What disease is characterized by weakened bones?

Osteoporosis is characterized by weakened bones due to a decrease in bone density and overall bone strength. This condition leads to an increased risk of fractures, as the bones become fragile and can break easily even from minor falls or injuries. The weakening of bones occurs because the body either loses too much bone or makes too little bone, resulting in porous and less durable bone structures.

In contrast, arthritis is primarily an inflammation of the joints, which can lead to pain and stiffness but does not specifically weaken bones. Muscular dystrophy is a genetic disorder that causes progressive weakness and degeneration of skeletal muscles, affecting muscle function rather than bone strength. Tendonitis involves inflammation of tendons, which connect muscles to bones, and similarly does not pertain to the condition of bones themselves. Understanding these distinctions highlights why osteoporosis is the correct answer regarding the weakening of bones.