Adductor Canal Mid-thigh and Adductor Canal Distal Thigh: Is Cutaneous Sensory Blockade Similar Among Block Techniques?

Potential subjects will be identified at the orthopedic presurgical clinic, the anesthesia preoperative clinic or the Day Surgery Unit. The electronic medical record (Epic) will also be used for prescreening potential subjects. Recruitment and consenting at will occur at anesthesia preoperative clinics, Day Surgery Unit. A computer generated randomization list will be used for randomization list. The research intervention of this study will take place within the standard clinical context. The patient will receive an ACB regardless of their participation in this research in accordance with their anesthetic plan and their desires The experiment will be conducted as follows: A 20-point grid will be drawn on the subject's leg that will receive medial foot, ankle or leg surgery. Two baseline measurements will be taken prior to administration of the adductor block: distribution of sensation using pinprick (Neuropen) method, and muscle contraction strength using a dynamometer. The number of grid cells with sensation will be counted and recorded. The randomized block will be administered allowing 20 minutes for anesthetic to take full effect. Post-block measurements include pinprick in each of the grid cells, where patient will indicate whether sensation is felt or not. The cells where sensation is perceived will be circled and number of cells will be recorded. After sensation is recorded, maximum voluntary isometric contraction (MVIC) will again be measured with the dynamometer to record the maximal contraction strength. Within 24 hours of surgery, the subject will be asked to rate their pain on a scale of 0-10, and will be recorded again after discharge, in conjunction with opiates required to reduce pain. A more detailed explanation of experimental steps can be read below.

20-Point Grid: The 20-point grid will be marked starting with anatomical landmarks at the knee joint: the medial inter-knee joint where the tibia meets the femur, the mid medial patella, the mid lateral patella, and along the same line at the semitendinosus tendon at 5 cm posterior from that point. Then 5 cm intervals will be plotted progressing cephalad to a total of 15 cm.

Neuropen test:

Prior to administration of randomized blockade technique a pinprick test will be administered using a Neuropen on a scale of 0-1, with 1-normal sharp sensation and 0=dull change of sensation. Mechanical stimulation with pinprick testing is routinely used to test nociception in the bedside neurologic examination. Sharpness can be considered a surrogate for nociception because whereas sharpness is not necessarily painful, mechanical thresholds for sharpness closely parallel those for pain. The subject will be asked to determine whether the stimulus feels sharp. The number of grid-points with a change in sensation from baseline will be recorded at baseline and 20 minutes after the block.

MVIC: