Joints and Arthritis

by Robert Tallitsch, PhD | April 21, 2022

Video on joints of the bones including an explanation of synarthrosis and diarthrosis and the difference between osteoarthritis and rheumatoid arthritis!

Written by: Robert Tallitsch, PhD

If you had to define the term “joint” as it applies to the skeletal system what would you write? Well — if you included the word “movement” anywhere within your definition you would be incorrect. This Brain Builder will discuss the anatomy of a synovial joint, provide some examples of a synovial joint, and will follow everything up with a discussion of arthritis.

Arthrology is the study of joints, and a joint is defined as the junction between two or more bones. Joints are classified according to the potential for movement at the joint.

Classification of Joints Based on its Potential for Movement

This classification scheme results in two major classifications of joints.

1. Synarthroses:

In this type of joint, the junction between two or more bones allows for little or no movement at the joint. Further examination of the structure of this type of joint allows for two subclassifications of synarthroses:

Fibrous joints: Here fibrous connective tissue joins the bones of the joint. Examples of a fibrous joint would be the joint between the tibia and fibula of the leg, or the sutural joints between the bones of the cranium.
Cartilaginous joints: Cartilaginous synarthroses are characterized by fibrous cartilage or hyaline cartilage joining the bones of the joint. Two examples are the joints between adjacent vertebral bodies, which are joined by fibrous cartilage, and the joints between ribs and the sternum, which are joined by hyaline cartilage.

2. Diarthroses (Synovial joints):

This type of joint allows for considerable range of motion. This type of joint demonstrates seven anatomical characteristics.

Joint capsule composed of fibrous connective tissue surrounding the joint.
Hyaline cartilage covering the articulating surfaces of the bones of the joint.
Synovial membrane lining the inner surface of the joint capsule.
Secretion of synovial fluid by the synovial membrane. This fluid fills the joint capsule, nourishes, and lubricates the hyaline cartilage covering the articulating surfaces of the bones of the joint.
Presence of localized fibrous connective tissue thickenings of the joint capsule. These thickenings are termed ligaments, and they serve to limit extreme range of motion movements at the joint.
Small blood vessels and capillaries penetrating the joint capsule.
Sensory nerves supplying the ligaments and external layer of the joint capsule with receptors for proprioception and pain.

Types of Movements at a Joint

Not all synovial joints are able to move in all three axial planes. Some joints, termed uniaxial joints, are able to move only in one axial plane, such as the humeroradial joint (elbow). Other joints (biaxial joints) are able to move in two axial planes, such as the carpometacarpal joint of the thumb. Finally, some joints are multiaxial, and are able to move in all three axial planes, such as the glenohumeral (shoulder) joint.

Now that we know that synovial joints are freely movable joints, it is important to understand the types of movements that may occur at this type of joint.

Flexion and Extension

Flexion: A movement that decreases the angle at a joint.
Extension: A movement that increases the angle at a joint.

Abduction and Adduction

Abduction: Moving a part of the body away from the midline.
Adduction: Moving a part of the body towards the midline.

Medial and Lateral Rotation

Medial Rotation: Rotating a part of the body towards the median plane.
Lateral Rotation: Rotating a part of the body away from the median plane.

Eversion and Inversion

Eversion: Moving the sole of the foot away from the median plane.
Inversion: Moving the sole of the foot towards the median plane.

Arthritis

Arthritis is the presence of chronic swelling or inflammation at one or more joints. The main symptoms of arthritis are joint pain and stiffness, which typically increase with age.

The two most common forms of arthritis are:

Osteoarthritis
Rheumatoid Arthritis

Osteoarthritis, which typically involves the hips, knees, or hands, is the most common form of arthritis. With osteoarthritis the hyaline cartilage covering the articulating surfaces of the bones breaks down, affecting the deeper bone tissue. These changes progressively worsen slowly over the years.

Common causes for osteoarthritis are:

obesity
gender, with women over 50 affected more frequently than men
age
joint injury or overuse
genetics, in that people with family members with osteoarthritis are more likely to develop osteoarthritis later in life.

Rheumatoid arthritis is an autoimmune disease in which the immune system attacks the synovial membrane of the joints, ultimately causing bone destruction and deformation of the joint. This form of arthritis typically affects multiple joints simultaneously, most commonly involving the hands, wrists, and knees.

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Key Terms:

Diarthrosis - A type of joint that allows a considerable range of motion.

Synarthrosis - A type of joint that allows for little or no range of motion at the joint.

Synovial membrane - The membrane that lines the capsule of a diarthrosis. This membrane secretes synovial fluid.

Eversion - Moving the sole of the foot away from the midline of the body.

Flexion - A movement that decreases the angle of the joint.

Medial rotation - Rotating a part of the body towards the midline.

Biaxial joint - A joint that is able to move in two planar axes of the body.

Rheumatoid arthritis - An autoimmune form of arthritis that attacks the synovial membrane of joints, ultimately causing bone destruction and deformation of a joint.

Questions:

A synarthrosis joint allows for little or no range of motion at the joint. This classification of joints may be further subdivided into two subcategories. What are these two subcategories of synarthroses?
A: Fibrous and cartilaginous joints
True or False? Osteoarthritis is an autoimmune disease.
A: False
True or False? A synarthrosis possesses a synovial membrane.
A: False
True or False? All synovial joints move in all three axial planes of the body.
A: False
Define a joint as it pertains to the skeletal system.
A: The junction between two or more bones.
True or False? Medial rotation is moving a part of the body closer to the midline.
A: False. Medial rotation involves rotating a part of the body towards the midline.
True or False? Women over the age of 50 are affected by osteoarthritis more commonly than men.
A: True
True or False? Osteoarthritis is the most common form of arthritis.
A: True
Explain the effect(s) of osteoarthritis.
A: In osteoarthritis the hyaline cartilage covering the articulating surfaces of the bones breaks down, affecting the deeper bone tissue.
True or False? An individual that is clinically obese is more likely to develop rheumatoid arthritis than an individual that is not clinically obese.
A: False. The statement applies to osteoarthritis.

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