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

This is a randomized noninferiority interventional study to determine the equivalence of two adductor canal block (ACB) methods: mid-thigh and distal thigh in patients undergoing medial foot, medial ankle, or medial leg surgery. Sixty eight patients will be identified during their orthopedic presurgical clinic visit, anesthesia preoperative clinic visit or Day Surgery Unit (Zale Lipshy Hospital, Clements University Hospital, and University of Texas Southwestern Outpatient Surgery Center) for eligibility. Eligible individuals may be introduced to the study in the orthopedic presurgical clinic or the anesthesia preoperative clinic by staff. After consent patients will be randomized (break-seal method) to receive either a mid-thigh or distal thigh block using ropivacaine prior to foot, ankle, or leg surgery. The following measurements will be obtained to determine the change in sensory distribution: pinprick test with Neuropen, maximum voluntary isometric contraction before and after block, postoperative pain scores (24 hrs and at discharge) and postoperative opiate consumption.

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:

Additionally, MVIC will be measured by a handheld dynamometer (Lafayette Instrument Company, Lafayette Indiana) to determine muscle strength at baseline and after the adductor block. The patient will be in a seated position with the thigh parallel to the floor and the knee at a 90-degree angle with the feet off the floor. The dynamometer is applied to the leg 5 cm above the transmalleolar axis and perpendicular to the tibial crest. The patient is instructed to extend the leg at the knee with sustained maximal force for 5 seconds. This will be repeated 3 times with 30 seconds rest between each movement, and the force will be recorded (Newtons).

Adductor Canal Blockade The adductor canal block will be performed using a linear HFL38xp or a linear HFL38x ultrasound probe (X-Porte or M-Turbo; SonoSite; Bothell, Washington). The site that is to receive the ACB will be sterilized with chlorhexidine gluconate 2% and 70% isopropyl alcohol prep. A skin weal of lidocaine 1% (2-5mL) will be delivered. A Tuohy needle (17 gauges) will be inserted through the skin wheal under ultrasound guidance towards the target nerve location. Ropivacaine 0.5% 15ml will be injected for either adductor canal locations.27 Pain Scores and Opiate Consumption A follow-up visit will be performed in person for inpatients or via phone for outpatients within 24 hours from discharge to assess for pain control, and monitoring side effects. It will take 10 minutes. Adverse events will be monitored during the 24-hour period of the study.

Potential Risks Potential risks include loss of confidentiality or mild discomfort associated with the pinprick for sensory testing. Risks that are involved with administration of ropivacaine are primarily damage to surrounding tissues, including nerves, and may cause bleeding or infection from injection or an unknown allergy to ropivacaine that develops during the administration of the drug. There are no additional physical or psychological risks that may result from participation in this research protocol since patients will have determined that they desire perineural blockade before study inclusion is even proposed.

Subject Safety and Data Monitoring Any serious adverse reaction, including allergy and local anesthetic systemic toxicity, will result in immediate discontinuation of study related procedures and treatment as necessary. Serious adverse events will be reported to the Institutional Review Board. The data already obtained from a participant who has had a serious adverse event will be analyzed according to intention-to-treat principle.

If non-inferiority between the two neurosensory blockade techniques is significantly detected at 50% enrollment (or enrollment of 34 patients), the study will be stopped. The study will also be stopped in the event that there is overwhelming statistical evidence at interim analysis that the two blocks are different, or in the very small chance that there are multiple adverse events in the study population.

Eligibility Criteria:
Inclusion Criteria:

* Adults aged 18 years or older
* Individuals undergoing surgery of the medial foot, medial ankle, or medial leg for which the anesthetic plan includes an adductor canal nerve block

Exclusion Criteria:

1. Any known deficit of the ipsilateral lumbar nerve roots, ipsilateral lumbar plexus, ipsilateral femoral nerve, obturator nerve or saphenous nerve including diabetic peripheral neuropathy
2. Any local disorder of the skin or otherwise where blockade is to be performed
3. Body mass index \>50
4. American Society of Anesthesiologists (ASA) classification greater than 3
5. Allergy to amide local anesthetic medications
6. Pregnancy
7. Incarceration
8. Inability to understand study procedures including inability to understand the English language