Avoiding Complications in Minimally Invasive Spine Procedures

50 Avoiding Complications in Minimally Invasive Spine Procedures


Gabriel A. Smith and David J. Hart


Abstract


This chapter is a review of many of the most frequently utilized minimally invasive spine surgery procedures, presented from the perspective of complication avoidance with a particular emphasis on avoiding complications through awareness and anticipation of these complications. Thus, prevention is emphasized as the best means of managing complications whenever possible. Cervical, thoracic, and lumbar procedures are reviewed, with both common pitfalls and rare but potentially devastating complications discussed. Anterior, lateral, posterolateral, and posterior procedures are included. Tubular access, endoscopic, and percutaneous approaches are discussed. Anatomic and technical considerations are evaluated with a goal of understanding the potential risks of each procedure, and complication management is discussed for cases when prevention fails.


Keywords: minimally invasive spine surgery, complications, minimal access spine surgery, percutaneous, complication avoidance


50.1 Introduction


The use of minimally invasive spine (MIS) procedures is rapidly increasing. This is partly due to patient demand, improvements in techniques, and the physician’s desire to provide less invasive treatment options. These techniques can also result in improved patient outcomes and a reduction in costs. The less invasive nature of these techniques reduces approach-related morbidity by preserving normal anatomic muscular, ligamentous, and bony structures of the spine. These procedures attempt to focus the operative dissection on the pathologic condition being treated. Currently effective minimally invasive approaches have been proven efficacious and safe for pathology in the cervical,1,2,3,4 thoracic,5,6,7,8,9,10 and lumbar spine.11,12,13,14,15,16 However, long-term outcomes are still under investigation in most instances.


Whether the surgeon is operating through a tubular retractor, with an endoscope, or under a microscope, a mastery of the anatomy and pitfalls must be understood to avoid complications. Comfort with these techniques starts with understanding the equipment used in each particular procedure. Using tubular retractors makes orientation difficult, but concurrent use of an operating microscope or loupe magnification permits better visualization and can help facilitate these procedures. To help guide the surgeon, fluoroscopy or image guidance technology can be used. In some cases, complications can be higher, such as the incidence of dural tears, particularly in early case series, until the operator becomes more proficient with the technique.17 Training in live animal and cadaver surgeries, as well as working closely with a surgeon experienced in MIS, can lead to mastery of these techniques. Fellowships, training courses, and instructional material are increasingly becoming available to facilitate the mastering of MIS procedures and reducing patient risks.


50.2 Cervical Complications


50.2.1 Minimally Invasive Posterior Cervical Laminoforaminotomy


Recently microsurgical techniques have been applied to perform decompression for foraminal stenosis causing cervical radiculopathy using the microendoscopic discectomy (MED) technique and instrumentation.1,3,18 This muscle-splitting approach is effective in limiting postoperative pain and muscle spasms while maintaining the integrity of midline posterior muscular and ligamentous attachments to the spine. This technique can be performed in the semisitting position (image Fig. 50.1) or prone. Under fluoroscopic guidance a Kirschner wire (K-wire) or small dilator should be docked directly over the facet joint of interest (image Fig. 50.2). If the surgeon is not careful, the initial K-wire or smaller dilators can be inadvertently pushed between the cervical laminae, leading to potential serious spinal cord or nerve root injury during the approach. Additionally, lateral displacement of the K-wire or dilators can result in nerve root or vertebral artery injury, or brisk venous bleeding from the venous plexus surrounding the vertebral artery. Once the final dilator and tubular retractor are placed over the facet complex, the surgeon can continue with the facetectomy and foraminotomy.


A dural tear is the most commonly encountered complication. Adamson1 retrospectively reviewed 100 cases of patients undergoing posterior cervical microendoscopic laminoforaminotomy (MEF) and reported complications in three patients; two cases of dural puncture required no intervention other than Gelfoam, and in one case a superficial wound infection was reported. Khoo et al4 reported three complications in 25 patients that were attributable to surgical technique. These included two small cerebrospinal fluid (CSF) leaks and one case of partial-thickness dural violation. After 2 to 3 days of routine lumbar drainage for patients with CSF leaks, none of these patients went on to have long-term clinical sequelae. Primary repair or tamponade with a small piece of Gelfoam or DuraGen followed by fibrin glue application are other options for repair. Patients should be well advised of this potential complication, but also counseled that with appropriate management it generally results in no long-term complications.19


50.2.2 Anterior Cervical Foraminotomy


An anterior cervical foraminotomy is effective for unilateral radicular symptoms, but has not been readily adopted due to technical difficulties and risk of vertebral artery injury.2,18 The primary risk of the procedure is inadvertent injury to the vertebral artery during drilling of the uncovertebral joint.


Jho2,18 identified three potential sites of vertebral artery injury: at the C6–C7 level, lateral to the uncinate process, and at the transverse foramen. The C6–C7 site has a high risk of injury to the vertebral artery because it courses between the transverse process of C7 and the longus colli muscle. To avoid vertebral artery injury, Jho recommended incising the longus colli muscle at the level of the C6 transverse process. The muscle stump is then reflected toward the C7 transverse process to expose the vertebral artery, which lies under the longus colli muscle. At the uncinate process, vertebral artery injury can also be avoided by leaving a thin layer of cortical bone during drilling of the uncovertebral joint.2,3,18 This bone is then removed with a curette after drilling is completed. However, the transverse foramen should not be entered during drilling to avoid vertebral artery injury, and brisk venous bleeding is a warning the venous plexus that surrounds the vertebral artery in the foramen has been encountered.




Injury to the vertebral artery could be lethal and difficult to repair.20,21,22 Packing with Gelfoam, muscle, and/or bone wax, followed by angiography, should be performed if primary repair cannot be performed. Direct exposure of the vessel in the foramen is exceptionally challenging, even in the most skilled surgeon’s hands.20,21,22


The sympathetic chain is another structure that can be injured because it lies just anterior to the longus colli muscle. Injury results in Horner’s syndrome. Efforts to adequately retract the longus colli muscle laterally and restricting muscle dissection to the most medial aspect can reduce the risk of sympathetic chain injury.


Failure to adequately decompress the nerve root by leaving residual disc or osteophyte due to unfamiliarity with the surgical approach can be avoided by performing a cadaveric anterior cervical foraminotomy study before performing this procedure. Additional complications can be related to poor patient selection. Those patients with mechanical neck pain do poorly with simple nerve root decompression. Performing this procedure at junctional levels (i.e., cervicothoracic junction and levels adjacent to previous fusions) may result in mechanical neck pain after partial removal of the uncovertebral joint because of preexisting poor biomechanics. Similarly, patients with asymptomatic contralateral foraminal narrowing at the same level may develop new radicular symptoms contralateral to the anterior cervical foraminotomy, likely because of hypermobility after the procedure.23


50.2.3 Microendoscopic Anterior Cervical Discectomy and Fusion


Microendoscopic anterior cervical discectomy and fusion has recently been performed using a tubular retractor and endoscopic visualization to perform the procedure. The muscle dilators and tubular retractor are placed only after the cervical vertebral bodies are approached and identified through a standard fascial approach medial to the sternocleidomastoid muscle. Dilators should never be placed blindly, because significant potential for injury to the anterior neck structures exists (e.g., carotid artery, esophagus, and trachea). The tube through which the procedure is performed simply acts as a retractor. Difficulties encountered with this technique include the limited working space and inability to distract the disc space. The potential benefits of this approach may include reduced postoperative dysphagia. A recent clinical study did find the tubular retractor technique useful for anterior odontoid screw fixation in repairing type II odontoid fractures.24 The primary risks associated with anterior odontoid screw fixation are related to exposure and relatively blind passage of the screw during placement.25 The tubular retractor technique appears to facilitate safe screw placement by maximizing intraoperative visualization and rigid fixation of the retractor to the table.24


50.3 Thoracic Complications


50.3.1 Thoracoscopic-Assisted Decompression Techniques


The potential complications associated with thoracoscopic procedures are similar to those associated with open thoracotomy, although the incidence varies. There is a reduced incidence of post-thoracotomy pain, intercostal neuralgia, pulmonary dysfunction, and scapular dysfunction associated with a thoracoscopic compared to an open approach.26,27,28,29,30,31 Complications may arise from patient positioning, port placement and access, and manipulation of instruments with injury to the lung parenchyma or thoracic vascular structures.28 Expertise in performing an open thoracotomy does not necessarily translate to expertise in thoracoscopic procedures, and additional training to master this technique is required.32,33,34 Many surgeons elect to have a thoracic surgeon assist with the opening to avoid or minimize these risks.


Patient selection is important to avoiding complications. Extensive lung adhesions, prior thoracic procedures resulting in extensive scar formation, severe scoliosis, and advanced thoracic vascular disease such as an aortic aneurysm often make the approach perilous. Single lung ventilation is required for access, and patients with a history of smoking and chronic obstructive airway disease are often difficult to adequately ventilate, which can lead to serious intraoperative hypoxia and acidosis from CO2 retention. These patients need to undergo preoperative testing of pulmonary function prior to elective surgery and urgent cases must be performed with caution. Complications resulting from prolonged nonventilation of one lung may lead to the accumulation of excessive secretions in the airways.35,36 Therefore, in prolonged operative procedures, an aggressive postoperative pulmonary toileting can prevent significant “down-lung” atelectasis and pneumonia. Additionally, intraoperative positive end-expiratory pressure (PEEP) on the ventilated lung and continuous positive airway pressure (CPAP) on the nonventilated lung can significantly reduce these complications.


Patients undergoing thoracoscopic procedures are placed in the lateral decubitus position; therefore, adequate padding by placing an axillary roll under the chest to prevent pressure on the brachial plexus in the axilla is critical.5,6 Traction injuries to the brachial plexus by abducting the arm on the operated side must be prevented. Other pressure points, particularly the common peroneal nerve at the fibular head, should also be adequately padded to avoid postoperative peroneal nerve palsy.


The initial port is commonly placed at the sixth or seventh intercostal space for mid- and lower thoracic spine pathology and in the fourth or fifth intercostal space for upper spine pathology. The initial endoscopic port is the only port that is placed blindly and can result in injury to the lung parenchyma and other vascular structures in the chest. Therefore, lung adhesions, which cause the lung to adhere to the chest wall, can result in lung injury during port placement and postoperative pneumothorax. To prevent this complication, a finger is passed through the port site and swept circumferentially within the chest cavity to release any adhesions before placement of the port.


With the lung collapsed, the diaphragm can ride up and be perforated during placement of lower thoracic ports, with possible injury to structures under the diaphragm. To overcome this problem, all ports after the initial port should be placed under direct endoscopic vision. Injury to the intercostal nerve, artery, or vein is also possible during trocar placement. Damage to the nerve can result in severe postoperative pain and dysesthesia.6,37


It is imperative that all ports, after the initial endoscopic port, be placed under continuous endoscopic vision and that all instruments be visualized from entry to exit from the chest cavity. Bleeding from port sites can be more a nuisance than a complication and can be controlled with bipolar coagulation. If the bleeding at the port site is severe, a Foley catheter can be inserted and the balloon inflated to tamponade the bleeding. If the bleeding cannot be stopped by the aforementioned techniques, the wound may need to be enlarged to identify and control the bleeding. Injury to large intrathoracic vessels rarely occurs, but a thoracotomy tray must be in the room ready to be opened in the event of uncontrollable bleeding. Pneumothorax requiring a chest tube is common and many surgeons leave a pigtail catheter or chest tube in place for a few days after the procedure.6,36,37,38,39,40,41


50.3.2 Thoracoscopic Microdiscectomy


Thoracic disc herniation is a relatively common disorder identified by magnetic resonance imaging as 14.5% of all disc herniations.42 The vast majority of these herniations are asymptomatic and do not require surgical intervention. Surgery is reserved for those patients with long-tract signs of myelopathy and with thoracic radicular pain corresponding to the herniated disc level who have failed conservative management.


With improvements in operative instrumentation, the treatment of this condition using thoracoscopic techniques has evolved.10,37,43,44,45,46,47 Nevertheless, the steep learning curve, instrumentation setup cost, and infrequency of symptomatic thoracic disc herniations have limited the widespread use of thoracoscopic discectomy. Complication rates vary per series, but the types of complications are similar to those seen in open thoracotomy procedures. Reports cite a lower incidence of costovertebral neuralgia, postoperative respiratory complications, and chest pain using thoracoscopic techniques compared to the more traditional open procedure.6,36,37,38 In one series, the incidence of complications of disabling intercostal neuralgia (50% open vs. 16% thoracoscopic) and postoperative atelectasis and pulmonary dysfunction (33% open vs. 7% thoracoscopic) clearly showed less postoperative discomfort.47


50.3.3 Minimally Invasive Costotransversectomy Approach


Recent developments have been made in the application of a minimally invasive costotransversectomy technique to treat thoracic disc herniations and neoplasms. The advantage of this technique is that the approach is via a posterior muscle-splitting technique and avoids entering the thoracic cavity. Complication avoidance relies on adequate fluoroscopic visualization and level localization along with proper docking of the K-wire, muscle dilators, and tubular retractor in a paramedian fashion. Calcified disc herniations should be approached by more conventional means, namely, thoracotomy or MIS thoracoscopic approaches. The lateral approach taken, generally 3 to 5 cm off the midline depending on patient size, as well as the angled visualization used in this technique, reduces the risk of thoracic spinal cord manipulation over a traditional posterior approach. Obvious complications that should be reviewed with the patient include the risk of spinal cord injury, pneumothorax, and dural tear with CSF leak. Fluoroscopy, in both the anteroposterior (AP) and lateral views, is helpful in orienting the surgeon during the surgical approach. Although recently introduced, this procedure has been successful in treating patients with acceptably low complication rates.48,49,50


50.3.4 Vertebroplasty and Kyphoplasty


Vertebroplasty has become an effective treatment modality for painful debilitating osteoporotic vertebral body compression fractures.51,52 Methylmethacrylate is currently the most widely used vertebral cement filling product. Further applications beyond the treatment of osteoporotic compression fractures have included spine fractures caused by spinal metastasis and myeloma.53,54 The reported incidence of complications with vertebroplasty is less than 10% with most coming from cement leakage outside the vertebral body.52,54,55,56,57 There is a reported higher incidence of cement leakage leading to radiculopathy or spinal cord compression in those patients undergoing vertebroplasty for metastasis or myeloma compared to those treated for osteoporotic compression fracture.51 The reported incidence of radiculopathy and cord compression from cement migration was 4% and less than 0.5%, respectively, in those patients treated for osteoporotic compression fractures.56,58,59


To reduce the incidence of complications related to cement migration, more recent reports suggest that partial filling of vertebral bodies (< 30% by volume of the vertebral body) can result in successful clinical outcomes (reduced pain, adequate strengthening, and stabilization of fractured vertebrae).51 One recent study by Liebschner et al suggests that only approximately 15% volume fraction is needed to restore stiffness to pre-damaged levels and that greater filling may result in a substantial increase beyond an intact level.60 Another study has shown vertebral body strength restoration and favorable clinical outcomes with as little as 2 mL of cement injected.54,56 Smaller filling volumes could conversely reduce the risk of cement extravasation outside the vertebral body and reduce load-bearing forces on adjacent vertebral bodies.


The kyphoplasty procedure was developed to help restore vertebral body height as well. The vertebroplasty technique requires that methylmethacrylate cement be injected directly into the vertebral body compression fracture under relatively high pressure, which could result in cement extravasation. Conversely, the kyphoplasty technique insufflates a balloon within the compression fracture, restoring the vertebral body height. The cement is then injected into the cavity made by the balloon under low pressure, thus reducing the incidence of cement extravasation. Preliminary data suggest that kyphoplasty is a safe procedure associated with a lower risk of cement extravasation than vertebroplasty, and it can restore vertebral body height.55,56,61,62


50.4 Lumbar Complications


50.4.1 Minimally Invasive Microdiscectomy


Tubular retractor systems combined with a microscopic or endoscopic technique allow spine surgeons to reliably decompress a symptomatic lumbar nerve root via a minimally invasive approach with limited morbidity.16,63 These systems offer the surgeon a direct working corridor to the nerve root while minimizing tissue trauma, yielding less postoperative pain, a smaller incision size, and lower hospital lengths of stay.


Using fluoroscopic guidance to localize the level of interest, a 2-cm incision is made roughly 1 cm off the midline on the symptomatic side. A K-wire is used to dock onto the facet joint and tubular dilators are then used to spread the muscle apart prior to placement of the retractor system. A serious technical complication can occur with improper K-wire placement. Most surgeons recommend using fluoroscopy and ensuring that the K-wire is docked onto the medial aspect of the facet prior to proceeding with tubular dilation. Thecal sac penetration or nerve root injury can occur if the K-wire is not docked carefully. The most common technical complication is a dural tear, estimated to occur at an incidence of 5%, but clinical series have shown low morbidity.63 In a series of 100 consecutive patients, complications included 3 patients with dural tears that were all repaired intraoperatively and 1 patient with a delayed pseudomeningocele formation.64 A prospective multicenter clinical study has shown the efficacy of this system in treating lumbar disc disease.14,63,65


50.4.2 Automated Percutaneous Lumbar Discectomy


Automated percutaneous discectomy is reserved for a small number of highly selected patients with an isolated herniated disc, excluding those patients with sequestered disc fragments, synovial cyst, or bony compression as a cause of radicular symptoms.14,64,66,67,68 However, it is estimated that only 3 to 4% of disc patients treated surgically actually meet the criteria for percutaneous nucleotomy.69,70


The primary morbidity of the procedure is discitis, which may result from scraping of the end plates by the automated Nucleotome during disc removal. Only two cases of cauda equina injury have been reported; these occurred in heavily sedated or anesthetized patients.71


50.4.3 Percutaneous Thoracolumbar Pedicle Screw Instrumentation


Innovations in the application of thoracolumbar spine instrumentation have resulted in systems that can now be applied in a less invasive manner.72,73,74 Percutaneous pedicle screw placement is commonplace now, but pitfalls do exist that can lead to serious complications. Inaccurate image guidance or poor visualization on fluoroscopy can lead to poor screw placement. Medial breach of the pedicle can cause injury to the neural elements and must be avoided.75 After accessing the pedicle, careful manipulation of the K-wires must be taken as these can bend or fracture if the surgeon is not careful. Rod placement can oftentimes be difficult if screws are poorly aligned, scoliosis is present, or long-segment fixation is being performed. The first mistake is often trying to pass the rod above the fascia. A lateral X-ray can prevent this by visualizing the rod at the level of the screw heads. Next, as the rod is passed through each screw head in succession, the surgeon should confirm this is going through the tower by manual manipulation of the rod and attempting to rotate the screw extensions—if the rod has been passed successfully, they will not rotate.


Recently a variation in this technique has been developed that employs the use of a specially designed device that sits on top of the superior facet complex to act as a guide for K-wire placement through the pedicle (P-C Pedicle Access Device; Spinal Concepts, Austin, TX). Once an AP view of the pedicle is achieved, the K-wire can be passed through the pedicle in a “bull’s-eye” fashion (image Fig. 50.3). Although the K-wire and subsequent tap and pedicle screw are placed directly down the middle of the pedicle, a less medial trajectory reduces the potential risks of violating the medial wall of the pedicle. In a series of 100 consecutive percutaneous pedicle screws placed in 25 patients by means of this technique and evaluated with postoperative computed tomography, 96% of pedicle screws were found to be directly within the pedicle (image Fig. 50.4), 3% had slight medial screw thread violation not requiring repositioning, and 1% had slight lateral screw thread violation not requiring repositioning.74,76 Therefore, this technique for percutaneous pedicle screw placement can add a margin of safety to preventing medial wall violation and neural injury. Robotic percutaneous screw placement is also being investigated as a possible means to reduce screw malpositioning.77,78


50.4.4 Minimally Invasive Posterolateral and/or Transforaminal Lumbar Interbody Fusion


Posterior minimally invasive techniques for lumbar fusion are one of the hallmarks in MIS. Two- to three-level open lumbar fusions can be exceptionally morbid procedures with high rates of postoperative pain, long lengths of stay in the hospital, and dissatisfied patients from large incisions. Using a minimally invasive tubular retractor system, a paramedian approach can be taken. Similar techniques to percutaneous pedicle screw placement can be performed, but the addition of a tubular retractor can allow posterolateral arthrodesis and fusion or the placement of a transforaminal interbody device into the disc space to aid in fusion.12,15 Identification of the transverse processes laterally and decortication can be performed prior to placement of pedicle screws on the contralateral side to where the interbody will be placed. After placement of screws on the contralateral side, if a spondylolisthesis is present, a reduction can be attempted. Risks to performing a reduction include nerve root injury, or screw failure with pullout or fracture.79 A tubular retractor can then be used to visualize the facet joint on the interbody side of the procedure. After removal of the facet joint and identification of the nerve root, the disc space can be accessed and an arthrodesis can be performed for placement of an interbody graft to promote fusion. Nerve root injuries from traction or direct damage can occur during placement of an interbody cage or from instruments used to prepare the disc space for fusion. Wong et al80 published a retrospective series of 513 patients undergoing MIS transforaminal lumbar interbody fusion (TLIF) to evaluate complication rates. Their overall complication incidence was 15.6% (80/513), broken down into durotomies (5%, 26/513), urinary retention (1.4%, 7/513), K-wire fracture (1.2%, 6/513), pulmonary embolism (1.0%, 5/513), cage migration (1.0%, 5/513), nerve root injury (0.8%, 4/513), ileus (0.8%, 4/513), hematoma (0.8%, 4/513), and others (0.4%, 2/513).80 The incidence of complications was comparable to open TLIF in the literature and suggests MIS TLIF is safe and efficacious.


50.4.5 Lateral Retroperitoneal Transpsoas Interbody Fusion


Lateral minimally invasive techniques for lumbar decompression are becoming mainstream in modern spine surgery. A lateral retroperitoneal transpsoas approach allows the surgeon access to midlumbar pathology with ease, and allows for indirect and direct decompression for pathologies ranging from neoplasm to deformity. Careful patient selection is paramount as the transpsoas approach is perilous and can result in serious complications. Prior infections or retroperitoneal procedures could cause significant scarring of the retroperitoneum, making the dissection dangerous to large vessels or the lumbar plexus coursing through the psoas muscle.76,81,82,83,84,85,86 High-grade spondylolisthesis will also cause displacement of the lumbar plexus and should not be considered for this procedure. Above L2, the surgeon must take into account the 12th rib and crural attachments of the diaphragm. Below the L4–L5 disc space, the iliac crest may prevent docking, and nerve root injury through a transpsoas approach has been shown to be more common at L4–L5 compared to more cephalad levels due to the posteriorly located lumbar plexus.87,88 Placement of the patient in the lateral decubitus position must be performed with an axillary roll to prevent brachial plexus injury. Skin incision and dissection should only be carried out once true AP and lateral position is confirmed with imaging.88,89,90 Electrocautery can be used until the external oblique fascia is identified, but blunt dissection should be performed through the external oblique, internal oblique, and transverse abdominis muscles until retroperitoneal fat is seen. Sharp dissection can lead to breach of the peritoneum leading to significant morbidity. After palpating the transverse process, the quadratus lumborum, and the psoas muscle, some surgeons opt at this point to place their retractor superficial to the psoas muscle prior to dilation.88,89,90,91 Continuous neuromonitoring is recommended during transpsoas dilation at all levels as nerve root injury rates have been estimated between 3 and 10% persisting up to 18 months after surgery.92 An extremely important point is to ensure that chemical neuromuscular blockade is worn off prior to proceeding. Once the initial probe reaches the annulus of the disc or vertebral body, the probe should be docked into the disc space to prevent migration during dilation, which has led to great vessel injury.82,91 During preparation of the disc space or corpectomy site, caution must be taken not to fracture the end plates or plunge laterally out the contralateral side, potentially resulting in contralateral muscle, vascular, and/or plexus injury. The latter complication is of particular concern when transecting the contralateral annulus fibrosis as part of the anterior release of the disc. Reoperation rates from subsidence, pseudoarthrosis, or persistent symptoms after lateral interbody fusion have been estimated at 10%.93


Oct 17, 2019 | Posted by in NEUROSURGERY | Comments Off on Avoiding Complications in Minimally Invasive Spine Procedures

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