What Causes Muscle Spasms On Left Side Chest After Having Cortisone Hip Injection?

My son had a cortisone hip injection on friday and within 24 hrs he began having very bad muscle spasms mostly on the left side of his chest which is now radiating to the left side of his back. I took him to the emergency room, they said the pain was not coming from his heart that it appeared to be muscle spasms but the place he had the injections done at said muscle spasms are not an effect or related to cortisone injections of the hip. Is this true? he has never had this before. It's going on 4 days since the injection and he is still having pain. He is 14 years old.