Before lumbosacral decompression surgery for radicular pain, selective nerve root block(SNRB) is a common procedure to identify the responsible compressed nerve root(RCNR) and predict surgical outcomes. However, the diagnostic accuracy of conventional SNRB is unsatisfactory, especially in terms of specificity. The main limitation is the uncontrolled distribution of anesthetics during injection: when anesthetics spread to surrounding soft tissues instead of acting directly on the RCNR, false-negative results may occur with persistent radicular pain; when anesthetics diffuse to two or more nerve roots including the RCNR, false-positive results may occur even if a normal nerve root is punctured, leading to misdiagnosis.

This study aims to evaluate the diagnostic accuracy of a novel three-dimensional computed tomography multiplanar volume reconstruction (3D-CT MPVR) guided selective intraperineural nerve root block(SINRB) for identifying the RCNR in patients with lumbosacral radicular pain. The investigators hypothesize that this technique will achieve higher diagnostic specificity and overall accuracy than conventional SNRB, by ensuring anesthetics are delivered directly to the target nerve root. This improvement will help clinicians make more accurate surgical plans, achieve better targeted decompression, and ultimately improve postoperative pain relief and functional recovery for patients.

The main research questions to be addressed in this study are:

• What is the procedural success rate of SINRB?
• Whether SINRB may cause clinically detectable nerve injury?
• Whether sciatica is relieved after SINRB when only the responsible compressed nerve root is blocked?
• Whether sciatica is relieved after SINRB when only a normal unaffected nerve root is blocked?

Participants will:

• Undergo one or two SINRB procedures and a single-level lumbar decompression surgery
• Get assessment of pain, mobility disorder and neurological function

[Background] It has been reported that approximately 85% of sciatica cases result from nerve root compression secondary to lumbar disc herniation or lumbar spinal stenosis, a clinical entity defined as radicular pain that manifests as radiating pain involving the buttocks and lower extremities. For patients with an inadequate response to conservative management, surgical decompression of the compressed nerve root serves as a conventional and highly effective therapeutic option. Furthermore, if the pain generator can be confirmed to arise from a single nerve root, targeted single-level decompression of that individual nerve root is generally sufficient for pain relief. However, limitations of conventional imaging examinations coupled with overlapping innervation territories of multiple lumbosacral nerve roots often make accurate identification of the symptomatic compressed nerve root challenging in certain patient populations. Misidentification of the pathological nerve root may consequently lead to surgical failure. To address this clinical dilemma, diagnostic selective nerve root block (SNRB) is regarded as the most valuable adjunct modality. In routine clinical practice, complete pain remission following SNRB indicates that the nerve root infiltrated by local anesthetics is the primary pain source.

Regrettably, prior relevant studies have demonstrated that conventional SNRB exhibits relatively low overall diagnostic accuracy, failing to achieve satisfactory sensitivity and specificity simultaneously. Uncontrolled diffusion of injectable agents is recognized as the predominant contributor to such poor diagnostic performance. Specifically, unintended anesthetic contamination of adjacent unaffected nerve roots may trigger false-positive outcomes, while insufficient delivery of local anesthetics to the targeted nerve root can result in false-negative findings. At present, no techniques or strategies for precisely regulating drug distribution during SNRB procedures have been reported in the existing literature.

Interestingly, during the nerve root fluorography in some patients in our team, when linear striation opacities are visualized within the nerve root, which indicates occurrence of intraperineural, the contrast medium typically diffuses only inside and around the targeted nerve root. This phenomenon can also be observed in the illustrative images from a previous study on therapeutic SNRB, yet it seems to have attracted little attention from researchers. Additionally, the findings of this study demonstrated that intraperineural injection occurred in approximately 30% of patients undergoing therapeutic SNRB with accidental intraperineural injection, and no cases of neurological injury were documented during follow-up. Therefore, it is reasonable to hypothesize that intraperineural injection is a safe, feasible approach that enables precise distribution of agents to the targeted nerve root.

Using the postoperative efficacy of single-segment single-nerve-root decompression as the gold standard for identifying the compressed nerve root, the present study aimed to investigate the diagnostic accuracy, safety, and technical feasibility of selective intraperineural nerve root block (SINRB) in patients with radicular pain. A double-blind approach was implemented, with participants and assessors masked to the nerve root status (responsible vs. non-responsible) during evaluations. Meanwhile, to improve the success rate of intraperineural injection, to the best of our knowledge, the present study is the first to adopt three-dimensional computed tomography multiplanar volume reconstruction (3D-CT MPVR) imaging to visualize the anatomical course of the nerve root within the intervertebral foramen.

[Sample Size Estimation] To ensure adequate statistical power for accurately evaluating the diagnostic accuracy of selective intraperineural nerve root block (SINRB) in identifying the responsible compressed nerve root (RCNR) in patients with radicular pain, sample size calculation was performed based on diagnostic test design principles, incorporating the following key parameters: (from preliminary pilot data) an expected sensitivity of 95%, specificity of 96%, 95% confidence level, ±5% margin of error, and a 10% allowance for potential missing data or patient dropout. Using the single-proportion estimation method, the required numbers of positive and negative events were calculated separately for sensitivity and specificity. The sample size required for sensitivity was 80 cases, and for specificity was 66 cases. Accordingly, we plan to enroll 66 patients with single-level lesions (anticipated to yield one positive and one negative result each) and 14 patients with multi-level lesions (anticipated to yield one positive result each). This sample size sufficiently meets the statistical power requirements for the primary study objective-evaluating the sensitivity and specificity of SINRB for RCNR identification-ensuring the scientific rigor, stability, and generalizability of the study findings.

Inclusion Criteria

• Unilateral sciatica >1 month with activity/daily life impairment.
• Suspected L5/S1 root compression at L4-5/L5-S1 with unconfirmed pain correlation, including disc herniation (MSU 1-B/1-A/2-A), lateral recess/foraminal stenosis (Lee grade 2/3), atypical sciatica, or imaging-exam inconsistency.
• Candidates for single-segment, single-root lumbar decompression, electing surgery after informed consent.

Exclusion Criteria

• No significant pre-SINRB/surgery pain, or weakness/numbness as primary symptom.
• Unidentifiable responsible compressed nerve root (RCNR) per surgery.
• Suspected compression of the same nerve root at more than one segment.
• Pregnancy, active malignancy, or surgical contraindications.
• Inability to cooperate with assessment due to comorbidities or dysfunction.

Due to ethical restrictions and patient privacy confidentiality requirements, individual participant data will not be shared

Blinding design was adopted for bias control. Both participants and independent outcome assessors remained fully blinded during diagnostic SINRB evaluation. Neither subjects nor assessors knew whether each injection targeted the suspected symptomatic responsible nerve root or a non-responsible nerve root. Participants were only informed of the predefined clinical rule: once complete pain relief was achieved following a single SINRB, subsequent blocking procedures would be discontinued. In addition, an injection may also be administered to non-responsible nerve roots to serve as a negative control, and participants would remain unaware of whether the responsible or non-responsible nerve root was injected first. Independent assessors performed clinical evaluations before and after each SINRB using separately recorded video footage. The order of video files was randomized to ensure that assessors remained unaware of how many SINRB procedures each participant had undergone.