Bone and Fracture Repair Flashcards
What is the name of the process to lengthen long bones?
Endochondrial ossification
How do most flat bones develop?
Intra-membranous ossification
Name some flat bones that develop by intra-membranous ossification:
Skull, clavicle, scapula, pelvic bones
Stages of intra-membranous ossification:
- Small cluster of mesenchymal stem cells form a cluster of cells (nidus)
- MSCs become osteoprogenitor cells
- Osteoprogenitor cells become osteoblasts and lay down an extracellular matrix (osteoid)
- Osteoid mineralises to form rudimentary bone tissue spicules
- The spicules join to form trabeculae
- These merge to form woven bone and is replaced by lamellae of nature compact bone
Which cells develop into osteoprogenitor cells?
Mesenchymal stem cells
Which cells become osteoblasts?
Osteoprogenitor cells
Which cells lay down the extracellular matrix (osteoid)?
Osteoblasts
Which type of collagen did in the osteoid?
Type I
Which cells remodel the bony spicule once it has formed?
Osteoblasts, osteocytes, osteoclasts
Describe cancellous bone:
Network of fine bony columns, spaces filled with marrow.
Which canals carry blood vessels in bone?
Haversian (vertical) and Volkmann’s canals (horizontal)
How are osteocytes arranged in immature bone?
Randomly
How are osteocytes arranged in mature bone?
In the concentric lamellae of osteons
How does a cutting cone work?
Osteoclasts release H ions and lysosomal enzymes to tunnel through bone.
What factors allow bone to resist fracture?
High tensile strength and compressive strength.
Degree of flexibility
Four stages of bone repair overview:
- Blood clot forms
- Procallus of granulation tissue replaced by fibrocartilagenous callus
- Endochondrial and intramembranous ossifications make bony callus of spongy bone
- Cancellous bone replaced by compact cortical bone
Haematoma formation steps:
Blood vessels in bone break
Clotted blood (Haematoma) forms
Swelling occurs
Phagocytic and osteoclasts removed damaged tissue
Macrophages remove clot
Fibrocartilaginous callus formation steps:
New blood vessels infiltrate the haematoma
Procallus of granulation tissue forms
Fibroblasts make collagen fibres that span the break
Fibrocartilaginous matrix splints the bone
Osteoblasts form spongy/trabecular bone
Bony callus formation steps:
Trabeculae develop as former fibrocartilaginous callus is converted to hard bony callus
Endochondrial ossification replaces all cartilage with cancellous bone
Bone remodelling steps:
Material bulging is removed by osteoclasts
Final shape is same as pervious due to the same mechanical stressors
What is osteoporosis?
A metabolic bone disease in which mineralised bone is decreased in mass
At what age range does bone mass peak?
25-35
What are the most common forms of osteoporosis?
Primary (type 1 and 2)
When does type I osteoporosis occur?
Postmenopausal women. Increase in osteoclast number due to oestrogen withdrawal
