Stress or fatigue fractures are common in young racehorses as a result of repeated, high loading cycles during training. These can occur in different sites of the skeleton, such as the tibia, pelvis and humerus: they occur when the accumulation of micro-damages in the bone is faster than its repair or remodeling. Bone damage occurs over time, but lameness is generally of sudden onset.
As a consequence of chronic micro-damage, bones try to heal themselves forming a callus, which is a stabilising bridge across a fracture: this is visible on X-rays as a slightly elevated opaque mass on the outside of the tibia (exostosis) or on the inside (expanding onto the medullary cavity - exostosis), or both. These injuries can occur below the stifle, mid-shaft or more commonly distally, just above the hock.
Do not think of tibia stress fractures as a true breakage in 2 or more pieces (as on th pic below): the tibia is the strongest bone in the body - it’s what cavemen used to use to beat each other up! Luckily tibia stress fractures are (in most cases) incomplete - In other words, the bone is still one single piece, only suffering micro-fractures. We don’t want to see complete fractures as these are catastrophic and generally can’t be repaired.
What should I do after the vet has left?
Stick to the rehab plan as advised. Painkillers can be beneficial in the first couple of weeks. Box rested is indicated until the horse is sound in trot again, typically in 4 weeks. This is followed by 8 to 10 weeks of controlled walking exercise. Radiographic recheck is indicated after that, and it will dictate whether the horse will need more time or can resume training.
Generally these injuries heal in 4 to 6 months. The prognosis is good.
What is it?
A cause of lameness generally affecting juvenile horses (2 to 4 years of age) in full training.
Time Window Onset is normally acute and after a session of fast work, however they can also develop slowly and progressively over time. Lameness is often significant so these require veterinary examination.
Unilateral limb lameness
Seldom bilateral lameness
Distal limb palpates normal, with no obvious areas of concern
Occasionally soreness to palpation of the tibia, inside and above the hock.
In case of complete fracture, severe, non weight-bearing lameness and bone displacement
What should I do?
If lameness is visible, marked and there are no obvious causes of pain, a vet examination is indicated.
What should I NOT do?
Do not ignore visible hindlimb lameness as it will inevitably get worse.
Do no administer painkillers which would only mask the lameness and make things worse.
What will the vet do?
Tibia stress fractures cannot be nerve blocked so diagnosis relies on clinical exam and radiography however this is sometimes not conclusive and a bone scan might be necessary. Ultrasound scanning can be helpful in identifying bone surface changes, which are indicative of stress remodeling.
Based on the severity of the findings, the vet will recommend a rehab plan.