Dog striking

While there are a number of injuries that can cause this to occur as it’s the result of either the front foot twisting outwards or the hind leg twisting inward during the stride that causes the nails of the front foot to cut into the skin over the metatarsals of the hind leg.

However the most common reason would be damage to whip muscle (sartorious) of the right hind leg.
These muscles like any other muscle in the body can and do become damaged, in addition due to the minimal attachement of these muscles to the front of the thigh it often partially splits along that area.

Two things, gentle massage along the muscle in a stretching motion with a warming liniment such as Iodised oil, and also gentle massage to the area where the muscle connects to the thigh to ensure that there are no painfull adhesions.

There is no doubt that damage and poor function of one of these sartorious muscles cause the hind leg to pull inwards and delay extension which then results in the nails of the front foot abrading and possibly cutting the skin on the top of the hind foot during the inward portion of the stride.

Cheers,
Tom