The enarthrosis or spherical joints are multi-axial synovial joints. They are lubricated by a transparent and sticky fluid called synovium.
Also called spheroidal joints, the spherical joints are formed by the rounded or “ball-shaped” head of a bone that fits into the cup-like cavity of another bone.
The articulated bone adapts to the cavity and allows the distal bone to move. The joints of the hip and shoulder are examples of the spherical joint.
Key terms in enarthrosis
- Shaft/axes: Central structure on which something rotates or is arranged. The cup-shaped design of the spherical joint is the axis where the distal bone rotates.
- Dysplasia: Dislocation of a bone from its proper place. The displacement of the hip or shoulder is two of the most well-known types of dysplasia.
- Multiaxial: Having more than one axis. The ball joint has at least three axes on which it rotates.
- Synovial fluid: It is a transparent and viscous fluid found in synovial joints. Lubricates the ball joint for more effortless movement.
The function of the enartrosis and types
The purpose of the joints is to provide movement for the body. Different types of joints move in different ways.
The spherical joint is completely mobile under the control of the muscles, ligaments, and tendons. The ends of the bones are covered with hard cartilage and are lined with the synovial membrane.
Each joint contains a small amount of synovial fluid that lubricates it providing protection for the spherical joint and allowing movement without tension.
The ball joint provides rolling and rotating movements. The articulated bone is received in the cavity of another bone, which allows the distal bone to move around three main axes with a common center.
The joint has to stabilize ligaments that limit the directions and the degree to which the bones can move. However, the spherical joint is the most mobile of the body.
Role in human health
The spherical joints are the most mobile and intricate of all the joints; they are also the most prone to diseases and prone to require medical intervention.
Hip or shoulder replacements are common forms of surgical intervention that restore the patient’s quality of life by replacing the worn joints of the ball and socket with prostheses.
Common diseases and disorders
Many disorders and diseases can affect the synovial joints, making the spherical joint vulnerable to pain and discomfort.
Degenerative or inflammatory diseases, conditions that affect the membranes that surround the joints, congenital and generalized disorders, dislocations, and fractures can cause spherical joint damage.
Arthritis: It is one of the conditions that cause pain and dysfunction in the spherical joint. There are several types of arthritis, but osteoarthritis and rheumatoid arthritis are the most common.
Osteoarthritis: It is a degenerative disease that affects the cartilage of the joints and can cause inflammation in the tissues surrounding the joint or the affected joints.
Degeneration is commonly thought to be caused by stress on the joints or by injuries to the joint lining.
Osteoarthritis can affect all joints, but it is usually found in the fingers, feet, hips, spine, and knees.
It causes stiffness and pain in the joints. The symptoms of osteoarthritis can be treated, but the disease is irreversible.
Rheumatoid arthritis is an inflammatory disease that affects the muscles and linings of the cartilage membrane and joints.
The most commonly affected areas are the hands, hips, knees, legs, and joints. Symptoms include low fever, stiffness in the morning, and redness, pain, warmth, and tenderness in the affected joints.
Rheumatoid arthritis can cause paralyzing pains and deformities in the hands and causes painful swelling of the joints.
Hip dysplasia is a dislocation of the hip joint that can be caused by a congenital condition or by accident.
Dysplasia occurs when the femur does not fit properly or comes out of the cup-shaped socket in the hip bone. If a congenital condition causes hip dysplasia, the acetabulum is too shallow to support the head of the femur.