Welcome aboard.
If it was a dislocation/break it has probably `healed' in the `improper' position/location and/or sterile abscess/inflammation at point/in area of what was the acute injury. Is he able to roost normally, or is he sleeping on the floor in a corner of the coop? Has he become increasingly less active, guarding the leg more, now? Or pretty much as he was just after you first noticed the limping/favoring of leg?
Have you thoroughly examined him: discoloration of skin on thigh/flank, obvious swelling as compared to other leg, checked both feet - can he grasp finger equally with both, or is there a difference? Had there been any illness in the flock? Mycoplasma can `resolve' and leave chooks arthritic/gouty. How old is he?
What are you feeding him? Since he is `thin', you should probably augment his diet (scrambled eggs/meal worms/etc. - separate feeding area from rest of flock). You can try aspirin (if something inflammatory is going on this can help).
The suggested dose is 5mg/kg, three times a day. EX: 8lb roo. 8/2.2 = ~3.5kg, so 17.5mg. Crush an 81mg aspirin, divide into 4 `equal' piles ~20mg per pile. Daub up one pile with a half a grape and let him munch (adjust for your roo's wt. - some aspirin will be lost on the way in - spillage - so a little more is better than a little less). Another method is to dissolve 5, 325mg, aspirins in a gallon of water - dosage dependent on roo's water intake. Observe for increase in activity/scratching around/wt. bearing/eased gait.
Is there still another roo around giving the injured fellow grief? If so, separate.
Good luck to you and your roo!