Principles Of Lag Screw + Platting

AO Principles

1. PRINCIPLES OF LAG SCREW AND PLATTING
(STANDARD / DINAMIC PLATE)
NEWHAM UNIVERSITY
HOSPITAL
Mr. Jose A. Rico-Pecero
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2. CONCEPTS
•Biology of bone healing
•Screws
•Compression
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3. •Rigid Fixation - bone heals directly to bone
Biology of Bone Healing
Primary bone healing
- Requires rigid internal fixation
and intimate cortical contact
- Cannot tolerate soft tissue
interposition
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4. •Non-rigid fixation or immobilization - the
body forms a fibrous matrix which
transitions to cartilage, calcified cartilage,
disorganized woven bone, and finally
organized lamellar bone.
Secondary Bone Healing = CALLUS FORMATION

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Biology of Bone Healing

5. Practically speaking...
•Plates and screws = primary bone healing
•Cast = callus formation
•IM Rods = primarily secondary bone
healing/callus - depends on location of
fracture, size of nail, quality of bone…
•Small wire/tension band = usually callus
formation unless bone quality is excellent in
which case rigidity may be achieved.
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6. Practically speaking...
•Most fixation probably involves components of
both types of healing. Even in situations of
excellent rigid internal fixation one often sees
a small degree of callus formation...
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7. •Cortical
•Cancellous
•Partial threaded
•Full Threaded
•Non-cannulated
•Cannulated
•Non-self-tapping
•Self tapping

Screws
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8. Screws
•Cortical screws:
– greater surface area of
exposed thread for any given
length
– better hold in cortical bone
•Cancellous screws:
– core diameter is less
– the threads are spaced farther
apart
– lag effect option with partially
threaded screws
– theoretically allows better
fixation in soft cancellous
bone.
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9. Compression
•Fundamental concept critical for primary bone
healing
•Compressing bone fragments decreases the gap
the bone must bridge creating stability by
preventing fracture components from moving in
relation to each other.
•Achieved through lag screw or plating
techniques.
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10. Methods of compressionMethods of compression
•Lag ScrewLag Screw
•By Compression plate pre-bendingBy Compression plate pre-bending
•Dynamic Compression Plate (DCP)Dynamic Compression Plate (DCP)
•Tension Band fixation
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11. Lag Screw
•Used to compress fracture fragments
•Use to hold plates on bone
•Threads only engage far cortex
•Can be achieve with:
- Partially threaded screw
- Fully threaded with ver drilling near cortex
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12. Lag Screw
Partially Threaded cancellous screw
Threads must be completely across the fracture to
achieve compression and purchase far cortex if
possible
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13. Lag Screw
Fully threaded cortical screw
The near cortex must be “over-drilled” to
achieve inter-fragmentary compression
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14. Lag Screw
The screw on the right has not been drilled to the outer
diameter on the near cortex and the result is lack of
compression and gap at the fracture.
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15. Lag Screw: Orientation
It is drilled at 90° to the fracture
line
√ X
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16. Plates
•Protection/Neutralization
•Compression (DCP, LC-DCP)
•Buttress
•Reconstruction
•Locking (LCP)
•Etc
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17. Terminology - Plates
•Plate size
- Determined by screw
- 4.5 DCP is not 4.5 mm thick
•Narrow / Broad
•Shape: Straight, semitubular, T-shape, L
shape, etc
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18. The Neutralization Plate
•The primary fixation of the fracture is the lag screw which by
itself is insufficient fixation of the fracture. The addition of a
supplemental plate protects against harmful rotational and
axial forces which the inter-fragmentary screw alone would
not be able to withstand.
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19. The Neutralization Plate
•The two lag screws
provide compression
and initial stability.
•The plate bridges the
fracture and protects
the screws from
bending and torsional
loads.
•Plate protects primary
repair.
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20. Dynamic Compression Plates
-The objective of compression plating is to produce absolute stability,
eliminating all inter-fragmentary motion.
- Compression of the fracture is usually produced by eccentric screw
placement at one or more of the dynamic compression plate holes.
- The screw head slides down the inclined plate hole as it is tightened,
with the head forcing the plate to move along the bone, thereby
compressing the fracture
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21. •Note the screw holes in the
plate have a slope built into
one side.
•The drill hole can be purposely
placed eccentrically so that when
the head of the screw engages the
plate the screw and the bone
beneath are driven or compressed
towards the fracture site one
millimeter.
Dynamic Compression Plates
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22. Dynamic Compression Plates
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23. THANK YOU
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