Often we will provide the surgical anesthesia with a spinal/epidural and provide pain relief after surgery with a femoral nerve block. The numbness lasts an average of 16 hours. Studies from HSS show that the pain-relieving properties of a femoral nerve block last much longer-up to 3 days. The block alone is usually not enough pain relief, so patients will have either narcotics or an epidural to help with pain, in addition to the femoral nerve block.