Musculoskeletal Growth/Injury and Repair - Bone

Question 1

Describe the growth of bone

Answer 1

• Starts out as a hyaline cartilage model
• Primary ossification centre develops within the diaphysis and ossification begins
• Secondary ossification centres at each epiphysis
• Ossification occurs, epiphyseal plate is left between diaphysis and each epiphysis to allow for continued bone growth

Question 2

What are the two types of bone?

Answer 2

• Cortical / compact

- Cancellous / trabecular: spongy bone designed to take load

Question 3

Describe cortical bone: where on long bones does it occur? How is it laid down? What forces does it resist?

Answer 3

Usually occurs at diaphysis

Laid down circumferentially, usually less biologically active bone

Resists bending and torsion forces

Question 4

Describe cancellous bone: where on long bones does it occur? How is it laid down? What forces does it resist?

Answer 4

Usually occurs at metaphysis

Usually the site of longitudinal growth, very biologically active

Resists / absorbs compression forces

Question 5

What is a bone fracture? What is the clinical shorthand sign for a fracture?

Answer 5

• Break in the structural continuity of bone

is the shorthand sign for a fracture in clinical settings

Question 6

What is the unique characteristic of bone fracture healing in regards to general healing of body structures? What are the stages of bone fracture healing?

Answer 6

Bone fractures heal without a scar

1 - inflammation
2 - soft callus
3 - hard callus
4 - bone remodelling

Question 7

Describe stage 1 of bone fracture repair

Answer 7

• formation of haematoma and fibrin clot around the injury
• Infiltration of immune cells, lysosomal enzymes, fibroblasts, mesenchymal cells and osteoprogenitor cells
• Angiogenesis (hypoxia drives macrophages to produce angiogenic factors around injured area)

Question 8

What are some factors that may hinder the progression of stage 1 of fracture repair?

Answer 8

• NSAIDs
• Loss of the haematoma (via open fracture / surgery)
• Extensive tissue damage such as in open fractures (makes sufficient angiogenesis difficult)

Question 9

What is an example of a clinical practice that can accelerate the progression of stage 1 of fracture repair?

Answer 9

Administering platelet concentrates (centrifuged blood) can facilitate the first stage by providing hormones:

• platelet derived growth factor, transforming growth factor beta, IGF, VEGF
• Often used when the initial fibrin clot has been lost

Question 10

How long does stage 1 of fracture repair last?

Answer 10

Inflammatory stage lasts 10-14 days

Question 11

What is stage 2 of fracture repair? What characterizes this stage?

Answer 11

Soft callus stage:

• Stage is characterized by the laying down of collagen fibres by the fibroblasts
• Stage lasts until the bony fragments are united by cartilage or fibrous tissue
• Provides some stability to fracture, there is a continued increase in vascularity, but the bone is still flimsy

Question 12

What can be done to facilitate stage 2 of fracture repair?

Answer 12

• If haematoma was compromised and there is a lack of cartilage, surgeons can place DMB (demineralized bone matrix) in the fracture as a substitute for endogenous cartilage
• Surgeons can also place bone grafts or bone substitutes into the fracture and skip the cartilaginous phase

Question 13

What is the gold standard choice of material for bone grafts? What are some complications associated with this?

Answer 13

Autogenous cancellous bone graft: take some of the persons own cancellous bone to place into the fracture. Is very osteoconductive and osteoinductive

• Have to injure a bit of the persons own bone to obtain the cancellous bone for the graft

Question 14

What is osteoconduction? What is osteoinduction?

Answer 14

• Placing a hard material within a fracture to act as a base for bone to grow along
• The process of inducing osteogenesis

Question 15

What is allograft bone? Uses?

Answer 15

• It is bone taken from a donor or cadaver for insertion into a patient
• Has good osteoconductive properties but isn’t very osteoinductive. Gets replaced by new bone as it grows

Question 16

What is stage 3 of fracture repair? What characterizes this stage?

Answer 16

Hard callus stage

• Endochondral bone formation (replace cartilage with bone)
• Woven bone replaces cartilage, woven bone can be loaded in any direction and will adapt according to Wolff’s law

Question 17

What is stage 4 of fracture repair? What characterizes this stage?

Answer 17

Bone remodelling stage

• Woven bone is converted to lamellar bone, structure of the bone is remodelled according to Wolff’s law
• In children there is full recovery of bone, in adults there will always remain some swelling or sign of injury

Question 18

How does strain on a fracture during healing affect the healing of that bone?

Answer 18

• If strain is too low the mechanical induction of tissue differentiation fails
• If strain is too high the cartilaginous matrix never progresses to bone formation
• Need a bit of strain but not too much

Question 19

What is delayed union?

Answer 19

Failure of a fracture to heal within the expected time

Question 20

What can cause delayed union?

Answer 20

• High energy injury
• distraction (?)
• instability
• Infection
• Steroids / immunosuppressants
• Smoking / warfarin / NSAIDs / ciprofloxacin

Question 21

What are some interventions that may be performed when there is delayed healing of a fracture?

Answer 21

• Differ fixation: add nail to bone etc.
• Bone grafting
• Dynamisation: move the ends of the fracture closer together

Question 22

What is non union? Causes? Presentation?

Answer 22

Non union is failure of a fracture to heal

Can be caused by failure of fibrocartilage calcification, instability causing osteoclasis of any formed bone

Presents with pain + tenderness, as well as with a persistent fracture line on x ray, and sclerosis