Chris Whitton BVSc FACVSc PhD

The Science of Horsemanship Working with bone to prevent injury in racehorses

Equine Vet

Research team

• Collaborators ‒ Prof Eleanor Mackie, University of Melbourne ‒ Prof Ego Seeman, Austin Hospital ‒ Prof Marcus Pandy, University of Melbourne ‒ Prof Peter Lee, University of Melbourne ‒ Dr Simon Harrison, CSIRO, Victoria ‒ Prof Chris Kawcak, Colorado State University ‒ Prof Sue Stover, University of California, Davis

• Funding ‒ RIRDC ‒ Racing Victoria ‒ Victorian Government

Research team

• Postdocs and postgraduate students ‒ Dr Michiko Mirams ‒ Gareth Trope ‒ Dr Ebi Bani Hassan ‒ Fatemeh Malikipour ‒ Sandra Martig ‒ Josie Holmes ‒ Babatunde Awodele ‒ Amy Williamson ‒ Megan Thomas

Horsemanship

• Observant • Aware of horses needs • Proactive

Racehorse injury

• What’s the problem? • How injury occurs

‒ Bone fatigue ‒ Bone adaptation and

repair • Injury prevention

Racehorse

• Extreme athlete ‒ 500kg ‒ 70km/hr

Racehorse

• Extreme athlete ‒ Joint loads

• 4 tonnes (Harrison et al. 2010)

Injury

• Bone injury ‒ Fetlock

Injury

• Bone injury ‒ Fetlock

Injury

• Bone injury ‒ Fetlock

Injury

• Bone injury ‒ Fetlock

Injury

• Bone injury ‒ Fetlock

Injury

• Bone injury ‒ Fetlock

Injury rates

• Victoria flat racing ‒ 1 death/2272

starts ‒ 69% deaths

due to limb injuries

‒ 92% due to bone fatigue

Injury rates

• Victoria flat racing ‒ 1 death/2272

starts ‒ 63% of all

deaths due to bone fatigue

Injury rates

Prevalence • Joint surface lesions

‒ Hong Kong • 70-80%

‒ Victoria • Forelimbs 66% • Hindlimbs 58%

Racing injuries

Bone fatigue

Repeated high loads

Bone damage

Racing injuries

Bone fatigue • Injuries specific for racehorses • Accumulation of high speed exercise a risk factor • Fractures occur spontaneously • Pre-existing pathology observed • Microcracks identified at predeliction sites

Flat racing

Risk of fatality • Longer career duration

• Greater number of races in career

• Greater number of races in last 30d

• Started 1-14 days prior

Accumulation of damage over time

Rapid accumulation of damage

Flat racing

Risk of joint surface injury • Total lifetime races

• Multiple racing seasons

• Shorter time between races

• Shorter time since last race

Accumulation of damage over time Rapid accumulation of damage

Fatigue injuries

Consequences • Fatalities • Jockey injuries • Premature retirement • Poor performance

Fatigue injuries

Jockey injuries

Conclusions: Prevention of the most common catastrophic injuries and conditions of the racehorse, e.g. fetlock injuries, may be the most effective at decreasing rates of falls and injuries to jockeys during racing.

Results: Jockey falls occurred in 24% of TB race-related horse fatalities, and jockey injury occurred in 64% of falls.

Fatigue injuries

Consequences • Bone fatigue in joints

‒ Catastrophic failure ‒ Joint surface failure

Fatigue injuries

Consequences • Bone fatigue in joints

‒ Catastrophic failure ‒ Joint surface failure

Fatigue injuries

Consequences • Bone fatigue in joints

‒ Catastrophic failure ‒ Joint surface failure

Fatigue injuries

Consequences • Bone fatigue in joints

‒ Catastrophic failure ‒ Joint surface failure

Fatigue injuries

Consequences • Bone fatigue in joints

‒ Catastrophic failure ‒ Joint surface failure

Fatigue injuries

Poor performance • Horses with bone injury identified on bone scan

‒ Performance inferior to age matched controls

Bone fatigue

Prevalence • Microfractures

‒ 46/48 horses had microfractures in fetlock

‒ Both 2-year-olds resting from training

Bone fatigue

Prevalence • Microfractures

‒ Increase with career duration

‒ Increase with training duration

Bone fatigue

Fatigue behaviour • Gradual degrading of mechanical properties due to repeated loading

‒ Molecular debonding ‒ Microcracks ‒ Complete failure

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

n/nf

En/Emax

Bone fatigue

Fatigue life • No. of cycles to failure • Related to load

No. of cycles

Load

Bone fatigue High loads • Short fatigue life

Bone response

Man made structures • Overengineering

Bone response

Evolution • Minimum amount of bone to get the job done • Bone

‒ Heavy ‒ Requires energy

Bone response

Adapt • Net increase or decrease in bone volume

Repair • Removal and replacement of bone • No net change in bone volume

Adaptation

Increased loading • Adaptation by increase in bone volume

Adaptation

Adaptation • Greater risk of fracture (Parkin et al. 2005)

‒ Horses that do no gallop work prior to racing ‒ Horses in their first year of racing

Adaptation

Adaptation • Condylar fractures

Bone response

Repair • Normal process • Remodelling

– Resorption and deposition resulting in replacement of bone

Repair

Remodelling • Replacement of bone repairs fatigue damage • Remodelling inhibited when bone subjected to high repeated load

Repair Training Resting

Repair Training Resting

Repair

Subchondral bone repair • Inhibited when training

Bone injury

Subchondral bone • Resting horse

‒ Constantly replacing bone ‒ Repair increased in response to damage

Time

Damage

Repair

Bone injury

Subchondral bone • Galloping horse

‒ Damage accumulating ‒ Repair reduced

Time

Repair

Damage

Bone injury High load environment

Repair inhibited

Fatigue accumulates Failure

Bone replaced

Rest

Resorption

Bone injury

Microdamage accumulation

Mic

roda

mag

e

Rest Rest Time

Prevention

Why? • Early detection challenging • Many injuries unrepairable • Avoids prolonged rehabilitation • Low grade injuries impair performance

Fatigue

Management • Inspect • Replace with a safety margin

Fatigue management

Inspection • Prerace veterinary examination

– Hong Kong - 90% of fatalities - no abnormalities

Fatigue

Management • Inspect • Replace with safety margin

Fatigue

Determining safe level of training

Fatigue damage

No of Horses

Fracture

Joint injury

Fatigue

Determining safe level of training

Fatigue damage

No of Horses

Fracture

Joint injury

Fatigue

Determining safe level of training

Volume of training

Perfo

rman

ce

Prevention

Military recruits (Finestone & Milgrom 2008)

Incidence 31% in 1983

Incidence 10% in 2003

Modifications

Prevention

Military recruits • Reduce number of cycles of load

‒ Reduced stress fractures by more than half

‒ Did not impair performance

Horsemanship

Working with bone • Bone is a dynamic tissue • Facilitate and maximise adaptation • Allow bone repair

Working with bone

Adaptation • When first commencing training • When returning to training from a rest period

Prevention

Maximise adaptation • Humans

‒ Greatest potential is prior to puberty (Kannus et al. 1995)

‒ Benefits persist through adulthood (Warden et al. 2007)

• Horses ‒ Longer career and more starts

with younger age at 1st start (Bailey et al. 1999, Velie et al. 2012)

Prevention

Maximising adaptation • Most responsive prior to skeletal maturity

‒ Distal MC adaptation with 8 weeks of canter (Boyde & Firth 2005)

‒ When increasing speed reduce distance (Nunamaker 1996)

Prevention

Adaptation • Horses returning from spell

Bone

vol

ume

Rest Rest Time

Prevention

Adaptation • Horses returning from spell

5 weeks

8 weeks

Prevention

Adaptation • Potential to develop highly porous bone

‒ Horse rested for greater than 10-14 days

‒ Horses in training

2 weeks rest

Full work

Repair

Where we go wrong • Inhibit remodelling too much • Train for too long • Rest periods too short

Repair

Rest periods

Mic

roda

mag

e

Rest Rest Time

Repair

Rest periods

Mic

roda

mag

e

Rest Rest Time

Prevention

Bone replacement • Duration of training

– Less than 20 weeks • Duration of rest

periods ‒ Benefit maximised in

first 10 weeks

Future

Reducing injuries • Monitor injury rates • Educate the industry

‒ Continuing education mandatory • Invest in research

‒ More work on bone fatigue ‒ Define a safe level of training ‒ What affects loads in joints ‒ How to maximise bone adaptation and repair

Horsemanship

• A large proportion of limb injuries are due to bone fatigue

‒ Bone fatigue is preventable

‒ Every injury is a failure

Horsemanship

• Bone can adapt and repair

‒ Understanding bone better • Fewer injuries horses

and jockeys • Better performance

Horsemanship

• Minimum amount of work for optimum fitness • Maximise adaptation to high speed • Allow adequate time for bone repair