Causes of knee pain
From crawling to walking upright, humans have made an important evolutionary step. Walking upright allowed us to save more energy, and in order to “stand up”, our ancestors did “whatever it takes”, so to speak, and today we have to pay for it – suffering from Foot pain and knee injuries.
There are many causes of knee pain, and arthritis is one of the most common, especially in the elderly. Arthritis occurs when the cartilage in the knee joint degenerates and wears down due to age, resulting in pain. Why is the knee joint prone to degeneration and pain? It is mainly related to upright walking and heavy joint loading of the lower extremities.
The function of the knee joint is to bear weight through a small joint surface in order to perform functions such as standing, walking, and walking up and down steps. This means that the stresses within the knee joint are unusually high, as it is not only subject to gravity, i.e., weight, but also to the muscle contraction forces around the joint. It has been measured that when walking normally, the load transmitted through the knee joint is 3 to 4 times the body weight, while when the knee joint is flexed to bear weight, the load on the patellofemoral joint surface is 9 to 10 times the body weight. In addition to weight bearing and stress transmission, the knee joint needs to have good motor function. This requires the joint surface to have not only good weight-bearing capacity but also good lubrication to reduce cartilage wear.
Therefore, the function of cartilage within the knee joint is to provide lubrication, reduce friction, and absorb impulse. One of the pathological changes of arthritis is the destruction or breakdown of cartilage. When arthritis causes damage to the cartilage layer of the joint, the bone beneath the cartilage rubs together, causing pain. In addition to weight bearing and degeneration, there are many diseases that cause joint destruction, collectively referred to as arthritis. These include abnormal forces, cartilage insufficiency, inflammation (or swelling), infection, and trauma. These causes lead to destruction and wear of the articular cartilage and eventually to cartilage loss and exposure of the subchondral bone. This results in clinical symptoms such as joint pain and dysfunction.
Clinical symptoms of arthritis include joint swelling, stiffness, loss of mobility, claudication, pain that progressively increases with activity and weight bearing, and nocturnal pain. Although most pathologic changes in arthritis are irreversible, there are a range of treatments that can be used clinically to relieve pain and improve function. Although arthritis affects joint function, it is generally not life-threatening. There are multiple causes and theories of the etiology of arthritis, but there is not yet a definitive cause to explain it, and because of this, many arthritis are difficult to cure.
To date, there are approximately hundreds of different types of arthritis recognized in medicine. The most common are osteoarthritis (i.e., degenerative arthritis), traumatic arthritis, rheumatoid arthritis, and ankylosing spondylitis.
Osteoarthritis
Osteoarthritis, also known as osteoarthrosis or degenerative arthritis, is the most common form of arthritis in the elderly population. In the United States, millions of people have symptomatic or asymptomatic osteoarthritis. In China, the prevalence of osteoarthritis is about 3%, and this percentage is increasing year by year with the progress of the aging population in the country. the prevalence can reach 10% in middle-aged and older adults over 40 years of age, and 80% of those over 60 years of age have x-ray changes of osteoarthritis. Thus, it is one of the most prevalent and widely affected diseases with the longest progression in the middle-aged and elderly population. One third of the population over 45 years of age has the following symptoms in at least one joint: from occasional joint stiffness and pain after activity to progressive joint pain with progressive loss of mobility. Most of the joints affected are in the lower extremities, especially the knee joints. These diseases have a great impact on the work, life, family and even society of patients. (Figure 2, normal cartilage and osteoarthritis)
Although the cause of osteoarthritis is not fully understood, the pathogenesis is fairly well understood medically. One of the main causes of cartilage wear and destruction is mechanical. Long-term, repetitive and overloaded joint movements lead to wear and tear of the articular cartilage. The weakness and degeneration of articular cartilage in the elderly makes them more susceptible to osteoarthritis due to these factors.
Genetic and hereditary factors also play a role in the development of osteoarthritis. Although the genetic factors of this disease are not as obvious as the genetic shapes such as eye and hair color, there is a tendency for it to be inherited. It may also be related to the lifestyle of the entire family, etc. In addition, other causes such as obesity or overweight are also potential causes of the disease, and the accumulation of excessive joint wear and tear due to chronic overloading of the joints will cause early onset of joint symptoms.
Traumatic arthritis
Traumatic arthritis is a secondary form of arthritis. It occurs secondary to intra-articular trauma to the knee such as intra-articular fractures, cruciate ligament and meniscal injuries, and following resection. Trauma results in weak and fragile intra-articular cartilage and reduced weight-bearing capacity. After healing of intra-articular fractures, if the articular cartilage is poorly aligned, joint wear is aggravated. Congenital poor alignment of the lower extremity such as inversion and valgus of the knee causes asymmetry of the weight-bearing surface of the articular cartilage, and ligament injury around the knee joint causes abnormal weight-bearing within the joint, etc., which accelerates the wear of cartilage. Overload sports by athletes can also accelerate the wear and tear of articular cartilage and degeneration. Once cartilage degeneration begins, the pathological progression is similar to that of other degenerative arthritis.
Rheumatoid arthritis
Rheumatoid arthritis is a disease caused by inflammatory lesions in the lining of the joint called the synovium. The inflammation and swelling of the synovial tissue eventually leads to the erosion and destruction of joint cartilage. The prevalence of rheumatoid arthritis in China is 0.32% to 0.36% (source: Ministry of Health Second National Health Service Survey Results Statistics 1998). The incidence of this disease is twice as high in women as in men. Rheumatoid arthritis is considered to be an autoimmune disease in which the body perceives its own joints as a foreign tissue and attacks them, eventually leading to joint destruction. The joint destruction caused by rheumatoid arthritis is systemic, but the lower extremities are still the most affected and have the greatest impact on the lives of patients. The cause of rheumatoid arthritis is not known, but some scholars believe that it is related to viral infections, and some believe that it is related to environmental factors.
Ankylosing spondylitis
Ankylosing spondylitis is a chronic inflammatory disease that primarily involves the spine, the medial skeleton, and the large joints of the extremities and is characterized by fibrosis and ossification of the intervertebral disc rings and adjacent connective tissue and joint ankylosis. Ankylosing spondylitis usually first affects the sacroiliac joints, and then, as the disease develops, it gradually involves the lumbar, thoracic, and cervical spine, resulting in blurring of the intervertebral joint synapses, loss of fusion and osteoporosis and destruction of the vertebral body, and ossification of the ligaments, leading to spinal ankylosis or hunchback fixation, and even loss of work capacity. In the past, the disease was considered to be the central type of rheumatoid arthritis or its variants, so there is rheumatoid spondylitis, rheumatoid arthritis central type of the name. Compared with rheumatoid arthritis, the two are different from each other in terms of age of onset, gender, site of disease, laboratory tests, x-ray and response to treatment, etc. In particular, the discovery of rheumatoid factor and histocompatibility antigen HIA-B27 further proves that rheumatoid arthritis and ankylosing spondylitis are two completely different diseases. It is now recognized that this disease is a seronegative spondyloarthropathy and is not a type of rheumatoid arthritis, but a separate disease. The prevalence of ankylosing spondylitis varies widely among ethnic groups, and Kellgren’s synthesis of national reports suggests that the average prevalence of this disease is about 0.1% of the population, with males far more common than females.
Other types of arthritis
The above-mentioned types of arthritis are the most common types of arthritis in clinical practice, and the knee is one of the most vulnerable joints in the course of the disease. There are other less common types of arthritis, such as gouty arthritis, psoriatic arthritis, systemic lupus erythematosus, juvenile arthritis, Reiter’s syndrome, Lyme disease, and infectious arthritis. Other factors can also contribute to the development of arthritis, such as the traumatic arthritis mentioned above, as well as some osteonecrotic diseases (blockage of blood vessels supplying bone, ischemic bone necrosis due to ischemia) and tumors. These diseases can destroy the integrity of the subchondral bone within the joint, causing degeneration of its superficial cartilage due to loss of nutrients.
Diagnosis of arthritis
When arthritis develops, a diagnosis of the type of arthritis can be made by a rheumatologist or orthopedic surgeon. Experienced physicians can make a correct diagnosis of some diseases based on the history and clinical presentation. A detailed clinical examination is essential to the diagnosis. X-rays are important in making a definitive diagnosis and in determining the extent of joint pathology. For osteoarthritis of the knee joint, X-ray examination can observe the size of the joint space, the proliferation of surrounding bones and changes in the force lines of the lower limbs (Figure 3 X-ray manifestations of osteoarthrosis). Since cartilage wear is the core lesion of arthritis, and cartilage is not visible on X-ray, it only appears as joint space. Therefore, the thinner the cartilage wear, the smaller the joint space. Laboratory tests are indispensable for certain arthritis. For example, rheumatoid arthritis, gout, etc. For arthritis that is difficult to diagnose, arthroscopy can be performed to directly observe the lesions in the joint through the arthroscope, and the diseased tissue can be removed for pathological examination.
Regardless of the type of arthritis, the ultimate change is the destruction of cartilage and the loss of low-friction function of the joint surface. Therefore the treatment of many arthritic conditions is similar.
Frequently Asked Questions
1. What is the cause of knee joint swelling?
Normal joints have a small amount of fluid in them, which serves to nourish the cartilage and lubricate the joint. An increase in joint fluid in the joint is known as joint swelling. This is due to the fact that when arthritis occurs, the inflammatory reaction is a chemical process known as synovitis. This chemical reaction produces and releases some inflammatory mediators and inflammatory products into the knee joint cavity, and these substances lead to increased secretion of joint fluid, causing swelling of the knee joint. As a result, the increased joint fluid has altered physical properties and chemical composition compared to the joint fluid in normal conditions. Therefore, some drugs can be targeted to change the properties of the joint fluid to reduce the symptoms of arthritis.
2.What are the causes of joint pain due to knee osteoarthritis?
There are many causes of knee pain. Swelling (i.e., excessive production of joint fluid) leads to an increase in the limited volume of the joint cavity, and pain occurs as the synovial lining of the joint swells and stretches. In degenerative knee joints, cartilage degeneration leads to a decrease in its ability to withstand pressure and relieve impulse to protect the subchondral bone, resulting in forceful impingement of the subchondral bone within the joint during weight bearing, which stimulates nearby nociceptive nerves and results in joint pain. For joints with poor force lines in the lower extremities, strain inflammation caused by unbalanced weight bearing in the medial and lateral joints during weight bearing, resulting in higher ligament stress on one side, is also a cause of knee pain.
3. Why is my knee joint stiff?
There are many causes of knee stiffness. Excessive swelling and fluid accumulation in the joint causes the joint cavity space to become smaller, and increased tension in the soft tissues during movement can cause stiffness due to difficulty moving the joint. When the cartilage in the joint is damaged, the joint surface becomes rough and unsmooth, and the lubricating properties of the joint are lost, resulting in increased friction and stiffness when the joint is moved. Inflammation, swelling, and hyperplasia of the ligaments around the joints may also cause stiffness due to changes in elasticity, toughness, and lubrication. Another reason is that when a joint becomes painful, joint movement is intentionally reduced to alleviate the pain. Long-term restriction of movement leads to joint stiffness, which in turn increases the loss of joint mobility, thus creating a vicious cycle of joint stiffness. This condition is more likely to occur in rheumatoid and ankylosing spondylitis than in osteoarthritis.
4.What causes osteoarthrosis in the knee joint and is the pain caused by osteoarthrosis?
Bone redundancy, commonly known as bone spurs or osteophytes, is a pathological change that occurs due to wear and tear of joint cartilage during arthritis, and is a reactive proliferation that occurs due to abnormal stress and inflammation of the cartilage surface in the joint. There is a misconception that joint pain is “caused” by bone spurs. In fact, bone spurs are not the initial cause of joint pain, but rather the result of joint degeneration, cartilage wear, and abnormal intra-articular stresses. Osteomalacia is a natural pathological reaction of the body to increase the stress area of the joint and reduce the stress on the joint surface. However, if the bone spur grows very large, it can also cause joint pain and affect the mobility of the joint.