Human limb joints can withstand considerable pressure, especially the joints of the feet. Most difficult to account for the hip joint. The upper end of the femur, its head, articulated with the bones of the pelvis, are spherical shape with a diameter of about 4 centimeters. It is well-fitting to a spherical cavity of the pelvic bones, the second element of the joint. Due to the spherical form of articulated surfaces of this joint multi-axis, ie articulated in its bones have the opportunity to perform three types of movements, allowing the movement of the legs in six directions. Man is able to make a leg forward and retract as it happens while walking, take the leg to the side and in towards the other foot, and finally turning it around the long axis and clockwise in the opposite direction, so that the fingers instead of its normal position can be rotated and the right and left. When a person makes the usual step, his foot on which he had just drawn, rotated with respect to the human body by about 57 , with the femoral head, sliding on the surface of the acetabulum, is a path equal to 2 centimeters. Pressure on the femoral head the entire mass of the human body is sufficiently large.
When a person with a body weight about 70 kilograms of compliance with immobility, relying on both legs, his hips falls load equal to 55-60 kilograms. However, the actual pressure experienced by these joints, much more – it is 1,6 times greater than the weight based on their body parts. This is because the center of gravity of the human body is not located directly above the line connecting the femoral head, and therefore to maintain a vertical posture several major pelvic muscles contract, the force pressing the surface articulated to each other and not allowing the body to bend. Therefore, the real pressure on these joints have semidesyatikilogrammovogo person reaches 95 pounds, and if he has behind him a backpack, which weighs 20 kilograms, the pressure will grow to 125 kilograms. For porter, who had raised on his back a sack of flour weighing 50 kilograms, it increases up to 175 pounds, well, how much pressure have hips athlete-lifter, lifting heavy rod, count yourself. Bone are highly durable.
Tibia human being in an upright position, is able to withstand the weight of 1800 pounds, and thigh – a half tons, the weight of the average car. Crushed bone much harder than breaking. At high bone strength, however, have brittle, and therefore injuries, bruises, falls are often accompanied by fractures. Most frequently occurring fractures of the femur in her neck. The fact that the shape of the femur, in contrast to other long bones, is far from the ideal line. With an advanced human neck of femur moves away from its main part at an angle of 115 to 140 . In other words, the upper part of the femur is shaped like an arc. Therefore, when falling on his legs apart or side bending of the bone is strengthened, and in the neck, the thinnest part, there is a fracture.