Fracture Repair

Question 1

Describe Step 1

Answer 1

Blood vessels in bone and periosteum break.

Question 2

Describe Step 2

Answer 2

Haematoma forms in which a procallus of granulation tissue arises. Fibroblasts produce collagen fibres that span the break. Others differentiate into chondroblasts that give rise to a sleeve of hyaline cartilage.

Question 3

Describe Step 3

Answer 3

Bone cells at the fracture edge die as there is no blood supply. Swelling and inflammation occur.

Question 4

Describe Step 4

Answer 4

Phagocytic cells and osteoclasts begin to remove dead and damaged tissue. Macrophages will eventually remove the blood clot.

Question 5

Describe Step 5

Answer 5

Centrally, osteoblasts from the nearby periosteum and endosteum, (and multipotent cells from the bone marrow) invade the fracture site and begin bone reconstruction by forming spongy bone. Within a week, new bone trabeculae begin to appear in the fibrocartilaginous callus.

Question 6

Describe Step 6

Answer 6

Trabeculae develop as the fibrocartilaginous callus is converted into cancellous bone. Bone callus formation continues for about two months until a very firm union is formed.

Question 7

Describe Step 7

Answer 7

Intramembranous ossification also produces new cancellous bone in the area. The callus of spongy, cancellous bone is remodelled into compact bone in the cortical region. This process occurs for several months.

Question 8

Describe Step 8

Answer 8

The material bulging from the outside of the bone, and inwards, into the medullary cavity, is removed by osteoclasts.

Question 9

Why is the final shape of the remodelled area the same as that of the original unbroken bone?

Answer 9

it responds to the same set of mechanical stressors.