PSD (top of the suspensory) is being diagnosed all over the place at the moment. Straight legged cobs are particularly vulnerable, and too much work in arenas is also being blamed.
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Ddft or sdft? I have known both injuries and have come back to race again. It also depends ln the cause of the injury.
My big Ginger lad who was a show horse by this point bashed his hoof off of his fetlock and knocked a 50% hole in his sdft round the fetlock. He came back 100% sound and it refilled with tendon fibre.
2 at work got injuries to the skin on the fetlock and got an infection which started to eat into the tendon so needed scraped and cleaned. One returned to race again. The other one will about 8 months time.
One tore a hole in the ddft racing and it has healed ok so far, he will clme back into work in a couple of months.
As to a common cause - none really. All damaged for different reasons.