At Hospital for Special Surgery, the femoral block has been an effective weapon against pain after surgery on the knee. Patients undergoing total knee replacement or anterior cruciate ligament reconstruction have especially benefited from femoral nerve blocks.
The first step of the femoral nerve block is to provide some sedation to the patient. This is usually the last part of the procedure you will remember. Once you are adequately sedated, the anesthesiologist will clean off your groin on the side of the planned surgery. We use an iodine based antiseptic, which you may notice after surgery. Next, he or she will use a thin, 2-inch needle to locate the femoral nerve. We employ a very low amount of electrical current through the needle to stimulate the nerve. Some patients recall their leg twitching automatically -- this is precisely the response your anesthesiologist is trying to obtain.
Once an adequately low level of current is obtained, your anesthesiologist will inject a long-acting medicine similar to lidocaine to numb the front of the knee. Because the femoral nerve block doesn’t numb the back of the knee, it is inadequate for anesthesia for surgery. 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.
As with any anesthetic, there are risks and benefits to femoral nerve blocks. These particulars can be discussed with your anesthesiologist before your surgery.