A device and methods for use in determining the trajectory of a patella (116) ofa patient during a navigated knee replacement surgical procedure (200) are described.The device includes a first component (138) including a mounting (144) for attachmentto a posterior surface of the patient's patella and a second component (140)having an outer surface presenting a formation (146, 152) adapted to engage witha femoral part of the patient's knee. A slider mechanism (168, 170) allowsthe second component to translate relative to the first component in a substantiallymedial-lateral direction (176) of the patient when the first component is attachedto the patient's patella. The device can be used in a method to help determinethe medial-lateral position for a patella implant.
