hello dear thanks for your query at HCM it might be due to tetanus induced brachial neuritis, Neuralgic amyotrophy otherwise known as Parsonage-Turner syndrome or brachial neuritis is thought to be an immune-mediated problem affecting the nerves in the arm following a number of events such as vaccinations, surgery, dental cleaning, extreme stress, injections. The EMG will be very important in localization of the problem. Will likely show evidence of plexus/multiple nerve involvement as typical of this syndrome. The overall prognosis in most patients is very good. it will take some time to heal . till then go for physiotherapy , hot fermentation of the area .if still problem persists consult physcian. regrads