Evaluation of a Continuous Saphenous Nerve Block to Supplement a Continuous Sciatic Nerve Block for Postoperative Analgesia Following Ankle Surgery

Interventions and Interactions Study participants will be asked to report a preoperative baseline pain score (Numeric Pain Scale (0-10)), and have quadriceps strength measured (see below) prior to any sedation being administered. Patients will undergo placement of a continuous subgluteal sciatic nerve catheter, and dosage with 25ml of 0.25% bupivacaine with epinephrine 1:200,000 and clonidine 25 mcg per usual technique after sedation. A perineural catheter will then be placed for primary saphenous nerve block and postoperative saphenous infusion. This continuous saphenous catheter will be placed using ultrasound guidance (Sonosite Turbo ™, Bothell, WA) (6-13MHz linear probe). The superficial femoral artery will be identified in short axis at approximately the midpoint or distal third of the femur as the artery lies deep to the sartorius muscle in the adductor canal. Using aseptic technique, an 18 gauge tuohy needle will be inserted in-plane from lateral to the transducer and advanced to a position anteromedial to the artery, between sartorius and vastus medialis muscles. Proper positioning will be confirmed by injection of saline, a 20g multiorifice catheter will be inserted 3-4 cm beyond the needle tip and the catheter will be tunneled and taped up the medial surface of the thigh. The catheter will be test dosed with 1.5% lidocaine with 1:200,000epinephrine to confirm position and rule out IV injection. The primary saphenous nerve block will be produced by incremental injection through the catheter of 10ml of 0.25% bupivacaine with epinephrine 1:200,000 and clonidine 15 mcg. Successful saphenous block will be defined as loss of sensation to pinprick in the mid, anteromedial leg measured at 15 and 30 minutes post-block. A 3-point scale will be used to define sensory block: 0=full sensation, 1= touch without sharp sensation, 2=absent sensation.

To determine the effect of saphenous block on quadriceps function, patients will have knee extension muscle strength tested pre-block and 30 min post-block using a Hoggan Health microFET 2 MT Digital Handheld Dynamometer. After placement of both the saphenous and sciatic nerve catheters, patients will receive either neuraxial or general anesthesia for surgical anesthesia at the discretion of the attending anesthesiologist medically directing their primary anesthetic technique.

Patients with evidence of sciatic and saphenous nerve block will be randomized to receive a postoperative continuous infusion of either saline (control) or 0.2% ropivacaine by elastomeric infusion pump at 5ml/h started within 6h of catheter placement. The randomization will occur by sealed envelope provided to the OR Pharmacy (block randomization in blocks of 10) and the OR pharmacy will prepare the 300 ml elastomeric pump with active or control solution. The On-Q C-Bloc™(300ml capacity) (I-Flow corporation) pump will be attached to the saphenous catheter in the PACU, or within 6h of primary block; the catheter will infuse for 60 hours.

The patients, physicians, nurses and investigators will be blinded to treatment group.

The sciatic infusion will be managed per usual practice: postoperatively all patients will receive 0.2% ropivacaine through their sciatic nerve catheter at a basal infusion rate of 10ml/h, . The sciatic pump will be an On-Q™ pump per usual practice. All patients will have oral and IV opioids prescribed while hospitalized, and oral opioids prescribed after hospital discharge. In the event of breakthrough pain, patients will be instructed to adjust the sciatic nerve pump, and/or to take oral opioids for the pain.