Hello there Well it may or may not be related to your shoulder disloaction..... however the only assumption in this case could be any trauma to trapezius muscle which inturn could had a bearing on cervical spine...otherwise its remotely related....also the type and nature of headache is important. Have you visited your local NHS GP...what does he/she say? Regards

Dear Sir, One of the reason of getting headaches when your shoulder muscles are weak is Neck problem. If your upper trapezium muscle is tight it should stretched and get flexible. Kindly consult your Primary care Physician for the check up n if he finds neck problem to be the reason of headache, then after his approval kindly see a skilled Physical therapist regarding treatment of your neck problem or cervicogenic headache. All the best