Minimally invasive laminectomy for lumbar spinal stenosis in patients with and without preoperative spondylolisthesis: clinical outcome and reoperation rates

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OBJECT

Surgical decompression is the intervention of choice for lumbar spinal stenosis (LSS) when nonoperative treatment has failed. Standard open laminectomy is an effective procedure, but minimally invasive laminectomy through tubular retractors is an alternative. The aim of this retrospective case series was to evaluate the clinical and radiographic outcomes of this procedure in patients who underwent LSS and to compare outcomes in patients with and without preoperative spondylolisthesis.

METHODS

Patients with LSS without spondylolisthesis and with stable Grade I spondylolisthesis who had undergone minimally invasive tubular laminectomy between 2004 and 2011 were included in this analysis. Demographic, perioperative, and radiographic data were collected. Clinical outcome was evaluated using the Oswestry Disability Index (ODI) and visual analog scale (VAS) scores, as well as Macnab's criteria.

RESULTS

Among 110 patients, preoperative spondylolisthesis at the level of spinal stenosis was present in 52.5%. At a mean follow-up of 28.8 months, scoring revealed a median improvement of 16% on the ODI, 2.75 on the VAS back, and 3 on the VAS leg, compared with the preoperative baseline (p < 0.0001). The reoperation rate requiring fusion at the same level was 3.5%. Patients with and without preoperative spondylolisthesis had no significant differences in their clinical outcome or reoperation rate.

CONCLUSIONS

Minimally invasive laminectomy is an effective procedure for the treatment of LSS. Reoperation rates for instability are lower than those reported after open laminectomy. Functional improvement is similar in patients with and without preoperative spondylolisthesis. This procedure can be an alternative to open laminectomy. Routine fusion may not be indicated in all patients with LSS and spondylolisthesis.

ABBREVIATIONSBMI = body mass index; LSS = lumbar spinal stenosis; MCID = minimum clinically important difference; ODI = Oswestry Disability Index; VAS = visual analog scale.

OBJECT

Surgical decompression is the intervention of choice for lumbar spinal stenosis (LSS) when nonoperative treatment has failed. Standard open laminectomy is an effective procedure, but minimally invasive laminectomy through tubular retractors is an alternative. The aim of this retrospective case series was to evaluate the clinical and radiographic outcomes of this procedure in patients who underwent LSS and to compare outcomes in patients with and without preoperative spondylolisthesis.

METHODS

Patients with LSS without spondylolisthesis and with stable Grade I spondylolisthesis who had undergone minimally invasive tubular laminectomy between 2004 and 2011 were included in this analysis. Demographic, perioperative, and radiographic data were collected. Clinical outcome was evaluated using the Oswestry Disability Index (ODI) and visual analog scale (VAS) scores, as well as Macnab's criteria.

RESULTS

Among 110 patients, preoperative spondylolisthesis at the level of spinal stenosis was present in 52.5%. At a mean follow-up of 28.8 months, scoring revealed a median improvement of 16% on the ODI, 2.75 on the VAS back, and 3 on the VAS leg, compared with the preoperative baseline (p < 0.0001). The reoperation rate requiring fusion at the same level was 3.5%. Patients with and without preoperative spondylolisthesis had no significant differences in their clinical outcome or reoperation rate.

CONCLUSIONS

Minimally invasive laminectomy is an effective procedure for the treatment of LSS. Reoperation rates for instability are lower than those reported after open laminectomy. Functional improvement is similar in patients with and without preoperative spondylolisthesis. This procedure can be an alternative to open laminectomy. Routine fusion may not be indicated in all patients with LSS and spondylolisthesis.

ABBREVIATIONSBMI = body mass index; LSS = lumbar spinal stenosis; MCID = minimum clinically important difference; ODI = Oswestry Disability Index; VAS = visual analog scale.

Symptomatic lumbar spinal stenosis (LSS) unresponsive to conservative therapy is commonly treated using direct surgical decompression.33 Current guidelines recommend additional arthrodesis in patients with LSS and preexisting spondylolisthesis.21,24,31,49,50,52 Various techniques are currently used for direct decompression of LSS. Standard open laminectomy has been shown to be an effective procedure for LSS decompression.36,46,54,60–64,66 However, wide laminectomies violating stabilizing bony and ligamentous structures may exacerbate preexisting spondylolisthesis.19,37 Minimally invasive laminectomy through tubular or similar retractors is a recently introduced alternative procedure for decompression of LSS.47 This technique avoids detachment of the paraspinal muscles and may promote preservation of stabilizing ligamentous and bony spinal structures.29,30,39,41–45 Biomechanical studies indicate that compared with open laminectomy, minimally invasive laminectomy may result in less postoperative instability.1,6,12,23,34

The current study had two main goals: first, to evaluate the efficacy of minimally invasive laminectomy as a decompressive procedure for the treatment of patients with LSS. The second aim was to compare the clinical and radiographic outcomes of minimally invasive laminectomy in patients with and without preexisting stable spondylolisthesis.

To better achieve the first goal, outcomes for LSS following minimally invasive laminectomies in our retrospective case series were compared with those achieved via other surgical interventions described in the literature.

Methods

Patient Population

Institutional approval for this study was obtained from Weill Cornell Medical College. Data for this retrospective case series were extracted from the prospectively collected hospital database. We sought all patients who had undergone minimally invasive laminectomy for decompression of LSS between 2004 and 2011. Demographic and perioperative data on these patients were collected. For the demographic data, age, sex, body mass index (BMI), smoking status, history of diabetes, and steroid medication use were recorded. Operative and anesthesia reports as well as hospital charts were reviewed to add data on estimated blood loss, number and levels of surgery, complications, and length of hospital stay. The presence of preoperative spondylolisthesis was determined on radiographic studies. Postoperative radiographs were evaluated to assess changes in the amount and grade of previous spondylolisthesis and/or the development of new slippage. Standardized radiographs were used for assessments, both preoperatively and postoperatively. Patients who had presented with preoperative spondylolisthesis and primarily mechanical back pain and/or instability on flexion/extension films were not included in this study. Comparisons were made between the outcomes of minimally invasive laminectomies in our cohort and the outcomes of other decompressive surgical interventions for LSS, as published in the literature.

Operative Procedure

With the patient lying prone under general anesthesia, a small skin incision is made overlying the target level approximately 1.5 cm lateral to the midline. An 18- or 19-mm tubular retractor is placed over a series of tubular dilators for retraction, and under the microscope, the inferior edge of the lamina and the inferior edge and base of the spinous process are exposed (Fig. 1). The decompression is performed step by step starting with an ipsilateral partial laminectomy using a 3-mm curved matchstick drill bit and bayonet-shaped 2- and 3-mm Kerrison punches (Fig. 2). To achieve appropriate visualization of contralateral structures, the operating table is tilted away from the surgeon and the tubular retractor is angled medially. Next, the spinous process and the contralateral lamina are undercut using the drill and rongeurs (Fig. 3). The ligamentum flavum is completely exposed bilaterally and cranially until its insertion under the lamina. During the laminectomy, the ligamentum flavum protects the dura. Next, we insert a nerve hook and then a Kerrison rongeur in the midline where the two leaves of the ligamentum flavum meet, an area that is typically identified by the presence of epidural fat (Figs. 4 and 5). These techniques minimize risks of injury to the dura. The ligamentum flavum is then removed (Fig. 6). Great care is taken to completely decompress the lateral recess and entirely remove the yellow ligament. This also allows visualization and decompression, if needed, of the contralateral exiting and traversing nerve root.

FIG. 1.
FIG. 1.

An 18- or 19-mm tubular retractor is placed over a series of tubular dilators for retraction, and under the microscope, the inferior edge of the lamina and the inferior edge and base of the spinous process are exposed. Illustration by Thomas Graves. Copyright Roger Härtl. Published with permission.

FIG. 2.
FIG. 2.

The decompression is performed starting with an ipsilateral partial laminectomy using a 3-mm curved matchstick drill bit and bayonetshaped 2- and 3-mm Kerrison punches. Illustration by Thomas Graves. Copyright Roger Härtl. Published with permission.

FIG. 3.
FIG. 3.

The operating table is tilted away from the surgeon, and the tubular retractor is angled medially to achieve appropriate visualization of contralateral sublaminar structures. Next, the spinous process and the contralateral lamina are undercut using the drill and rongeurs. The ligamentum flavum is completely exposed cranially until its insertion under the lamina. Illustration by Thomas Graves. Copyright Roger Härtl. Published with permission.

FIG. 4.
FIG. 4.

A nerve hook is inserted in the midline where the two leaves of the ligamentum flavum meet, an area that is typically identified by the presence of epidural fat. Illustration by Thomas Graves. Copyright Roger Härtl. Published with permission.

FIG. 5.
FIG. 5.

The ligamentum flavum is then carefully removed using Kerrison rongeurs. Illustration by Thomas Graves. Copyright Roger Härtl. Published with permission.

FIG. 6.
FIG. 6.

Dural exposure and decompression after complete removal of the ligamentum flavum. The contralateral approach allows visualization and decompression, if needed, of the contralateral exiting and traversing nerve root. Illustration by Thomas Graves. Copyright Roger Härtl. Published with permission.

Adequate decompression is always confirmed by identifying certain landmark structures and achieving particular surgical end points, as follows: contralaterally and caudally by palpating the pedicle using a ball tip instrument, cranially by confirming complete removal of the yellow ligament and the absence of bony compression of the dura mater, and ipsilaterally by complete removal of the ligamentum flavum and by clear identification of the lateral aspect of the thecal sac and inspection of the traversing nerve root. As the next and final step, the table and retractor are brought back into the initial position, and the ipsilateral decompression is completed.

Clinical Outcome Evaluation

The preoperative and latest available follow-up Oswestry Disability Index (ODI)14 and visual analog scale (VAS) scores for back, buttock, and leg pain were collected and compared. Functional outcome was evaluated using Macnab's criteria.35 Patients without late follow-up outcome scores recorded in the hospital's database were contacted by phone, and the ODI and VAS pain scores and Macnab's level of satisfaction were assessed. These patients were also asked if they had undergone any further lumbar spine surgery at outside medical centers.

A 12-point improvement on the ODI3,20,22 and 3-point improvement on the VAS were regarded as the minimum clinically important difference (MCID).15,16,22 As for functional outcome, 4 levels were defined according to Macnab's criteria: excellent (no pain; no restriction of activity), good (occasional back or leg pain of sufficient severity to interfere with the ability to work), fair (improved functional capacity but handicapped by intermittent pain of sufficient severity to curtail work), or poor (no improvement or insufficient improvement to enable increase in activities; further operative interventions required).35

The patients who required another operation and underwent a second surgery at our and other institutions were identified. The indication for the second operation and a description of the procedure were recorded.

Radiographic Evaluation

In patients with postoperative radiographic studies, the latest study was used to assess changes in the amount and grade of previous spondylolisthesis and/or development of new slippage.

Statistical Analysis

Patients with preoperative radiographic studies, who had been evaluated for the presence or absence of preoperative spondylolisthesis, were divided into 2 groups: patients with concomitant preoperative spondylolisthesis and those without. We reported results for the entire group of patients as well as for each of the 2 groups separately. Comparisons were made between the 2 different groups and between each group and the entire study group.

Continuous variables are shown as the mean ± standard deviation. Percentages were calculated for categorical variables. Differences in categorical variables were assessed using the chi-square test. Differences in continuous variables were tested using the independent t-test, and differences for repeatedly measured variables were assessed using the repeated measures t-test. All analyses were performed using appropriate statistical software (SPSS, version 18.0.0.1, SPSS Inc.). A p value of < 0.05 was considered statistically significant.

Results

Patient Demographics

One hundred ten consecutive patients, 58 males and 52 females, with isolated LSS who had undergone minimally invasive laminectomy surgery for decompression were included in our study. The mean age at surgery was 68.5 years (range 32–89 years; Table 1), and the mean BMI was 28.6 kg/m2. A history positive for smoking, diabetes, and steroid medication use was present in 11.8%, 14.8%, and 4.6% of patients, respectively. In 97 patients with available preoperative imaging, spondylolisthesis Grade I was present in 51 patients (52.6%), whereas 46 patients (47.4%) did not have preoperative spondylolisthesis.

TABLE 1

Summary of preoperative characteristics in 110 patients with LSS with and without spondylolisthesis

CharacteristicAll PatientsPatients w/ SpondylolisthesisPatients w/o Spondylolisthesisp Value
No. of patients1105146
Mean age at surgery in yrs*68.5 ± 12.7772.4 ± 12.6964.4 ± 12.330.002
Sex
 Male58 (52.7%)24 (47.1%)23 (50%)0.84
 Female52 (47.3%)27 (52.9%)23 (50%)
Mean BMI in kg/m²*28.6 ± 4.7428.5 ± 4.9429.2 ± 4.680.49
Diabetes
 Yes14.8%12.2%19.6%0.40
 No85.2%87.8%80.4%
Smoking
 Yes11.8%9.1%7.9%0.84
 No88.2%90.9%92.1%
Steroid medication use
 Yes4.6%2%6.5%0.35
 No95.4%98%93.5%
Preop spondylolisthesis level
 L2–35 (8.1%)5 (8.1%)
 L3–415 (24.2%)15 (24.2%)
 L4–537 (59.6%)37 (59.6%)
 L5–S15 (8.1%)5 (8.1%)
— = not applicable.

Values expressed as the mean ± standard deviation.

Statistically significant.

Fifty-one patients, 62 levels.

Surgical Details

One-, 2-, and 3-level surgeries were done in 57 patients (51.8%), 47 (42.7%), and 6 (5.4%), respectively. A total of 169 levels were operated on in 110 patients, and the most common level of surgery was L4–5 (50.3% of cases). The L3–4 level made up 29% of cases; L5–S1, 11.2%; and L2–3, the remaining 9.5%. The median estimated blood loss for 1-, 2-, and 3-level surgeries was 25, 50, and 150 ml, respectively (Table 2). More than half of the patients (56%) were discharged on either the day of surgery or the first postoperative day, while the mean duration of hospitalization was 2.2 ± 2.63 days (range 0–13 days).

TABLE 2

Summary of surgical details in 110 patients who underwent laminectomy

CharacteristicAll PatientsPatients w/ SpondylolisthesisPatients w/o Spondylolisthesisp Value
No. of patients1105146
No. of operated levels1697871
No. of levels/patient
 157 (51.8%)28 (54.9%)23 (50%)
 247 (42.7%)19 (37.3%)21 (45.7%)0.60
 36 (5.5%)4 (7.8%)2 (4.3%)
Level of surgery
 L2–316 (9.5%)9 (11.5%)5 (7%)0.39
 L3–449 (29.0%)19 (24.4%)23 (32.4%)0.22
 L4–585 (50.3%)42 (53.8%)36 (50.7%)0.62
 L5–S119 (11.2%)8 (10.3%)7 (9.9%)0.94
Estimated blood loss (ml)*
 1-level op25 (0;550)20 (0;150)50 (0;550)0.04
 2-level op50 (0;400)75 (0;200)50 (0;400)0.61
 3-level op150 (100;300)125 (100;300)2500.80
Hospital stay (days)*1 (0;13)1 (0;12)1 (0;13)0.28

Values expressed as the median (min;max).

Statistically significant.

Single case.

Clinical Outcome

The mean preoperative ODI was 45.3 ± 19.62 (range 0–88; Tables 3 and 4), which decreased to 28.9 ± 21.76 at a mean follow-up of 28.8 months. An MCID (defined as improvement on the ODI by 12 or more points3,20,22) was achieved in 54.8% of patients (Table 5). The median preoperative VAS back, buttock, and leg pain scores were 8, 4.5, and 4.6, respectively. At the latest follow-up, the median VAS back, buttock, and leg pain scores decreased to 3.5, 0, and 0, respectively. Three-point improvement on the VAS was regarded as the MCID.15,16,22 The MCID for VAS back, buttock, and leg pain was achieved in 50.0%, 45.2%, and 52.4% of the patients, respectively. All 4 scores indicated statistically significant improvement at the latest follow-up. A comparison of ODI and VAS outcome scores in patients with and without preoperative spondylolisthesis showed no significant difference between the 2 groups (Tables 4 and 5).

TABLE 3

Summary of clinical outcome measures in 84 patients with available preoperative and postoperative data*

MeasurePreopLast FUp Value
Mean preop ODI (out of 100)45.3 ± 19.6228.9 ± 21.76<0.0001
VAS back8 (0;10)3.5 (0;10)<0.0001
VAS buttock4.5 (0;10)0 (0;10)<0.0001
VAS leg4.6 (0;10)0 (0;8)<0.0001
FU = follow-up.

The mean follow-up duration was 28.8 ± 19.39 months.

Statistically significant.

TABLE 4

Summary of clinical improvement in patients with and without spondylolisthesis

ParameterAll PatientsPatients w/ SpondylolisthesisPatients w/o Spondylolisthesisp Value
No. of patients*843738
FU duration in mos0.81
 Mean ± SD28.5 ± 19.6326.7 ± 18.6027.7 ± 19.43
 Median (min;max)22.8 (6.2;74.3)20.7 (8.5;74.3)20.5 (6.2;74.3)
% ODI improvement16.00 (−48.8;62.2)11.00 (−37.8;62.2)19.45 (−48.8;53.0)0.55
VAS back improvement (points)2.75 (−10;10)3.00 (−6;10)2.00 (−10;9)0.26
VAS buttock improvement (points)2.25 (−10;9)3.50 (−10;8)2.50 (−5;9)0.54
VAS leg improvement (points)3.00 (−5;10)3.00 (−1;9)3.50 (−5;10)0.88

Preoperative and follow-up outcome scores were available in 84 patients; 9 of these patients had no preoperative imaging data.

TABLE 5

Summary of improvements on ODI and VAS

ParameterAll PatientsPatients w/ SpondylolisthesisPatients w/o Spondylolisthesisp Value
Total843738
w/ ODI improvement59 (70.2%)24 (64.9%)26 (68.4%)0.80
w/ MCID in ODI46 (54.8%)18 (48.6%)23 (60.5%)0.35
w/ VAS back pain improvement56 (66.7%)25 (67.6%)24 (63.2%)0.80
w/ MCID in VAS back pain42 (50.0%)21 (56.8%)17 (44.7%)0.35
w/ VAS buttock pain improvement55 (65.5%)26 (70.3%)24 (63.2%)0.62
w/ MCID in VAS buttock pain38 (45.2%)19 (51.4%)17 (44.7%)0.64
w/ VAS leg pain improvement62 (73.8%)30 (81.1%)24 (63.2%)0.12
w/ MCID in VAS leg pain44 (52.4%)19 (51.4%)20 (52.6%)0.91

Functional outcome, as assessed using Macnab's criteria,35 was excellent and good in 71.6% of the patients. A comparison of Macnab's results in patients with and without preoperative spondylolisthesis showed no significant difference (Table 6).

TABLE 6

Summary of Macnab results

ParameterAll PatientsPatients w/ SpondylolisthesisPatients w/o Spondylolisthesisp Value of Difference
No. of patients*743234
Outcome
 Excellent & good53 (71.6%)23 (71.9%)26 (76.5%)0.67
 Fair & poor21 (28.4%)9 (28.1%)8 (23.5%)

Data were only available in the listed number of patients.

Sixteen cases with dural injuries were not associated with CSF leakage and were intraoperatively repaired using DuraSeal. There were no intraoperative and/or inpatient complications. At a mean follow-up of 28 months, the reoperation rate at the same level (with or without surgery at a different level) for the entire study group was 12.9%. Among the 11 reoperated patients, 7 (8.2%) underwent repeat decompression without fusion at the same level (with or without surgery at a different level), whereas in 3 patients (3.5%) a fusion was performed at the same level. Comparison of total reoperation rates as well as reoperation with fusion in patients with and without preoperative spondylolisthesis showed no significant difference between the 2 groups (Table 7).

TABLE 7

Reoperation rate

ParameterAll PatientsPatients w/ SpondylolisthesisPatients w/o Spondylolisthesisp Value
No. of patients*853838
FU duration in mos0.81
 Mean ± SD28.5 ± 19.6326.7 ± 18.6027.7 ± 19.43
 Median (min;max)22.8 (6.2;74.3)20.7 (8.5;74.3)20.5 (6.2;74.3)
Total reop rate11 (12.9%)5 (13.2%)6 (15.8%)0.74
Isolated decompression of the same (w/ or w/o different) level(s)7 (8.2%)3 (7.8%)4 (10.5%)0.55
Fusion w/ or w/o decompression of same (w/ or w/o different) level(s)3 (3.5%)2 (5.2%)1 (2.6%)
Time btwn 1st & 2nd op in mos (min;max)16.9 (0.2;39.7)23.1 (6.5;38.1)10.5 (0.2;39.7)0.25

Data were available in the listed number of patients. The type of reoperation procedure performed was unknown in 1 patient.

Radiographic Results

Because postoperative imaging was not routinely done in this retrospective case series, only a limited number of patients (41) had available follow-up imaging. In patients with preoperative spondylolisthesis the mean slippage prior to surgery was 5.5 ± 3.04 mm, which increased to 6.4 ± 3.5 at the latest follow-up. This increase did not reach statistical significance. None of the imaged patients without preoperative spondylolisthesis demonstrated any slippage at the latest follow-up. Although we report the radiographic follow-up for the study group, we emphasize that radiographic outcome was not used to draw definite conclusions in this study. Instead, clinical outcome has been mainly used as evidence to draw possible conclusions.

Learning Curve

The first 55 patients were grouped into an early experience group and the second 55 cases into a late experience group. Operative time, estimated blood loss, dural injury rates, clinical outcome, Macnab's criteria, and reoperation rate were compared between these 2 groups. Comparisons showed no statistically significant difference in operative time, estimated blood loss, clinical outcome, and Macnab results in the 2 groups. Dural injuries occurred in 15 cases (27.3%) in the early experience group and in only 1 case (1.8%) in the late experience group (p < 0.0001). Moreover, 9 patients (23.7%) in the early experience group needed reoperation, whereas only 2 patients (4.2%) in the late experience group underwent a second operation (p = 0.008). The follow-up duration for clinical outcome and Macnab's criteria estimation was 45.7 ± 17.03 months in the early group and 15.5 ± 7.03 months in the late experience group. Similarly, the follow-up duration for reoperation was 44.5 ± 18.34 months in the early group and 15.5 ± 7.03 months in the late experience group. Nonetheless, the period between the first and second operation was found to be similar and not statistically different between the early and late experience groups. The median interval between the first surgery and the reoperation was 16.9 months (minimum 0.2; maximum 39.7).

Discussion

Background

Several less-invasive surgical techniques have been introduced for direct decompression of the lumbar spine. The introduction of a less-invasive retractor system dates back to 1991 when Caspar and colleagues proposed the use of less-invasive specular retractors for discectomies.7,17 Independently, Foley and Smith, in 1997, described the tubular microendoscopic discectomy in the lumbar spine, in which endoscopes were used through tubular retractors to perform a discectomy.18 They had worked on this approach in the laboratory since 1994, and the first clinical case was performed in early 1996 (K. Foley, personal communication, 2004). The METRx tubular retractor system was introduced in 2003 and permitted the use of the microscope, which allows excellent illumination and visualization of pathology. The use of tubular retractors to access spinal pathology has been associated with several biomechanical and clinical advantages: First, the approach through a minimally invasive retractor can spare attachments of paraspinal ligaments and muscles, which stabilize the spine. Minimizing injury to paraspinal ligaments and muscles allows for postoperative strengthening of back muscles and maintains stabilization of the motion segment. Second, the minimally invasive approach allows contralateral decompression of the spinal canal, lateral recess, and foramen without another incision while also sparing part of the lamina, spinous process, and interspinous ligaments.2,67

The anatomical description and clinical results of a unilateral laminotomy for contralateral decompression were first reported by Spetzger in 1997.55,56 Similar observations were also described by McCulloch in 1999.38,59 Adopting tubular retractors for this approach led to excellent decompression of the contralateral lateral recess and even foraminal disc herniations and contralateral foraminal stenosis.2,67 For example, we reported that synovial cysts can be resected safely and without compromising the facet joint by approaching them from the contralateral side and from “normal” dura and anatomy via tubular retractors.28 Biomechanical and laboratory results indicate that laminectomy via tubular retractors or bilateral laminotomies are associated with less destabilization than an open bilateral laminectomy.1,5,6,12,23,34,57 In their biomechanical study, Lee et al. demonstrated that bilateral laminotomy was associated with significantly less hypermobility and stiffness reduction than a full laminectomy, and they proposed that this could be attributed to preservation of the central posterior osteoligamentous structures in laminotomy.34 In summary, minimally invasive laminectomy via tubular and similar retractors achieves effective neural decompression with simultaneous preservation of the stability of motion segments. Figure 7 features a case of LSS in which was achieved complete decompression and a favorable outcome after treatment via this technique.

FIG. 7.
FIG. 7.

Images obtained in a patient with severe LSS at L4–5 treated using minimally invasive laminectomy through tubular retractors. Left: Preoperative axial T2-weighted MR image of the lumbar spine at the L4–5 level showing severe stenosis. Right: Postoperative MR image at the same level showing marked and effective decompression of the neural elements.

Minimally Invasive Decompression of LSS

Minimally invasive laminectomy through tubular retractors has been shown in previous studies to be a feasible and effective technique for treating LSS.8,30,39,41–45 In the present study we evaluated the outcome of this procedure in a larger group of patients with a longer duration of follow-up. The results were compared with those of other decompressive procedures published in the literature (Table 8). Our study produced results corroborating the findings in previous studies on the same technique. Parikh et al. and Pao et al. reported higher ODI and pain score improvements than we did in the present study;44,45 this may be explained to some extent by the shorter follow-up duration in those studies (9 and 15 months, respectively) compared with ours (28 months).

TABLE 8

Comparison of outcome among different decompressive procedures, as reported in the literature

Authors & YearType of StudyNo. of CasesFU DurationODI Improvement (out of 100)VAS Back Pain ImprovementVAS Leg Pain ImprovementSatisfactionTotal Reop RateReop w/ Fusion Rate
Open surgery
 Wilby et al., 2006Prospective cohort1002 yrsNA76% of pts improved87% of pts improvedNANANA
 Weinstein et al., 2007Randomized (& observational) cohort3242 yrs24.2NANANA11%2.6%
 Malmivaara et al., 2007Randomized clinical trial502 yrs12.8NANANA6%NA
 Weinstein et al., 2008Randomized (& observational) cohort3352 yrs20.5NANANA8%NA
 Yaşar et al., 2009Prospective case series1252 yrs16NANANANANA
 Weinstein et al., 2009Randomized (& observational) cohort2644 yrs23NANANA15%NA
 Weinstein et al., 2010Randomized (& observational) cohort924 yrs18.7NANANA13%NA
 Parker et al., 2011Prospective cohort542 yrs18.1NA4.15 pointsNANANA
 Slätis et al., 2011Randomized clinical trial472 yrs13.44.2 points3.7 pointsNA2.1%NA
Less-invasive open surgery (open decompression w/ less-extensive removal of pst stabilizing elements of spine)
 Thomé et al., 2005Randomized cohort40 (in each of 2 groups)1 yrNAResidual pain: 2.3 points (bilat laminot), 3.6 points (unilat laminot)NAOverall satisfaction: 97% (bilat laminot), 74% (unilat laminot)2.5% (bilat laminot), 5% (unilat laminot)NA
 Yamashita et al., 2006Prospective observational705 yrsNA2.5 points4.5 pointsNA4.2%NA
 Cavuşoğlu et al., 200710Prospective5022 mos17.14.7 points4.7 pointsNA0%0%
 Cavuşoğlu et al., 20079Prospective randomized cohort50 (in each of 2 groups)5.4 yrs17 (unilat laminot) 17 (unilat laminec)NANANA2% (unilat laminec), 0% (unilat laminot)0% (unilat laminec), 0% (unilat laminot)
 Costa et al., 2007Retrospective3745 yrsNA5 pointsNANA0%0%
 Orpen et al., 2010Prospective1003.5 yrs325 points6 pointsNANA4% required, (2% refused)
 Hong et al., 2011Retrospective cohort24 (unilat laminot), 29 (bilat laminot)4 yrs12.2 (unilat laminot), 15 (bilat laminot)2.3 points (unilat laminot), 4.1 points (bilat laminot)4.7 points (unilat laminot), 5.1 points (bilat laminot)NANA0% (unilat laminot), 3.4% (bilat laminot)
Other MI procedures (MS &/or FE)
 Ruetten et al., 2009Randomized clinical trial80 (MS), 81 (FE)2 yrs55 (MS), 56 (FE)−1.1 points (MS), 0.4 points (FE)7.2 points (MS), 6.7 points (FE)NA6.2%NA
 Castro-Menéndez et al., 2009Prospective50*4 yrs30.20.84 points6.02 points72% excellent to good10%4%
 Komp et al., 2011Prospective722 yrs540.6 points6.5 pointsNA9.5%NA
MI tubular retractor laminectomy
 Palmer et al., 200242Prospective173 mosNANANANANANA
 Parikh et al., 2008Prospective & retrospective609 mos29.64.53 points5.43 pointsNA3.4%NA
 Pao et al., 2009Prospective5015 mos47.6NANANANANA
 Kim et al., 2012Retrospective observational cohort5742 mosNANANANA15%7%
 Müslüman et al., 2012Prospective observational8424 mos161.63 pointsNA80% excellent to good1.2%0%
 Palmer et al., 2012Prospective5427 mosNA3 points6 points80% overall satisfactionNA2%
Present caseRetrospective8428 mos16 (70% of pts improved)2.75 points (67% of pts improved)3.0 points (74% of pts improved)72% excellent to good12.9%3.5%
FE = full endoscopy; laminec = laminectomy; laminot = laminotomy; MI = minimally invasive; MS = microsurgery; NA = not applicable; pst = posterior; pts = patients.

All patients underwent microendoscopic decompression.

All patients underwent full endoscopic decompression.

There is wide variability in the clinical outcome of different decompressive procedures in the literature, which makes it difficult to draw definite conclusions (Table 8). Nonetheless, comparisons between the minimally invasive laminectomy through tubular retractors and open laminectomy suggest that the former can have clinical outcomes comparable to those for the open procedures, while also having the benefits of minimally invasive surgery.36,46,54,60–64,66 Moreover, previous studies reporting reoperation rates for minimally invasive laminectomy suggest that there is an overall lower reoperation rate associated with this technique compared with that for open laminectomy.30,36,39,45,60–63

Lumbar Spinal Stenosis and Spondylolisthesis

Little research has been done to compare the outcome of different decompressive procedures in patients with and without preoperative spondylolisthesis. Clinical results of the current investigation showed no significant difference in outcome for patients with and without preoperative spondylolisthesis. However, it must be remembered that our cohort included only patients with “stable” spondylolisthesis, without movement on flexion/extension films, and with neurogenic claudication in the absence of mechanical back pain. The radiographic results corroborated the clinical outcomes. They showed no significant progression of the slippage after surgery in patients with preoperative spondylolisthesis. Similarly, in patients without preoperative spondylolisthesis, no slippage developed after surgery. However, we reemphasize that although we have reported on the radiographic presence and extent of slippage in patients with available follow-up imaging, no direct conclusions have been made based on the radiographic results per se given the limited availability of these studies. The radiographic findings have been reported to provide a more comprehensive picture of the study group and have been discussed and interpreted with caution. On the contrary, in the current study we have mainly focused on clinical outcome and have used it to provide possible evidence and draw careful conclusions. The clinical outcome included pain and functional outcome scores, satisfaction level, as well as the reoperation rate. Palmer et al., who studied the feasibility of minimally invasive laminectomy via tubular retractors in 2002, also reported no radiographic progression of the slippage at 3 months' follow-up in 8 patients with preoperative slippage.42,43 Given the small sample size and the short follow-up, conclusions for that study were limited. Findings in the current study are consistent with those of Pao et al. and Müslüman et al., who reported no progression of spondylolisthesis following a microsurgical unilateral approach for tubular bilateral decompression after 2 years' follow-up.39,44 The reoperation rates in our study compare favorably with those of Kim et al., who reported a 15% total reoperation rate and 7.1% reoperation rate with fusion following bilateral tubular decompressive surgery via a unilateral approach using tubular retractors.30 Those authors concluded that decompression without fusion is more cost-effective than instrumented fusion for a selected group of patients whom they defined as those with leg-dominant pain and stable Grade I spondylolisthesis.

A small number of studies have looked at the outcome in patients with preoperative spondylolisthesis treated using other minimally invasive decompressive techniques such as the full-endoscopic interlaminar approach. These studies all reported very low reoperation rates and/or minimal progressive spondylolisthesis postoperatively.

Standard open laminectomy, with or without fusion, is currently the most common procedure to treat LSS. However, conventional open laminectomy in the presence of preexisting spondylolisthesis can be associated with a high rate of subsequent instability requiring delayed fusion surgery. Radiographic results in Iguchi et al.'s study demonstrated the development of new spondylolisthesis in 6% of the patients without preoperative slippage at 10 years' follow-up, and the average progression of slippage was 2.3 mm.26 In Epstein's study, progression from Grade I to Grade II spondylolisthesis at the 2-year follow-up was seen in 31.4% of cases.13 In a well-designed prospective study on open laminectomy in 58 patents with preoperative slippage, Blumenthal et al. found that the reoperation rate with fusion was 37.5% at 3 years' follow-up.4 Current surgical guidelines state that the “best medical evidence available in the literature confirms the utility of fusion for improving patient outcomes following decompression for stenosis associated with spondylolisthesis.”51

Despite all the variations in outcome among the different decompressive procedures, minimally invasive laminectomy through tubular retractors seems to result in clinical outcome and reoperation rates comparable to those for other decompressive procedures.8–11,25,32,36,40,46,53,54,58,60–66 However, the radiographic results suggest that this technique is associated with a lower instability rate than the full-open procedures, probably because of the preservation of posterior elements of the lumbar spine. Results from a cost-utility study showed that tubular retractor–guided decompression without fusion in this setting is more cost-effective than conventional decompression and fusion (Table 9).30

TABLE 9

Comparison of outcome among different types of decompressive procedures in patients with Grade I spondylolisthesis

Authors & YearType of StudyNo. of Pts w/ GIS*FU Duration (yrs)ODI Improvement (out of 100)Points Improvement on VAS BackPoints Improvement on VAS LegSatisfaction% Pts w/ Spondylolisthesis Among All PtsPostoperative Progression of SpondylolisthesisTotal Reop RateReop w/ Fusion Rate
Open laminectomy
 Iguchi et al., 2000Retrospective study10/15110JOA improvement: 55.8%NANANA6%6% new spondylolisthesis; average progression of slippage: 2.3 mmNANA
 Epstein, 2004Not specified35 pts w/ GIS, 45 w/o any spondylolisthesis2NANANA58% to 63% excellent to good surgeon-based outcome43%31.4% of pts w/ GIS progressed to GIIS14.2% in pts w/ GIS, 6.6% in pts w/o any spondylolisthesis8.5% in pts w/ GIS, 4.4% in pts w/o any spondylolisthesis
 Weinstein et al., 2009Randomized (& observational) cohort264423NANANA100%NA15%NA
 Blumenthal et al., 2013Prospective study403.615NANANA100%NA37.5%NA
MI laminectomy
 Podichetty et al., 2006 (microdecompression & microendoscopic decompression)Retrospective case series69/2200.25NANANANA31%NANA1.4%
 Iwatsuki et al., 2007 (microscopic decompression using Caspar retractor)Not specified7/472NANANANA15%No progressionNA0%
MI tubular retractor laminectomy
 Palmer et al., 200243Retrospective case series8/170.25NANANANA47%No progressionNANA
 Pao et al., 2009Prospective study12/601.2547.6NANANA20%No progressionNANA
 Müslüman et al., 2012Prospective observational study25/842161.63NA80% excellent to good30%No progression1.2%0%
 Kim et al., 2012Retrospective observational cohort573.5NANANANA100%NA15%7.1%
 Present caseRetrospective study51 pts w/ GIS, 46 w/o any spondylolisthesis2.416 (70% of pts improved)2.75 (67% of pts improved)3.0 (74% of pts improved)72% excellent to good52%No progression13.2% in pts w/ GIS, 15.8% in pts w/o any spondylolisthesis5.2% in pts w/ GIS, 2.6% in pts w/o any spondylolisthesis
GIS = Grade I spondylolisthesis; JOA = Japanese Orthopaedic Association.

Listed alone, per the total number of patients in the study, or along with the number of patients without any spondylolisthesis.

We divided the patients into early and late groups, and no significant differences in operative time, estimated blood loss, and clinical outcome were observed between the two. In contrast, the CSF leakage rate and reoperation rates were higher in the early group. These differences are probably attributable to the learning curve associated with this technique.

Study Limitations

Finally, several limitations of the current study should be noted. It is a retrospective case series based on a prospectively collected database. The most important limitation lies in the fact that it was not designed to compare the outcome of different decompressive procedures. Thus, we attempted to compare the results of this study with those in the published literature. The wide variety of outcome measures used in these studies complicated the interpretation. In addition, because a number of between-group analyses may have been underpowered given the available sample size, the lack of observed statistical differences between the groups should be interpreted with caution. The current study provides preliminary estimates of differences between groups that can be used to power larger studies. The p values for between-group comparisons in the range of 0.06–0.20 should be considered as potential evidence for underpowered evaluations, and readers may wish to consider these differences as suggestive of nonsignificant trends. Another limitation of the study lies in the fact that comparison between preoperative and follow-up imaging was possible in only a small group of patients. For a small number of patients, neither pre- nor postoperative imaging was available in the hospital database; therefore, the presence or absence of spondylolisthesis was not determined in this group. Consequently, the small sample size for the radiographic comparison necessitates interpretation with caution.

Conclusions

Minimally invasive laminectomy through retractors is an effective procedure to treat LSS and shows similar results in patients with and without preoperative spondylolisthesis with low reoperation rates. This procedure is associated with a lower postoperative instability rate than the conventional open decompressive procedures but has a comparable clinical outcome. Moreover, it has the benefits of minimally invasive surgery such as less blood loss and shorter hospital stay. In light of this and other studies demonstrating the potential benefit of tubular and other minimally invasive retractors in decompression surgery, the need for routine fusion surgery in LSS patients with preexisting spondylolisthesis and multilevel LSS should be critically reevaluated.

Acknowledgments

We acknowledge Dr. Paul Christos for helping in the statistical analysis of the current study. We also thank AOSpine and Baxter for supporting Marjan Alimi's fellowship.

Author ContributionsConception and design: Härtl, Alimi, Hofstetter, Pyo. Acquisition of data: Alimi, Paulo. Analysis and interpretation of data: Härtl, Alimi, Hofstetter. Drafting the article: Alimi. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Statistical analysis: Alimi, Hofstetter. Study supervision: Härtl.
Supplemental InformationPrevious PresentationPortions of this work were presented in abstract/poster form at the 29th Annual Meeting of the AANS/CNS Section on Disorders of the Spine and Peripheral Nerves held in Phoenix, Arizona, on March 6–9, 2013.

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Article Information

Contributor Notes

Correspondence Roger Härtl, MD, Department of Neurological Surgery, Weill Cornell Brain and Spine Institute, 525 E. 68th St., Box 99, New York, NY 10065. email: roh9005@med.cornell.edu.ACCOMPANYING EDITORIAL DOI: 10.3171/2014.8.SPINE14687.INCLUDE WHEN CITING Published online January 30, 2015; DOI: 10.3171/2014.11.SPINE13597.DISCLOSURE The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. Dr. Härtl is a consultant for DePuy-Synthes, Lanx, Spine Wave, Brainlab.

© AANS, except where prohibited by US copyright law.

Headings
Figures
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    An 18- or 19-mm tubular retractor is placed over a series of tubular dilators for retraction, and under the microscope, the inferior edge of the lamina and the inferior edge and base of the spinous process are exposed. Illustration by Thomas Graves. Copyright Roger Härtl. Published with permission.

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    The decompression is performed starting with an ipsilateral partial laminectomy using a 3-mm curved matchstick drill bit and bayonetshaped 2- and 3-mm Kerrison punches. Illustration by Thomas Graves. Copyright Roger Härtl. Published with permission.

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    The operating table is tilted away from the surgeon, and the tubular retractor is angled medially to achieve appropriate visualization of contralateral sublaminar structures. Next, the spinous process and the contralateral lamina are undercut using the drill and rongeurs. The ligamentum flavum is completely exposed cranially until its insertion under the lamina. Illustration by Thomas Graves. Copyright Roger Härtl. Published with permission.

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    A nerve hook is inserted in the midline where the two leaves of the ligamentum flavum meet, an area that is typically identified by the presence of epidural fat. Illustration by Thomas Graves. Copyright Roger Härtl. Published with permission.

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    The ligamentum flavum is then carefully removed using Kerrison rongeurs. Illustration by Thomas Graves. Copyright Roger Härtl. Published with permission.

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    Dural exposure and decompression after complete removal of the ligamentum flavum. The contralateral approach allows visualization and decompression, if needed, of the contralateral exiting and traversing nerve root. Illustration by Thomas Graves. Copyright Roger Härtl. Published with permission.

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    Images obtained in a patient with severe LSS at L4–5 treated using minimally invasive laminectomy through tubular retractors. Left: Preoperative axial T2-weighted MR image of the lumbar spine at the L4–5 level showing severe stenosis. Right: Postoperative MR image at the same level showing marked and effective decompression of the neural elements.

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