Figure 1		Figure 1

The Knee Joint

Whereas the hip joint consists of two bones (the pelvis and the thigh bone), the knee joint has three bones: the thigh bone (femur), the shin bone (tibia) and the kneecap (patella). The kneecap represents one more part that needs to be designed, one more source of pain.

Knee Replacement: The Classic

The classic knee replacement has three parts: the metallic cap that covers the end of the thigh bone (femur), the plastic tray that covers the flat, top portion of the shin bone (tibia), and the plastic piece affixed to the underside of the kneecap (patella). In the last twenty years or so, the plastic covering the top of the shinbone has in fact been placed onto a metallic tray, and it is this metallic tray that is fixed to the bone.

The term “total knee replacement” isn’t very good in my opinion because it conjures up the image of big chunks of bone being whacked out. In fact only slivers of bone are removed. The end of the thighbone is shaped into connecting flat surfaces that will match a metallic cap. The upper shin bone is cut approximately at a right angle to its long axis, removing usually no more than a quarter inch of bone or so.

The kneecap is a hard bone with a very soft cartilaginous underbelly. This cartilage can wear out just like any other cartilage in the knee. In the classic knee replacement the worn out cartilage of the kneecap is removed along with a sliver of the underlying bone and is replaced by a plastic button. The kneecap is then said to have been resurfaced.

As is the case with hip replacements the implants can be fixed to the bone with cement or can be “press-fit”.

Total Knee replacement without kneecap resurfacing.

In this common variation, the kneecap is left alone, and just the thighbone and shinbone are operated on.

You should know that this is one of the major controversies in knee replacement surgery.

*Excerpted from What Your Doctor May NOT Tell You About Hip and Knee Replacement Surgery, Warner Books 2004.