The pressure to contain costs and deliver value in the current health care environment continues to drive the expansion of outpatient spine surgery. Today, not only are more overall spine procedures being performed on an outpatient basis, but also the percentage of all spine procedures being performed in free-standing ambulatory facilities has increased significantly with approximately one quarter of all outpatient spine surgeries occurring at such centers.1 Early case series were the first to report successful outpatient discectomy in the late 1980s and early 1990s.2–4 Since that time, the safety and efficacy of outpatient primary lumbar decompression have been well established, with large series demonstrating complication rates ranging from 0.4% to 3.3%.1,5–9
The literature on the type of spine surgery that is safe to perform outside the hospital setting continues to evolve.10 Although reports have shown satisfactory outcomes after primary cervical and lumbar procedures, limited data exist on the outcomes of revision surgery in the ambulatory setting. Hospital-based studies comparing primary and revision lumbar decompression have historically reported higher rates of complication in revision cases, primarily related to incidental durotomy.11 These reports, however, described revision cases performed via a traditional open approach. More recent studies using minimally invasive techniques have not shown an increased risk of durotomy in revision decompression cases.12,13 Nevertheless, perceived increased risk of complication and increased technical difficulty may deter spine surgeons from performing outpatient revision lumbar decompression. To the authors knowledge, no prior study has reported on the safety and efficacy of revision lumbar decompression procedures performed outside of the hospital setting. The purpose of the current study was to compare complication rates and immediate perioperative outcomes for patients undergoing revision minimally invasive lumbar decompression (MIS LD) in a hospital-based center (HBC) versus at a free-standing ambulatory surgery center (ASC).
MATERIALS AND METHODS
Following institutional review board approval (ORA #14051301), patients were retrospectively reviewed using a prospectively maintained surgical registry. Within the registry, patients were identified who underwent a revision one to three-level lumbar decompression using minimally invasive techniques, performed by a single surgeon at a free-standing ASC between 2013 and 2017. Revision lumbar decompression was defined as reoperation at the level identical to that of the index lumbar decompression. Thirty-five patients were identified who underwent revision MIS LD at an ASC were propensity matched to revision MIS LD patients who underwent surgery at an HBC to adjust for measured confounding variables, including patient age, comorbidity burden as measured by Charlson Comorbidity Index14 (CCI), and preoperative diagnosis. Patients in whom the procedure was performed emergently were excluded. Pain management was standardized according to a multimodal analgesia protocol developed by a team of surgeons and anesthesiologists at our institution.
The hospital and ASC cohorts were then compared with respect to perioperative characteristics, length of stay, immediate postoperative pain scores, immediate postoperative narcotic consumption, and perioperative complications. Surgical complications recorded included superficial and deep wound infection, dural tear, epidural hematoma requiring repeat surgery, and new motor deficit. Incidence and time to index level reoperation were also compared. Narcotic consumption in the immediate postoperative period was recorded and converted to oral morphine equivalents (OMEs) per hour.
The following surgical technique was used in all cases. The patient was placed prone on a Jackson table. Preoperative imaging was used to assess the relationship of the primary laminotomy to the dura and underlying pathology. The previous incision was used for access through which tubular dilators were placed. Sequential dilation was performed and an 18-mm tubular retractor was positioned as a surgical working channel. Soft tissue overlying the laminotomy was cleared to identify the borders of the laminar defect. Once the edge of the laminotomy was identified, a curved curette was used to detach scar tissue from the edge and undersurface of the lamina and facet complex. A high-speed burr was used to resect any additional lamina and facet to re-establish the normal epidural space. Any adhesions were mobilized cautiously between the dura and adjacent soft tissue. Contralateral residual ligamentum flavum and/or subarticular bony stenosis was addressed with a Kerrison rongeur on an as needed basis. In cases of recurrent disc herniation, the ipsilateral traversing root was retracted to identify underlying disc space. An annulotomy was created if there was no disruption in the annulus to extract the herniated disc material. Pituitary rongeurs were then used to extract residual loose disc material with care being taken not to enter into the intervertebral space.
Statistical analysis was performed using Stata/MP 13.1 for Mac (StataCorp LP, College Station, TX). Statistical tests were conducted utilizing Student t test and Pearson Chi-squared analysis for continuous and categorical variables, respectively. An alpha level of less than 0.05 denoted statistical significance.
Thirty-five patients were identified in the database who underwent revision lumbar decompression at the ASC. Propensity score matching was used to identify a comparable cohort of 35 patients who underwent revision lumbar decompression at the HBC. Patient characteristics are described in Table 1. The surgery center and hospital cohorts were similar with regard to age, gender, worker's compensation status, smoking, comorbidity burden, and preoperative diagnosis.
Perioperative characteristics are displayed in Table 2. The surgery center cohort tended to include a greater proportion of single level decompressions (N = 32) as compared to the hospital-based center (N = 27), but this difference was not statistically significant (P = 0.220). Operative time was equivalent between the two cohorts (43 ± 19 vs. 43 ± 12 minutes, P = 0.901). Mean operative time was also similar between cohorts (30 ± 10 vs. 27 ± 7, P = 0.232). There were no intraoperative complications in either group.
Postoperative outcomes are described in Table 3. Length of stay at the ASC was significantly shorter (2.7 ± 1.0 vs. 11.6 ± 11.9 hours, P < 0.001). Inpatient visual analog scale (VAS) pain scores on the day of surgery were similar between groups (4.4 ± 1.9 vs. 3.8 ± 2.6, P = 0.37). Hospital-based patients trended toward higher postoperative hourly OME consumption (9.8 ± 12.0 vs. 6.3 ± 9.1 OME, P = 0.228), but this did not reach statistical significance. There was one postoperative complication of superficial wound infection in the ASC cohort, which resolved after treatment with oral antibiotics.
Four patients in the hospital-based group and three patients in the ASC group ultimately required reoperation (P = 0.612), all in the form of transforaminal lumbar interbody fusion (Table 4). All reoperations for patients in the surgery center group were performed for a diagnosis of repeat recurrent disc herniation. In the hospital-based cohort, one patient had reoperation for a diagnosis of spondylolisthesis, whereas the other three had a second recurrent disc herniation.
As outpatient spine surgery has become commonplace in both the U.S. and abroad over the last decade, more spine procedures are being performed in free-standing ASCs.1,7,15 A recent study of a national commercial insurance claims database found that in 2014, 5% to 10% of single-level lumbar decompressions occurred at a free-standing ASC.16 As this transition to the nonhospital setting continues, it is important that spine surgeons consider its potential impact on patient outcomes, complication rates, and resource utilization. To the authors’ knowledge, no prior study has compared the complication profile and perioperative outcomes of revision lumbar decompression in a free-standing ASC with that of an HBC.
Revision lumbar decompression has been traditionally considered to be of higher risk when compared to primary lumbar decompression; however, reported complication rates in the literature vary widely.17 Incidental durotomy is the primary concern in revision cases due to epidural scar and adhesion. In a study of 95 revision discectomy cases, Palma et al18 reported a 4% rate of dural tear compared with 1% in 1546 primary cases. Other reports have described an incidence as high as 14% in revision cases.11,19 It is important to note that these series included cases performed using a traditional, open approach. More recent studies of minimally invasive tubular approaches have not demonstrated any increased risk of durotomy in revision decompression.13,20 No patients in the current study sustained a dural tear in either cohort. Furthermore, no complications were encountered in either group with the exception of one superficial wound infection treated with a short course of oral antibiotics. These data suggest that revision lumbar decompression in the ASC setting can be done with similar safety and efficacy as compared to the HBC, in an appropriately selected patient population.
Operative time and estimated blood loss were also similar between cohorts. This is unsurprising given that the baseline characteristics of the patient groups are similar and that the senior surgeon has significant experience with minimally invasive decompression. This similarity does suggest, however, that nonsurgeon facility factors such as perioperative staff experience, instrument quality/availability, and anesthetic technique at the surgery center are equivalent to that of the hospital setting. These variables are difficult to quantify but important to consider when examining the feasibility and safety of spine procedures outside of a traditional HBC.
Postoperative pain management is an important consideration in the ASC, as inadequate pain control is a potential barrier to discharge and can result in unplanned hospital readmission in severe cases. In this series, postoperative VAS pain scores were equivalent between cohorts (4.4 vs. 3.8) despite a trend toward lower narcotic consumption at the ASC. This finding was to be expected, as the surgeon uses the same opioid-sparing analgesia protocol at both centers.
Postoperative length of stay was significantly longer at the hospital center than at the ASC (11.6 vs. 2.7 hours). This difference was much larger than expected and is likely the result of multiple factors. The ASC at which the senior surgeon operates does not have an overnight stay option, as is the case in the hospital setting. As such, preparing patients for discharge post procedure is a primary focus of the perioperative staff. Patients are generally given assistance ambulating within 1 hour of the procedure and encouraged to void once ambulatory. Anesthesiologists providing intraoperative care are also responsible for overseeing the recovery unit at the ASC and are accustomed to anesthetic technique suited for same-day discharge. Contributing factors to this observed shorter length of stay for an equivalent population undergoing the same procedure by the same surgeon are of great interest and deserve future study.
This analysis has certain limitations. This study was designed to evaluate immediate perioperative and postoperative data and was not designed to examine long-term patient-reported outcomes. It is reasonable to expect that the medium to long-term clinical outcomes would be comparable given the similar patient populations, procedures, and complication rates. Data demonstrating equivalent long-term outcomes of revision lumbar decompression, as well as other types of spine procedures, would be a valuable contribution to the literature on spine surgery performed outside of a traditional hospital setting. The ASC where patients were treated in this series performs a substantial volume of spine surgery, and thus, has experienced perioperative staff and a full complement of surgical equipment. The operating tables, positioning equipment, tubular retractor systems, and microdecompression instruments are also identical to that of the HBC. Thus, the results described may not be generalizable to all surgery centers where spine cases are performed. In addition, all procedures were performed by a single surgeon with extensive experience with tubular approaches for lumbar decompression. The learning curve associated with minimally invasive spine surgery is substantial and has been well documented.21,22 Surgeons without substantial experience with tubular decompression may not find equivalent results. Given that this analysis involves only tubular-based procedures, it is also unclear whether open approaches to microdiscectomy would have similar perioperative outcomes in the surgery-center setting.
The current study suggests that MIS LD yields similar intraoperative and immediate perioperative results with shorter length of stay in the ASC setting as compared to the HBC setting. Revision MIS LD appears to be safe to perform at a free-standing ASC with an experienced perioperative staff and surgical equipment similar to that of the hospital. Further study of patient outcomes following spine surgery performed outside of the traditional hospital setting is crucial, as the delivery of care in the ambulatory setting continues to grow in popularity.Key PointsA comparison between ambulatory and hospital-based outcomes in patients undergoing revision lumbar decompressions has not been thoroughly explored.Patients undergoing ambulatory or hospital-based revision minimally invasive lumbar spine decompressions exhibited similar postoperative pain scores and narcotics consumption during surgical stay.Ambulatory patients had significantly shorter lengths of postoperative stay as compared to hospital-based patients.Revision minimally invasive lumbar spine decompression can be safely preformed in both an ambulatory or hospital setting.
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