Question: Can you tell me what is bone?
This question prompts a further one in rapid succession: “Draw me the structure mentioning relevant points”:
- Composite of mostly inorganic hydroxyapatite (Ca10(PO4)6OH2) and organic matrix (cells, collagen I).
- Normal cortical bone - lamellar structure with a haversian system, interspaced osteocytes communicating via canaliculi.
- Osteocytes (bone cells) derived from osteoblast precursor cells.
- Osteoclasts are multinucleate giant cells with a ruffled border, resorbing bone by secreting tartrate resistant acid phosphatase (TRAP) and other enzymes into an acidic environment.
- Etc, etc
Question : Ok, tell me how as Orthopaedic Surgeons we can alter the environment to affect how bone healing occurs
Discussion about absolute versus relative stability:
- Definitions of each. “Give me an example of when we use absolute (compression plate for simple clavicle fracture) “and relative..” (POP cast, intramedullary nail).
- “Describe a cutting cone. What is a lag screw and how do you apply a plate in compression mode” (eccentric drill hole).
- Relative stability: Perrens theory of relative strain.
- “What is a locking plate?” (fixed angle device, separate thread on the head to lock into the plate)
- “In a situation of nonunion, what factors do you consider?”: biological (poor blood supply, patient factors); mechanical (lack of rigidity).
Question: Have a look at this xray, what can you see? (moving the scenario onto a discussion of atypical bisphosphonate associated fractures). What are bisphosphonates and what are their side effects?
- Bisphosphonates act on osteoclasts.
- Nitrogen and non-nitrogen containing
- Either work by producing a toxic ATP analogue inducing apoptosis or on farnesyl pyrophosphate synthase pathway.
- Maintain bone mass (such as for treatment of osteoporosis).
- Used in osteogenesis imperfecta.
- Atypical fractures associated with bisphosphonates are difficult to treat, requiring additional input from a metabolic bone specialist for teriparatide.
- Osteonecrosis of the jaw also recognized.