Your thighbone, or femur, is the large bone between your knee and your hip. Your femur bends inward at the top. The part of your femur at this bend is called the neck. The rounded end of your femur is called the ball, or femoral head. The head of your femur fits into a socket in your pelvis to form your hip joint. If a break happens anywhere in the top quarter of the femur, it is considered a hip fracture. Most hip fractures occur from falls in older adults. In younger adults, hip fractures are often caused by a direct hit to the side of the hip, such as during a motor vehicle crash or a high fall. Hip fractures happen more often in women. Your risk for hip fractures increases with age. Having weak bones, or osteoporosis, can also increase your risk. Some types of cancer and stress fractures, or stress injuries, can also weaken your bones. Stress fractures are tiny cracks in a bone that can be caused by overuse.