Minimally Invasive Spine Surgery: Advanced Surgical Techniques Alexander R Vaccaro, Kern Singh
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Introduction to Minimally Invasive Spine SurgeryChapter 1

Kern Singh,
Alejandro Marquez-Lara,
Sreeharsha V Nandyala,
Alexander R Vaccaro
 
INTRODUCTION
Minimally invasive spine surgery (MISS) has gained considerable momentum as growing evidence suggests comparable clinical outcomes as well as less postoperative morbidity and faster patient recovery than conventional open surgery. Since the inception of MISS in the late 1970s, significant advancements in instrumentation, imaging modalities, and surgical techniques have improved visualization, guidance, and enabled surgeons to address a wide spectrum of spinal pathology while sparing important soft tissue structures.
 
PRINCIPLES AND PATIENT SELECTION FOR MISS
 
Basic Principles1
  • Preservation of anatomic structures
    • Anatomic neurovascular and muscular planes are utilized to access the spine.
      • An intermuscular working plane (Wiltse plane) (Fig. 1.1) is developed utilizing blunt sequential dilators (Fig. 1.2) that minimize tissue injury thereby reducing postoperative pain.
      • Narrow self-retaining retractors provide a steady visual field while avoiding excessive muscle retraction (Fig. 1.3).
    • The tendon attachment sites of key muscles (e.g. multifidus) are preserved with MISS. This anatomic approach reduces the potential risk for muscle denervation and postoperative paraspinal muscle weakness.
  • Surgical feasibility
    • MISS techniques aim to avoid important anatomic structures (e.g. neural structures, great vessels) that are traditionally at risk with open surgery.
      • Precise knowledge of the patient's anatomy and the utilization of neuromonitoring devices (e.g. continuous electromyographic stimulation) can prevent injury to vital structures.
    • Surgical magnification (microscope or loupes) enable detailed identification of critical neurovascular structures for safe manipulation and dissection.2
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Fig. 1.1: Magnetic resonance imaging cross-section of the L4-L5 disc space highlighting the paraspinal muscles: multifidus (M), iliocostalis (IL) longissimus (LO), quadratus lumborum (QL), intertransversarii (IT), and psoas muscles.1
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Fig. 1.2: Blunt sequential dilators are utilized to create an intermuscular surgical working channel and minimize soft tissue injury.
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Fig. 1.3: A self-retaining retractor is fixed in place with a table mounted arm.
  • Awareness of the patient's three-dimensional bony anatomy and its correlation to the two-dimensional radiographic imaging will help guide the trajectory and depth of the instruments utilized in MISS (Figs. 1.4A to C).
 
Factors Affecting Patient Selection in MISS
  • Clinical presentation—Similar to the success of an open procedure, patient selection remains the mainstay of ensuring excellent clinical outcomes after MISS.
  • Obesity—The girth of the surrounding soft tissue may limit the utilization of open surgical retractors. However, obese patients may benefit the most from an MISS procedure.3
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Figs. 1.4A to C: (A) Anteroposterior intraoperative fluoroscopic image demarcating important anatomical landmarks (e.g. spinous process, medial wall of the pedicle). (B) Lateral intraoperative fluoroscopic image delineating the posterior vertebral wall. (C) Cannulated pedicle probes placed in the correct orientation and depth for cement augmentation.
  • Revision surgery—Previously altered anatomy and scar tissue pose a significant challenge for a minimally invasive approach. Although feasible, this should be reserved for surgeons with ample experience with MISS techniques.
  • Surgical learning curve—The number of cases required to become proficient is dependent upon the technical skill of the surgeon and complexity of the procedure.
  • Complexity of the procedure—Minimally invasive techniques have been developed to address multilevel cases with or without deformity. However, these cases should only be attempted by experienced surgeons.
 
ANATOMIC AND PHYSIOLOGIC CONSIDERATIONS WITH MISS
 
Paraspinal Muscles
  • Deep paramedian transversospinalis muscles
    • Multifidus
      • The multifidus is the most important posterior stabilizer of the spine.4
      • Multiple separate fasciculi are characteristic of the multifidus muscle. Each fasciculus originates from the transverse process of the corresponding vertebrae and inserts into the spinous process of the cephalad vertebrae 1–4 levels above its origin.
      • This unique structure provides a large physiologic cross-sectional area that enables the multifidus to create large forces over short distances.
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    Figs. 1.5A and B: (A) A scatter plot of the physiological cross-sectional area versus fiber length, which illustrates the functional design of the paraspinal muscles. The data demonstrate that the multifidus has the largest force generating capacity in the lumbar spine (B) The sarcomere length operating range of the multifidus plotted on the human skeletal muscle sarcomere length tension curve (black line).1
    • At rest, each sarcomere is positioned along the ascending portion of the length–tension curve (Figs. 1.5A and B).
      • This physiologic quality enables the multifidus to produce greater force as the spine flexes forward at its most vulnerable position.
  • Superficial and lateral erector spinae muscles
    • Longissimus
      • The muscle fibers originate from the transverse and accessory processes and insert distally into the ventral surface of the posterior superior iliac spine.
    • Iliocostalis
      • The muscle fibers originate from the tip of the transverse processes and adjacent thoracolumbar fascia and insert distally into the ventral edge of the iliac crest.
    • The longissimus and iliocostalis muscles run lateral to the multifidus, contain longer muscle fibers, and have a relatively small cross-sectional area. As such, they function to extend, rotate, and bend the trunk.
 
The Sequelae of Open Surgery
  • Posterior midline approaches to the lumbar spine can potentiate muscle atrophy.
    • The multifidus is most likely to be injured with an open approach.
      • This disruption of the multifidus can compromise the dynamic stability of the spine and delay patient recovery.5
    • Physiological events that potentiate muscle atrophy
      • Direct muscle injury
      • The utilization of powerful self-retaining retractors creates areas of ischemia. Depending upon the procedural time and the amount of force against the soft tissue, permanent damage may result.
    • In addition, once the retractors are released, the remaining muscle fibers are prone to reperfusion injury.
      • Muscle denervation
      • The multifidus receives a monosegmental innervation from the medial branch nerve that originates from the dorsal rami of each lumbar spinal nerve.
      • The monosegmental innervation leaves the muscle particularly vulnerable to injury.
  • If the latissimus and iliocostalis muscles are injured, postoperative extension strength can be significantly compromised.
 
HOSPITAL COSTS ASSOCIATED WITH MISS
  • Direct costs2,3
    • Blood bank costs
      • MISS procedures are associated with less blood loss and blood transfusion volume.
      • Standard type and cross-match studies are done on a case-by-case basis and are rarely done with elective MISS procedures.
    • Pharmacy costs
      • Smaller incisions and less soft tissue damage associated with minimally invasive procedures will result in less postoperative pain and narcotic requirements.
    • Room and board (length of stay)
      • The shorter hospital stay after a minimally invasive procedure will reduce hospital resource utilization.
    • Surgical service costs
      • The procedural and anesthesia times are significantly reduced with minimally invasive techniques.
    • Implant costs
      • In both open and MISS techniques, the cost of implants contributes to the majority of the total direct costs.
  • Indirect costs
    • Postoperative complications
      • A less invasive surgical approach has been associated with fewer postoperative complications including surgical site infections.
    • Discharge disposition
      • Less postoperative pain enables participation in outpatient rehabilitation and may potentiate a faster recovery.
    • Reoperation and revision procedures
      • MISS has demonstrated lower reoperation rates when compared with open techniques in the early postoperative period.
      • However, there is limited data regarding the long-term outcomes associated with minimally invasive techniques.6
    • Missed days of work
      • Less postoperative pain and a faster recovery after MISS may enable the patient to return to work sooner when compared with an open procedure.
 
ANESTHESIA TECHNIQUES AND POSTOPERATIVE ANALGESIA IN MISS4
 
Preoperative Considerations
  • Patients with a history of chronic opioid dependence may benefit from a preoperative evaluation by a pain specialist.
  • Screening for obstructive sleep apnea (OSA) is important to determine if patients are amenable to a fast-track postoperative pain protocol.
    • Postoperative opioids may cause significant respiratory collapse in patients with OSA.
  • A combination of nonsteroidal anti-inflammatory drugs (NSAIDs) and sustained release opioids can be initiated 2–3 days prior to the procedure.
    • This enables the accumulation of medication to suppress the inflammatory response associated with the surgical procedure (e.g. prostaglandin E2).
  • Preoperative analgesics (day of surgery)
    • High-dose NSAIDs (e.g. 400 mg of celecoxib) orally
      • In the case of fusion surgeries, this is not recommended.
    • Acetaminophen (1000mg)
    • Sustained release oxycodone (10–20 mg).
    • Other pain medications that may benefit patients include:
      • Gabapentin (600 mg)
      • Pregabalin (100–150 mg)
  • Nonanalgesic medication
    • IV fluid administrated may reduce perioperative nausea, dizziness, and drowsiness.
    • Antiemetics
      • 5-HT3 blockers (ondansetron 4 mg IV)
      • Scopolamine patch
 
Intraoperative Anesthesia
  • General anesthesia
    • Induction—Propofol
    • Maintenance—Sevoflurane or desflurane
    • IV opioids—Sufentanil or remifentanil
      • IV opioids provide a steady state of anesthesia.
  • Anesthesia effect on neurophysiological monitoring [somatosensory-evoked potentials (SSEP)].
    • Inhalation agents can reduce the amplitude and latency of SSEP signals.
    • Alternate analgesics (short-acting opioids) may be preferred.7
  • Local anesthetic
    • Generous infiltration of lidocaine 1% in the surgical incision site is recommended as it will reduce the patient's analgesic requirements.
    • Deep tissue should be infiltrated with bupivacaine 0.25%.
      • Care must be taken to assure the anesthetic does not spread to the nerve roots, as this can obscure neurologic assessment postoperatively.
  • Other medications
    • IV fluids and vasopressors as needed to minimize hypotension.
    • Antiemetics (5-HT3 blockers)
 
Postoperative Analgesia
  • NSAIDs should be continued for 2 weeks after surgery.
    • NSAIDs should not be utilized after spinal fusion procedures.
  • Sustained release oxycodone is continued in the postoperative period.
  • Muscle relaxants (tizanidine or baclofen) will address muscle spasms related to the surgical intervention.
  • Gabapentinoids (gabapentin and pregabalin) can be utilized depending upon the extent of the surgical trauma.
REFERENCES
  1. Kim CW. Scientific basis of minimally invasive spine surgery—prevention of multifidus muscle injury during posterior lumbar surgery. Spine 2010;35:S281–6.
  1. Lucio JC, Vanconia RB, Deluzio KJ, et al. Economics of less invasive spinal surgery: an analysis of hospital cost differences between open and minimally invasive instrumented spinal fusion procedures during the perioperative period. Risk Manag Healthcare Policy 2012;5:65–74.
  1. Wang MY, Lerner J, Lesko J, McGirt MJ. Acute hospital costs after minimally invasive versus open lumbar interbody fusion—data from a US national database with 6106 patients. J Spinal Disord Tech. 2012;25:324–8.
  1. Buvanendran A, Thillainathan V. Preoperative and postoperative anesthetic and analgesic techniques for minimally invasive surgery of the spine. Spine 2010;35:S274–80.
REFERENCE SUMMARY
  1. Kim CW. Scientific Basis of Minimally Invasive Spine Surgery—Prevention of multifidus muscle injury during posterior lumbar surgery. Spine 2010;35:S281-S286.
  1.   Summary: A literature review describing the paraspinal musculature along with the structure, insertion, innervation, and function. The authors report the significant anatomic and physiologic consequences of disturbing these structures with an open spinal procedure.
  1. Lucio JC, Vanconia RB, Deluzio KJ, Lehmen JA, Rodgers JA, Rodgers W. Economics of less invasive spinal surgery: an analysis of hospital cost differences between open and minimally invasive instrumented spinal fusion procedures during the perioperative period. Risk Management and Healthcare Policy 2012;5:65–74.
  1.   Summary: A retrospective review comparing the costs associated with 101 open posterior lumbar fusions and 109 minimally invasive procedures. The authors report an average cost savings of $2825 with MIS procedures. In addition, the authors noted significantly less blood loss, shorter hospital stay, and lower complication rates in the MIS cohort.

  1. 8 Wang MY, Lerner J, Lesko J, McGirt MJ. Acute hospital costs after minimally invasive versus open lumbar interbody fusion- data from a US national database with 6106 patients. J Spinal Disord Tech 2012;25:324–328.
  1.   Summary: A retrospective analysis of hospital charges, length of stay, and dicharge disposition in 74 patients treated with 1- and 2-level MIS and open posterior lumbar fusions. The authors reported that MIS procedures resulted in a shorter hospital stay, reduced hospital charges, and lower transfer rates to inpatient rehabilitation centers.
  1. Buvanendran A, Thillainathan V. Preoperative and postoperative anesthetic and analgesic techniques for minimally invasive surgery of the Spine. Spine 2010;35:S274-S280
  1.   Summary: A literature review of the current anesthesia and analgesia protocols utilized in minimally invasive spine surgery. The authors highlight the literature supporting the utilization of multimodal analgesic therapy with a fast-track anaesthesia with MISS.