The DPEL Scope (Tokibo K.K., Tokyo) is a full endoscopic spinal surgical system for lumbar laminectomy developed by Dr. Akira Dezawa (Dezawa Akira PED Clinic, Kawasaki City, Japan), optimized for oriental patients and manufactured in Germany. He also devised 3.5mm and 4.0 mm high-speed drill (Nakanishi K.K. Kanuma City, Japan), which is essential for this surgery. Compared to the conventional 8 mm full-endoscope (Richard Wolf K.K., Germany), this endoscope has a wider scope diameter of 10 mm, a shorter effective length of 74 mm, and a larger working channel of 6.4 mm, allowing the use of larger instruments and making laminectomy more efficient (Figure 1). In particular, the skillful use of Kerrison Rongeurs facilitates laminectomy.

Figure 1. Full endoscopic spinal system.

Full endoscope 1: 8mm Wolf scope, 2: 10mm DPEL scope

Working channel 3: Wolf scope 4.1mm, 4: DPEL scope 6.4mm

Large instrument 5: 5mm bone curette, 6: 5mm forceps, 7: 3mm Kerrison Rongeurs

In this study, we describe the short-term results of using this DPEL scope according to his surgical method, and discuss the complications that occurred and their countermeasures.

The subjects were 52 patients (34 males and 18 females) with single level lumbar spinal canal stenosis (L3/4 15 patients, L4/5 34 patients, L5/S1 3 patients; Meyerding Grade I spondylolisthesis 18 patients 35%; cauda equina and mixed type 37 patients, nerve root type 15 patients; palsy 31 patients 60%) treated with a unilateral approach using a DPEL scope and followed during a five-year period from August 2019 to July 2024, with an average age of 74.2 (58-90) years. Mean follow-up period is 14.3 (2-47) months. The clinical outcomes were evaluated using the visual analogue scale (VAS) for pain intensity, Japanese Orthopaedic Association scoring system for low back pain [1] and modified MacNab criteria [2]. Statistical analysis was used Mann-Whitney U test.

Surgical Method of Laminectomy Using DPEL Scope??

After making a 10-mm skin incision, a DPEL scope is placed over the affected interlaminar space.

Bone Resection of Lower End of Cranial Lamina

First, the lower end of the cranial lamina is removed with a drill to a thickness of approximately 3mm from the base of the spinous process to the inferior articular process. The jaw of Kerrison Rongeurs is inserted between the lamina and the yellow ligament. The yellow ligament is then detached from the lamina by swinging the Kerrison from side to side and the lamina is resected. When the lower end of the lamina is resected, the epidural space can be observed a little (Figure 2).

Figure 2: The lower end of the cranial lamina resecting with Kerrison Rongeurs The epidural space can be observed a little (arrow).

After confirming the midline with frontal fluoroscopy, the lower end of the lamina is also resected on the contralateral side. However, it is not yet necessary to completely detach the yellow ligament from lamina.

Bone Resection of Upper End of Caudal Lamina

Return to the entry side. After a thin osteotomy of the facet joint, the upper end of the caudal lamina is exposed. The superficial layer of the yellow ligament attached to the upper end of the caudal lamina is peeled off using a drill and forceps. The yellow ligament in the interlaminar space can then be thinned (Figure 3). A hole leading to the epidural space is made in the thinned yellow ligament with a 3mm small bone curette. Kerrison Rongeurs are inserted through this hole and the upper end of the lamina is resected (Figure 4). This procedure is quick and safe because it does not require the use of a drill for bone resection.

Figure 3: Superficial layer of the yellow ligament (?) being removed from the attachment of the caudal lamina (arrow) with forceps.

Figure 4: Upper end of the caudal lamina being resected with Kerrison Rongeurs The epidural space is observed (arrow).

Bone Resection of Facet Joint and Nerve Decompression at Contralateral Side

Nerve decompression on the contralateral side begins by using a drill to detach the yellow ligament that is attached to the inferior articular process. Near the nerve root, small Kerrison or bone curette is used to remove the yellow ligament up to the lateral side of the nerve root, but it is sufficient to be able to insert a dissector just outside the nerve root (Figure 5).

Figure 5: Decompression of nerve root on the contralateral side, lateral X-ray Dissector (?) can be easily inserted outside of the nerve root (arrow).

Removal Of Yellow Ligament

The thinned yellow ligament was then removed from the caudal side toward the cranial side from the contralateral side to the midline. At this point, the yellow ligament may adhere to the dura mater (Figure 6), so it should be removed carefully. A 5mm large bone curette (Figure 1-5), is sometimes useful to help detach the yellow ligament at the cranial side. If the yellow ligament cannot be removed due to adhesions, it is left in place (Figure 7).

Figure 6: Yellow ligament (?) adhering to the dura mater (arrow).

Figure 7: Thinned yellow ligament before extraction The cranial, caudal, medial and lateral sides of the yellow ligament were detached from their attachments.

Bone Resection of Facet Joint and Nerve Decompression at Entry Side

Finally, nerve decompression is performed on the entry side. The first remaining facet joint and the yellow ligament are extracted using a bone curette and Kerrison Rongeurs (Figure 8).

Figure 8: Decompression of nerve root on the entry side, lateral X-ray Dissector (?) can be easily inserted outside of the nerve root (arrow).

Insertion of Two Drains

Two closed silicone drains (SB back, Sumitomo Bakelite Co., Ltd. Tokyo) with a diameter of 3.5 mm were inserted: one on the dorsal side of the lamina and the other near the dura mater (Figure 9-E). After returning to the hospital room, the drain placed on the dorsal side of the lamina was milked to remove hematoma from the surgical wound. Milking was performed 2 to 3 times a day, and the drains were removed in the evening of the second postoperative day. In cases of dural tear, it was removed on the day after surgery.

Activities After Returning to Hospital Room

Patients were allowed to walk and to eat from the evening of the day of surgery, but were limited to moving in the hospital ward until the drain is removed. By the 7th postoperative day, the patients underwent X-ray, MRI, and CT scans, received explanations of the postoperative condition such as decompression and hematoma, and were given future lifestyle advice before being discharged from the hospital.

The mean operation time was 185 (72-276) minutes. The average length of stay in hospital was 12.8 (3-48) days. There was no case of the progress of the slip of spondylolisthesis over 2 mm. The JOA score improved significantly from 15.4 (5-19) points preoperatively to 27.0 (19-29) points at the final follow-up (p<0.0001), with an improvement rate of 85%. The mean VAS score for leg pain improved from 60 (20-100) mm to 1.3 (0-30) mm (p<0.0001) and that of low back pain improved from 30 (0-80) mm to 4.3 mm (0-30) (p<0.0001). Based on modified MacNab criteria, the final outcomes were found to be excellent in 32 patients (61.5%), good in 12 patients (23.1%), fair in 7 patients (13.5%), and poor in 1 patient (2%). Nerve root prolapse due to dural tear was rated poor outcome.

Complications occurred in 4 cases (8%), including contralateral nerve root injury in one case (2%) and dural tear in three cases (6%). These occurred among 30 cases during the first 2.5 years of surgery. Nerve root injury occurred in one case in which the yellow ligament outside the nerve root was thoroughly removed, requiring one year for recovery. One of the three cases of dural tear also suffered nerve damage and required six months to recover after the tear was sutured. In all three cases, dural tear occurred during removal of the yellow ligament. In two of these cases, the tear was caused by adhesion to the dura mater, but the cauda equina did not prolapse (Case 1). In the remaining case, the dura and the yellow ligament were grasped with Kerrison Rongeurs, resulting in prolapse of the cauda equina (Case 2).

All three cases of dural tear were treated with a modified method of the Shibayama’s patch technique [3] (Figure 9-D). In the end, cerebrospinal fluid leaked from the drain in all cases. Fortunately, in the two cases in which the cauda equina did not prolapse, the patients had no symptoms of cerebrospinal fluid leakage and were able to be discharged without an extension of hospital stay. However, in one case in which the cauda equina prolapsed, the patient continued to have pain in the low back and lower limbs and was unable to get out of bed, so the dura was sutured on the sixth day after surgery (Figure 10-E). In this case, there was a dural defect at the site of the dural injury (Figure 10-D) and a few cauda equina had prolapsed (Figure 10-C).

There were no cases in which leg pain or paralysis occurred due to hematoma. The drain could be removed by the evening of the second postoperative day. The mean postoperative bleeding in the drain was 108 (30-230) mL in the 49 cases without dural tear. In contrast, in three cases with dural tear, cerebrospinal fluid was drained along with blood, and the average amount was 260 (160-400) mL by the morning of the day after surgery. Cerebrospinal fluid leaked mainly from the drain near the dura. Therefore, this drain was constricted and fluid was drained from that of the dorsal side on the lamina without milking. The increase in the amount in the drain was limited to less than 15 mL by the evening of the day after surgery, at which time the drain was removed.

Case 1. 77-Year-Old Woman: Dural Injury Without Prolapse of Cauda Equina (Figure 9)

Diagnosis: L4/5 spinal canal stenosis, L4 spondylolisthesis (% slip 22%), calcification of yellow ligament, facet joint cyst (A)

Chief complaints: bilateral buttock pain, numbness and pain in both legs (intermittent claudication at 30 m distance), left L5 nerve palsy

Surgery: bilateral decompression from the left side; before removal of yellow ligament, facet joint cysts were extracted (B). The yellow ligament had adhered to the dura mater, resulting in a dural injury when the yellow ligament was removed (C). A modified method of the patch technique (D) was used to repair the injury, and two drains were inserted (E).

Figure 9A: MRI before surgery of Case 1.

Figure 9B: Facet cyst stained with indigo carmine, excised specimen.

Figure 9C: Dural tear (arrow) without cauda equina prolapse.

Figure 9D: Modified patch technique A few PGA sheets cut to a size of 5-8 mm are attached over the damaged area of the dura mater in such a way that it pulls the damaged dura mater closer together. When free fat collected from the subcutaneous area is placed on the PGA sheet, the subcutaneous fat adheres to the PGA sheet without floating in the water. A PGA sheet is then placed on top. This procedure is repeated 2-3 times, and the end of the PGA sheet is sandwiched between the ventral side of the excised lamina using a bone curette (arrow).

Figure 9E: Placement of two drains, frontal X-ray One 3.5 mm silicone drain is placed on the dorsal side of the lamina ? and the other in the spinal canal?. PGA sheet is visible in the depth (arrow).

After surgery, cerebrospinal fluid leaked, however there were no symptoms due to the leakage. The bleeding with cerebrospinal fluid in the drain increased a little from the morning after surgery, and the drains could be removed in the evening at 160 mL.

Walking started at noon on the day after surgery. MRI (F) and CT (G) performed on the 6th day after surgery showed good decompression and no cerebrospinal fluid retention.

Figure 9F: MRI on the 6th postoperative day showing good decompression and no spinal fluid retention.

Figure 9G: Transverse view of the CT scan of the upper edge of the L5 vertebra after myelography before surgery (a), and on day 6 after surgery (b).

She was discharged from the hospital 14 days after surgery. At that time, The VAS score for leg pain improved from 60 mm before surgery to 0 mm, and the JOA score increased from 18 points preoperatively to 28 points. Three years after the surgery, the patient is still free of leg pain, and her JOA score is 29 points (maximum).

Case 2. 79-Year-Old Man: Dural Injury with Cauda Equina Prolapse (Figure 10)

Diagnosis: L3/4 spinal canal stenosis, L3 spondylolisthesis (% slip 12%) (A)

Chief complaint: intermittent claudication within 500m due to both leg pain, mild urinary dysfunction

Surgery: bilateral decompression from the left side; the dural tear was caused by the grasping of the dura mater and the yellow ligament (B), resulting in partial absence of the dura mater and prolapse of the cauda equina. Once the prolapsed cauda equina was contained within the dura mater, it was repaired using a modified patch technique and two drains were inserted.

Post-operatively, the patient had difficulty getting out of bed due to back and leg pain, even when turning. On postoperative day 3, a few cauda equina had prolapsed on re-examination (C), so that the dura mater was sutured on postoperative day 6 (D, E).

On the third day after reoperation, the patient was able to walk with reduced low back and leg pain and was discharged six weeks after reoperation. The MRI performed at that time showed no spinal fluid leakage (F).

Figure 10A: MRI before surgery of Case 2.

Figure 10B: Dura and yellow ligament being grasped with Kerrison Rongeurs The dura mater appears “white” when it is grasped (arrow).

Figure 10C: A few of cauda equina prolapsing at the second look.

Figure 10D: Defect in dura mater (arrow) before suturing Defect becomes larger than the time of injury - 3x5mm in size.

Figure 10E: Dural tear being sutured with 6-0 threads made of proline The sutures are then covered with free fat graft, PGA sheets and fibrin glue.

Figure 10F: MRI before discharge from hospital six weeks after reoperation showing good decompression and no spinal fluid retention.

At 6 months postoperatively, there was no leg pain. Dysuria and post-operative paralysis of the lower limbs had disappeared. The JOA score improved from 12 points preoperatively to 21 points.

Dural tears are the most common complication of full endoscopic spine surgery. Since the endoscope has only one working channel, it is difficult to detach the yellow ligament from the dura mater if they are adhered. In such cases, the adhesions are carefully peeled off little by little, but if this is not possible, consideration may be given to leaving the yellow ligament in place. Furthermore, when the video images of the case required dural suture was carefully observed after surgery, it was important to note that the dura mater appeared white when it was grasped (Figure 10-B). Therefore, careful observation during removal procedure of the yellow ligament may have minimized dural damage.

 Dural tear did not occur before the removal of the yellow ligament. Therefore, removal of the yellow ligament in one block has recently been discontinued. Instead, the yellow ligament is gradually thinned during surgery, so that if adhesions are found, the yellow ligament can be left in place without resection (Figure 7). In the past, there was no experience of using a gelfoam and TachoSil selant patch [4], and dural damage has been repaired using the subcutaneous free fat or a patch technique using PGA (polyglycolic acid) sheets in microendoscopic spine surgery reported by Shibayama et al. in 2008 [3]. However, since the free fat floated in the water, it was necessary to stop the perfusion and wait until the fat adhered to the hematoma and stopped moving, making subsequent surgical operations difficult. When PGA sheets were used, the sheets adhered to the dura mater even in the water, but because fibrin glue could not be used, cerebrospinal fluid leaked out after surgery. The modified method reported in this study is a variation of the patch technique that combines the two methods, but ultimately cerebrospinal fluid leaked into the drain. However, the outflow of blood including cerebrospinal fluid decreased the day after surgery, and the drain could be removed by the next evening, suggesting that this method would be useful for dural tears.

The mean operative time was long (185 minutes), complications occurred in 8% of cases, and dural suture was performed in one case, however there were no symptoms due to hematoma.

The combination of 2-3 layers of PGA (polyglycolic acid) sheet with the subcutaneous free fat was effective for repair of the dural tear in two patients without cauda equina prolapse.

Despite the number of cases is fewer (52) and the follow-up period was short (14.3 months), there was a marked improvement in low back and leg pain, JOA score and modified MacNab criteria, suggesting that this surgical procedure using a DPEL scope is a highly effective method of treating lumbar spinal canal stenosis.

1. Matsumoto M, Watanabe K, Ishii K, Tsuji T, Takaishi H, Nakamura M, et al. Posterior decompression surgery for extraforaminal entrapment of the fifth lumbar spinal nerve at the lumbosacral junction. J Neurosurg Spine 2010; 12: 72-81.
2. MacNab I. Negative disc exploration. J Bone Joint Surg [Br]. 1971; 53-A: 891-903.
3. Shibayama M, Mizutani J, Takahashi I, Nagao S, Ohta H, Otsuka T. Patch technique for repair of a dural tear in microendoscopic spinal surgery. J Bone Joint Surg [Br]. 2008; 90-B: 1066-1067.
4. Tang S, Mok TN, He Q, Li L, Lai X, Sin TH, et al. Comparison of clinical and radiological outcomes of full-endoscopic versus microscopic lumbar decompression laminectomy for the treatment of lumbar spinal stenosis: a systematic review and meta-analysis. Ann Palliat Med. 2021; 10: 10130-10146.