Knee Replacement Surgery Overview

In general, Total Knee Replacement is a very safe and effective procedure. However, it is a major operation that is quite invasive.

The outline below is indicative of the "standard" approach. A minimally invasive technique is similar, but the incision and disruption to surrounding soft-tissue is reduced. An incision is made a few inches above the knee cap and extends just below the knee into the shin. The outer capsule of the joint is opened and the bones of the knee are inspected. In one type of procedure, both the ACL and PCL are removed (if present). The ACL (anterior cruciate ligament) and the PCL (posterior cruciate ligament) are the primary front-to-back stabilizers of the knee joint. In patients with advanced disease, these ligaments are compromised or absent. (See section on different types of implants)

The link below is an excellent interactive overview of knee surgery-you get to be the surgeon! (it is animated so you do not have to worry if you are a bit squeamish). Having developed both implants and instrumentation, I was amazed at how "realistic" this is. They have some nice photos of actual surgery as well for those of you that are really curious.

http://www.edheads.org/activities/knee/swf/surgery.htm

Femoral Preparation in Total Knee Replacement

A small hole is drilled in the end of the femur (at about the center of the knee joint.

A long rod is placed in the intramedullary canal of the femur (the hollow portion of the bone where the marrow is).

A cutting guide is placed on the rod and rotated so that it sets up a slot to make the femoral distal cut. This is a cut that created a plane that is roughly parallel to the floor if you were in a standing position. This cut is made such that it is perpendicular to a line connecting the center of the hip and the center of the ankle. This line is the mechanical axis of the lower extremity and it is important that the implant is aligned properly with respect to this. In doing so, the load distribution across the implant is optimized and the longevity of the implant maximized.

Next, a cutting guide is placed on the plane of the distal cut, it is aligned in rotation and 4 more cuts are made. The rotational alignment here (which is called internal/external rotation) is important in balancing the soft tissue and aligning the patella track of the implant. The patella track is literally a track or groove in the implant in which the patella moves during knee motion. Incorrect alignment of this track can lead to pain and/or accelerated wear of the patella component.

Once these cuts are made, the preparation is basically finished. Some implants have small fixation pegs on the distal surface so two holes are sometimes drilled for these. In the case of a PS implant (see PS implant post), a "box" is cut out from roughly the center of the prepared femur to make space for the cam/post mechanism of the PS implantThe outline below is indicative of the "standard" approach. A minimally invasive technique is similar, but the incision and disruption to surrounding soft-tissue is reduced.

More on total knee replacement surgery

Medical Disclaimer:
The contents of this website and the links are for information only and are not a substitute for medical advice. This information should not replace necessary medical consultations with a qualified physician or health care provider.