A Prospective, Randomized Study Comparing Continuous Femoral and Tibial Nerve Blocks vs. Continuous Femoral and Single Shot Sciatic Nerve Block in Total Knee Arthroplasties.

The aim of this study is to compare and measure the effects of Ropivicaine given through catheters located in the femoral and tibial nerves on indices of sensory blockade after total knee arthroplasties. This is a randomized, prospective study designed to address the primary research question: Does placing a continuous femoral & tibial catheter infusion lead to superior analgesia and patient satisfaction during the entire hospital stay? The secondary research question is: Will selectively placing a continuous tibial catheter decrease the episodes of transient foot drop to zero? Investigators know from own regional institutional practices that by performing a continuous femoral with a single shot sciatic nerve block provides adequate analgesia of the entire leg, but by post-operative day 2 patient's begin to experience pain with rehabilitation and rest in the posterior-lateral aspect of the knee and leg secondary to wearing off of the sciatic nerve block anesthetic. Also, it is known that by blocking the sciatic nerve proximal to its bifurcation may lead to episodes of transient foot drop due to common peroneal nerve blockage and irritation. It is hypothesized that placement of continuous catheters in the femoral and tibial nerves would provide better analgesia and lead to no episodes of foot drop as compared to the patients that receive continuous femoral and single shot sciatic blocks. Currently at Texas Tech Health Science Center-El Paso and University Medical Center, about 95% of patient's undergoing total knee arthroplasty's (TKAs) receives a continuous femoral infusion and a single shot sciatic with an initial bolus of 30mL (femoral) and 20mL (sciatic) of Ropivicaine 0.5% and an infusion of Ropivicaine 0.2% at a rate of 10cc/hr (usually started post-op) for at least the first 48-72 hours post-operatively. For our study, Orthopedic clinic will provide a copy of the consent form to the subject so that they can review it, and if interested in participating in the study, the patient can then contact the Principal Investigator or Study Coordinator directly. After informed consent is obtained, patients will be randomized during that time using a numbering system enclosed in sealed envelopes. Group 1 will receive a pre-operative continuous femoral catheter and a post-operative single shot sciatic with both given an initial bolus of 30 mL (femoral) 0.5% Ropivicaine and 20mL (sciatic) 0.2% Ropivicaine. Following surgery the femoral infusion will be started, which will be running Ropivicaine 0.2 at 10cc/hr. Group 2 will receive a pre-operative continuous femoral catheter and a post-operative continuous tibial catheter with an initial bolus of 30 mL 0.5% Ropivicaine (femoral) and 20mL 0.2% Ropivicaine (tibial), which will be followed by infusions post-operatively running at the same rate and dosage as group 1. All nerve blocks performed will be placed using a nerve stimulator (with no twitches lower than 0.2mA) under ultrasound-guidance. Proper catheter placement will be confirmed by injecting 3mL of air and visualizing by ultrasound. Once confirmed, the bolus dose as mentioned earlier of either Ropivicaine 0.5% (femoral) or 0.2% (sciatic/tibial) will be injected. All TKA cases will be performed under general anesthesia with laryngeal mask airway. Considering the fact that by placing a selective continuous tibial catheter pre-operatively, we run the risk of the catheter being the surgical field during the case. For this reason, it was decided that placement after the procedure would be best. Therefore, the patient will be taken back to the block room post-operatively and a continuous tibial nerve catheter or single shot (depending on what group assigned) will be placed and bolused using the same technique as previously described. To detect a 30% reduction in the pain score from 3-4 to a 1-2 would be required for an observed post-operative pain control difference. In order to achieve a statistically significant result to detect the previously observed difference, a sample of 38 patients in each group (total of 76) would be required. Assuming a high consent rate and given the fact many TKA's it is projected that this study can be completed in approximately 12 months.