Mo. Rev. Stat. § 510.040
In an action in which the mental or physical condition of a party is in controversy, the court in which the action is pending may order him to submit to a physical or mental examination by a physician, chosen by the party requesting the examination. The order may be made only on motion for good cause shown and upon notice to the party to be examined and to all other parties not in default and shall specify the time, place, manner, conditions, and scope of the examination and the person or persons by whom it is to be made. Such physician shall be deemed the witness of the party procuring the examination unless called as a witness in court by the opposing party. Upon his request and without cost to himself the party examined shall be furnished by such order with a full written report of the examination.
§ 510.040, RSMo