Minimally Invasive Spine Surgery: An Algorithmic Approach Kern Singh
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1Cervical Spine
Chapters Outline
  • Minimally Invasive Posterior Cervical Foraminotomy
  • Matthew Oglesby, Steven J Fineberg, Kern Singh
  • Posterior Minimally Invasive Cervical Fusion
  • Michael Y Wang2

Minimally Invasive Posterior Cervical Foraminotomy1

Matthew Oglesby,
Steven J Fineberg,
Kern Singh
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INTRODUCTION
A minimally invasive posterior cervical foraminotomy (MIS PCF) is an established procedure for the treatment of cervical radiculopathy. The advantages of minimally invasive spine surgery over the standard open approach include reducing iatrogenic muscle injury, smaller skin incisions, diminished operative time, reduced blood loss, lowered analgesic requirements for postoperative pain and decreased hospital stay with faster recuperation times.16
 
PATIENT EVALUATION
It is important to begin with a thorough history and physical examination when evaluating a patient for an MIS PCF. Patients may present with radiating upper extremity, shoulder, back or neck pain that is described as sharp, tingling, dull, aching, or burning. Routine imaging should consist of anterior-posterior (AP) and lateral flexion/extension views to rule out occult spinal instability that may necessitate a spinal fusion. An MRI is obtained to evaluate the neural elements and any associated disc herniations. Disc herniations that are lateral and foraminal are ideal for a posterior approach. Those disc herniations that are more central may not be accessible through the foraminotomy.
The indications for an MIS PCF are: cervical radiculopathy due to foraminal stenosis and postero­laterally herniated discs, persistent radiculopathy after an anterior cervical discectomy and fusion (ACDF), and in patients with whom an anterior approach is contraindicated.2,8
 
POSITIONING
There are several ways in which to position the patient; the author's preference is a modified prone position discussed in this section, alternatively a sitting position may also be utilized.2,9,10 After induction of general anesthesia, the patient's head is placed in a Mayfield three-point pin holder and the pins are tightened to 60–80 psi.10 The patient is then log-rolled into the prone position with chest rolls placed with the neck slightly flexed. With the patient secured, the table is 4placed approximately 30° in the reverse Trendelenburg position so that the cervical spine is parallel to the floor, with the head above the level of the heart allowing for venous drainage (Fig. 1).2,9,10 When operating on lower cervical levels, the shoulders are gently depressed with tape allowing for radiographic visualization. The surgeon is positioned on the side of the pathology, and the fluoroscopic C-arm and image monitor on the contralateral side. The retractor arm is attached to the bedrail opposite the surgeon.
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Fig. 1: Patient is placed prone on a regular operating room table with Mayfield head holders gently flexing the neck
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Fig. 2: Initial dilator placement with fluoroscopic confirmation
 
PROCEDURE
Lateral fluoroscopic images are obtained to identify the proper level using a spinal needle. A 15 mm incision is made 5 mm from the midline centered over the operative level.7,9,10 The approach is carried down to the muscular fascia using electrocautery and a fascial incision is made equal in length to the skin incision. Incising the fascia allows for easy passage of serial tubular dilators without placing any unnecessary downward force.9,11 It is important not to force the dilators through the muscular layers to prevent plunging as the smaller dilators may be small enough to penetrate the interlaminar space.12 With the use of fluoroscopy, the serial dilators are placed, ensuring that they are docked at the appropriate level and do not migrate (Figs 2 and 3).7 Once the final dilator is reached, the tubular retractor is placed and locked into the mounted retractor arm. Bovie electrocautery and pituitary rongeurs are used to remove any remaining soft tissue from the lateral mass and facet joint (Fig. 4).
The medial third of the inferior articular process of the cephalad vertebra is removed using a high-speed burr until the superior articular process of the inferior level is visualized (Fig. 5).
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Fig. 3: Continued serial tubular dilation is used to spread paraspinal muscles in order to minimize muscle damage
5
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Fig. 4: Soft tissue removal allows visualization of the facet joint and the inferior portion of the superior lamina. For purposes of orientation, the top of the image represents the midline, the bottom represents lateral, the left towards the head and the right is towards the foot
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Fig. 5: A high-speed burr is used to remove the medial third of the inferior articular process (IAP) of the cephalad vertebrae
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Fig. 6: Hemostasis is achieved through electrocautery and ample visualization can be obtained of the nerve root exiting the neuroforamen
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Fig. 7: A closer inspection of the nerve root as it exits the neuroforamen
The superior articular process (SAP) can be removed either with a burr or a Kerrison rongeur. The SAP is the source of bony compression and impingement in the neural foramen. Care must be taken not to resect more than 50% of the facet joint complex in order to preserve spinal stability.2,9,13 During the foraminotomy, the epineural venous plexus may be encountered as the anterior cortex is removed, it is important to maintain hemostasis with bipolar electrocautery, bone wax, or a procoagulant sponge (Figs 6 and 7).12 Once the foraminotomy is complete, the ligamentum flavum is identified and resected using a 1- or 2-mm Kerrison rongeur.2,7 The nerve root can be carefully mobilized using a blunt nerve hook. The disc herniation can be identified by gently retracting the nerve superiorly. Oftentimes the disc herniation can be removed with a pituitary rongeur. The nerve root is then re-evaluated for adequate decompression, which is complete when a nerve probe can easily be placed into the neuroforamen. The wound is copiously irrigated and hemostasis is achieved prior to wound closure.2,7,96
 
PEARLS, PITFALLS AND COMPLICATIONS OF MIS PCF
Two steps where surgical errors are prone to occur are during tubular access and decompression. During advancement of the dilators, the surgeon must always be cognizant of an interlaminar breach. If the dilators do not pass smoothly, it is imperative that one does not plunge medially or laterally. To remedy the potential hazard, one can bluntly dissect the fascial and muscle planes with Metzenbaum scissors.
During decompression, the facet joint may become incompetent with too great a facet resection (>50%). A smaller visual field in MIS PCF requires the surgeon to palpate with a bayoneted Penfield no. 4 lateral to the tubular retractor to assess the size of the facet. Care should be taken to avoid stripping the facet capsule while assessing the amount to be resected. The senior author prefers to identify the laminar-facet junction as the key landmark for determining the amount of facet resection.7 As mentioned earlier, it is important to resect no more than 50% as consequences of excessively resecting the facet joint may result in increased neck pain with possibility of spinal instability.1315
While resecting the medial facet and lateral lamina, bony bleeding may occur that can obscure the operative field. Hemostasis can be achieved with application of bone wax and/or a thrombotic agent. Bleeding can be minimized with the appropriate positioning mentioned earlier. It is paramount to keep the head slightly elevated allowing venous drainage. There may also be bleeding from the perineural venous plexus that can be treated with a cottonoid and a procoagulant.
The associated complications of MIS PCF are superficial wound infections, cerebrospinal fluid fistulae, dural lacerations, nerve root injury, cervical instability with hypermobility (>50% resection and/or bilateral procedures are performed at the same level), and spinal cord injury.14,1619 In general, durotomies do not require a formal repair. Once the decompression is complete the tubular retractor is removed and the muscular envelope closes the dead-space. The fascia is then closed securely preventing any egress of cerebral spinal fluid.
A frequent neurological complication is transient nerve root paresis.18,20,21 It is hypothesized this is secondary to edema and concurrent revascularization of a previously ischemic nerve root and typically involves the C5 nerve. C5 neuropraxia classically presents 24–48 hours after surgery. Close observation and re-imaging are important to rule out any compressive pathology. Most neuropraxias resolve quickly without any additional intervention.
 
OUTCOMES
A review of articles compiled by Riew et al. regarding the outcomes of posterior cervical foraminotomies demonstrated significant pain reduction, resolution of upper extremity motor deficits, decreased narcotic use and quicker recoveries when compared to alternative methods.14,19 Radiologic outcomes were addressed in a study by Jagganathan, wherein 162 patients were treated with posterior cervical foraminotomies and 92% of them had improvement in Neck Disability Index score, and 95% had reduced symptoms with a mean follow-up of 77.3 months.19,22 The most prevalent factors in determining the surgical success are neurological deficits and the length of preoperative symptoms in so much as those with shorter durations tend to have better outcomes.14
 
CONCLUSION
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