Abstract:This article explores the clinical features and risks of misdiagnosis of severe bladder-origin pain following spinal anesthesia（subarachnoid block）, aiming to raise awareness of urological causes in the differential diagnosis of acute postoperative pain. This article reports a case of a 62-year-old female patient who developed sudden severe lumbosacral pain 2 hours after removal of internal fixation for a left tibial fracture under spinal anesthesia, accompanied by nausea and right renal angle tenderness. Initial suspicions included serious complications such as spinal epidural hematoma or aortic dissection. However, imaging revealed no acute spinal or abdominal pathology. Physical examination showed a distended suprapubic area. After placement of a urinary catheter, urine was drained and the pain rapidly resolved, leading to a final diagnosis of referred pain from acute urinary retention of bladder-origin. Multiple risk factors—including spinal anesthesia-induced detrusor dysfunction, postoperative immobility, and underlying autonomic dysregulation-led to excessive bladder distension, stimulating S2-S4 nerve roots and compressing the sacral plexus, thereby generating severe lumbosacral pain resembling radicular pain. The pain was partially relieved by specific body positions, which added to the diagnostic challenge. Symptoms completely resolved after catheterization, and the patient recovered uneventfully. Severe bladder-origin pain can present as intense radiating lumbosacral pain, and its positional characteristics may be confused with spinal emergencies. Therefore, perioperative management should emphasize early recognition of postoperative urinary retention. Routine bladder assessment（e.g., percussion, ultrasound）is essential, particularly in high-risk patients undergoing spinal anesthesia, lower limb surgery, elderly individuals, or those with underlying diseases. Standardized monitoring and intervention protocols should be established to avoid un necessary advanced imaging and invasive procedures, thereby ensuring patient safety.