Most moving joints in the body have a similar structure. Surrounding the joint is the joint capsule, a tough fibrous connective tissue that helps hold the bones together, providing strength and stability. Inside the joint capsule, the synovial membrane plays a particularly important role: it produces synovial fluid, a nutrient- and water-rich liquid that acts as a lubricant, helping the ends of the bones slide smoothly over each other and reducing friction during movement.
When you have arthritis, one or more of these components are damaged, leading to pain, stiffness, and limited mobility.
How Does Arthritis Cause Joint Pain?
1. Joint Pain Due to Lack of Synovial Fluid
The inside of the synovial membrane is covered by a layer of synovial membrane, a membrane whose cells are responsible for secreting synovial fluid. Synovial fluid, along with water, acts as a lubricant to help smooth the sliding motion between the bones.
Rheumatoid arthritis is a chronic inflammatory disease that affects the synovial membrane, causing severe joint pain and loss of function. It is an autoimmune disorder characterized by faulty signals that cause immune cells to destroy the body’s own tissues. Rheumatoid arthritis typically affects the hands and feet, with symptoms including: Inflammation and swelling of the synovial tissue; Pain, stiffness, and swelling of the joints.
As the disease progresses, enzymes eventually break down bone and cartilage, changing the alignment of the joints and leading to further pain and immobility. Systemic symptoms such as fatigue and muscle aches are also common.
2. Joint pain due to worn cartilage
Another important component of the joint is cartilage. Cartilage is a type of connective tissue that has a sponge-like structure and is able to absorb and repel water. This slippery tissue provides another lubricating surface, while the water-filled spongy structure acts as a large shock absorber during weight-bearing activities.
This cartilage degeneration is what causes osteoarthritis. When cartilage breaks down, the cushioning between joints is reduced and the uneven surfaces slide over each other, creating painful friction. In addition, because cartilage is less able to withstand the pressure of movement, surrounding structures such as bones, joint capsules, ligaments, and tendons become increasingly strained.
Why use heat for arthritis?
Heat therapy is an easy, inexpensive, and drug-free way to relieve pain and stiffness in some types of arthritis. Heat therapy can:
1. Promote the healing of damaged tissue
When warm heat is applied to a joint, the blood vessels in the muscles and soft tissues dilate. This dilation increases blood flow, bringing more oxygen and nutrients to the damaged area. Oxygen plays an essential role in cell regeneration and removing metabolic waste products that accumulate around the joint, thereby reducing inflammation.
Although articular cartilage is not able to regenerate significantly due to lack of blood supply, other tissues such as muscles, tendons, ligaments and joint capsules can still be restored better when provided with adequate blood and nutrients. Therefore, applying heat not only helps to relieve immediate symptoms but also supports the long-term recovery process.
2. Reduce joint stiffness
One of the most common discomforts of arthritis is a feeling of stiffness in the joints, especially in the morning or after sitting for a long time. Warm temperatures increase the elasticity of connective tissue and relax muscles, thereby helping joints move more flexibly.
When muscles and ligaments become soft, you will find it easier to perform movements such as bending, stretching or rotating joints without feeling “stuck” or sore. This is especially helpful before practicing therapeutic exercises or participating in light physical activities.
3. Stimulates Synovial Fluid Production
Synovial fluid acts as a “lubricant” for the joint, helping to reduce friction and distribute nutrients to the cartilage. When a joint is inflamed or degenerated, this fluid can decrease, causing the joint to become dry and painful.
Warming the joint, combined with gentle bending and stretching movements, can stimulate the synovial membrane to produce more fluid. The new synovial fluid will help improve mobility, reduce creaking when moving, and protect the structures inside the joint from wear.
4. Reduce pain signals to the brain
The pleasant warmth from a hot compress or towel not only affects the joint but also affects the sensory nervous system. Heat receptors on the skin will send “warm” signals to the brain, competing with and partially inhibiting the “pain” signals coming from the inflamed joint area.
This mechanism is similar to when you accidentally bump into something and reflexively rub the painful area, which will make the brain temporarily “forget” the initial pain. Thanks to that, hot compresses help the patient feel relaxed, reduce mental stress and feel more comfortable when resting or sleeping.
