Thanks Ginger
I will try the medication
When nails are too long it can affect the whole gait, and yes, put strain on joints and ligaments. The best thing to do is not to ever let the nails get too long in future. The strain should ease up in a few days, and in the meantime, don't put him through any particularly strenuous, or athletic movements. Just gentle exercise, like walking. No agility, or leaping around if it can possibly be avoided. Then things SHOULD heal naturally, and get back to balance.
Unless, he has joint problems generally, or you feel he could have a touch of arthritis. In which case start him on Glucosamine and Chodroitin supplements. It wouldn't do him any harm to have them anyway, as a regular everyday supplement.
My dog weighs 28lbs and I give her 500mg Glucosamine and 200mg Chondroitin daily (in 1 capsule) So if he weighs 40-50lbs he could have twice that dosage.