Joint injections are a tricky thing, even under the best of skill and conditions. Any time the synovial sheath is compromised/interrupted, the potential for infection/complication is high. Granted, some vets are better at this than others.
Joint injections are commonly applied to arthritic conditions as well as ligament and tendon inflammation. I have had knees and hocks (arthritis) done here with good results but the aftercare and subsequent maintenance requires a watchful eye, a clean environment and careful exercise when cleared to do so.
Sure there's right and wrong but mostly there's just a whole lotta different.