Well, the cervical spine surgery is possibly the cause of the cervical dystonia. Spasmodic torticollis is another name for cervical dystonia and it simply means that the neck muscle namely, sternocleidomastoid muscle is having spasms, while there are other treatments, Botox has shown to provide temporary relief in most patients, but what needs to be understood is that botox only alleviates the spasms by paralyzing selective muscle fibers, it does not do anything to treat the cause.
The spasms are being caused by an impinged nerve or a set of nerves around the cervical spine that are supplying the overlying skin in the area. The accessory nerve that supplies the Sternocleidomastoid muscle does not originate from the C spine and is a cranial nerve, it is however, possible, that this nerve can get damaged during cervical spine surgery especially in the anterior approach. So, the best thing will be to visit a Neurosurgeon, get an MRI done and a Nerve conduction study and Electromyogram done to see what is actually causing your spasms and what can be done to get rid of them permanently.
I have not heard Botox causing pain, it does not. However, paralysis of the Sternoclidomastoid muscle where the botox was injected could have caused further load on the C spine causing impingement of the nerves further and aggravating the pain. Botox is temporary, affects last for 4 to 5 months, so waiting is the best solution and mean while, the doctor should top you up with pain killers - opiate and NSAIDs and a soft neck collar.
Hope this helps.
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