Peripheral nerves often lie adjacent to blood vessels within neurovascular bundles surrounded by a sheath composed of layers of fascia.1–5 The purpose of the sheath is to allow friction-free movement of nerves against surrounding structures.6 This sheath has been termed the common epineural sheath,5 complex fascial layer,7 adventitia of the nerve,6 and gliding tissue of the nerve.8 To avoid confusion, it was suggested that the sheath be called the paraneural sheath and the space below it the subparaneural space.2 More recently, it was proposed that the sheath be called the circumneural sheath and the space below it the subcircumneural space.3,9
The subcircumneural space is sometimes referred to as the “sweet spot of the nerve” by anesthesiologists, representing the site where a nerve block provides a fast onset and satisfactory duration.3 The circumneural sheath itself has clinical importance because it may delay diffusion of local anesthetic solution into the nerve when the solution is deposited outside the sheath.2,3,8 The purpose of the study reported here was to determine whether injection of a local anesthetic solution outside the circumneural sheath of the palmar digital nerves (ie, outside the neurovascular bundle) at the base of the proximal sesamoid bones would ameliorate lameness caused by pain within the region innervated by this nerve.
No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.
The authors thank Jessica Brown for technical assistance.
Difference between the local maximum head height before right forelimb stance and the local maximum head height before left forelimb stance
Difference between the local minimum head height during right forelimb stance and the local minimum head height during left forelimb stance
Carbocaine-V, Zoetis Inc, Kalamazoo, Mich.
Isovue-370, Bracco Diagnostics Inc, Monroe, NJ.
Q with Lameness Locator, Equinosis LLC, Columbia, Mo.
PROC MIXED, SAS, version 9.1, SAS Institute Inc, Cary, NC.
2. Andersen HL, Andersen SL, Tranum-Jensen J. Injection inside the paraneural sheath of the sciatic nerve: direct comparison among ultrasound imaging, macroscopic anatomy, and histologic analysis. Reg Anesth Pain Med 2012;37:410–414.
3. Boezaart AP. Sweet spot of the nerve: is the “paraneural sheath” named correctly, and does it matter? Reg Anesth Pain Med 2014;39:557–558.
4. Prasad NK, Capek S, deRuiter GCW, et al. The subparaneurial compartment: a new concept in the clinicoanatomic classification of peripheral nerve lesions. Clin Anat 2015;28:925–930.
5. Vloka JD, Hadžić A, Lesser JB, et al. A common epineural sheath for the nerves in the popliteal fossa and its possible implications for sciatic nerve block. Anesth Analg 1997;84:387–390.
6. Millesi H, Hausner T, Schmidhammer R, et al. Anatomical structures to provide passive motility of peripheral nerve trunks and fascicles. Acta Neurochir Suppl 2007;100:133–135.
7. Missair A, Weisman RS, Suarez MR, et al. A 3-dimensional ultrasound study of local anesthetic spread during lateral popliteal nerve block: what is the ideal end point for needle tip position? Reg Anesth Pain Med 2012;37:627–632.
8. Boezaart AP, Zasimovich Y, Parvataneni HK. Long-acting local anesthetic agents and additives: snake oil, voodoo, or the real deal? Pain Med 2015;16:13–17.
9. Denoix J-M. The equine distal limb: atlas of clinical anatomy and comparative imaging. Ames, Iowa: Iowa State University Press, 2000.
10. Keegan KG, Yonezawa Y, Pai PF, et al. Evaluation of a sensor-based system of motion analysis for detection and quantification of forelimb and hind limb lameness in horses. Am J Vet Res 2004;65:665–670.
11. Keegan KG, MacAllister CG, Wilson DA, et al. Comparison of an inertial sensor system with a stationary force plate for evaluation of horses with bilateral forelimb lameness. Am J Vet Res 2012;73:368–374.
12. Keegan KG, Kramer J, Yonezawa Y, et al. Assessment of repeatability of a wireless, inertial sensor-based lameness evaluation system for horses. Am J Vet Res 2011;72:1156–1163.
13. McCracken MJ, Kramer J, Keegan KG, et al. Comparison of an inertial sensor system of lameness quantification with subjective lameness evaluation. Equine Vet J 2012;44:652–656.
14. Keegan KG, Wilson DA, Kramer J, et al. Comparison of a body-mounted inertial sensor system-based method with subjective evaluation for detection of lameness in horses. Am J Vet Res 2013;74:17–24.
15. Keegan KG. Objective assessment of lameness. In: Baxter GM, ed. Adams and Stashak's lameness in horses. 6th ed. Chichester, England: Wiley-Blackwell, 2011;154–164.
16. Keegan KG, Pai PF, Wilson DA, et al. Signal decomposition method of evaluating head movement to measure induced forelimb lameness in horses trotting on a treadmill. Equine Vet J 2001;33:446–451.
17. Audigié F, Pourcelot P, Degueurce C, et al. Fourier analysis of trunk displacements: a method to identify the lame limb in trotting horses. J Biomech 2002;35:1173–1182.
18. Keegan KG, Arafat S, Skubic M, et al. Detection of lameness and determination of the affected forelimb in horses by use of continuous wavelet transformation and neural network classification of kinematic data. Am J Vet Res 2003;64:1376–1381.
19. Schumacher J, Taintor J, Schumacher J, et al. Function of the ramus communicans of the medial and lateral palmar nerves of the horse. Equine Vet J 2013;45:31–35.
20. Donnell JR, Frisbie DD, King MR, et al. Comparison of subjective lameness evaluation, force platforms and an inertial sensor system to identify mild lameness in an equine osteoarthritis model. Vet J 2015;206:136–142.
21. Pfau T, Boultbee H, Davis H, et al. Agreement between two inertial sensor gait analysis systems for lameness examinations in horses. Equine Vet Educ 2016;28:203–208.
22. Littell RC, Henry PR, Ammerman CB. Statistical analysis of repeated measures data using SAS procedures. J Anim Sci 1998;76:1216–1231.
24. Littell RC, Pendergast J, Natarajan R. Modelling covariance structure in the analysis of repeated measures data. Stat Med 2000;19:1793–1819.
25. Bassage LH II, Ross MW. Diagnostic analgesia. In: Ross MW, Dyson SJ, eds. Diagnosis and management of lameness in the horse. 2nd ed. St Louis: Elsevier Saunders, 2011;100–135.
26. Nagy A, Bodó G, Dyson SJ, et al. Diffusion of contrast medium after perineural injection of the palmar nerves: an in vivo and in vitro study. Equine Vet J 2009;41:379–383.
27. Nagy A, Bodó G, Dyson SJ, et al. Distribution of radiodense contrast medium after perineural injection of the palmar and palmar metacarpal nerves (low 4-point nerve block): an in vivo and ex vivo study in horses. Equine Vet J 2010;42:512–518.
28. Dyson S. Equine lameness: clinical judgment meets advanced diagnostic imaging, in Proceedings. 59th Annu Conv Am Assoc Equine Pract 2013;92–122.
29. Silva GB, De La Côrte FD, Brass KE, et al. Duration and efficacy of different local anesthetics on the palmar digital nerve block in horses. J Equine Vet Sci 2015;35:749–755.
30. Hoerdemann M, Smith RL, Hosgood G. Duration of action of mepivacaine and lidocaine in equine palmar digital perineural blocks in an experimental lameness model. Vet Surg 2017;46:986–993.