Osteogenesis imperfecta (OI) is a disease that affects your bones. OI is also called brittle bone disease. If you have OI, you have bones that are weak and break easily.

Tendinitis is swelling and pain in a joint. It is a common condition, usually caused by repeated injuries to a tendon, which is the part of the joint that connects muscles to bones.

Marfan syndrome is a disorder that affects connective tissue. Connective tissue supports many parts of your body. You can think of it as a type of “glue” between cells.

Marfan syndrome can affect many parts of the body, such as:

It is usually passed from parent to child through the genes.

A sprain is an injury to a ligament (tissue that connects two or more bones at a joint). When a sprain happens, one or more ligaments is stretched or torn.

A strain is an injury to a muscle or tendon (fibrous cords of tissue that connect muscle to bone). In a strain, a muscle or tendon is stretched or torn.

Knee problems happen when you injure or develop disease in your knee and it can’t do its job.

The knees provide stable support for the body. They also allow your legs to bend and straighten. Both flexibility and stability are needed to stand, walk, run, crouch, jump, and turn. Other parts of your body help the knees do their job. These are: