The pain and tightness in your breast may not be due to "muscle spasm" but may be from other causes. Depending on the type of reconstruction you had and your cancer treatment surrounding the reconstruction (chemotherapy, radiation, etc), these factors all contribute to changes in the breast with implant based reconstruction. I suspect that you may have something called capsular contracture which can lead to tightness and pain around the implant. This condition can be treated in many ways but sometimes necessitates removal of the implant. I would suggest that you seek a consultation with either the person who did your reconstruction or a local board certified plastic surgeon to discuss the problem and review possible options for treatment.Good luck to you!