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Plates for Fracture Repair

- See: Orthopaedic Trauma Implants: Know Your Implants (from Synthes web site)

- Discussion: 
    - Bone Healing w/ Plates
    - Characteristics of Metal Implants 

    - concepts:
          - tension side of the fracture:
                 - when plating a fracture the plate should be applied to tension side of the fracture (which is often the convex side);
                 - ideally when bone is plated, the bone itself carries the majority of the compression load;
                 - optimally when a plate tends to close a fracture, placing the plate under tension, a significant portion of the load is
                           supported by bone, thereby diminishing beding moment on the plate;
                 - in this situation there will be little benefit accued from increasing either, the breadth of the plate or the size of screws, but
                           when plate was increased in length from 3-6 inches, the strength of the assembly was doubled;
          - mechanical considerations:
                 - theoretically the most secure plate fixation would be that achieved by having two plates on opposite sides of bone,
                         however, this is biologically unsound;
                 - plating of shafts by two plates at 90 deg is also mechanically sound, but involves soft tissue stripping; 
                         - however, bone is able to heal w/o periosteal callus, provided the endosteal circulation is intact;
          - comminuted frx:
                 - a plate placed across a comminuted segment is known as bridging plate;
                 - if marked comminution is present on the compression side of fracture then non union is more likely;
                 - consider cancellous or cortico-cancellous bone grafts;
                 - cortico-cancellous bone graft can be wedged into a frx gap, w/ appropriate lag screws applied into the graft, along w/
                        dynamic compression applied across the cortico-cancellous graft; 

Dynamic Compression Plates
        - AO foundation: Compression plating (midshaft)

- Prebending vs. Lag Screws:
    - prebending is superior for small bones and for porous bones, while lag screw compression is superior in large and dense bones;
    - another advantage of prebending is that it tolerates incidences of overload;
           - overloaded prebent plate returns to normal function, whereas screw threads are irreversibly stripped;
    - transverse frx:
           - in transverse frxs consider prebending plate inorder to equalize compression; of both cortices;
           - because a lag screws can not be placed, compression must be achieved w/ plates alone (see: dynamic compression plates)
    - oblique frx:
           - attempt to apply lag screw, followed by neutralization plate;
           - it is also possible to place the lag screw thru the plate;
           - neutralization plate is applied w/o dynamic compression;
           - never attempt to insert a lag screw after plate has been applied; 

- Locking Plates: general concepts

 - Methods to Avoid Frx Following Plate Removal:
    - as pointed out by Beaupre GS, et al (1992), plate constructs that used unicortical end screws were significantly weaker than
              bicortical end screws;
    - refracture may occur through unhealed frx site if plate is removed prematurely;
    - plates should be retained for at least 18-21 months to allow bone density to return to its prefrx level before removal of plates;
    - forearm should be protected for six weeks following removal;
    - risk factors for frx:
            - frx w/ initial comminution;
            - plating w/ 4.5-mm DCP;
            - early plate removal;
    - references:
            - Refracture of bones of the forearm after plate removal.
            - Refracture of bones of the forearm after the removal of compression plates
            - Year Book: Refractures After Forearm Plate Removal.  
            - A Comparison of Unicortical and Bicortical End Screw Attachment of Fracture Fixation Plates.
            - Bone weakness after the removal of plates and screws. Cortical atrophy or screw holes?
            - Removal of forearm plates. A review of the complications.

- Misc Plates:
       - One-Third Tubular Plates
       - Reconstruction Plates, 3.5 mm
       - Reconstruction Plates, 4.5 mm
       - Semitubular Plates
       - T Plates



The Effect of Divergent Screw Placement on the Initial Strength of Plate-to-Bone Fixation.

Force transfer between the plate and the bone: relative importance of the bending stiffness of the screws friction between plate and bone.