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 1973, 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.
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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.[78910]
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[1112] [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.[151617] 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.[1920] This may cause spondylodiscitis postoperatively. Bowel and ureter injuries with the use of laser and forceps have also been described in literature.[2122] 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.[2324]
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.[2526]
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.[272829303132333435363738] 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.[4640]
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.[2315163637]
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.[4243]
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.[4445] 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.[1316]
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.[5051]
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 2011. In their analysis of 1503 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.[5657]
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
- 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.
- Epidural scarring and fibrosis: This complication can occur only with interlaminar endoscopy and is hardly seen with transforaminal procedures.
- 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.[5960]
LIMITATIONS OF ENDOSCOPIC SPINE SURGERY
Apart from these surgical complications, there are some limitations of the endoscopic spine surgery, which are discussed as follows:
- 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.
- The cost of the instrumentation is significant. This hinders its applicability in developing countries.
- The radiation exposure associated with transforaminal procedures is more than other minimally invasive techniques. Hence, care should be taken for exposure prevention.[39]
- 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:
- 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.[6263]
- 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.
- 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.
- 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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