Joint Development

Development of Joints

Movable joints are formed at the intersection of bones and are covered by cartilage, which allows them to move freely.

Learning Objectives

Explain the development of joints

Key Takeaways

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.

This diagram of a long bone indicates the epiphysis, diaphysis, articular cartilage, epiphyseal line, spongy bone, medullary cavity, nutrient foramen, endosteum, and periosteum.

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.

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Hyaline Cartilage: Histological image of the hyaline cartilage which coats the articular surfaces of joints.

Joints and Aging

Aging is a common cause of chronic joint pain, as wear and tear from years of use results in inflammation and osteoarthritis.

Learning Objectives

Describe the effects of aging on joints

Key Takeaways

Key Points

  • As a person ages, the body’s ability to regenerate and repair damage to the joints diminishes, resulting in chronic inflammation. This is one of the most common causes of joint pain.
  • Osteoarthritis, the degenerative inflammation of the joints, is the leading cause of disability in people older than age 55. Osteoarthritis causes the joint’s protective cartilage to erode over time, exposing the bone underneath.
  • Joint injuries become more common with age. Contributing factors include decreased balance and motor control, which can lead to falls, and degeneration of the bone from osteoporosis, which can result in greater damage from small injuries.
  • Heating pads, braces, and physical therapy can fully or partially ease symptoms. Prescription pain medications can also be used to alleviate joint pain. In cases of severe osteoarthritis, surgical joint replacement is often recommended.

Key Terms

  • osteoporosis: A disease in which the bones become extremely porous and are subject to fracture, most common among postmenopausal women.
  • fibromyalgia: Chronic pain, stiffness, and tenderness of the muscles, tendons, and joints.
  • osteoarthritis: A form of arthritis affecting mainly older people, caused by chronic degeneration of the cartilage and synovial membrane of the joints leading to pain and stiffness.

Examples

Analysis of skeletal material from archaeological sites has shown that an individual’s primary activities can be deduced from development of osteoarthritis. For instance, osteoarthritis of the toes, knees, and hips of female skeletons from the site of Abu Hureyra is clear evidence that they spent most of their days grinding flour on stone querns while kneeling on the ground.

Joint pain can be caused by a variety of health problems, from arthritis to fibromyalgia. Many temporary conditions, such as a virus or the flu, can also cause joint pain. Joint pain occurs in all age groups, but becomes more common with age as wear and tear on the joints from years of use results in inflammation and osteoarthritis. Older adults are also more prone to injuries that can cause joint pain.

Inflammation

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Osteoarthritis: X-ray image of osteoarthritis of the big toe. The red box shows the normal joint.

One of the most common causes of joint pain, inflammation is the body’s response to pain, infection, and other threats. As the joints become inflamed, their regeneration and repair process slows, making them weaker. As a person ages, the body’s ability to regenerate and repair damage to the joints diminishes, resulting in chronic inflammation.

Osteoarthritis

Osteoarthritis, the degenerative inflammation of the joints, is the leading cause of disability in people older than age 55. Osteoarthritis is typically caused by mechanical stress on the joints, resulting in chronic inflammation leading to the loss of cartilage. With this condition, the protective cartilage of the joint erodes over time, exposing the bone underneath. The bones of the joint then rub together during movement, causing pain and stiffness. As a result of decreased movement secondary to pain, regional muscles may atrophy and ligaments become more lax.

Injuries

Sprains, bruising, broken bones, and many other temporary conditions can result in joint pain. Many of these injuries may not be to the joints themselves, but to their surrounding cartilage and ligaments. Joint injuries become more common with age as decreased balance and motor control lead to falls. In addition, bone degeneration caused by osteoporosis can result in greater damage from small injuries.

Treatment Options

Many remedies for joint pain are available. Heating pads, braces, and physical therapy can often minimize symptoms. Prescription pain medications can also be used to alleviate joint pain. In cases of severe osteoarthritis, surgical joint replacement is often recommended.

Arthroplasty

Arthroplasty is a surgical procedure in which an arthritic or dysfunctional joint surface is replaced or repaired.

Learning Objectives

Describe the purpose and process of arthroplasty

Key Takeaways

Key Points

  • Arthroplasty can include removing or remodeling damaged surfaces and replacing them with silicone.
  • Prosthetic replacements of hip and knee joints have become common arthroplastic surgeries.
  • Wear of the bearing surfaces of components is an issue of joint replacement that can lead to damage to surrounding bone and contribute to eventual failure of the implant.

Key Terms

  • arthroplasty: The surgical repair of a joint, or creation of an artificial joint, such as a hip replacement.

Examples

Hip fractures from falls are common among the elderly. Partial arthroplasty (replacing the hip socket and femur head and neck) may be done to relieve pain and improve mobility. However, as with all surgeries, complications can occur that for the elderly may prevent life-threatening challenges. Special care must be made when deciding to proceed with arthroplasty in the elderly patient.

Arthroplasty (literally “surgical repair of joint”) is an orthopedic surgical procedure in which the arthritic or dysfunctional joint surface is replaced and/or the joint is remodeled or realigned.

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Planning Arthroplasty: CAD-assisted planning for a total hip arthroplasty.

Common types of arthroplasty include:

  • Interpositional arthroplasty with interposition of skin, muscle, or tendon to keep inflammatory surfaces apart.
  • Excisional arthroplasty in which the joint surface and bone are removed, leaving scar tissue to fill in the gap.

Other forms of arthroplasty include resectional arthroplasty, resurfacing arthroplasty, mold arthroplasty, cup arthroplasty, and silicone replacement arthroplasty, among others. Osteotomy to restore or modify joint congruity is also an arthroplasty.

For the last 45 years, the most successful and common form of arthroplasty has been the surgical replacement of degenerated joint surfaces with prostheses. For example, a hip joint that is affected by osteoarthritis may be replaced entirely (total hip arthroplasty) with a prosthetic hip. This would involve replacing both the acetabulum (hip socket) and the head and neck of the femur. The purpose of this procedure is to relieve pain, restore range of motion, and improve walking ability, thus leading to the improvement of muscle strength.

One of the main problems with joint replacements is wear of the bearing surfaces of components. This can lead to damage to surrounding bone and contribute to eventual failure of the implant. Use of alternative bearing surfaces has increased in recent years, particularly in younger patients, in an attempt to improve the wear characteristics of joint replacement components. These include ceramics and all-metal implants (as opposed to the original metal-on-plastic). The plastic (actually ultra high-molecular-weight polyethylene) can also be altered in ways that may improve durability.