Influence of the Insertion Distance on Loss of Sensation Produced by Femoral Perineural Catheters in the Context of Major Knee Surgery.

Pain after knee surgery is reported as severe for 60% of patients, and is a major concern in both hospitalised and ambulatory surgery patients. Pain control is particularly important, as adequate analgesia allows rapid mobilisation of the operated knee and prevents complications related to immobility. Several methods have been proposed to treat this pain, the most promising being injection of local anesthetic close to the femoral nerve. The injection of local anesthetics around the femoral nerve reduces sensation from the knee and provides better pain relief after surgery than narcotic medication. To prolong the duration of the analgesia, a small catheter must be positioned next to the nerve. Through this catheter, small quantities of local anesthetics can be continuously delivered for several hours after surgery, effectively relieving the worst of the pain.

To date, the administration of local anesthetics through a catheter next to the femoral nerve has been shown to improve pain relief after knee replacement surgery. These pain relief benefits have resulted in faster recovery after total knee replacement. Until recently, catheter techniques were not frequently used due to technical difficulties encountered when attempting to find the femoral nerve, as well as difficulties related to catheter displacement after surgery. Due to recent improvements in nerve and catheter localisation, catheter installation has become easier, more precise and more reliable. However, the distance at which the catheter must be advanced next to the femoral nerve in order to provide the best pain relief remains unknown. Insertion distance could influence the initial quality and distribution of the freezing, its duration, or both. Therefore, this study is designed to compare two catheter insertion distances, in order to help determine which is best for pain relief after knee surgery.

Patients will be randomly assigned to the following groups:

• Group 1: 3 cm insertion
• Group 2: 7 cm insertion

The anesthesiologist will insert a catheter close to the femoral nerve, at the junction of the thigh and torso immediately before beginning of anesthesia for surgery. The usual medication will be used to make installation more comfortable. The exact location where the catheter will be put into place will be identified using an ultrasound machine. This device will allow the anesthesiologist to identify the various anatomical structures. A specially designed needle will be inserted next to the femoral nerve, and its position will be confirmed with a neurostimulator. Once the adequacy of needle position is confirmed, the anesthesiologist will introduce 3 cm(Group 1) or 7 cm (Group 2)of the catheter through the needle, and then will withdraw the needle. The catheter will be fixed in place to avoid displacement.