ABSTRACT
The trend toward less invasive surgical options continues to dominate the field of spinal surgery. In the current article, we will discuss the most popular minimally invasive spinal procedures in use today. These procedures share certain features which include a reduced incision size, less soft tissue injury, less intraoperative bleeding, a reduced risk of surgical site infection, and a more rapid recovery compared to traditional approaches. They rely on proper surgeon training and the presence of enabling technologies such as fluoroscopy, operative microscopy, specialized retractor systems, and advance spinal implants. These approaches should be within the armamentarium of the modern spinal surgeons as they represent valuable tools in the treatment of spinal disease.
INTRODUCTION
Advances in the field of spinal surgery continue to provide new options for spinal patients. There is a continued trend in the field toward less invasive spinal procedures. This article will review the leading new techniques for less invasive treatment of common spinal problems in the field of spinal surgery.
TUBULAR RETRACTOR SPINAL DECOMPRESSION
Decompression of the lumbar spine for stenosis and herniated disk disease is a time honored spinal procedure. Surgical treatment of these pathologies responds favorably to surgery which is able to relieve neurogenic claudication and/or radiculopathy. Traditional surgery, although effective, has the drawback of muscle damage, perineural scaring, and spinal instability. In contrast, minimally invasive decompression is associated with smaller incisions, less muscle dissection, less bleeding, a lower infection rate, and less iatrogenic instability.1,2 In addition to reduced surgical complications, minimally invasive lumbar decompression allows for a quicker recovery and reduced surgical pain compared to open decompressions. Moreover, the supporting bony and ligamentous structures (spinous processes, intraspinous and supraspinous ligaments) are spared with minimally invasive decompression, reducing the risk of iatrogenic instability. The surgical indications for minimally invasive decompression are identical to open decompression (Figures 1.1A to C).2
Figures 1.1A to C: (A) Lateral fluoroscopic image of the lumbar spine with a needle placed at the proposed site of the surgical incision; (B) Tubular retractor in place to address pathology at the L4-5 disc space; (C) View down the tubular retractor.
Generally, a minimally invasive lumbar decompression is performed through a small (15–20 mm) paramedian incision. Access to the spinal pathology is ensured by localizing the surgical incision with fluoroscopy prior to making the incision. Serial dilation is then used to dilate the surgical corridor through the paraspinal muscles, followed by the placement of a tubular retractor. The tubular retractor is secured to maintain an optimal trajectory to the surgical site. The operative field is best visualized with the assistance of an operative microscope.
Although minimally invasive tubular decompression has a documented learning curve, many surgeons have adopted this technique within their practices. One study documented a rapid decrease in operative times with an asymptote reached after roughly 30 procedures.3 The current literature supports favorable clinical outcomes for tubular decompression in properly selected patients.4,5
Ipsilateral or bilateral decompression is often performed through a single incision utilizing a tubular retractor system. Bone and ligament removal is performed using standard spinal surgical instruments including a high-speed drill and Kerrison Rongeurs. In situations requiring bilateral decompression, the tubular retractor and microscope are angled to undercut the spinous processes allowing access to the contralateral side of the spinal canal. In the setting of a herniated disk, the traversing nerve root is retracted and the herniated material is resected using traditional instruments. As with open surgery, the goal with a minimally invasive lumbar decompression is to remove all compressive pathology. At the conclusion of the decompression, the surgeon should utilize a ball tipped probe to palpate the spinal canal and neural foramen to ensure an adequate decompression has been achieved. When the surgeon is satisfied that an adequate decompression has been achieved, the tubular retractor is withdrawn, allowing the muscle tissue along the surgical corridor to fall back into position. Bipolar cautery is used to manage any bleeding as the tube is withdrawn. The fascia and skin are then repaired using traditional suturing techniques.
MINIMALLY INVASIVE TRANSFORAMINAL LUMBAR INTERBODY FUSION
Patients with documented instability of the spine in addition to compressive pathology require a decompression and fusion procedure. In recent years, there has been a growing 3interest in performing this type of procedure as a minimally invasive transforaminal lumbar interbody fusion (MIS TLIF). Like the minimally invasive decompression, the indications for a MIS TLIF are identical to those for an open TLIF procedure. MIS TLIF procedures have demonstrated comparable long-term results to open TLIF with lower rates of infection and bleeding.6–8 Blood transfusions have been shown to be significantly reduced with MIS TLIF compared to open TLIF.9 A learning curve of 25–30 cases of MIS TLIF should also be anticipated when adopting this technique.10
When performing a MIS TLIF, the approach to the disk space is typically performed from the side of the patient's worst leg pain. This affords the surgeon the opportunity to achieve an aggressive decompression of the symptomatic neurologic structures. C-arm fluoroscopy should be used to localized the paramedian surgical incisions which normally lies 4–5 cm lateral to the midline. Both the skin and fascia should be incised in line with the trajectory required to reach the ipsilateral facet joint. Serial dilation is utilized to prepare the surgical corridor and then a tubular retractor is docked on the dorsal surface of the facet joint and lateral lamina. Fluoroscopy should be used to ensure that the retractor is aligned with the disk space on the lateral view.
The facet joint is then resected using an osteotome or high-speed burr. The bone of the facet is saved to be used as local autograft for the fusion. The traversing and exiting nerve roots are identified and decompressed as needed. If a contralateral decompression is required, the tubular retractor is angled to undercut the spinous process allowing decompression of the contralateral spinal canal and neural foramen as described above (Figures 1.2A to C).
Following the decompression, the tubular retractor is positioned to access the posterolateral disk space on the ipsilateral side. A nerve root retractor is used to protect the traversing nerve root. The disk is incised with a scalpel and a thorough discectomy is performed while carefully avoiding damage to the bony endplates which are needed to support the interbody device. Disk space collapse is restored by interbody dilation and trial implants can be used to establish the appropriately sized interbody cage to be used. The disk space is packed with bone graft and then the interbody cage is impacted into place and countersunk below the posterior margin of the vertebral body.
Figures 1.2A to C: (A) Sagittal MRI of a patient with disabling leg pain due to spondylolisthesis of the L5-S1 level; (B) Anteroposterior radiograph of the lumbar spine following MIS TLIF; (C) Lateral radiograph of the lumbar spine following MIS TLIF.
4Confirmatory imaging is obtained to ensure proper localization of the device and good reconstruction of the interbody space. The neural structures are examined to ensure that they are free of any compression, meticulous hemostasis is achieved, and the tubular retractor system is withdrawn. The contralateral facet joint or intertransverse region may be decorticated and bone grafted according to the preferences of the surgeon.
Pedicle screw instrumentation is routinely utilized to stabilize the surgical construct. Pedicle screws are generally placed percutaneously, utilizing fluoroscopic guidance as described below. After placing pedicle screws and rods, the interbody construct is compressed prior to final tightening. Some surgeons prefer to place the pedicle screws on the contralateral side from the disk space approach prior to performing the interbody fusion to assist with disk space distraction. Other surgeons routinely place bilateral pedicle screws following the interbody fusion.
LATERAL INTERBODY FUSION
Lateral interbody fusion (often called XLIF or DLIF) has become popular in recent years and is a powerful tool for achieving interbody fusion of the lumbar spine. Lateral interbody fusion is performed through a muscle splitting incision with fluoroscopic guidance. Due to the anatomic location of the neural and vascular structures and iliac crest, lateral interbody fusion is not feasible at the L5-S1 disk space. The advantages of a lateral interbody fusion include the minimally invasive nature of the surgical approach, as well as the large surface area of the interbody devices that are used for this procedure. With lateral interbody fusion, the interbody devices are place on the outer apophyseal ring (the strongest portion of the vertebral body) where the chances of subsidence are minimized. Challenges with lateral interbody fusion include the proximity of the lumbar plexus and great vessels which lie close to the surgical corridor.
The patient is positioned in a lateral decubitus position. The approach side is chosen to provide the most favorable access to the disk space. The patient should be secured to the operating table and a bump is placed in the dependent flank to slightly side bend the patient away from the side of the approach. An overly aggressive side bend maneuver should be avoided as this may cause undue stretch to the lumbar plexus.
Following the sterile preparation and draping, the surgical incision site is localized with fluoroscopy. Next, a muscle splitting approach is utilized to traverse the abdominal wall musculature and enter the retroperitoneal space. The retroperitoneal contents are swept in an anterior direction and the psoas muscle is identified. The psoas muscle is split using serial dilators placed anterior to the lumbar plexus structures. Many surgeons use neurostimulation or neuromonitoring during this maneuver to reduce the risk of injury to the lumbar plexus. A tubular retractor is then docked on the disk space and secured in position. Imaging is used to ensure optimal positioning of the retractor. Next, the annulus is incised and a thorough discectomy is performed. The contralateral annulus is released to provide deformity correction in the coronal plane. An appropriately sized interbody device is selected and packed with bone graft. Additional bone graft is packed into the disk space and then the interbody device is impacted into place and positioned to span the disk space and rest on the outer apophyseal ring. Imaging is utilized to confirm correct localization of the device within the disk space before standard closure of the wound is performed (Figures 1.3A to C).5
Figures 1.3A to C: (A) Sagittal MRI of a patient with severe neurogenic claudication due to spinal stenosis and degenerative spondylolisthesis of the L3-4 level; (B) Anteroposterior radiograph of the lumbar spine following a lateral interbody fusion of L3-4 with posterior percutaneous fixation; (C) Lateral radiograph of the lumbar spine following a lateral interbody fusion of L3-4 with posterior percutaneous fixation.
PERCUTANEOUS PEDICLE SCREW INSTRUMENTATION
Percutaneous pedicle screw instrumentation has dramatically reduced the trauma to the lumbar paraspinous muscles associated with posterior column stabilization of the spine. These systems may be used in conjunction with interbody fusion procedures such as MIS TLIF or lateral interbody fusion or alone, particularly in the treatment of spinal trauma.11–13 The placement of percutaneous pedicle screws is dependent on fluoroscopy or other imaging technologies that allow the surgeon to accurately target the pedicles. Percutaneous pedicle screw systems may utilize cannulated or noncannulated pedicle screws, and often incorporate a unique strategy for rod introduction.
The most vital step in the safe implantation of percutaneous pedicle screws is to obtain properly aligned, high-quality images of the vertebra to be instrumented. The fluoroscopic views utilized for this procedure include the true anteroposterior view (true AP), the true lateral view and the en face view (Figures 1.4A to C). The surgeon must understand how to obtain properly aligned fluoroscopic views prior to performing percutaneous pedicle fixation. In a properly aligned AP view, the superior endplate of the target vertebrae will be parallel to the X-ray beam and will project as a single radiolucent line. The pedicles will be symmetrical with the spinous process and should appear just caudal to the superior endplate. The vertebrae should be centered within the fluoroscopy image to avoid parallax or distortion of the image.
Once a properly aligned true AP image has been obtained, the location of the surgical incisions is localized approximately 1–2 cm lateral to the lateral margin of the pedicle shadows. The incision should be adequate in length to accommodate the implant system that is being utilized and should divide both the skin and fascia. A Jamshidi needle is commonly used for targeting of the pedicles. The tip of the needle is docked over the entry to the pedicle.6
Figures 1.4A to C: (A) True AP view of the lumbar spine; (B) True lateral view of the lumbar spine; (C) En Face view of the lumbar spine.
Figures 1.5A and B: (A) Intraoperative photograph of a patient with percutaneous pedicle screw towers in place; (B) Intraoperative photograph percutaneous pedicle screw towers during subfascial rod passage.
The pedicle entry site is located at the 9 o'clock and 3 o'clock (right and left sides, respectively) positions of the pedicle shadow on the true AP image. If the surgeon prefers to use the en face view, the center of the pedicle shadow should be targeted. After the needle tip has been properly positioned, the needle is tapped lightly to seat the needle tip a few millimeters into bone and another image is obtained to ensure that the needle position remains on target. The needle shaft is then marked 20 mm above the skin level. This mark will allow the surgeon to follow the depth of the Jamshidi needle and to determine when the needle tip is at the approximate depth of the base of the pedicle. The Jamshidi needle is then held in alignment with the pedicle and is gently tapped through the pedicle to the 20 mm depth. Fluoroscopic images are checked to ensure that the Jamshidi needle has safely traversed the isthmus of the pedicle and then a guide wire is placed. The remainder of the pedicles in the construct is targeted in the same manner, and then the pedicle screw implants are placed over the guide wires. After determining the length of the rod to bridge the construct, the rod and screws are placed and secured according to the technique specified by the manufacturer. Final fluoroscopic images are obtained to ensure correct placement of the implants and closure of the incision is performed using standard suture techniques (Figures 1.5A and B).7
CONCLUSION
Recent advances have allowed spine surgeons to perform decompressive and reconstructive spinal procedures with less surgical trauma and a reduced likelihood of heavy bleeding and surgical site infection.14–16 Each new procedure has certain nuances which must be learned by the surgeon in order to achieve success. These new surgical approaches are dependent on assistive technologies including fluoroscopy, operative microscopy, specialized retractor systems, and surgeon training.
REFERENCES
- Asgarzadie F, Khoo LT. Minimally invasive operative management for lumbar spinal stenosis: Overview of early and long-term outcomes. Orthop Clin North Am. 2007;38:387–99; abstract vi-vii.
- Shih P, Wong AP, Smith TR, et al. Complications of open compared to minimally invasive lumbar spine decompression. J Clin Neurosci. 2011;18(10):1360–4.
- Nowitzke AM. Assessment of the learning curve for lumbar microendoscopic discectomy. Neurosurgery. 2005;56:755–62.
- Mikami Y, Nagae M, Ikeda T, et al. Tubular surgery with the assistance of endoscopic surgery via midline approach for lumbar spinal canal stenosis: a technical note. Eur Spine J. 2013;22(9):2105–12.
- Gandhi SD, Kepler CK, Anderson DG. Lumbar decompression using a tubular retractor system. In: Phillips F, Lieberman I, Polly D (Eds). Minimally Invasive Spine Surgery. Springer: New York, NY; 2011. pp. 136–40.
- Rodriguez-Vela J, Lobo-Escolar A, Joven E, et al. Clinical outcomes of minimally invasive versus open approach for one-level transforaminal lumbar interbody fusion at the 3- to 4-year follow-up. Eur Spine J. 2013;22(12):2857–63.
- Lee KH, Yue WM, Yeo W, et al. Clinical and radiological outcomes of open versus minimally invasive transforaminal lumbar interbody fusion. Eur Spine J. 2012;21:2265–70.
- Parker SL, Adogwa O, Witham TF, et al. Post-operative infection after minimally invasive versus open transforaminal lumbar interbody fusion (TLIF): literature review and cost analysis. Minim Invasive Neurosurg. 2011;54(1):33–7.
- Schwender JD, Holly LT, Rouben DP, et al. Minimally invasive transforaminal lumber interbody fusion (TLIF). J Spinal Disord Tech. 2005;18:S1–S6.
- Lee JC, Jang HD, Shin BJ. Learning curve and clinical outcomes of minimally invasive transforaminal lumbar interbody fusion: our experience in 86 consecutive cases. Spine. 2012;37:1548–57.
- Mobbs RJ, Sivabalan P, Li J. Technique, challenges and indications for percutaneous pedicle screw fixation. J Clin Neurosci. 2011;18:741–9.
- Schmidt O, Strasser S, Kaufmann V, et al. Role of early minimal-invasive fixation in acute thoracic and lumber spine trauma. Indian J Orthop. 2007;41:374–80.
- Takami M, Yamada H, Nohda K, et al. A minimally invasive surgery combining temporary percutaneous pedicle screw fixation without fusion and vertebroplasty with transpedicular intracorporeal hydroxyapatite blocks grafting for fresh thoracolumbar burst fractures: prospective study. Eur J Orthop Surg Traumatol. 2014;24 Suppl 1:S159–65.
- Kim CW, Siemionow K, Anderson DG, et al. The current state of minimally invasive spine surgery. J Bone Joint Surg Am. 2011;93(6):582–96.
- Wang MY, Anderson DG, Ludwig SC, et al. Handbook of Minimally Invasive and Percutaneous Spine Surgery. St. Louis: Quality Medical Publishing Inc; 2011.
- Ee WW, Lau WL, Yeo W, et al. Does minimally invasive surgery have a lower risk of surgical site infections compared with open spinal surgery? Clin Orthop Relat Res. 2014;472(6):1718–24.