Partial Knee Replacement
When somebody comes in for knee replacement surgery, one of my first considerations is to check their age and whether they’re a more suitable candidate for partial knee or total knee. When you consider all the joint replacement surgeries for an arthritic knee, about one out of three are good candidates for partial knee replacement surgery and about two out of three are good candidates for total knee replacement.
They both have advantages and disadvantages. The partial knee is one third as much surgery, so that’s the obvious big advantage of a partial knee replacement. But then you’ve got to qualify for having one compartment worn out as opposed to both inside and outside compartments.
With total knees, the majority of total knee replacements are fixed bearing, and by that I mean the plastic is rigidly fixed to the tibia. When the femur glides over it with knee motion, there’s a sheer stress of shiny metal against the plastic. Over time, or with heavy people with too much weight or angulatory deformities, that plastic starts wearing, especially on active individuals. Then you get particulate debris from the plastic in the joint, and that’s not a good combination. The English version of the partial knee replacement is a mobile bearing, so instead of the plastic being rigidly fixed, it actually is mobile and moves with flexion and extension. That’s because the metal tray that the polyethylene rests on is polished, and the plastic moves are over it and slips back and forth, creating much less sheer stress and polyethylene wear.
When you injure the knee, many times either the inside or the outside compartment will take the hit and have cartilage damage. When you have one side of the knee with cartilage damage, the total cartilage cushion becomes narrow from the cartilage damage or the cartilage loss. When that happens, the knee tends to tilt more towards the side because the cushion on that side in now narrow, and the bones become closer together on that side.
The longer model shows that if you tip you get the bowleg that the cowboys get. If the outside compartment is damaged, or if you have a genetic predisposition to having knock knees, then as the knee knocks and comes inward, you wear out the outer part of the knee. The inside of the knee is spared. There’s no cartilage wear with all your activities because you knock knees and wear out the outside. So, in those cases you can have a partial knee to the outside for knock knees, or a partial knee to the inside if you have a bowleg.
When one compartment has worn out, it works very effectively, and the recovery rate is much quicker because you’re only doing one-third as much surgery. It gets people back into the workforce sooner. Many times the surgery is less, and they don’t even need formal physical therapy. If they do require formal physical therapy, it’s not near as lengthy as recovery from a total knee.