Patella tracking

A method for assessing the positioning of a patella implant for a patient during a navigated knee replacement surgical procedure, the method comprising:

• attaching a trial patella implant to the posterior of the patient's patella by a first component of the trial patella implant, wherein a second component of the trial patella implant can translate relative to the first component in the medial-lateral direction;
• and
• determining the trajectory of the patella as the knee joint is articulated while the second component is free to translate relative to the first component;
• and
• determining the medial-lateral displacement of the second component relative to the patella over at least a part of the trajectory.

A device for use in determining the trajectory of a patella of a patient during a navigated knee replacement surgical procedure, the device including:

• a first component including a mounting by which the first component can be attached to a posterior surface of the patient's patella;
• a second component having an outer surface presenting a formation adapted to engage with a femoral part of the patient's knee in use;
• and
• a slider mechanism by which the second component can translate relative to the first component in a substantially medial-lateral direction of the patient when the first component is attached to the patient's patella in use.