Joints

Joints, also known as articulations, are sites where two or more bones meet.
Functions of joints include providing mobility to the skeleton and holding the skeleton together.

Based on the material that binds the joints and whether a cavity is present.
Three types of structural joints:
- Fibrous Joints: Connected by dense fibrous connective tissue, no joint cavity, mostly immovable.
- Cartilaginous Joints: Connected by cartilage, no joint cavity, not highly movable.
- Synovial Joints: Separated by a fluid-filled joint cavity, all are freely movable.

Based on the movement allowed by the joint.
Three types of functional joints:
- Synarthroses: Immovable joints.
- Amphiarthroses: Slightly movable joints.
- Diarthroses: Freely movable joints.

Fibrous joints are where bones are joined by dense fibrous connective tissue.
No joint cavity is present, and most are immovable, depending on the length of connective tissue fibers.
Three types of fibrous joints:
- Sutures
- Syndesmoses
- Gomphoses

Rigid, interlocking joints found in the skull.
Allow for growth during youth, containing short connective tissue fibers that permit expansion.
In mid-adulthood, sutures ossify and fuse, becoming immovable joints that protect the brain.
Closed, immovable sutures are referred to as synostoses.

Bones are connected by ligaments, which are bands of fibrous tissue.
Movement varies based on fiber length;
- Short fibers allow little to no movement (e.g., inferior tibiofibular joint).
- Longer fibers enable a larger range of movement (e.g., interosseous membrane connecting radius and ulna).

Peg-in-socket joints; the only examples are the connections of teeth in alveolar sockets.
The fibrous connection is provided by the periodontal ligament, holding the tooth in place.

Cartilaginous joints unite bones through cartilage and have no joint cavity.
These joints are not highly movable and consist of two types:
- Synchondroses
- Symphyses

A bar or plate of hyaline cartilage unites the bones.
Almost all are synarthrotic (immovable).
Examples include the temporary epiphyseal plate joints which become synostoses after closure and the cartilage of the 1st rib with the manubrium of the sternum.

Fibrocartilage unites bone in symphysis joints, with hyaline cartilage also present as articular cartilage on bony surfaces.
Symphyses are strong and amphiarthrotic (slightly movable) joints.
Examples include intervertebral joints and the pubic symphysis.

Synovial joints are characterized by bones separated by a fluid-filled joint cavity.
All synovial joints are diarthrotic (freely movable) and include almost all limb joints.
Six general features:
- Articular cartilage: Covers the ends of bones.
- Joint (synovial) cavity: Space filled with synovial fluid.
- Articular (joint) capsule: Two layers, external fibrous layer and inner synovial membrane.
- Synovial fluid: A viscous, slippery filtrate of plasma and hyaluronic acid.
- Reinforcing ligaments: Various types exist, enhancing joint stability.
- Nerves and blood vessels: Supply the joint with necessary nutrients and sensory information.

Bursae are bags of synovial fluid acting as lubricating “ball bearings”; not strictly part of synovial joints but closely related.
Tendon sheaths are elongated bursae that completely surround tendons subjected to friction.

Three factors determine joint stability to prevent dislocations:
- Shape of articular surface: Minor role; shallow surfaces are less stable than ball-and-socket types.
- Ligament number and location: A limited role; the more ligaments, the stronger the joint.
- Muscle tone: Keeps tendons taut as they cross joints, significantly reinforcing shoulder and knee joints and arches of the foot.

Located at the junction of the skull and the mandible, the TMJ allows two types of movements:
- Hinge Movement: Depression and elevation of the mandible.
- Gliding Movement: Side-to-side (lateral excursion), facilitating grinding of teeth.
The TMJ is noted as one of the most easily dislocated joints in the body.
Homeostatic Imbalance Symptoms:
- Ear and facial pain, tender muscles, popping sounds when opening the mouth, joint stiffness.
- Usually caused by teeth grinding but can also be due to jaw trauma or poor occlusion of teeth.
Treatment for Grinding Teeth: May include using a bite plate; relaxing the jaw muscles can also help.

The elbow joint is formed where the humerus articulates with the radius and ulna.
It is primarily a hinge joint, formed by the trochlear notch of the ulna articulating with the trochlea of the humerus.
Allows only flexion and extension.
The anular ligament surrounds the head of the radius, supporting the joint structure.
Two capsular ligaments restrict side-to-side movement:
- Ulnar Collateral Ligament
- Radial Collateral Ligament

A condition where the annular ligament surrounding the head of the radius allows dislocation, often occurring in young children during rough play or abuse.

Reinforcing ligaments include stabilizing ligaments to the ilium, ischium, and pubis, as well as the ligament of the head of the femur.
The ligament of the head of the femur is slack during most movements, thus not critical for stabilization, but contains an artery supplying the head of the femur.
The greatest stability is derived from the deep ball-and-socket joint formed by the acetabulum and the acetabular labrum, which is cartilage encasing the head of the femur.

The knee joint consists of several ligaments:
- Patellar Ligament
- Tibial Collateral Ligament (MCL)
- Fibular Collateral Ligament (LCL)
- Anterior Cruciate Ligament (ACL)
- Posterior Cruciate Ligament (PCL)
Torn ACL is often associated with the Unhappy Triad: a common injury where the tibial collateral ligament, medial meniscus, and anterior cruciate ligament are all torn.

Sprains: When ligaments are stretched or torn. Treatment usually involves allowing time for healing, immobilization, or possible surgical intervention like stitching ends together or grafting.
Dislocations (Luxations): Occur when bones are forced out of alignment, often accompanied by sprains, inflammation, and restricted movement.
Tendonitis: An inflammation of tendon sheaths, typically resulting from overuse.

Refers to over 100 different types of inflammatory or degenerative diseases that damage joints, recognized as the most widespread crippling disease in the U.S.
Symptoms include pain, stiffness, and swelling in the joints.
Types of arthritis can be categorized into acute forms (caused by bacteria, treated with antibiotics) and chronic forms, which include:
- Osteoarthritis
- Rheumatoid Arthritis
- Gouty Arthritis.