20.Metal osteosynthesis - types and indications. Flashcards
what are the different types of screws ? and how do screws work ?
there is cortical and cancellous screws
turning rotation force into linear motion
what is the difference between cortical and cancellous screw ?
Cortical screws have closely-spaced, shallow threads
Cortical screws are stronger. They are usually blunt ended
cancellous screw have more deeply cut and more widely spaced threads compared to cortical screw. Since cancellous bone is much less dense than cortical bone, the screw threads cut their path in the bone when the screw is inserted
cortical screws are almost all threaded ideal for lag screws
Partialy threaded cancellous screws are often used as lag screws for metaphyseal fractures
describe a lag screw ?
A lag screw is not a particular type of screw, but rather refers to how a screw is inserted
the screw is inserted to a predrilled hole
Cortical screws are used as lag screws in fractures of diaphysial bones
cancellous screws for metaphyseal fractures.
These screws produce uniform static fracture compression.
As the screw continued to be tightened, it closed the gap
describe cannulated screws?
Cannulated screws have a hollow central shaft
Cannulated cancellous screws are used for metaphyseal fractures
while cannulated and noncannulated cortical screws are used as lag screws for fixation of diaphyseal fractures.
The main advantage of cannulated screws is that they can be inserted over a guide k wire or guide pin.
what is a dynamic hip screw ?
used for internal fixation of fractures of the femoral neck and intertrochanteric region. The screw is a large cancellous lag screw
the compression plate it is attached to is fixed to the femur with self tapping screws cortical screws
what is self tapping screws ?
A self-tapping screw is a screw that can tap its own hole as it is driven into the material
what is locking screw ?
contains threading on screw head which tightenings with the locking plate
it stabilises the segments without the need to compress the bone to the plate like conventional screws and plates
the screws are unlikely to loosen from the plate giving a more stable fixation rather than the conventional plate and screw system
what is a herbert screw
a headless compression screwcompress small fractures fragments
One end of the screw has cancellous threads
the other end cortical screw thread
The cancellous screw is inserted first and crosses the proximal fracture, screwing into the bone of the distal fragment
Each turn of the screw causes the distal end to travel farther into bone than the proximal end, compressing the fracture
what is buttress plate ?
used to rigidly hold in place fractures at the end of long bones
these plates are broadened and carefully contoured at the joint end, provide adequate fixation works as a compression plate
configurations are T-shaped, L-shaped
what is a standard compression plate called ?
standard compression plate is usually referred to as a dynamic compression plate
how does compression plate work?
The nail holes in the plate have sloped edges distal to fracture , the slopping facing the fracture
the slope causes the nails and its attached bone to move towards the fracture compressing it
what are the disadvantages OF COMPRESSION plat ?
union without call formation
stress fractures occurs at the end of the plate
bone present under the plate is AVN
what is locking compression plate ? and when is it used ?
standard oval holes used for compression and circular threaded holes used for locking the plate and bone to the screws
The compression holes are oriented away from the center of the plate and locking circular holes are oriented toward the center
used when there is osteoporotic bones - bone is not stable
what is reconstruction plate ?
limited contact dynamic compression plate which can be bend to fit any shape
used in pelvis fractures
