Why Do I Have Pain in Muscle Pocket 3 Years After Bilateral Mastectomy?

It sounds like you may be suffering from capsular contracture around your L breast implant.  Does the breast implant feel soft?  A hard mass in the area may also be caused by a hematoma that has consolidated in the area.  It may be beneifcial to have an MRI to ensure the implants are fine 3 years after reconstruction.  If capsular contracture is the cause, excising the capsule, exchanging the implant and using a dermal graft should improve your symptoms. 

Pain that is that severe is not normal.  You should be seen and examined by your plastic surgeon.  First I look at these issues with ultrasound so if a specific area needs to be biopsied it can be done.  If this is not helpful then an MRI can be useful.  If all of this appear to be due to scarring around the implant then I remove all of the scar, the implants, and replace them with your own tissue. I do this most frequently with you own lower abdominal tissue.  This is called the DIEP flap.  Other options include TUG flaps, SGAP flap, and latissimus flaps. 

It is NOT normal to have discomfort or pain once mastectomies and reconstructions heal. Persistent or new onset pain, tissue thickening or a new mass should be investigated first by physical examination and as needed with a MRI. I would suggest you see your Plastic surgeon,

Peter A Aldea, MD
Memphis, TN