Peripheral neuropathy is an uncommon cause of forelimb lameness in horses.1 This condition can involve the nerve roots of the brachial plexus, the brachial plexus itself, or nerves arising from it. The ventral roots from the sixth to the eighth cervical nerves and from the first and second thoracic nerves converge between the scalene muscles and the medial aspect of the shoulder to form the brachial plexus in the axillary space.2–5 Nerves arising from the brachial plexus include the suprascapular nerve (innervating the supraspinatus and infraspinatus muscles), axillary nerve (innervating the deltoideus, teres minor, and cleidobrachialis muscles), radial nerve (innervating the extensor muscles of the elbow joint, carpus, and digit), musculocutaneous nerve (innervating the flexor muscles of the elbow joint), and the median and ulnar nerves (innervating the caudal antebrachial flexor muscles).2–5 Trauma (including pressure, stretching, and transection) is the most frequent cause of peripheral neuropathy of a forelimb.6 Nerve lesions resulting from mechanical trauma have been classified into 3 categories according to the degree of damage to a single nerve fascicle: neurapraxia results from mild compression of the fascicle without morphological change of the axon, axonotmesis is caused by crushing with damage to the axon and preservation of the myelin sheath, and neurotmesis results from severing of the entire fascicle (axon and myelin sheath).6–10
Compression between the scapula and the ribs has been considered as the most common cause of injury to the brachial plexus or to the proximal part of the nerves emanating from the plexus.10,11 The suprascapular nerve is mainly susceptible to injury in the region where it crosses the thin cranial border of the scapula.6,7,10,12–17 Local subclinical neuropathy at this level, even in apparently healthy horses, can increase fragility of the nerve and its susceptibility to injury when the limb is suddenly thrust backward.7,18 Clinical signs of suprascapular nerve injury include subsequent neurogenic atrophy of the supraspinatus and infraspinatus muscles and, in most cases, lateral instability of the shoulder during the stance phase of the gait.6,7,9,10,12–17 Instability of the shoulder (commonly called sweeny) has also been reported secondary to lesions of the brachial plexus or of the ventral roots of its contributing nerves.19 Radial nerve fibers can be overstretched during hyperextension of the limb in a backward direction or in extreme abduction of the shoulder18,20; the nerve can also be compressed during general anesthesia of horses positioned in lateral recumbency,11,20,21 and it can be torn or compressed by trauma to the humerus or the elbow joint.9,11 The clinical signs of radial nerve injury depend on the severity, extent, and nature of the lesion as well as the site or sites of damage, and range from distal displacement of the olecranon tuberosity (ie, dropped elbow sign) and complete inability to stand on the affected limb to a slight tendency to stumble.1,6,9,11,19,20,22 Injury to the musculocutaneous nerve is rare and results in atrophy of the biceps brachii and brachialis muscles; typically, no clinically relevant gait abnormality is observed in affected horses.1,6,9,11 The median and ulnar nerves can be injured by direct external trauma or following a humeral fracture,6,9 with signs including hyperextension of the distal aspect of the affected limb and a somewhat stiff gait, but the effect on locomotion is moderate because the stay apparatus of the forelimb and the numerous intramuscular aponeuroses in the caudal antebrachial muscles partly compensate for the neurologic impairment.2–5
Although the literature includes several reports7,10,12,14–16,22,23 of horses with peripheral neuropathy of forelimbs, to our knowledge, no retrospective study of these injuries in a large number of horses has been published. Therefore, the purpose of the study reported here was to determine the clinical, radiographic, and ultrasonographic findings and outcomes of horses with peripheral neuropathy of a forelimb.
Supported by the Conseil Régional de Basse-Normandie and the European Parliament (European Regional Development Funds).
The authors declare that there were no conflicts of interest.
1. Bernard WV, Beech J. Neurological examination and neurological conditions causing gait deficits. In: Ross MW, Dyson SJ, eds. Diagnosis and management of lameness in the horse. 2nd ed. St Louis: Elsevier-Saunders, 2011;135–145.
2. Barone R. Muscles de la ceinture et du membre thoracique. In: Barone R, ed. Anatomie comparée des mammifères domestiques. Tome 2 Arthrologie et Myologie. 5th ed. Paris: Vigot-Maloine, 2010; 580–702.
3. Barone R. Plexus brachial. In: Barone R, Simoens P, eds. Anatomie comparée des mammifères domestiques. Tome 7 Neurologie II. Paris: Vigot, 2010; 157–231.
4. Budras KD, Sack WO, Rock S. In: Budras KD, Sack WO, Rock S, eds. Anatomy of the horse. 6th ed. Hannover, Germany: Schlutersche Verlag, 2012;4–7.
5. Kainer RA. Functional anatomy of equine locomotor organs. In: Baxter GM, ed. Adams and Stashak's lameness in horses. 6th ed. Oxford, England: Wiley-Blackwell, 2011; 25–39.
6. Furr M. Disorders of the peripheral nervous system. In: Furr M, Reed S, eds. Equine neurology. 2nd ed. Oxford, England: Blackwell Publishing, 2008;329–336.
7. Duncan ID, Schneider RK. Equine suprascapular neuropathy (sweeny): clinical and pathologic observations, in Proceedings. 31st Annu Conv Am Assoc Equine Pract 1985;415–428.
8. Mayhew IG. Clinical application of needle electromyography to evaluate lesions involving nerves of the brachial plexus. Equine Vet Educ 1993; 5:103–105.
10. Mayhew J. Paresis or paralysis of one limb. In: Mayhew J, ed. Large animal neurology. 2nd ed. Oxford: Wiley Blackwell, 2009; 157–162.
11. Hahn CN, Mayhew IG, MacKay RJ. Diseases of the peripheral (spinal) nerves. In: Colahan PC, Mayhew IG, Merritt AM, et al, eds. Equine medicine and surgery. 5th ed. St Louis: Mosby, 1999;975–977.
12. Adams OR, Schneider RK, Bramlage LR, et al. A surgical approach to treatment of suprascapular nerve injury in the horse. J Am Vet Med Assoc 1985; 187:1016–1018.
13. Devine DV, Jann HW, Payton ME. Gait abnormalities caused by selective anesthesia of the suprascapular nerve in horses. Am J Vet Res 2006; 67:834–836.
14. Dutton DM, Honnas CM, Watkins JP. Nonsurgical treatment of suprascapular nerve injury in horses: 8 cases (1988–1998). J Am Vet Med Assoc 1999; 214:1657–1659.
15. Schneider JE, Adams OR, Easley KJ, et al. Scapular notch resection for suprascapular nerve decompression in 12 horses. J Am Vet Med Assoc 1985; 187:1019–1020.
17. Hubert J, Stashak TS. Suprascapular nerve injury (sweeny). In: Baxter GM, ed. Adams and Stashak's lameness in horses. 6th ed. Oxford: Wiley-Blackwell, 2011; 718–720.
18. Rooney JR. Biomechanics of lameness in horses. In: Rooney JR, ed. Biomechanics of lameness in horses. 2nd ed. Malabar, Fla: Robert E Krieger Publishing Co, 1977; 114–126.
19. Dyson SJ. The elbow, brachium and shoulder. In: Ross MW, Dyson SJ, eds. Diagnosis and management of lameness in the horse. 2nd ed. St Louis: Elsevier-Saunders, 2011;456–474.
20. Hubert J, Stashak TS. Paralysis of the radial nerve. In: Baxter GM, ed. Adams and Stashak's lameness in horses. 6th ed. Oxford: Wiley-Blackwell, 2011; 705–707.
23. Cauvin E, Munroeg A, Mitsopoulos A. Peripheral neuropathy involving brachial plexus nerves in two horses. Equine Vet Educ 1993; 5:90–94.
24. American Association of Equine Practitioners. Lameness exams: evaluating the lame horse. AAEP lameness scale. Available at: www.aaep.org/info/horse-health?publication=836. Accessed Jul 13, 2016.
25. Coudry V, Dupays A-G, Carnicer D, et al. Long-term follow-up of superficial digital flexor tendonitis treated by a single intralesional injection of a regenerating agent in 51 horses. J Equine Vet Sci 2014; 4:1357–1360.
26. Denoix JM, Dyson SJ. The thoracolumbar spine. In: Ross MW, Dyson SJ, eds. Diagnosis and management of lameness in the horse. 2nd ed. St Louis: Elsevier-Saunders, 2011;592–605.
27. Decherchi P, Dousset E, Marqueste T, et al. Muscle electrostimulation and functional recovery of a denervated muscle. Sci Sports 2003; 18:253–263.
28. Denoix JM. Muscle groups and their actions. The forelimb. In: Denoix JM, ed. Biomechanics and physical training of the horse. Boca Raton, Fla: CRC press, 2014; 14–24.
29. Dyson SJ. The cervical spine and soft tissue of the neck. In: Ross MW, Dyson SJ, eds. Diagnosis and management of lameness in the horse. 2nd ed. St Louis: Elsevier-Saunders, 2011;606–616.
30. Reef VB. Ultrasonography and orthopedic (nonarticular) disease. In: Ross MW, Dyson SJ, eds. Diagnosis and management of lameness in the horse. 2nd ed. St Louis: Elsevier-Saunders, 2011;212–215.
31. Denoix JM. Ultrasonographic examination in the diagnosis of joint disease. In: McIlwraith CW, Trotter CW, eds. Joint disease in the horse. Philadelphia: WB Saunders Co, 1996; 165–202.