Transforaminal microtubular discectomy for extraforaminal disc herniation using a 14-mm retractor
Article information
Abstract
Study Design
Retrospective observational study.
Purpose
We report our experience with minimally invasive transforaminal (TF) microtubular discectomy using a 14-mm tubular retractor in 20 patients with extraforaminal (EF) disc herniations.
Overview of Literature
Despite the popularity of the TF approach with an open and endoscopic approach, little is known regarding TF microtubular discectomy using a 14-mm diameter tubular retractor.
Methods
A group of 20 patients who failed conservative treatment underwent surgery via the TF approach using a 14-mm tubular retractor from March 2018 to January 2024. Preoperative and postoperative Visual Analog Scale (VAS) and Oswestry Disability Index (ODI) scores were monitored.
Results
A 14-mm tube over the METRx system (Medtronic-Sofamor-Danek) was successfully utilized in all patients. The mean intraoperative blood loss was 29.85±7.02 mL, whereas the mean operative time was 30.50±5.38 minutes. The affected levels were L3–L4 (eight patients), L4–L5 (five patients), L5–S1 (four patients), and L2–L3 (three patients). The VAS score for the leg improved from 7.6±0.77 to 2.0±0.56 immediate after surgery (p<0.001), whereas the postoperative VAS score for the back was 1.23±0.83. The mean ODI score improved significantly from 57.20%±9.36% before surgery to 12.60%±3.18% at 1 year after surgery (p<0.001). One patient had L5–S1 EF recurrent herniation.
Conclusions
TF microtubular discectomy using a 14-mm tubular retractor offers an adequately sized foraminal working channel for effective decompression of the EF disc herniation while reducing pain, improving functional outcomes, and preserving integrity.
Introduction
Extraforaminal (EF) lumbar disc herniations, also known as far-lateral lumbar disc herniations, are quite uncommon, accounting for 1%–12% of all lumbar disc herniations [1–3]. These far-lateral herniations are more challenging to surgically treat than are the more common paramedian variants of the pathology. This complexity in surgical treatment has been attributed to the inherent difficulty of anatomical access to the disc, located lateral to the interpedicular compartment, without risking nerve injury or segmental instability. Disc access is particularly challenging at the L5–S1 level considering that the proximity of the iliac crest limits the corridor for tube docking. Although the transforaminal (TF) approach using an open technique and endoscopic approach have been popular, limited studies have been available regarding the use of these approaches with a tubular retractor, especially a 14-mm diameter tube [4]. The present study aimed to report on our experience with a muscle-splitting system using a 14-mm diameter tubular retractor in a series of 20 patients with EF lumbar disc herniations.
Materials and Methods
Among 536 patients who underwent MIS lumbar discectomy between March 2018 and January 2024, 21 were diagnosed with EF disc herniation. One patient was lost to follow-up and excluded from the final analysis. The remaining 20 patients who failed a trial of conservative management underwent TF microtubular discectomy using a 14-mm tubular retractor system. This retrospective observational study was approved by the Bombay Hospital and Medical Research Centre (IRB approval no., BH-EC-0230). Informed consent for the procedure was obtained from all patients. All patients provided consent after being informed regarding our intent to submit all data collected for publication.
The inclusion criteria were as follows: Lumbar EF disc herniation with failed conservative trial for at least 6 weeks. The exclusion criteria were as follows: concomitant instability, median/paramedian lumbar disc herniation, history of previous spine surgery, requiring multilevel surgery.
Preoperative standing lumbosacral spine radiographs (anteroposterior and lateral views) and magnetic resonance imaging (MRI) were obtained from the hospital records. Leg pain was assessed before the surgery, whereas leg and surgical site pain were assessed after the surgery using the Visual Analog Scale (VAS) score. Patients were followed up at 6 weeks, 6 months, and 1 year after the surgery for clinical assessment of VAS leg pain. Functional outcomes were evaluated using the Oswestry Disability Index (ODI) before and 6 months and 1 year after the surgery.
Data were entered into Microsoft Excel for Windows 10 ver. 2021 (Microsoft Corp., Redmond, WA, USA), and analyses were conducted using the IBM SPSS software ver. 27.0 for Windows (IBM Corp., Armonk, NY, USA). Descriptive statistics, such as mean and standard deviation for continuous variables, and frequencies and percentages were calculated for categorical variables. Normality of data was assessed using the Shapiro-Wilk test. Repeated measure analysis of variance (ANOVA) was used to compare VAS and ODI from baseline preoperative to postoperative at various time intervals. Line diagrams were used to show trends in ODI and VAS over time. The level of significance was set at 0.05.
Surgical procedure
All surgeries were performed in the prone position over horizontal bolsters under general anesthesia on a radiolucent surgical table. Three lines were marked under fluoroscopic guidance: line (a): a longitudinal midline along the spinous process; line (b): a line parallel and approximately (4–6 cm) lateral to line (a); and line (c) a horizontal line along the superior margin of the inferior transverse process (along the disc space). A spinal needle (20G) was inserted at the intersection of lines (b) and (c) (point d) and directed at the junction of the superior articular process and superior margin of the inferior transverse process in the TF space and confirmed under fluoroscopy. A 14-mm vertical skin incision was made centering point d. The first dilator was placed just lateral to the superior articular facet (SAP) line using the spinal needle. Serial dilators were docked over it, aiming the perpendicular angle between superior articular facet and superior endplate of the inferior vertebral border (Kambin’s triangle), which was maintained in place by a table-mounted, multi-axis flexible arm METRx system (Medtronic-Sofamor-Danek, Memphis, TN, USA). A tubular dilator system was used to introduce a 14-mm diameter tubular retractor of varying lengths, which was used in all patients. The surgical microscope was then positioned over the tube for the remainder of the surgery. After the tube landed on the disc, the overlying soft tissue was dissected using a bipolar cautery. A Penfield dissector was cautiously used to dissect and palpate the junction between the SAP and superior vertebral endplate of the inferior vertebra to confirm adequate docking. The inferior medial boundary of the intertransverse ligament was then exposed. While taking advantage of the exiting nerve root being displaced superiorly by the herniated disc, dissection was performed from the inferomedial corner to the superolateral aspect of the tubular retractor while exposing the prolapsed disc. This maneuverer prevents any direct nerve injury. In most cases, the herniation was observed as a sequestered fragment, and discectomy was completed via the conventional microsurgical technique. Adequate nerve root decompression was confirmed intraoperatively based on a freely mobile and pulsatile nerve, as well as an unobstructed passage of a nerve hook along its course within the TF space. The amount of disc material retrieved intraoperatively was correlated with the preoperative MRI findings. After achieving hemostasis, the tubular retractor was withdrawn, allowing the split paraspinal muscles to return to their native orientation. Closure was performed in layers using absorbable sutures. In two out of the four cases with L5–S1 EF disc herniation, a Medtronic burr was used to burr the lateral aspect of the superior articular facet to achieve adequate decompression and improve anatomical access.
Postoperative protocol
All patients achieved out-of-bed mobilization approximately 6 hours after surgery on the same day and started with lower limb static exercises. After changing the dressings to a lighter waterproof material the next morning, the patients were discharged uneventfully on postoperative day 1.
Case 1: Right L5–S1 foraminal and EF disc herniation
A 56-year-old male with right L5–S1 disc herniation had 8 months of radicular pain and motor weakness (power 3/5) in the right L5 distribution (Fig. 1). The patient underwent targeted L5–S1 discectomy via a TF microtubular approach (Fig. 2) through a paramedial incision 5.5 cm away from the midline (Fig. 3A–D). Intraoperative clinical images of adequate decompression are presented in Fig. 3D and E.
Imaging of right L5–S1 foraminal and extraforaminal (EF) disc herniation. (A) Parasagittal magnetic resonance imaging (MRI) cut demonstrating right L5–S1 EF herniation compressing right exiting nerve root. (B) Axial MRI cut showing the herniated disc impinging on the right L5 nerve root.
Case of right L5–S1 extraforaminal disc herniation. (A) Anteroposterior radiograph showing insertion of a 20G needle through point D, targeting the right L5–S1 foramen. (B) Lateral radiograph confirming needle placement at the L5–S1 disc level. (C) Lateral fluoroscopic image demonstrating docking of a 14 mm working tube. (D) AP fluoroscopic image showing the 14 mm tube positioned lateral to the superior articular facet and above the sacral ala. (E, F) A 3 mm nerve hook is passed along the course of the L5 exiting nerve root to confirm adequate decompression.
Intraoperative clinical image. (A, B) Intraoperative photograph demonstrating exposure through a MEDTRONICS METRx system with a 14 mm working tube docked over the L5–S1 extraforaminal zone. (C) Clinical photograph showing the skin incision, located approximately 5.5 cm lateral to the midline, within the typical range of 4–6 cm for extraforaminal L5–S1 access. (D) Clinical image of the herniated disc fragment retrieved from the foramen. (E) The L5 exiting nerve root (white arrow) is compressed by the herniated disc fragment (yellow arrow) as seen through a 14 mm tubular retractor system. (F) A Penfield dissector (white arrow) passing freely beneath the nerve root, demonstrating complete decompression.
Case 2: Left L3–L4 foraminal and EF disc herniation
A 70-year-old male with a 14-month history of left L3 dermatome pain was diagnosed with left L3–4 EF disc herniation (Fig. 4). The patient was managed surgically using targeted discectomy via a TF microtubular approach (Fig. 5). A tubular retractor system (14 mm) was docked at the affected level through a skin incision approximately 6 cm from the midline, which achieved adequate decompression.
Case 2: left side L3–4 extra-foraminal disc herniation. (A, B) Sagittal magnetic resonance imaging (MRI) showing left-sided extra-foraminal disc herniation. (C, D) Axial MRI demonstrating the disc protrusion on the left side.
Minimally invasive transforaminal discectomy at L3–4 (left side). (A, B) Anteroposterior and lateral fluoroscopic images showing docking of a 14 mm tubular retractor at the L3–4 level on the left side. (C) Retrieved disc material following discectomy.
Case 3: Right L4–L5 EF and foraminal disc herniation with degenerative scoliosis
An 80-year-old female presented with right-sided L4–L5 radiculopathy. Imaging revealed a right-sided EF and foraminal disc herniation at L4–L5, along with underlying degenerative scoliosis (Fig. 6). The patient underwent TF microtubular discectomy (Fig. 7).
L4–L5 right-sided foraminal and extra-foraminal disc herniation. (A, B) Sagittal magnetic resonance imaging showing right-sided foraminal and extra-foraminal disc herniation at L4–L5. (C–F) Axial T2- and T1-weighted images demonstrating the disc herniation on the right side.
Transforaminal approach at L4–L5 (right side). (A, B) Anteroposterior and lateral fluoroscopic images showing docking of the tubular retractor at the right L4–L5 level via a transforaminal approach. (C) Post-discectomy image demonstrating free passage of a 3 mm nerve hook through the foramen, confirming adequate decompression.
Results
A total of 20 patients (12 males and eight females; mean age of 53.60±13.53 years; range, 30–80 years) underwent surgery using the described minimally invasive TF microtubular technique between March 2018 and January 2024. Their body mass index ranged from 22.4 to 34.77 kg/m2. Among the 20 patients, the most commonly affected level was L3–L4, which was observed in eight patients (40%), followed by L4–L5 in five patients (25%), L5–S1 in four patients (20%), and L2–L3 in three patients (15%). Moreover, 13 patients (65 %) and seven patients (35%) had right-sided and left-sided EF disc herniation, respectively. The mean intraoperative blood loss was 29.85±7.02 mL, whereas the mean operative time was 30.50±5.38 minutes. None of the patients required conversion to open surgery. All patients reported immediate relief from radicular leg pain after surgery. The mean VAS score improved significantly from 7.65±0.77 before surgery to 2.0±0.56 immediately after surgery. The mean postoperative VAS score for back pain was 1.23±0.83. All patients were followed for a minimum of 1 year, with the mean follow-up duration being 4.9±1.2 years. The mean VAS scores decreased progressively from 7.65±0.77 before surgery to 2.0±0.56, 1.40±0.50, 1.05±0.83, and 0.60±0.31 immediately, 6 weeks, 6 months, and 1 year after surgery, respectively. Repeated measures ANOVA demonstrated a significant reduction in VAS scores over time (Wilks’ Lambda=0.007, F=595.294, p<0.001) (Fig. 8). The mean ODI score improved significantly from 57.20%±9.36% before surgery to 25.60%±5.21% at 6 months and further to 12.60%±3.18% at 1 year after surgery (Wilks’ Lambda=0.038, F=230.201, p<0.001). Minimal residual numbness in the affected dermatome was reported in six patients (30%) at the 1-year follow-up. One patient developed recurrent L5–S1 EF herniation 2 months after surgery. This patient was managed conservatively through selective nerve root block and remains under follow-up at 1.8 years. None of the patients had any surgical site infection or new onset neurological symptoms.
Line diagram representing pre surgery and post-surgery clinical outcomes. (A) Visual Analog Scale (VAS) score for leg pain. (B) Oswestry Disability Index (ODI) score. Preop, preoperative; Postop, postoperative.
Discussion
The current study details our experience with a TF microtubular discectomy technique utilizing a 14-mm muscle-splitting tubular retractor system under a surgical microscope. Far lateral lumbar disc herniation accounted for around 7%–10% of all lumbar disc herniations. Within this group, EF disc herniations account for 3%–4% of the cases [1–3]. EF herniation is extremely painful and presents with neurological deficits (either motor or sensory) in approximately 75% of patients [5,6]. These herniations trigger significant pain/sensory disturbances/tingling/numbness along the dermatomal distribution associated with the concerned exiting nerve root. This condition has been associated with much more pain than its median/paramedian counterparts, with a greater tendency for neurological deficits due to compression of the adjacent dorsal root ganglion [6–9]. Studies have reported that 72%–92% of patients achieve successful surgical removal of the free disc fragment [10–15]. The surgical techniques used for the treatment of EF herniations have ranged from midline incision with subperiosteal dissection to paramedian approaches [12,16,17]. However, these traditional techniques carry the risk of postoperative segmental instability due to extensive facet resection, nerve root injury, and even inadequate decompression due to poor anatomical access [18–20]. Advancements in surgical techniques have introduced TF endoscopic discectomy and TF microtubular discectomy, which have been widely described in literature [9]. As such, the current study aimed to simply describe our experience and excellent results with this surgical technique throughout the years.
TF microtubular discectomy aims to reduce postoperative discomfort and recovery time while maintaining adequate visualization of the essential anatomical structures required for effective neural decompression [9,14,16,21]. The unequivocal advantages of the described technique include a shortened operative time with minimal blood loss; no extensive muscle or soft tissue destruction, which reduces scar tissue formation; and most importantly, facet joint preservation. The microendoscopic discectomy technique for the treatment of far-lateral disc herniations had first been reported by Foley et al. [14,16] in a case series of 11 patients. These patients, who had herniations at L3–4 or L4–5, all achieved excellent or good results based on the Macnab criteria [14,16]. Cervellini et al. [21] reported their experience in 17 patients with far-lateral disc herniations at L3–4 and L4–5 who underwent surgical treatment using the microendoscopic discectomy technique. Both studies highlighted the use of larger-diameter tubular retractors for far-lateral discectomy. Notably, none of the reported cases involved the L5–S1 level.
A case series by Antony et al. [22] in 2022 showed that far-lateral L5–S1 tubular microdiscectomy was successfully performed using a 16–18 mm tubular retractor and a 2 cm incision. In an in vivo three-dimensional computed tomography morphometric analysis, Senoo et al. [23] reported mean lumbar foraminal heights of 17.2, 16.1, and 15.9 mm at L3–L4, L4–L5, and L5–S1, respectively, along with comparatively decreased foraminal height in older populations. Based on these finding and the authors’ experience, the use of larger-diameter tubular retractors can be encroached upon by the paraspinal muscles. In contrast, the narrow profile of the 14-mm tubular retractor facilitates sharper and more streamlined penetration, which allows for direct docking onto the lower lumbar disc with better foraminal height matching, particularly in the older population with comparatively reduced foraminal height.
The transiliac endoscopic approach, as described in the literature, offers a valuable alternative when the iliac crest or patient anatomy obstructs conventional TF access to L5–S1, although it requires the creation of an iliac bony window, which is an additional time-consuming step [24].
The present study highlights the advantages of TF microtubular discectomy using a 14-mm tubular retractor. The smaller tube provides a targeted trajectory to the disc space without compromising visualization or the working channel, which is particularly useful at the L5–S1 level, where the iliac crest limits access (without the need for a bony trans iliac window). To the best of our knowledge, this study has been the first to describe TF tubular discectomy using a 14-mm tube. The successful outcomes obtained after surgery in our case series undoubtedly reflect the viability of the procedure.
The present study has several important limitations that must be acknowledged. The primary limitation of this study was our small sample size, which can be attributed to the relatively low incidence of EF disc herniation and the single-center study design. Furthermore, this study represents a single-center experience performed by surgeons familiar with microtubular systems, which may introduce selection and performance bias. At the time of the study, the authors were not aware of other centers employing the same surgical technique, which precluded the design of a multi-centered study. However, such collaboration may be feasible in future investigations.
The absence of a comparative cohort precluded direct comparison with open, endoscopic, or larger-diameter tubular techniques for EF disc herniation.
Cost-effectiveness analyses were not performed; therefore, broader conclusions regarding economic benefit cannot be drawn. Despite these limitations, the study was intended primarily as a technical and feasibility-oriented report describing a targeted minimally invasive approach using a 14-mm working channel. Our findings may serve as a foundation for future multi-centered, prospective, or comparative studies.
Conclusions
TF microtubular discectomy using a 14-mm tubular retractor represents a feasible and reproducible minimally invasive technique for the management of EF lumbar disc herniations. The approach allows targeted neural decompression with minimal soft tissue disruption and preservation of facet integrity, including at anatomically challenging levels such as L5–S1, without the need for a transiliac corridor. Despite the limitation in study design, the present series demonstrates consistent clinical improvement and acceptable perioperative outcomes. As such, this technique may serve as a practical alternative for surgeons experienced with microtubular systems.
Key Points
This study reported on the use of a 14-mm trans-foraminal microtubular discectomy technique for precise neural decompression.
At lower lumbar levels, the 14-mm tubular retrac-tor may better correspond to the foraminal height, allowing sharper, more streamlined, and poten-tially more controlled docking onto the disc with-out compromising visualization and the working channel.
This technique is especially advantageous at the L5–S1 segment given that it can be performed without interference from the iliac crest.
Notes
Conflict of Interest
No potential conflict of interest relevant to this article was reported.
Author Contributions
Conceptualization: AGK. Data curation: DJ, PK, BGT, PO, M. Formal analysis: DJ. Investigation: DJ, BGT. Validation: AGK. Visualization: AGK, DJ. Supervision: AGK. Writing–review and editing: AGK. Writing–original data: AGK, DJ, PK, BGT, PO, M. Final approval of the manuscript: all authors.