Prospective, Double-blind, Randomized, Placebo-controlled Trial of Continuous Saphenous Block to Supplement Continuous Sciatic Block Following Major Ankle Surgery: Analgesia and Quadriceps Motor Function
Weller, RS, Henshaw, DS, et al
Patients undergoing major ankle surgery often have significant postoperative pain. Our clinical experience using continuous sciatic and single-injection saphenous blocks suggested that many patients reported significant pain after resolution of saphenous blockade. This study was designed to test our hypothesis that these patients would have improved analgesia if a continuous saphenous block were added.
Materials and Methods:
Subjects, aged 18-75 and using <40 mg-equivalents oxycodone/day, undergoing either elective ankle fusion or bi/tri-malleolar ORIF with overnight admission, gave written, informed consent for this IRB-approved investigation. Baseline preoperative quadriceps strength was tested with a handheld digital dynamometer. All patients had an ultrasound-guided (SAXIP), mid-thigh saphenous catheter placed, and dosed with 10mL of 0.25% bupivacaine (w/epinephrine 5 mcg/mL and clonidine 1.7 mcg/mL). All patients had a subgluteal sciatic catheter placed using nerve stimulation, which was dosed with 25mL of 0.25% bupivacaine (w/epinephrine 5 mcg/mL and clonidine 1.7 mcg/mL ). Quadriceps strength was re-tested 30’ after the saphenous block. Spinal or general anesthesia was utilized and all patients received a sciatic infusion of 0.2% ropivacaine @10mL/hr postoperatively (elastomeric pump). Patients were randomized to receive a saphenous infusion of either saline or 0.2% ropivacaine @5mL/hr via another elastomeric pump (prepared by pharmacy for blinding). Quadriceps strength was re-tested at 24h, and numeric pain scores (numeric rating scale NRS) with rest and movement were recorded at 24 and 48h. In addition, 24/48h opioid consumption (oxycodone equivalents), nausea/vomiting, and sleep interruptions were recorded. The primary endpoint was NRS pain score at 48h. A 2-point reduction was defined as clinically relevant and power analysis indicated a targeted recruitment of 74 patients.
The study was closed after enrolling 32 patients because these surgeries shifted to primarily outpatient procedures. Complete 48h data was collected on 29 patients (15 ropivacaine/14 saline).
The groups were comparable in age, BMI, preoperative pain scores and opioid use, anesthetic type, and type/side of surgery (Table 1). There was no significant difference in pain scores at 48h, although the ropivacaine group’s mean pain scores appeared lower at each time point, and at 24h approached significance (2.4 vs 4.7 p=0.06) (Fig 1). Quadriceps strength was maintained in both groups (Fig 2). There was no difference in time to first analgesic, 24 and 48h opioid use, nausea/vomiting or sleep interruptions (Tables 2,3).
It remains unclear how much of the pain following complex ankle surgery is subserved by the saphenous innervation. High variability in pain scores and opioid use may have masked any potential improvement in analgesia due to continuous saphenous nerve blockade. With a near-significant pain improvement at 24h, it is tempting to speculate that a difference may have been found if full recruitment had been achieved, but this cannot be concluded by our data. Other investigators found no difference in 48h morphine consumption (primary endpoint) or pain score ≤3 (secondary endpoint) with the addition of continuous saphenous block in 44 ankle surgery patients (1).
Quadriceps motor function was well preserved with continuous saphenous block. While this has now been shown by a number of investigators, it had not been proven when this study was initiated (2,3)
These preliminary results do not support the complexity of a dual catheter analgesic regimen, but a type-II error cannot be excluded.
Fisker AK, et al. Can J Anaesth. 2015;62(8):875-82.
Jaeger P, et al. Reg Anesth Pain Med. 2013;38(6):526-32
Grevstad U, et al. Reg Anesth Pain Med. 2015;40(1):3-10