Musculoskeletal Disorders

Musculoskeletal Disorders INAG 120 – Equine Health Management November 14, 2011

Musculoskeletal Disorders • Normal muscle physiology • Muscle response to injury • Muscle problems • Tendon disorders • Ligament problems

Normal Muscle Physiology Type 1 – Slow Twitch • High oxidative capacity, lots of mitochondria • Aerobic metabolism • Low glycogen storage capacity • Narrow muscle, slim

Normal Muscle Physiology Type 2a & 2b – Fast Twitch • Well-developed glycolytic pathway, few mitochondria • Anaerobic metabolism • High glycogen storage capacity • Quarter horses, big muscles

Muscle Tissue Response to Injury • Muscle can repair well if the supporting structures remain intact • Atrophy = decrease in volume due to a decrease in size of the individual muscle cells • Generalized = symmetrical; may be due to ↓ nutritional status, old age • Localized = due to paralysis, area of damage • Neurogenic = deprivation of nerve supply

Classification of Muscle Diseases in Horses • Muscle damage • Non-exertional • Inflammatory, nutritional, toxic or metabolic • Exertional • Sporadic or chronic • Muscle atrophy • Neurogenic • EMND, EPM, focal nerve damage • Myogenic • Immune-mediated, chronic disease, malnutrition, disuse, Cushing’s disease, PSSM

Classification of Muscle Diseases in Horses • Abnormal muscle twitching • Myogenic • Myotonia, HYPP, electrolyte imbalance, botulism • Neurogenic • Shivers, myoclonus, focal nerve damage, ear ticks • Muscle weakness and exercise intolerance • Metabolic disorders

ExertionalRhabdomyolysis • Exercise-related myopathy • Monday Morning Disease • Exercise-induced myositis • Tying-up • Azoturia Most Affected Muscles

Tying Up • Equine Exertional Rhabdomyolysis • Clinical signs varied, depending on severity: • Mild – somewhat stiff after exercise • Severe – incapacitation; horse unable to stand or bear weight • Muscles of hindquarters most severely affected

Tying Up • Pain persists for several hours • Exhausted Horse Syndrome  common in endurance horses • Depression • Severe dehydration • Hyperthermia • “Thumps” (fluttering of the diaphragm) • Extensive muscle damage with or without cramping

Tying Up • Severe cases  dark red-brown colored urine • Myoglobinuria • Diagnosis = presence of creatine kinase (CK) and aspartate aminotransferase (AST) in the blood, muscle biopsy, genetic testing © Knottenbelt DC, Pascoe RR, Diseases and Disorders of the Horse, Saunders, 2003 © IVIS Reviews in Veterinary Medicine

Tying Up – Causes • Two broad categories: • Sporadic exertional rhabdomyolysis • Horses which, on rare occasion, experience tying up • Chronic exertional rhabdomyolysis • Horse experiences repeated episodes with the first usually occurring at a young age

Sporadic ER • Exercise exceeds the horse’s fitness level • Horse competing after a lay-off and only minimal training before the event • Electrolyte imbalance • Deficiencies of vitamin E and/or selenium • Horses with concurrent illness • Respiratory viral infections

Chronic ER • Animals prone to relapse  limit athletic career! • Many different breeds affected (Thoroughbreds, Arabians, Standardbreds, QH, drafts and warmbloods) • Possible causes: • Hormonal imbalances (low thyroid) • Lactic acidosis within muscle • Diet • High grain diet • Vitamin E and/or selenium deficiency • Electrolyte imbalances • Calcium? • Genetics

Chronic ER • Study by Valberg et al. (1999) uncovered two specific causes of Chronic ER: • Polysaccharide storage myopathy (PSSM) • Recurrent ExertionalRhabdomyolysis (RER)

PSSM • Polysaccharide Storage Myopathy • Storage of excess carbohydrate in the muscle • Muscle glycogen concentrations are 1.5 – 4 times higher • Affects drafts, Quarter Horses, warmbloods and a few Thoroughbreds • Clinical signs often develop at a young age when horse begins training • Hereditary?

PSSM • 40% of the type II muscle fibers have been found to have an acid mucopolysaccharide inclusion • Abnormal metabolism  increased uptake of glucose from the blood and quicker storage as glycogen • CK and AST levels are elevated • CK may remain high weeks after event (esp. in QH) • Seen in calm, sedate horses that are heavily muscled

Heredity of PSSM • Genetic mutation occurred early on • Present in many different horse breeds • Accounts for over 90% of PSSM cases in some horse breeds • P = horse carries mutant gene • N = normal gene • P/P = more severely affected, harder to manage (rare) • P/N = affected with PSSM, clinical signs vary • N/N = unaffected w/ PSSM type 1 • Second mutation (MH) intensifies the clinical signs in Quarter Horses and related breeds

Treatment PSSM attack • Treatment: • Oral or IV fluids to correct dehydration • Physical therapy • 24 hours after episode = large box stall to move around • Few minutes of hand-walking ok, but best to allow horse to move on its own • Small paddock turnout with quiet horse • Duration and frequency of walking bouts should be increased over a week • Massage therapy • Detailed diagnostic exam if chronic

RER • Recurrent Exertional Rhabdomyolysis • Defect in the mechanism of muscle contraction • Increased sensitivity to contraction when exposed to certain stimuli • Abnormal location of nuclei in muscle biopsies • Abnormal regulation of calcium movement within cells • Common in Thoroughbred, Arabian and Standardbred horses • May be hereditary in Thoroughbreds • Increased levels of CK after exercise

Predispositions for RER • Age • 2 year old >> 3 year old > 4 year old, etc. • Gender • 65% are fillies • Temperament • Nearly half characterized as “nervous” • Lameness • Lameness is more common in horses that tie up • Diet • Fed >10lbs of grain/sweet feed per day • Exercise intensity • Tie up more often when gallop training than breezing or racing • Three-day-event horses tie-up after the steeplechase, prior to cross-country phase • Racing Standardbreds tie-up after 15 minutes of jogging.

Management of horses with RER • Keep horse in quiet area of the barn • Train first rather than last • Turn-out • Avoid training regimes like holding back at a gallop or intervals that excite the horse • Tranquilize before exercise to prevent excitement • Attention to and treatment of lameness • Avoid stall rest or lay-up • Use medications that affect intracellular calcium regulation • dantrolene 4mg/kg orally 1 hour before exercise

Tying Up – Prevention of attacks • Feeding: • Fat supplemented diets • Diets high in carbohydrates can cause excitement (RER) • In horses with PSSM, problem is one of excess carbohydrate storage in muscle, so elimination of grain is a must • 20-25% of calorie requirements from fat! • Balanced electrolytes, water and Ca:P ratio, Vitamin E and Selenium • High quality forage (alfalfa or grass)

Muscle Cramping • Due to overactivity • Endurance horses • Exertional rhabdomyolysis • Hypocalcemia (not enough Ca) • Stiffness, pain, periodic spasms • Increase in muscle enzymes

Endurance Horse Muscle Cramping • Clinical Signs • Elevated temperature, pulse, respiration • May be seen with “Thumps” • Stiffness, pain, periodic spasms • NO increase in muscle enzymes • Treatment • Rest • Rehydration with appropriate electrolytes

Thumps • Synchronous Diaphragmatic Flutter • Diaphragm contracts synchronously with the heart • Seen as a flank twitch coincident with heart rate • Causes • Endurance exercise during hot weather • Hypocalcemia, digestive disturbances, some medications

Post-anesthetic Related Myopathies • Localized • Found in individual muscle groups which are in contact with hard surface for prolonged periods • Musculature starved of blood • Generalized • Involves multiple muscle groups, increased heart & respiratory rate, sweating and myoglobinuria • Reaction to anesthetic used

Equine Sports Massage Therapy • Equine Sports Massage Therapy differs from other forms of massage: • Focuses on the cause of the muscle injury • Relieves pain • PREVENTION of future injuries to those muscles • Involves a full body massage at every session

When and Why to Massage • Pre-Event: • Supple muscles • Enhance range of motion • Positive effect on the contraction and release process of the muscles • Post-Event: • Reduce post-performance anxiety and stress • Prevents soreness • Release tension so the horse's muscles can relax

When and Why to Massage • Post-Injury: • Reduce inflammation and swelling in joints • Stall Bound: • Stimulate circulation of blood and lymph throughout the body • Increase production of vital fluids in joints • Maintenance: • Maintain fitness by enhancing the muscle tone

Benefits of Massage • Increased blood flow to tissues • More nutrients to cells  quicker removal of waste products • Increased lymphatic flow • Reduction in swelling and removal of waste products • Relief from muscle spasms • Stretching and warming of muscle tissues allows for relaxation • Fibrosis and scar tissue inhibited • Pain relief through release of endorphins

Tendon Properties • Tendons connect muscle to bone • Tough, inelastic band of fibers • Shock absorbers in locomotion • Change with age: become more prone to damage • Poor at functional adaptation • Original tendon strength after damage is not as high

Tendon Injury • Catastrophic failure • Massive overload  exceeds strength of tendon (VERY unusual) • Apparent catastrophic failure • Weakening of structure due to accumulated micro-damage • Partial failure • Micro-damage limited to portion of tendon (tendonitis) (most common)

EquineEmergency! Tendon Injuries • Treatment • Ice/cold therapy • 20 minutes every hour for 1st 24 hours • NSAIDs • High doses; watch for ulcers, toxicosis • Wrap legs • No heating agents or liniments; keep well-wrapped for first few months • PSGAG’s (e.g., Adequan) • Controversial; may be injected into lesion

Tendon injuries… • Controlled exercise program/ rehabilitation • Therapeutic ultrasound? • Stem Cell Therapy? • Treatments losing favor: • Tendon splitting • Blistering/pin-firing • BAPN – “bapten” – plant derived substance that is injected into lesion to prevent formation of collagen during healing

EquineEmergency! Tendon Lacerations • Require IMMEDIATE specialist attention • May prove fatal (may involve damage and subsequent infection of joint capsule) • Septic tenosynovitis • Difficult to treat if left for more than a few hours

Ligament Properties • Connect bone to bone • Prevent displacement of tendons and joints • Ligament that has been damaged loses elasticity and can obstruct movement

Annular Ligament Constriction • Clinical signs • Non-specific lameness • Possible history of trauma to fetlock • Lameness worsens with exercise/ doesn’t improve with rest • Treatment: • Surgical resection • Good prognosis if only ligament involved • If damage to tendon  guarded

Suspensory Ligament Rupture • Complete rupture • Partial rupture • POOR PROGNOSIS • Racing injury • May occur with fractures of sesamoids • Treatment = humane euthanasia • May immobilize joint for breeding stock

Suspensory Desmitis • Inflammation of suspensoryligament • Runs along the back of the cannon bone • Splits to become a medial and lateral branch • Attach to the proximal sesamoid bones and the proximal phalanx • Similar to tendonitis – less well diagnosed • Severe damage usually means the sesamoid bone has been cracked • Treatment = same as for tendonitis

Sususpensory Ligament Desmitis

Musculoskeletal Disorders