Ultrasound-guided needle knife therapy for ligamenta flava in two patients with lumbosacral radiculopathy: case and procedure description

Introduction

Low back pain (LBP) is a common condition, with approximately two-thirds of adults experiencing back pain at some point in their lives (1). Interestingly, disc disease is believed to be the underlying etiology in fewer than 5% of patients with LBP (2). LBP covers a broad spectrum of pain types (e.g., nociceptive, neuropathic, nociplastic, and nonspecific) that frequently overlap. The elements composing the lumbar spine (e.g., soft tissue, vertebrae, zygapophyseal and sacroiliac joints, intervertebral discs, and neurovascular structures) are prone to different stressors, and each of these, alone or in combination, can contribute to LBP (3).

Lumbosacral radiculopathy (LBRP) is characterized by pain resulting from compression or irritation of one or more lumbosacral nerve roots, along with numbness, weakness, and reflex changes (4). In the general population, the annual prevalence of LBRP, described as LBP with leg pain traveling below the knee, varies from 9.9% to 25% (5,6).

A comprehensive query of history and physical examination is essential for diagnosing LBRP. This includes assessing upper motor neuron findings (e.g., Babinski sign, clonus, and spasticity). The Lasègue test, or straight leg raise test, is widely used in clinical settings. Magnetic resonance imaging (MRI) without contrast is considered the gold standard for evaluating LBRP (7).

Needle knives are outpatient surgical tools that offer the advantages of minimal invasion, reduced pain, and low risk of infection. They are commonly used in the treatment of various musculoskeletal joint diseases (8-11), and the addition of ultrasound guidance has made this technique even more precise, safe, and effective (12,13). In this report, we describe two cases to demonstrate the utility of ultrasound-guided needle knife in releasing the ligamenta flava for treating LBRP.

Case presentation

Patient source

This is a single-center, noncontinuous study conducted at the China-Japan Friendship Hospital, and patients were not recruited. The basic contraindications for needle knife therapy are heart disease, grades 2–3 hypertension, and severe diabetes.

Case 1

A 51-year-old male complained of radiating pain in the left buttock and left lower limb for 3 months. He was diagnosed with lumbar disc herniation in two other hospitals. Both of them suggested surgical treatment, which the patient refused. The findings from physical examination were as follows: positive sign on Kernig’s test, which induced pain at 60°; grade V left lower-limb myodynamia accompanied by numbness and pain in the left buttock, radiating to lateral aspect of the left thigh and calf; and a Visual Analogue Scale (VAS) score of 7. MRI showed left side nerve root edema in the L4–L5 segment but no obvious disc herniation (Figure 1).

Figure 1 MRI before treatment (transverse plane and sagittal plane). The enlarged nerve roots (L4–L5) are circled in red. MRI, magnetic resonance imaging.

We decided to perform ultrasound-guided needle knife releasing of the ligamenta flava once every 7 to 10 days. After four treatments, the patient was examined, with the findings being as follows: negative sign on Kernig’s test, no numbness or pain in the lumbar and leg regions, and a VAS score of 3. We also used the 36-Item Short Form Health Survey (SF-36) of medical outcomes to assess the patient’s quality of life (Table 1). Review MRI confirmed significant morphological changes in the responsible nerve root after treatment and disappearance of the spinal canal indentation (Figure 2).

Figure 2 MRI after treatment (transverse plane and sagittal plane). The normal nerve roots (L4–L5) are circled in red. MRI, magnetic resonance imaging.

Case 2

A 48-year-old female complained of radiating pain in the left buttock and left lower limb for 6 months. She was diagnosed with a lumbar disc herniation in another hospital and was recommended to undergo surgical treatment. The findings from physical examination were as follows: positive sign on Kernig’s test, which induced pain at 53°; grade IV left lower-limb myodynamia accompanied by pain and numbness in the buttock radiating to the lateral aspect of the left thigh and calf, and even the left foot; and a VAS score of 8. MRI indicated left side nerve root edema in the L4–L5 segment but no obvious disc herniation (Figure 3).

Figure 3 MRI before treatment [transverse plane (A) and sagittal plane (B)]. The enlarged nerve roots (L4–L5) are circled in red. MRI, magnetic resonance imaging.

After analysis, we judged that the patient’s symptoms were caused by edema of the L4–L5 left nerve root. Therefore, we decided to perform ultrasound-guided needle knife releasing of the ligamenta flava once every 7 to 10 days. After four treatments, the patient was examined, with the findings being as follows: negative sign on Kernig’s test; a marked decrease in the numbness and pain in the lumbar and leg regions, with the pain no longer affecting normal life; and a VAS score of 3. We also used the SF-36 scale to assess the patients’ quality of life (Table 2). MRI confirmed that the morphology of the responsible nerve root had changed significantly before and after the treatment and indicated the disappearance of the spinal canal indentation (Figure 4).

Figure 4 MRI after treatment [transverse plane (A) and sagittal plane (B)]. The normal nerve roots (L4–L5) are circled in red. MRI, magnetic resonance imaging.

Treatment process

Preoperative preparation

Informed consent

All procedures performed in this study were in accordance with the ethical standards of the Ethics Committee of the China-Japan Friendship Hospital(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patients for the publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Positioning

With the patient in the prone position, the skin of the lumbar region is fully exposed. In case the surgeon is right-handed, he or she should operate on the patient’s left side.

Localization of the responsible inferior articular process (e.g., L4–L5)

The procedure involves using a convex array low-frequency probe (2–5 MHz), which is placed on the affected side of the lumbar region with the mark point facing the cephalad direction. First, the L5 transverse process (the first transverse process above the iliac crest) is identified. The probe is then moved horizontally inward until the L4/5 facet joint becomes visible, from which the location of the L4 inferior articular process can be determined. Alternatively, the probe may be placed directly over the lumbar facet joint in its body surface projection, immediately adjacent to the spinous process. The L5–S1 facet joint is used to identify the L5 inferior articular process, and the probe is then slid upward to the L4 inferior articular process. Once the correct position is achieved, the probe is rotated clockwise by 90°, with the mark point end facing inward. At this point, the L4 spinous process appears centered in the image, with the inferior articular processes of the L4 located on both sides. The midpoint of the nonmark point end is selected as the entry point and marked on the skin (Video 1).

Skin preparation and sterilization

The skin is routinely sterilized with complex iodine three times at the site of operation, and the fenestrated sheet is draped with the entry point facing the midpoint.

Ultrasound localization and treatment

Ultrasound-guided local anesthesia for facet joints

The operator wears sterile gloves and wraps the probe with a sterile cover. The probe is placed at the treatment point mentioned above. With the outer midpoint of the probe being used as the insertion point, in-plane puncture anesthesia is then performed (0.35 mm × 90 mm). The probe is stopped when the tip reaches the inferior articular process of L4, and the tip is lifted slightly by 1–2 mm and then withdrawn to confirm that there is no blood return. After this, 1.5–2 mL of 2% lidocaine is injected and followed by a wait of 5 minutes.

Ultrasound-guided needle knife release of the ligamenta flava

The needle knife (1.2 mm × 90 mm) (Figure 5) is used to make an in-plane incision, with the point located on the outside midpoint of the probe (nonmark point end) (Figure 6).

Figure 5 Needle knife. Horizontal plane and vertical plane.

Figure 6 Needle knife insertion position (A) and ultrasound image (B). The L4 spinous process is the black shadow in the middle, and the bone surface of the L4 inferior articular processes is on both sides.

The needle knife is aimed at the bony surface of the inferior articular process of the L4 (Figure 7). When the tip reaches the surface of the inferior articular process, the tip is lifted slightly by 1–2 mm so that the tip slides from the medial edge of the inferior articular process into the ligamenta flava (Figure 8). At this point, the surgeon should feel the ligament tissue being cut with the needle knife, control the cutting amplitude to 3–4 mm, and cut 4–5 times; there may be a breakthrough sensation during the cutting process (Figure 9). If the patient has paresthesia radiating to the lower limb, this indicates that the ligamenta flava has been penetrated and the nerve root has possibly been touched, and the depth of the needle knife insertion should be adjusted immediately.

Figure 7 Three-dimensional computed tomography reconstruction. The triangle indicates the needle knife.

Figure 8 Anatomical approach. The triangle indicates the needle knife. IAP, inferior articular process; LF, ligamenta flava; SAP, superior articular process; SP, spinous process.

Figure 9 Cutting amplitude. The triangle indicates the needle knife. ES, epidural space; LF, ligamenta flava; SDM, spinal dura mater.

After treatment, the patients are instructed to lie flat for at least 30 minutes to prevent cerebrospinal fluid leakage.

Postoperative care

Wound care

After the operation, the wound is pressed with gauze for 15 minutes to prevent bleeding and resterilized with alcohol. The residual complex iodine is wiped off, and the wound is bandaged with clean gauze. Patients are instructed to keep the wound clean and dry for 3 days and to change the gauze to disinfect the wound by themselves every 24 hours if possible.

Activity restriction

Patients are advised to reduce strenuous activities or weight-bearing for 30 days to prevent negative effects on tissue healing.

Follow-up appointment and monitoring of complications

After four treatment sessions, patients are scheduled for follow-up in 1–2 weeks. We ask our patients to undergo lumbar MRI again before the visit to assess the efficacy. During this period, patients can call or report discomfort symptoms, such as bleeding and infection, at any time during the visit.

Patient education

Detailed postoperative instructions are provided to patients in written form, including information on signs of infection, wound care, rehabilitation exercise positions, and advice on lifestyle habits. The importance of daily care and follow-up appointments is emphasized.

Discussion

LBRP is treated in a variety of ways and mainly includes open surgical treatment and conservative treatment. Disc surgery may provide pain relief (14) but can also interfere with the efficacy of other therapies, such as dorsal root ganglion pulsed radiofrequency (15). In subacute LBRP, transforaminal corticosteroid administration provides short-term pain relief and improves mobility, but long-term efficacy is extremely limited (16). In chronic LBRP, pulsed radiofrequency treatment adjacent to the spinal ganglion can provide pain relief for a longer period in patients. In cases of refractory pain, epidural adhesiolysis and spinal cord stimulation can be considered (17).

As our cases demonstrate, the implications of open surgical treatment for patients with LBRP, especially without disc herniation, are not clear. In both cases, the herniated disc was not the primary cause of the nerve root compression; rather, it was the nerve root edema pressing against the ligamenta flava that caused the nerve compression. Discectomy or open surgery of the ligamenta flava may resolve the patient’s issues, but its associated high surgical costs, long bed rest, more intense scarring pain, and frequency of postoperative complications are not acceptable for all patients.

Minimally invasive surgery of the lumbar spine is now becoming the mainstream form of therapy (18). The treatment protocol described here introduces a novel ultraminimally invasive surgical protocol for treating LBRP: an ultrasound-guided needle knife technique for loosening the ligamenta flava of the responsible lumbar vertebrae. Needle knife loosening reduces local pressure and accelerates the dissipation of inflammation while reducing nerve root compression, thus treating nerve root edema. This technique is a conservative treatment option, with advantages of considerably reduced pain, minimal invasiveness, and low risk of infection. According to the morphometric measurements of the lumbosacral plexus root thickness, the diameter gradually increases from the L1 to S1. The L1 has the thinnest root (3.9±0.81 mm), while the S1 has the thickest root (5.45±0.8 mm) (19). In addition, under ultrasound guidance, the anatomical structure around the lumbar vertebrae can be clearly seen, and the pathway of needle knife puncture can be controlled, with the cutting amplitude of the needle knife being 3–4 mm. This allows for the ligamenta flava to be cut precisely. To prevent injury to the dura mater, all our incisions are based on ultrasound and bone surface positioning. The needle knife is kept close to the bone surface to fix the needle insertion path and prevent excessive cutting. This confers the ability to prevent accidental injury to the nerves and blood vessels, ensuring the efficacy and safety of the cutting. Many musculoskeletal joint disorders are often accompanied by aseptic inflammation, which can frequently lead to localized edema and increased pressure (20). Cutting tissues with a needle knife can release soft tissue pressure, thereby promoting inflammatory regression (21).

Despite the many advantages of the ultrasound-guided needle knife technique, it is important to recognize its potential limitations. The small size of the needle knife incision means that the cutting efficacy is relatively low and is not substantial in patients with severe lumbar disc herniation. Severely compressed nerve roots and an extremely narrow spinal canal are beyond the scope of needle knife treatment, and open surgery may be a more suitable option in such cases. In addition, this technique often requires the operator to master interdisciplinary expertise, such as ultrasound techniques, needle knife technology, and human anatomy.

The indications for our surgery are not limited to patients with LBRP, and patients with mild-to-moderate lumbar disc herniation are also suitable candidates. The purpose of this paper is to introduce a novel therapy for lumbar nerve root compression, which can prevent unnecessary medical interventions such as surgery. Other conservative therapies, such as epidural injections, can be combined with this method in clinical practice to enhance the therapeutic effect.

Further development and research into ultrasound-guided needle knife technology are warranted. The integration of interdisciplinary techniques often leads to the development of novel treatment options. This technology may provide an alternative choice for patients with musculoskeletal joint disorders who do not reach the point of surgery in the clinical setting. It may also reduce the cost of health care for certain diseases, but the true long-term economic benefits should be determined via a comprehensive cost-benefit analysis.

Conclusions

Using an ultrasound-guided needle knife to loosen the ligamenta flava of the responsible lumbar vertebrae relieves or even cures LBRP caused by edema of the nerve roots.

Acknowledgments

None.

Footnote

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-968/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the Ethics Committee of the China-Japan Friendship Hospital(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patients for the publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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