Background:Cauda equina syndrome (CES) is a rare complication of spinal or epidural anesthesia. It is attributed to direct mechanical injury to the spinal roots of the cauda equina that may result in saddle anesthesia and paraplegia with bowel and bladder dysfunction.Case Description:The first patient underwent a hip replacement and received 5 mL of 1% lidocaine epidural anesthesia. Postoperatively, when the patient developed an acute CES, the lumbar magnetic resonance imaging (MRI) scan demonstrated clumping/posterior displacement of nerve roots of the cauda equina consistent with adhesive arachnoiditis attributed to the patient's previous L4-L5 lumbar decompression/fusion. The second patient underwent spinal anesthesia (injection of 10 mg of isobaric bupivacaine for an epidural block) for a total knee replacement. When the patient developed an acute CES following surgery, the lumbar MRI scan showed an abnormal T2 signal in the conus and lower thoracic spinal cord over 4.3 cm.Conclusions:Acute CES should be considered in patients undergoing spinal or epidural anesthesia for joint replacement surgery. Prompt evaluation with MRI studies may lead to appropriate medical/surgical measures to reverse the deficit.