The surgical treatment of single level multi-focal subarticular and paracentral and/or far-lateral lumbar disc herniations: the single incision full endoscopic approach.

BACKGROUND: Surgery for same level multi-focal extruded lumbar disc herniations is technically challenging and the optimal method controversial. The subarticular disc herniation may pose the most challenging subtype requiring partial or complete facetectomy with or without fusion. The far-lateral disc herniation, often treated using a Wiltse approach, can also be difficult to access especially in the obese patient. When both the subarticular and far-lateral subtypes are simultaneously present at the same level with or without a paracentral disc herniation, a total facetectomy and interbody fusion (TLIF) or a total disc replacement (TDR) may be necessary. Endoscopic surgical techniques may reduce the need for these more invasive methods.
METHODS: Fifteen patients (6 male and 9 female) who had same level multi-focal (subarticular as well as far-lateral and/or paracentral) extruded disc herniations underwent single incision unilateral endoscopic disc excision by the same surgeon at a single institution. Patients were prospectively followed for an average of 15.3 months (range 14-18 months) and outcomes were evaluated radiographically and clinically (Visual Analogue Scale (VAS) and Oswestry Disability Index (ODI).
RESULTS: The mean operative time was 52 minutes with minimal blood loss in all cases. Fourteen of the 15 patients were discharged to home on the day of their surgery. The mean ODI and leg VAS scores improved from 22.9 ± 3.2 to 12.9 ± 2.7 (p < 0.005), and from 8.6 ± 1.6 to 2.1 + 0.4 (p < 0.005), respectively.
CONCLUSIONS: After an average of 15.3 months of follow-up, the clinical and radiographic results of full endoscopic surgical treatment of single level multi-focal (subarticular as well as far-lateral and/or paracentral) disc herniations are excellent. This study is a case series with mid-term follow-up (Level IV). CLINICAL RELEVANCE: Foraminal and extra-foraminal full endoscopic decompression appears to offer a safe minimally invasive solution to a complex pathologic problem.

Introduction

Posterior open treatment methods such as lumbar posterior discectomy, micro-lumbar discectomy, and micro-endoscopic discectomy (MED) have been used to treat uni-focal central, paracentral, or far-lateral lumbar disc herniations causing symptomatic lumbar radiculopathy.[1-17] Approximately three decades ago, Kambin described the endoscopic posterolateral approach using the triangular region he termed the “safe zone”.[18-23] More recent research has explored the use of full endoscopic techniques to treat lumbar disc herniations at various anatomical locations.[24-40]

Most, if not all, of these open as well as endoscopic discectomy studies have focused on the treatment of uni-focal disc herniations. To the best of our knowledge, multi-focal herniations that include a combination of central/paracentral, subarticular, and far-lateral herniations have not been studied. Our paper explores the use of modern full endoscopic techniques in the treatment of multi-focal lumbar disc herniations at a single intervertebral level.

Materials & Methods

This Institutional Review Board approved study enrolled patients with symptomatic and recalcitrant radicular pain secondary to multi-focal lumbar disc herniations. All patients had magnetic resonance imaging (MRI) evidence of at least 2 uni-level foci of lumbar disc herniation. The herniation foci were classified as either; (1) central/paracentral, (2) subarticular, or (3) far-lateral.

All patients underwent preoperative MRI and computed tomography (CT) of the lumbar spine. Plain X-rays (standing antero-posterior, lateral, and flexion / extension views) were obtained preoperatively and 1 year postoperatively. Preoperative and postoperative (6 week, 6 month and 12 month) clinical outcome data (back and leg VAS and ODI scores) were collected along with clinical assessments of motor strength (graded 0-5), light touch, pain, reflexes, and proprioception. All of the cases were performed by the same surgeon at a single institution.

The surgical approach was either the intra-foraminal approach (Figure 1) as described by Reutten[32-34] or the intradiscal approach described by Kambin and Yeung.[38] Surgeries were performed in the prone position on a Wilson frame using fluoroscopic guidance under combined local and intravenous sedation. Spinal cord stimulation was not utilized. All patients received preoperative antibiotic prophylaxis.

Fig. 1

Intra-foraminal needle starting point just anterior to the posterior facet line.

Regardless of the pattern of multi-focal disc herniation, the subarticular component was excised first prior to addressing either the intra-canal or far-lateral herniation. If the preoperative assessment of the foraminal anatomy revealed bony stenosis (especially in the inferior foraminal zone), endoscopic decompression was not performed due to the risk of pinching the nerve between the pedicle and the upwardly displaced endoscope. Even in the absence of bony foraminal stenosis, care was taken to approach the disc space from the inferior aspect of the disc and to slowly remove subarticular herniated fragments so as to not displace herniated disc material cranially towards the exiting nerve root.

Results & Statistical Methods

Six male and 9 female patients, with an average age of 46 years (range 24-53 years), were determined to have single-level multi-focal lumbar disc herniations (Table 1). Six patients demonstrated simultaneous paracentral and subarticular herniations at the L3-4 (2) and L4-5 (4) levels; 6 patients exhibited concurrent paracentral, far-lateral, and subarticular herniations (L3-4 (1) and L4-5 (5)); and three patients were found to have subarticular and far-lateral disc herniations (L3-4 (1) and L4-5 (2)). Three patients had undergone previous decompression attempts. Mean operative time was 52 minutes with minimal blood losses. All patients received local/intravenous sedation for surgical anesthesia. Fourteen of the 15 patients were discharged to home on the same day of surgery and all patients were followed for a minimum of 14 months.

Table 1

Case Distribution

	Subarticular + Paracentral/Central	Subarticular + Far lateral	Subarticular + Far lateral and Paracentral/Central
L3–4	2	1	1
L4–5	4	2	5

The average Oswestry Disability Index score improved from 22.9 ± 3.2 to 12.9 ± 2.7 (p < 0.005), and the average leg Visual Analog Scale improved from 8.6 ± 1.6 to 2.1 ± 0.4 (p < 0.005). No significant changes in disc height or range of motion (ROM) were noted on plain radiographs. Return to work averaged 7 days postoperatively. No patients required reoperation. There were no incidental durotomies, infections, vascular or visceral injuries. One patient, 6 months following surgery, experienced isolated extensor hallucis longus (EHL) weakness without foot drop – a recurrent disc herniation was not identified on repeat imaging.

Case #1

54 year old white male

5'10” 225 lb BMI 31.82 kg/m2

Attorney, Non-smoker

Injured back while lifting a 200 lb tree 2 months prior to initial presentation

Primary Complaint: Burning left-anterior thigh pain (minimal axial back pain)

Preoperative Imaging: Figure 2A & B.

Fig. 2

A: Sagittal MRI (the red arrow identifies the foraminal herniated nucleus pulposus (HNP)). B: Sub-articular (SA) and far-lateral (FL) disc herniations.

Intraoperative Imaging: Figure 3A, B, & C.

Fig. 3

A: Left L3 nerve root (NR) with far lateral herniated nucleus pulposus (HNP) medial to the nerve. B: L3 nerve root (NR) partially decompressed. HNP (herniated nucleus pulposus). C: L3 nerve root decompressed. Kambin (K) triangle visualized. D: Normal full left hip extension 10 days post-operative.

Postoperative Clinical Function: Figure 3D.

Case #2

48 year old white female

5'4” 135 lb BMI 23.2 kg/m2

Waitress, Non-smoker

History of a hypercoagulation disorder

Injured back while walking in deep snow

Primary Complaint: Severe right buttock and leg pain

Preoperative Imaging: Figure 4A & B.

Fig. 4

A, B: Subarticular (SA) and paracentral (PC) herniated nucleus pulposus (HNP). C: Extruded disc (HNP) surrounding nerve root (NR). D: Post-discectomy, decompressed nerve root (NR) surrounded by epidural fat.

Intraoperative Images: Figure 4C & D.

Postoperative Imaging: Figure 5A & B.

Fig. 5

A, B: Post-operative MRI 5 months after discectomy.

Case #3

62 year old white female

5'2 110 lb BMI 20.3 kg/m2

History of two prior L4-5 decompressions / laminotomies by Wiltse approach

Primary Complaint: Left buttock and leg pain

Preoperative Imaging: Figure 6; Figure 7.

Fig. 6

A, B: Preoperative MRI demonstrating L4-5 foraminal/subarticular herniated nucleus pulposus (HNP) and far-lateral HNP. Nerve root (NR) compression demonstrated.

Fig. 7

Pre-operative back showing two previous surgical incisions.

Intraoperative Images: Figure 8; Figure 9; Figure 10.

Fig. 8

Intradiscal starting (INTRA) line more medial and extra discal / intra foraminal (EXTRA) starting line more lateral. Dark line is posterior facet line (PFL).

Fig. 9

A: Subarticular herniated nucleus pulposus (HNP).B: L3 nerve root.

Fig. 10

Postoperative incision (9 mm).

Case # 4 (Not included in study population): Uni-focal disc herniation (Figure 11).

Fig. 11

A, B: MRI of uni-focal herniated nucleus pulposus (HNP).

30 year old white male

6'1’ 290 lb BMI 38.3 kg/m2

Presented to clinic in July and needed to be sufficiently recovered to return to work as a school teacher no later than August 15th

No traumatic injury

Primary Complaints: Back and bilateral buttock pain (R > L)

Discussion

Traditional (posterior open and microdiscectomy) lumbar discectomy research has been focused primarily, if not exclusively, on uni-focal disc herniations (Figs 11A and 11B).[1–17, 41–49] These papers have analyzed either paracentral/central or far-lateral disc herniations but have not included the sub-articular sub-type. Patients with single-level multi-focal disc herniations have been largely ignored. This study examines the surgical outcomes of patients who exhibit a multi-focal pattern of disc herniation (Figure 2; Figure 3; Figure 4; Figure 5; Figure 6; Figure 7; Figure 8; Figure 9; Figure 10). Specifically, we enrolled patients who, at a single lumbar level, experienced a subarticular disc herniation coupled with either a far-lateral and / or a paracentral / central disc herniation. Approximately one quarter of our patients had previous decompression attempts.

Kitagawa recently published a case report on the endoscopic treatment of the simultaneously occurring “intracanal and extracanal” lumbar herniation[28]. Numerous other articles have been published delineating the efficacy of the endoscope for decompressing the far-lateral, paracentral, or subarticular lumbar disc herniation.[24, 25, 27, 29, 30, 32, 34, 36, 38–40, 50–65] We present the outcomes of patients with multi-focal disc herniations who were similarly treated utilizing a full endoscopic technique with direct visualization of the respective discs and neurological structures. Our patients experienced significant short-term improvement in their radicular and axial back symptoms with maintenance of this recovery at an average of 14 months postoperatively.

Endoscopic techniques require a detailed understanding of intra- and extra-foraminal anatomy. The enhanced optics of the endoscope permits intra-canal visualization of the foramen - an essential component of the successful treatment of the multi-focal lumbar disc herniation. In any pattern of the multi-focal disc herniation, excision of the subarticular component should occur first followed by removal of either the intra-canal or far-lateral herniation. The far-lateral disc component is approached inferiorly sweeping cranially with the endoscope to protect the exiting nerve root. Initial needle placement should be performed to facilitate this caudal to cranial inclination of the endoscope.

Postoperatively, patients were permitted to immediately resume their usual activities of daily living and return to clerical forms of work within 7 days. Clerical levels of work were maintained for 6 weeks and then restrictions slowly reduced over a period of 4 weeks. No intra-operative complications were experienced. One case of mild EHL weakness occurred 8 weeks postoperatively but without a radiographically apparent recurrent disc herniation (Fig 5A and 5B). No other neurological problems were encountered.

Potential deficiencies of our study include: (1) the relatively short follow-up, (2) the mixed population of patients - 3 patients with prior lumbar decompressions, and (3) the absence of patients with L5-S1 disc herniations.

The multi-focal lumbar disc herniation has been considered the most difficult pattern of disc disruption to approach surgically often mandating dual approaches and / or fusion techniques. Our early term data suggest that a uni-portal single incision full endoscopic approach can satisfactorily decompress these challenging patterns of disc herniation. Careful preoperative clinical and radiographic assessment utilizing plain X-rays, CT, and MRI is essential to assess the foraminal anatomy for bony facet overgrowth that could necessitate a foraminoplasty prior to discectomy and to identify calcification of the lateral disc complex. In cases that involve decompression of a far-lateral disc herniation, local / intravenous sedation should be considered to permit awake intra-operative neurological monitoring. Activities of daily living and clerical forms of employment can be safely initiated within 7 days following discectomy. Uni-focal endoscopic cases should be attempted prior to undertaking the multi-focal pattern of disc herniation, as the latter requires an advanced level of technical proficiency.