Complications and Management of Endoscopic Spinal ...

A total of 103 articles related to complications of endoscopic spinal surgery were reviewed and analyzed.

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Complications of full endoscopic surgery were reported in 38 articles in cervical spinal disease, 4 on complications of full endoscopic cervical surgery ( ), and 11 on full endoscopic anterior cervical approach ( ), 19 on full endoscopic posterior cervical approach ( ), and 4 on biportal endoscopic cervical surgery ( ) [7-44].

Twelve articles on complications of endoscopic thoracic spinal surgery were reported, 2 on review articles of full endoscopic thoracic surgery ( ), 7 on full endoscopic transforaminal thoracic approach ( ), and 3 on full endoscopic interlaminar thoracic approach ( ) including complications. However, there is no articles on biportal endoscopic thoracic surgery including complications [45-55].

Complications of lumbar endoscopic surgery were reported in 53 articles on full endoscopic lumbar decompression. Regardless of the transforaminal or interlaminar approach method, complications of full endoscopic lumbar decompression were reported in a total of 5 studies ( ).

A total of 24 studies reported complications for full endoscopic transforaminal lumbar decompression ( ) and total 24 articles describing interlaminar approach contained complications ( ).

The overall incidence of clinically symptomatic complications is below 10%. Most complications were minor, and life-threatening complications, such as thromboembolism, sepsis, severe bleeding, or pulmonary complications are less frequent than open surgery. The complications of endoscopic cervical surgery at approximately 5% with both anterior and posterior approaches had an incidence equivalent to that expected from open cervical surgery.

According to the complication analysis of endoscopic spinal surgery, regardless of the cervical, thoracic or lumbar spine, regardless of the uniportal or biportal approach, main complications such as dural tears, postoperative hematoma, neurological irritation (dysesthesia), untreated pain are commonly reported.

Regardless of the cervical anterior or posterior approach method, several literatures on the complications of full endoscopic cervical surgery have already been reported. According to the analysis of complications of endoscopic spinal surgery, Guo et al. [ 41 ] reported total complication rate of 4.7% and a reoperation rate of 1.1% in cervical endoscopic surgery. In anterior full endoscopic cervical surgery, recurrent laryngeal nerve injury and swallowing dysfunction are unique complications of this method. In addition, numbness, hematoma, discitis, vascular injury, and persistent pain were reported as complications.

In addition, Wang et al. [ 65 ] reported the results of a single-arm rate meta-analysis, which showed that the overall complication rate of unilateral biportal endoscopic treatment of lumbar spinal stenosis was 6.27%, the incidence of dural tear was 2.49%, the incidence of transient paresthesia was 0.14%, postoperative spinal epidural hematoma was 0.27%, and postop headache, inadequate decompression, root injury and infection were 0%.

In UBESS, Liang et al. [ 64 ] reported the overall complication rate was 5% and dural tears were the most frequent complications at 2%, followed by epidural hematoma with an incidence of 1%. The remaining complications included nerve root injury, inadequate decompression, and postoperative headache.

Ju et al. [ 63 ] reported a study of narrative analysis, comparing the complications of the transforaminal and interlaminar approaches. They found that dural tears are overwhelmingly common (2.19%) in interlaminar decompression followed by epidural hematoma (0.76%) and transient dysesthesia, whereas in transforaminal decompression, dysesthesia (1.46%) was the most common, followed by untreated pain (1.20%) and dural tearing.

Fan et al. [ 62 ] reported complications and risk factors of percutaneous endoscopic transforaminal discectomy (PETD). In this study, the incidence of different types of complications was 9.76% (72 of 738). The complications and occurrence rates were as follows: 2.30% (17 of 738) of recurrence, 3.79% (28 of 738) of persistent lumbosacral or lower extremity pain, 1.90% (14 of 738) of dural tear, 0.81% (6 of 738) of incomplete decompression, 0.41% (3 of 738) of surgical site infection, 0.27% (2 of 738) of epidural hematoma and 0.27% (2 of 738) of intraoperative posterior neck pain.

Lin et al. [ 61 ] reported a systematic review of unilateral biportal endoscopic spinal surgery (UBESS), reporting a mean incidence of complications of 6.7%. The most common complication was a dural tear. The total mean incidence of dural tears was 4.1% after the UBESS procedure in 6 studies (range, 2.9%&#;5.8%).

Regardless of the lumbar transforaminal or interlaminar approach method, literatures on the complications of full endoscopic surgery have already been reported [ 56 - 59 ]. According to the analysis of the complications of endoscopic spinal surgery, dural tears, postoperative hematomas, neurological complications, lower condyle fractures, and epidural lipomatosis were reported.

4. Management of Complications of Endoscopic Spinal Surgery

1) Dural tear

Dural damage is the most common complication of endoscopic spinal surgery, and it can lead to serious complications if an accurate diagnosis and appropriate treatment are not performed. The overall rate of dural tears in endoscopic spinal surgery was 2.7%, range from 0% to 8.6% [58]. The incidence of a dural tears was much greater in cases with lumbar stenosis (3.7%) than in lumbar discherniation (2.1%). The risk of dural tears is greater in bilateral decompression procedures than unilateral decpmpression.

Pan et al. [66] reported that the incidence of dural rupture increased to 1.1% when percutaneous endoscopic lumbar discectomy (PELD) was switched from an &#;inside-out&#; technique to an &#;outside-in&#; technique. Dural injury by instruments or radiofrequency, spinal canal adhesions, large disc fragments, and a loose dura are risk factors for dural tears.

However, Klingler et al. [67] reported that the occurrence of complications after durotomy in minimal invasive surgery is lower than after open surgery because of the preservation of the paraspinal musculature. The paraspinal musculature is not dissected during minimally invasive surgery and slides back to its original position after removal of the tubular retractor.

In UBESS, Liang et al. [64] reported dural tears were the most frequent complication at 2%. Wang et al. [65] reported that the incidence of dural teara was 2.49%. There are several main reasons for spinal dural tears caused by UBE spine endoscopic surgery. (1) Beginners easily make mistakes because the visual field under endoscopy is a 2-dimensional plane and is easily blurred. (2) UBE does not require retraction of the anatomical structure to expose the dura mater, which is quite different from other techniques. (3) Patients with complex conditions require operations of long duration, increasing the risk of spinal membrane tears. (4) During the operation, the injected saline squeezed both sides of the dura mater, causing the area to fold. The central area may be damaged during ligamentum flavum resection. (5) When using high-speed drills, the peripheral fibrous bands and vascular bundles of the dura may stretch around the drill neck, causing larger tears.

Several methods have been introduced for the treatment of incidental dural tears during endoscopic spinal surgery. An autologous muscle or fat graft in combination with fibrin glue or a fibrin-sealed collagen sponge seems to be a good and safe method for the management of dural tear in lumbar endoscopic spine surgery [9].

Kim et al. [56] reported the incidence of incidental durotomy was 8.2% and classified the incidental durotomy during endoscopic decompression according to lumbar levels, 40.7% occurred at L3&#;4, 44.4% at L4&#;5, and 14.8% at L5&#;S1. They also divided incidental durotomy into 4 types: 29.6% are type 1 (peripheral type), 70% are type 2 (central type), 7.4% are type 3 (complex type), and 3.7% are type 4 (unrecognized). They recommended the endoscopic patch blocking dura repair technique should be considered in type 1 to type 3A of dura tears with a good prognosis and clinical outcome. However, open surgical repair is recommended in types 3B, 3C. and 4 dura tears with fair to poor outcome.

Nam et al. [68] introduced double-Layer TachoSil packing technique for incidental durotomy in endoscopic surgery. A hemostatic agent, TachoSil (Nycomed, Linz, Austria), is used for control of local bleeding in several types of surgery, but its use in dural repair in endoscopic spinal surgery has not been described. When TachoSil packing is performed, the intradural TachoSil is inserted to avoid spilling, and the extradural TachoSil is sealed over the intradural TachoSil. Therefore, TachoSil did not cause a mass effect. Nevertheless, a thin layer of TachoSil must be applied; the application of larger quantities results in pooling that could lead to serious side effects such as compression of the spinal cord and nerve roots. If used incorrectly, excess TachoSil may cause additional iatrogenic dural tearing. In our experience, mild swelling of the TachoSil in the intradural space reinforces the dural repair site and prevents secondary rupture; it also ensures good adhesion of the edge of the TachoSil to the intact surrounding dura. Second, while maneuvering TachoSil intradurally, the cast side will dissolve in cerebrospinal fluid and adhere to nerve roots, which could be dangerous and difficult to reverse. Thirdly, thrombin is proinflammatory and could cause arachnoiditis and neuritis in the postoperative period if deployed intradurally.

2) Postoperative epidural hematoma

An epidural hematoma occurs mainly after an interlaminar approach. Recently, as endoscopic surgery for spinal stenosis and intervertebral discectomy has increased, the complication rate has also increased. It is also one of the most common complications in biportal endoscopic surgery.

The incidence of postoperative epidural hematoma is approximately 0.27%. Continuous saline irrigation is necessary during biportal endoscopic spine surgery [69-71]. The use of an infusion pump during surgery may be an unavoidable risk factor. However, it may increase the epidural pressure and, subsequently, result in meningeal irritation, indicated by neck pain or headache [69-71]. When the outflow of saline solution is blocked, the pump continues to infuse saline to increase the pressure in the surgical field, cover up bleeding points, and cause intraoperative hemostasis. Lack of saline solution may cause postsurgical epidural hematoma [72].

There are 2 possible mechanisms of increased epidural and intracranial pressure by continuous saline irrigation [73]. The first is the direct pressure effect by continuous irrigation of saline. The second is direct cranial movement of irrigation fluid. Prolonged operating time or poor patency of the irrigation fluid can increase epidural pressure during biportal endoscopic surgery [72]. In the biportal endoscopic approach, continuous saline is passed from the endoscopic portal to the working portal. The patency of saline outflow and constant flow is important for maintaining epidural pressure. An infusion pump pressure >50 mmHg can increase the cervical epidural pressure in this surgery. Reducing the operation time and maintaining the pump pressure below 40 mmHg may be useful in reducing the complications caused by the increase in epidural pressure [74-76]. Additionally, postoperative epidural Hemovac insertion may help to drain excessive irrigation fluid. Neck pain or headache can be improved with bed rest and conservative treatments.

Although symptomatic postoperative epidural hematoma is relatively rare (the incidence rate is 0.02% to 4.6%) [74], it can lead to serious consequences such as cauda equina syndrome and even lower limb paralysis, which affects patients&#; quality of life. Therefore, early detection and handling are important.

Ahn et al. [73] reported that postoperative epidural hematoma is one of the complications that are considered to develop more often in biportal endoscopic surgery than in conventional spine surgery. The radiological thecal sac compression by hematoma was 39.8% of grade 1 (thecal sac compression less than a quarter), 30.1% of grade 2 (between a quarter and a half), 26.5% of grade 3 (between a half and three quarters), and 3.6% % of grade 4 (over three quarters) in biportal endoscopic surgery.

Kim et al. [74] reported that the overall occurrence rate of postoperative hematoma was 23.6% after biportal endoscopic spinal surgery. Female sex, old age (> 70 years), preoperative anticoagulation medication, and usage of intraoperative water infusion pump were significantly correlated with the occurrence of postoperative hematoma. Although symptomatic postoperative hematoma was extremely rare (1.9%), radiologic hematoma confirmed by postoperative magnetic resonance imaging (MRI) was higher (23.6%). The perioperative risk factors of postoperative hematoma after biportal endoscopic spinal surgery include female sex, older age (> 70 years), preoperative anticoagulation medication, usage of intraoperative water infusion pump, and surgery requiring more bone work (laminectomy or interbody fusion).

Additionally, Kim et al. [75] reported that the total number of patients with hematoma was 39 (24.7%) according to T2-weighted axial postoperative MRI. The incidence of postoperative spinal epidural hematoma after biportal endoscopic spinal surgery according to postoperative MRI was higher than expected, regardless of the patients&#; postoperative symptoms. Postoperative hematoma has a decisive influence on postoperative results, and revision surgery may be necessary if canal encroachment is >50% with concomitant symptoms.

Symptomatic postoperative spinal epidural hematoma is a devastating complication that could develop after biportal endoscopic spine surgery [76]. Gelatin-thrombin matrix sealant (GTMS) is commonly used to prevent postoperative spinal epidural hematoma. Intraoperative use of a GTMS during biportal endoscopic spine surgery may be related to a reduction in the occurrence rate of epidural hematoma. Specifically, patients treated with GTMS appliances showed a marked decrease in the occurrence of postoperative spinal epidural hematoma and had better clinical outcomes.

3) Retroperitoneal hematoma

Although rare, hematomas can occur as a result of vessel injury during the full endoscopic transforaminal approach. A small amount of bleeding is not a problem even with conservative treatment, however, if the segmental artery branch is damaged, a large retroperitoneal hematoma may occur and cause symptoms. To avoid blood vessel damage, it is important to carefully insert the needle into the relatively safe avascular area by touching the bone of the facet in the safety zone during the transforaminal approach [77-79].

In addition, because damaged blood vessels may not be seen well in the field of view of endoscopic surgery when the endoscope is removed after the surgery, it is necessary to check slowly that there is no bleeding in the surrounding tissue. Bleeding control during surgery is the most important thing, and when bleeding occurs, the method using the radiofrequency probe is mainly used, or another electrocautery or bone wax is used when there is bone bleeding. However, in cases of severe bleeding, it is often difficult to identify the bleeding site because it is difficult to secure a visual field. At this time, a hemostatic agent such as GTMS, can be helpful, and while the surgical field is secured for a while with the hemostatic agent, you must check the bleeding site and perform sufficient hemostasis with radiofrequency or other electrocautery before leaving. Additionally, if bleeding continues even after hemostasis, Hemovac drainage after surgery can be a good way to prevent hematoma.

4) Postoperative dysesthesia

Postoperative dysesthesia often occurs in the transforaminal approach, and this surgical method can be caused by direct irritation of the exiting nerve root that anatomically borders the safety zone.

Ju et al. [63] reported that dysesthesia and untreated pain are relatively common complications of the transforaminal approach after decompressing ipsilateral foraminal and lateral recess stenosis.

Silav et al. [80] reported that postoperative dysesthesia is caused by irritation of the instruments and improper operation. The dorsal root ganglion (DRG) lies in the intraforaminal region and is vulnerable to disc herniation, foraminal stenosis, and mechanical damage by operative instruments. Damage to the DRG brings symptoms different from those associated with primary pathology. As a unique complication of PETD, postoperative dysesthesia greatly affects recovery and the postoperative quality of life. Cho et al. [81] applied the floating retraction technique to prevent postoperative dysesthesia and revealed that this technique was effective in 154 patients. Fluoroscopy is essential to locate guiding wire and working cannula to avoid mechanical stretch or damage to the upper DRG.

For the prevention of postoperative dysesthesia, the foraminoplasty is performed to expand the safety zone without causing an exiting nerve root irritation [63,82-84]. Foraminoplasty is not always needed during the endoscopic transforaminal approach to prevent postoperative dysesthesia. However, it is an especially useful method for widening the safety zone in cases of narrowed intervertebral foramina, such as facet hypertrophy or superior articular process overriding. It is also a safe and effective technique for entering the epidural space without exiting nerve root injury, especially in cases of central disc herniation or a downward migrated disc herniation, which have a high risk of causing an exiting nerve root injury. To effectively remove herniated disc material, the insertion angle of the endoscope was modified depending on the type of disc herniation. Significantly, the closer the incidence angle is to that of the vertical axis, the wider the safety zone, thereby reducing the possibility of exiting nerve root injury; however, it is difficult to access the epidural space and to secure the field of view. On the other hand, if the angle of incidence is close to that of the horizontal axis, accessing the epidural space and securing the field of view is easier, but the safety zone is narrowed, which increases the possibility of exiting nerve root injury. Therefore it is important to determine the appropriate angulation based on the pattern of disc herniation. To reduce exiting nerve root irritation within the safety zone as much as possible. Keeping the endoscopic cannula steep and located in the inferior disc space rather than the superior disc space is important [82].

In biportal endoscopic surgery. the incidence of transient paresthesia is approximately 0.14% [65]. The main reason for transient paresthesia after surgery is that palsy and pain are both caused by sensory nerves. The pain is transmitted by small unmyelinated fibers, and the conductive palsy is thick [85-88]. The structure of unmyelinated fibers is relatively simple, and the postoperative recovery is faster, while myelin fibers need to undergo a longer and more complex repair process; In addition, pain is a more acute and uncomfortable sensation than palsy, thus, surgery is often covered up. After the postoperative pain is weakened or recovered, the palsy is exposed [87]. Most patients will relieve the palsy. However, because palsy is positively related to illness time and degree of stenosis, the recovery times of different patients are different [88].

5) Incomplete decompression

Whether resection of the herniated disc is complete depends on the position of the working cannula, type of disc herniation, and size of the herniated fragments. Incomplete discectomy is particularly common in downward migration or high canal compromised disc herniation. Choi et al. [89] retrospectively analyzed 10,228 patients treated by PETD, and found 283 cases of incomplete resection, among which 95 were caused by improper location. Regarding the type of herniation, there were 91 cases with central herniation (32.2%), 70 with migrated herniation (24.7%), 63 with axillary type herniation (22.3%), 18 with shoulder-type herniation (6.4%), and 12 with foraminal/extraforaminal herniation (4.2%). Lee et al. [90] found that herniations with high canal compromise and high-grade migration make it harder for PELD to efficiently remove herniated disc. Herniated disc fragments should be adequately released from the annulus before they are grasped and removed. Detailed planning of the puncture route is the key for complete removal. A careful check for residual fragments is necessary, and placing the bevel of the working cannula toward the fragments helps achieve sufficient removal of the herniated disc. On the other hand, excessive resection of the herniated disc may increase the risk of dural tears and damage to the nerve root, thus, surgeons need to restore the normal motion and pulsation of the nerve root [78.91].

In the transforaminal approach, the foraminoplastic technique is a safe and reliable method for discectomy, and the migrated disc can be easily removed using a curved probe or forceps. Because the field of view of endoscopic surgery is narrow, it may not be possible to check the lesion area, and dura free pulsation must be checked to ensure sufficient decompression.

During spinal stenosis decompression, unilateral and bilateral decompression should be performed to sufficiently decompress the superior articular process in the lateral recess area to confirm the traversing nerve root, and sufficient laminectomy is required for sufficient decompression.

Decompression is usually excellent in UBESS for lumbar spinal stenosis. However, decompression may be inadequate in patients with severe lumbar spinal stenosis. Deviations in the preoperative assessment and intraoperative decompression range have been the main reasons for inadequate decompression [92]. Choi et al. [93] showed that for early cases, postoperative MRI revealed inadequate resection of the proximal and contralateral ligamentum flavum. These patients&#; acute neurologic symptoms were relieved, although they had complained of tiredness in the affected calf. Choi et al. [93] reported that angled curettes were more useful in performing adequate flavectomy than Kerrison punches. Angled curettes, but not straight curettes or Kerrison punches, might scrape the ligamentum flavum under the lamina without excessive laminectomy. To decompress the contralateral side, Liang et al. [64] reported that a wider interspinous gap should be created to allow for simultaneous insertion of an endoscope and an instrument into the small midline space, with partial resection of the upper and lower ends of the spinous processes using a high-speed burr.

Intraoperative irregularities and thermal injuries from radiofrequency ablation have been the main causes of nerve root injury. The use of an arthroscopic radiofrequency ablation tip in the spinal canal can cause significant thermal damage to the neural structures. Therefore, it is important to be gentle during the procedure, to identify nerve structures carefully, and to reduce the voltage of the radiofrequency device if necessary [64].

6) Recurrence of disc herniation

Recurrent lumbar disc herniation (LDH) is defined as a recurrence of disc herniation at the same site of a previous discectomy in a patient who has experienced a pain-free interval after surgery. However, the minimum length of the pain-free interval is debatable, ranging from any interval of pain resolution to 6 months [94-97]. Moreover, recurrent disc herniation should be discriminated from incomplete discectomy or endoscopic operative failure.

The purpose of PELD is not to remove nucleus pulposus totally but to remove partially the herniated disc fragments and decompress nerve root. Therefore, recurrence of LDH sometimes occurs with aging, inappropriate weight-bearing, and other factors like male gender, obesity (body mass index [BMI] &#; 25 kg/m2), old age (&#; 50 years), trauma history, and central disc herniation. But PELD also has some unique risk factors for LDH recurrence, such as surgeons&#; having less experience with PELD (&#; 200 cases) and performing operations in the early development stage of PELD [91,97]. Especially, early recurrence after PELD is associated with several risk factors such as BMI, degeneration scale, combined herniation nucleus pulposus, and early ambulation [98]. Preoperatively, surgeons should study imaging examinations and design the puncture route carefully. Postoperative instructions like lumbar muscle exercise, proper weight burden, and appropriate sitting posture are essential to decrease the possibility of LDH recurrence [63].

7) Increased epidural pressure

With UBESS via the interlaminar approach, the use of high intraoperative water pressure can increase cerebrospinal fluid pressure and intracranial pressure, leading to postoperative headache and can even induce seizures [85,86]. Therefore, we searched for the early symptoms of seizures after surgery, such as neck pain, headache, blurred vision, and drowsiness. To avoid the occurrence of postoperative headache, it is crucial to prevent high intraoperative water pressures. Rather than attempting to obtain a clear vision by increasing the infusion pressure, Kim et al. [99] reported that it would be preferable to improve the outflow by applying an extension or crosscut of the fascia incision via the working portal, which will allow for a clear view and prevent the occurrence of postoperative headache. Czigléczki et al. [100] reported that irrigation could lead to meningeal irritation and postoperative headache; however, reducing the operative time can avoid such complications. Choi [101] recommended that the irrigation pump pressure should be kept at < 30 mmHg when using the pump.

8) Intervertebral infection

The incidence of intervertebral infection after spine surgery ranges from about 0.1% to 4.5%, most cases are caused by bacterial infection [98-104]. However, because of the continuous saline irrigation and short operation time in endoscopic spinal surgery, postoperative infection is rare. Additionally, the low trauma of PELD makes intervertebral infection uncommon, but the risk still exists.

Gu et al. [105] reported an incidence being 0.47%, among 209 cases of LDH treated by PETD, they found only one infected patient recovered through intravenous antibiotics after 2 weeks. Pyogenic spondylodiscitis is a devastating complication after spinal surgery and causes severe spinal nerves dysfunction. Even if the infection is not suspected after endoscopic spinal surgery, early tests such as erythrocyte sedimentation rate and C-reactive protein should be performed. MRI is of little value in early diagnosis. Needle biopsy of the disc guided by fluoroscopy is diagnostic and helpful in identifying pathogenic bacteria. Once diagnosed, patients with mild symptoms need positive antibiotics and a braking system on the bed. As for patients with severe symptoms and signs, intervertebral washing and drainage should be performed. Open debridement and fusion are necessary if conservative therapy is of no benefit. Postoperative MRI alone is very difficult to make an early diagnosis of infection and is of little value. Disc needle biopsy by fluoroscopy allows for a definitive diagnosis and helps identify pathogenic bacteria. Once diagnosed, patients with mild symptoms require positive antibiotics and bed rest. In patients with severe symptoms and signs, intervertebral lavage and drainage should be performed. If conservative treatment does not help to control symptom, open debridement and fusion are required.

9) Postoperative instability and facet joint injury

Postoperative segmental instability or facet joint injury is another complication of biportal endoscopic laminotomy [106-108]. In addition, iatrogenic inferior articular process fractures can occur during laminotomy, and these complications are similar to those from conventional or microscopic surgery. Therefore, preoperative instability is a contraindication of biportal endoscopic lumbar decompression.

10) Cervical and thoracic endoscopic spinal surgery

Cervical and thoracic endoscopic spinal surgery is currently performed in hospital in the Far East, but is not popular in Europe or the United States. Attempts were made to remove cervical discs with minimally invasive anterior approaches in the s, but the techniques used were not widely adopted because the inherent risks associated with the surgical approach and the lack of well-designed equipment [40].

Although it is well recognized that posterior cervical lamino-foraminotomy for discectomy and root decompression with foramen widening will minimize blood loss and enhance patient recovery compared to anterior cervical surgery, the benefits regarding clinical outcomes are less well established [40].

This is because a various posterior surgical methods have been used by surgeons, from microsurgery with tubular retractors to purely endoscopic techniques [109]. It is not clear endoscopic techniques leads to better surgical outcomes than the former.

Surgical complications of approximately 5% in both the anterior and posterior approaches were the same as expected in open cervical surgery, and there appeared to be a low rate of reoperation. The posterior approach may reflect the generally shorter clinical follow-up [7,110,111].

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Choi et al. [42] reported the 3 main complications of cervical endoscopic spinal surgery: (1) neurological injury like damage to the cervical cord or nerve root due to inadvertent use of forceps or laser (transient with laser), (2) vascular injury like carotid vessels during percutaneous endoscopic cervical discectomy (PECD) and vertebral artery while foraminotomy. (3) visceral injury, mainly oesophagus because it is soft collapsible tube and highly prone to injury while needle insertion in PECD.

In the anterior cervical approach, the essential technical factor is the precise targeting of disc pathology. The surgeon should feel the carotid pulse and push the anterior neck down into the space between the carotid artery and tracheoesophagus until the fingertips touch the anterior surface of the vertebral body [112]. The tracheal air shadow on the fluoroscopic view may be a good indicator of the position of tracheoesophagus. For the patient with a short and thick neck, the shoulder shadow may interfere with C6&#;7 or lower level. An oblique fluoroscopic view can be useful to approach the C6&#;7 level. Regarding selective discectomy, direct fragment removal with small instruments is difficult because of tenacious annular anchorage. Careful release of fibrotic adhesion around the herniated fragment is mandatory before the removal of the freely movable herniation fragment [112-115].

In the posterior cervical approach, a definitive dissection of bony structures and identification of the laminofacet junction (so-called &#;Y-point&#;) is essential for a safe and precise cervical foraminotomy. To prevent postoperative instability, the extent of facetectomy should be limited to no more than 50% of the facet joint. After adequate foraminotomy, the herniated foraminal disc fragment should be removed while preventing a dural tear. The dissection between the herniated disc and the neural tissues can be performed with a blunt dissector. The exposure of herniated fragment with firm nerve retraction can be achieved by rotating the bevel ended tip of the working cannula. After adequate nerve retraction, the herniated piece can be removed by endoscopic forceps and supplementary radiofrequency or laser. Epidural bleeding may occur from flourishing venous plexus. A gentle tamponade with hemostatic agents or hydrostatic pressure may be useful with a bipolar coagulator [115].

In thoracic endoscopic spinal surgery, 3 main complications of thoracic endoscopic surgery were reported: (1) neurological injury like damage to the spinal cord and its nerve roots, (2) vascular injury like damage to the inferior vena cava or thoracic aorta can be life threatening, (3) visceral injury like damage to the lung or mediastinal viscera [42]. In endoscopic transforaminal thoracic surgery, intercorstal neuralgia is a unique complication of insertion of a working cannula between the intercostal spaces. Above all, since thoracic surgery can cause serious neurological damage such as myelopathy, the operation must be performed very carefully and safely.

INTRODUCTION

Endoscopic spine surgery is becoming the standard of care for degenerative disease of the lumbar spine. Since the introduction of nonvisualized needle aspiration discectomy by Kambin in , the field of percutaneous endoscopic spine surgery has evolved immensely. The innovation in the field of optics and instrumentation has played a major role in this evolution. With increasing indications of endoscopic spine surgery, surgeons have reported its applications not only for paramedian disc herniations but also for central disc herniations, highly migrated disc herniations, sequestered herniations, thoracic and cervical disc herniations, and more recently, lumbar canal stenosis. It is logical that with broadening indications and applicability, the risk of unexpected adverse events is bound to increase. Hence, it is essential for the endoscopic spine surgeons to be aware of the potential hazards and unexpected complications of the procedure so that appropriate care is taken to avoid adverse events as much as possible. The purpose of this review was to summarize the reported complications of transforaminal endoscopic discectomy for lumbar disc herniations. In the end, we also have provided a synopsis into the disadvantages of percutaneous instrumentation.

SURGICAL TECHNIQUE

The technical procedure is described in numerous reports.[123] We describe the conventional inside&#;out technique in this note. The procedure is performed under local anesthesia in a prone position on a Wilson frame on a radiolucent table. Intravenous sedation is midazolam (0.1mg/kg). It is used to reduce anxiety and as an adjunct to analgesics. Under C-arm guidance, the midline, the iliac crest, the lower margin of the rib cage, and the transverse disc line of the concerned level in anteroposterior (AP) view is marked. In lateral view, a line parallel to the disc space midway between the two vertebral endplates is drawn. The junction of the two discal lines is the entry point. Before making the skin incision, the lateral border of the back muscles is palpated and entry lateral to it is avoided as it may cause abdominal organ injury. The entry point moves laterally as one moves from above to below [Figure 1]. Under C-arm guidance, an 18-G-long spinal needle is introduced into the disc space. The tip of the spinal needle should lie in the lower half of the foramen and near the posterior vertebral border in lateral view when the needle reaches the medial pedicular line in AP view. Indigo carmine dye is injected to delineate the degenerated fragment for easy identification and removal during endoscopy. The spinal needle is replaced with a guide wire. Next an obturator is inserted and then the working channel is inserted and hammered into the disc space. Then the obturator is replaced by the endoscope into the working channel. At first, we can see the subannular disc tissue. Initial subannular discectomy is carried out using forceps and radio-frequency (RF) probe.

Figure 1:

The entry point for transforaminal endoscopic approach moving laterally as one moves from upper to lower lumbar levels (The red line is the lateral border of back muscles, lateral to the red line is soft on palpation and medial to the red line is firm on palpation. Blue line is the lateral safe extent of entry for scope to prevent bowel and renal injuries.)

As shown in Figure 2, then the various anatomic structures, namely traversing nerve root (a), epidural fat (b), epidural space (c), defect in annulus (d), posterior longitudinal ligament (e), and annulus (f), are assessed in a &#;half-and-half view&#; (half inside the disc, half outside the disc view). The herniated fragment is generally anchored by fibrotic annular fissure. The release of this anchorage is a key step for successful discectomy. Using cutting forceps and RF probe, the herniated fragment is freed from the annular fissure. The fragment can be easily identified by blue stain. Using endoscopic forceps and adjusting the working channel, the herniated fragment is removed. Endoscope may need to reverse back out of the disc and pointing the camera of endoscope dorsal to the annulus along with foraminoplasty obtaining a good &#;half-and-half view&#; may be required in some cases to access the fragment lying in the epidural space. Free pulsation of the dural sac or nerve roots and free passage of endoscopic nerve hook into the epidural space marks the end of discectomy. The patient, at this point, can also feel the relief of symptoms.

Figure 2:

Anatomy of the structures visualized through the endoscope via transforaminal approach (traversing nerve root (a), epidural fat (b), epidural space (c), defect in annulus (d), posterior longitudinal ligament (e), and annulus (f))

COMPLICATIONS OF ENDOSCOPIC SPINE SURGERY

The complications of endoscopic spine surgery are summarized in Figure 3. Individual complications are discussed in the following sections.

Figure 3:

Summary of complications of endoscopic spine surgery

INTRAOPERATIVE COMPLICATIONS - LOCAL

Injury to neural structures and dural tear

The approach for transforaminal procedures is through the Kambin&#;s triangle, which is bounded medially by the traversing nerve root, caudally by the superior endplate of the caudal vertebra, and laterally by the exiting nerve root. Hence, theoretically, the exiting nerve root, traversing nerve root, dural sac, dorsal ganglion, and furcal nerve (if present) are all at risk of injury during the procedure. Hence, the first step of needle placement is done cautiously under C-arm guidance. As described in the procedure earlier, the tip of the needle should target the lower half of the foramen and should lie at the posterior vertebral margin on reaching the midpoint of the pedicle.

Extra caution is required in cases of extraforaminal disc herniations, upper lumbar levels, foraminal stenosis, and central disc herniations. Patient feedback is very important during the procedure. Intractable radicular pain during the procedure may be related to nerve root irritation. It is important to analyze the magnetic resonance imaging (MRI) preoperatively to check the presence of furcal nerves and conjoined nerve root or a low-lying nerve root. The size of the foramen is an important preoperative parameter to be analyzed before performing the procedure.

In central disc herniations, a more horizontal approach (~20°&#;25°) and foraminoplasty is required. The horizontal approach can injure the traversing nerve root. In these cases, it is better to hit the needle to the superior facet first and then graze the needle ventral to the superior articular process (SAP).[456] If the patient complains of severe pain during the working channel insertion procedure, the working channel floating technique is recommended.

In extraforaminal disc herniations, the exiting nerve root is displaced posteriorly. Hence, a more medial skin entry point with a less horizontal access (~45°) and targeting the mid-pedicular line avoid this risk.[]

For upper lumbar disc herniations, it is important to know that the dural sac lies more laterally and anteriorly. The posterolateral portion of the disc is covered by the dural sac. The dural sac at these levels is more tightly packed with neural tissue and has less cerebrospinal fluid (CSF) buffer. Hence, for L1-L3 levels, a steeper approach (35°&#;45°) and a more lateral landing point are recommended[] [Figure 4].

Figure 4:

Transforaminal endoscopic discectomy at L2-L3 level. Note that the entry point is relatively medial and the angle is steeper compared to L4-L5 level

Dural tear of the thecal sac and the nerve root can occur. The tear may be caused by endoscopic forceps or laser. If recognized intraoperatively, it should be sealed with a fibrin sealant. If unrecognized, serious neurological deficits may develop due to nerve root herniation and strangulation through the rent. Patients with unrecognized dural tear show less-favorable outcomes than those with a recognized dural tear.[13] Hence, the instruments should be handled gently and under vision. Any tug on the forceps that causes pain indicates a bite on the neural structures and should be released immediately. An unrepaired dural tear may be the cause of a residual pain if an intradural herniation develops.[14]

Injury to vascular structures

There are no major vascular structures at risk in the transforaminal endoscopic approach. Nevertheless, few reports of vascular injury have been described in literature.[] The lumbar radicular artery can be injured during the procedure. This can cause a retroperitoneal hematoma, which may require a surgical evacuation.[18] Use of intraoperative angiography and embolization via an iliac artery to treat the injured lumbar artery has also been described.[17]

Bleeding from the epidural venous plexus may also be notorious some time. If not controlled adequately, it may cause an epidural hematoma.

Sometimes in extraforaminal disc herniations, when the approach is more vertical, inadvertent perforation of the anterior discal margin may cause abdominal vasculature injury.[18]

Injury to the peritoneal contents

A too medial or a too lateral entry point may cause the needle to enter into the peritoneal sac. The needle may perforate the bowel, the ureter, or even the vasculature. If the needle enters a bowel before entering the disc space, it may cause contamination of the disc space with the intestinal flora.[] This may cause spondylodiscitis postoperatively. Bowel and ureter injuries with the use of laser and forceps have also been described in literature.[] Entry of the needle should always be localized to the area of the back musculature, which can be analyzed on axial MRI as the safety triangular zone [Figure 5].

Figure 5:

The safe triangular zone of needle trajectory seen on axial MRI. Lateral to this zone is the peritoneum that should be avoided at all costs

Hence, it is important that the needle tip is posterior to the posterior vertebral line in lateral view. If intestinal penetration is suspected, a new needle is used. Careful evaluation of the abdominal contents on axial section of the computed tomography scan or MRI along the planned approach is essential.

If an unexpected contamination of the needle is recognized intraoperatively, copious irrigation of the disc space with antibiotic saline is recommended. Postoperatively, a careful watch on the laboratory markers is essential. C-reactive protein and erythrocyte sedimentation rate (ESR) are important markers of early infection.[]

Missed fragment

An inadequate decompression with incomplete removal of the fragment is possible in the early phase of the learning curve of the procedure. Even in experienced hands, certain herniations are technically difficult. In literature, huge central disc herniations and highly migrated disc herniations have high failure rates.[]

The success of the procedure lies in proper preoperative planning based on the MRI. Inaccurate docking of the working channel is a common mistake leading to incomplete removal of the fragment. The approach may be modified depending on the type of herniation. Numerous approaches have been described in literature. A highly migrated disc may require an ipsilateral interlaminar approach, a contralateral interlaminar approach, a transpedicular approach, a contralateral transforaminal approach, or a transfacetal approach.[] A modified &#;mobile outside-in&#; technique has also been introduced.[39]

A central disc herniation requires a more horizontal approach and foraminoplasty with down levering of the working channel to reach the herniated fragment.[]

Adequate decompression can be judged by free pulsation of the dural sac and nerve root, correlation of the removed fragments with the size calculated on preoperative MRI, and free passage of the nerve hook into the epidural space.[41]

Other local complications

Other uncommon complications include injury to the pedicle during transpedicular approach, instrument breakage during the procedure, and facetal violation due to excess drilling and wrong-level surgery.[]

INTRAOPERATIVE COMPLICATIONS - SYSTEMIC

These complications occur at a site remote to the site of surgery. These are uncommon but are serious and hence need to be kept in mind.

Posterior neck pain and seizures

The occurrence of seizure is rare (0.02%), although it is a potential serious complication during the procedure. Irrigation of the working field with saline is the cause. Increased pressure of irrigation to control bleeding or longer operative time causing massive saline infusion may lead to rise in the epidural pressure. This in turn causes shift of CSF cranially toward the brain and raising the intracranial pressure, which may cause seizures. The onset of the complication is indicated by posterior neck pain. Hence, such a complaint by the patient during the procedure must be heeded to and the procedure should be stopped immediately.[]

POSTOPERATIVE COMPLICATIONS - IMMEDIATE

Postoperative dysesthesia

It is a complication that is distressing to both the patient and the surgeon. The etiology is the excessive manipulation of the dorsal root ganglia of the exiting nerve root or injury to exiting nerve root. This leads to pain in a dermatome different from the preoperative pain that distresses the patient.[] Sometimes, injury to the furcal nerve may also be the cause.[2]

The symptom is usually transient with reported incidence of 2%&#;3% and subsides on its own with conservative management.[2] It is generally common with extraforaminal disc herniations.[8]

Careful handling of the instruments and proper needle targeting under C-arm is the key to avoid this complication. Excessive craniocaudal angulation of the scope to access a highly downmigrated disc herniation may also cause exiting nerve root compression and postoperative dysesthesia.

Residual pain

Persistent pain after surgery, without a period of short-term relief, is termed as residual pain and is an indication of failure of the procedure. The most common cause is incomplete removal of the disc fragment, leading to persistent compression of the neural elements. Other less common causes may be a nerve root injury by the laser or forceps or a dural tear causing nerve root herniation.[13]

The pain caused by residual fragment is more likely with migrated and huge central disc herniations as mentioned earlier. Hence, a proper preoperative planning is essential to address the herniated fragments. The release of the annular anchorage of the herniated fragment is the key to success. This can be carried out using a cutting forceps or a laser. The herniated fragment is composed of the epidurally extruded fragment and an intradiscal portion. The complete removal of both parts is necessary for a complete herniectomy. The tip is to see the other end of the annular fissure to mark a complete herniectomy.[3] The end point of the procedure is by the signs mentioned previously, that is, free mobilization of dural sac and nerve root and correlation of the removed fragments with the size measured on preoperative MRI.

De novo disc prolapse

This is a unique complication of the inside&#;out technique of transforaminal discectomy, which has been described recently.[46] In their report, Choi et al. described postoperative MRI of three patients who underwent the inside&#;out technique and developed new upmigrated disc herniation. Two of three patients were treated conservatively, whereas one required a repeat transforaminal endoscopy. They postulated that increased pressure of intradiscal dye injection and hammering the obturator led to increased intradiscal pressure causing extrusion of more nucleus pulposus into the epidural space. Hence, they recommend gentle dye injection and serial dilatation before gentle insertion of the obturator to avoid this complication. Although rare (0.2%), the possibility of de novo disc prolapse should be kept in mind.

Neurological deficit

It is an uncommon, but ghastly disastrous complication of the procedure. Injury to the exiting or the traversing nerve root or herniation of the nerve root through an unrepaired dural rent may be the cause.[]

Sometimes, an epidural hematoma may compress on the thecal sac and cause these symptoms.[47]

Epidural hematoma

An unrecognized injury to the lumbar artery or more commonly, bleeding from the epidural venous plexus may lead to a local hematoma formation. The hematoma may compress the neural elements and cause radicular pain and/or neurodeficit.[17]

Most of the cases of epidural hematoma are benign and require no intervention. However, in cases of late presentation or with worsening neurodeficit, a repeat endoscopic exploration is warranted.

Psoas hematoma

This is a rare complication that results from lack of adequate hemostasis during the procedure. The epidural venous plexus communicates with the ascending lumbar vein. Uncontrolled bleeding from these vessels leads to psoas hematoma that manifests in the form of anterior thigh pain.

This is a self-limiting complication that resolves with conservative management.[48]

Retroperitoneal hematoma

This is caused by the injury to the vasculature around the operative level as described earlier. The management of these conditions is stated previously.[18]

Other Complications

Although rare, systemic complications such as dyspnea, respiratory failure, and deep vein thrombosis have also been reported.[49]

POSTOPERATIVE COMPLICTIONS - DELAYED

Postoperative spondylodiscitis

This is one of the dreaded and uncommon complications of endoscopic discectomy. The diagnosis is suspected by severe back pain out of proportion to the physical signs and absence of radicular pain. Even the slightest movement causes spasm of back muscles and back pain. The patients are confined to the bed and may have fever. Laboratory parameters such as C-reactive protein and ESR are raised. MRI with a gadolinium contrast is the gold standard for diagnosis.[]

The etiology is varied. The infection may come from improperly sterilized instruments and endoscope, dye, bacteremia from a urinary tract infection, or the intestine. Iatrogenic perforation of the bowels by spinal needle leading to spondylodiscitis has been described earlier. In the latter case, Escherichia coli is the most common pathogen isolated.[18]

Usually, a repeat endoscopic exploration with thorough wash and debridement is recommended.[52] Samples should be taken for culture and biopsy during the procedure. After organism isolation, sensitive antibiotics may be continued for 4&#;6 weeks until the infection subsides.[23]

In some cases of fulminant infection or accompanying instability or vertebral osteolysis, one may need to perform an open debridement and bone grafting with autologous bone and posterior instrumentation.[52]

Psoas abscess

A single case report of psoas abscess caused by needle penetrating the intestine and seeding the pathogen into the psoas muscle has also been described in literature.[53]

Post-discectomy pseudocyst formation

The pathology was first described in patients with post-endoscopic discectomy by Kang and Park[54] in . In their analysis of cases, 15 patients (1%) developed this condition. A post-discectomy pseudocyst appears on MRI as a cystic lesion at the site of discectomy, which is hyperintense in T2-weighted images and hypointense in T1-weighted images.[54]

Clinically, the patients complain of radicular pain similar to that before the surgery. About half of the cases resolve with conservative treatment. In their series, the authors operated five patients with repeated endoscopy. The development of post-discectomy pseudocyst was more related to interlaminar endoscopy and less to transforaminal procedures. As they do not have a cystic wall lining, they are called pseudocyst. The pathogenesis is due to inflammation of the connective tissue at the operated disc site. The condition develops on an average of 2 months after the index procedure.[54]

Recurrence of herniation

Recurrence of herniation is defined by reappearance of radicular pain after an initial symptom-free period. The period may be in weeks or months. The recurrent herniation may occur at the same level and the same side or on the contralateral side.

The recurrence rate with endoscopic discectomy is similar to the gold standard microdiscectomy procedures.[55] A repeat endoscopic surgery is equally effective for recurrent disc herniations.[]

Although the notion prevails that selective fragmentectomy as opposed to conventional aggressive discectomy may increase recurrence rates, recent studies have disproved this hypothesis.[58]

Other complications

1. Instability: This may be caused by excess removal of the disc material during discectomy. The probability of this complication with transforaminal procedure is very unusual and may occur with interlaminar endoscopy and aggressive discectomy.
2. Epidural scarring and fibrosis: This complication can occur only with interlaminar endoscopy and is hardly seen with transforaminal procedures.
3. Chronic axial back pain: This complication too is less likely with transforaminal procedures. The annuloplasty procedure performed during transforaminal discectomies may have an effect on reducing back pain.[6] However, in cases of huge disc prolapse leading to massive loss of nucleus pulposus may be a cause of chronic back pain necessitating fusion.[]

LIMITATIONS OF ENDOSCOPIC SPINE SURGERY

Apart from these surgical complications, there are some limitations of the endoscopic spine surgery, which are discussed as follows:

1. The learning curve is substantial. Although most of the surgeons are not exposed to spinal endoscopy during their residency, it is generally difficult to incorporate it into routine practice.
2. The cost of the instrumentation is significant. This hinders its applicability in developing countries.
3. The radiation exposure associated with transforaminal procedures is more than other minimally invasive techniques. Hence, care should be taken for exposure prevention.[39]
4. Again, it should be remembered that conventional microdiscectomy/interlaminar endoscopic discectomy may be a more favorable option in some cases such as a highly downmigrated disc herniation at L5-S1, calcified disc herniations, and associated central stenosis.

COMPLICATIONSAND LIMITATIONS OF PERCUTANEOUS INSTRUMENTATION

The use of percutaneous implants is increasing with the rise of minimally invasive spine surgery. The complications and limitations of percutaneous instrumentation are as follows:

1. Increased radiation exposure: As the implants are introduced under C-arm guidance in most of the cases, the radiation exposure to the operating room personnel increases significantly. Hence, necessary safety precautions such as use of lead gloves, lead apron, and radiation protection glasses are necessary.[61] The introduction of three-dimensional navigation has reduced the radiation exposure and increased the precision markedly.[]
2. Difficulty with long-segment constructs: Although short-segment constructs are easy with percutaneous instrumentation, it is cumbersome for long-segment constructs in inexperienced hands or surgeons performing long-segment MIS surgeries rarely. The contouring and insertion of the rod and placement of bone graft are the main technical issues. However, we hope that with further advancements in instrumentation, these technical difficulties will be taken care of.
3. Biomechanical restoration: Sometimes, it is difficult to achieve a good natural curvature of the spine with percutaneous rods. Also, bone grafting is limited and hence in long-segment fusions, additional procedure such as anterior grafting may be required.
4. Other disadvantages: These include difficulty with revision procedure, difficulty with use of instruments, and difficulty at junctional levels such as cervicothoracic junction and lumbosacral junction.

CONCLUSION

The concept of transforaminal endoscopic procedures is targeted fragmentectomy with minimal disruption of normal anatomy. The technical advances have broadened the indications of the procedure and have also improved its efficacy. However, with increasing applications, the risk of unexpected adverse events increases. Hence, diligent handling of the instruments with insight into the potential complications is necessary to improve the outcome.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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