Protracted Effect of Combined Nerve Blocks After Total Knee Arthroplasty

Purpose:

The purpose of this study is to evaluate the postoperative analgesic effect of a combined Saphenous nerve block and Obturator nerve block with local infiltration analgesia in the tissue around the knee after surgery with knee replacement. In the combined nerve blocks we use a mixture of Bupivacaine, Adrenaline, Clonidine and Dexamethasone ("protracted mixture") and the local infiltration consist of Ropivacaine, Adrenaline and Toradol. Our hypothesis is that the combined nerve blocks with protracted mixture prolongs block duration, reduces pain and reduces the need for morphine and thus reduce side effects such as nausea, vomiting and lethargy compared to the current treatment with local infiltration analgesia.

Background:

Nerve blocks as analgesic treatment after orthopedic surgery is a recognized and proven procedure. The nerve blocks have the disadvantage that not only do they anesthetize the sensory nerve fibers but also the nerve fibers to the muscles of the leg. The Saphenous nerve block causes only stunning of sensory nerves to the knee region. The Obturator nerve block causes both stunning of the sensory nerves to the knee region and the thighs inward leading muscles, and does not affect the patient's mobilization capacity.

Both blocks are known to be a good addition to the analgesic treatment. Bupivacaine is a well-known local anesthetic. Adrenaline, Clonidine and Dexamethasone have also been used in other studies, in addition to the local anesthetic agent, and has been shown to prolong the effect of the nerve block. Saphenous and Obturator nerve block with all four drugs Bupivacaine, Adrenaline, Clonidine and Dexamethasone has not been systematically investigated in knee replacement surgery, and it is not known whether this method will provide better pain treatment.

Method

The patient can receive one of three treatments, determined randomly:

* A. Saphenous and Obturator nerve block with active anesthetics (Bupivacaine, Adrenaline, Clonidine, Dexamethasone) and local block around the knee joint with placebo medicine (normal saline). * B. Saphenous block with active anesthetics and both Obturator nerve block and local block around the knee joint with placebo medicine (normal saline). * C. Both block with placebo medicine (normal saline) and local block around the knee joint with effective local anesthetic.

Neither patient, investigator or staff around the patient will have knowledge of which treatment the patient has received.

The blocks will be injected before the operation and local infiltration around the knee joint will be given by the surgeon during the operation.