Fracture healing and remodelling

Question 1

Outline the steps of fracture healing

Answer 1

1. Fracture hematoma formation
    When a bone breaks, blood vessels surrounding the bone and periosteum are damaged, causing blood to haemorrhage into the surrounding areas
    Within 6-8 hours a fracture hematoma forms – a pool of blood at the site of the fracture
    The hematoma formation causes the blood vessels to constrict and stop bleeding
    In response to hematoma, blood cells degenerate and die off, causing inflammation and swelling around the injury
2. Fibrocartilaginous callus formation
    Fibroblasts from the periosteum invade the fracture site and replicate, producing collagen fibres. They intersperse with blood vessels and inflammatory cells to form granulation tissue.
    The formation of granulation tissue leads to the development of a Fibrocartilaginous callus, which is made of collagen fibres and cartilage.
    The callus helps to bridge the 2 ends of the broken bone together
3. Body callus formation
    In areas surrounding the fracture with healthy vascular tissue, osteoblasts are formed and migrate towards the Fibrocartilaginous callus
    Spongy bone is laid along the marrow cavity inside the bone as well as on the bones outer edges, which joins the broken ends of the bone together
    Eventually the areas of fibrocartilage are converted into spongy bone, creating a bony callus.
4. Bone remodelling (within fracture repair – see later for generalise bone remodelling)
    Osteoclast activity increases removing any dead or damaged cells surrounding the bony callus
    Spongy bone is replaced with compact bone along the outside surface, creating a strong thick area where the fracture once was
    If there are no complications, remodelling will occur successfully and the injury wil heal completely

Question 2

When does bone remodell itself

Answer 2

bone remodels constantly

Question 3

How many years does it take for compact bone to replace itself

Answer 3

10 years

Question 4

How many years does it take for spongy bone to replace itself

Answer 4

3-4 years

Question 5

Outline the steps of bone remodelling

Answer 5

1. Bone resting
    Inactive osteoblast cells called bone lining cells cover all surfaces of the resting bone (also known as quiescent)
    When bone lining cells become activated, they change into an active state, initiating the next step of remodelling
2. Bone resorption
    Bone resorption involves the loss of minerals and collagen fibres from bone tissue due to osteoclast actions
    Osteoclast precursor cells are recruited to the activated surface, where they fuse to form multinucleated osteoclasts
    Here, osteoclasts resorb some bone, creating a groove as they move along the cell surface as they break down the extracellular matrix
    The osteoclast still remains in contact with the bones surface via its ruffled border, which secretes 2 destructible substances: lysosomal enzymes and hydrochloric acid
    Lysosomal enzymes digest the matric and HCA breaks down calcium salts and converts them to a soluble form
    The dissolved materials are transported through the osteoclast cell, along with the products from the digested matrix, and enter the blood via the interstitial fluid
3. Bone reversal
    Occurs once osteoclasts have completed their bone removal
    Mononuclear cells on the cells surface deposit proteoglycan to form a cement line
    Proteoglycan releases growth factors that initiate the bone formation phase of the remodelling cycle
    Osteopregenitor cells (osteoblast precursor cells) are recruited to the area, and differentiate into mature osteoblasts
4. Bone formation
    New bone is formed via bone deposition
    An osteoid (a matrix of minerals and collagen fibres) is added to the newly formed bone cavity by osteoblast action
    Osteoids are laid between an area of un-mineralised bone matrix (called an osteoid seam) and the area of old mineralised bone
5. Bone mineralisation
    Once embedded un the osteoid, osteoblasts become trapped and mature into osteocytes
    The osteoblasts lying on the surface of the newly formed bone become quiescent (are resting), until they bone active again and the cycle repeats itself.

Question 6

Name some minerals effecting bone growth and remodelling

Answer 6

Calcium and phophate are 2 most important

Question 7

How does vitamin c effect bone growth and remodelling

Answer 7

required for the synthesis of collagen - which is required for the regulation of bone growth

Question 8

Why are vitamins important in bone growth and remodelling

Answer 8

Essential for maintaining normal cell growth and developement

Question 9

How does vitamin A effect bone growth and remodelling

Answer 9

Responsible for stimulating osteoblasst activityt

Question 10

How oes vitamin d effect bone growth and remodelling

Answer 10

Increases the absorption of calcium

Question 11

How does human growth hormone effect bone growth and remodelling

Answer 11

hormone stimulates growth, reproduction of cells and regeneration in the body. It is released by pituitary gland and is responsible for the release of the hormone insulin-like growth factor (IGF) which is crucial in bone growth in young children

Question 12

How do IGF’s effect bone growth and remodelling

Answer 12

produced by the liver and bone tissue as an endocrine hormone. They act directly on the epiphyseal plate and along the periosteum, promoting cell division and stimulating osteoblasts

Question 13

How do T3 AND T4 effect bone growth and remodelling

Answer 13

promote bone growth by stimulating the production of osteoblasts during bone ossification and remodeling.

Question 14

Name some factors that effect fracture healing

Answer 14

Age - older people heal slower than the young
Mobility at the fracture site - excess mobility = disturbs the binding of the bony callus
type of fracture
poor nutrition
comorbidities ie. smoking and osteoporosis
type of bone - upper limb heals wuicker than lower limb