Research study to determine the proportion of cases in which an interscalene brachial plexus nerve block produces hand and forearm anesthesia.

This is a research study to prospectively determine the proportion of cases in which an interscalene brachial plexus nerve block produces hand and forearm anesthesia. The investigators will investigate this issue in patients having shoulder and not hand/forearm surgery. We will test hand grip strength and sensation to determine if the hand and forearm are responding to the anesthesia.

Inclusion Criteria:

• 18 years of age or older
• unilateral orthopedic shoulder surgery
• already desiring an interscalene brachial plexus nerve block for postoperative analgesia with the anesthetic plan including a preoperative interscalene nerve block with mepivacaine

Exclusion Criteria:

• any known contraindication to study medications or testing hand grip strength pre/post-op
• insulin-dependent diabetes mellitus
• neuropathy of any etiology in the affected extremity
• any anticipated incision site apart from the shoulder
• Obesity
• Pregnancy
• Incarceration
• inability to communicate with the investigators and hospital staff

Study population will consist only of patients undergoing orthopedic shoulder surgery.