A data processing method performed by a computer (2) for determining implant orientation data representing a range of functional orientations of a first implant part relative to a first bone, the first implant part being part of an implant pair which further comprises a second implant part for a second bone, the implant pair being envisaged to be implanted in a patient, comprising the steps of: acquiring second implant orientation data representing the orientation of the second implant part relative to the second bone, acquiring implant shape data representing the shapes of the first and second implant parts, acquiring activity data representing at least one desired activity of the patient to be possible after implanting the implant, and calculating the implant orientation data from the second implant orientation data, the implant shape data and the activity data.
