9.2 & 9.3
9.2 Fibrous Joints
Learning Objectives:
Describe the structural features of fibrous joints.
Distinguish between suture, syndesmosis, and gomphosis.
Provide examples of each type of fibrous joint.
Definition:
A fibrous joint is a type of joint where adjacent bones are directly connected to each other by fibrous connective tissue, meaning there is no joint cavity present between them.
The gap between the bones can be either narrow or wide.
Types of Fibrous Joints:
Suture:
A suture is a narrow fibrous joint found between most bones of the skull.
The fibrous connective tissue in sutures binds or sews the adjacent skull bones together, contributing to protecting the brain and forming the face.
In adults, the skull bones are closely opposed, and fibrous connective tissue fills the narrow gaps between the bones.
Functionally classified as a synarthrosis, though some sutures may allow slight movement between cranial bones.
In newborns, wider areas of connective tissue known as fontanelles are present, providing flexibility during birth and allowing for rapid growth of the skull and brain.
Fontanelles decrease in width within the first year after birth.
Once the connective tissue reduces to a narrow layer, joints become sutures, while some sutures may ossify, leading to synostosis (fusion of bones).
Example: The frontal and maxillary bones at birth consist of right and left halves connected by sutures that fuse by the eighth year.
Syndesmosis:
A syndesmosis is characterized by two parallel bones being united by fibrous connective tissue.
The gap between the bones may be narrow with ligaments or wider filled by an interosseous membrane.
Examples:
Between the radius and ulna in the forearm (interosseous membrane).
Between the tibia and fibula in the leg (also united by an interosseous membrane).
A variant, the distal tibiofibular joint, has no cartilage on the articulating surfaces, and the tension is maintained by fibrous connective tissue and ligaments on both anterior and posterior aspects, forming a tibiofibular syndesmosis.
Classified as an amphiarthrosis due to limited movement allowed.
Provides strength during weight-bearing activities and allows rotation of the radius for forearm movement.
Damage to syndesmosis can result in pain and instability of the bones.
Gomphosis:
A gomphosis is a specialized fibrous joint that anchors the root of a tooth into its bony socket in either the maxilla (upper jaw) or mandible (lower jaw).
Known as a peg-and-socket joint.
Numerous short bands of dense connective tissue known as periodontal ligaments span between the bony walls of the socket and the root of the tooth.
Functionally classified as a synarthrosis due to the immobility of the joint.
9.3 Cartilaginous Joints
Learning Objectives:
Describe the structural features of cartilaginous joints.
Distinguish between synchondrosis and symphysis.
Provide examples of each type of cartilaginous joint.
Definition:
At cartilaginous joints, adjacent bones are united by cartilage, which is a tough but flexible type of connective tissue that does not involve a joint cavity.
The bones are joined together by either hyaline cartilage or fibrocartilage.
Types of Cartilaginous Joints:
Synchondrosis:
A synchondrosis is a cartilaginous joint where bones are joined by hyaline cartilage.
It can be classified as temporary or permanent.
Temporary Synchondrosis: The epiphyseal plate (growth plate) in long bones allows for growth in length.
Comprises growing hyaline cartilage that unites the diaphysis to the epiphysis of a long bone.
As growth ceases in late teens/early 20s, the epiphyseal plate is replaced with bone, leading to a synostosis.
Permanent Synchondrosis: Examples include the first sternocostal joint and the costal cartilages of the ribs.
Both types are classified as synarthrosis due to the lack of movement between bone and cartilage.
Symphysis:
A symphysis is a cartilaginous joint where bones are joined by fibrocartilage.
Notable for higher ability to resist forces due to thick collagen fibers in fibrocartilage.
Classified as an amphiarthrosis as it allows limited movement.
Examples include the pubic symphysis (between the pubic portions of the hip bones, united by fibrocartilage) and manubriosternal joint (between the manubrium and body of the sternum).
The intervertebral symphyses consist of fibrocartilaginous pads (intervertebral discs) that cushion and unite adjacent vertebrae, allowing movement while providing cushioning during activities like running or jumping.