Bone Fractures and Bone Remodeling

Wolf's Law

a bone grows or remodels in response to the forces or demands placed upon it

Hematoma formation

a mass of clotted blood forms at fractured site, site becomes swollen, painful, and inflamed

Displaced fracture

bone ends are out of normal alignment

Simple fracture (closed)

bone ends do not penetrate the skin

Compound fracture (open)

bone ends penetrate the skin

Non-Displaced fracture

bone ends retain normal position

Comminuted fracture

bone fragments into three or more pieces; common in the elderly

Complete fracture

bone is broken all the way through

Compression fracture

bone is crushed; common in porous bone (vertebrae, wrist)

Incomplete fracture

bone is not broken all the way through

Depressed fracture

broken bone portion pressed inward; typical skull fracture

Epiphyseal fracture

epiphysis separates from diaphysis along epiphyseal line (along growth plate); occurs when cartilage cells are dying

Bone homeostasis

every week we recycle 5-7% of our bone mass, spongy bone is replaced every 3-4 years, compact bone is replaced approximately every 10 years

Bone remodeling

excess material on bone shaft exterior and its the medullary canal is removed, compact bone is laid down the reconstruct shaft walls

Bony callus formation

fibrocartilaginous callus converts into a bony (hard) callus, bone callus begins 3-4 weeks after injury, and continues to firm union is formed 2-3 months later

Fibrocartilage callus

forms when osteoblasts and fibroblasts migrate to the fracture and begin reconstructing the bone

Stages of healing a bone fracture

hematoma formation, fibrocartilage callus, bony callus formation

Greenstick fracture

incomplete fracture where one side of the bone breaks and the other side bends; common in children

Bone fractures are classified by:

position of bone ends after fracture, the completeness of the break, the orientation of the bone to the long axis, whether or not the bones ends penetrate the skin

Spiral fracture

ragged break when bone is excessively twisted; common sports injury

Hormonal mechanism

rising blood Ca2+ levels trigger the thyroid to release calcitonon, falling Ca2+ levels signal the parathyriod glands to release PTH

PTH

signals osteoclasts to degrade bone matrix and release Ca2+ into the blood

Calcitonin

simulates calcium salt deposit in bones

Linear fracture

the fracture is parallel to the long axis of the bone

Transverse fracture

the fracture is perpendicular to the long axis of the bone