Adductor Canal Block Versus Femoral Block on Pain and Quadriceps Strength

Effects of Ultrasound-guided Adductor Canal Block Versus Femoral Nerve Block on Pain and Quadriceps Strength After Ambulatory Knee Arthroscopic Surgery

The purpose of this study is to compare the effects of a femoral nerve block vs. an adductor canal block on pain and quadriceps muscle strength for knee arthroscopy surgery.

Patients undergoing arthroscopic knee surgery (ACL and non-ACL surgery) typically receive an ultrasound-guided femoral nerve block or an adductor canal block in the pre-operative phase for post-operative pain control. While an effective method for post-operative analgesia, the femoral nerve block is associated with profound quadriceps weakness for the duration of the nerve block, which can impair ambulation, rehabilitation, and increase the risk of falls. The more distal adductor canal block, however, contains primarily sensory branches of the femoral nerve and has been been purported by small volunteer studies to provide equally effective analgesia with minimal motor block and quadriceps weakness (as compared to femoral nerve block). The investigators will prospectively randomize patients undergoing knee arthroscopy at the UCSF Orthopaedic Institute to receive either a single-shot femoral nerve or adductor canal block pre-operatively after taking baseline measurements of quadriceps strength (quantified by maximum voluntary isometric contraction). The quadriceps muscle strength will be checked 20 minutes after the nerve block to assess strength. All patients will subsequently undergo a general anesthetic. The primary outcome variable will be post-block quadriceps strength as a percentage of baseline from pre-block values. Secondary outcome variables that will also investigated include: VAS pain score in the post anesthesia recovery unit and post-operative day 1, time to onset of sensory block, duration of nerve blockade, block performance time, patient satisfaction score, perioperative opioid use, perioperative analgesic consumption, incidence of paresthesias, number of needle passes, incidence of post-operative nausea, vomiting, constipation, and any other complications.

Patients scheduled for knee arthroscopy will have a femoral nerve block done using 0.5% ropivacaine 20ml before surgery.

Patients scheduled for knee arthroscopy will have an adductor canal block done using 0.75% ropivacaine 13.3ml before surgery.

Quadriceps strength will be tested with a dynamometer before the nerve block and 20 minutes after the nerve block prior to surgery. We are trying to measure the effect of both femoral and adductor canal nerve blocks on quadriceps strength.

As this is an outpatient surgery, we will collect Numerical Pain Scores from the recovery room medical record after surgery as well as from the patients for the first 24 hours after surgery by contacting them at home the following day. We will evaluate the difference in patient pain scores between the two nerve blocks under study

Patients will be contacted after surgery to determine when the nerve block wore off based on their increase in pain

Data on the amount of pain medication consumed for the 1st 24 hours after surgery will be collected based on medications that were administered during surgery, in the recovery room and medications that patients took at home after discharge from the recovery room. All pain medications will be converted to morphine equivalence in milligrams and reported that way. The comparison will be the difference in mg morphine equivalence consumption between the two nerve block groups.

Inclusion Criteria: American Society of Anesthesia I-III classification, Scheduled for arthroscopic knee surgery (meniscal debridement/repair, ACL reconstruction) Exclusion Criteria: Age younger than 18 years Non-English speaking Any contraindication for regional anesthesia, such as allergy to local anesthetics or opioids, -Coagulopaty or severe thrombocytopenia Infection at puncture sites Pre-existing neuropathy in operative limb Need for post-operative nerve function monitoring Dementia Patient refusal High pre-operative opioid requirements