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Suprascapular Neuropathy in Horses

(Sweeney)

By

Marcus J. Head

, BVetMed, Rossdales Equine Hospital and Diagnostic Centre

Last full review/revision Sep 2015 | Content last modified Oct 2015

This syndrome describes the physical appearance of the horse’s shoulder. It is not a diagnosis in itself, because there are a number of potential causes. The most common cause is injury to the suprascapular nerve.

All cases have atrophy of the supraspinatus and infraspinatus muscles that cover the scapula. This results in the scapular spine becoming prominent; in severe cases, the muscles virtually disappear. The atrophy is unusual in that it is often profound and very localized, which are hallmarks of an injury to a single lower motor nerve. The nerve involved is the suprascapular. Although the site of damage is rarely documented clinically, most cases involve trauma to the cranial shoulder at the point where the nerve is exposed to potential compression as it courses over the cranial aspect of the scapula. The severity of damage determines the degree of atrophy and the chances of recovery. If nerve function is severely compromised, the shoulder joint becomes unstable (it is a synarthrosis with no true collateral ligaments, relying on the surrounding muscles to support it) and the joint “pops out” sideways as the horse bears weight. This subluxation does not appear overtly painful to the horse, but if the joint cannot be stabilized, it may have significant implications for the longterm health of the joint and the horse’s athletic career.

Therapy is aimed at maintaining muscle health during the period of nerve recovery and maximizing neurogenesis. Horses should be restricted to stable rest or a very small paddock. Complete immobilization may negatively impact the nerve and muscles, but activity probably hastens joint degeneration. A surgical procedure to remove part of the scapula over which the nerve courses has been described, aiming to provide optimal conditions for nerve recovery. This should be considered, but its usefulness is open to debate. Muscle stimulation, under the guidance of a trained physiotherapist, will help to limit muscle fibrosis and may encourage nerve regeneration. The vast majority of cases seem to be a result of neuropraxia or axonotmesis (based on clinical observations and rates of recovery), and function is recovered with time. However, this process can take many months, and frequently some loss of muscle bulk will remain. The prognosis seems most affected by duration of injury before diagnosis, degree of atrophy at diagnosis, and willingness of the owner to perform time-consuming physical treatments for many months.

Other causes of sweeney include disuse atrophy (which does not appear focal and is rarely severe), brachial plexus injury (which usually disrupts a number of nerves; atrophy is not focal but observable in a number of muscle groups), and caudal cervical disease resulting in spinal nerve radiculopathy (in which a number of motor nerves are also affected so that other muscles atrophy). Careful assessment of the muscles involved and radiography of the neck and shoulder will aid differentiation. Scintigraphy is useful for rapid screening of the proximal limb and cervical and thoracic vertebra for damage that may have an adverse effect on prognosis.

OTHER TOPICS IN THIS CHAPTER

Lameness in Horses
Overview of Lameness in Horses
The Lameness Examination in Horses
Imaging Techniques in Equine Lameness
Arthroscopy in Equine Lameness
Regional Anesthesia in Equine Lameness
Disorders of the Foot in Horses
Osseous Cyst-like Lesions in the Distal Phalanx in Horses
Bruised Sole and Corns in Horses
Canker in Horses
Fracture of Navicular Bone in Horses
Fracture of Distal Phalanx in Horses
Keratoma in Horses
Laminitis in Horses
Navicular Disease in Horses
Pedal Osteitis in Horses
Puncture Wounds of the Foot in Horses
Pyramidal Disease in Horses
Quittor in Horses
Quarter Crack in Horses
Scratches in Horses
White Line Disease in Horses
Sheared Heels in Horses
Sidebone in Horses
Thrush in Horses
Disorders of the Pastern and Fetlock
Fractures of the First and Second Phalanx in Horses
Fractures of the Proximal Sesamoid Bones in Horses
Osteoarthritis of the Proximal Interphalangeal Joint in Horses
Palmar/Plantar Metacarpal/Metatarsal Nonadaptive Bone Remodeling in Horses
Sesamoiditis in Horses
Chronic Proliferative Synovitis in Horses
Digital Sheath Tenosynovitis in Horses
Disorders of the Metacarpus in Horses
Tendinitis in Horses
Suspensory Desmitis in Horses
Inferior Check Desmitis in Horses
Bucked Shins in Horses
Exostoses of the Second and Fourth Metacarpal Bones in Horses
Fractures of the Small Metacarpal (Splint) Bones in Horses
Fracture of the Third Metacarpal (Cannon) Bone in Horses
Disorders of the Carpus in Horses
Fracture of the Carpal Bones in Horses
Subchondral Bone Disease of the Third Carpal Bone in Horses
Tearing of the Medial Palmar Intercarpal Ligament in Horses
Osteoarthritis of the Carpus in Horses
Distal Radial Exostosis and Osteochondroma of the Distal Radius in Horses
Carpal Hygroma in Horses
Rupture of the Common Digital Extensor Tendon in Horses
Disorders of the Shoulder in Horses
Developmental Diseases of the Shoulder in Horses
Fractures of the Shoulder in Horses
Bicipital Bursitis in Horses
Infection of the Shoulder in Horses
Suprascapular Neuropathy in Horses
Osteoarthritis of the Shoulder in Horses
Disorders of the Elbow in Horses
Developmental Orthopedic Disease in the Elbow of Horses
Fractures of the Elbow in Horses
Osteoarthritis of the Elbow in Horses
Collateral Ligament Injury in the Elbow of Horses
Disorders of the Metatarsus in Horses
Bucked Shins/Dorsal Cortical Fractures of the Third Metatarsal Bone in Horses
Exostoses of the Metatarsal Bones in Horses
Diaphyseal Fracture of the Third Metatarsal Bone in Horses
Incomplete Longitudinal Fractures of the Plantar Aspect of the Third Metatarsal Bone in Horses
Focal Bone Reaction and Avulsion Fractures of the Third Metatarsal Bone in Horses
Fractures of the Second and Fourth Metatarsal Bones in Horses
Enostosis-like Lesions of the Third Metatarsal Bone in Horses
Disorders of the Tarsus in Horses
Failure of Ossification of the Distal Tarsal Bones in Horses
Osteoarthritis of the Distal Tarsal Joints in Horses
Osteoarthritis of the Talocalcaneal Joint in Horses
Osteoarthritis of the Tarsocrural Joint in Horses
Synovitis/Capsulitis of the Tarsocrural Joint in Horses
Osteochondrosis of the Tarsocrural Joint in Horses
Osteitis of the Calcaneus in Horses
Fractures of the Distal Tarsal Bones in Horses
Fracture of the Talus in Horses
Fracture of the Fibular Tarsal Bone (Calcaneus) in Horses
Fracture of the Lateral Malleolus of the Tibia in Horses
Tarsal Joint Luxation in Horses
Desmitis of the Collateral Ligaments of the Tarsus in Horses
Rupture of the Fibularis (Peroneus) Tertius in Horses
Stringhalt
Curb in Horses
Disorders of the Tarsal Sheath in Horses
False Thoroughpin in Horses
Luxation of the Superficial Digital Flexor Tendon from the Tuber Calcanei in Horses
Gastrocnemius Tendinitis in Horses
Calcaneal Bursitis in Horses
Capped Hock
Disorders of the Stifle in Horses
Osteochondrosis of the Stifle in Horses
Subchondral Cystic Lesions in Horses
Meniscus and Meniscal Ligament Injuries in Horses
Cranial and Caudal Cruciate Ligament Injuries in Horses
Collateral Ligament Injuries in Horses
Intermittent Upward Fixation of the Patella and Delayed Patella Release in Horses
Fragmentation of the Patella in Horses
Patellar Luxation in Horses
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Musculoskeletal
In all animals, the motor unit of skeletal muscle consists of the motor neuron, the neuromuscular junction, and muscle fibers. Muscle dysfunction—such as ataxia, paresis, or paralysis—most commonly originates in which of the following locations?
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