“Knee replacement is the replacement of damaged bone and cartilage in the knee joint with artificial biomaterials, simply by removing the worn and damaged joint surface and putting an artificial joint on the surface of the joint. This technique began in the 1960s and was the most important breakthrough in the field of orthopedics in the 20th century. After more than half a century of development, both artificial joint products and joint replacement techniques have been greatly improved and have become very sophisticated clinical treatments. These advances have led to greatly improved surgical outcomes, and knee replacement surgery is becoming more common, bringing benefits to patients with osteoarthritis in bone and joint disease, especially in the elderly.
In order to provide patients with a better understanding of the basics of knee replacement and to facilitate communication and consensus on treatment, we have prepared the following Q&A. We hope to help you better understand osteoarthritis of the knee and knee replacement surgery, and better cooperate with the preoperative preparation and postoperative rehabilitation to achieve the best treatment results.
Q1. How does the normal knee joint work?
The knee joint is the largest joint in the body and we cannot do our daily activities without it. The knee joint is the joint formed between the thigh bone (femur) and the lower leg bone (tibia). The ends of the bones are covered with a smooth layer of articular cartilage (known as the articular surface), so they can slide smoothly against each other. The patella, or kneecap, is a movable bone in the front of the knee joint, wrapped within the quadriceps tendon in the front of the thigh and connected downward to the lower leg bone by the patellar ligament. The lower surface of the patella is also covered with articular cartilage, which slides in a groove in front of the thigh bone called the femoral glide. The other surfaces of the bone are covered with a thin layer of smooth synovial tissue, and the articular cartilage is lubricated by synovial fluid secreted by the synovial membrane. This fluid is wrapped in a layer of soft tissue called the joint capsule.
Normally, the parts of the knee joint work in harmony with each other. Once disease or injury exists in these structures, then this harmony will be broken, producing pain, muscle weakness and decreased function.
Q2. What are the common causes of knee pain and decreased function?
The most common cause of chronic pain and decreased function of the knee is arthritis, of which degenerative osteoarthritis is the most common, followed by rheumatoid arthritis and traumatic arthritis.
Degenerative osteoarthritis: referred to as osteoarthritis, usually occurs after the age of 50, the cartilage on the surface of the joint softens and wears away, and the joint surface becomes uneven. In severe cases, “bone grinding bone” occurs, producing pain and stiffness in the knee joint.
Rheumatoid arthritis: The lesions originate in the synovial membrane within the joint, which becomes inflamed, thickens, and secretes excessive synovial fluid to fill the joint cavity. This chronic inflammation eats away at the cartilage, eventually leading to cartilage loss, pain and stiffness.
Traumatic arthritis: occurs after various joint injuries, such as fractures, tears of the meniscus and ligaments of the knee. Over time it causes cartilage destruction, producing knee pain and limited function.
Q3. What factors are associated with the occurrence of osteoarthritis?
– Age: As we age, the ability of cartilage to repair itself gradually decreases. Osteoarthritis mainly occurs in middle-aged and elderly people.
– Genetics: Some genes have now been found to be associated with the development of osteoarthritis, and patients with a family history of osteoarthritis are more likely to get it.
– Weight: The heavier you are, the heavier the burden on your knee joint and the more likely you are to develop osteoarthritis.
– Trauma: People who have had previous trauma, such as sports injuries, are more likely to develop osteoarthritis in middle and old age.
– Overuse: Working in jobs that require repeated squatting or prolonged squatting, frequent weight-bearing and excessive walking can cause repeated stress stimulation in the knee joint, making it more susceptible to osteoarthritis.
– Other diseases: If you have other diseases of the knee joint, such as gout and joint infections, you are at higher risk of developing osteoarthritis.
Q4. Why does severe osteoarthritis require artificial joint replacement?
As mentioned above, the articular cartilage depends mainly on the infiltration of synovial fluid for nutrition and therefore lacks the ability to repair itself, making it difficult for the articular cartilage to heal itself when it wears out.
Mild osteoarthritis can be treated and relieved by lifestyle changes (e.g., less squatting, less walking up and down stairs, and less weight bearing), oral medications (cartilage repair promoting drugs and anti-inflammatory and analgesic drugs), intra-articular injections (e.g., sodium glacial, hormones, etc.), physical therapy, and some surgeries (e.g., arthroscopic debridement, high tibial osteotomy, etc.).
However, in severe osteoarthritis, the joint cartilage wears away or is missing, “bone grinds bone,” and weight bearing and movement on this uneven joint surface can cause severe pain. These degenerated joints can form bone spurs or bones, and contracture of the ligaments and capsule around the joint can add to the mobility problems. If the joint becomes deformed (e.g., “rotundity” or “X” shaped leg), the line of gravity of the joint changes, further aggravating the development of the disease and creating irreversible lesions.
The above conditions cannot be relieved by oral medication, intra-articular injections and arthroscopic surgery, and cannot be completely cured. Only by replacing the worn and damaged joint surface with a smooth new joint surface, changing the line of gravity through surgery, and removing bone spurs and bones can we obtain a pain-free and functional knee joint and achieve a long-term cure.
Q5: How can I tell if I need a total knee replacement?
Knee replacement is considered to solve the problem when
– Because severe knee pain limits daily activities, including walking, walking up and down stairs, squatting, etc. For example, you cannot walk 2-3 stops without pain, or you need the assistance of a walking aid such as a cane.
– Moderate to severe rest pain, either during the day or night.
– Chronic inflammation and swelling of the knee joint that is not relieved by rest or medication.
– Joint deformity, with the lower leg bending inward or outward (inversion or valgus).
– Stiffness of the joint, inability to fully straighten or fully bend the knee.
– Pain that cannot be relieved by taking anti-inflammatory and analgesic medication.
– Pain in the joint, but the use of analgesics is not allowed due to other physical conditions.
– Other treatments have failed, such as joint cavity injections, physical therapy or other surgery.
Q6. At what age is a knee replacement suitable?
First, it is important to realize that knee replacement is not a “big” surgery and can be performed at any age in adults. Most patients undergoing total knee replacement are between the ages of 50-80, but the surgeon will evaluate the patient on an individual basis. Suitability for surgery depends on the patient’s level of pain and functional limitations, not on age.
After deciding on surgery, your surgeon will perform a comprehensive evaluation of your condition. A discussion is held with you in conjunction with your knee and general condition to determine if knee replacement is the best approach for you. The potential risks and complications of knee replacement will also be explained to you, both for the surgery itself and for those that occur long after the surgery. The surgery will be performed in a safe manner.
Q7. How many years will my artificial joint last?
The hip and knee joints, being the major load-bearing joints of the body, have a certain lifespan for the use of their prosthesis. The use of artificial joints is like driving a car, under normal circumstances if] there is an accident, it can last for many years, even more than 20 or 30 years without problems. If the car is overloaded, it may not reach the end of its useful life before the car is scrapped. By following up the artificial joints that were replaced more than ten years ago, there are still 90%; or more patients are still using them. Therefore, artificial joints made with contemporary high-tech concepts and advanced materials should theoretically have a service life of more than 20 years if they are properly installed.
However, young, overweight, active and osteoporotic patients are prone to premature wear and loosening of the artificial joints. Therefore, after receiving an artificial joint replacement, patients should be followed up regularly, and exercise and maintenance should be performed under the guidance of a physician.
Q8. Why is the concept of “putting off joint replacement as long as possible” questionable?
Some people choose to postpone joint replacement for as long as possible because they are concerned about the longevity of the artificial joint and do not want to have another joint replacement during their lifetime. In fact, doctors and patients are generally in agreement on this point. As long as the pain and functional decline are not severe and the needs of daily life can be met, joint replacement can be postponed. However, it is not advisable to think that “the later the better” for joint replacement.
First of all, the human body is a complex organism composed of multiple systems, and each system and organ is closely related to each other. Osteoarthritis occurs mainly in older patients, and the pain and dysfunction of osteoarthritis can greatly limit daily activities, reduce exercise, and prevent cardiopulmonary function from being exercised and maintained. This can indirectly increase the incidence of cardiopulmonary and cardiovascular disease or further aggravate pre-existing medical conditions. Diabetic patients also cannot control their blood sugar well and their whole body functions will gradually decline. These can pose a greater threat to health and life.
Secondly, the older you are, the less able you will be to withstand the blows of surgery. The chance of perioperative complications increases with age, and some patients may even be unable to withstand anesthesia and surgery due to poor health, losing a good opportunity for joint replacement.
In addition, the longer the arthritis has been present, the more pronounced the local pathological changes in the joint become: increased bone spurs, increased joint deformity, osteoporosis, and so on. These changes not only make the operation more difficult, prolong the operation time, increase complications, and affect the post-operative results, but also shorten the life of the artificial joint due to the decrease in bone quality. In this way, it is not worthwhile to postpone the surgery in exchange for pain and reduced quality of life.