Ultrasound Landmarks in the Approach to the Common Peroneal Nerve in a Sheep Model-Application in Peripheral Nerve Regeneration

Abstract

Peripheral nerve injury (PNI) remains a medical challenge with no easy resolution. Over the last few decades, significant advances have been achieved in promoting peripheral nerve regeneration, and new assessment tools have been developed, both functional and imaging, to quantify the proportion and quality of nerve recovery. The exploration of new animal models, larger, more complex, and with more similarities to humans, has made it possible to reduce the gap between the results obtained in classic animal models, such as rodents, and the application of new therapies in humans and animals of clinical interest. Ultrasonography is an imaging technique recurrently used in clinical practice to assess the peripheral nerves, allowing for its anatomical and topographic characterization, aiding in the administration of anesthesia, and in the performance of nerve blocks. The use of this technique in animal models is scarce, but it could be a useful tool in monitoring the progression of nerve regeneration after the induction of controlled experimental lesions. In this work, sheep, a promising animal model in the area of peripheral nerve regeneration, were subjected to an ultrasonographic study of three peripheral nerves of the hind limb, the common peroneal, and tibial and sciatic nerves. The main aim was to establish values of dimensions and ultrasound appearance in healthy nerves and landmarks for their identification, as well as to perform an ultrasound evaluation of the cranial tibial muscle, an effector muscle of the common peroneal nerve, and to establish normal values for its ultrasound appearance and dimensions. The results obtained will allow the use of these data as control values in future work exploring new therapeutic options for nerve regeneration after induction of common peroneal nerve injuries in sheep.

Keywords: peripheral nerve; peroneal common nerve; ultrasonography; ultrasound landmarks sheep model.

Figure 1

(a) Schematic representation of the distribution of the sciatic nerve (1) and its branches and tibial (2) and common peroneal (3) nerves in the hind limb; (b) demonstration of the applied ultrasound technique.

Figure 2

(a) Schematic representation of the location of the cranial tibial muscle on the cranial surface of the leg; (b) demonstration of the applied ultrasound technique. The blue dashed lines indicate the measurement sites.

Figure 3

Ultrasound image of the left sciatic nerve of a sheep after emergence from the greater sciatic foramen: (1) greater trochanter of the femur; (2) biceps femoris muscle; arrow—curvature of the sciatic nerve when passing between the reference bone structures. DIST1 represents the measurement of the diameter of the sciatic nerve.

Figure 4

Ultrasound image of the left sciatic nerve of a sheep nerve halfway through the thigh: (1) sciatic nerve, identified by an arrow (nerve fascicles enclosed by perineurium); (2) epineurium, identified by an arrow; (3) biceps femoris muscle; (4) piriformis muscle; (5) adductor muscles. DIST1 represents the measurement of the diameter of the sciatic nerve halfway through the thigh.

Figure 5

Ultrasound image of the left sciatic nerve and its ramifications in a sheep: (1) sciatic nerve, identified by an arrow; (2) tibial nerve, identified by an arrow; (3) common peroneal nerve, identified by an arrow; (4) biceps femoris muscle; (5) adductor muscles.

Figure 6

Schematic representation of the measurement sites for the diameter of the sciatic, common peroneal, and tibial nerves. The measurement sites are identified by the red dashed lines.

Figure 7

Ultrasound image of the left cranial tibial muscle taken close to its origin, bounded by the red dashed circle. (1) Tibialis cranialis muscle; (2) extensor digitorum longus muscle; (3) tibia. DIST1 (vertical red dashed line) and DIST2 (horizontal red dashed line) represent the thickness and width of the muscle, respectively.

Figure 8

Ultrasound image of the left sciatic nerve before its branching site, cross section (black arrow). In this plane, the nerve appears as an echogenic tubular structure surrounded by the musculature of the region. (1) Biceps femoris muscle; (2) vastus lateralis muscle; (3) Semitendinosus muscle (4) adductor muscles. DIST1 represents the measurement of the diameter of the sciatic nerve before its branching site.

Figure 9

Ultrasound image of the left peroneal nerve in a sheep subjected to a transection lesion followed by the application of a tube guide. (a) After 1 week, it is possible to observe the tube guide as a hyperechogenic tubular structure (black arrows) at the ends of which the ends of the transected nerve are inserted (white arrows). DIST1 represents the length of the gap left between the two nerve ends. (b) After 3 months, the tube continues to be perfectly visible (black arrows), and the nerve is introduced into its lumen (white arrows); but now, instead of the gap between the nerve tops, an anatomical continuity of the nerve is observed along the entire tubular lumen (beige arrow), indicating a nerve reconnection. In the center of the tubular lumen, a hypoechoic space not filled by nervous tissue is also observed (brown arrow), indicating that the regenerating nerve has not yet occupied all the available space inside the tube guide. DIST1 represents the nerve diameter, and DIST2 represents the inner diameter of the tube guide.

Figure 10

Ultrasound image of the left peroneal nerve in a sheep subjected to a transection lesion followed by the application of an end-to-end suture. (a) After 1 week, it is possible to observe that the nerve continuity is still interrupted by a gap between the two nerve tops that have not yet fully reconnected (black arrow). DIST1 represents the nerve diameter, which is enlarged and with an increased hyperechogenic appearance due to interstitial edema and inflammatory infiltrate. (b) After 3 months, the nerve already presents an anatomical continuity, it is less hyperechogenic, and its diameter has decreased considerably (DIST1).