Saphenous Nerve Block Versus Femoral Nerve Block for Total Knee Arthroplasty

Currently, the regional anesthetic standard of care for total knee replacement surgery is combined spinal/epidural, with or without a femoral nerve block, or FNB. Lasting approximately 18 hours, the FNB works by numbing the femoral nerve (and its branches), which is the major nerve controlling the knee joint. The femoral nerve also provides movement and sensation. While this regional anesthetic technique offers significant postoperative pain relief, it is possible that it may cause muscle weakness and increase patients' recovery time. Hence there is a need for an alternative technique, one that may help minimize postoperative pain as effectively as the FNB, while not causing weakness of the quadriceps muscle.

The saphenous nerve, a branch of the femoral nerve, provides sensation to the knee. Thus it is hypothesized that by "blocking" or anesthetizing the saphenous nerve with local anesthetic closer to where it branches off, the area around and below the knee will feel numb. Yet unlike with the FNB, the quadriceps muscle itself will still be able to function.

Patients will be randomized to receive FNB or saphenous nerve block. Quadriceps strength will be tested using a dynamometer before surgery (baseline), 6-8 hours following anesthesia administration, and on postoperative days 1 and 2. It is hypothesized that patients who receive FNB will experience a 50% decrease in quadriceps strength compared to baseline.