Dog Claw Problem

I have noticed that a claw on each of my dogs paws has worn down to the quick and are sore. We recently took him to the beach and noticed it looked as if he was dragging his back legs but if you watch him walking it is not noticeable We have of course booked an appointment with the vets but wondered if anyone had any ideas. We are at present restricting his walks to grass until we have seen the vets.

i wouldn't like to say what could be causing it but when my dog had SLO and the backs of his claws split i used tape to cover them and a more permanent solution claw caps.Hope you find was the problem is