- Discussion:
- exactly contoured plates produce asymmetric compression (ie the near cortex is compressed more than the far cortex);
- ie the far cortex may not be compressed at all;
- when prebent plate is fixed to the bone, the bend is straightened out;
- due to its elastic recoil, the plate
has a tendency to recover the bend which was applied by plastic (irreversible) deformation;
- it therefore exerts a bending moment which tends to close and to compress the far fracture gap;
- to provide compression of the far cortex the plate is applied after exact contouring but with an additional bend of
the plate segment bridging the fracture;
- w/ respect to stabilization against torque and bending, compression of the far cortex is far more important than that of the near cortex;
-
goals of prebending:
- goal is to balance forces on the near and far corticies;
- good stability only requires that the far cortex be compressed enough to maintain contact under physiologic loading w/o being overloaded;
- it should be noted that it is not aim of prebending to produce equal compression in both cortices;
- slight prebending, results in minimal compression of the far cortex;
- if two large an amount of prebending is applied, near cortex is not compressed efficiently;
-
sharp vs smooth bending:
- bend is such that the mid section of the plate is elevated from the bone surface prior to fixation to the bone;
- most active portion of prebending spans the distance between the inner screws;
- therefore a comparitively sharp bend should be applied;
- angle of bend should be such that an 8 hole, 4.5 mm small DCP should be elevated about 2 mm from the bone surface;
-
order of screw insertion:
- to fix prebent plate to bone, inner screws should be applied first and the outer last;
- if outer screws are applied first, near cortex opens because plate is too long in relation to the bone
spanned between outer screw holes;
- to fix a straight plate to a curved bone (here plate is relatively prebent);
- outer screw holes are inserted first, which has the effect of shortening the plate as the plate conforms to the bone;
- the net effect is compression across the frx site;
[Pre-bending and and tension adjustment of narrow 4.5 mm AO titanium LC-DCP (limited contact dynamic compression plate)]
[Biochemical and mathematical studies of the pre-bending and pre-stressing of the small fragment DC plate]
A radiological and histological analysis of fracture healing using prebending of compression plates.
Experimental examinations in plate-prebending--a contribution to the biomechanics of compression osteosynthesis (author's transl)]
