Semi Constrained Knee Replacement Information

The knee is the largest joint in the human body, and to have it removed and replaced with a prosthesis requires a great deal of cutting and brute force. It is a long and difficult recovery, but in most cases it makes a tremendous improvement in the quality of life of the patient and is well worth the pain and effort. In some cases, doctors will use a special kind of knee replacement, called a semi-constrained knee replacement. Knowing what this is and why it is used will help a patient to better understand their options going into surgery.

Significance of the Knee Joint

• The upper and lower leg bones are joined by a complex array of ligaments, tendons, muscles and cartilage. Floating above all this is the kneecap, or patella, which serves as a bony fulcrum for the knee muscles to slide over and amplify strength and torque. The knee can not only bend and flex, it can twist and rotate, making exceptional athletic moves possible. But in addition to allowing possibilities for motion, it is vulnerable to injury. If a knee sustains a blow while rotating or twisting, considerable damage can be done. Wear and tear sustained by the knee on a daily basis over a lifetime eventually eats the joint away, leaving the bones grating painfully together.

Knee Replacement Surgery

• The function of knee replacement surgery is to take an end-stage knee joint, which has worn out all its cartilage and is essentially causing more harm than good (or has sustained an injury that makes replacement a must), and cutting it out. The lower part of the upper leg bone (femur) and the upper part of the lower leg bone (tibia) are cut off and removed, along with the kneecap (patella). A prosthesis, made before the surgery to the unique specifications of the patient, is inserted and secured with bone cement, pins and screws. The joint is tested, then closed, and healing and rehabilitation begin.

Semi-Constrained Knee Replacement

• In a standard knee replacement operation, a non-constrained prosthesis is used. This means that the two pieces that are placed into the knee joint are not connected and rely exclusively on the body's muscles, ligaments and tendons to keep the kneecap in place, just as a normal kneecap would do. In a semi-constrained knee replacement, there is some stability built into the prosthesis. The two pieces are connected with a hinge-like device that keeps the joint in-line and helps support the kneecap's proper alignment and function. Surgeons will opt for this type of knee replacement in cases where the knee has already had a history of instability or where the knee's ligaments, tendons and muscles are compromised in some way. Semi-constrained knee replacement is also used when the surgeon chooses to remove the ligaments during a knee replacement surgery.

Effects

• The effects of a semi-constrained knee replacement are the same as in a standard knee replacement. The diseased and damaged bone is removed, and the degenerating joint is replaced with man-made material that mimics the function of the natural knee joint without the osteoarthritic pain. The difference between the two is in stability. A standard knee replacement relies on the natural state of the muscles and tendons surrounding the replaced knee to make it function and keep it in place. A semi-constrained knee replacement has a hinge that attaches the upper and lower pieces of the knee replacement together, keeping the knee aligned and making sure the new kneecap works in a straight line with the femur.

Warning

• Some things that patients need to be aware of going into knee replacement surgery are that their new knees are not the same as the ones they were born with and that they can and will wear out. Man-made materials can never replace nature in durability. A knee replacement is doing great if it can last fifteen years. A semi-constrained knee replacement usually does not last this long. The wear and tear of the human body is tremendous on the knee joint, and the harder you use it, the quicker it will wear out. Keep in mind that most people can only have two knee replacements in one lifetime, so taking care of your new knee needs to be a priority.