If Cellfina treatment does not leave any scars why did I end up with this ugly cut? (Photo)

I would recommend you contact your surgeon immediately. Scars require combination treatment to get the best result. Lasers, microneedling and subcision may all be needed. Best, Dr. Emer

Most likely, the vibrating blade was turned on when it was on top of (rather than below) your skin. Stitches will allow this to close with a minimal scar. A scar revision can always be performed after it heals, if needed.

Cellfina is a very successful treatment for cellulite but does involve a small entry site through which the needle from the device penetrates the skin and breaks up the attachments in the subcutaneous fatty plane. As the needle moves back and forth like a windshield wiper under the skin, there is a little friction at the entry site (where the needle doesn't need to move back and forth much) and this can cause a slight depression and in some patients prone to post inflammatory hyperpigmentation, they may see some darkening. I have not seen as large or deep wound from Cellfina as your photograph displays.  Please see your doctor immediately to evaluate this wound. You must have had many other entry sites and your doctor will compare this area with the others. There may need to be some prescriptions needed to help heal the wound and then followup appointments to see how you are progressing. The information provided in Dr. Shelton's answer is for educational purposes only and is not intended to constitute medical advice.  The information provided should not be relied upon as a substitute for consultations with a qualified health professional who may be familiar with your individual medical needs.