# An Explorative Anatomical Study on Inter-Individual Variation of the Tibial Nerve and Landmarks for Perineural Anesthesia in Horses

## TL;DR

This study examines the tibial nerve in horses to improve perineural anesthesia techniques by identifying consistent injection landmarks.

## Contribution

The study identifies specific anatomical landmarks for tibial nerve injections in horses, independent of anatomical variations.

## Key findings

- No anatomical variations of the tibial nerve were observed in cadaveric horse limbs.
- The recommended injection site is 10 cm proximal to the calcaneal tubercle and 11 mm cranial to the superficial digital flexor.
- The thickness of the tibial nerve and surrounding tissue may challenge successful anesthesia.

## Abstract

Perineural anesthesia of the tibial nerve can be performed ultrasound-guided or blindly, with the latter still being commonly used in equine practice due to practical constraints, despite its lower accuracy and hence, its common failure to achieve desensitization. This may be associated with anatomical variations or inadequate landmarks for injection. In this anatomical study on the course of the tibial nerve on paired cadaveric limbs, we found that problems with perineural anesthesia cannot simply be attributed to anatomical variations. The large diameter of the tibial nerve (6 ± 1 mm) and the substantial amount of perineural tissue may present specific challenges for achieving adequate desensitization. Regarding landmarks, this study confirms that perineural injection should be performed 10 cm proximal to the proximocranial aspect of the calcaneal tubercle and 11 mm cranial to the superficial digital flexor.

Perineural anesthesia of the tibial nerve can be performed ultrasound-guided or blindly, with the latter still being commonly used in equine practice due to practical constraints, despite its lower accuracy and hence, common failure to achieve desensitization. This may be associated with anatomical variations or inadequate landmarks for injection. To examine the course of the tibial nerve, document potential anatomical variations, and determine optimal landmarks for perineural injection, dissection was conducted along the medial aspect of the tibia in 10 paired cadaver hindlimbs. No anatomical variations of the tibial nerve were observed. Mean tibial nerve thickness was 6 ± 1 mm. The junction with the plantar nerves was located at a maximum of 85 mm and the junction with the medial cutaneous branch was at a maximum of 150 mm proximal to the proximal aspect of the calcaneal tubercle. The mean distance of the tibial nerve to the cranial border of the superficial digital flexor was 11 ± 6 mm. In conclusion, problems with perineural anesthesia of the tibial nerve cannot simply be attributed to anatomical variations. The thickness of the nerve and the amount of perineural tissue may present specific challenges for achieving adequate desensitization. Our results support the generally recommended site for tibial nerve perineural injection at 100 mm proximal to the calcaneal tubercle and 11 mm cranial to the superficial digital flexor.