The hock is the the achilles tendon and heel in humans. The tendon is originating from the calf muscle which is attached to the back of the stifle as well which moves dependent on the pelvis. Some horses get arthritis in the hock from repetitive movement issues in the stifle and pelvis and some just have inflammation of the tendon.
Your vet will inject for pain and inflammation but this will not correct any abnormal biomechanical movements that cause the pain. If your vet is not trained in animal chiropractic then they will not look to these other causes.
Please contact Dr Bruce with any questions. Chiropractic is not a substitute for Vet care but rather augments it.
Indekchiropractic@gmail.com