The knee joint is a structure composed of three bones: the femur (thigh bone), the tibia (shin bone) and the patella (knee cap). The bones are covered with smooth cartilage surfaces that act as a cushion during weight-bearing activity.
The bones of the knee are connected by strong ligaments and powerful muscles that are attached to the thigh and calf by tendons and provide side-to-side stability. In a healthy knee, all of these structures work together to allow the knee to flex (bend) and extend (straighten) the lower leg smoothly.
Arthritis is a disease that affects the surface of the joint (cartilage) wearing down so it no longer moves smoothly and loses the ability to acts like a cushion. Damaged cartilage causes a roughened surface and may lead to bones rubbing directly together, causing persistent pain, clicking, a catching sensation, and limited range of motion.
There are three common types of arthritis:
Osteoarthritis or Degenerative Joint Disease is the most common type of arthritis, which is a slow progressive disease that wears down the cartilage. The normally smooth surface of the joint becomes roughened and may cause increased pain, stiffness, and limited motion.
Rheumatoid arthritis or Inflammatory arthritis is a systemic process that may involve multiple joints at the same time. Rheumatoid arthritis may affect people at any age and often is treated with very specific medications. The symptoms vary somewhat as pain usually worsens after periods of rest and inactivity as joints stiffen. Some may experience pain, swelling, redness and warmth, especially in the morning.
Post-traumatic arthritis may occur following an injury to the ligaments, cartilage, and bone that causes instability to the joint and leads to increased wearing of the cartilage surfaces.
The knee joint may develop cysts, bone spurs, or loss of cartilage. The absence of cartilage will cause friction and narrowing of the joint space.
Symptoms include knee joint aching, soreness and pain, and swelling and stiffness. Sometimes this leads to reduced activity and muscle weakness. Weakened muscles can lead to instability and decreased ability to control the knee, further limiting the ability to participate in enjoyable activities.
The likelihood of arthritis increases with a family history and advancing age. Patients who are overweight and those who have undergone trauma to the knee joint may also experience early wearing of cartilage.
Fig. 1: While the image on the left shows the healthy anatomy of the knee, the image in the center details the various signs of arthritis. The image on the right displays a total knee implant and its placement within the knee. Click on each image to view a larger, more detailed version.
It is difficult to predict the timing and progression of the arthritic condition. Sometimes pain increases and the ability to participate in daily activities decreases despite non-surgical treatment plans. In those cases, a total knee replacement surgery may be recommended.
Total Knee Replacement Surgery
The artificial joint or prosthesis replaces the damaged and worn-out surfaces on the ends of the femur (thigh bone) and tibia (shin bone) and the underside of the patella (knee cap) with a new smooth joint surface that will be fixed to the bones.
There are many types of knee replacements that are made from different materials. Some pieces are made of metal or ceramic, and others are made of a strong and smooth plastic. Your surgeon will discuss various options and help determine the best choice and most appropriate one for your individual needs.
Your surgeon will discuss your condition and treatment plan. For any questions regarding the above information please feel free to contact the HSS Patient Education Programs at 212.606.1263.