Continuous peripheral nerve blocks (CPNB; also known as "perineural" catheters) provide target-specific pain control for a variety of surgeries. There has been increasing interest in the use of ultrasound guidance for regional anesthesia, and many techniques using ultrasound alone for perineural catheter insertion have been described. Catheters may be placed at various points along the brachial plexus (for upper extremity procedures) or in proximity to the femoral and/or sciatic nerve (for lower extremity procedures). To date, the optimal ultrasound scanning technique, catheter insertion endpoint, catheter placement location per indication, for the majority of ultrasound-guided continuous peripheral nerve blocks remain unknown. This study will help provide important information related to optimal ultrasound scanning techniques and will help identify ways to improve the success rates, onset times, and analgesic effectiveness of these techniques for real patients undergoing surgical procedures.

Primary Aim: To determine if there is an optimal scanning technique for ultrasound-guided perineural catheter insertion that will result in the most accurate tip placement in proximity to the target nerve or plexus.

Secondary Aim: To determine if there is an optimal location for ultrasound-guided perineural catheter insertion along a target nerve or plexus that will result in maximum local anesthetic infusion benefits.

Inclusion criteria:

• At least 18 years of age;
• Undergoing unilateral, upper (at or distal to the elbow) or lower (hip or distal) extremity orthopedic surgery, with moderate-to-severe postoperative pain expected; and
• Desiring a continuous perineural catheter for postoperative analgesia.

Exclusion criteria:

• Patients who will have difficulty understanding the study protocol or caring for the infusion pump/catheter system; or
• Patients with any known contraindication to study medications, insulin-dependent diabetes mellitus, neuropathy of any etiology in the affected extremity;
• Patients with a contraindication to regional blockade (eg, clotting deficiency);
• Patients with any known acute or chronic hepatic or renal insufficiency or failure;
• Patients with any additional surgical site outside of the catheter-affected area (eg, iliac crest bone graft in addition to hand surgery);
• Patients with chronic opioid use (defined as daily use for more than 4 weeks prior to surgery) or active illicit substance abuse;
• Patient weighing < 40 kg;
• Pregnancy;
• Incarceration; or
• Inability to communicate with the investigators and hospital staff.