Consent: written vs. verbal

Dr. James warned Ms. Hairy about the risks of scarring from her laser hair removal procedure. Because his practice is very busy, Dr. James no longer obtains written consent prior to these procedures. Unfortunately, Ms. Hairy is scarred from the procedure. Ms. Hairy contends she was never warned about the risk of scarring. Does the lack of a written consent form make it likely that Dr. James will lose a malpractice case? Is verbal consent enough prior to the performance of a procedure?