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Neurospine > Volume 21(2); 2024 > Article
Pao: Preliminary Clinical and Radiological Outcomes of the “No-Punch” Decompression Techniques for Unilateral Biportal Endoscopic Spine Surgery

Abstract

Objective

To avoid the most offending surgical instrument for dural tears, we develop a “no-punch” decompression technique for unilateral biportal endoscopic (UBE) spine surgery.

Methods

This retrospective study enrolled 68 consecutive patients with degenerative lumbar spinal stenosis segments. The treatment results were evaluated using the visual analogue scale (VAS) for low back and leg pain, the Japanese Orthopaedic Association (JOA) scores, and the Oswestry Disability Index (ODI). Radiological outcomes were evaluated using the preoperative and postoperative magnetic resonance imaging.

Results

This study included 36 male and 32 female patients who received 109 segments of decompression, with an average age of 68.7 (37–90 years). The average operation time was 52.2 minutes. The average hospital stay was 3.1 days. There were no dural tears but 3 minor surgical complications, all treated conservatively. The VAS for low back and leg pain improved from 4.6 and 7.0 to 0.8 and 1.2. The JOA score improved from 16.2 to 26.8, with an improvement rate of 82.0%. The ODI improved from 50.1 to 18.7. All these improvements were statistically significant. The cross-sectional dural area improved from 61.1 to 151.3 mm2, with an average increase of 90.2 mm2 and 205.3%. 87.1% of the ipsilateral facet joints and 84.7% of the contralateral facet joints were preserved. In 61% of the decompressed segments, the ipsilateral facet joints were preserved better than the contralateral facet joints.

Conclusion

The UBE “no-punch” decompression technique effectively avoids the dural tears. It provides effective neural decompression, excellent facet joint preservation, and good treatment outcomes.

INTRODUCTION

Minimally invasiveness is a trend in every surgical field. Minimally invasive spine surgery has rapidly evolved, and endoscopic spine surgery has gained worldwide popularity because of the rapid advancements in endoscopic techniques and surgical instruments. In recent years, the unilateral biportal endoscopic (UBE) technique has drawn much attention from spine surgeons. This minimally invasive technique is a revolutionary endoscopic technique performed through 2 independent portals with continuous irrigation of normal saline. The normal saline provides hydrostatic pressure to suppress bleeding, carrying away bone debris and oozing. Combined with a high-resolution endoscopic system, UBE delivers a clear, bright, and magnified surgical field, enabling surgeons to perform delicate surgical procedures without excessive soft tissue damage. UBE has been applied to address a variety of spinal pathologies, such as discectomy for lumbar disc herniation, laminotomy for degenerative lumbar spinal stenosis (DLSS), lumbar interbody fusion for disc degeneration or spondylolisthesis, and cervical foramen stenosis, all of which demonstrated good clinical efficacy and satisfactory outcomes [1-7].
Endoscopic spine surgery is technically demanding, with a steep learning curve. A high incidence of complications usually occurs in the early learning curve [8-10]. The UBE technique cannot be exempted from this. The most common complication is incidental dural tear, followed by epidural hematoma and incomplete decompression [11]. Most studies claim that dural tears in endoscopic spine surgeries are usually small and can be managed conservatively with few sequels [12,13]. However, severe neurological sequels that impair the treatment outcomes do occur. In contrast to traditional open surgeries, dural tears are difficult to repair under the endoscope. As practice does not guarantee perfect results, we need a thorough understanding of the injury mechanisms of dural tears and new surgical techniques to prevent their occurrence.
The Kerrison punch was designed by an English physician, Robert Maters Kerrison, in the eighteenth century. It has been used as the most crucial surgical instrument in modern spine surgery for the decompression of neural elements. However, in our experience of more than 4,000 cases of minimally invasive spine surgeries, we realized that the Kerrison punch was the most offending surgical instrument to cause dural tears or nerve root injuries. Therefore, we developed the “no-punch” technique for UBE surgeries, trying not to use the Kerrison punch while performing the decompressive procedures.
This study aims to introduce the novel UBE “no-punch” decompression technique and review its clinical and radiological outcomes for the treatment of DLSS.

MATERIALS AND METHODS

1. Patient Selection

The study was conducted after obtaining proof from the Research Ethics Review Committee of Far Eastern Memorial Hospital (No. 113052-E). Sixty-eight patients who received UBE “no-punch” decompression surgery for DLSS from March 2022 to June 2023 were included in this retrospective study.
The indications for UBE spine surgeries are axial back pain, radicular leg pain, single or multiple lumbar radiculopathies, and neurogenic intermittent claudication due to DLSS. All patients have at least 3 months of conservative treatment before surgical intervention. All patients had plain x-rays of anteroposterior, lateral, and dynamic lateral views before and 6 months after the surgery. Magnetic resonance imaging (MRI) was arranged before and 6 months after the surgery. All the diagnoses must have radiological evidence corresponding to the patient’s clinical presentation. The author performed all the surgeries in a single institute. We excluded patients who had lumbar disc herniation, segmental instability with more than 4-mm translation on the dynamic lateral x-rays, more than grade II spondylolisthesis, scoliosis of more than 20°, infection, and a history of prior lumbar spine surgeries.

2. Evaluation of Clinical Data and Outcomes

We retrieved demographic data, clinical data, surgical complications, and treatment outcomes from chart reviews. We also reviewed all the operation notes and video records to examine the occurrence, mechanism, offending surgical instrument, and management of surgical complications. All patients had at least 6 months of follow-up after the surgery. The treatment outcomes were evaluated using the Japanese Orthopaedic Association (JOA) score and the Oswestry Disability Index (ODI) before surgery and 1, 3, and 6 months after the surgery [14,15].
We used the Schizas grading system to evaluate the stenosis severity. The Schizas system classifies stenosis severity into 4 grades using the axial T2-weighted MRI images. Grade A is no or minor stenosis with an oval spinal canal and clear cerebral spinal fluid space. Grade D is the most severe, with a collapsed spinal canal and no cerebral spinal fluid space [16]. When the postoperative MRI was available, we measured the crosse-sectional dural area and the width of ipsilateral and contralateral facet joints using the ImageJ software (https://imagej.net/) to evaluate the decompression efficacy and facet joint preservation [1].
The results of patient-reported outcome measures were analyzed using Wilcoxon signed-rank test. The results of radiological measurements were analyzed using the paired t-test. A p-value of < 0.05 was considered statistically significant.

3. Surgical Techniques

We will use the UBE unilateral laminotomy for bilateral decompression (ULBD) for DLSS at L4–5 from the left-side approach as an example to describe the “no-punch” decompression technique in detail.
The surgery is performed under endotracheal general anesthesia with the patient placed in the prone position on a radiolucent surgical table. The surgical field is disinfected in the usual manner. Because the UBE surgery is performed with continuous saline irrigation, a water-tight draping with a sound drainage system is essential to prevent soaking and resultant hypothermia of the patient.
The initial target area is the spinolaminar junction, which is the junction of the lower margins of the spinous process and the lamina of L4 on the left side. The skin incisions are localized at the intersection of the medial pedicle line and the lower pedicle lines of the L4 and L5 pedicles on the left side. For a righthanded surgeon, the cranial skin incision (about 6 mm long) will be the entry for the endoscope, and the caudal skin incision (about 10 mm long) will be the entry for the surgical instruments (Fig. 1A).
We prefer transverse skin incisions for better cosmesis. After marking the skin landmarks under the fluoroscope, we incise the skin and deep fascia using a No. 11 scalpel. We insert the endoscopic sheath and its trocar into the endoscopic portal and a blunt dilator into the working portal. These 2 instruments meet at the spinolaminar junction to establish the triangulation, confirmed using the fluoroscope (Fig. 1B). The soft tissues at the spinolaminar junction are gently dissected. Then, the trocar and blunt dilator are replaced by the endoscope (4 mm× 30°, ConMed, Largo, FL, USA) and the radiofrequency wand (ArthroCare, Austin, TX, USA) with the inflow of normal saline. We use the radiofrequency wand to ablate the soft tissue and coagulate the bleeders in the muscles to create a clear endoscopic surgical field. The saline bags are hung about 30 cm higher than the level of the surgical site. The circulating nurse monitors and adjusts the saline bags’ height to maintain adequate hydrostatic pressure. A semitubular tube at the working portal is very helpful in maintaining a good saline outflow (Fig. 1C). A good control of saline inflow/outflow is mandatory for hemostasis and a clear surgical field, especially when using the high-speed drill.
We prefer using the high-speed drill with a 4-mm coarse diamond ball tip (Primado II, NSK, Tokyo, Japan) as the primary instrument for removing bone. We design a set of osteotomes with 3 different curved angles: 0°, 10°, and 20° for the “no-punch” decompression technique. The osteotomes are 4 mm wide and 2 mm thick with a symmetric tapered shape to the tip (Fig. 1D). The surgical procedure will be explained step-by-step as follows:
(1) Use the high-speed drill to start the laminotomy from the spinolaminar junction at L4 (Fig. 2). The laminotomy is widened medially and cranially until the underlying cranial end of the ligamentum flavum is free from its attachment and the epidural fat is exposed (Fig. 3).
(2) Widen the laminotomy laterally and move the drill caudally. The joint capsule covering the facet joint should be preserved as much as possible. Then, use the blunt elevator to dissect and remove the superficial part of ligamentum flavum away from the cranial margin of the L5 lamina (Fig. 4). Use the drill to trim out the cranial border of the L5 lamina and the base of the L5 spinous process until the caudal end of the deep part of the ligamentum lamina is free from its attachment (Fig. 5).
(3) Advance the drill contralaterally along the upper margin of the L5 lamina. If possible, remove the superficial part of the contralateral ligamentum flavum. This will provide more working space for contralateral decompression.
(4) Identify the inferior margin of the spinous process. Use the blunt elevator to separate the ligamentum flavum from the spinous process and contralateral lamina of L4 (Fig. 6). Advance the drill into the space between the contralateral lamina and ligamentum flavum to perform sublaminar decompression. The drill can be advanced very deep to the contralateral lateral recess if the ligamentum flavum remains, which protects the underlying neural tissues (Fig. 7). Keep the ligamentum flavum intact until the end of bony decompression. The fluted cutting drill is not recommended in this step because it may destroy the ligamentum flavum and lead to catastrophic neural injury. Then, the drilling work is done.
(5) Use the curved osteotome to decompress the ipsilateral lateral recess. Find the medial border of the L5 superior articular process (SAP) and the L4 inferior articular process (IAP). The curved osteotome is used to undercut the fact joint from L5 SAP to L4 IAP (Fig. 8). Then, the bony fragments are separated using twisting maneuvers. Use the angled curette to separate the bony fragments further and detach the ipsilateral ligamentum flavum from underneath the L4 IAP and lamina (Fig. 9A). Then, the micropituitary rongeur is used to grasp the bony fragments and take them out along with the ipsilateral ligamentum flavum as a whole piece.
(6) Use the curved osteotome to chop the cranial margin of the contralateral L5 lamina. Follow the lamina to identify the contralateral L5 SAP. Use the osteotomes to undercut the contralateral L5 SAP (Fig. 9B). Use the elevator or curette to separate the bony fragments and the contralateral ligamentum flavum from its attachment. Elevate the ligamentum flavum and release the underlying epidural adhesion. Then, use the micropituitary rongeur to grasp the ligamentum flavum firmly and take it out along with the bony fragments as a whole piece (Fig. 10).
(7) Check for residual stenosis. Use the osteotomes and curettes to remove residual osteophytes and ligamentum flavum. Use the radiofrequency wand to coagulate the bleeders. Use bone wax to seal all the cutting surfaces of the bone. Stop the saline irrigation temporarily to check for any occult bleeding. A negative suction drain is indicated when the hemostasis is in doubt.

RESULTS

There were 68 patients receiving 109 segments of UBE “no-punch” decompression for DLSS, including 36 male and 32 female patients, with an average age of 68.7± 9.9 (37–90 years). All the patients had at least 6 months of follow-up after the surgery.
Of the 68 patients, 54 patients had pure DLSS (79.4%), 9 patients also had low-grade spondylolisthesis (13.2%), and 5 patients also had degenerative scoliosis of less than 20° (7.4%). One-segment decompression was performed in 38 patients (55.9%), 2-segment in 19 patients (27.9%), and 3-segment in 11 patients (16.2%). The decompression was most frequently performed at L4–5 (56 patients, 51.4%), followed by L3–4 (31 patients, 28.4%) and L2–3 (14 patients, 12.8%). Schizas grade D stenosis was observed in 62 segments (56.9%), grade C in 23 segments (21.1%), and grade B in 24 segments (22.0%). The operation time was 52.2± 20.3 minutes. We could not precisely measure the intraoperative blood loss because the normal saline diluted all the bleeding. No patients required blood transfusion. Drain tubes were used in 12 patients (17.6%). The anesthesiologist recommended overnight intensive care in the surgical intensive care unit for 4 patients (5.9%). The average hospital stay was 3.1± 1.0 days (2–9 days). We observed 3 surgical complications: 1 root injury by the radiofrequency wand, 1 incomplete decompression, and 1 transient radicular leg pain. There was no dural tear in the 68 patients. All the complications were managed conservatively with no sequel, and no patient required secondary surgery. There was no progression of spondylolisthesis or scoliosis in the follow-up period. The data are summarized in Table 1.
The preoperative average VAS scores for back pain and leg pain were 4.6 ± 3.2 and 7.0 ± 2.0, which improved to 0.8 ± 1.2 and 1.2± 1.5 after the surgery. The JOA scores improved from 16.2 ± 6.1 to 26.8 ± 2.4, with an average improvement rate of 82.0%± 19.0%. The ODI improved from 50.1± 18.7 to 12.6± 14.3. All these improvements were statistically significant, with p-values < 0.001. The results are summarized in Table 2.
Postoperative MRI was available in 49 patients with 83 segments of decompression. The average cross-sectional dural area (CSDA) significantly increased from 61.1± 26.4 mm2 to 151.3± 39.5 mm2 after the surgery (p< 0.001), with an average increase of 90.2± 35.2 mm2, corresponding to 205.3%± 206.1% increase. The ipsilateral facet joints were better preserved than the contralateral facet joints (87.1%± 12.1% vs. 84.7%± 11.9%). However, the difference did not reach a statistically significant level. Of all the decompression segments, ipsilateral facet joints were better preserved than the contralateral facet joints in 61%. The data are summarized in Table 3.

DISCUSSION

Like in other surgical fields, minimal invasiveness is undoubtedly the trend in spine surgery. Minimally invasive spine surgery is usually done through a tubular retractor system with a microscope. Recently, most of these minimally invasive procedures can be accomplished using endoscopic techniques with compatible treatment results [17-20]. The UBE technique has proved revolutionary and gained worldwide popularity among these endoscopic techniques, starting in South Korea [1-6].
The learning curve is always a critical issue for minimally invasive surgery. The learning curve is even steeper for the endoscopic technique [8-10,21,22]. In the early learning curve, the operation time is prolonged, with a higher rate of surgical complications, secondary surgery, and prolonged hospitalization [13]. Most studies claimed that complications in endoscopic spine surgery can be managed conservatively with no severe sequels. However, potential sequels of these complications did occur and should not be taken for granted [12,13].
The most common complication in UBE surgery is dural tears, with an estimated incidence of 4.1% to 4.5% [11,23]. UBE surgery is performed under continuous irrigation of normal saline, and the neural tissues are subject to potential injury from the hydrostatic pressure. When a dural tear occurs, normal saline or air bubbles may enter the cerebral spinal fluid space to cause direct injury to the brain [24]. Small tears can be repaired using the fibrin sealant or the patch compression technique. A more than 10-mm tear should be repaired using nonpenetrating hemostatic clips or direct sutures [12,13,25,26]. However, direct repair under the endoscope is highly technically demanding and can only be feasible in an expert’s hands [27].
There are several injury mechanisms for dural tears in UBE surgery. The hydrostatic pressure of normal saline provides a clear surgical field by suppressing bleeding from muscles and epidural vessels. When saline flows into the epidural space, the dura is also suppressed bilaterally and forms a central fold just beneath the central slit of the ligamentum flavum [13]. The surgeon tends to insert the Kerrison punch into the central slit to bite the ligamentum flavum. This movement is generally safe if fatty tissue between the dura and ligamentum flavum exists. However, epidural ligaments may tether the dura, or the fatty tissue may be replaced by epidural adhesion in case of severe stenosis [26]. Using the Kerrison punch may cause a dural tear in this way. Similarly, nerve root injury will occur if we insert the Kerrison punch blindly into the lateral recesses without clearing the epidural space or releasing the epidural adhesion.
Our “no-punch” decompression technique effectively reduces the risk of dural tear and nerve root injury by avoiding the above-mentioned injury mechanisms. A retrospective study conducted by Kim et al. [13] reported that 56% of the dura tears occurred while using a Kerrison punch for laminotomy. We have the same experience that the Kerrison punch is the most offending instrument for dural tears. Therefore, we develop a set of osteotomes with varying curves for laminotomy. The curved osteotomes are designed to undercut the facet joint from its medial aspect. Instead of using the Kerrison punch to piecemeal resect the ligamentum flavum, we detach the ligamentum flavum as a whole piece from its peripheral attachment along with the laminotomy chips (Fig. 10). Under the endoscope, we can check and release the epidural adhesion before taking out the ligamentum flavum. Following these principles, we have no neural injury except one nerve root injury by the radiofrequency wand.
Effective decompression is the primary concern in the surgical treatment of DLSS. Our UBE “no-punch” decompression technique can achieve good decompression with a significant increase in CSDA after the surgery. The postoperative CSDA increased to 151.3 mm2 and 205.3% compared to the preoperative CSDA. The patient-report treatment outcomes evaluated by VAS for back and leg pain, JOA scores, and ODI all show significant improvement and excellent results at the final follow-up.
ULBD is the most frequently adopted concept in minimally invasive spine surgery [28-30]. It can be accomplished using the traditional open technique, minimal access technique with the tubular retractor system, minimally invasive technique with the microendoscopic system, or endoscopic technique with the uniportal or biportal endoscopic system [31-35]. No matter what technique is adopted, medial facetectomy is required to decompress the lateral recess and release the nerve roots. However, excessive facet joint destruction may result in iatrogenic segmental instability, which may necessitate a secondary spinal fusion surgery [36,37]. Our “no-punch” decompression technique preserves more than 80% of the facet joints, either ipsilateral or contralateral. This result suggests that this novel decompression technique not only provides effective decompression but also preserves the facet joints well.
Based on the cadaver study for ULBD, the decompression for the ipsilateral lateral recess should be as effective as the contralateral one [37,38]. However, because of limited visualization and technically demanding access for the contralateral side, the ipsilateral side is usually better decompressed but more destructed [39,40]. Curved instruments, such as punch and high-speed bur, are also recommended to minimize the invasion and better decompression for the ipsilateral lateral recess [15]. Most studies suggest the ULBD approach from the dominant symptoms side to ensure adequate decompression. However, in our study, the “no-punch” decompression provides comparably good preservation for either ipsilateral or contralateral facet joints. In 61% of the decompression segments, the ipsilateral facet joints were preserved better than the contralateral facet joints. Therefore, the surgeon can choose an approach from the patient’s right or left side, depending on his preference or the patient’s specific anatomical features.
There are some limitations in this study. This study is a retrospective case series study, and the patient selection is subjected to a bias based on the surgeon’s preference. The surgeries are performed by an experienced surgeon with a particular interest in minimally invasive and endoscopic spine surgery. The treatment results cannot be extrapolated to surgeons with less experience or novice surgeons. The specialized curved osteotomes are designed by and custom-made for the author and are currently only available in Taiwan and his institute. However, surgeons inspired by the “no-punch” concept can request the local manufacturer to produce the osteotomes or chisels according to their preferences and design ideas. The cohort in our study is small, with a limited follow-up period. This study aims to propose a new surgical technique and use the preliminary treatment results to evaluate its potential advantages. Comparative studies with longer-term follow-up are necessary to evaluate the benefits of the UBE “no-punch” decompression technique.

CONCLUSION

Our study introduces a novel decompression technique for UBE surgery by not using the Kerrison punch. The “no-punch” decompression technique provides good treatment results, adequate neural decompression, excellent facet joint preservation, and a low complication rate.

NOTES

Conflict of Interest

The author has nothing to disclose.

Funding/Support

The Far Eastern Memorial Hospital supported the study with grant No. FEMH-2024 C-046.

Author Contribution

Single author.

ACKNOWLEDGEMENTS

Special thanks to Ji Woon William Chun for his help in manufacturing the custom-made Pao’s osteotomes.

Fig. 1.
(A) The fluoroscopic image illustrates the skin markings for the cranial endoscope portal and the caudal instrument portal for the left-side approach. (B) The fluoroscopic image shows the triangulation at the spinolaminar junction and the use of the semitubular tube. (C) The semitubular tube (dissembled) used to maintain saline outflow. (D) The Pao’s osteotomes with 3 different curve angles.
ns-2448376-188f1.jpg
Fig. 2.
The illustration and endoscopic photo show the initial target for drilling.
ns-2448376-188f2.jpg
Fig. 3.
The illustration and endoscopic photo show the cranial end of the ligamentum flavum and the exposure of the underlying fatty tissue (asterisk).
ns-2448376-188f3.jpg
Fig. 4.
The illustration and endoscopic photo show the elevator being used to detach the superficial ligamentum flavum from the cranial margin of the lower lamina.
ns-2448376-188f4.jpg
Fig. 5.
The illustration and endoscopic photo show the ligamentum flavum’s caudal end and the epidural space’s exposure (asterisk).
ns-2448376-188f5.jpg
Fig. 6.
The illustration and endoscopic photo show the lower corner of the spinous process (asterisk) and the elevator used to detach the ligamentum flavum.
ns-2448376-188f6.jpg
Fig. 7.
The illustration, endoscopic photo, and fluoroscopic image show the safe advancement of the bur between the lamina and the ligamentum flavum to decompress the contralateral lateral recess.
ns-2448376-188f7.jpg
Fig. 8.
The illustration and endoscopic photo show the curved osteotome is used to undercut the ipsilateral superior articular process (asterisk) and inferior articular process (double asterisks).
ns-2448376-188f8.jpg
Fig. 9.
The illustrations and endoscopic photos show how to use the curved osteotomes to undercut the ipsilateral (A) and contralateral (B) facet joints to minimize neural injury.
ns-2448376-188f9.jpg
Fig. 10.
The endoscopic photos show the over-the-top views after drilling (A), after removing the ipsilateral half of ligamentum flavum (B), and after removing all the ligamentum flavum and the end of the decompression (C). (D) The photo shows en-bloc removal of the ligamentum flavum with laminotomy chips on its margin (white arrowheads).
ns-2448376-188f10.jpg
Table 1.
Clinical data (n=68)
Variable Value
Sex
 Male 36 (52.9)
 Female 32 (47.1)
Age (yr) 68.7 ± 9.9 (37–90)
Diagnosis
 DLSS 54 (79.4)
 Spondylolisthesis 9 (13.2)
 Scoliosis 5 (7.4)
Segments of decompression (n = 109)
 1-Segment 38 (55.9)
 2-Segment 19 (27.9)
 3-Segment 11 (16.2)
Level of decompression (n = 109)
 L1–2 1 (0.9)
 L2–3 14 (12.8)
 L3–4 31 (28.4)
 L4–5 56 (51.4)
 L5–S 7 (6.4)
Schizas grade of stenosis (n = 109)
 A 0 (0)
 B 24 (22.0)
 C 23 (21.1)
 D 62 (56.9)
Operation time (min) 52.2 ± 20.3 (40–90)
Drain tube usage (n) 12 (17.6)
SICU stay (n) 4 (5.9)
Hospital stay (day) 3.1 ± 1.0 (2–9)
Complications (n = 68)
 Root injury 1 (1.5)
 Incomplete decompression 1 (1.5)
 Transient radicular pain 1 (1.5)

Values are presented as number (%) or mean±standard deviation (range).

DLSS, degenerative lumbar spinal stenosis; SICU, surgical intensive care unit.

Table 2.
Patient-reported treatment outcome
Variable Mean ± SD Median (range) p-value
VAS for low back pain < 0.001*
 Preoperative 4.6 ± 3.2 6 (0–10)
 Postoperative 0.8 ± 1.2 0 (0–4)
VAS for leg pain < 0.001*
 Preoperative 7.0 ± 2.0 6 (2–10)
 Postoperative 1.2 ± 1.5 0 (0–4)
JOA score < 0.001*
 Preoperative 16.2 ± 6.1 18 (-5 to 25)
 Postoperative 26.8 ± 2.4 28 (21–29)
 Improvement 1.6 ± 5.7 10 (2–27)
 Improvement rate % 82.0 ± 19.0 90 (33.3–100)
ODI < 0.001*
 Preoperative 50.1 ± 18.7 52 (10–90)
 Postoperative 12.6 ± 14.3 8 (0–42)
 Improvement 37.6 ± 17.2 38 (2–76)

SD, standard deviation; VAS, visual analogue scale; JOA, Japanese Orthopaedic Association; ODI, Oswestry Disability Index.

* p<0.05, statistically significant differences.

Wilcoxon signed-rank test.

Table 3.
Magnetic resonance imaging evaluation in 49 patients with 83 segments of decompression
Variable Mean ± SD Range p-value
Cross-sectional dural area (mm2) < 0.001*
 Preoperative 61.1 ± 26.4 (8.7–162.5)
 Postoperative 151.3 ± 39.5 (72.6–254.0)
 Increment 90.2 ± 35.2 (11.1–196.9)
 Increment % 205.3 ± 206.1 (10.7–1,337.9)
Ipsilateral facet width (mm) < 0.001*
 Preoperative 10.1 ± 2.3 (6.3–17.1)
 Postoperative 8.8 ± 2.4 (4.1–16.2)
 Preservation % 87.1 ± 12.1 (40.6–100)
Contralateral facet width (mm) < 0.001*
 Preoperative 9.9 ± 2.3 (4.5–17.1)
 Postoperative 8.4 ± 2.5 (3.3–15.6)
 Preservation % 84.7 ± 11.9 (43.6–100)
Facet joint preservation (%) 0.166
 Ipsilateral 87.1 ± 12.1
 Contralateral 84.7 ± 11.9
Which side of facet joint is better preserved?
 Ipsilateral, n (%) 51 (61)
 Contralateral, n (%) 32 (39)

SD, standard deviation.

* p<0.05, statistically significant differences.

Paired t-test.

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