Is the only way to fix a 5.5 cm diastasis recti with abdominoplasty?

Hello and thank you for your
question. A 5.5cm diastasis and umbilical hernia can be repaired with an abdominoplasty.  This can be done
through a low and short incision, all completely below the bikini line.  The belly button can be designed to look
natural and have no scars on the exterior.  
Your muscles can also be plicated resulting in a flat abdomen.  Make sure you specifically look
at before and after pictures of real patients who have had this surgery
performed by your surgeon and evaluate their results.  The most important
aspect is to find a surgeon you are comfortable with. I recommend that you seek
consultation with a qualified board-certified plastic surgeon who can evaluate
you in person.
Best wishes and good luck.
Richard G. Reish, M.D. FACS
Harvard-trained plastic surgeon

Thanks for this question.Separation of the recti muscles and the formation of the diastasis is an anatomical problem which can only be treated with surgery. See an expert plastic surgeon.