Under the section 6002 of the Physician Payment Sunshine Act, manufacturers of pharmaceutical medical devices that make payments to physicians exceeding $10 are required to disclose this information to the public. This also includes declaring a shareholding by a doctor or any family member of the doctor in the manufacturers' company if the stock is not publicly traded.
Though this law has been approved the implementation of the disclosure norms has yet to begin. The rules for what information has to be collected and stored by the Centers for Medicare and Medicaid Services are expected to be finalized by Jan 2013 and then the collection of the same would start.
A doctor would not have to personally inform a patient about his/her shareholding in a prosthetic manufacturer but if the information falls under the purview of the law it would be in the public domain and could be accessed by the patient.