30.4A: Development of Joints
Movable joints are formed at the intersection of bones and are covered by cartilage, which allows them to move freely.
- Explain the development of joints
Key Points
- Cartilage is a flexible material found between joints, initially formed by chondrification (also known as chondrogenesis).
- Following the initial chondrification, cartilage growth consists mostly of the development of immature cartilage to a more mature state.
- Remodeling of cartilage is predominantly affected by changes to the collagen matrix, which responds to tensile and compressive forces.
- Cartilage growth generally refers to collagen matrix deposition, but can include both growth and remodeling of the extracellular matrix.
- The pressure epiphyses, which take the weight of the long bones, include the head of the femur at the hip joint and the head of the humerus at the shoulder joint.
Key Terms
- Chondrogenesis : The process by which cartilage is developed.
- cartilage : A type of dense, non-vascular connective tissue, usually found at the end of joints, the rib cage, the ear, the nose, in the throat and between intervertebral disks.
- Pressure epiphysis : The region of the long bone that forms the joint.
EXAMPLES
Knowledge of joint growth and development is useful in forensic contexts. For instance, if a skeleton is found and the epiphyses are missing or unfused to the diaphyses, then the examiner knows that the skeleton is that of a juvenile or young adult: if female, probably under age 18; if male, probably under age 25. Other clues, such as dental eruption, can refine the age estimate.
Epiphyseal Plate : Image shows the location of the epiphyseal plates (or lines) and the articular surfaces of long bones.
Articular cartilage is a flexible material found between bones at movable joints. Chondrification (also known as chondrogenesis) is the process by which cartilage is formed from condensed mesenchyme tissue, which differentiates into chondroblasts and begins secreting the molecules that form the extracellular matrix. Following the initial chondrification that occurs during embryogenesis, cartilage growth consists mostly of the development of immature cartilage to a more mature state.
Cell division within cartilage occurs very slowly, so growth is not based on a mass increase of the cartilage itself. Articular cartilage function is dependent on the molecular composition of its extracellular matrix (ECM), which consists mainly of proteoglycans and collagens. Articular cartilage is maintained by embedded chondrocytes that comprise only 1% of the cartilage volume. Remodeling of cartilage is predominantly affected by changes to the collagen matrix, which responds to tensile and compressive forces. Cartilage growth generally refers to matrix deposition, but can include both growth and remodeling of the extracellular matrix.
The epiphysis is the rounded end of a long bone, at its joint with adjacent bone(s). Between the epiphysis and diaphysis (the long midsection of the long bone) lies the metaphysis, including the epiphyseal plate (growth plate). At the joint, the epiphysis is covered with articular cartilage; below that covering is a zone similar to the epiphyseal plate, known as subchondral bone. The region of the long bone that forms the joint is called pressure epiphysis. For example, the head of the femur (which is a part of the hip joint complex) is a pressure epiphyses. These epiphyses assist in transmitting the weight of the human body and are the regions of the bone that are under pressure during movement or locomotione. Another example of pressure epiphysis is the head of humorus, part of the shoulder complex.
Hyaline Cartilage : Histological image of the hyaline cartilage which coats the articular surfaces of joints.