Suprascapular Nerve Injury / Sweeney

Suprascapular nerve injury, commonly known as Sweeney or sweeny, is a condition in horses caused by damage to the suprascapular nerve that supplies the supraspinatus and infraspinatus muscles of the shoulder. This nerve injury results in characteristic atrophy (wasting) of these important shoulder-stabilizing muscles, creating a distinctive appearance where the spine of the scapula becomes prominently visible as the overlying muscles shrink. The condition has been recognized in horses for centuries, with the traditional name Sweeney reflecting its long history in equine medicine and agriculture. While modern veterinary understanding has clarified the neurological basis for this condition, the traditional terminology remains widely used among horse owners and veterinarians alike.

Sweeney occurs in horses of all breeds but has historically been associated with working horses and draft breeds that experience direct trauma to the shoulder region from ill-fitting collars or harnesses. Today, the condition is seen across all horse types and can result from various traumatic incidents including collisions with solid objects, falls, kicks from other horses, or any impact that damages the suprascapular nerve as it courses over the scapula. The nerve is particularly vulnerable where it wraps around the cranial border of the scapular spine, making this location especially susceptible to compression or stretching injuries. Any horse that experiences significant shoulder trauma may develop Sweeney regardless of breed or use.

The impact of suprascapular nerve injury on equine health and performance depends on the severity of nerve damage and whether complete or partial function can be restored. The supraspinatus and infraspinatus muscles are essential for stabilizing the shoulder joint during weight-bearing, preventing lateral displacement of the scapula during the support phase of stride. When these muscles atrophy due to nerve damage, the shoulder becomes unstable, causing the characteristic outward swinging of the shoulder during movement known as shoulder slip. This instability affects gait quality, reduces athletic performance, and can predispose to secondary musculoskeletal problems. Severely affected horses may have difficulty with normal locomotion and be unsuitable for athletic pursuits.

Treatability of Sweeney depends largely on the severity and type of nerve injury. Cases involving neurapraxia, where the nerve is temporarily stunned but structurally intact, carry the best prognosis and may resolve with rest and time. More severe injuries involving axonal damage require longer recovery periods and may not fully resolve. Surgical intervention to decompress the nerve or release scar tissue has shown success in some refractory cases. Early recognition of the condition and appropriate management during the recovery period optimize outcomes. Working with an equine veterinarian to accurately assess the injury and develop a treatment plan provides the best chance for returning affected horses to soundness.

The primary cause of suprascapular nerve injury is direct trauma to the shoulder region where the nerve is anatomically vulnerable. The suprascapular nerve originates from the sixth and seventh cervical spinal nerves, passes between the supraspinatus and subscapularis muscles, and wraps around the cranial border of the scapular spine to reach the infraspinatus muscle. This tortuous course over a bony prominence creates a location where the nerve is susceptible to compression, stretching, or crushing injuries. Direct impact to the point of the shoulder, collision with solid objects such as fence posts or stall walls, falls, and kicks from other horses all commonly cause Sweeney. The nerve may be damaged by a single severe traumatic event or by repeated lesser traumas that cumulatively injure the nerve.

Historically, ill-fitting harness collars were the predominant cause of Sweeney in working horses, giving rise to the condition's traditional name and its strong association with draft breeds. Collar pressure concentrated over the shoulder point would compress the suprascapular nerve against the underlying bone, causing injury that developed gradually with continued work. While harness-related Sweeney is less common today with decreased reliance on working horses, it remains a risk for horses used in driving and draft work. Poorly fitted saddles that create pressure points over the shoulder can similarly contribute to nerve damage, making proper tack fit an important consideration for all horses.

Environmental and management factors influence the risk of traumatic shoulder injuries that lead to Sweeney. Housing conditions play a significant role, as narrow stalls or doorways force horses to squeeze through tight spaces where shoulder impact is likely. Pasture hazards including trees, posts, and equipment create collision risks during turnout, especially when horses are running or playing. Herd dynamics matter, as horses housed with aggressive companions face increased risk of kick injuries to the shoulder. Transportation mishaps where horses scramble or fall against trailer partitions can cause shoulder trauma. Any environment that increases the likelihood of shoulder impact increases Sweeney risk.

Risk factors for developing Sweeney include conformational characteristics, with horses having narrow chests or prominent shoulder points potentially more susceptible to nerve compression from impact. Young horses engaged in rough play may be more prone to traumatic injuries. Horses in certain disciplines face elevated risk, including those that jump where rotational falls can involve shoulder impact, polo ponies that experience frequent contact, and roping horses subject to sudden forces. Draft breeds retain higher risk due to continued use in harness work and their large size which generates significant force during impacts. Previous shoulder injuries may predispose to Sweeney by creating scar tissue or altered anatomy that affects nerve vulnerability.

The pathophysiology of suprascapular nerve injury involves disruption of nerve function at the site of trauma. Neurapraxia, the mildest form, occurs when the nerve is compressed or stretched but maintains structural integrity, causing temporary conduction block that resolves as inflammation subsides. Axonotmesis involves damage to the axons within the nerve while the supporting structures remain intact, allowing potential regeneration but requiring extended recovery time. Neurotmesis, the most severe form, involves complete disruption of the nerve and its supporting structures, carrying a poor prognosis for recovery without surgical intervention. The degree of muscle atrophy and functional deficit correlates with the severity and duration of nerve dysfunction, with denervated muscles progressively losing mass until nerve function is restored.

Early warning signs of suprascapular nerve injury may be subtle and easily attributed to general soreness or minor lameness before the characteristic muscle atrophy becomes apparent. In the days immediately following injury, horses may show mild forelimb lameness, reduced willingness to bear weight on the affected leg, or slight stiffness in shoulder movement. Careful observation may reveal subtle asymmetry in shoulder muscle appearance or mild swelling over the shoulder point from the initial trauma. Because horses naturally mask discomfort as prey animals, they may not demonstrate obvious lameness despite significant nerve injury. Owners who notice shoulder trauma should monitor carefully for developing signs of Sweeney even if initial lameness appears minimal.

Common symptoms of established Sweeney include progressive atrophy of the muscles overlying the scapula, creating the characteristic appearance that gives the condition its name. The supraspinatus muscle, which fills the hollow above the scapular spine, and the infraspinatus muscle, which fills the hollow below the spine, both waste away as they lose innervation. This atrophy makes the scapular spine and the shoulder joint prominences increasingly visible and palpable, creating a hollowed-out or sunken appearance compared to the normal opposite shoulder. The muscle wasting typically becomes noticeable within two to three weeks following injury and progresses over subsequent weeks to months if nerve function does not recover.

Behavioral changes associated with Sweeney reflect both the initial traumatic injury and the resulting shoulder instability. Horses may show reluctance to move the affected forelimb freely or demonstrate shortened stride length on that side. Some horses develop compensatory movement patterns, shifting weight to the opposite forelimb or altering head position during locomotion. Performance horses may refuse jumps, show reluctance to work, or demonstrate decreased athletic ability. The horse may resist activities that stress the shoulder such as turning sharply toward the affected side or moving up and down hills. General attitude may change if chronic discomfort affects the horse's normal demeanor.

Physical signs beyond muscle atrophy include the distinctive shoulder slip or shoulder instability that occurs during weight-bearing on the affected limb. When the horse steps on the affected forelimb, the shoulder appears to slide outward away from the body as the weakened muscles fail to stabilize the scapula against the chest wall. This lateral deviation of the shoulder is most visible when the horse is walked directly toward the observer. The degree of shoulder slip reflects the severity of muscle weakness and provides a functional measure of the condition's impact. In severe cases, the instability is dramatic and clearly visible at every step, while mild cases may show only subtle asymmetry detectable primarily during careful examination.

Symptom progression in Sweeney follows a predictable pattern reflecting the underlying nerve pathology. Following initial trauma, lameness and swelling peak within the first few days then gradually subside. Muscle atrophy becomes apparent over the following two to four weeks as denervated muscle fibers shrink. The atrophy progresses to maximum severity over approximately two to three months, at which point the condition stabilizes unless nerve regeneration begins. If recovery occurs, gradual muscle filling returns over several months as regenerating nerve fibers reestablish connections with muscle tissue. The rate and completeness of recovery depend on the severity of original nerve damage and can range from complete resolution to permanent deficit.

Emergency symptoms requiring immediate veterinary care in the context of shoulder injury include severe lameness that prevents normal weight-bearing, obvious fracture or dislocation of the shoulder region, extensive swelling suggesting hemorrhage or severe soft tissue damage, and signs of systemic illness such as fever or depression following trauma. While uncomplicated Sweeney is not an emergency condition, the initial traumatic event that causes it may involve more serious injuries requiring urgent attention. Any horse that has experienced significant shoulder trauma should receive veterinary evaluation to assess for fractures, joint involvement, or other injuries that require immediate treatment beyond management of nerve damage.

Physical examination for Sweeney begins with visual inspection comparing the affected shoulder to the normal opposite side. The veterinarian looks for asymmetry in muscle mass, prominence of bony landmarks, and any visible swelling or abnormality over the shoulder region. Palpation of the shoulder muscles assesses muscle tone, identifies areas of atrophy, and detects any pain response. The scapular spine becomes readily palpable as overlying muscle mass decreases. The veterinarian observes the horse in motion, watching for the characteristic shoulder slip during weight-bearing and evaluating overall gait quality and soundness. The timing of symptom onset relative to any known traumatic event helps establish the diagnosis and estimate the injury's age.

Diagnostic tests support the clinical diagnosis and help rule out other conditions affecting the shoulder. Radiography of the shoulder region evaluates for fractures of the scapula, humerus, or shoulder joint that might accompany or mimic nerve injury. While radiographs cannot directly image the nerve, they identify bony abnormalities that could contribute to nerve compression. Ultrasonography provides detailed evaluation of soft tissue structures including muscles, tendons, and the nerve itself when performed by experienced practitioners. Ultrasound can demonstrate muscle atrophy, identify areas of nerve thickening or abnormality, and detect hematomas or other lesions that might compress the nerve. Blood work is not specifically diagnostic for Sweeney but may be performed to assess overall health status.

Advanced diagnostics provide detailed information about nerve function and structure in cases where surgical intervention is being considered or when the diagnosis is uncertain. Electromyography (EMG) detects abnormal electrical activity in denervated muscles, confirming nerve dysfunction and potentially providing prognostic information about nerve recovery potential. Nerve conduction studies measure the speed and quality of electrical signal transmission along the nerve. Advanced imaging including computed tomography (CT) or magnetic resonance imaging (MRI) can visualize the nerve pathway in detail, identifying compression points, scar tissue, or structural abnormalities that might guide surgical planning. These advanced tests are typically reserved for refractory cases or those where significant investment in treatment is planned.

Differential diagnosis for shoulder atrophy and forelimb lameness includes several conditions that must be distinguished from Sweeney. Equine protozoal myeloencephalitis (EPM) can cause focal muscle atrophy including shoulder muscles and should be considered when atrophy distribution is atypical or other neurological signs are present. Shoulder joint pathology including osteoarthritis or osteochondrosis causes lameness but does not typically produce the severe muscle atrophy characteristic of Sweeney unless chronically severe. Brachial plexus injury affects multiple nerves and produces more widespread forelimb dysfunction. Cervical vertebral stenotic myelopathy can cause forelimb ataxia and weakness. Neoplasia affecting the brachial plexus or shoulder region is rare but possible. Careful examination and appropriate diagnostic testing distinguish these conditions from suprascapular nerve injury.

Emergency and immediate treatment following shoulder trauma focuses on managing the acute injury while setting the stage for optimal nerve recovery. Initial care includes rest to prevent further injury, application of cold therapy to reduce inflammation and swelling at the trauma site, and administration of non-steroidal anti-inflammatory drugs (NSAIDs) to control pain and inflammation. If significant swelling or hematoma is present over the nerve pathway, anti-inflammatory treatment may help prevent secondary nerve compression. Confining the horse to a stall for the first few days following injury limits movement that could exacerbate nerve damage. The veterinarian assesses for concurrent injuries requiring specific treatment and develops a management plan based on the severity of the initial trauma.

Medical management of Sweeney primarily involves providing optimal conditions for nerve healing while maintaining the affected muscles and preventing secondary complications. Continued rest during the acute phase allows initial healing without additional stress on the injured nerve. Anti-inflammatory medications may be beneficial in the early post-injury period. Some veterinarians recommend vitamin E supplementation or other nutraceuticals that support nerve health, though evidence for efficacy is limited. As the acute phase resolves, the focus shifts to maintaining muscle mass and shoulder joint mobility while awaiting nerve recovery. Most cases receive a trial of conservative management for three to six months before considering surgical options.

Surgical options exist for cases that fail to improve with conservative management or where significant mechanical compression of the nerve is identified. Surgical nerve decompression involves releasing the suprascapular nerve from fibrous tissue or scar that has developed following trauma, allowing the nerve to heal without ongoing compression. The surgery is performed under general anesthesia, accessing the nerve through an incision over the shoulder. Neurolysis, the careful freeing of the nerve from surrounding adhesions, requires delicate technique to avoid further nerve damage. Some surgeons perform nerve transposition to reduce tension on the nerve at its point of vulnerability. Success rates for surgery vary depending on the duration of denervation, the severity of original injury, and individual healing responses.

Supportive care throughout treatment aims to maintain muscle mass, joint mobility, and overall soundness while awaiting nerve recovery. Controlled exercise, typically starting with hand-walking and progressing as appropriate, prevents complete muscle atrophy and maintains cardiovascular fitness. Range-of-motion exercises for the shoulder joint prevent stiffness and contracture. Some rehabilitation programs incorporate electrical muscle stimulation to maintain muscle bulk in denervated muscles, though this requires specialized equipment and expertise. Physical therapy modalities including therapeutic ultrasound, massage, and stretching may support recovery. Proper nutrition ensures adequate substrate for nerve regeneration and muscle maintenance.

Rehabilitation and return to work protocols extend over months as nerve recovery progresses. The timeline depends on the severity of initial injury, with milder cases potentially returning to work within three to six months while severe cases may require a year or longer. Gradual reintroduction of exercise allows monitoring of shoulder stability and identification of any persistent weakness. Work intensity increases progressively as muscle mass returns and shoulder stability improves. The horse's intended use influences rehabilitation goals, as some disciplines demand more complete recovery than others. Regular veterinary reassessment guides progression through rehabilitation phases.

Treatment decision factors include the severity and duration of the condition, the horse's value and intended use, owner resources and commitment, and response to initial conservative treatment. Mild cases with early presentation often warrant conservative management, as many recover without intervention. Severe cases or those failing to show improvement after three to six months of conservative care may benefit from surgical evaluation. The horse's age and general health influence healing potential. Economic considerations are realistic factors, as treatment and rehabilitation costs accumulate over the extended recovery period. Honest discussion of prognosis and expected outcomes helps owners make informed decisions about treatment intensity.

Recovery timeline for suprascapular nerve injury varies considerably based on the severity of nerve damage and individual healing capacity. Mild cases involving neurapraxia may show improvement within four to six weeks as inflammation resolves and nerve conduction returns to normal. More significant injuries involving axonal damage require regeneration of nerve fibers, which occurs at approximately one to two millimeters per day. Given the distance from the injury site to the muscles, complete reinnervation may take six to twelve months or longer. Some horses achieve full recovery with complete return of muscle mass and shoulder stability, while others retain permanent deficits despite treatment. The first three months following injury provide important prognostic information, as cases showing early improvement generally have better outcomes.

Post-treatment care and monitoring require ongoing attention throughout the extended recovery period. Regular veterinary evaluations assess muscle mass through palpation and visual inspection, comparing the affected side to the normal shoulder over time. Observation of gait and shoulder stability during movement documents functional improvement. If surgery was performed, incision monitoring and appropriate wound care are necessary during initial healing. Photography or video documentation at regular intervals provides objective records of recovery progress. Adjustments to exercise programs are made based on recovery status, gradually increasing work as muscle strength returns. Owner involvement in daily monitoring catches subtle changes that inform management decisions.

Prognosis factors affecting recovery include the severity of original nerve injury, with neurapraxia carrying excellent prognosis while neurotmesis has guarded to poor prognosis without surgery. The duration of denervation before treatment matters significantly, as prolonged denervation leads to irreversible muscle changes that may not recover even when nerve function returns. Younger horses generally have better regenerative capacity than older animals. Compliance with rest and rehabilitation protocols influences outcomes, as premature return to work can reinjure healing nerves. Cases that show improvement within the first three to four months generally continue to improve, while those showing no progress during this period have more guarded long-term prognoses.

Long-term soundness outlook depends on the degree of recovery achieved and the horse's intended use. Horses that regain full muscle mass and shoulder stability can return to all previous activities including demanding athletic pursuits. Those with incomplete recovery but functional shoulder stability may be suitable for lighter work or pleasure riding. Horses retaining significant shoulder instability may be limited to breeding or retirement. Some cases demonstrate cosmetic residual atrophy without functional deficit, remaining fully sound with visible asymmetry. Periodic reassessment throughout the horse's career monitors for any late deterioration, though recurrence is uncommon in horses that achieve stable recovery.

Management practices focused on preventing shoulder trauma form the primary prevention strategy for Sweeney. Facility design should eliminate hazards that could cause shoulder impact, including protruding objects at shoulder height, narrow doorways that force horses to squeeze through, and sharp corners in traffic areas. Stalls should be appropriately sized for the horse's body, with adequate room to turn without contacting walls. Paddock and pasture fencing should be well-maintained and visible to prevent collision injuries. Gate placement and design should allow horses to pass through easily without risk of shoulder impact. Regular facility inspection identifies developing hazards before injuries occur.

Nutritional considerations for nerve health include ensuring adequate intake of vitamins and minerals that support neurological function. Vitamin E, a fat-soluble antioxidant, supports nerve membrane integrity and is commonly supplemented in performance horses. B vitamins play roles in nerve function and myelin maintenance. Ensuring overall nutritional adequacy through quality forage and appropriate supplementation supports the horse's ability to heal from any injuries that do occur. While no specific nutritional intervention prevents traumatic nerve injury, optimal nutritional status supports recovery should injury occur.

Exercise and conditioning programs can reduce injury risk through improved proprioception and body awareness. Horses that are well-conditioned and accustomed to their environment move more confidently and are less likely to panic or make sudden movements that result in collision injuries. Gradual introduction to new environments allows horses to learn the layout without rushing. Turnout management that minimizes aggressive interactions between horses reduces kick injury risk. For working horses, proper conditioning prepares them for the physical demands of their job without fatigue that might lead to accidents.

Environmental factors influencing Sweeney risk require attention in multiple settings. Stable design and management have been discussed above. Trailer design and horse positioning during transport should prevent shoulder impact during sudden stops or starts. Competition venues should be evaluated for hazards, and horses should be given time to acclimate to new environments. Herd dynamics and pasture companion selection reduce aggression-related injuries. Weather conditions affecting footing increase fall risk and should prompt exercise modifications. Consistent handling and training reduce unpredictable behavior that could lead to accidents.

For horses engaged in harness work, proper collar and harness fitting is essential for preventing the traditional form of Sweeney. Collars should distribute weight across the shoulders without concentrated pressure points over the nerve pathway. Regular assessment of collar fit accounts for changes in the horse's condition throughout the working season. Harness adjustments ensure even load distribution without shoulder point pressure. Periods of work should be managed to prevent fatigue, which increases injury risk. Inspection of all harness components identifies wear that could alter fit or cause failure. Proper training and conditioning prepare draft horses for the demands of harness work without undue stress on the shoulder region.

Daily management adjustments for horses with Sweeney focus on accommodating shoulder instability while supporting recovery. Horses in the acute phase require stall rest to prevent further injury, with careful attention to providing safe, comfortable housing. Bedding should be deep and supportive to cushion the forelimbs during rest. Water and feed containers should be positioned to avoid requiring awkward neck or forelimb positions that stress the shoulder. As recovery progresses, daily routines incorporate prescribed exercise programs while avoiding activities that might reinjure the healing nerve. Handlers should approach and handle the horse in ways that avoid bumping or putting pressure on the affected shoulder.

Housing and turnout considerations balance the benefits of movement against injury risks for horses with shoulder instability. Initially, stall confinement protects the healing nerve and prevents falls or collisions that could worsen damage. As veterinary guidance permits, small paddock turnout on level, safe footing allows controlled movement and mental stimulation without excessive risk. Turnout companions should be selected carefully to avoid aggressive interactions. The transition to larger turnout areas occurs gradually as shoulder stability improves and the horse demonstrates ability to navigate safely. Full pasture turnout typically awaits substantial recovery, as sudden movements or rough terrain could cause falls in horses with significant shoulder weakness.

Exercise modifications throughout recovery follow veterinary guidance and the horse's individual response to increasing activity. Initial exercise consists of hand-walking on flat, even surfaces, allowing controlled movement without risk of sudden turns or stops. Duration and intensity increase gradually as shoulder stability improves. Lunging and round pen work require caution, as the constant turning may stress an unstable shoulder. Under-saddle work begins only when muscle mass has substantially returned and the shoulder demonstrates adequate stability. The specific exercise progression depends on the horse's discipline and intended use, with performance horses requiring longer rehabilitation before returning to demanding work.

Monitoring and ongoing care include regular assessment of muscle mass, shoulder stability, and overall soundness. Owners learn to palpate the shoulder muscles to track changes in muscle bulk over time. Observation of gait during daily handling identifies improvement or deterioration in shoulder function. Communication with the veterinarian about progress guides decisions about exercise progression and need for reassessment. Body condition monitoring ensures the horse maintains appropriate weight despite any exercise restrictions. Hoof care continues on regular schedule, as abnormal weight distribution can affect hoof wear patterns. Documentation of progress through photographs or video supports objective evaluation of recovery.

Quality of life and use considerations require honest assessment as recovery progresses and stabilizes. Horses achieving full recovery enjoy normal quality of life and can return to all previous activities. Those with partial recovery may lead comfortable lives with modified use expectations. Horses with persistent significant shoulder instability may be limited in their use but can often serve as pleasure horses for light riding or as companions. Career changes may be necessary for performance horses that cannot return to their previous discipline. Throughout management, the horse's comfort and welfare guide decisions. Significant persistent lameness or inability to move normally raises welfare concerns requiring veterinary discussion about appropriate management or humane options.

Draft breeds including Clydesdales, Percherons, Belgians, Shires, and Suffolk Punches carry historically elevated risk for Sweeney due to their traditional use in harness work. The concentrated pressure from ill-fitting collars over the suprascapular nerve pathway caused the classic form of Sweeney that gave the condition its name. While harness work is less common today, draft horses continue to face this risk when used for driving, logging, or agricultural work. Their large body size also generates significant force during any traumatic impact, potentially causing more severe nerve damage from collisions or falls. Draft horse owners should be particularly attentive to proper harness fitting and facility safety.

Use and discipline considerations influence Sweeney risk across all breeds. Horses engaged in activities involving collision risk face elevated exposure to shoulder trauma. This includes polo ponies that experience frequent contact during play, roping horses subject to sudden forces transmitted through the shoulder, and eventing horses that may fall during cross-country jumping. Working ranch horses navigating rough terrain and handling cattle encounter multiple injury opportunities. Even horses in supposedly lower-risk disciplines can develop Sweeney from stall accidents, turnout injuries, or transportation mishaps. No discipline is entirely free from Sweeney risk, and vigilance regarding environmental hazards benefits all horses.

Conformational factors may influence individual susceptibility to suprascapular nerve injury. Horses with narrow chests or prominent shoulder points may have less soft tissue protection over the nerve pathway, potentially increasing vulnerability to compression injuries from impact. Conversely, heavily muscled horses have greater tissue mass protecting the nerve but also generate more force during impacts. No specific genetic testing exists for Sweeney susceptibility, and breeding recommendations focus on general soundness rather than specific Sweeney prevention. Selection against horses with conformational faults that predispose to shoulder injuries serves broader soundness goals. Individual horses that have recovered from Sweeney can generally be bred without concern about passing the condition to offspring, as it is traumatic rather than hereditary.

Commonly co-occurring conditions with Sweeney include injuries sustained during the same traumatic event that damaged the suprascapular nerve. Soft tissue bruising and swelling over the shoulder region accompany most cases and resolve during the acute phase. Concurrent fractures of the scapula, humerus, or shoulder joint structures may occur with severe trauma and require separate management. Secondary musculoskeletal problems can develop as horses compensate for shoulder weakness, including opposite forelimb strain, back soreness, and altered hoof loading patterns. Chronic cases may develop joint stiffness from reduced shoulder movement during the period of instability. Recognition and management of these concurrent problems supports overall recovery.

Conditions with similar symptoms require differentiation from Sweeney to ensure appropriate treatment. Equine protozoal myeloencephalitis (EPM) can cause focal muscle atrophy and should be tested for when atrophy pattern is atypical or other neurological signs exist. Other peripheral nerve injuries affecting the forelimb, including brachial plexus damage, produce different patterns of weakness and atrophy. Shoulder joint pathology causes lameness but does not typically cause severe muscle atrophy unless disuse is prolonged. Cervical spine problems can affect forelimb function and muscle mass. Neoplasia affecting the brachial plexus or shoulder region is rare but possible. Diagnostic testing clarifies the specific cause of shoulder atrophy when clinical findings are ambiguous.

Potential complications of Sweeney include permanent muscle atrophy and shoulder instability when nerve recovery fails to occur. Chronic lameness from ongoing shoulder dysfunction affects welfare and limits use. Secondary joint problems including osteoarthritis can develop from altered biomechanics during periods of instability. Compensatory strain on other limbs predisposes to additional injuries. Psychological stress from movement difficulty and chronic discomfort may affect the horse's overall demeanor. Appropriate management throughout recovery minimizes complication risk and addresses problems as they develop. Open communication between owners and veterinarians ensures timely intervention when complications arise.