Old technicque, new applications: Can the H-reflex be a possible Real-Time Indicator in endoscopic surgery for decompression of acute disc herniation at the S1 root?

Abstract Background: The Hoffmann (H-) reflex is a monosynaptic electrophysiological response that reflects S1-root integrity. Although widely used in experimental neurophysiology, its intra-operative application during endoscopic lumbar surgery is rarely reported. We present the first real-time documentation of H-reflex normalization immediately after endoscopic decompression of an acute L5–S1 disc herniation. Case Description: A 49-year-old woman presented with acute right-sided S1 radiculopathy (ankle dorsiflexion/plantar-flexion MRC grade III; hallux extension grade I). MRI showed a large, right sub-articular L5–S1 disc extrusion compressing the S1 nerve root. Unilateral biportal endoscopic discectomy was performed under general anesthesia with multimodal intra-operative neuromonitoring (MEPs, free-run EMG, and continuous tibial-nerve H-reflex). Baseline recordings revealed marked side-to-side asymmetry: right-leg MEP amplitudes were depressed, and the right H-reflex was low and unstable. During foraminoplasty and fragment removal, a sudden, sustained 100 % surge in right H-reflex amplitude occurred, coincidence with root decompression, while MEPs remained unchanged. Free-run EMG discharges abated after the H-reflex improved. Post-operative recovery was uneventful. At 2 months the patient demonstrated near-complete motor recovery (MRC IV–V) and full pain relief. Conclusion: Continuous H-reflex monitoring provided an immediate, sensitive marker of S1-root decompression when conventional MEPs failed to reflect functional recovery. This single-case experience supports the feasibility and potential prognostic value of adding H-reflex surveillance to the neuromonitoring toolkit for endoscopic lumbar surgery. Prospective studies in larger cohorts are warranted to validate threshold criteria, refine stimulation parameters, and determine cost-effectiveness.