Joint

Joint types fall into three broad categories. Fibrous joints, such as skull sutures, hold bones tightly with little or no movement. Cartilaginous joints like the discs between vertebrae or the pubic symphysis allow limited motion while absorbing pressure. Synovial joints, the most common kind, feature a capsule filled with slippery fluid that enables wide ranges of movement.

Synovial joints come in different shapes aligned to their functions. Hinge joints such as elbows bend in one plane, ball-and-socket joints like hips rotate in multiple directions, pivot joints allow rotation at the neck, and gliding joints slide at the wrists and ankles. Their articular cartilage cushions bone ends, while synovial fluid nourishes the cartilage and acts like oil in an engine.

Ligaments reinforce joint capsules, preventing bones from moving too far, and tendons anchor muscles nearby so contractions translate into motion. Menisci and labra—specialized cartilage pads—deepen socket joints and distribute weight, particularly in the knee and shoulder.

Joint health depends on balanced movement and protective habits. Regular exercise keeps surrounding muscles strong, supporting alignment, while stretching maintains flexibility. Proper footwear, ergonomics, and maintaining a healthy weight reduce stress on weight-bearing joints. Injuries such as sprains or dislocations can damage ligaments or cartilage; early treatment helps prevent chronic problems.

Diseases like osteoarthritis, rheumatoid arthritis, and gout affect joints by wearing down cartilage, inflaming membranes, or depositing crystals. Treatments include physical therapy, anti-inflammatory medicines, joint injections, and when necessary, surgical repair or replacement. Advances in biomechanics and regenerative medicine aim to restore joint function with customized implants, biologic lubricants, or lab-grown cartilage.