Avascular Necrosis Flashcards
What are the functions are structure of bones
- Mechanical support/protection/movement. Mineral storage (calcium and phosphate) and haematopoiesis.
- The shaft is the diaphysis, ends are the epiphysis, The metaphysis is the transitional area between the two.
Describe features of cortical bone
- It is strong, compact bone organised in Haversian system/osteons. It has a slow turn over rate.
An osteon consists of osteocytes surrounded by lacuna and canaliculi which allow for communication
Describe features of cancellous bone
This is the spongey/trabecular bone which can be found in the metaphysis and epiphysis of long bones and centrally in cuboid bones. Has a higher turnover rate but is less dense
What are the different bone cells
- Osteogenic cells (stem cells)
- Osteoblast (forms bone matrix. Can turn into osteocytes, apoptosis, bone lining cell)
- Osteocyte (maintains bone tissue)
- Osteoclast (Has abundant mitochondria and lysosomes which reabsorb bone)
Describe features of inorganic and organic bone matrix?
- Inorganic: Abundant calcium phosphate. Responsible for compressive strength
- Organic: Abundant type 1 collage. It’s responsible for tensile strength
What is the bone growth plate called?
Physis - it allows for remodelling after fracture. If the physeal blood supply is damaged it will lead to growth arrest
What are the two methods of fracture healthing?
Indirect healing (secondary) this is where a callus forms. Direct healing (primary) occurs with surgical repair
Describe the process of indirect fracture healing
- Fracture haematoma and inflammation. Occurs 6-8 hours after injury with removal of dead tissue/bone cells.
- Fibrocartilage callus
- Bony callus - Osteoblasts make woven bone
- Bone remodelling - osteoblasts/clasts remodel woven bone into compact bone
Throughout the process a degree of movement is desirable to promote differentiation
Explain the formation of a fibrocartilage callus in fracture healing
- New capillaries organise haematoma into granulation tissue called a procallus.
- Fibroblasts and osteogenic cells invade the procallus and make collagen fibres to connect ends of broken bone together. Chondrocytes begin to produce fibrocartilage.
Describe the process of direct fracture healing
- This occurs in a surgical situation which relies in absolute fracture stability.
- There is no callus formation and instead cutting cones cross fracture site with osteoclast reabsorption and osteoblastic formation.
What is the blood supply of bone?
- Endosteal arteries supply the inner 2/3rds of bone under high pressure.
- Periosteal arteries supply outer 1/3rd of bone by low pressure
- Metaphyseal-epiphyseal vessels supply the ends of long bones
What is the blood supply of the femoral neck?
- Medial and lateral circumflex arteries of the profunda femoris form the extracapsular arterial ring. This sends ascending cervical vessels up the femoral neck and gives of epiphyseal branches
What fractures are the most prone to causing avascular necrosis?
- Proximal pole of scaphoid fracture,
- Talar neck fracture,
- Intracapsular hip fractures,
- Surgical neck of humerus
What can prevent fracture healing?
- Increasing age,
- Diabetes,
- Anaemia,
- Malnutrition,
- Peripheral vascular disease,
- Hypothyroidism,
- Smoking,
- Alcohol
- Medications: NSAIDs, steroids and bisphosphonates
How can NSAIDs and bisphosphonates impact fracture healing?
- NSAIDs can reduce local vascularity at the fracture site.
- Bisphosphonates inhibit osteoclast activity which prevents bone remodelling.
