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Principles Of Lag Screw + Platting
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Principles Of Lag Screw + Platting


AO Principles

AO Principles

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  • Figure from: Schatzker J, Tile M: The Rationale of Operative Fracture Care. Springer-Verlag, New York, p. 8, 1987.
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  • Figure from: Schatzker J, Tile M: The Rationale of Operative Fracture Care. Springer-Verlag, New York, p.9, 1987.


  • 2. CONCEPTS • Biology of bone healing • Screws • Compression www.ricopecero.site90.net
  • 3. Biology of Bone Healing • Rigid Fixation - bone heals directly to bone Primary bone healing - Requires rigid internal fixation and intimate cortical contact - Cannot tolerate soft tissue interposition www.ricopecero.site90.net
  • 4. Biology of Bone Healing • 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 www.ricopecero.site90.net
  • 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. www.ricopecero.site90.net
  • 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... www.ricopecero.site90.net
  • 7. Screws • Cortical • Cancellous • Partial threaded • Full Threaded • Non-cannulated • Cannulated • Non-self-tapping • Self tapping www.ricopecero.site90.net
  • 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. www.ricopecero.site90.net
  • 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. www.ricopecero.site90.net
  • 10. Methods of compression • Lag Screw • By Compression plate pre-bending • Dynamic Compression Plate (DCP) • Tension Band fixation www.ricopecero.site90.net
  • 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 www.ricopecero.site90.net
  • 12. Lag Screw Partially Threaded cancellous screw Threads must be completely across the fracture to achieve compression and purchase far cortex if possible www.ricopecero.site90.net
  • 13. Lag Screw Fully threaded cortical screw The near cortex must be “over-drilled” to achieve inter-fragmentary compression www.ricopecero.site90.net
  • 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. www.ricopecero.site90.net
  • 15. Lag Screw: Orientation It is drilled at 90° to the fracture line √ X www.ricopecero.site90.net
  • 16. Plates • Protection/Neutralization • Compression (DCP, LC-DCP) • Buttress • Reconstruction • Locking (LCP) • Etc www.ricopecero.site90.net
  • 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 www.ricopecero.site90.net
  • 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. www.ricopecero.site90.net
  • 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. www.ricopecero.site90.net
  • 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 www.ricopecero.site90.net
  • 21. Dynamic Compression Plates • 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. www.ricopecero.site90.net
  • 22. Dynamic Compression Plates www.ricopecero.site90.net
  • 23. THANK YOU www.ricopecero.site90.net