The role for minimally invasive surgery (MIS) continues to expand in the management of spinal pathology. In the setting of trauma, operative techniques that can minimize morbidity without compromising clinical efficacy have significant value. MIS techniques are associated with decreased intraoperative blood loss, operative time, and morbidity, while providing patients with comparable outcomes when compared with conventional open procedures. MIS interventions further enable earlier mobilization, decreased hospital stay, decreased pain, and an earlier return to baseline function when compared with traditional techniques. This article reviews patient selection and select MIS techniques for those who have suffered traumatic spinal injury.
Key points
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In the setting of trauma where patients can be structurally unstable and hemodynamically labile, operative techniques that minimize morbidity without compromising clinical efficacy have significant value.
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Minimally invasive surgery (MIS) techniques have been associated with decreased intraoperative blood loss, operative time, and morbidity, while providing patients with comparable outcomes when compared with conventional open procedures.
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MIS interventions enable earlier mobilization, decreased hospital stay, decreased pain, and an earlier return to baseline function when compared with traditional techniques.
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MIS techniques designed to reestablish anterior column support include percutaneous vertebral body augmentation procedures and mini-open lateral corpectomy.
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MIS posterior stabilization largely consists of percutaneous fixation techniques that minimize the surgical access footprint and adjacent tissue injury.
Introduction
Traumatic spine fractures represent 75% of all spinal injuries, thus accounting for 160,000 annually, most of which occur at the thoracolumbar junction (T10–L2) due to the transition from the mobile lumbar spine to the rigid thoracic spine. These fractures are typically caused by high-impact injuries, such as motor vehicle accidents and falls, and can result in persistent pain and disability even without neurologic compromise. Early surgical management can potentially prevent, and sometimes reverse, neurologic injury; this may involve decompression, reduction, anterior column support, and/or restoration of the posterior tension band. Operative stabilization with pedicle screw instrumentation via a posterior approach for reduction and fixation of fractures has traditionally demonstrated good clinical and radiographic outcomes and remains the prevalent treatment for most fractures. However, open surgical approaches have been associated with a mixed array of perioperative complications, including infection, significant blood loss, and extended hospitalizations.
Minimally invasive surgery (MIS) has been increasingly used in the treatment of degenerative spinal pathology; however, its utilization in traumatic injury was not reported until 2004 and indications for its usage remained controversial. Due to evolving advancements in MIS technology and practice over the past decade, spine surgeons have established 360° MIS access to the vertebral column enabling anterior, lateral, and posterior less-invasive surgical approaches. Select examples of MIS procedures include percutaneous segmental fixation, vertebroplasty/kyphoplasty, and mini-open lateral access corpectomy/fusion, enabling a less destructive method of fixation and stabilization with limited adjacent tissue destruction. Moreover, proper use of these techniques has been shown to shorten hospital and recovery times, as well as reduce blood loss and perioperative complications. Here we summarize the techniques, controversy, and indications for the use of minimally invasive procedures in traumatic spine injuries.
Preoperative Considerations and Indications
The goals of spinal surgery in the setting of trauma remain consistent with those associated with all forms of spinal pathology, and irrespective of surgical invasiveness: decompression of neural elements, and realignment and stabilization of the vertebral column. The maintenance of adequate spinal perfusion remains critical before, during, and even after decompression of neural elements is achieved. Any injury that results in compression or spinal cord swelling can interrupt the blood supply to the spinal cord; it is thus recommended to elevate Mean Arterial Pressure (MAP) to greater than 90 mm Hg to mitigate hypoperfusion ischemic injury. If intravenous fluids alone cannot achieve target MAP, the use of vasopressors can be initiated to augment spinal perfusion.
The role of intraoperative neurophysiologic monitoring has expanded considerably with the advancements in MIS techniques, as direct visualization of neural structures is limited or absent. The use of electromyography (EMG), motor evoked potentials, and somatosensory evoked potentials (SSEPs) enables the detection of alterations in spinal cord and peripheral nerve function secondary to mechanical or ischemic events.
Patients with minor stable injuries are routinely managed nonoperatively. Those with unstable spinal injuries requiring surgical intervention can largely be divided into 2 groups: those requiring anterior column reconstruction and those requiring posterior segmental stabilization. MIS techniques designed to reestablish anterior column support include percutaneous vertebral body augmentation procedures and mini-open lateral corpectomy. Posterior stabilization largely consists of percutaneous fixation techniques that minimize access footprint and adjacent tissue injury. The following select techniques represent the preponderance of trauma-related MIS procedures in modern day spine practice:
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Vertebroplasty : indicated in patients with focal back pain without evidence of cord compression, minimal loss of vertebral body height (<50%), absence of abnormal angulation (<20°), and no evidence of posterior wall involvement.
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Kyphoplasty : indicated in patients with focal back pain, significant loss of vertebral body height (>50%), and/or kyphotic angulation (>20°) without evidence of canal compromise or posterior wall involvement.
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Lateral Mini-Open Corpectomy : indicated in patients with canal stenosis secondary to comminuted or “burst” fracture patterns, kyphotic angulation, and a greater degree of instability (ie, disco-ligamentous involvement) seen on static or dynamic imaging.
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Percutaneous Posterior Segmental Fixation : indicated in patients with comminuted or “burst” fracture patterns with canal compromise, but with evidence of an intact posterior longitudinal ligament (PLL). Instrumentation serves as a form of “internal brace” to stabilize the segment while fracture healing occurs.
Vertebral Body Augmentation
Vertebral compression fractures commonly occur in the aging osteoporotic population and account for more than $1 billion annual medical expenditures in the United States. MIS treatments are ideal for this population due to their numerous medical comorbidities and risk of perioperative complications, particularly in those suffering and deemed unsuitable for operative intervention. Vertebral body fracture treatment considerations include evaluation of spinal stability, focal kyphotic angulation, presence of canal retropulsion, and involvement of the posterior vertebral wall and ligament. These procedures have historically low operative morbidity and high patient satisfaction rates, and remain an excellent option for elderly patients and those with multiple medical comorbidities in whom greater interventions could not be tolerated. In osteoporotic patients, some institutions advocate prophylactic cement augmentation adjacent to the index fracture level to fortify neighboring vertebral bodies. Rates of new vertebral body fractures in osteoporotic patients following initial vertebral body augmentation have been reported in the literature at rates ranging from 5% to 18%.
Percutaneous vertebroplasty
Patients with focal back pain secondary to a vertebral compression fracture with the posterior wall intact are candidates for vertebral body augmentation. In patients in whom the vertebral body height is grossly maintained (<50% loss), with kyphotic angulation <20°, MIS techniques can be used to perform percutaneous vertebroplasty in which the injured vertebral level is augmented with polymethylmethacrylate (PMMA) to diminish pain by eliminating micro-motion within the fracture. The procedure involves bipedicular cannulation to access the injured vertebral body. The patient is placed in the prone position on the operating table. Anesthesia is delivered via intravenous conscious sedation or alternatively endotracheal intubation. Fluoroscopy is used to identify the target level. The skin is prepped and local anesthetic injected. The needle is carefully introduced under fluoroscopic guidance in a lateral to medial trajectory. The ideal docking site is mid-pedicle on lateral fluoroscopy, and the lateral border of the pedicle on anteroposterior (AP) projection. Tactile resistance of intrapedicular cancellous bone and fluoroscopic confirmation are used to confirm intrapedicular position. PMMA is injected under live fluoroscopy to verify injection site and lack of cement extravasation in real-time. If cement extravasation is detected, the needle can be carefully repositioned to fill the remaining portion of the vertebral body.
Percutaneous kyphoplasty
In the setting of significant vertebral body collapse (>50%) or kyphotic angulation (>20°), kyphoplasty offers a viable option to restore vertebral body height and fortify the effected vertebral body. Kyphoplasty uses the same positioning and approach required to perform a vertebroplasty; however, before cement augmentation, a balloon is introduced into the vertebral body and expanded under live fluoroscopy to reestablish vertebral body height and reduce focal kyphotic angulation. Similarly, PMMA is injected into the vertebral body to provide permanent stability within the fracture.
A systematic review found that vertebroplasty and kyphoplasty provided significant pain relief in 87% and 92% of patients, respectively. However, cement extravasation was seen in up to 41% of patients with vertebroplasty and 9% with kyphoplasty. Postprocedural rates of adjacent level vertebral body fractures after vertebral body augmentation in the vertebroplasty group was approximately 7.4% and 6.5% in kyphoplasty. This is thought to be due to alteration of forces distributed across adjacent levels secondary to increased stiffness at the treated segment. Other factors that contribute to an increased rate of adjacent level vertebral body fractures are decreased bone mineral density, and postprocedure kyphotic angulation (>9°). Remotely, there have been rare case reports of pulmonary embolus secondary to hematogenous spread of bone cement via the epidural venous plexus.
Anterior Approach
In cases in which trauma to the spine results in injury to the anterior and middle columns, it is important to determine if surgical intervention needs to include anterior column support and stabilization. The thoracolumbar junction is particularly prone to injury given the unique biomechanical properties of the region. Angulated 2-column fractures, 3-column fractures, and fractures with evidence of disco-ligamentous involvement represent injury patterns that are traditionally treated with anterior column repair techniques, as it enables direct visualization of the anterior spinal elements and thecal sac.
Mini-open corpectomy
Patients are placed in the true lateral position. After padding of all pressure points, including the brachial plexus with an axillary roll, proper patient positioning is confirmed with fluoroscopy using both AP and lateral projections. On AP fluoroscopy, it is important to eliminate endplate parallax at each level of interest and confirm the spinous process bisects the pedicles. On lateral imaging, endplate parallax also should be eliminated and the pedicles well-defined. For lower lumbar levels, it is important to assess the superior aspect of the iliac crest, as a high-riding crest can present a relative contraindication to the mini-open approach. Similarly, the ribs may impede direct access to the rostral lumbar levels. Manipulation of the table can be used to enhance access to the spinal column; however, recent evidence suggests that the latter maneuver increases the risk of postoperative iliopsoas weakness.
An oblique incision is fashioned directly above the fractured vertebral body and careful dissection is performed through the muscle layers of the abdominal wall (external oblique, internal oblique, and transversus abdominis) and fascia into the retroperitoneal space. The transverse process is palpated and the finger turned to sweep the peritoneal contents anteriorly away from the psoas. Lateral fluoroscopy is used to confirm the level before introducing a dilator and Kirschner wire (K-wire) into the target disc space above or below the fractured vertebrae. Serial dilators are then advanced using continuous EMG neuromonitoring to safely advance the retractor while minimizing injury to the traversing lumbar plexus. Complete discectomy and annulotomy is performed above and below the fractured body. The intervening bone is then removed with the drill and rongeurs being mindful not to disrupt the anterior longitudinal ligament. The PLL can then be carefully taken to complete the decompression and expose retropulsed fragments in the canal. Once complete, an appropriately sized and angled cage is deployed in the intervertebral space. Supplemental stabilization can be achieved with lateral plating or percutaneous segmental pedicle screw and rod instrumentation.
When performing the lateral approach to the thoracic spine, the incision is fashioned along the superior aspect of the inferior adjacent rib. A right-sided approach is favorable for patients with fractures from above, and a left-sided approach is preferred for lower thoracic fractures to avoid retraction on the liver and injury to the inferior vena cava. Careful dissection of the rib from the underlying pleura is performed while mindful of the neurovascular bundle traversing the caudal border of the superior rib. The corridor can be created between the ribs or a small section of rib overlying the index vertebrae can be removed, which later can be used to provide autograph for fusion. The dilators are advanced along the posterior rib wall and gently swept forward to land atop the lateral edge of the spine. The lung is protected by using a spatula retractor as the surgical access corridor is widened. The crus of the diaphragm can be lifted or incised if it presents an obstruction to docking. Once positioned and the level is confirmed, the corpectomy is carried out similar to what was described previously, from discectomies to removal of the intervening bone including the medial rib heads depending on the necessity for canal exploration. Inadvertent injury to the pleura during the approach may necessitate a chest tube that can either be pulled as the chest wall is sealed via purse string suture under positive pressure ventilation, or after a postoperative chest radiograph rules out pneumothorax.
Reported fusion rates in patients with lateral mini-open corpectomies and minimum 1-year follow-up range from 85% to 93%, with significant improvements on Short Form-12 and Oswestry Disability Index patient satisfaction surveys. Hardware subsidence was reported in 8.1% with an overall complication rate of approximately 12%.
Posterior Approach
Posterior approaches to the spine remain the surgical workhorse in both open and MIS techniques when treating patients with destabilizing traumatic spinal injuries. MIS options aim to decrease disruption of the overlying paraspinal musculature, thus minimizing blood loss and hospitalization as these adjacent tissues contribute extensively to spinal recovery and rehabilitation. Patients with burst fractures with an intact PLL are often suitable candidates for percutaneous pedicle screw fixation and ligamentotaxy to reduce the retropulsed fracture fragments. This is represented numerically in patients with a Thoracolumbar Injury Classification and Severity score of less than 5 or Magerl type A fractures. Fractures with resultant neural deficits almost always require open decompression, in addition to those with significant rotational deformity, pedicle fractures, and adjacent vertebral body fractures, particularly when occurring over multiple levels.
Percutaneous pedicle screw placement
The patient is placed on an open Jackson radiolucent table in the prone position. Intraoperative fluoroscopy is used to confirm proper anatomic alignment and surgical level. Pedicle cannulation is performed similarly as described in the vertebral body augmentation procedures; however, the initial incision must take into account the distance to be traveled from the skin to the lateral facet/transverse process junction. Jamshidi needles are inserted and fluoroscopy is used to a confirm a mid-pedicular starting point on the AP projection. The needle is advanced approximately 1 cm to the AP midpoint of the pedicle, after which a lateral projection is then performed to confirm traversal into the pedicle and lack of any medial breach. Pedicular cannulation is completed and the K-wire is passed, followed by removal of the Jamshidi, and advancement of tissue dilators, and the pedicle screw itself. Serial fluoroscopy is used to confirm screw depth and position. This is typically accomplished either 1 or 2 levels above and below the index fracture, depending on the fracture severity and stabilization required, as well as the fracture site itself. The rods are then introduced and secured and reduction techniques performed via distractive instrumentation. Ease of rod passing is facilitated by a properly sized and bent rod inserted from where the screws are most superficial to where they are deepest, typically in a cranial to caudal direction. Final cap placement and tightening is completed and imaging obtained to verify spinal alignment and hardware placement.
For young healthy patients with pure bone injuries, short-segment fusions can be used as internal bracing to provide ample rigid fixation for fracture healing. For segments with kyphotic angulation, or those that cross the thoraco-lumbar junction, increased construct lengths are often necessary. It is important to note that this is not a fusion procedure, as no arthrodesis is performed. Controversy remains regarding the necessity to remove the hardware after adequate time for fracture healing has occurred, but sufficient data to support hardware removal are currently lacking.
A meta-analysis of 12 studies identifying 279 patients with percutaneous fixation compared with 340 open fixation procedures found statistically significant shorter operative duration ( P = .0002), shorter hospital stay ( P = .0007), reduced infection rates ( P = .05), and improved visual analog scale clinical outcomes ( P = .001). There was no difference noted in screw malpositioning ( P = .56), postoperative Cobb angles ( P = .22), body angles ( P = .66), or anterior body height ( P = .19). These differences are particularly important in the trauma population where comorbidities and physiologic demands increase the propensity for intraoperative blood loss and perioperative complications, such as infection.
Related posts:
Update on New Imaging Techniques for Trauma
Thoracolumbar Trauma Classification
Classification and Management of Pediatric Craniocervical Injuries
Classification and Management of Pediatric Subaxial Cervical Spine Injuries
Pediatric Thoracolumbar Spine Trauma
Complications in the Management of Patients with Spine Trauma
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