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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

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musculoskeletal disorders

Musculoskeletal Disorders

INAG 120 – Equine Health Management

November 14, 2011

musculoskeletal disorders2
Musculoskeletal Disorders
  • Normal muscle physiology
  • Muscle response to injury
  • Muscle problems
  • Tendon disorders
  • Ligament problems
normal muscle physiology
Normal Muscle Physiology

Type 1 – Slow Twitch

  • High oxidative capacity, lots of mitochondria
  • Aerobic metabolism
  • Low glycogen storage capacity
  • Narrow muscle, slim
normal muscle physiology4
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 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
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 horses7
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
exertional rhabdomyolysis
  • Exercise-related myopathy
  • Monday Morning Disease
  • Exercise-induced myositis
  • Tying-up
  • Azoturia

Most Affected Muscles

tying up
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 up10
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 up11
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
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
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
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 er15
Chronic ER
  • Study by Valberg et al. (1999) uncovered two specific causes of Chronic ER:
    • Polysaccharide storage myopathy (PSSM)
    • Recurrent ExertionalRhabdomyolysis (RER)
  • 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?
  • 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
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 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
  • 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
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
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
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
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
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
  • 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
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
  • 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
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 massage30
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
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
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
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)
tendon injuries


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 injuries35
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
tendon lacerations


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