Checking for Size

Here you see a computer-generated 3-D image, based on a CT scan of an individual patient's knee.

With the click of a mouse, a surgeon can pull images of different types and sizes of implants and "try them out" to see how they will fit with each patient's anatomy.

In this case, the implant being "tried on" electronically is too big to fit well.

Checking for Alignment

This replacement is the right size. However, when it is put in the usual place, the axis of the knee joint [red line] is not where it should be [white line].

The angle of the knee implant needs to be adjusted so that this patient can walk in the same way after surgery.

The Perfect Fit

This implant is the right size and has been aligned so that the replacement joint will copy the motion of the existing joint.

• Finding the right material
• Designing the shape
• Figuring out how to put the new joint in place
• Getting it to stay in place
• Reducing wear and strain