The optimal surgical approach to treating patients with degenerative lumbar spondyloslithesis (DS) with lumbar spinal stenosis (LSS) remains controversial. Surgery in the setting of DS often involves fusion to limit postoperative instability that can result from a decompressive laminectomy.1 Instability following laminectomy alone may lead to deterioration of symptoms.2 Decompression with instrumented fusion has been the general recommendation for the past few decades in patients with DS.1,3,4
Reoperation rates for laminectomy have historically been much higher than laminectomy with fusion in patients with DS.1,5,6 However, surgical treatment has become progressively less invasive, with reduced blood loss and length of stay.7,8 The technique of unilateral laminotomy for bilateral decompression (ULBD) was developed to better preserve the facet joints, the dorsal ligamentous complex, as well as the neural arch and muscular attachments of the contralateral side.9,10 A few studies with 5-year follow-up have suggested that less invasive decompression procedures have excellent outcomes in patients with lumbar stenosis with or without DS.7,11–13 However, no long-term follow-up studies exist regarding rate of reoperation for patients with DS that exclusively underwent ULBD. Furthermore, limited data exists on the outcomes of ULBD compared with posterior decompression and fusion at long term follow-up.13,14
The purpose of this study is to compare the rate of reoperation, and evaluate the types of reoperations, at 5 years of follow-up in patients surgically treated for DS with ULBD versus posterior decompression with instrumented fusion (Fusion) in a multicenter, integrated health care system database. Secondary outcomes include complication, readmission, and reoperation rates within 90 days of surgery.
MATERIALS AND METHODS
In this retrospective cohort study, patients were identified via an electronic medical record database from five centers within the Kaiser Permanente Northern California (KPNC) healthcare system from January 1, 2007 to December 31, 2011. International Classification of Diseases Ninth Revision, Clinical Modification (ICD-9-CM) and Current Procedural Terminology codes were used to identify patients with a diagnosis of DS and LSS who underwent lumbar decompression or posterior lumbar decompression with Fusion.
Patients were excluded if they had surgery for tumor, infection, disc herniation, trauma, were younger than 18 years, and/or if they had an anterior approach or a history of previous lumbar surgery (Figure 1). In addition, patients with gaps in insurance membership during the 5 years following their surgery as well as those with lack of membership in the 12 months before the surgery were also excluded. Given that there was no separate procedure code for ULBD versus laminectomy or bilateral laminotomy, charts were reviewed to determine whether the decompression performed was ULBD at the level of DS. We first identified all laminectomy or bilateral laminotomy patients with a recorded diagnosis of DS restricting to surgeons who performed ULBD within KPNC and applied our exclusion criteria above. A total of 743 such patients were identified, and their charts were reviewed to confirm a total of 164 patients with ULBD for DS included in the ULBD group. Next, a total of 3457 patients who underwent Fusion for DS were identified, applying our exclusion criteria. These 3457 Fusion patients were then propensity score-matched using the nearest neighbor matching method with the 164 patients in the ULBD group on age, sex, race/ethnicity, and smoking status with the goal of obtaining three Fusion cases for each ULBD case. Owing to elimination during chart review in the Fusion group for those identified with previous surgeries or nonposterior fusion surgeries, the propensity score matching process was repeated to get additional matches from the Fusion group. A total of 914 charts were reviewed to obtain 437 confirmed cases in the Fusion group. Baseline demographic and clinical characteristics were obtained for our final cohort of 601 patients including the Charlson comorbidity index for each patient, a widely known and well-studied index using a weighted score based on diagnoses for 17 serious health conditions in the year before cohort entry.15,16
The review and analysis of the data were approved by the Kaiser Permanente Northern California Institutional Review Board (CN-16–2742).
The primary outcome was any type of second lumbar surgery during the follow-up period. The primary objective was the incidence of reoperation between ULBD and Fusion groups at 5-year follow-up. Secondary outcomes were types of re-operations (decompression or fusion), location of reoperations (adjacent or index surgery level), and 90-day postoperative complications, reoperations, and return to emergency room (ER) visits. Data were also collected on operative time, estimated blood loss, and length of stay in the hospital.
Summary statistics were calculated for the demographic and clinical characteristics and outcomes including length of stay and perioperative complications among the patients in the 2 groups. For continuous variables such as age, length of stay, t tests were used to compare the means between the ULBD and Fusion groups. For categorical variables of interest such as race, presence of various comorbidities, χ2 or Fisher exact tests were used to compare the two surgical groups. A logistic model was used to produce the predicted probability (propensity score) of being in one of the study groups adjusting for age, sex, race/ethnicity, and smoking status. Using the predicted probabilities from this logistic model, we used the nearest neighbor matching algorithm to obtain the matched Fusion sample of 437 from the overall pool of 3457 Fusion patients. Once the cohort of final ULBD and Fusion patients was identified we used logistic regression models on the matched cohort to determine the odds ratios for the 2 surgical groups for 5-year reoperation rate, controlling for potential confounders. Final follow-up was determined to be 5 years from discharge date of surgery. All analyses were carried out using SAS version 9.3.
A total of 164 patients underwent ULBD and were propensity matched with 437 patients who underwent Fusion. The characteristics of the cohort are presented in Table 1. As expected there were no significant differences between the two groups with respect to age, sex, ethnicity, and history of smoking due to the propensity score matching. In addition, there were no statistically significant differences between the two groups for the body mass index (BMI) and Charlson comorbidity index categories.
Table 2 depicts the characteristics of the procedures performed and the postoperative period. ULBD had significantly decreased mean length of stay (2.3 vs. 4.6 days), mean blood loss (82 vs. 445 mL), and reoperation rates at 5-year follow-up (10.4% vs. 17.2%) compared to Fusion. ULBD had a higher return to ER within 90 days (12.2% vs. 5.0%) compared to Fusion. There were no significant differences in postoperative complications or reoperations within 90 days between the two surgical groups.
Table 3 shows the characteristics of the reoperations. Patients that underwent ULBD were more likely to have a reoperation involving the index level (70.6%, 12/17) than at the index with an adjacent level (11.8%, 2/17) or at an adjacent level (17.7%, 3/17). Patients who underwent Fusion were more likely to have a reoperation at an adjacent level (68%, 51/75 reoperations) than at the index level (32%, 24/75). The type of reoperation was not significantly different between the two groups. Fusion was the most common reoperation (ULBD 70.6% and Fusion 60.0%).
Table 4 summarizes the odds ratios of the 5-year reoperation rate between the two surgical groups after adjusting for various clinical characteristics such as BMI, Charlson comorbidity score, perioperative complications, estimated blood loss, length of stay. Having an index fusion operation was associated with increased odds of reoperation (aOR = 4.52, 95% confidence interval [CI] = 1.42=17.52). Perioperative complications were associated with increased odds of reoperation (aOR = 2.55, 95% CI 1.01–6.19) as were complications within 90 days (aOR = 4.35, 95% CI 1.92–9.94).
DS is one of the most frequent etiologies of chronic back pain, neurogenic claudication, and lumbar radiculopathy. DS represents a significant economic burden to healthcare systems. This is because of patient progressive disability and health care costs for both nonoperative and operative treatments. However, DS is not one homogeneous entity. Several classifications attempted to harmonize nosology: patients present a variety of symptoms combining lumbar stenosis, slippage as well as sagittal balance modifications. Etiology, topography, and slippage grading are common descriptors.17–20 More recently, Ghailane et al21 showed that DS could be classified according to its impact on local, regional, and global sagittal balance. Gille et al22 reported good clinical relevance of that classification.
These attempts at better defining this pathology show a lack of standardization in diagnosis and, therefore, treatment. Decompression with instrumented fusion has been the “criterion standard” for the past two decades.1,3,23,24 However, surgical experience worldwide is showing that decompression alone can lead to good outcomes.25–27 A shift in treatment has been because of refining the definition of instability, sagittal imbalance, and severity of stenosis. Currently, there is no consensus providing a treatment algorithm for DS.
Our study demonstrates that ULBD for lumbar stenosis is a viable option for carefully selected patients with symptomatic DS. The reoperation type was most commonly a fusion procedure in either group. An attractive aspect of choosing ULBD as a surgical treatment is that the most common reoperation involves fusing the same level while adjacent segment disease following fusion involves fusing a second level. This may mitigate the risk of adjacent segment fusions after the index procedure. Furthermore, the two-fold reduction in length of stay that was observed is economically and medically relevant at a time when outpatient spine surgery is becoming normalized. At this time, ULBD is routinely performed in the outpatient setting for the proper patient.
Complication rates were not significantly different between the two groups. This is not surprising since the classic belief that fusion causes significant morbidity by itself is being challenged. Indeed, more evidence is pointing towards patient comorbidities and preoperative functional status as the main predictor of postoperative complications.28,29
Although this technique is becoming increasingly popular, limited data focused on ULBD in patients with LSS in the setting of DS are available. Multiple authors showed high satisfaction rates with good to excellent functional scores.10,30–32 Sasai et al31 showed that patients with spondylolisthesis had increased slip percentages at follow-up, but did not result in symptomatic instability. Jang et al32 noted that slip percentage for patients without sagittal motion on dynamic x-rays did not increase, and those with sagittal motion on dynamic x-rays had an increase of about 5%. Only one study has compared ULBD with Fusion in patients with DS. Park et al compared ULBD with decompression versus fusion for patients with DS and noted a shorter recovery time and an economic advantage of ULBD, whereas all fused patients developed adjacent segment degeneration.14
Previous studies have shown substantially higher reoperation rates with decompression alone compared to fusion for patients with DS. Recently, a randomized, controlled trial by Ghogawala et al1 compared decompressive laminectomy with laminectomy with posterolateral instrumented fusion for patients with DS, known as the SLIP trial. At a 4-year follow-up, decompression-alone was shown to lead to more reoperations than fusion (34% vs. 14%). Sato et al33 reported a 33.8% reoperation rate in the decompression alone group (unilateral laminotomy) versus 14.4% in the fusion group.
In contrast, recent studies have noted reoperation rates of decompression alone techniques that were similar or decreased compared with laminectomies. Vorhies et al34, in a population-based analysis, determined that the reoperation rate between decompression alone compared with fusion was similar at 5 years. Midline sparing spinous process osteotomy has demonstrated lower reoperation rates than laminectomy at mid-term (∼3 year) follow-up (11 to 17%).26,35 Concerning ULBD specifically, Scholler et al36 noted a reoperation rate of 17.0% at more than a 5-year follow-up, noting that good initial clinical results may fade over time. The present study shows a reoperation rate of 10.4% in patients with DS and LSS, which is less than those that underwent fusion procedures.
Surgical technique to preserve soft tissue attachments and prevent instability while achieving a thorough decompression is important to success of decompression. The ULBD technique involves creating a laminotomy with an ipsilateral partial medial facetectomy, undercutting the ventral surfaces of the spinous process and the contralateral lamina, and performing a partial medial facetectomy of the contralateral facet joint. Thus, a wide decompression of the central canal and bilateral lateral recesses to the medial aspect of the bilateral pedicles within the spinal canal is achieved. This structure-sparing approach retains the ligamentous and bony midline structures, which serve as resistance to further translation. It should be noted that this type of decompression will address central and lateral recess stenosis; ULBD does not improve foraminal stenosis.
However, there are limitations to our study. First, the study is retrospective. There also may be selection bias, as surgeons determined whether a decompression without or with fusion was going to provide patients with the best possible outcome. Although not assessed in this study, patients with DS with radiographic parameters indicating potential instability may have been more likely to either receive instrumented fusion in the index procedure or be at higher risk for postoperative instability and/or persistent or recurrent symptoms. In addition, we did not include patients who expired before the 5-year follow-up which could bias our cohort toward people who are healthier.
Second, within the Fusion cohort, surgeries included both interbody and posterolateral fusions, and the bone graft material was chosen by the surgeon. Third, prospective patient-reported outcomes were not assessed. Fourth, radiographs at 5-year follow-up were not routinely available for patients; it was not customary practice to obtain lumbar radiographs who did not require follow-up at that point. Thus, radiographic parameters that could lead to postoperative instability in the ULBD group were not studied. Another limitation was that preexisting adjacent level degeneration was not compared between the two groups, which could represent an obstacle to comparing revision rates at 5-years. However, because this was not integrated in our decision-making process, whether it resulted in fusion or not, we speculate that its impact is not significant.
Despite inherent limitations of its retrospective nature, this study represents the largest cohort of patients with DS and LSS that underwent ULBD. The continuous follow-up during the 5-year postoperative period via the electronic medical record in the integrated healthcare system allowed for accurate, granular data based on our study criteria, characteristics and outcomes. The data represent five spine surgery centers and numerous surgeons, reflecting actual surgical practice. Since this study period, more patients with stable DS with LSS undergo ULBD within our system. Patients that present with grade 1 spondylolisthesis and symptoms of neurogenic claudication and/or radiculopathy without imaging findings of foraminal stenosis, sagittal facet joint orientation, facet joint diastasis, or significant motion on dynamic imaging studies are typically indicated for ULBD as the index procedure.
In conclusion, this study demonstrates a lower reoperation rate, decreased blood loss, shorter operative time, and reduced length of stay for ULBD when compared to patients who underwent Fusion. For reoperations, the patients with ULBD were more likely to have surgery at the index level, whereas those with Fusion had more reoperations at adjacent levels. Further prospective longer-term studies using randomized trial design in patients with DS are needed to assess the risk factors for failure of ULBD and better indications for inclusion of instrumented fusion at the index procedure.
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