Glossary of Total Knee Replacement 

While the following words and concepts are not specific to TKRs, they are useful in constructing a framework to explain why specific exercises are beneficial to TKR recovery. To be an informed participant in discussions about your knee and not just the recipient of good advice, you need to know the names of the parts of the body – your body – that are important to the rehab process. This includes:

Knee Joint: A hinge made where the ends of the femur (thighbone), and the tibia (shin bone) meet. This hinge is covered by the patella (knee cap) which slides back and forth in a groove surrounded by cartilage. The knee joint is the largest weight bearing joint in the body. While it is relatively stable in itself, as part of the kinetic chain, see below, it is impacted by weaknesses in the lower extremities (foot and ankle) as well as in the hips. If the knee cap does not slide smoothly because of pressures from other parts of your body, it will limit your ability to walk properly.

Cartilage: A firm, flexible connective tissue that covers the ends of the femur and tibia as well as the back of the patella. Cartilage functions to reduce friction between the bones of the knee joint and allow smooth movement. When cartilage is damaged due to injury or disease, the knee no longer moves smoothly, bringing additional stresses to bear on tissue around it.

Ligaments and Tendons:  These dense bands of tough, fibrous connective tissues are made up of collagen – the substance in the body also responsible for giving skin strength and elasticity. Ligaments connect bone to bone and tendons connect bone to muscle.

Knee Joint Capsule: As with any hinge, the knee joint needs to be lubricated to function well, and this lubrication is provided by fluid produced inside the joint capsule, which is like a sleeve made of dense, fibrous connective tissue. This capsule is reinforced by other ligaments surrounding the knee.
For more detailed analysis of knee anatomy see: http://www.sportsinjuryclinic.net/anatomy/knee- anatomy

Muscles: The quadriceps and the hamstrings are the two main muscle groups responsible for moving the knee joint. The quadriceps, as the name implies, consist of four different muscles that come together on the front of the thigh and extend into the quadriceps tendon and patella tendon. Together, these muscles and tendons are responsible for knee extension i.e straightening the leg. The hamstring muscles, located at the back of the thigh, allow the knee to flex or bend.

Fascia: Fascia is another layer of collagen-based tissue in the body. Until recently, it was viewed as a highly elastic but passive substance that wrapped around muscles (including the quadriceps and the hamstrings) and organs to stabilize and separate them. Now, however, in addition to its strength and flexibility, it is recognized as having significant amounts of both blood vessels and sensory receptors. This makes fascia important to TKR patients because when knees become stiff and don’t move well, fascia also stiffen and loose flexibility. Adhesions may form among fascial fibers causing them to become rigid, compressing muscles and nerves and reducing mobility.

Trigger Points: This is a name for hyper-irritable points – tight bands or knots of fibers – in the muscle-fascia tissue matrix surrounding the knee joint that can cause pain and affect mobility.

Kinetic Chain: refers to the concept that all parts of the body - joints, muscles, fascia, ligaments and tendons - are involved in movement. When we walk, we walk with the entire body. Therefore, when we replace a defective knee joint, we are not just dealing with that joint alone. We are also dealing with everything that attaches, directly or indirectly, to that joint as well. The concept of “the ankle bone attaches to the shin bone” is just the beginning.

Gait Mechanics: The process of walking is usually taken for granted. Just putting one foot in front of the other doesn’t seem like a big deal – until it does. There is a particular order to muscle contraction and the activation of foot, ankle, leg and hip joints and bones in normal locomotion. This order is referred to as gait mechanics. Most likely, all candidates for TKR have suffered significant compromises to their gait mechanics, i.e. the way in which they walk, because of their knee problems. The restoration of proper gait mechanics is one of the primary goals of TKR surgery.

Range of Motion, Flexion and Extension: These terms all relate to the distance and direction in which the knee joint can move. Flexion describes the contraction of the hamstring muscles which bend the knee. Extension refers to the contraction of the quadriceps muscles which straighten the knee and the leg. The term range of motion (ROM) is a marker, an easy way to describe a knee’s ability to function. Some common ROM benchmarks are: flexion of 65 degrees to walk on level ground, 70 degrees to get out of a chair and 90 degrees to ascend and descend stairs. Research studies have found that the best predictor of range of motion post-surgery is the range of motion pre-surgery. This suggests that postponing an inevitable knee surgery is not in your best interest.

Tension Recoil: The adhesions and restrictions between fascia and muscle fibers that make extending and contracting the leg painful can also cause pain when that effort is reversed. For instance, if the patient is attempting to increase flexion by bending the knee and holding it for 15 – 20 seconds, there will be a surge of discomfort when the knee is relaxed and the leg is straightened. It is heartening to know that the more you repeat this exercise and reduce the number of adhesions and restrictions, the less pain will result from tension recoil.