Microscopic tubular unilateral laminotomy for bilateral decompression: a detailed surgical illustration and single-arm cohort study on outcomes in lumbar canal stenosis

Abstract

Background

Microscopic tubular unilateral laminotomy for bilateral decompression (MT-ULBD) is a minimally invasive technique for lumbar spinal stenosis (LSS) that aims to achieve adequate neural decompression while minimizing tissue disruption. This study evaluates its clinical and radiological outcomes and documents key surgical steps through detailed illustrations.

Methods

This single-center, single-arm cohort study was conducted at Amala Institute of Medical Sciences between September 2024 and April 2025 (IRB No. 34/EC/24/AIMS-16). Patients aged 20–60 years with LSS unresponsive to at least 6 months of conservative therapy were included after obtaining informed consent. Outcomes included pain relief (VAS), functional improvement (ODI), and radiological decompression (canal diameter). Operative parameters, hospital stay, and complications were recorded. Statistical analysis was performed using SPSS version 29.0 (IBM Corp., Armonk, NY); P < 0.05 was considered significant.

Results

Of 44 enrolled patients, 41 completed follow-up (28 females, 13 males; mean age 48.6 ± 8.3 years). Mean VAS scores improved from 7.0 ± 1.2 to 2.0 ± 1.1 (P < 0.001), and ODI from 52.4 ± 8.6 to 22.3 ± 6.1 (P < 0.001). Mean canal diameter increased from 10.8 ± 1.2 to 14.8 ± 1.4 mm (P < 0.001). Mean operative time was 26.3 ± 6.4 min, blood loss 7.5 ± 6.8 mL, and hospital stay 4.0 ± 1.1 days. Two patients (4.9%) had small dural tears successfully repaired with 6–0 Prolene; three (7.3%) developed superficial infections managed conservatively. No neurological deficits or postoperative instability were observed.

Conclusions

MT-ULBD provides significant clinical and radiological improvement with minimal morbidity, making it an effective and safe minimally invasive alternative for the treatment of LSS. Surgical illustrations aid in the understanding and reproducibility of the technique.

Introduction

Lumbar spinal stenosis (LSS) is a degenerative spine disorder characterized by the progressive narrowing of the spinal canal, leading to the compression of neural elements [1]. It is a leading cause of pain and disability in older adults, commonly manifesting as neurogenic claudication, radiculopathy, and lower extremity weakness [2]. With the aging population increasing, the prevalence of LSS is expected to rise, thereby elevating the demand for effective and long-lasting treatment options [3].

The standard surgical intervention for LSS has traditionally been open laminectomy, which involves direct decompression of neural structures. However, this procedure is associated with substantial soft tissue dissection, extended recovery times, heightened postoperative pain, and an increased risk of iatrogenic spinal instability, often necessitating additional fusion surgery [4, 5]. To address these drawbacks, minimally invasive spine surgery (MISS) techniques have been developed to achieve adequate decompression while preserving spinal stability and minimizing perioperative morbidity [6].

Microscopic tubular unilateral laminotomy for bilateral decompression (MT-ULBD) is a MISS technique that allows bilateral neural decompression through a unilateral approach. By minimizing muscle dissection and preserving key stabilizing structures, this technique has the potential to provide pain relief and functional recovery while reducing the risk of postoperative complications [7, 8]. To further aid in the understanding of this technique, detailed surgical illustrations are provided, highlighting key steps of the MT-ULBD procedure. Despite its growing adoption, further studies are required to assess its efficacy and long-term outcomes [9].

This study aims to evaluate the clinical and radiological outcomes of MT-ULBD in patients with symptomatic lumbar canal stenosis who have failed conservative management. The primary objective is to assess the extent of pain relief and functional improvement following surgery. Secondary objectives include evaluating radiological decompression, operative efficiency, and postoperative complications. We hypothesize that MT-ULBD offers comparable or superior clinical benefits to conventional laminectomy, while minimizing the risk of postoperative instability and promoting faster recovery [10].

Subjects and methods

This was a single-center, single-arm cohort study conducted at a high-volume orthopedic spine center between September 2024 and April 2025. The study aimed to evaluate the clinical and radiological outcomes of microscopic tubular unilateral laminotomy for bilateral decompression (MT-ULBD) in patients with lumbar spinal stenosis. Participants were recruited from outpatient spine clinics, and all surgeries were performed by a single, experienced spine surgeon. Data collection was prospective, with follow-up assessments conducted at 1 week, 3 months, and 6 months postoperatively.

Ethical approval

This study was approved by the Institutional Review Board of Amala Institute of Medical Sciences (IRB No. 34/EC/24/AIMS-16). All procedures were performed in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki declaration and its later amendments. Written informed consent was obtained from all participants before inclusion in the study.

Inclusion and exclusion criteria

Inclusion criteria comprised patients aged 20–60 years who exhibited clinical signs and symptoms of lumbar canal stenosis, with or without Meyerding Grade I lumbar spondylolisthesis, and who had failed at least 6 months of conservative management.

Patients with Grade I spondylolisthesis were included only when the predominant pathology was central canal stenosis and neural compression, rather than instability requiring fusion. These patients were treated with decompression alone to maintain uniformity in surgical management.

Exclusion criteria included:

• acute lumbar disc herniation causing lateral recess stenosis,

• a suprapedicle notch distance greater than 1.6 cm from the root of the spinous facet to the articular surface on CT,

• lumbar spondylolisthesis greater than Grade I,

• prior lumbar spine decompression surgery,

• spinal infection or tumor (including tuberculosis), and

• unwillingness to comply with the follow-up protocol.

A total of 44 patients were initially enrolled, and 41 completed the 6-month follow-up.

Statistical analysis

Data were analyzed using IBM SPSS Statistics, version 29.0 (IBM Corp., Armonk, NY, USA). Continuous variables are expressed as mean ± standard deviation (SD) or median with interquartile range (IQR), depending on the distribution. Categorical variables are presented as frequencies and percentages. Normality of continuous data was verified using the Shapiro–Wilk test.

For paired continuous outcomes (e.g., pre- and postoperative VAS and ODI scores), the paired t-test was applied for normally distributed data, while the Wilcoxon signed-rank test was used for non-normally distributed variables. To validate the robustness of results in this modest sample size, permutation-based paired tests (10,000 iterations) were additionally performed, confirming the consistency of P values. Categorical paired data were compared using McNemar’s or Fisher’s exact test, as appropriate. All tests were two-tailed, and a P value < 0.05 was considered statistically significant.

Because this was an exploratory, hypothesis-generating study, no formal a priori sample-size or power analysis was performed.

Surgical technique

Microscopic tubular unilateral laminotomy for bilateral decompression (MT-ULBD “over the top” decompression) is the minimally invasive procedure for direct decompression of lumbar spine stenosis. The main advantage is that a unilateral approach can be used for bilateral decompression, which minimizes muscle dissection and bleeding. Compared to traditional open decompression procedures, it also minimizes the risk of producing iatrogenic instability that would require fusion.

The patient is positioned prone on a Mecca frame table (Fig. 1) after the administration of general anesthesia. This position ensures flexion of the lumbar spine at the desired level so that the inter-laminar space widens up. Adequate padding is placed at all bone prominences, including the knees, hips, and elbows. Shoulders are abducted to 90° with elbows flexed and placed over the arm table. Care is taken not to hyperextend the shoulders. A 24G needle is first used to mark the surgical level under fluoroscopic guidance. Another 18G needle is pierced just laterally to aid during the incision and visualize the needle prick. The surgical approach is planned between the inter-laminar space of the desired level (Fig. 2).

Fig. 1.

Patient positioned in customised Mecca frame to achieve adequate lumbar spine flexion

Fig. 2.

Axial section through the pathological level

In lumbar canal stenosis, thickened ligamentum flavum becomes hypertrophied and infolded, reducing canal diameter. Facet joint hypertrophy and osteophytes due to degenerative changes lead to medial encroachment into the canal from the lateral recess. Epidural fat reduction and venous congestion further narrow the space. The needle is placed parallel to the disc space on the opposite side of the planned incision, directed toward the inferior edge of the target lamina. Placing the needle on the opposite side does not hinder the surgical field by hematoma formation.

A 1.5 cm skin incision is made 0.5 cm away from the midline, just lateral to the lateral edge of the spinous process. The incision is typically made on the side with more stenosis, the symptomatic side, which is marked prior to the surgery. The fascia is opened longitudinally in a semi-circular manner. The paraspinal muscles are elevated subperiosteally from the lateral surface of the spinous process and the inferior edge of the superior lamina using a specialized Cobb’s elevator. Adequate hemostasis is maintained throughout the dissection. Once the bony landmarks are exposed for visualization, a tubular retractor speculum is placed (Fig. 3), and the level is reconfirmed using a C-arm in inverted C position (Fig. 4). A dark carbon-coated retractor speculum is used to prevent reflection of light from the microscope.

Fig. 3.

Placement of tubular retractor speculum

Fig. 4.

Allis forceps placed over the overhanging lamina to reconfirm the spinal level

Laminotomy is initiated with a high-speed coarse burr at the inferior edge of the overhanging lamina on the ipsilateral side (Fig. 5). The lamina is then burred in a caudal-to-cranial direction until approaching the insertion of the ligamentum flavum. During this part of the burring, the thick ligamentum flavum protects the dura from the burr. This region is typically identified by the presence of epidural fat.

Fig. 5.

Inferior border of the superior overhanging lamina is burred out

A Penfield dissector is used to identify the midline separation in the ligamentum flavum through which a right-angled ball-tipped probe is inserted to separate any adhesions with the dura. The hypertrophied ligamentum flavum is then removed with Kerrison’s rongeurs (Fig. 6) to expose the medial and lateral extension of the thecal sac. Decompression begins medially and proceeds laterally to the lateral edge of the ligamentum flavum. Sizes of Kerrison’s rongeurs are kept changing according to the local anatomy. Hypertrophied facet joint and osteophytes that project into the spinal canal are carefully burred out using a diamond burr (Fig. 7). It is ensured that not more than one-third of the facet joint is cleared to prevent the occurrence of instability.

Fig. 6.

Removal of ipsilateral hypertrophied ligamentum flavum

Fig. 7.

Removal ipsilateral osteophytes and facetal hypertrophy projecting into the canal

After completing ipsilateral decompression (Fig. 8), the table is tilted 10–20 degrees away from the surgeon, and the tubular retractor is angled medially. The burr is placed just along the sides of the spinous process to clear out the ventral-most part of the spinous process (Fig. 9). This maneuver allows visualization of the contralateral ligamentum flavum, which is then removed using a Kerrison rongeur (Fig. 10). The undersurface of the contralateral lamina is then curetted using specialized angled curettes. Additionally, hypertrophied facets and osteophytes are removed on the contralateral side using a high-speed diamond burr while suction is used to protect the thecal sac (Fig. 11).

Fig. 8.

Removal of lateral ligamentum flavum after facetal decompression

Fig. 9.

Spinal canal adequately decompressed on the ipsilateral side

Fig. 10.

Burr is placed close to the spinous process so that the base is cleared to provide access to the contralateral side

Fig. 11.

Hypertrophied ligamentum flavum being removed on the contralateral side

The adequacy of decompression is assessed using a ball-tipped probe in a clockwise manner, beginning contralaterally before moving to the ipsilateral side. Decompression is ensured till the lateral recess on the contralateral side (Fig. 12). Upon confirming satisfactory decompression, the speculum is removed (Fig. 13). Final hemostasis is ensured before closing the wound in layers. Intradermal absorbable sutures are preferred for skin closure (Figs. 14, 15).

Fig. 12.

Osteophytes and hypertrophied facet joint projecting into the spinal canal being removed on the contralateral side

Fig. 13.

Decompression done on the contralateral side till the lateral recess

Fig. 14.

Adequacy of decompression is checked in clockwise manner

Fig. 15.

Wound less than 2 cm is closed with absorbable monocryl sutures

Results

A total of 44 patients were initially enrolled in the study, of whom three were lost to follow-up, leaving 41 patients for the final analysis. Reasons for loss to follow-up included inability to attend scheduled postoperative evaluations and personal reasons unrelated to surgery. The final cohort comprised 28 females and 13 males, with a mean age of 48.6 ± 8.3 years (range 20–60 years). All patients had clinically and radiologically confirmed lumbar canal stenosis, and the mean follow-up duration was 6 months.

Baseline characteristics

Among the 41 patients analyzed, 19 (46.3%) had L4–L5 stenosis, 17 (41.5%) had L5–S1 stenosis, and 5 (12.2%) had L3–L4 stenosis. Ten patients (24.4%) presented with cauda equina syndrome, with associated bowel and bladder dysfunction. The mean preoperative symptom duration was 10.2 months (range 6–18 months). Motor weakness was documented in 25 patients (60.9%), manifesting as foot drop or extensor hallucis longus (EHL) weakness. Preoperative MRI demonstrated a mean spinal canal diameter of 10.8 ± 1.2 mm.

Primary outcomes

The mean preoperative VAS score for pain was 7.0 ± 1.2, which improved significantly to 2.0 ± 1.1 at the 6-month follow-up (P < 0.001). Functional outcomes also improved markedly, with the mean Oswestry Disability Index (ODI) decreasing from 52.4 ± 8.6 preoperatively to 22.3 ± 6.1 at 6 months (P < 0.001). Permutation-based paired tests (10,000 iterations) were also performed for the primary continuous outcomes and confirmed the robustness of the above findings.

Radiological and surgical outcomes

Postoperative MRI revealed a significant increase in the mean spinal canal diameter to 14.8 ± 1.4 mm (P < 0.001), confirming effective decompression. The mean operative time was 26.3 ± 6.4 min (range 20–30 min). Estimated intraoperative blood loss was minimal, averaging 7.5 ± 6.8 mL. The mean length of hospital stay was 4.0 ± 1.1 days (range 2–6 days). No patient required intraoperative conversion to open surgery.

Complications and secondary outcomes

Intraoperatively, two patients (4.9%) experienced small dural tears, both of which were successfully repaired using 6–0 Prolene under microscopic visualization. No postoperative cerebrospinal fluid (CSF) leakage or pseudomeningocele formation was observed in either case. Postoperative infections occurred in three patients (7.3%) and were managed conservatively with antibiotics, with no further complications. No cases of postoperative neurological deterioration or iatrogenic instability were encountered.

At the 6-month follow-up, 12 of the 25 patients (48%) with preoperative motor weakness demonstrated significant improvement in muscle power. Persistent paresthesia was reported by 30 patients (73.2%), suggesting slower sensory recovery compared to motor recovery. Two patients (4.9%) had poor outcomes according to the modified Macnab criteria—one required secondary posterior lumbar interbody fusion due to recurrent stenosis, and the other underwent revision MT-ULBD.

Overall clinical outcome

According to the modified Macnab criteria, 25 patients (61.0%) achieved excellent outcomes, 12 (29.3%) had good outcomes, 2 (4.9%) had fair outcomes, and 2 (4.9%) had poor outcomes at the final follow-up.

Discussion

This study demonstrates that microscopic tubular unilateral laminotomy for bilateral decompression (MT-ULBD) is an effective minimally invasive surgical technique for treating lumbar spinal stenosis. The findings are consistent with previous studies supporting minimally invasive decompression techniques [11]. Suri et al. reported that MT-ULBD provides comparable pain relief and functional improvement to open laminectomy while minimizing tissue damage and postoperative morbidity [12]. Similarly, Lee et al. found that MT-ULBD significantly reduced operative time, intraoperative blood loss, and length of hospital stay compared to traditional decompression methods [13]. Kim et al. demonstrated that unilateral laminotomy for bilateral decompression preserves spinal stability better than conventional laminectomy, reducing the need for subsequent fusion surgery [14].

In our study, we observed a significant reduction in the mean VAS score from 7.0 ± 1.2 preoperatively to 2.0 ± 1.1 postoperatively (P < 0.001), as well as an improvement in the ODI score from 52.4 ± 8.6 to 22.3 ± 6.1 at 6 months (P < 0.001). Radiological outcomes confirmed adequate decompression, with an increase in mean spinal canal diameter from 10.8 ± 1.2 to 14.8 ± 1.4 mm (P < 0.001) [15]. These findings reinforce the procedural efficiency of MT-ULBD, with significant improvements in pain and functional outcomes, reduced VAS scores, improved ODI scores, and increased spinal canal diameter [16]. The procedure also demonstrated favorable surgical parameters, including minimal operative time and blood loss [17].

The findings of this study suggest that MT-ULBD can be a viable alternative to traditional open decompression for lumbar spinal stenosis. Given that the study was conducted in a high-volume orthopedic center with a standardized surgical protocol, the results are likely generalizable to similar institutions with experienced spine surgeons [18]. However, broader applicability may require further validation in multicenter trials and diverse patient populations [19].

We selected the microscopic tubular unilateral laminotomy technique for the current series for several pragmatic reasons. Compared with endoscopic decompression, the microscopic tubular approach allows use of a wider instrument set and provides improved tactile feedback during bone removal and hemostasis, which can be advantageous when handling hypertrophied facets or calcified ligamentum flavum. The microscope also facilitates a rapid conversion or extension of exposure if unexpected pathology or a durotomy occurs. Moreover, for surgeons already trained with the operative microscope, the learning curve may be shorter than for full endoscopic techniques. We acknowledge that endoscopic approaches have advantages—such as smaller skin incisions and potentially less postoperative pain—and that a direct randomized comparison between endoscopic and microscopic tubular techniques would be valuable.

Despite these benefits, a substantial proportion of patients (73.2%) in our study reported persistent numbness and tingling postoperatively, highlighting the need for further investigation into sensory recovery following decompression surgery [20].

One of the notable strengths of our study is the inclusion of detailed stepwise surgical illustrations corresponding to each key procedural step. These images not only serve as a visual guide to the MT-ULBD technique but also enhance the educational value of the article for trainees and practicing surgeons. The use of high-quality intraoperative photographs and schematic figures adds clarity to complex anatomical and technical nuances, which is often lacking in similar studies.

This study has several limitations. First, it is a single-center study with a relatively small sample size, which may limit the external validity of the findings [21]. Second, the follow-up duration of 6 months is relatively short, and longer-term outcomes, including delayed complications and recurrence rates, remain unknown [22]. Third, the study lacked a control group undergoing conventional open decompression, making direct comparisons challenging [23]. Finally, the assessment of functional outcomes relied on patient-reported measures, which, while validated, may introduce subjective bias [24]. Future studies with larger sample sizes, longer follow-up periods, and comparative analyses against traditional techniques are needed to further establish the efficacy of MT-ULBD [25].

Author contributions

NIR was responsible for the conceptualization of the study, assisted in surgical procedures, collected clinical data, and drafted the initial manuscript. SCJ performed the surgical interventions, conducted radiological evaluations, and contributed to manuscript editing and final proofreading. AAV carried out the statistical analysis, prepared the illustrative diagrams, and supervised patient follow-up. All authors reviewed and approved the final manuscript and agree to be accountable for all aspects of the work.

Funding

The authors received no specific funding for this work.

Data availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

The study was approved by the Institutional Ethical Committee (IRB No. 34/EC/24/AIMS-16). Informed consent was obtained from all individual participants included in the study.

Consent for publication

Written informed consent was obtained from the individuals for the publication of any potentially identifiable data or images.

Competing interests

The authors declare no competing interests.