Skeletal System Lecture

Day 2: Joints, Fractures, and the Healing Process

Joints hold bones together, giving stability, yet at the same time, give our skeleton mobililty.

There are three types of joints:•Fibrous: bones connected by fibrous tissue (no movement)

•Cartilaginous: bones connected by cartilage (slightly movable)

•Synovial: articulating bone ends are separated by a joint cavity and inside is synovial fluid (allows for more movement)

Examples of Fibrous joints

Bones of skullPelvic bones

Examples of Cartilaginous joints

Examples of Synovial joints

Synovial joints are found in all limbs and allow for various movements.

There are 6 main types of synovial joints:a) Plane joints (gliding movements i.e. in wrist)

b) Hinge joints (uniaxial movement i.e. in elbow)

c) Pivot joints (rotation movements i.e. radioulnar joint)

d) Condyloid joints (some sideways movements i.e. in metacarpels)

e) Saddle joints (slight rotation & sideways movements i.e. in thumb)

f) Ball and socket joints (uniaxial movements & full rotation i.e. in hip and shoulder)

Bone Fractures & Healing

Although bones are strong, they are susceptible to breaks (fractures) all throughout life.

The most common times in life for fractures to occur are during youth (due to excessive activity, sports, and bad judgement) and in the elderly (due to bone thinning and weakening, often due to osteoporosis).

Six most common types of fractures:

1) Comminuted2) Compression3) Depressed4) Impacted5) Spiral6) Greenstick

Comminuted fractures: bone breaks in many fragments.

Compression fractures: bone is crushed.

Depressed fractures: bone is pressed inward.

Impacted fractures: broken bone ends are forced into each other.

Spiral fractures: ragged break occurs during twisting.

Greenstick fractures: bone breaks incompletely (like a young twig).

The process of fracture/bone healing:

1) A hematoma is formed. Blood vessels are ruptured when bone breaks. As a result, a blood-filled swelling forms. Bone cells are deprived of nutrition and die.

hematoma (swelling)

2) The break is splinted by a fibrocartilage callus. Connective tissue cells of various types form a mass of repair tissue called fibrocartilage callus (containing cartilage matrix, bony matrix, and collagen fibers) which act to “splint” the broken bone, closing the gap.

3) A bony callus is formed. Osteoblasts and osteoclasts migrate tothe area and multiply. Thus the fibrocartilage callus is graduallyreplaced by one made of spongy bone, known as the bony callus.

4) Lastly, bone remodeling occurs. Over the next few weeksto months, the bony callus is remodeled in response to mechanicalstresses placed on it, so that it forms a strong permanent (bone) patch at the fracture site.

The end!