A new fenestrated (multiple side-ports) needle has recently been cleared by the FDA for performing peripheral nerve blocks. Experience with this needle suggests that it can make ACB technically easier and safer to perform.This is due in large part because it eliminates the need to position the needle in close proximity to large blood vessels in the thigh.
The objectives for this study would be to prospectively compare nerve blocks performed for postoperative analgesia performed using conventional (single bevel) needles to those performed using the fenestrated needle. Specifically, the investigators would compare metrics such as; time to perform the block, number of attempts, unintentional blood vessel puncture, and successful injection rates. Successful injection rates would be quantified by comparing the distribution of sensory loss after each injection. Those injections resulting in a loss of sensation over the skin surfaces innervated by nerves of the adductor canal would be judged to be "successful". An absence of sensory change in these surfaces would be judged as "unsuccessful".
Procedures:
All patients will be randomized to receive treatment with one of two nerve block needles. Neither the investigators nor the patients will be blinded. Randomization will be based solely on the results of a computer generated random sequence.
All patients participating in the study will receive the same anesthetic, surgery, postoperative care, and pain management that is provided currently for patients (including those not enrolled in this study protocol) having knee replacement at the University of Utah. This investigation is designed to compare only the efficacy of two needle designs that are currently used and FDA approved for peripheral nerve block.
Patients consenting to participate in the study will be randomized to receive an ACB performed with either a single bevel (conventional) or a fenestrated needle. The ACB will be placed in the preoperative holding area approximately 30 minutes before being transported to the operating room. During performance of the nerve block, the time to complete the nerve block, the number of attempts used to complete the nerve block, the incidence of blood vessel puncture and/or blood aspiration will be recorded for each case. All patients will also be assessed for sensory changes in the lower extremity as a metric for block efficacy.
In the operating room, patients will be anesthetized using a spinal block and will receive intravenous sedation at the discretion of the attending anesthesiologist.
During the postoperative period, the quality and duration of analgesia will be primary metrics used to compare the two study needles. Specifically, numerical pain scores reported by the patients and opioid consumption will be compared for both groups.
All patients for whom the is a possible "failed nerve block" will be offered a repeat "rescue" nerve block after surgery. A failed block would be defined by an absence of sensory changes in the extremity associated with poor pain control reported by the patient.
Additional metrics for comparison would be the time to ambulation after surgery and the time to hospital discharge.
Statistical Methods, Data Analysis and Interpretation
The study will be prospective and randomized for two groups of patients having nerve blocks as part of their pain management protocol for total knee replacement.
