Chickens definitely experience pain. But they are good at hiding it. I've learned that a chicken signals pain in several ways. One is to favor the hurting limb by limping or/and pecking at it. When pain becomes overwhelming, it can cause shock, and that will cause the chicken to withdraw and...
I've been in this situation. I had an EE hen that went completely lame. Yet she remained perky and interested in flock life for two years, at which point she went downhill fast and I euthanized her.
But for those two years, she was a special needs chicken. She slept in a basket in the garage...