principles of lag screw + platting

PRINCIPLES OF LAG SCREW AND PLATTING (STANDARD / DINAMIC PLATE)

NEWHAM UNIVERSITY HOSPITAL

Mr. Jose A. Rico-Pecero

www.ricopecero.site90.net

CONCEPTS

• Biology of bone healing

• Screws

• Compression


• 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


• 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


Biology of Bone Healing

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.


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...


• Cortical• Cancellous

• Partial threaded• Full Threaded

• Non-cannulated• Cannulated

• Non-self-tapping• Self tapping

Screws


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.


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.


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


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


Lag Screw

Partially Threaded cancellous screwThreads must be completely across the fracture to

achieve compression and purchase far cortex if possible


Lag Screw

Fully threaded cortical screwThe near cortex must be “over-drilled” to

achieve inter-fragmentary compression


Lag ScrewThe 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.


Lag Screw: Orientation

It is drilled at 90° to the fracture line

√ X


Plates

• Protection/Neutralization • Compression (DCP, LC-DCP)• Buttress• Reconstruction • Locking (LCP)• Etc


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


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.


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.


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


• Note the screw holes in theplate have a slope built intoone 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


Dynamic Compression Plates


THANK YOU


principles of lag screw + platting

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