A horse would need their back (SI) joint injected if he/she has any type of SI pain. This helps alleviate the pain and help lubricatethe joints so they can move freely without pain. SI pain is common in a lot of jumping horse as they get a lot of impact in that area especially when being started at jumping at a young age, and other causes such as injuries etc.. but these of course can be treated so they don’t get worse. Injection come into the question when the pain is high and it has been ignored by the owner or they hadn’t noticed it and it got progressively worse. So in that case injection would help the horse come back.