To determine if the way local anesthetic, or numbing medication, is delivered through a tiny tube next to the nerves that go to the thigh affects the strength and sensation in the thigh.

Specific Aim: Research study to test the hypothesis that differing the location of the perineural catheter tip during a continuous femoral nerve block (anterior vs. posterior) impacts quadriceps muscle strength. These results will help define the optimal perineural catheter tip location relative to the femoral nerve used for continuous peripheral nerve blocks and help guide both clinical care and future research in this clinically-relevant area.

Inclusion Criteria:

• 18 years of age or over
• Willing to have bilateral femoral perineural catheters placed with a subsequent ropivacaine infusion and motor/sensory testing for 6 hours, requiring an overnight stay in the UCSD GCRC/CTRI to allow dissipation of local anesthetic infusion effects by the following morning

Exclusion Criteria:

• current daily analgesic use
• opioid use within the previous 4 weeks
• any neuro-muscular deficit of either femoral nerves and/or quadriceps muscles
• body mass index > 30 kg/m2
• pregnancy
• incarceration