SAPHENOUS AND CYATIC NERVE BLOCKING IN DOGS (analgesia/anaesthesia for knee surgery)
Author: Miguel Martínez Fernández
EBVS & RCVS Specialist in Veterinary Anaesthesia and Analgesia
In this article, Miguel Martínez Fernández, our veterinarian with a European Diploma in Anaesthesia and Analgesia, tells us how to perform a correct saphenous and sciatic nerve block in dogs.
The use of regional anesthesia techniques allows an optimal control of analgesia during and after knee surgery. Sensory and motor innervation of the hindlimb comes from the ventral branches of the lumbosacral trunk of the spinal cord.
Specifically,innervation of the knee area comes primarily from the saphenous nerves (femoral nerve branch) on the medial aspect and the sciatic nerve on the anterior, posterior and lateral aspects. In some dogs (10-20%) there is a contribution from the obturator nerve.
We aim Perineural injection of an adequate volume and concentration of local anesthetic transiently blocks the transmission of the nociceptive impulse via ascending sensory pathways and prevents sensitization of the central nervous system (anaesthesia/analgesia).
HOW TO PERFORM SAPHENOUS AND SCIATIC NERVE BLOCK IN DOGS
The saphenous and sciatic nerve block for knee surgery can be performed by blind localization using anatomical landmarks or by ultrasound visualization (ultrasound-guided), which is ideal.The block is extremely effective and easy to perform and complications are rare, allowing a reduction in the use of other anaesthetics and analgesics (balanced anaesthesia). The use of loco-regional anaesthesia is known to reduce anaesthetic morbidity and mortality in dogs.
LOCALIZATION A SAPHENOUS NERVE
The saphenous nerve is located in the medial aspect of the thigh superficially accompanying the femoral artery and vein (Photo 1).
For a blind block, the nerve is located cranial to the artery, which is easily located by palpating the pulse (Photo 2).
Ultrasound visualization is simple by placing a linear probe in the middle of the medial aspect of the thigh transversal to the longitudinal axis of the femur (Photo 3). For knee surgery it is recommended to use long acting local anesthetics such as bupivacaine 0.5% or ropivacaine 0.5% at volumes of approximately 0.1ml/kg (although this depends on the ultrasound visualization of the local anesthetic around the nerve). The saphenous nerve is only sensitive, so it does not produce motor paralysis of any innervated muscle (it maintains the mobility of the quadriceps).
LOCATION OF THE SCIATIC NERVE
The sciatic nerve (composed of the tibial and common peroneal nerves within the same sheath) runs along the caudo-lateral aspect of the thigh starting from the trochanteric fossa between the powerful muscles of the area (Photo 4). For its blind block it can be easily located 1-2 cm deep in the trochanteric fossa between the greater trochanter of the femur and the ischial tuberosity (deep plane of the gluteal muscles) (Photo 5).
For the ultrasound-guided block we place the linear probe perpendicular to the longitudinal axis of the femur distal to the trochanteric fossa on the lateral aspect of the thigh (Photo 6). The injection of local anesthetic (approximately 0.1ml/kg) produces a long-lasting sensory block (analgesia) and a motor block of shorter duration.
Performing this block is simple with a little practice and provides optimal conditions for surgery and patient recovery. Once you try it, you will not be able to do without it.
And remember, if you want to expand your knowledge about the saphenous and sciatic nerve block in dogs, consult our courses, always conducted by internationally renowned specialists.