In T 906/01 the alleged public prior use concerned the implantation of a correction device into a patient. There remained some doubt as to the I. Spinal System which was really implanted. The board considered that a device having an investigational status, being implanted and tested within the restricted area of a hospital, under the responsibility of a surgeon operating within the framework of an investigator's agreement which included a confidentiality clause, had to be regarded as a prototype device. Usually the development and test phases of such products or devices were necessarily surrounded by secrecy as long as said products or devices had not been approved and commercialised (see also T 818/93). The board followed the reasoning of T 152/03 that, in this field, there was a prima facie assumption that any person involved in a medical process was obliged to maintain confidentiality, given the need for patient confidentiality and the need to protect the development and testing of prototype devices, and that any evidence proving the contrary was important and had to be produced as soon as possible.