Knee Arthritis
Normal Anatomy
The bones of the knee are the femur (thigh bone), tibia (shin bone) and patella (kneecap). The femur and tibia meet to form the knee joint which is a hinge with the knee cap(patella) in front of these two bones acting as a mobile shield to protect the joint. The patella slides up and down in a groove in the femur called the femoral groove as the knee is bent and straightened.
Ligaments hold the knee together and give it stability. The medial (inner) collateral ligament (MCL) and outer (lateral) collateral ligament (LCL) limit sideways motion of the knee. The posterior and anterior cruciate ligaments (PCL and ACL) limit forward and backward translational motion of the knee bones, keeping them stable and allowing the knee to function as a unit.
Two structures known as menisci sit between the femur and the tibia and act as cushions or shock absorbers for the knee. Menisci are one of two types of cartilage in the knee. The other type, articular cartilage, is a smooth and very slick material that covers the end of the femur, the femoral groove, the top of the tibia and the underside of the patella. This articular cartilage allows the bones to move smoothly without pain. If this layer wears away, it is called arthritis and then the motion becomes painful.
Tendons connect muscles to the bones of the knee. The quadriceps muscles on the front of the thigh are connected to the top of the patella by the quadriceps tendon, which covers the patella and becomes the patellar tendon. The patellar tendon then attaches to the front of the tibia. The hamstring muscles in the back of the leg attach to the leg bone (tibia) at the back of the knee. The quadriceps muscles straighten the knee and the hamstring muscles bend the knee both of which are required for walking, running or simply standing.
Pathology
Knee arthritis is the loss of the cartilage cushion in the joint contact surfaces that normally allows for smooth, pain-free gliding during knee range of motion. When arthritis occurs, patients may have pain with fully straightening or bending the knee, activities, especially such as walking and climbing stairs, swelling, clicking, catching, locking, a grinding noise or feeling with knee movement called crepitance, decreased motion and overall limited function. Knee arthritis can have several causes. When arthritis results from wear and tear over time, as occurs with aging, it is called osteoarthritis or degenerative arthritis. When a fracture or broken bone extends into the joint and heals improperly or a joint dislocation injures the joint cartilage, it is called post-traumatic arthritis. Arthritis that occurs at a younger age (less than 40 yrs) is rare and commonly due to genetic causes that are inherited. Arthritis can be caused by infection or inflammatory conditions such as rheumatoid arthritis, lupus, psoriatic arthritis, or from various crystalline diseases. These crystalline diseases, called gout or pseudogout, result from inflammatory cells in the body attempting to clean up invading particles and in the process, destroy the joint inadvertently.
X-rays are necessary to determine the location and extent of arthritis present within the knee joint. Rarely, a CT scan or an MRI is necessary to look for other bony or soft tissue abnormalities, respectively. A physical exam is important to determine the patient’s range of motion, muscle strength, ligamentous stability, dynamic stability with walking, and to determine the best course of treatment.
Treatment
Arthritis treatment starts with the basics of a non-surgical program. Therapy includes gentle range of motion exercises, thermal modalities, and strengthening. Oral anti-inflammatory medication and injections help with pain considerably. There are two types of medication that can be injected for knee arthritis. Cortisone is the most potent anti-inflammatory medication and often gives patients considerable pain relief. In addition, there are lubricating injections that help the structures within the knee joint glide past each other smoothly. The body makes lubricating joint fluid on its own, but the fluid made tends to become less viscous as arthritis advances. These lubricating injections also stimulate the body to make new, more viscous joint fluid. Modifying how certain key activities are performed takes much of the stress off the joint. A small proportion of patients will require some form of surgical treatment. The simplest form of surgery consists of cleaning the arthritic debris out of the knee joint, removing bone spurs to improve motion, and cleaning out any torn or frayed cartilage. This can be done arthroscopically with a fiber-optic camera and no significant scars. Rehabilitation after this operation emphasizes daily motion exercises to ensure that the patient regains as much function as possible and strengthening exercises to protect the knee joint.
Patients with osteoarthritis, post-traumatic arthritis, and inflammatory arthritic conditions, will sometimes need to go on to more advanced forms of surgical treatment. Depending on where the arthritis is within the knee joint, portions of the knee joint or the whole knee joint is replaced with a prosthesis made of metal and high density plastic. After joint replacement, rehabilitation is needed to regain full motion, strengthen the muscles of the leg, and to be able to walk normally. However, the patient is instructed on very stringent limitations that the prosthesis can handle in terms of aggressive types of activity such as running and jumping. All types of surgery are very effective in terms of relieving pain. The patient and surgeon must choose carefully to match the type of surgery with the amount and type of arthritis present and the lifestyle the patient wishes to live.