What We Already Know about This Topic Reducing the volume of local anesthetic administered for neural blockade may increase safety Local anesthetic administration can result in nerve damage What This Article Tells Us That Is New The low volume intraneural injection of ropivacaine 1% provided complete sensory-motor nerve block Reductions in action potential amplitudes lasting at least 6 months from the time of nerve block suggest that additional safety studies will be required Background Both extra- and intraneural sciatic injection resulted in significant axonal nerve damage. This study aimed to establish the minimum effective volume of intraneural ropivacaine 1% for complete sensory-motor sciatic nerve block in 90% of patients, and related electrophysiologic variations. Methods Forty-seven consecutive American Society of Anesthesiologists physical status I-II patients received an ultrasound-guided popliteal intraneural nerve block following the up-and-down biased coin design. The starting volume was 15 ml. Baseline, 5-week, and 6-month electrophysiologic tests were performed. Amplitude, latency, and velocity were evaluated. A follow-up telephone call at 6 months was also performed. Results The minimum effective volume of ropivacaine 1% in 90% of patients for complete sensory-motor sciatic nerve block resulted in 6.6 ml (95% CI, 6.4 to 6.7) with an onset time of 19 ± 12 min. Success rate was 98%. Baseline amplitude of action potential (mV) at ankle, fibula, malleolus, and popliteus were 8.4 ± 2.3, 7.1 ± 2.0, 15.4 ± 6.5, and 11.7 ± 5.1 respectively. They were significantly reduced at the fifth week (4.3 ± 2.1, 3.5 ± 1.8, 6.9 ± 3.7, and 5.2 ± 3.0) and at the sixth month (5.9 ± 2.3, 5.1 ± 2.1, 10.3 ± 4.0, and 7.5 ± 2.7) ( P < 0.001 in all cases). Latency and velocity did not change from the baseline. No patient reported neurologic symptoms at 6-month follow-up. Conclusions The intraneural ultrasound-guided popliteal local anesthetic injection significantly reduces the local anesthetic dose to achieve an effective sensory-motor block, decreasing the risk of systemic toxicity. Persistent electrophysiologic changes suggest possible axonal damage that will require further investigation.

Background Cytokines have crucial role in the development and maintenance of inflammation and pain in arthritis. Activation of prostaglandin receptor subtype EP(4) suppresses cytokine production in immune cells. The purpose of this study was to evaluate whether a novel EP(4) agonist would be able to suppress thermal and mechanical hyperalgesia and paw swelling in acute and chronic phases in rat monoarthritic model. Methods Monoarthritis was induced by an injection of complete Freund's adjuvant (CFA) intracapsularly into the tibiotarsal joint of the rats. Withdrawal latencies to thermal stimulation on the hind paw, withdrawal thresholds to mechanical stimulation, paw volume, and ankle diameter were measured 24 h and 4 weeks after the CFA injection. A novel selective EP(4) receptor agonist, ONO-AE1-329 (10, 25, or 50 microg) or saline was administered intracapsularly into the joint. Results Withdrawal latencies and withdrawal thresholds were significantly (P < 0.05) shortened and decreased, respectively, on the arthritic side but not on the contralateral side 24 h and 4 weeks after the CFA injection. In addition, significant (P < 0.05) increases in paw volume and ankle diameter on the arthritic side were observed. Intracapsularly administered ONO-AE1-329 showed significant (P < 0.05) inhibition of thermal and mechanical hyperalgesia and significant (P < 0.05) decrease in paw volume and ankle diameter in a dose-dependent manner at 24 h and 4 weeks after CFA. Conclusion Intracapsular administration of EP(4) receptor agonist effectively inhibited mechanical and thermal hyperalgesia and inflammatory reactions in acute and chronic monoarthritis. An EP(4) agonist would be a potential strategy for inflammatory pain in arthritis.