SPINE Volume 40, Number 18, pp E1025-E1030 ©2015, Wolters Kluwer Health, Inc. All rights reserved.
SURGERY
Primary Versus Revision Single-level Minimally Invasive Lumbar Discectomy Analysis of Clinical Outcomes and Narcotic Utilization Junyoung Ahn, BS,* Ehsan Tabaraee, MD,* Daniel D. Bohl, MPH,† Khaled Aboushaala, MD,* and Kern Singh, MD*
Study Design. Retrospective cohort analysis of a prospectively maintained registry. Objective. To compare the intraoperative variables, surgical outcomes, and narcotic utilization between primary and revision 1-level minimally invasive (MIS) lumbar discectomies. Summary of Background Data. Revision spine surgery may be associated with longer procedural time and greater soft tissue disruption. Few studies have analyzed the surgical outcomes and narcotic utilization associated with MIS revision lumbar discectomies. Methods. A retrospective analysis of 227 consecutive cases of MIS 1-level lumbar discectomy for degenerative spinal pathology between 2009 and 2014 by a single surgeon was performed. Patients were stratified into primary and revision cohorts. Demographics, comorbidity, intraoperative parameters, peri- and postoperative outcomes, and reoperations were assessed. Postoperative narcotic utilization was compared between cohorts. Statistical analyses were performed using Student t-test and Pearson χ2 test. A P < 0.05 denoted statistical significance. Results. Of the 227 cases included, 186 patients (81.9%) and 41 patients (18.1%) were included in the primary and revision cohorts, respectively. Demographics, comorbidity, smoking status, preoperative visual analogue scale (VAS) scores, and estimated blood loss did not differ between cohorts. However, the revision cohort demonstrated a longer procedural time, increased length of hospitalization, and higher postoperative narcotic utilization. From the *Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL; and †Department of Orthopaedics and Rehabilitation, Yale School of Medicine, New Haven, CT. Acknowledgment date: December 9, 2014. First revision date: February 25, 2015. Second revision date: March 25, 2015. Acceptance date: April 30, 2015. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. Relevant financial activities outside the submitted work: board membership, consultancy, royalties. Address correspondence and reprint requests to Kern Singh, MD, Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W. Harrison St, Suite #300, Chicago, IL 60612; E-mail: [email protected] DOI: 10.1097/BRS.0000000000000976 Spine
Although not statistically significant, revision patients trended toward higher 6-week postoperative VAS scores and reherniation rates. In addition, revision patients were more likely to undergo subsequent lumbar fusion than primary patients. Conclusion: The findings suggest that revision MIS lumbar discectomy may be associated with increased procedural time, increased length of hospitalization, and increased postoperative narcotic utilization. Whereas revision patients trended toward higher postoperative VAS scores at 6 weeks, both cohorts demonstrated similar pain levels at final follow-up. Finally, revision patients may be at a greater risk of reherniation and subsequent reoperation. Further studies are warranted to characterize the independent risk factors for a revision lumbar discectomy. Key words: lumbar discectomy, MIS discectomy, minimally invasive decompression, revision discectomy, revision decompression, revision minimally invasive discectomy, reherniation, recurrent herniation, fragmentectomy, annular defect, surgery. Level of Evidence: 3 Spine 2015;40:E1025–E1030
T
he 8-year results of the Spine Patient Outcomes Research (SPORT) trial have demonstrated that a lumbar discectomy is an efficacious treatment modality for lumbar disc herniation.1 In addition, Yorimitsu et al demonstrated significant improvement in the clinical outcomes during a 10-year follow-up period as quantified by the Japanese Orthopedic Association (JOA) scores after lumbar discectomy.2 However, the SPORT trial demonstrated that the rate of reoperation in patients with lumbar disc herniation may be as high as 9% within 4 years and 13% within 8 years of the index procedure.1 In addition, approximately 85% of reoperations were due to recurrent herniation at the level identical to the index surgery.1 Reoperation for the management of lumbar spinal pathology has been associated with a higher rate of complications compared with primary surgery. Dural tear rates of 15.9% and 7.6% have been demonstrated in revision and primary lumbar surgery, respectively.3 However, the majority of the literature assesses differences in complications and outcomes www.spinejournal.com
E1025
Copyright © 2015 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. SPINE141594_LR E1025
16/08/15 9:25 AM
SURGERY between primary and revision surgery in the setting of open lumbar discectomy.4,5 The differences in outcomes between primary and revision minimally invasive (MIS) lumbar discectomy have not been well characterized. As such, the purpose of the present study is to assess the differences in clinical outcomes and narcotic utilization in patients who undergo primary versus revision MIS 1-level lumbar discectomy.
MATERIALS AND METHODS Patient Population Following institutional review board approval, a retrospective cohort study was conducted using a prospectively maintained clinical registry. Within the registry, patients were identified who underwent primary or revision MIS 1-level lumbar discectomy for degenerative spinal pathology between 2009 and 2014 performed by a single surgeon. Revision discectomy was defined as reoperation at the level and side identical to that of the index lumbar discectomy. Of the 227 total consecutive cases of MIS lumbar discectomy, 186 and 41 patients were included in the primary and revision cohorts, respectively (Figure 1). From the primary cohort, 10 patients underwent revision surgery to be included in the revision cohort. The remaining 31 patients in the revision cohort had undergone an index procedure from either an outside hospital or from the remote past with an open, microscopic discectomy (prior to 2009). All patients had undergone nonoperative treatment modalities prior to surgical intervention. Patients in whom the procedure was performed emergently were excluded. Similarly, patients with less than 6-month of postoperative followup were excluded.
Revision MIS Lumbar Discectomy • Ahn et al
Demographic and Outcomes Analysis Patients were stratified into primary and revision cohorts and compared with respect to demographics, comorbidity burden, Charlson Comorbidity Index (CCI), smoking status, intraoperative parameters, perioperative outcomes, and postoperative complications. Patient comorbidity was assessed using a modified CCI.6 These modifications included (1) an omission of a history of myocardial infarction and (2) the adjustment of liver disease to have a weight of 2 points for mild disease and 3 points for moderate-to-severe liver disease. Previous studies have demonstrated that slight modifications to the CCI have minimal impact on the overall score.6,7 Any reoperations were recorded according to whether the additional surgeries were identical (“index”) or nonidentical (“adjacent”) to the side and operative level of the index procedure. For the primary patients, subsequent surgeries performed at the index level/side were designated as “revision,” whereas the term “second surgery” was designated to include additional procedures at either index or adjacent levels (Figure 1). Similarly, for the revision cohort, reoperations were recorded and classified as “rerevision” or “adjacent” according to whether the operative level and side were identical or nonidentical to that of the revision surgery, respectively. For these patients, “rerevision” was designated to specify procedures performed at the index level and side, whereas “third surgery” included procedures at either index or adjacent levels. Narcotic consumption in the immediate postoperative period was recorded and converted to oral morphine equivalents (OME) utilizing the conversion ratios referenced from the American Pain Society and the National Comprehensive
Figure 1. Flowchart demonstrating patient cohort stratification and rates of reoperation according to operative levels and type of procedure. *“Revision” = Procedures only at the level and side identical to that of the primary procedure or “first surgery”. †Includes 31 patients who underwent “first surgery” at an outside hospital or open, microscopic discectomy in the remote past (prior to 2009). ‡“Rerevision” = Procedures only at the level and side identical to that of the revision procedure of “second surgery”.
E1026
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September 2015
Copyright © 2015 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. SPINE141594_LR E1026
16/08/15 9:25 AM
SURGERY Cancer Network.8,9 The sum of the OME values from postoperative days 0 and 1 were compared between cohorts. In addition, reoperation rate as well reoperation type and time to second surgery were identified.
Surgical Technique The following surgical technique was used in all cases for primary procedures. The patient was placed prone on a Jackson table. Fluoroscopy was used to localize the target level. A 1–2 cm incision was made lateral to the midline at the level of interest. Sequential dilation was performed until an 18 mm tubular retractor was placed as a surgical working channel. A burr and Kerrison rongeurs were used to perform a hemilaminotomy. Great care was taken to preserve the pars interarticularis and 50% of the facet joint. The ligamentum flavum was resected and the traversing nerve root was safely retracted. 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. For the revision cases, preoperative imaging was obtained to assess the relationship of the primary laminotomy to the dura. The previous incision was used for access with the tubular dilators serving as the working channel. 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 the underlying disc to identify the underlying disc herniation.
Statistical Analysis SPSS Inc. v22.0 (IBM Corp: Armonk, NY) was used for statistical analysis. Statistical tests were conducted utilizing Student t-test for continuous variables and Fisher Exact Test for categorical data. An alpha level of less than 0.05 denoted statistical significance.
RESULTS Patient characteristics are described in Table 1. Of the 227 patients who met the inclusion criteria, 186 (81.9%) were primary and 41 (18.1%) were revision patients. Patient demographics (age, sex, ethnicity), comorbidity burden, smoking status, and level of pathology were similar between cohorts. In addition, both primary and revision cohorts demonstrated similar preoperative VAS scores (6.6 ± 1.9 vs. 6.7 ± 1.8, respectively; Table 1). Revision patients demonstrated increased operative times (42.4 ± 14.5 vs. 36.1 ± 16.8 min; P < 0.05) while maintaining similar estimated blood loss (EBL) when compared with the primary cohort (43.7 ± 21.8 vs. 41.1 ± 23.3 cc; Table 2). The revision cohort demonstrated a significantly longer length of hospitalization (18.6 ± 17.4 vs. 13.1 ± 13.8 hr; P < 0.05; Table 2). Revision patients trended toward higher 6-week postoperative VAS scores (3.3 ± 2.9 vs. 2.5 ± 2.5; Table 3). However, Spine
Revision MIS Lumbar Discectomy • Ahn et al
12-week and 6-month VAS scores were similar between the primary and revision cohorts. In addition, revision patients demonstrated a significantly higher 6-month complication rate and a trend toward a higher rate of reherniation (14.6% vs. 7.0%, P = 0.09). The revision cohort demonstrated a significantly greater rate of reoperation (third surgery) than the primary cohort (second surgery) [31.7% (n = 13/41) vs. 14.5% (n = 27/186), respectively; P < 0.05; Table 3; Figure 1]. In addition, the revision cohort was more likely to undergo reoperation at the index level/side than the primary cohort (“revision” for the primary cohort and “rerevision” for the revision cohort; [31.7% (n = 13/41) vs. 11.3% (n = 21/186); P < 0.01; Table 3; Figure 1]. However, the rates of lumbar decompression at the index as
TABLE 1. Patient Characteristics P
Primary
Revision
100% (186)
100% (41)
Male
71.0% (132)
70.7% (29)
Female
29.0% (54)
29.3% (12)
40.0 ± 12.0
39.7 ± 12.1
0.90
0.4 ± 1.2
0.1 ± 0.3
0.20
29.4 ± 6.7
30.5 ± 7.4
0.40
Caucasian
68.8% (128)
70.0% (29)
African American
14.5% (27)
10.0% (4)
Hispanic
14.5% (27)
17.5% (7)
Asian
1.1% (2)
2.5% (1)
Other
1.1% (2)
0
Yes
19.3% (36)
26.8% (11)
No
80.7% (150)
73.2% (30)
4.3% (8)
4.9% (2)
Worker’s compensation
36.5% (68)
41.5% (17)
Other
59.1% (110)
53.7% (22)
6.6 ± 1.9
6.7 ± 1.8
0.90
L4–L5
51.1% (95)
41.5% (17)
0.26
L5–S1
48.9% (91)
58.5% (24)
Total number of patients (n) Sex (n)
Age (mean ± SD, years) Comorbidity index Body mass index (kg/m ) 2
0.92
Ethnicity (n)
0.74
Smoker (n) 0.25
Insurance type Medicare
Preoperative VAS
0.70
Level of pathology
SD indicates standard deviation; VAS, visual analogue scale.
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E1027
Copyright © 2015 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. SPINE141594_LR E1027
16/08/15 9:25 AM
SURGERY
Revision MIS Lumbar Discectomy • Ahn et al
TABLE 2. Perioperative Characteristics
TABLE 3. Postoperative Outcomes and
Primary
Revision
P*
Procedural time (Mean ± SD, min)
36.1 ± 16.8
42.4 ± 14.5
SURGERY
Primary Versus Revision Single-level Minimally Invasive Lumbar Discectomy Analysis of Clinical Outcomes and Narcotic Utilization Junyoung Ahn, BS,* Ehsan Tabaraee, MD,* Daniel D. Bohl, MPH,† Khaled Aboushaala, MD,* and Kern Singh, MD*
Study Design. Retrospective cohort analysis of a prospectively maintained registry. Objective. To compare the intraoperative variables, surgical outcomes, and narcotic utilization between primary and revision 1-level minimally invasive (MIS) lumbar discectomies. Summary of Background Data. Revision spine surgery may be associated with longer procedural time and greater soft tissue disruption. Few studies have analyzed the surgical outcomes and narcotic utilization associated with MIS revision lumbar discectomies. Methods. A retrospective analysis of 227 consecutive cases of MIS 1-level lumbar discectomy for degenerative spinal pathology between 2009 and 2014 by a single surgeon was performed. Patients were stratified into primary and revision cohorts. Demographics, comorbidity, intraoperative parameters, peri- and postoperative outcomes, and reoperations were assessed. Postoperative narcotic utilization was compared between cohorts. Statistical analyses were performed using Student t-test and Pearson χ2 test. A P < 0.05 denoted statistical significance. Results. Of the 227 cases included, 186 patients (81.9%) and 41 patients (18.1%) were included in the primary and revision cohorts, respectively. Demographics, comorbidity, smoking status, preoperative visual analogue scale (VAS) scores, and estimated blood loss did not differ between cohorts. However, the revision cohort demonstrated a longer procedural time, increased length of hospitalization, and higher postoperative narcotic utilization. From the *Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL; and †Department of Orthopaedics and Rehabilitation, Yale School of Medicine, New Haven, CT. Acknowledgment date: December 9, 2014. First revision date: February 25, 2015. Second revision date: March 25, 2015. Acceptance date: April 30, 2015. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. Relevant financial activities outside the submitted work: board membership, consultancy, royalties. Address correspondence and reprint requests to Kern Singh, MD, Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W. Harrison St, Suite #300, Chicago, IL 60612; E-mail: [email protected] DOI: 10.1097/BRS.0000000000000976 Spine
Although not statistically significant, revision patients trended toward higher 6-week postoperative VAS scores and reherniation rates. In addition, revision patients were more likely to undergo subsequent lumbar fusion than primary patients. Conclusion: The findings suggest that revision MIS lumbar discectomy may be associated with increased procedural time, increased length of hospitalization, and increased postoperative narcotic utilization. Whereas revision patients trended toward higher postoperative VAS scores at 6 weeks, both cohorts demonstrated similar pain levels at final follow-up. Finally, revision patients may be at a greater risk of reherniation and subsequent reoperation. Further studies are warranted to characterize the independent risk factors for a revision lumbar discectomy. Key words: lumbar discectomy, MIS discectomy, minimally invasive decompression, revision discectomy, revision decompression, revision minimally invasive discectomy, reherniation, recurrent herniation, fragmentectomy, annular defect, surgery. Level of Evidence: 3 Spine 2015;40:E1025–E1030
T
he 8-year results of the Spine Patient Outcomes Research (SPORT) trial have demonstrated that a lumbar discectomy is an efficacious treatment modality for lumbar disc herniation.1 In addition, Yorimitsu et al demonstrated significant improvement in the clinical outcomes during a 10-year follow-up period as quantified by the Japanese Orthopedic Association (JOA) scores after lumbar discectomy.2 However, the SPORT trial demonstrated that the rate of reoperation in patients with lumbar disc herniation may be as high as 9% within 4 years and 13% within 8 years of the index procedure.1 In addition, approximately 85% of reoperations were due to recurrent herniation at the level identical to the index surgery.1 Reoperation for the management of lumbar spinal pathology has been associated with a higher rate of complications compared with primary surgery. Dural tear rates of 15.9% and 7.6% have been demonstrated in revision and primary lumbar surgery, respectively.3 However, the majority of the literature assesses differences in complications and outcomes www.spinejournal.com
E1025
Copyright © 2015 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. SPINE141594_LR E1025
16/08/15 9:25 AM
SURGERY between primary and revision surgery in the setting of open lumbar discectomy.4,5 The differences in outcomes between primary and revision minimally invasive (MIS) lumbar discectomy have not been well characterized. As such, the purpose of the present study is to assess the differences in clinical outcomes and narcotic utilization in patients who undergo primary versus revision MIS 1-level lumbar discectomy.
MATERIALS AND METHODS Patient Population Following institutional review board approval, a retrospective cohort study was conducted using a prospectively maintained clinical registry. Within the registry, patients were identified who underwent primary or revision MIS 1-level lumbar discectomy for degenerative spinal pathology between 2009 and 2014 performed by a single surgeon. Revision discectomy was defined as reoperation at the level and side identical to that of the index lumbar discectomy. Of the 227 total consecutive cases of MIS lumbar discectomy, 186 and 41 patients were included in the primary and revision cohorts, respectively (Figure 1). From the primary cohort, 10 patients underwent revision surgery to be included in the revision cohort. The remaining 31 patients in the revision cohort had undergone an index procedure from either an outside hospital or from the remote past with an open, microscopic discectomy (prior to 2009). All patients had undergone nonoperative treatment modalities prior to surgical intervention. Patients in whom the procedure was performed emergently were excluded. Similarly, patients with less than 6-month of postoperative followup were excluded.
Revision MIS Lumbar Discectomy • Ahn et al
Demographic and Outcomes Analysis Patients were stratified into primary and revision cohorts and compared with respect to demographics, comorbidity burden, Charlson Comorbidity Index (CCI), smoking status, intraoperative parameters, perioperative outcomes, and postoperative complications. Patient comorbidity was assessed using a modified CCI.6 These modifications included (1) an omission of a history of myocardial infarction and (2) the adjustment of liver disease to have a weight of 2 points for mild disease and 3 points for moderate-to-severe liver disease. Previous studies have demonstrated that slight modifications to the CCI have minimal impact on the overall score.6,7 Any reoperations were recorded according to whether the additional surgeries were identical (“index”) or nonidentical (“adjacent”) to the side and operative level of the index procedure. For the primary patients, subsequent surgeries performed at the index level/side were designated as “revision,” whereas the term “second surgery” was designated to include additional procedures at either index or adjacent levels (Figure 1). Similarly, for the revision cohort, reoperations were recorded and classified as “rerevision” or “adjacent” according to whether the operative level and side were identical or nonidentical to that of the revision surgery, respectively. For these patients, “rerevision” was designated to specify procedures performed at the index level and side, whereas “third surgery” included procedures at either index or adjacent levels. Narcotic consumption in the immediate postoperative period was recorded and converted to oral morphine equivalents (OME) utilizing the conversion ratios referenced from the American Pain Society and the National Comprehensive
Figure 1. Flowchart demonstrating patient cohort stratification and rates of reoperation according to operative levels and type of procedure. *“Revision” = Procedures only at the level and side identical to that of the primary procedure or “first surgery”. †Includes 31 patients who underwent “first surgery” at an outside hospital or open, microscopic discectomy in the remote past (prior to 2009). ‡“Rerevision” = Procedures only at the level and side identical to that of the revision procedure of “second surgery”.
E1026
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September 2015
Copyright © 2015 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. SPINE141594_LR E1026
16/08/15 9:25 AM
SURGERY Cancer Network.8,9 The sum of the OME values from postoperative days 0 and 1 were compared between cohorts. In addition, reoperation rate as well reoperation type and time to second surgery were identified.
Surgical Technique The following surgical technique was used in all cases for primary procedures. The patient was placed prone on a Jackson table. Fluoroscopy was used to localize the target level. A 1–2 cm incision was made lateral to the midline at the level of interest. Sequential dilation was performed until an 18 mm tubular retractor was placed as a surgical working channel. A burr and Kerrison rongeurs were used to perform a hemilaminotomy. Great care was taken to preserve the pars interarticularis and 50% of the facet joint. The ligamentum flavum was resected and the traversing nerve root was safely retracted. 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. For the revision cases, preoperative imaging was obtained to assess the relationship of the primary laminotomy to the dura. The previous incision was used for access with the tubular dilators serving as the working channel. 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 the underlying disc to identify the underlying disc herniation.
Statistical Analysis SPSS Inc. v22.0 (IBM Corp: Armonk, NY) was used for statistical analysis. Statistical tests were conducted utilizing Student t-test for continuous variables and Fisher Exact Test for categorical data. An alpha level of less than 0.05 denoted statistical significance.
RESULTS Patient characteristics are described in Table 1. Of the 227 patients who met the inclusion criteria, 186 (81.9%) were primary and 41 (18.1%) were revision patients. Patient demographics (age, sex, ethnicity), comorbidity burden, smoking status, and level of pathology were similar between cohorts. In addition, both primary and revision cohorts demonstrated similar preoperative VAS scores (6.6 ± 1.9 vs. 6.7 ± 1.8, respectively; Table 1). Revision patients demonstrated increased operative times (42.4 ± 14.5 vs. 36.1 ± 16.8 min; P < 0.05) while maintaining similar estimated blood loss (EBL) when compared with the primary cohort (43.7 ± 21.8 vs. 41.1 ± 23.3 cc; Table 2). The revision cohort demonstrated a significantly longer length of hospitalization (18.6 ± 17.4 vs. 13.1 ± 13.8 hr; P < 0.05; Table 2). Revision patients trended toward higher 6-week postoperative VAS scores (3.3 ± 2.9 vs. 2.5 ± 2.5; Table 3). However, Spine
Revision MIS Lumbar Discectomy • Ahn et al
12-week and 6-month VAS scores were similar between the primary and revision cohorts. In addition, revision patients demonstrated a significantly higher 6-month complication rate and a trend toward a higher rate of reherniation (14.6% vs. 7.0%, P = 0.09). The revision cohort demonstrated a significantly greater rate of reoperation (third surgery) than the primary cohort (second surgery) [31.7% (n = 13/41) vs. 14.5% (n = 27/186), respectively; P < 0.05; Table 3; Figure 1]. In addition, the revision cohort was more likely to undergo reoperation at the index level/side than the primary cohort (“revision” for the primary cohort and “rerevision” for the revision cohort; [31.7% (n = 13/41) vs. 11.3% (n = 21/186); P < 0.01; Table 3; Figure 1]. However, the rates of lumbar decompression at the index as
TABLE 1. Patient Characteristics P
Primary
Revision
100% (186)
100% (41)
Male
71.0% (132)
70.7% (29)
Female
29.0% (54)
29.3% (12)
40.0 ± 12.0
39.7 ± 12.1
0.90
0.4 ± 1.2
0.1 ± 0.3
0.20
29.4 ± 6.7
30.5 ± 7.4
0.40
Caucasian
68.8% (128)
70.0% (29)
African American
14.5% (27)
10.0% (4)
Hispanic
14.5% (27)
17.5% (7)
Asian
1.1% (2)
2.5% (1)
Other
1.1% (2)
0
Yes
19.3% (36)
26.8% (11)
No
80.7% (150)
73.2% (30)
4.3% (8)
4.9% (2)
Worker’s compensation
36.5% (68)
41.5% (17)
Other
59.1% (110)
53.7% (22)
6.6 ± 1.9
6.7 ± 1.8
0.90
L4–L5
51.1% (95)
41.5% (17)
0.26
L5–S1
48.9% (91)
58.5% (24)
Total number of patients (n) Sex (n)
Age (mean ± SD, years) Comorbidity index Body mass index (kg/m ) 2
0.92
Ethnicity (n)
0.74
Smoker (n) 0.25
Insurance type Medicare
Preoperative VAS
0.70
Level of pathology
SD indicates standard deviation; VAS, visual analogue scale.
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E1027
Copyright © 2015 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. SPINE141594_LR E1027
16/08/15 9:25 AM
SURGERY
Revision MIS Lumbar Discectomy • Ahn et al
TABLE 2. Perioperative Characteristics
TABLE 3. Postoperative Outcomes and
Primary
Revision
P*
Procedural time (Mean ± SD, min)
36.1 ± 16.8
42.4 ± 14.5
