Spine Surgery

Eugene J. Carragee MD, FACS¹

Ivan Cheng MD¹

Nima Salari MD¹

Adam P. Brown MD²

C. Philip Larson Jr. MD, CM²

¹SURGEONS

²ANESTHESIOLOGISTS

MINIMALLY INVASIVE POSTERIOR LUMBAR DISCECTOMY (MICRODISCECTOMY)

SURGICAL CONSIDERATIONS

Description: Since the mid-1990s, a number of techniques have been developed to allow the decompression of lumbar roots (removal of disc material) with as little trauma to the nerves and surrounding tissues as possible. In most instances, little or no bone is removed, and therefore, this is not technically a laminectomy or laminotomy. These minimally invasive procedures typically are carried out in healthy young or middle-aged adults with sciatica and are not done for more involved pathology, such as deformity, tumor, or infection. Transpedicular fixation and short-segment fusions may be attempted using modifications of these techniques.

Microdiscectomy approach: This can be done under GA, regional (epidural or spinal), or local anesthesia. The patient is placed in a prone or kneeling position, and the posterior landmarks are palpated to identify the approximate level (e.g., L4/5); then the overlying skin is infiltrated with local anesthetic. A spinal needle is placed to the level of the lamina, and an x-ray or fluoroscopic image is taken to confirm the level. A 1” incision is made over the proposed interspace, and using either traditional or specialized retractors, the soft tissue is displaced to expose the ligamentum flavum. With the use of an operating microscope, the ligamentum flavum is removed, the nerve retracted, and the extruded disc excised. For a single level, this should take between 30 and 90 min, depending on the size of the patient and whether there is any scarring or adhesions from previous surgery.

Variant approach: Percutaneous discectomy through a posterolateral approach is usually reserved for “contained discs”—protrusions into, but not through, the outer annulus of the disc. These are usually done under MAC with local anesthetic. The percutaneous instruments may be positioned using fluoroscopic guidance with or without a fiberoptic light source and camera/monitor setup. The disc space is entered posterolaterally. The surgeon usually avoids anesthetizing the area around the nerve root so that the patient can alert the team if the root is struck by an instrument (quite painful). After the disc space is entered, fluoroscopic or camera images are used to guide the surgeon in the removal of the herniated disc. The disc material can be removed with specialized grabbers or automatic power-driven shavers.

Usual preop diagnosis: Chronic back pain 2° herniated lumbar disc; lumbar radiculopathy

▪ SUMMARY OF PROCEDURES

	Microdiscectomy	Percutaneous Discectomy
Position	Prone or kneeling, with bolster or frame support. The abdomen must hang free to decompress the epidural veins.	Prone or lateral decubitus
Incision	Posterior midline or slightly off midline, at the appropriate vertebral level	About 8-12 cm lateral to the midline at the appropriate vertebral level
Special instrumentation	Microscope; light source; specialized retraction and dissection instruments for working in a small, deep incision	Percutaneous instruments, including trocars, sounds, and arthroscopic-type grabbers and shavers; fluoroscopy; and, sometimes, camera/monitor and fiberoptic light setup
Unique considerations	Often outpatient procedure. Need to make room for microscope at head of bed.	Patient must be alert enough to respond to pain if nerve roots are encountered.
Antibiotics	Cefazolin l g iv	⇚
Surgical time	0.5-1.5 h	1-2 h
Closing considerations	Minimal suturing	Usually no closure (Band-Aids)
EBL	25-100 mL	Minimal
Postop care	PACU. Mobilization as soon as tolerated. Usually discharged within 24 h.	PACU → home. Mobilization as tolerated.
Mortality	Very rare	⇚
Morbidity	Nerve injury Dural laceration Infection	Failure to decompress the nerve adequately – ⇚
Pain score	4	2

MINIMALLY INVASIVE ANTERIOR LUMBAR INTERBODY FUSION THROUGH A TRANSPSOAS APPROACH

SURGICAL CONSIDERATIONS

Description: Traditional open techniques of lumbar fusion have shown long-term clinical efficacy. However, the morbidity of the approach, extensive blood loss, and length of postop recovery can offset the benefits of the intervention. Recently, minimally invasive techniques have decreased morbidity. One approach involves lateral approach via a small incision through retroperitoneal fat and the psoas major muscle for access to the lateral lumbar spine with the aid of neuromonitoring to avoid nerves of the lumbar plexus.

The orientation of neural structures of the lumbar plexus has a relatively high level of variability, necessitating the use of neuromonitoring for this approach. After induction of GETA, the surgeon places needle electrodes into muscles of the bilateral lower extremities to record the EMG response to lumbar nerve stimulation. The EMG threshold is the current (mA) required to stimulate the nerve, producing a muscle contraction. Direct nerve stimulation studies have shown that normal nerves elicit an EMG response with an average of 2 mA. Neuromuscular blockade should be avoided, and the use of intravenous anesthesia is encouraged.

The patient is positioned in the lateral decubitus position and held in position with straps and tape. The arms should remain in a neutral position, and an axillary roll is placed just inferior to the axilla to support the area of the upper rib cage to relieve pressure on the axillary nerve and artery. The table is typically flexed to increase the distance between the iliac crest and the rib cage to gain access to the lateral lumbar spine. Fluoroscopic imaging is required to determine true anteroposterior and lateral axes of the desired spinal level. After the patient has been prepped and draped, an incision is made posteriorly at the border between the erector spinae muscles and the abdominal obliques to accommodate the surgeon’s index finger and help identify the retroperitoneal space. With care, perforation of the peritoneum is avoided, and the finger is used to sweep this anteriorly. After identifying the psoas muscle, the index finger is swept up to a previously marked direct lateral target over the center of the affected intervertebral segment. An incision is made on the patient’s side, through which dilators are placed, and the index finger is used to escort
them safely to the psoas muscle, all while protecting the intraabdominal contents. Careful passage of the dilators and EMG neuromonitoring avoid injury to the lumbar plexus. Once the self-retaining retractor system is positioned, care is taken to determine the course of the lumbar plexus in relation to the blades of the retractor. Once the retractor is positioned over the disc space, under direct vision, a discectomy is performed. Care is taken not to disrupt the anterior longitudinal ligament and risk injury to the main vascular structures coursing anteriorly.

Usual preop diagnosis: Chronic back pain; lumbar radiculopathy

▪ SUMMARY OF PROCEDURE

Position	Lateral decubitus with axillary roll. Table flexed.
Incision	Posterior border between erector spinae and abdominal oblique muscles
Special instrumentation	Fluoroscopic imaging
Unique considerations	EMG monitoring: avoid muscle relaxation
Antibiotics	Cefazolin 1g iv
Surgical time	2-3 h
Closing considerations	Minimal suturing
EBL	20-100 mL
Postop care	PACU. Mobilization as tolerated. Usually discharged within 24 h.
Mortality	Rare
Morbidity	Reported complication rates: 6.2-52% Iliopsoas weakness Anterior thigh numbness Quadriceps weakness Radiculopathy Foot drop Durotomy
Pain score	4-5

Suggested Reading

1. Adamus M, Hrabalek L, Wanek T, Gabrhelik T, Zapletalova J: Intraoperative reversal of neuromuscular block with sugammadex or neostigmine during extreme lateral interbody fusion, a novel technique for spine surgery. J Anesth 2011; 25(5):716-20.

2. Arnold PM, Anderson KK, McGuire RA Jr: The lateral transpsoas approach to the lumbar and thoracic spine: a review. Surg Neurol Int 2012; 3(Suppl 3):S198-215.

3. Ozgur BM, Aryan HE, Pimenta L, Taylor WR: Extreme Lateral Interbody Fusion (XLIF): a novel surgical technique for anterior lumbar interbody fusion. Spine J 2006; 6(4):435-43.

4. Rodgers WB, Gerber EJ, Patterson J: Intraoperative and early postoperative complications in extreme lateral interbody fusion: an analysis of 600 cases. Spine (Phila PA 1976) 2011; 36(1):26-32.

5. Tohmeh AG, Rodgers WB, Peterson MD: Dynamically evoked, discrete-threshold electromyography in the extreme lateral interbody fusion approach. J Neurosurg Spine 2011; 14(1):31-7.

6. Youssef JA, McAfee PC, Patty CA, et al: Minimally invasive surgery: lateral approach interbody fusion: results and review. Spine (Phila PA 1976) 2010; 35(26 Suppl):S302-11.

ANESTHETIC CONSIDERATIONS

PREOPERATIVE

Patients undergoing minimally invasive spine procedures are no more likely than the general population to have any specific medical condition; they require normal preop evaluation.

Musculoskeletal	Because these patients may have chronic back pain with radiculopathy, they may not be suitable candidates for regional anesthetic techniques. Postop exacerbation of symptoms may be incorrectly ascribed to the anesthetic technique. A careful motor and sensory evaluation of the lower extremities should be documented. Patients commonly taking centrally acting analgesics or narcotics may require higher doses of sedative-hypnotics and analgesics in the periop period.
Hematologic	Patients should stop taking aspirin or NSAIDs at least 2 wk before surgery. In addition, an INR or PT and PTT should be checked preop. Tests: Hct; Plt; INR
Laboratory	Other tests as indicated from H&P
Premedication	Standard premedication (see p. B-1)

INTRAOPERATIVE

Anesthetic technique: Minimally invasive spine procedures are commonly done under GA; however, local or regional anesthetic techniques are suitable in selected patients. Percutaneous discectomies typically require only MAC with sedation. These patients must be awake to alert the surgeon to inadvertent nerve root contact. In some centers, regional anesthesia (spinal or epidural) is the anesthetic of choice.

General Anesthesia:

Induction	Standard induction (see p. B-2). Consider using wire-reinforced ETT to prevent kinking, with patient in prone position.
Maintenance	Standard maintenance (see p. B-3). Usually 1-2 h operation. After exposure, further muscle relaxant use is unnecessary.
Emergence	No special considerations
MAC	See p. B-4-B-5.

Regional anesthesia:

Spinal	Patient in sitting, lateral decubitus, or prone position for placement of subarachnoid block. Doses of local anesthetics should be adequate to provide a high lumbar level of sensory anesthesia (e.g., bupivacaine 6-10 mg with fentanyl 10 mcg).
Epidural	Patient in sitting or lateral decubitus position for placement of epidural catheter. A test dose (e.g., 3 mL of 1.5% lidocaine with 1:200,000 epinephrine [5 mcg/mL]) is administered, and the patient is observed for development of subarachnoid block or Sx of an intravascular injection. Titrate lidocaine 2% with epinephrine (3-5 mL at a time) until desired surgical level is obtained.
Blood and fluid requirements	IV: 18-20 ga × 1 NS/LR @ 5 mL/kg/h	Blood not likely to be required.
Monitoring	Standard monitors (see p. B-1)
Positioning	[check mark] and pad pressure points [check mark] eyes	Lateral position: use axillary roll Prone position: Jackson table, Wilson frame, or bolsters to support shoulders/hips and optimize ventilation. Knee-chest position: Andrews table. Place head in cushioned holder with cutout for eyes, nose, chin (e.g., ProneView®). Make certain eyes, nose, and chin are free and clear. Ensure that there is no posterior pressure on the ET tube, as this may result in injury to the uvula or soft palate. Pad elbows, knees, other pressure points. Limit both upper arm abduction and elbow extension to < 90°.

POSTOPERATIVE

Complications

Urinary retention in the older patient

Transient numbness/paresthesias, weakness

Rx: Consider catheterization.

Due to nerve-root irritation from operation. Rx with analgesics and/or muscle relaxants methocarbamol, cyclobenzaprine.

Pain management

PCA (p. C-3)

Ketorolac 30 mg iv

Epidural analgesia (p. C-2)

PO analgesics may be suitable: acetaminophen and codeine (Tylenol #3 1-2 tab q 4-6 h) or oxycodone and acetaminophen (Percocet 1 tab q 6 h) Dose prior to the removal of an epidural catheter at the end of the case if it is already in place (p. C-2).

Tests

As indicated by patient status

Patient usually discharged from hospital within 24-48 h.