Ultrasound-Guided Block of the Sciatic and the Femoral Nerves in Rabbits—A Descriptive Anatomical Study

SIMPLE SUMMARY: Analgesia is an important part of peri-operative protocols in humans and animals. The direct administration of analgesic drugs to a specific nerve is more effective than the systemic administration of such drugs. With the aid of ultrasound, the success rate of nerve blocks can be further improved. We developed an ultrasound-guided approach to perform a block of the sciatic and femoral nerves in rabbits. After a first evaluation of the anatomy, we successfully tested the technique in 20 hind limbs of 10 cadavers. This technique can now be assessed in rabbits undergoing hind limb surgery for clinical or experimental purposes. ABSTRACT: The rabbit is a popular animal model for human biomechanical research involving surgery on the hind limb. Mortality is higher in rabbits when undergoing general anesthesia compared to dogs and cats. Moreover, due to their nature as prey animals, rabbits have a tendency to hide signs of pain, making it challenging to detect discomfort at an early stage. Incorporating regional anesthesia into an anesthetic protocol can greatly reduce the requirements for systemic anesthetic and analgesic drugs, thereby minimizing associated side effects. In other species, a block of the sciatic (ScN) and the femoral nerves (FN) is usually applied in patients undergoing hind limb surgery. In phase 1 of this study, the ScN and the FN have been localized and an appropriate approach has been evaluated under sonographic guidance. In phase 2, a mixture of new methylene blue and lidocaine have been administered to the ScN and the FN in 10 cadavers (20 hind limbs). Staining of the nerves was evaluated by dissection. Ultrasonographically, the ScN appeared as a binocular structure surrounded by a hyperechoic rim. The FN appeared as a hypoechoic structure in the dorsal part of the iliopsoas muscle (IPM), becoming hyperechoic/honey-comb-like in the ventral part. Both nerves could be successfully stained in all animals over a median length of 2.3 cm which was considered effective. This technique allows feasible and accurate access to block the ScN and the FN and may lead to successful analgesia in rabbits undergoing hind limb surgery.