Thanks for your question and for the photo.
Sorry you are experiencing issues with your incision. Wound separations are not unheard of with abdominoplasty surgeries as the flaps are closed under tension. Open wounds 4 weeks post-op which are not actively healing are unusual and of concern. The area should be cultured and you should be on some type of local wound care with or wothout antibiotics.
Return to your Plastic surgeon to ask for their advice on the best course of action.
Best of luck.
Go see your doctor. You paid them for the surgery and follow up -- now it is time for them to give you the proper advice and treatment for maximum wound healing.
Consult with your surgeon who will provide a wound management plan. In general, wounds may open because of an infection, but if treated properly, open wounds don't get infected. Adequate debridement, dressing changes and on some occasions antibiotics may be necessary. In regards to an abdominoplasty, the incision is closed under tension, which may cause the incision to separate. Furthermore, the suture material used to close the incision under tension may cause inflammation, redness, and tenderness. Best wishes!