Microscopic Lumbar Discectomy

Overview

Microscopic lumbar disc excision has replaced standard open laminectomy as the procedure of choice for herniated lumbar disc. It can be done as an outpatient procedure, with better lighting, magnification and angle of view through a much smaller exposure, less postoperative pain and a shorter stay (Campbell). More than 95% of lumbar disc ruptures occur at L4-5 or L5-S1 (Campbell).

Clinical Evaluation (Campbell)

• Typical history: recurrent low back and buttock pain relieved by rest, then a sudden flexion-related exacerbation with leg pain; radicular pain extends below the knee in a dermatomal pattern and is equal to or greater than back pain. Pain increases with sitting, driving, coughing and straining.

• Be skeptical when back pain predominates, when the pain pattern is bizarre or uniform, or when weakness and paresthesias are generalized.

• Lasègue / straight-leg raising reproducing pain below the knee; contralateral straight-leg raising pain is pathognomonic. The "flip sign" (leaning back to relieve pain) may be seen. Older patients may have a negative Lasègue sign. The femoral stretch test helps with upper lumbar herniations.

• Cauda equina syndrome: bilateral leg numbness and weakness, rectal and perineal numbness, sphincter paralysis; a post-void residual of 200 mL is the most accurate cutoff in a meta-analysis. Evaluate and treat aggressively.

• Differential diagnosis includes ankylosing spondylitis, myeloma, vascular insufficiency, hip arthritis, osteoporotic stress fracture, extradural tumor, peripheral neuropathy, herpes zoster, synovial cyst and sacroiliac dysfunction.

• MRI is the most useful test; plain radiographs do not show herniation but should be obtained if surgery is planned. Use CT after myelography when myelography is needed.

Nonoperative Treatment (Campbell)

• About 2 days of relative rest is better than longer; semi-Fowler side-lying position, ice, NSAIDs, brief oral steroids; resume ordinary activity within the limits of pain; physical therapy unless it aggravates radiculopathy.

• Natural history is favorable: about 95% return to previous work within 3 months. Failure to return within 3 months is a poor prognostic sign.

Indications for Surgery (Campbell)

• The optimal candidate has predominantly unilateral leg pain below the knee for at least 6 weeks, which improved with rest, anti-inflammatories or epidural steroids but returned after 6-8 weeks of conservative care; nerve tension signs and possibly objective neurologic deficit; imaging that matches the examination.

• Surgery is mandatory and urgent only for cauda equina syndrome; all other disc excisions are elective.

• Disc surgery relieves leg pain; patients with predominantly back pain may not benefit.

Technique 46.4: Microscopic Lumbar Discectomy (Campbell)

Setup

• General anesthesia; prone in the knee-chest position on a specialized frame (e.g., Andrews table) or on chest rolls. The free-hanging abdomen reduces epidural venous bleeding; the knee-chest position tensions the ligamentum flavum and opens the interlaminar space.

• Operating microscope (400-mm lens), small angled Kerrison rongeurs, microinstruments and a suction-nerve root retractor. Mark pituitary rongeurs at the maximal safe disc depth. Every sponge or patty must extend outside the wound. Control epidural bleeding with bipolar cautery.

Approach with a McCulloch retractor

1. Infiltrate muscle, subcutaneous tissue and skin with bupivacaine with epinephrine.

2. Incise from the midspinous process of the upper vertebra to the superior margin of the lower spinous process (about 25-30 mm); move slightly higher for upper lumbar levels.

3. Incise the fascia in the midline and elevate muscle subperiosteally from the spinous processes and lamina on the involved side only.

4. Confirm the level with a lateral radiograph and a clamp on the spinous process.

5. Sweep remaining muscle laterally with a Cobb elevator to expose the interlaminar space; cauterize bleeding.

6. Insert the McCulloch retractor with the shorter spike medial and the flat blade lateral.

Approach with a tubular retractor

1. Under fluoroscopy, insert an 18-gauge needle about the radius of the final tube lateral to the spinous process (e.g., 8 mm for a 16-mm tube), orthogonal to the target disc, usually in line with the superior endplate of the caudal vertebra.

2. Make a 20-mm incision; pass the blunt end of the guidewire only through the lumbodorsal fascia (never down to bone, to avoid entering the interlaminar space and dura).

3. Dilate sequentially to bone on the trailing edge of the cephalad lamina; mount a 14- to 16-mm tube (18-24 mm while learning) on a table arm and confirm position.

Decompression and discectomy (both approaches)

1. Elevate the superficial leaf of the ligamentum flavum from the leading edge of the caudal lamina and resect it to identify the critical angle: the junction of the leading edge of the caudal lamina and the medial edge of the superior articular process. The pedicle is always just lateral to it, the traversing root just medial to the pedicle, and the target disc just cephalad.

2. Drill the trailing edge of the cephalad lamina up to the ligamentum flavum insertion (and the medial inferior articular process if needed).

3. Detach the ligamentum flavum with an angled curette and excise it, ideally in one piece, with a Kerrison rongeur oriented parallel to the root, working caudal to cephalad along the medial superior articular process.

4. Palpate the medial wall of the pedicle; identify the traversing root just medial to it.

5. Mobilize the root medially, dissecting it gently off the fragment. Difficulty mobilizing the root suggests a conjoined root.

6. Explore extradurally under the root with a 90-degree blunt hook; magnification can make the dural edge look like the root.

7. When using bipolar cautery, let only one tip touch the root. Do not remove epidural fat.

8. Retract the root medially with the suction-root retractor; the disc appears white, fibrous and avascular.

9. Enlarge the annular tear with a Penfield No. 4 and remove fragments with a pituitary rongeur, never inserting it beyond the angle of the jaws (about 15 mm) to avoid anterior perforation and vascular injury. Pressure on the adjacent annulus can express subannular fragments.

10. Remove loose fragments, inspect the root and dura, and irrigate the disc space forcefully.

11. End points: the lateral recess is decompressed; a 90-degree probe passes behind the cephalad body, disc and caudal body to the midline without protrusions; the probe can be spun under the root (helicopter maneuver); and the root retracts freely medially and laterally. Dural pulsation alone does not confirm adequate decompression.

12. If the expected pathology is not found, review imaging and repeat level localization, considering transitional anatomy.

13. Close the fascia and skin with absorbable sutures (McCulloch); with a tube, simply remove it and close the skin, since the fascia was dilated rather than incised.

Postoperative care (Campbell)

• Usually outpatient. Bupivacaine in the paraspinal muscles at the start and end aids early mobilization. Skin glue without a dressing allows showering on the day of surgery; activity as tolerated once the incision has healed.

Complications (Campbell)

Dural tear repair (Eismont, Wiesel and Rothman) (Campbell)

1. Ensure an unobstructed, dry, well-exposed field.

2. Repair with 4-0 or 6-0 suture (simple or running locking); use a fat or fascial graft for large or inaccessible leaks. Fibrin glue helps but alone does not seal a significant leak.

3. Test the repair with reverse Trendelenburg and Valsalva.

4. Close muscle and fascia in two watertight layers with nonabsorbable suture; no drains.

5. With a good closure, mobilize the day after surgery; use extended bed rest with a lumbar drain only if the closure is questionable.

• After tubular (18 mm or smaller) or endoscopic discectomy, small tears without root herniation can usually be treated with fibrin glue, plus a 3-day course of acetazolamide; lie flat for 72 hours only if positional headaches occur; a blood patch or reexploration if headaches persist.

• Postural headache and a stormy course suggest an undetected leak; confirm with MRI.

References

1. Thompson KM. Degenerative disorders of the thoracic and lumbar spine. In: Azar FM, Sawyer JR, Throckmorton TW, eds. Campbell's Operative Orthopaedics. 15th ed. Philadelphia: Elsevier; 2026. Chapter 46, Technique 46.4.