Informed consent is required for a surgical procedure. "Informed" includes having knowledge of the risks. The relevant legal question would be whether the doctor in question did adequately apprise the patient of the risks.

On an individual basis, patient A could sue doctor X for the resulting harm. It is possible that 5 patients might sue the same doctor on this basis, which gets expensive and inefficient. If there is a well-defined and large-enough class, it may be possible for the action to be certified as a class action. 20 people might be a large-enough class.

The plaintiff would be "whoever is responsible for the wrong". That might be a single practitioner, or a hospital that the practitioner(s) work for. The hospital is an obvious plaintiff, if they failed in their duty to assure that their employees adequately informed patients of the risk.

Informed consent is required for a surgical procedure. "Informed" includes having knowledge of the risks. The relevant legal question would be whether the doctor in question did adequately apprise the patient of the risks.

On an individual basis, patient A could sue doctor X for the resulting harm. It is possible that 5 patients might sue the same doctor on this basis, which gets expensive and inefficient. If there is a well-defined and large-enough class, it may be possible for the action to be certified as a class action. 20 people might be a large-enough class.

The defendant would be "whoever is responsible for the wrong". That might be a single practitioner, or a hospital that the practitioner(s) work for. The hospital is an obvious plaintiff, if they failed in their duty to assure that their employees adequately informed patients of the risk.