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What is the area of relative weakness in an immature skeleton?
the growth plate
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What is the cause of growth deformity with growth plate injury?
- germinal zone= resting zone on the epiphyseal surface, which produces the rest of the cells
- if you damage the germinal zone by placing pressure on it (fixation, etc), they will not be able to repopulate
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What is the weakest part of the physis?
- zone of chondrocyte hypertrophy b/c the strength of the bone lies within the matrix
- the more cells, the more void b/w the cells--> weaker area
- the zone of hypertrophy has the greatest cell void
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Describe the Salter-Harris classification types.
- Type I: physis fracture
- Type II: physis and metaphysis are fractured
- Type III: fracture through epiphysis and physis
- Type IV: fracture through physis, metaphysis, and epiphysis
- Type V: crushing injury to the physis
- Type VI: injury to the peripheral portion of the physisand a resultant bony bridge formation which may produce an angular deformity
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Which type of salter-harris fracture has the worst prognosis and why?
Type III b/c it is intra-articular
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With acute femoral capital physeal fracture repair, you should remain cognizant of...
avoiding the vessels that supply the femoral head (run along the neck of the femur)--> if you take an approach that cuts these vessels, you will cause avascular necrosis of the femoral head
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Principals of acute femoral capital physeal fracture repair. (3)
- Early repair is crucial (<3 days)
- reduce in situ (don't disturb blood supply to femoral head)
- orthograde K-wires (don't need a massive amount of implants b/c this is a relatively stable fracture)
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What are the clinical aspects of chronic femoral capital physeal fracture? (3)
- related to early neuter and obesity in male cats- metaphyseal osteopathy, physeal dysplasia
- apple core remodeling of femoral neck
- primary repair is impractical--> perform femoral head and neck ostectomy
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What are the clinical aspects of distal femoral physeal fractures in obese male neutered cats? (5)
- salter-harris type III
- appears W-shaped on cranial-caudal and lateral radiographs
- epiphysis is pulled caudally b/c the hamstring muscles are pulling on it
- repair with 2 dynamic intramedullary crossed pins
- assess for intra-articular involvement- if present, address with a lag screw
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Describe the clinical aspects of tibial tuberosity avulsion. (2)
- salter-harris type I
- for repair, you must counter the distraction of the quadriceps on the tibial tuberosity with a figure 8 tension band wire and K wires
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What forces are acting on comminuted femoral fractures?
torsion, shear, compression, bending
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Why shouldn't you use an IM pin to address a comminuted fracture?
does not provide stability for compression, shear, or torsion (only bending)
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What is it no longer advised to remove all the fracture fragments when repairing a comminuted fracture?
fracture fragments can be incorporated into the bone callous during healing; removing them may disrupt the normal biology of healing by disturbing the periosteal blood supply
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Describe a locking bolt. (3)
- created to address screw deformation (3.5mm screws have a small core diameter--> occasional overload of screws w/ bending and breaking)
- longer life to fatigue
- self tapping
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Unlike plates, _________ in not protective of breakage in locking bolts.
screw occupancy of screw holes
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What is a "jig"?
guide that directs the drill through the bone, through the locking bolt screw hole, and into the opposite cortex
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Why can't you use standard nails in the locking bolt?
too much slack- they weren't robust enough or rigid fitting into the bolt--> wobble and subject to fail
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What is the best what to insert a nail into the femoral medullary cavity?
normograde through the trochanteric fossa
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Where is the ideal placement of a locking bolt?
within the metaphysis
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Are cats good candidates for locking bolt and nail fixation? Why?
- No- they don't make nails small enough
- Alternative- IM pin/ ESF tie-in
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What are the clinical aspects of IM pin/ ESF tie-in for repairing femoral fractures in cats? (4)
- [ESF= external skeletal fixation]
- tie-in increases bending stiffness
- safe entry points are via subtrochanteric and subcondylar routes
- use end-threaded ESF pins
- staged removal
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