Tourniquet-Induced Atypical Lower Back Pain Under Spinal Anesthesia: A Case Report and Mechanistic Exploration of Referred Pain.

Tourniquet-associated complications typically manifest as localized limb symptoms or systemic reactions. Here, we report a rare case of acute, severe lower back pain directly induced by a tourniquet during lower limb surgery under spinal anesthesia. A 32-year-old male developed intense lower back pain (VAS: 4-10) approximately 1.5 h after tourniquet application to the right thigh, accompanied by elevated blood pressure and agitation, while bilateral lower limb sensorimotor blockade remained intact (T11-S5 level). Intravenous analgesics provided only transient and limited relief. Crucially, within approximately two minutes of pausing the procedure and releasing the tourniquet, the patient's pain completely resolved (VAS: 0) without additional analgesia, and the anesthetic level was unchanged. This case provides the first clear documentation of tourniquet pain presenting as isolated truncal pain entirely remote from the ischemic region. We propose that this phenomenon arises because spinal anesthesia blocks somatic sensory input from the lower limbs, leading to nociceptive signals from ischemic muscle being transmitted via incompletely blocked visceral or sympathetic afferent pathways to the spinal cord. According to the convergence-projection theory, these signals are then misinterpreted by the brain as originating from the lower back (T10-L2 dermatomes). This finding reveals how regional anesthesia can fundamentally alter the clinical presentation of tourniquet pain, addresses a critical gap in the current understanding of this complication, and alerts clinicians to include atypical referred pain in their differential diagnosis to prevent misdiagnosis and excessive medical intervention.