Lumbar Discectomy: Is Tubular or Endoscopic Discectomy Better Than Traditional Microdiscectomies?

1 Lumbar Discectomy: Is Tubular or Endoscopic Discectomy Better Than Traditional Microdiscectomies?

MIS: Martin H. Pham, Alexander Tuchman, and John C. Liu
Open: John D. Attenello, Steven R. Garfin, and Richard Todd J. Allen

1.1 Introduction

Mixter and Barr 1 described the first discectomy for lumbar disc herniation in 1934, where they performed a laminectomy with a transdural approach to remove the intervertebral disc. A few years later, Love^2,3 described an intralaminar, extradural approach to disc removal. This procedure serves as the basis for open discectomy (OD) today and remained largely unchanged until the 1970s when the introduction of the surgical microscope gave rise to less invasive approaches with smaller incisions, less tissue dissection, and decreased surgical manipulation and trauma to the musculature and nerve roots. Yasargil⁴ and Caspar⁵ were the first to independently describe their use of the operating microscope to refine the previous approach into the open microdiscectomy, which is currently the most common surgical procedure for lumbar disc herniation worldwide.^6,7,8,9 Continued advancements in visualization technology prompted an increase in minimally invasive discectomy (MID) techniques¹⁰ designed to minimize postoperative pain and hospital stays and allow for quicker mobilization and resumption of daily activities.

In 1997, Foley and Smith¹¹ described microendoscopic discectomy (MED) as a transmuscular technique to gain access to the disc via dilators of increasing diameter and a tubular retractor, whereby simultaneous visualization and removal of disc can be performed through a single portal. This replaced the conventional subperiosteal approach. These minimally invasive techniques were introduced to speed up recovery rates and decrease morbidity while achieving comparable clinical outcomes; however, studies evaluating functional outcomes and complications, comparing MID and OD, have not shown consistent benefit.

1.2 Indications

Lumbar discectomy is an effective surgical treatment for lumbar disc herniation causing nerve root compression and presenting with radiating leg pain, paresthesias, and back pain. Severe symptoms refractory to conservative treatment for ≥ 6 weeks commonly necessitate the removal of all or part of the offending intervertebral disc fragment, to decompress the nerve root. Other indications for surgery include intractable pain, new or progressive weakness, saddle anesthesia, or bowel/bladder symptoms suggesting cauda equina syndrome. In cases of congenital stenosis requiring decompression, to minimize iatrogenic neural injury, and possibly in cases of cauda equina syndrome, an open approach may be favored to expand the bony decompression and access the disc/stenosis at multiple angles (sometimes limited by endoscopic and tubular approaches).

1.3 Advantages of Minimally Invasive Surgery

Traditional open surgery requires muscle dissection and retraction, of which the iatrogenic morbidity of soft-tissue injury has been well established.12,13,14 Minimally invasive surgery (MIS) approaches involve a less traumatic approach with tubular retractors to temporarily expand a surgical corridor through the soft tissue, which then falls back in place at the completion of the operation. The use of a tubular retractor for MIS discectomy minimizes tissue injury and ensures that deeper tissues are less exposed to potential pathologic organisms as a result of the restricted surgical field.^15,16,17 The advantages of minimally invasive surgical techniques also include smaller incisions with reduced soft-tissue damage and faster immediate postoperative recovery. This in effect allows for a shorter hospital stay and an earlier return to work.

1.4 Advantages of Open Surgery

A commonly cited advantage of OD is the historical success of the procedure. OD is well known to spine surgeons and has been developed and refined since the 1930s with consistently favorable results demonstrated in numerous studies since then.18,19,20,21,22,23,24,25 Furthermore, many of the most powerful or highest level studies evaluating patient outcomes in micro-discectomy are those primarily employing open techniques. The ubiquitous nature of the open approach avoids the steep learning curve of MIS techniques, which can be associated with unfavorable outcomes and increased risk of complications particularly early on and when extension to open is needed. Additional advantages of OD include greater visualization of the dural sac/neural elements and surrounding structural relationships, direct visualization of all anatomic structures, ability to access extruded/migrated fragments safely by extending the decompression or obtaining the optimal angle for disc removal, and lower costs for instrumentation.

1.5 Case Illustration

A 36-year-old man with a history of low back pain developed worsening left leg pain into the foot that failed anti-inflammatory medications, muscle relaxants, physical therapy, and activity modifications. Despite three epidural steroid injections over a 4-month period, he continued to have worsening leg pain and mild ankle dorsiflexion weakness. Imaging studies showed a left L4–L5 paracentral disc herniation ( Fig. 1.1a,b) without evidence of instability on flexion and extension lateral lumbar radiographs.

Fig. 1.1 (a) Sagittal and (b) axial magnetic resonance imaging of the lumbar spine demonstrating a broad central disc herniation at L4–L5 compressing the left L5 nerve root.

1.6 Surgical Technique in Minimally Invasive Surgery

After general endotracheal intubation is obtained, the patient is positioned prone onto a Jackson table with a Wilson frame. Arms are positioned up by the head, the neck is checked to be in appropriate neutral position, and all pressure points are appropriately padded. The bed attachment for the tubular arm is placed on the contralateral side of the planned MIS discectomy. The area is then prepped with antiseptic solution and draped in standard surgical fashion.

Anteroposterior fluoroscopy is used to confirm that the patient is not rotated, and then lateral fluoroscopy is used with a 22-gauge needle to mark the appropriate level and trajectory to the intended disc space. An 18-mm incision is made in the skin, which is then dissected down with monopolar electrocautery until fascia is reached. The fascia is then also opened with electrocautery. A Kirschner wire is then carefully docked on the lamina, and serial tubular dilation is used around the wire until the appropriate-sized tubular retractor is reached. Lateral fluoroscopy is used to confirm the correct level, and anteroposterior fluoroscopy can be used to confirm that the tube is medialized toward the spinous process. This last fluoroscopy film is especially important in patients with large facet joints, given the facet joint may be mistaken for the lamina if the tube has been docked too laterally.

The microdiscectomy portion of the operation then proceeds in standard fashion after the microscope or endoscope is brought in. The base of the spinous process and inferior edge of the lamina are identified after dissection of the soft tissue. A matchstick drill is then used to drill a laminotomy down to the ligamentum flavum. The ligamentum is carefully removed with a combination of curettes and Kerrison rongeurs until the dura and nerve root are identified. The thecal sac and nerve root shoulder are then carefully retracted and the offending herniated disc is subsequently removed. Appropriate decompression is then confirmed by tactile feel with a curette or nerve hook.

Copious irrigation is used to clean out the wound. The fascia, dermis, and skin are subsequently closed in multiple layers with absorbable sutures.

1.7 Surgical Technique in Open Surgery

Following informed consent, the patient is brought to the operating room and endotracheal anesthesia is administered. Preoperative antibiotics are given, lower extremity pneumatic compression devices are placed, and the patient is positioned prone on either a Wilson frame, or longitudinal or transverse gel rolls, or Jackson frame, with the abdomen free and all bony prominences padded. After partitioning off the region of interest, we prefer to prepare the operative area with chlorhexidine scrub, followed by drying and then using C-arm fluoroscopy imaging in anteroposterior and lateral planes, to mark our site for incision. The patient is then sterilely prepped and draped, and following an intraoperative time-out and the injection of 0.25% Marcaine with epinephrine, an incision is made in the midline with dissection toward the side of the herniation. The incision is typically just over 2 cm, but may be larger in larger patients. In most cases, we prefer the use of an intraoperative microscope, both for teaching purposes and for visualization. Dissection ensues through subcutaneous tissue, lumbodorsal fascia, and then onto the spinous process of the affected area. A Cobb and Bovie are used to expose the bony anatomy along the spinous process and onto the lamina. This plane is developed to the facet joint capsule, which is identified and preserved. The pars is identified above and below the facet joint, which often lies at the level of, and just caudal to, the more ventrally located herniated disc. A McCullough retractor is generally preferred. C-arm fluoroscopy imaging is brought in to verify the correct level of surgery prior to significant dissection. A spinal needle can be placed in the interspinous process ligaments on a Penfield 4 just under the inferior edge of the superior lamina of the space prior to obtaining the image. A matchstick burr can be used to thin the lamina overlying the disc, if needed (thick, overhanging) and a curette used to develop a plane on the underside of the remaining superior lamina and ligamentum flavum. Bone and ligamentum flavum are removed or released with Kerrison rongeurs to develop the working window laminotomy for discectomy, working proximally and laterally to free tethered ligamentum as needed. Once the epidural fat/space is identified, bipolar cautery and gentle retraction are used to optimize hemostasis and identify the offending disc herniation. An annulotomy knife is used, if necessary, and the disc is removed using a pituitary or other micro-instruments. Closure is done following irrigation and obtaining hemostasis, with #1 Vicryl, 0-Vicryl, and 2–0 Vicryl, and then Monocryl in running fashion. Dermabond is applied, followed by a sterile dressing. Ropivacaine can be infiltrated prior to final closure to help with postoperative anesthesia and pain control.

1.8 Discussion of Minimally Invasive Surgery

Multiple advantages of the MIS approach over standard approaches have been shown, with the MIS tubular technique showing lower infection rates, lower cerebrospinal fluid (CSF) leak rates, and shorter hospital stays, with outcomes similar to open surgery ( Table 1.1).

1.8.1 Level I Evidence in Minimally Invasive Surgery

Arts et al performed a prospective, multicenter, double-blinded randomized trial comparing 8-week and 1-year outcomes in patients undergoing tubular discectomy versus conventional open microdiscectomy for treatment of disc herniation refractory to conservative measures.26 In total, 167 patients were assigned to receive discectomy via endoscopic approach and 161 were assigned to a conventional microdiscectomy approach. At 1 year, patients in the open approach reported higher improvements in back and leg pain (visual analog scale [VAS]: −4.2 mm for open group vs. −3.5 mm for MIS group). Sixty-nine percent of patients in the MIS discectomy group reported good outcomes at 1 year, compared with 79% of patients in the conventional microdiscectomy group. However, when results were expanded to 2-year follow-up, no statistically significant differences were found in good clinical outcomes (71% of patients in MIS group vs. 77% of patients in open group) or reoperation rates (15% of patients in MIS group vs. 10% of patients in open group) between patients undergoing minimal invasive versus microdiscectomy. Of note, similar disc reherniation rates were seen between the two groups, with patients in the minimally invasive group having shorter hospital stays, earlier time to mobilization, and less progression of sensory and motor deficits postoperatively.

A Cochrane review by Rasouli et al compared the benefits and harms of MIS discectomy versus standard microdiscectomy or OD in symptomatic lumbar disc herniation.²⁷ They identified 11 randomized controlled trials (1,172 patients) which compared the two approaches for the treatment of adults with lumbar discectomy caused by discopathy. They found low-quality evidence that MIS approaches were associated with worse leg pain at follow-up from 6 months to 2 years, but differences were small (less than 0.5 points on a 0 to 10 scale) and did not meet thresholds for clinically meaningful significance. Low-quality evidence also suggested no significant differences in back pain comparing the two approaches out to 1 year of follow-up. The authors also found no differences on outcomes related to functional disability as measured by the Oswestry Disability Index (ODI). With regard to secondary outcomes, MIS approaches were associated with a lower risk of surgical site infections and shorter hospital stay, although available evidence was inconsistent.

Gempt et al randomized 60 patients to receive either a traditional open approach or an MIS approach discectomy for single-level lumbar disc herniations.²⁸ Over a mean follow-up time of 33 months, patients were evaluated with physical health, mental health, and pain relief questionnaires using the ODI, Short Form Health Survey (SF-36), and the VAS for back and leg pain. Patients in both groups demonstrated significant improvements in leg and low back pain with good to excellent recoveries by ODI and SF-36 evaluations. There was no statistically significant difference observed between the two groups with regard to long-term VAS, ODI, or SF-36 outcomes.

1.8.2 Level II Evidence in Minimally Invasive Surgery

Kamper et al recently conducted a meta-analysis of 29 studies examining differences between minimally invasive and conventional microdiscectomy in 4,472 patients with sciatica from lumbar disc herniation.29 They found low-quality evidence to support a shorter mean hospital stay in the MIS group, with a difference of 1.5 days. Although the analysis was in favor of the MIS group, the hospital times were variable and the source of the variability was unclear to the authors. There was moderate to low-quality evidence to suggest no differences in clinical outcomes, complications, or reoperations between MIS and open approaches for discectomy.

1.8.3 Level III and IV Evidence in Minimally Invasive Surgery

Harrington and French sought to compare operative times, length of hospital stay, and narcotic use in their retrospective review of single lumbar microdiscectomy patients performed by a single surgeon using a traditional open versus a minimally invasive approach.30 There were 35 patients in the open group and 31 in the minimally invasive group. No differences were found with regard to intraoperative complications, surgical time, blood loss, or outcome. However, 45.2% of MIS approach patients were discharged on the same day versus 5.75% in the OD group (p = 0.001). The MIS group also used less intravenous morphine (p = 0.04) and less hydrocodone (p = 0.03), and did not use any oxycodone for pain control (vs. an average of 11.7-mg oxycodone in the open group).

Lau et al also compared differences in microdiscectomy performed via MIS techniques or open approaches by a single surgeon.³¹ A retrospective analysis of 25 patients undergoing open microdiscectomy as compared with 20 patients receiving an MIS approach found no statistically significant differences in operative time, length of stay, outcome, or complication rates.

1.9 Complications in Minimally Invasive Surgery

Surgical site infections can be a source of significant morbidity that itself can lead to further major complications and worse outcomes.16,32,33,34,35,36,37 The treatment of these complications can require long-term antibiotic therapy, additional procedures or operations, and prolonged hospitalizations. Identifying risk factors to reduce infection is important toward developing a strategy of preventing this complication.

Ee et al conducted a retrospective review of 2,299 patients undergoing transforaminal lumbar interbody fusion, laminectomy, or discectomy and identified 27 cases of surgical site infections.15 After matching with controls and stratifying by procedure, they found that patients undergoing open spinal surgery were 5.77 times more likely to develop infections compared with MIS approaches. Specifically in patients undergoing laminectomy or laminotomy with or without discectomy, there were seven cases of infection in the open group as compared to three in the MIS group. Although their statistical significance was borderline, they suggested that surgical approach was an independent risk factor for postoperative surgical site infections.

O’Toole et al sought to determine the rate of surgical site infections for MIS spinal surgeries.¹⁶ They reviewed their experience of 1,338 MIS spinal surgeries and found an overall infection rate of only 0.22%. When looking specifically at MIS discectomy, foraminotomy, or decompression, the infection was lower at only 0.10% inclusive of both superficial and deep infections. This is in comparison to recent literature on open laminectomy reporting a surgical site infection of 1.0% among 6,365 patients.³⁸ Authors of other series have similarly reported rates of surgical site infections of 0.2 to 2% after simple open decompressive procedures, in particular microdiscectomy.^{16,31,32,33,38,39}