The knee is a vulnerable joint that bears a great deal of stress from everyday activities such as lifting and kneeling, and from high-impact activities such as jogging and aerobics.
The knee is formed by the following parts:
Tibia. Shin bone or larger bone of the lower leg
Fibula. Smaller of the 2 lower leg bones
Femur. Thighbone or upper leg bone
Each bone end is covered with a layer of cartilage that absorbs shock and protects the knee. Basically, the knee is 2 long leg bones held together by muscles, ligaments, and tendons.
There are 2 groups of muscles involved in the knee, including the quadriceps muscles (located on the front of the thighs), which straighten the legs, and the hamstring muscles (located on the back of the thighs), which bend the leg at the knee.
Tendons are tough cords of tissue that connect muscles to bones. Ligaments are elastic bands of tissue that connect bone to bone. Some ligaments on the knee provide stability and protection of the joints, while other ligaments limit forward and backward movement of the tibia (shin bone).
Compact tissue. The harder, outer tissue of bones.
Cancellous tissue. The sponge-like tissue inside bones.
Subchondral tissue. The smooth tissue at the ends of bones, which is covered with another type of tissue called cartilage. Cartilage is the specialized, gristly connective tissue that is present in adults, and the tissue from which most bones develop in children.
The tough, thin outer membrane covering the bones is called the periosteum. Beneath the hard outer shell of the periosteum there are tunnels and canals through which blood and lymphatic vessels run to carry nourishment for the bone. Muscles, ligaments, and tendons may attach to the periosteum.
Bones are classified by their shape–as long, short, flat, and irregular. Primarily, they are referred to as long or short.
There are 206 bones in the human skeleton, not including teeth and sesamoid bones (small bones found within cartilage):
80 axial bones. This includes the head, facial, hyoid, auditory, trunk, ribs, and sternum.
126 appendicular bones. This includes arms, shoulders, wrists, hands, legs, hips, ankles, and feet.
What are the functions of bone?
Bone provides shape and support for the body, as well as protection for some organs. Bone also serves as a storage site for minerals and provides the medium–marrow–for the development and storage of blood cells.
What are the different types of bone cells?
The different types of bone cells include the following:
Osteoblast. Found within the bone, its function is to form new bone tissue.
Osteoclast. A very large cell formed in bone marrow, its function is to absorb and remove unwanted tissue.
Osteocyte. Found within the bone, its function is to help maintain bone as living tissue.
Hematopoietic. Found in bone marrow, its function is to produce red blood cells, white blood cells, and platelets.
Fat cells are also found within the bone marrow.
Because of the complexities of a bone’s function, from providing strength and support for the body, to serving as a site for development and storage of blood cells, there are many disorders and diseases that can affect bone.
The vertebral column, also called the backbone, is made up of 33 vertebrae that are separated by spongy disks and classified into 4 distinct areas. The cervical area consists of 7 bony parts in the neck; the thoracic spine consists of 12 bony parts in the back area; the lumbar spine consists of 5 bony segments in the lower back area; 5 sacral* bones; and 4 coccygeal* bones (the number of coccygeal bones can vary from 5 to 3).
(* By adulthood, the 5 sacral vertebrae fuse to form 1 bone, and the 4 coccygeal vertebrae fuse to form 1 bone.)