I can't say for sure since I'm not a vet and I can't tell from the pix really good....but

Jack has several nails on each back foot like that. Only in Jack's case the fur is discolored as well. I finally figured out it was from him scratching his ears and it was a dirt/wax buildup on his nails. Jack's not really cooperative about frequent ear cleanings, nor having his nails scrubbed, hence the discolored fur.

I hope your vet finds something similarly benign going on with your Paddy's toenails and maybe his walking is just due to weight or something simple.

Keep us posted.