The knee consists of three bones: the femur (thigh bone), the tibia (shin bone), and the patella (knee cap). The fibula (smaller lower leg bone) makes a joint with the tibia, but is not involved in the articulation of the knee. These bones are lined with hyaline cartilage, which makes the surfaces almost frictionless and helps to lubricate the joint during movement. The knee joint is called a ‘hinge joint’ with the majority of the movement being flexion & extension (bending & straightening).
The bones are held together by ligaments, which are collagen fibres connecting one bone to another bone. They are responsible for stabilizing the bones together. Impairment of a ligament can make the joint loose. The four main ligaments of the knee are the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL). The cruciate ligaments (ACL & PCL) connect the femur and tibia inside the joint at the centres of the bones. They prevent forward and backward translation of the tibia and rotation. The collateral ligaments (LCL & MCL) are at the sides of the joint and they prevent sideways and gapping movements.
The knee contains two large fibrocartilage rings, each called a meniscus. These attach to the top of the tibia. The end of the femur sits onto the meniscus making the joint fit together better and providing some stability. They also function as shock absorbers for the knee joint.
The second type of cartilage in the knee is called hyaline cartilage. This type of cartilage is thin and covers the surfaces of the femur, patella, and tibia. Hyaline cartilage is extremely smooth and almost frictionless, allowing for ease of joint movement. This cartilage is also important for circulating joint synovial fluid.
This occurs with years of ‘wear and tear’ or compression on the knee joints. Gradually the hyaline cartilage that covers the bones wears away, leaving exposed bony surfaces for articulation. The exposed bone will be subjected to more force during activity and will make more bone in response to this. The bone develops ‘osteophytes’ or bone spurs which are bumpy outgrowths of the bone. Osteoarthritis makes for stiff, painful movement, initial feeling of laxity, swelling, and eventual loss of motion. The physiotherapy treatment for arthritis involves activity modification, acupuncture, stretching, and strengthening. If severe enough, a total knee replacement may be required.
Knee Replacement Surgery
This is known as a Total Knee Replacement. Sometimes only part of the joint surface needs to be replaced, which is called a Partial or Hemi Knee Replacement. Knee replacement surgery has been practiced for many years and offers very high success rates. 90% of people who have a knee replacement report significantly less pain and greater function. The lifespan of the components has also improved over the years, with 85% of prosthesis parts still functioning 20 years after surgery.
Specific exercises are extremely important following a knee replacement surgery. It is imperative that the knee joint regains functional range of motion and muscular strength. Balance retraining is also a major focus of rehabilitation. Several months of strength, mobility, and stability exercises are key to achieving maximal function of the new joint. Rehab exercises should be catered to each individual depending on the stage of rehabilitation, concurrent health issues, adjacent joint health, and current levels of strength, mobility, and balance.
Physiotherapy is another component of rehabilitation that is imperative to regaining function. In addition to prescribing exercises and monitoring expected progress, treatment consists of manual therapy. This means physically mobilizing the joint, releasing muscles, and manual stretching. Sometimes pain modulating therapies are used as well, such as cold, heat, TENS machines, and acupuncture. The amount of physiotherapy required varies amongst individuals. Physiotherapy is mandatory initially after surgery, usually for a period of 8 weeks.
However, many people require physiotherapy for several months following the surgery depending on their progress, desired functional goals, and health complications. Occasionally, individuals may not achieve expected strength and mobility following the surgery, which can lead to secondary issues months or years later. This includes altered walking patterns, imbalance, risk of falling, reduced walking endurance, and ‘new’ joint pain in the knee, hip, ankle, or lower back. That is why it is very important to meet the strength, mobility, and balance goals that are expected of your new joint.