Hi art.chick,
Such injections commonly contain both cortisone & a local anaesthetic. The local anaesthetic provides some direct pain relief but is temporary. The cortisone works longer-term to reduce inflammation. Do be aware that these injections can fail to relieve signs & symptoms as they can be expected to benefit only those resulting from inflammation. Other sources of pain may not be effected.
Given a properly & carefully administered injection, generally risks are quite low. Among things that can go wrong are infection, bleeding, including that which can cause a hematoma that presses on nerves, and mechanical damage to nerve roots contacted by the needle.
Of course, repeated injections into a joint increase the likelihood of such adverse events, and carry the additional risk that cortisone may eventually soften the cartilage between bony structures and worsen discomfort.
The risks that cervical spinal disorder may pose for scuba & vice-versa must also be assessed. For example, pain that distracts the diver, restricted range of motion or other troubling aspects must be carefully considered. Diving can also place substantial stress on the vertebral column. Although the cervical area seems less at risk than lower regions such as the lumbar spine, it nonetheless appears prudent to protect the neck from additional damage.
I am not aware of any studies on such injection & scuba. Beyond the theoretical possibility that it could mask some features of DCI in the cervical area, it would appear that if none of the above discussed potential problems were in play the treatment would not pose any direct threat.
This is educational only and does not constitute or imply a doctor-patient relationship. It is not medical advice to you or any other individual, and should not be construed as such. Your physician should be in the best position to advise on your fitness to dive.
Get better fast.
DocVikingo