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 mobility. There are three types of joints: Fibrous Cartilaginous Synovial

Fibrous: bones connected by fibrous tissue (no movement) Bones of skull Pelvic bones Examples of Fibrous joints

Cartilaginous: bones connected by cartilage (slightly movable) Examples of Cartilaginous joints

Synovial: articulating bone ends are separated by a joint cavity and inside is synovial fluid (allows for more movement) Synovial joints are found in all limbs and allow for various movements. Examples of Synovial joints

There are 6 main types of synovial joints: Plane/gliding joints Hinge joints Pivot/rotating joints Condyloid joints Saddle joints Ball and socket joints

Plane or Gliding Wide range of mostly sideways, gliding movement Examples: Wrist Ankles Spine

Hinge Joint Unaxial movement in one direction (like a door) Flexion/Extension Examples: Knee Elbow

Pivot/Rotating Joints Rotation around an axis Rotation of one bone around another Example: Radioulnar joint (in the forearm) Top of neck

Condyloid Joint Some sideways movements but no rotation Examples: Metacarpals (hand) Carpals (fingers) Jaw

Saddle Joints This type of joint allows for back and forth and side to side motion but limited rotation. Examples: In the thumb

Ball and Socket Joint Uniaxial movements & full rotation Examples: Hip 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: Comminuted Compression Depressed Impacted Spiral Greenstick

Comminuted fractures: Bone breaks in many fragments. Common to sporting accidents

Vertebrae become crushed. Common during falls Compression fractures: Vertebrae become crushed. Common during falls

Depressed fractures: Skull bone is pressed inward, causing a fracture Common to blunt force trauma

Broken bone ends are forced into each other. 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: 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)

Connective tissue cells of various types form a mass of 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 to the area and multiply. Thus the fibrocartilage callus is gradually replaced by one made of spongy bone, known as the bony callus.

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

The end!