I've had silicone, under muscle implants for 4 years. Is this line of skin under my arm normal?

Dear saramyers5465,
I understand your concern. However, without a proper assessment, it would be difficult to determine what is wrong. It is best that you visit your plastic surgeon for further assessment or ask for a second opinion. Only after a thorough examination, you can get proper recommendations and advice.
Daniel Barrett, MDCertified, American Board of Plastic SurgeryMember, American Society of Plastic SurgeryMember, American Society of Aesthetic Plastic Surgery

I would recommend an evaluation in person. This would include seeing how to muscle flexes. This could be lateral displacement/malposition of the implant. I would recommend seeing a board-certified (American Board of Plastic Surgery); ideally, a surgeon with also a history of proper aesthetic breast surgery training.

It's difficult to visualize your concern with the submitted photo. Implants do not generally cause skin folds under the arm. I encourage you to visit with your surgeon for a more detailed exam.