How do you choose an appropriately sized bone plate?
- there should be 3 screws proximal and distal to the fracture plane
- no screws in the fracture plane
- no empty holes
- plate should span entire length of bone
What is the AAAA scheme?
- Alignment, Apposition, Apparatus, Activity (activity of the bone at the level of the fracture)
- used to assess fixation of a fracture
What are the major reasons for failure of a fracture repair? (3)
- incorrect selection of implants
- techical errors in application
- inconsiderate tissue handling
Describe the stabilization achieved with simple IM pin fixation.
- only provides distraction to bending
- NOT to compression, shear, or rotation
- poor choice for complex/ comminuted fractures, not commonly used as sole fixator
Why shouldn't you pin the radius in a small dog (or any dog)?
- poor medullary blood supply, which is compromised by an IM device
- may not even be able to get a pin in the small medulla
What are the principals of cerclage? (5)
- reconstruct complete circumference of bone
- use large strong wires
- make wires tight
- space wires >1cm apart and space them evenly
- place wires >0.5cm from fracture ends
What are potential complications that can occur with cerclage wire?(3)
- pin migration associated with fracture instability (do not use cerclage as a single device or alone with an IM pin because the cerclage will act as a fulcrum and the pin will start to migrate)
- pin removal
- loose cerclage inhibits union
What are the 3 types of viable and 4 types of non-viable non-unions?
- Viable: hypertrophic non-union (elephants foot callus), slightly hypertrophic non-union (horses hoof callus), oligotrophic non-union
- Non-viable: dystrophic non-union, necrotic non-union, defect non-union, atrophic non-union
What is pseudoarthrosis?
specific type of non-union, where the fracture surface develops a synovial-like surrounding it and a cartilage-like surface; chronic complication
What is stress protection?
failure to load the limb after fracture fixation and atrophy of the bone
What is the fracture risk post-op after repair of a fracture?
- plate not long enough, creates a fulcrum and fracture distal to the plate [long lever arm]
- stifle arthrodesis--> risk for tibia fracture
What kind of clinical manifestations occur due to plate irritation, and how is it addressed?
- near joint, where there is little soft tissue cover, lick granuloma
- address by removing the implant
What are the radiographic characteristics of osteomyelitis? (8)
- soft tissue swelling
- periosteal reaction (irregular or smooth)
- cortical lysis/ sclerosis
- lysis around implants
- increased medullary density
- sequestrum and involucrum
- delayed union or non-union
- gas shadows in soft tissue
How do you address implant-associated osteomyelitis?
- treat with antibiotics and remove implant
- must remove implant because it will harbor biofilm, even if the infection responds to antibiotics successfully
- address fracture with cancellous bone autograft and ex-fix (can be removed without further surgery)
What are the types of implant failure, and in what patients does each usually occur?
- acute material failure: single fatigue failure after a single massive load; occurs in equine
- fatigue failure: implant fails after a time; common in small animal
Describe how fatigue failure of an implant occurs.
metal can fail in fatigue; if the fracture is repaired appropriately, the fracture will heal before the implant reaches its fatigue limit; if there is infection or the fracture is not repaired appropriately, it will continue to be loaded b/c fracture takes longer to heal, and be more likely to break in fatigue
What type of IM pin is more stable?
smooth pins are more stable; there is no benefit to using negative profile threaded IM pins (prone to fail at thread/ shaft junction)