CASP? (2) What is the comparative effectiveness and safety of operative versus operative treatment for lumbar CASP? (3) Describe the treatments, outcomes, and risk factors for outcomes in studies designed to evaluate the treatment of lumbar CASP.
MATERIALS AND METHODS
We conducted a systematic search in PubMed and the Cochrane Library for literature published through February 2012. The search results were limited to human studies published in the English language. Reference lists of key articles were also systematically checked to identify additional eligible articles. We included studies evaluating adult patients who have had treatment for lumbar CASP (Table 1). Our first goal (study question 1) was to identify therapeutic comparative studies (level I, II, or III evidence) comparing operative with nonoperative management in patients who have CASP as a result of a previous surgery. Our second goal (study question 2) was to identify therapeutic comparative studies (level I, II, or III evidence) comparing operative with operative management in patients who have CASP as a result of a previous surgery. Our third goal (study question 3) was to identify case series (level IV evidence) evaluating outcomes after the treatment of CASP as a result of a previous surgery. We were interested in the following outcomes: clinical, radiographical, patient-reported, and complications (Table 1). We were only interested in studies reporting on treatment of CASP after a previous lumbar surgery (as opposed to ASP as an outcome after surgery). Criteria for exclusion from our study included pediatric patients, infection, tumor, trauma, ankylosing spondylitis, neuromuscular scoliosis, and patients without ASP at the time of treatment. We also excluded studies where the revision surgery was done on the original operated levels and those studies in which ASP was reported as the outcome. Also, studies were excluded if they reported outcomes such as range of motion, kinematic measures, disc height, lordosis/angle changes at adjacent levels. Case reports or studies that consisted of an n < 10 were excluded. Other studies excluded were animal, cadaver, and biomechanical studies.
From the included articles, the following data were extracted: study design, patient demographics, inclusion/exclusion criteria, definition of CASP, interval between index surgery and treatment of CASP, follow-up duration and the rate of follow-up for each treatment group, treatment interventions, risk factors, results, and authors' conclusions.
Level of evidence ratings were assigned to each article independently by 2 reviewers (J.T.H, D.C.N.) using criteria set by the Journal of Bone & Joint Surgery, American Volume,1 for therapeutic studies and modified to delineate criteria associated with methodological quality and described elsewhere.2 (see Supplemental Digital Material, Supplemental Digital Content 1, available at http://links.lww.com/BRS/A702 for individual study ratings.)
Study Quality and Overall Strength of Body of Literature
Level of evidence ratings were assigned to each article independently by 2 reviewers (J.T.H., D.C.N.) using criteria set by the Journal of Bone & Joint Surgery, American Volume8 for therapeutic studies, and modified to delineate criteria associated with methodological quality described elsewhere.9 (See Supplemental Digital Material, Supplemental Digital Content 1, available at http://links.lww.com/BRS/A702 for individual study ratings.)
The overall body of evidence with respect to each key question was determined based on precepts outlined by the Grades of Recommendation Assessment, Development, and Evaluation working group10 and recommendations made by the Agency for Healthcare Research and Quality.11 Risk of bias was evaluated during the individual study evaluation described earlier in the section “Study Quality.” This system, which derives a strength-of-evidence grade of “high,” “moderate,” “low,” or “insufficient” for each outcome or key question, is described in further detail in the methodology article in this Focus Issue.9 A detailed description of how we arrived at the strength of evidence for each key question can be found in the Supplemental Digital Content (see Supplemental Digital Material, Supplemental Digital Content 1, available at http://links.lww.com/BRS/A702).
Descriptive statistics for all studies were reported because there were no comparative studies identified where data could be pooled or comparative effect estimates could be calculated. If reported by the authors, risk factors that were associated with outcome were reported based on the analytical statistics reported by the authors.
Clinical Recommendations and Consensus Statements
Clinical recommendations or consensus statements were made through a modified Delphi approach by applying the Grades of Recommendation Assessment, Development and Evaluation/Agency for Healthcare Research and Quality criteria that imparts a deliberate separation between the strength of the evidence (i.e., high, moderate, low, or insufficient) from the strength of the recommendation. When appropriate, recommendations or statements “for” or “against” were given “strong” or “weak” designations based on the quality of the evidence, the balance of benefits/harms, and values and patient preferences. In some instances, costs may have been considered. A thorough description of this process can be found in the methodology article in this Focus Issue.9
We identified 225 total citations from our literature search. Of these, 212 were excluded by the title/abstract and 13 full text articles were evaluated to determine if they met the inclusion criteria. From these 13 studies, 4 were excluded because they did not report outcomes of CASP treatment. Another study was excluded because authors treated pre-existing ASP at time of index surgery. Details of the excluded articles can be found in the supplemental digital material (see Supplemental Digital Material, Supplemental Digital Content 1, available at http://links.lww.com/BRS/A702). The remaining 8 studies met our inclusion criteria and are summarized in this report (Figure 1). No study was found that answered study question 1, comparing operative treatment with nonoperative treatment or study question 2, and comparing operative treatment with another operative treatment in the treatment of CASP. The 8 included studies answered question 3: to describe the treatments, outcomes, and risk factors for outcomes in studies specifically designed to evaluate the treatment of lumbar CASP. All 8 studies were case series (level of evidence IV).6–13 Treatment for CASP varied between studies. Five studies7–10,12 performed an extension of the index fusion to treat CASP. Two studies11,13 performed decompression. One study6 performed arthroplasty to treat CASP. The study published by Parker et al10 was designed specifically to derive the minimal clinically important difference (MCID) for several patient-reported outcome measures after revision surgery for CASP. This article contributes treatment outcome data but is also a sentinel article with respect to future research evaluating the treatment of CASP with respect to how to evaluate treatment success; therefore, a special section will be devoted to these findings.
Comparing Operative With Nonoperative Treatment for CASP
No studies comparing operative with nonoperative management of CASP were identified in the literature.
Comparing Operative With Operative Treatment for CASP
No studies comparing operative with other operative management of CASP were identified in the literature.
Patient Populations and Results for Patients With ASP Treated With Extension of the Index Fusion
Details of the fusion procedures can be found in Table 1 of the Supplemental Digital Material (see Supplemental Digital Material, Supplemental Digital Content 1, available at http://links.lww.com/BRS/A702). Chen et al7 performed posterolateral fusion (PSF) with instrumentation and a medial facetectomy. Djurasovic et al8 performed PSF in 95% of the patients with anterior spinal fusion and circumferential anteroposterior fusion performed in the other patients. Whitecloud etal12 performed PSF with and without instrumentation. Parker et al10 performed a posterior fusion with extension of the previous fusion construct with laminectomy. Glassman etal9 did not identify type of fusion, but also extended the previous fusion construct. The mean patient ages of the 5 fusion studies ranged from 52 to 61 years with male subjects making up 23% to 50% of the study population. The time between index surgery and fusion for CASP ranged from 4.8 to 11.5 years. Follow-up time after fusion for ASP ranged from 1.5 to 5 years. Chen et al7 defined ASP as spondylolisthesis or dynamic instability with slippage more than 4 mm and or angle change greater than 10°. The studies by Djurasovic etal8 and Whitecloud et al12 defined ASP as being symptomatic. Specifically, Whitecloud et al12 defined ASP as symptomatic degeneration and hypertrophy of the facet joints at adjacent levels after fusion surgery. Djurasovic et al8 defined ASP as stenosis and degeneration at an adjacent segment to a previous fusion. Parker et al10 defined ASP as low back and leg pain localized to adjacent level after previous fusion and radiographical evidence of pathology adjacent to previous fusion including: spinal stenosis, listhesis, or instability. Glassman et al9 defined ASP as spinal stenosis, spondylolisthesis, instability, degenerative disc disease, or discogenic pain that localized to the adjacent levels.
The outcome measurement methods among these 5 fusion studies were variable. Using modified Brodsky criteria of excellent, good, fair, and poor based on pain and work/leisure disability categories, 76.9% of the subjects achieved satisfactory results (good to excellent results). Djurasovic et al8 based their outcomes on previously published minimum clinically important difference (MCID) thresholds. At 2 years, only 38% and 40% of patients reached the MCID threshold for the Oswestry Disability Index (ODI) and 36-item short-form health survey (SF-36) physical component scale, respectively. Whitecloud et al12 reported postoperative pain relief to be 78.6%; however, using an informal outcomes measure taking into account pain, medication use, and return to work they determined that only 35.7% patients had a good outcome. Parker et al10 reported a statistically significant improvement for all patient reported outcomes 2 years after surgery: visual analogue scale (VAS) change for back pain, 4.80; VAS change for leg pain, 3.28; ODI change, 10.24; SF-12 physical component scale change, 8.69; SF-12 mental component scale change, 8.49; and EuroQol—5-dimensional change, 0.38. In the Glassman et al9 study, the authors reported on 3 outcomes: satisfaction, pain relief, and patient perception of overall outcome. With respect to satisfaction, those patients who had greater than 48 months surgical interval from index surgery to extension of fusion for ASP had 85% satisfaction rate versus those patients with less than 48-month surgical interval, 50% (P = 0.035). With respect to pain relief, there were 3 statistically significant demographic factors and 1 nearing significance. Pain relief versus no pain relief with initial fusion (P = 0.006); satisfaction versus dissatisfaction with initial fusion (P = 0.011); adjacent level fusion to L5 versus to S1 (P = 0.042) were all statistically significant. Patients older than 55 versus younger than 55 were more likely to report pain relief (P = 0.059). Regarding patient perception of overall outcome patients greater than 55 years versus younger than 55 years (P = 0.038) and patients with history of discectomies versus no history of discectomies (P = 0.029) were statistically significant.
Most notably, despite modest levels of improvement in health-related quality of life measures, Djurasovic et al8 discovered through a multivariate regression that patient reported improvement from the previous surgery was the most predictive factor for subsequent improvement. A multitude of other factors were examined but not determined to be associated with improvement Table 2. Furthermore, Whitecloud et al12 reported that the 3 patients with poor results in their population all had an interval of less than 3 years between surgeries and also suggested that osteoporosis may have lead to implant pullout. This pullout implied pseudoarthrosis, but the authors did not provide any analytical statistics to support this.
Patient Populations and Results for Patients With ASP Treated With Decompression
Decompression was performed in both the Phillips et al13 and Schlegel et al11 studies (see Table 2, Supplemental Digital Material, Supplemental Digital Content 1, available at http://links.lww.com/BRS/A702 for study details). In the Phillips et al13 study all patients received only decompression. In the Schlegel et al11 study, 62% of patients received decompression only and another 38% received both decompression and fusion. Outcomes from these 2 approaches were not compared. The mean patient ages in the two decompression studies ranged from 43 to 57 years with male subjects making up 35% to 38% of the study population. The time between index surgery and the extension of fusion to treat ASP was 7.8 to 13.1 years. Follow-up time after decompression for ASP ranged from 24 to 60 months. Inclusion criteria were similar in both studies. A symptom-free period of at least 2 years after previous lumbar fusion was required. Phillips et al13 defined ASP as a symptomatic spinal stenosis or instability adjacent to a previously asymptomatic lumbar fusion. Schlegel et al11 defined ASP as spinal stenosis, disc herniation, severe back and leg pain, and instability localized to adjacent level of a previous lumbar fusion. Phillips et al13 reported 57.7% patients with a satisfactory to perfect result. This was not based on a formal outcome measure, but took into account pain, functional abilities, patient opinion of operative result, and medication use. Schlegel et al11 reported a good to excellent result in 64.2% of patients. This assessment was based on pain, functional outcome, and the need for additional surgery. The postoperative VAS for back and leg pain was 4.0 and 2.3, respectively, representing a pain improvement of 4.2 points for back pain and 4.9 points for leg pain compared with preoperative scores (Figure 2).
Patient Population and Results for Patients With ASP Treated With Total Disc Arthroplasty
Bertagnoli et al6 performed lumbar total disc arthroplasty using the ProDisc (see Table 3 in Supplementary Digital Material for study details). The mean patient age was 50 years with men making up 50% of the study population. The time between the index surgery and arthroplasty for ASP was 4.5 years. Follow-up time after arthroplasty was 27 months. Patients were required to have undergone 9 months of failed conservative treatment and at least 2 years of follow-up. ASP was defined as disabling low back pain with or without radicular symptoms resulting from degenerative disc disease at L1–S1 confirmed by magnetic resonance imaging, computed tomography, or discography. At 24 months, 88.9% of patients had improved VAS for pain and ODI scores compared with the 3-month postoperative follow-up. At 3 months, VAS scores improved from a mean of 7.73 points to 4.25 points and ODI scores improved from a mean of 65.4 points to 42.0 points (both P < 0.0001). Compared with their 3-month follow-up, patients improved an average of 13 points in their ODI scores at the 24-month follow-up from a mean of 42.0 to 29.0 points (P = 0.002) (Figure 3). Although not statistically significant, patients improved an average of 0.75 points in their VAS scores from 4.25 to 3.50 points.
Measuring Successful Outcomes in the Treatment of CASP
Parker et al10 set out to determine the most appropriate surgery-specific MCID values for pain VAS, ODI, SF-12, and EuroQol—5-dimensional in patients undergoing revision decompression and extension of fusion for CASP. Two ad hoc anchors were used to demonstrate the anchor-based derivations of MCID. The first anchor asked patients to rate their current health compared with their health before surgery (also known as a health transition item anchor: worse, unchanged, slightly better, and markedly better). Patients answering “slightly better” or “markedly better” were classified as responders, whereas those answering “unchanged” or “worse” were classified as nonresponders. The second anchor used was derived by asking patients whether they were satisfied with the results of their surgery. Patients answering “yes” were classified as responders and those answering “no” were classified as nonresponders. This study used 4 anchor-based approaches to assess MCID after revision surgery for CASP. These are discussed in detail in the article but include “average change,” “smallest change” above measurement error, “change difference,” and “ROC curve,” all reported in the literature as acceptable approaches. To date, none are considered superior. The author reported only 48% of patients being satisfied with surgery, despite significant improvements in patient reported outcome measures leading them to suggest that current outcome measurements may be a poor proxy for patient satisfaction. The authors concluded that the health transition item anchor seemed to be the more valid anchor in the study due to superior sensitivity and specificity. The authors recommended that the MCID after revision lumbar surgery for CASP using the following patient-reported outcomes should be:
- Back pain VAS, 3.8 points
- Leg pain VAS, 2.4 points
- ODI, 8.8 points
- SF-12 physical composite score, 8.8 points
- SF-12 mental composite score, 9.3 points
- Quality of life years for the EuroQol—5-dimensional, 0.35
The final overall strength of the body of literature expresses our confidence in the estimate of effect and the impact that further research may have on the results. The overall strength of the evidence evaluating the comparative effectiveness and safety of operative or nonoperative versus other operative treatments for lumbar CASP is “insufficient”; we have low confidence that the evidence reflects the true effect, and the evidence is either unavailable or does not permit a conclusion (Table 3). Furthermore, the strength of evidence establishing surgery as a successful treatment for CASP or in establishing risk factors for poor outcomes after treatment for CASP is “insufficient” (Table 3). At this point, there is a paucity of literature evaluating these clinical questions; however, what is available is summarized in this systematic review provides the best available evidence on this topic.
The overall strength of evidence evaluating whether other motion preservation devices are associated with a lower risk of radiographical or CASP compared with fusion is “low” to “insufficient,” meaning we have low confidence that the evidence reflects the true effect, and the evidence is either unavailable or does not permit a conclusion. The overall strength of the evidence evaluating whether 1 type of motion preservation device is associated with a lower risk of ASP compared with other types is “insufficient,” meaning the evidence is either unavailable or does not permit a conclusion.
ASP is one of the long-term problems associated with spinal fusion. Many pathologies in the lumbar spine, such as adult scoliosis, spondylolisthesis, or instability require spinal fusion for proper treatment, yet the durability of such treatment may eventually be in jeopardy because of ASP. This may lead to reoperation after reoperation, frustrating both the patient and the physician. The “recurrence” of the patient's problem at the adjacent level—which is simply ASP—may lead the patient to think that the original physician did not properly treat them the first time, seeking another treating physician and eventually go “doctor shopping.” Such patient frustration—and potentially anger—may simply be the unavoidable consequence of the natural history of spinal fusion.
Many studies have shown that the rate of ASP is approximately 3% per year, both in the lumbar and cervical spine. One clinical question that arises is whether or not ASP can be managed nonoperatively, and if so how such nonoperative management compares with surgical management. Within our systematic review, no study directly compared nonoperative with operative management for CASP. However, from a clinical perspective, it stands to reason that nonoperative treatment would first be implemented and operative treatment undertaken only after failure of nonoperative treatment. Moreover, just as in primary lumbar pathology, surgical treatment is offered only after failure of nonoperative care. However, unlike primary lumbar pathology, because there are no studies directly comparing nonoperative care with surgical intervention for CASP, it is unclear how effective—if at all—nonoperative care is. Because no study directly compares the 2 treatments, clinical judgment, best available evidence, and patient preference are the current cornerstones that guide treatment.
Another issue to address is the type of operative treatment to pursue with CASP. Frequently, ASP may be associated with kyphosis, severe disc collapse, modic changes, or listhesis. On the contrary, ASP can simply present with a hypertrophied ligamentum flavum causing adjacent segment stenosis, without any significant deformity or any instability. Can the patient with a deformity and significant segmental changes be treated with an adjacent laminectomy only? Should the patient with only adjacent segment stenosis and no deformity or listhesis be treated with an anterior-posterior extension of fusion? Within this systematic review, we did not identify any studies addressing these specific questions. However, given the absence of data directly comparing different types of operative treatments, it stands to reason that clinical judgment, best evidence in treating a similar primary pathology, and patient preference dictate the type of treatment. Deformity correction, sagittal balance, nerve decompression, and bone quality probably all play a role in deciding the type of procedure for ASP. These considerations are balanced with patient preference and doctor-patient discussions regarding the morbidity of various procedures. Thus, in the absence of literature directly comparing 1 type of operative treatment with another type, the fundamental principles of surgical decision making and treatment experience may be the best guides for the practitioner.
The other question that our systematic review evaluated was patient outcomes in the treatment of lumbar adjacent segment disease. Although there was no direct comparison among treatment types, the main studies that were systematically identified reported outcomes of 3 types of surgical treatment: decompression alone, decompression with fusion, and decompression with disc arthroplasty. When evaluating outcomes for decompression alone, Phillips et al13 reported 57.7% of patients had satisfactory to perfect results, and Schlegel et al11 reported a good to excellent results in 64.2% of patients. When evaluating decompression and fusion, Chen et al7 reported 76.9% of the subjects achieved satisfactory results, and Whitecloud et al12 reported postoperative pain relief to be 78.6% (dropping to only 35.7% after taking into account medication and work status). Glassman et al9 reported an 85% satisfaction rate with decompression and extension of fusion. Bertagnoli et al6 reported 88.9% of patients had improved VAS for pain and ODI scores when treating CASP with disc arthroplasty. These data, however, must be taken in the context that these reports are case series without rigid controls, and no study had more than 50 patients in any treatment arm. Although the level of evidence is low, it is the best available evidence now, and on the basis of this, it may suggest that there is some benefit to the surgical treatment of CASP. However, the quality of the data is not high enough to clearly delineate if 1 type of treatment is superior over another. Hence, it is clear that clinical studies comparing operative versus nonoperative management of CASP as well as studies comparing different surgical treatments should be a high priority for future research given prevalence of ASP being reported and treated.
- Operative management for lumbar ASP should be considered after failure of non-operative management of ASP.Strength of Statement: Weak
- When considering the type of operative treatment for the treatment of lumbar ASP, clinical judgment, radiographic appearance, and patient preference should guide operative intervention.Strength of Statement: Weak
- Although the level of evidence for the outcomes of the treatment of lumbar ASP is weak, there does seem to be some benefit from the surgical treatment of lumbar ASP. Thus, if the patient's disability secondary to lumbar ASP is high enough, consideration should be given to operative treatment.Strength of Statement: Weak
- Operative management for lumbar CASP should be considered after failure of nonoperative management.
- When considering the type of operative treatment for lumbar CASP, clinical judgment, radiographical appearance, and patient preference should guide operative intervention.
- Although the strength of evidence for the outcomes of the treatment of lumbar CASP is insufficient, there does seem to be some benefit from the surgical treatment of lumbar CASP. Thus, if the patient's disability secondary to lumbar CASP is high enough, consideration should be given to operative treatment.
The authors thank Ms. Nancy Holmes, RN, for her administrative assistance. The authors M.D. and D.C. contributed to study concept, interpretation, manuscript preparation, and manuscript revision. The authors J.T.H and D.C.N. contributed to data analysis and interpretation, manuscript preparation, and manuscript revision.
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