In an attempt to improve these results, we have recently developed a new technique, using ultrasound imaging to "see" the nerves prior to giving the injection. Our initial results are very promising, implying that this may be a highly successful and safe approach. The purpose of this study is to determine if this technique is indeed more successful. In order to do that, we will ask 110 patients for their participation. They will be divided in two groups, at random. One group will receive the standard technique (transarterial, using a small needle to find the artery that is close to the nerves). The other group will receive the injection after identifying the nerves with ultrasound imaging. They will all receive the same type of medication, and they will be tested every 5 minutes for half an hour to determine if the block has been successful, according to pre-established criteria. Their pain control will be assessed after the surgery and they will be called 24 hours and 1 week after the surgery to assess their recovery and rule out any possible complications.