plates and screws 11

Plates and Screws Supervised by Dr. Marwan Abuhashem

By Dr. Ismael Al-jabiri

Al-Bashir Orthopedic Department Ministry Of Health Jordan

1. Anatomical Reduction.2. Stable internal fixation.3. Preservation of Blood supply4. Early mobilization.

Principles of Fixation :

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• “Surfaces of the fracture do not displace under functional load”

• Can only be achieved by interfragmentary compression

Absolute stability

• A plate by itself rarely provides absolute stability

• The key tool of absolute stability is the lag screw• Compression must sufficiently neutralize all forces[bending, tension, shear and rotation]

Relative Stability: 

A fixation device that allows small amounts of motion in proportion to the load applied. The deformation or displacement is inversely proportional to the stiffness of the implant. Examples: Intramedullary rod, bridge plating, external fixation.

PLATES

Introduction : Bone plates are like internal splints holding

together the fractured ends of a bone. A bone plate has two mechanical functions.

• It transmits forces from one end of a bone to the other, bypassing and thus protecting the area of fractures.

• It also holds the fracture ends together while maintaining the proper alignment of the fragments throughout the healing process.

History

Hansman’s Bone Plate (1886)

Hansmann’s plates were:Bent at the end to protude through the skinAttched to bone by screw with long shanks that projected outside the soft tissues.

Bone Suture Stabilization Inserts (Koenig, 1905)

History

Since 1958, AO has devised a family of plates for long bone fractures, starting with a round holed plate.

In 1969 the Dynamic Compression Plate was developed.

In 1994 LC DCP was created. In 2011 LCP with combination

holes has come into use.

Names of plates.

1. Shape (Semitubular, 1/3rd tubular)2. Width of plate (Small, Narrow,

Broad)3. Shape of screw holes. (Round, Oval)4. Surface contact characteristics. (LC,

PC)5. Intended site of application

(Condylar Plate)6. According to the function

Standard Plates

Narrow DCP-4.5 mm

Broad DCP – 4.5 mm

3.5 mm DCP

LC-DCP 3.5 & 4.5mm

Reconstruction plate 3.5 & 4.5mm

1/3 tubular plate 2.7, 3.5 & 4.5 mm

Special Plates

T Plates

T&L Buttress plates

Lateral proximal Tibial buttress plates

Condylar buttress plate

Narrow lengthening plates

Broad Lengthening plate

Spoon plate

Clover leaf plate

DCP - 3.5 and 4.5

First introduced in 1969 by Danis

Revolutionary concept of compression plating

Featured a new hole designed for axial

compression

Broad 4.5 for Femur & Narrow 4.5 for

Humerus & Tibia

DCP 3.5 for Forearm, Fibula, Pelvis & Clavicle

Advantage of DCP :

1. Inclined insertion 25°longitudinal and 7° sideways

2. Placement of a screw in neutral position without the danger of distraction of fragments

3. Insertion of a lag screw for the compression4. Usage of two lag screws in the main

fragments for axial compression5. Compression of several fragments individually

in comminuted fractures6. Application as a buttress plate in articular area

Problems with DCP

Unstable fixation leads to fatigue &

failure

Strict adherence to principles of

compression

Compromised blood supply due to

intimate contact with underlying cortex

“Refractures” after plate removal

LC-DCP Represents a design change Overcome problems with DCP Plate footprint reduced Minimized kinking at screw holes,

more countourable, reduced plate fatigue at

hole Allows more inclination of screw

in longitudinal plane and transverse

plane.

In the DCP (A), the area at the plate holes is less stiff than the area between them so while bending, the plate

tends to bend only in the areas of the hole.

The LC-DCP(B) has an even stiffness without the risk of buckling at the screw holes.

The LC-DCP offers additional advantage

Improve blood circulation by minimizing plate-bone contact

More evenly distribution of stiffness through the plate

Allows small bone bridge beneath the plate

Tubular plates

3.5 system - 1/3rd Tubular 4.5 system - Semitubular Limited stability-Oval holes – Axial

compression can be achieved.

-Low rigidity (1mm thick). Lateral malleolus Distal ulna / Olecranon Distal humerus

limited stability. The thin design allows for easy shaping and is primarily used on the lateral malleolus and distal

ulna. The oval holes allow for limited fracture compression with eccentric screw placement.

Reconstruction plates

Deep notches between holes

Accurate contouring in any plane

Pelvis Acetabulum Distal humerus Clavicle Olecranon

Reconstruction plates are thicker than third tubular plates but not quite as thick as dynamic compression plates. Designed with deep notches between the holes, they can be contoured in 3 planes to fit

complex surfaces, as around the pelvis and acetabulum. Reconstruction plates are provided in straight and slightly thicker and stiffer precurved lengths. As with tubular plates, they have oval screw

holes, allowing potential for limited compression.

LCP – Locking Compression Plate

LCP

Latest in the evolution

“ Internal fixator ” Combination of

locking screw with conventional screw

Extraperiosteal location of plate

LCP: internal external fixator

LCP

Combines advantages of DCP principle and locking head principle.

Flexibility of choice within a single implant. Screw hole have been specially designed to accept either:

cortical screw and locking screw

The locking screws, by achieving angular stability within the plate holes are able to produce a similar hoop with just two unicortical screws.

LCP

LOCKING COMPRESSION PLATE (LCP) Principle :

Angular-stability whereas stability of conventional plates is friction between the plate and bone

Screw locking principle

Provides the relative stability Healing by callus formation (Secondary Healing)

Stability under load

• By locking the screws to the plate, the axial force is transmitted over the length of the plate

• secondary loss of the intraoperative reduction is reduced

Blood supply to the bone

• No additional compression after locking

• Periosteal blood supply will be preserved

LCP used as internal fixator to bridge multifragmentary diaphyseal fracture zone.

Locking compression plate is used.

Standard cortical and cancellous screws are used as a traditional plate.

LCP

Principle of internal fixation using LCP :

1. 1st reduced the # as anatomical as possible2. Cortical screw should be used 1st in a fracture

fragment3. If the locking screw have been put, use of the

cortical screw in the same fragment without loosening and retightening of the locking screw is not recommended

4. If locking screw is used first avoid spinning of plate

5. Unicortical screws causes no loss of stability

6. In Osteoporotic bone bicortical screws should be used.

7. In comminuted # screw holes close to the fracture should be used to reduce strain.

8. In the fracture with small or no gap the immediate screw holes should be left unfilled to reduced the strain.

Principle of internal fixation using LCP :

Indications :

1. Osteoporotic #

2. Periprosthetic #

3. Multifragmentry #

4. Delayed change from external fixation to internal fixation.

Advantages :

1. Angular stability 2. Axial stability3. Plate contouring not required4. Less damage to the blood supply

of bone5. Decrease infection because of

submuscular technique6. Less soft tissue damage

Sizes of DCPName of plate Small Narrow Broad

Width 11 mm 13.5 mm 17.5mm

Profile 4 mm 5.4 mm 5.4 mm

Screw 2.7 , 3.5 cortex screw and 4 mm cancellous screw

4.5 mm cortex screw & 6.5mm canellous screw

4.5 mm cortex screw & 6.5mm canellous screw

Sizes of LCDCPName of plate Small Narrow Broad

Width 11 mm 13.5 mm 17.5mm

Profile 4 mm 5.4 mm 5.4 mm

Screw 2.7 , 3.5 and 4 mm cancellous screw

4.5 mm & 6.5mm canellous screw

4.5 mm & 6.5mm canellous screw

Name of plate Small Narrow Broad

Width 11 mm 13.5 mm 17.5mm

Profile 4 mm 5.0 mm 5.0 mm

Screw 4 mm locking screw 5 mm locking screw 5 mm locking screw

Sizes of LCP

LISS System

Preshaped plates with self drilling self tapping screws with threaded heads.

Through a small incision (using this jig ) plate is slid along the bone surface. position of plate and wire are checked radiologically before insertion of metaphyseal screw .

LISS-Less Invasive Stabilization System

LISS

Type of plate – Functional Regardless of their length, thickness,

geometry, configuration and types of hole, all plates may be classified in to 4 groups according to their function.

1. Neutralization plate.2. Compression plates.3. Buttress plate.4. Tension band plates.

NEUTRALIZATION PLATE

• Acts as a ""bridge”” protection

• No compression at the fracture site

• neutralization plate is to protect the screw fixation of • a short oblique fracture

• a butterfly fragment

• a mildly comminuted fracture of a long bone

• fixation of a segmental bone defect in combination with bone grafting.

The Neutralization Plate

Lag screws: compression and

initial stability

Plate: protects the

screws from bending and torsional loads

NEUTRALIZATION PLATE

COMPRESSION PLATE

• produces a locking force across a fracture site

• plate is attached to a bone fragment then pulled across the fracture site , producing tension in the plate

• Direction of the compression force is parallel to the plate

Compression Plate

Principle :

- a self compression plate due to the special geometry of screw holes which allow the axial compression.

Dynamic compression principle:a The holes of the plate are shaped like an inclined and transverse cylinder.b–c Like a ball, the screw head slides down the inclined cylinder.d–e Due to the shape of the plate hole, the plate is being moved horizontally when the screw is driven home.f The horizontal movement of the head, as it impacts against the angled side of the hole, results in movement of the plate and the fracture fragment already attached to the plate by the first screw (1).

This leads to compression of the fracture.

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Compression plate:eccentric DC (dynamic compression) hole

Removable device:compression device

Interfragmentary compression by plate

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External compression device

METHODS OF ACHIEVING COMPRESSION

With tension devise By overbending With dynamic compression principle

(DCP/LC-DCP) By contouring plate Additional lag screw thro plate

BUTTRESS PLATE• is to strengthen

(buttress) a weakened area of cortex

• The plate prevents the bone from collapsing during the healing process.

• A buttress plate applied a force to the bone which is perpendicular (normal) to the flat surface of the plate.

• The fixation to the bone should begin in the middle of the plate, closest to the fracture site on the shaft. The screws should then be applied in an orderly fashion, one after the other, towards both ends of the plate.

example : the T-plate used for the fixation of fractures of the distal radius and the tibial plateau.

BUTTRESS PLATE

Bridge Plating

Bridge Plating for comminuted fracture

-instead of individually fixing each fragment

-minimal disruption to blood supply

-reduction is performed indirectly

- compression is only sometimes possible

TENSION BAND PRINCIPLE

Tension-band principle.

Tension Band Principle :- Its describes how the tensile forces are

converted into compressive forces by applying a devise eccentrically or to the convex side of a curved tube or bone.

Indications :- Fracture Patella, olecranon, medial

malleolus, greater trochanter of the femur.

Static Dynamic

Dynamic and static tension band

In dynamic tension band the tensile forces are converted to compression on the convex side of an eccentrically loaded bone

Examples : Patella Olecranon Greater tuberosity

Tension band principle to the medial malleolus example of static tension band

HOW MANY SCREWS ?

Bones No. of Cortices

No. of Holes

Type of Plate

Forearm 5 to 6 Cortex 6 holes Small 3.5

Humerus

7 to 8 Cortex 8 holes Narrow 4.5

Tibia 7 to 8 Cortex 7 holes Narrow 4.5

Femur 7 to 8 Cortex 8 holes Narrow 4.5

Clavicle 5 to 6 Cortex 6 holes` Small 3.5

Timing of Plate Removal

Malleolar fractures. 8-12mo The tibial pilon. 12-18mo The tibial shaft. 12-18mo The tibial plateau. 12-18mo The femoral condyles. 12-24mo The femoral shaft. 24-36mo Upper extremity. 12-18mo Shaft of radius / ulna. 24-28mo Distal radius. 8-12mo Metacarpals. 4-6mo

SCREW: INTRODUCTION

An elementary machine to change the small applied rotational force into a large compression force

Function Holds the plate or other prosthesis to the

bone Fixes the # fragments ( Position screw) Achieves compression between the #

fragments (Lag screw)

SCREWS

4 functional parts Head Shaft\ Shank \Core Thread Tip

Head: Recess Types

1. Slotted 2. Cruciate 3. Philips 4. Hex/ Allen 5. Torx (eg Stardrive of Synthes)

Screw: Shaft/ Shank/ Core Smooth link Almost not present in standard

cortex screw Present in cortical SHAFT SCREW or

cancellous screw

Screw: Run out

Transition between shaft and thread Site of most stress riser Screw break

Incorrectly centered hole Hole not perpendicular to the plate

Screw: Thread

Inclined plane encircling the root Single thread May have two or more sets of

threads

V-thread profile: more stress at sharp corner

Buttress thread profile: less stress at the rounded corner

Core

Solid section from which the threads project out wards. The size of core determines the strength of screw and its fatigue resistance. The size of drill bit used is equal to the core diameter.

Screw: Core Diameter

Narrowest diameter across the base of threads

Also the weakest part Smaller root shear

off Torsional strength

varies with the cube of its root diameter

Screw: Thread Diameter

Diameter across the maximum thread width

Affects the pull out strength

Cancellous have larger thread diameter

Screw: Tip Designs

1. Self-tapping tip: Flute Cuts threads in the bone over which

screw advances Cutting flutes chisel into the bone

and direct the cut chips away from the root

Screw: 2.Non self tapping

Lacks flutes Rounded tip Must be pre-cut in the pilot hole by

tap Pre-tapped threads help to achieve

greater effective torque and thus higher inter-fragmental compression

Better purchase

Screw: 3.Corkscrew tip

Thread forming tips In Cancellous screws

which form own threads by compressing the thin walled trabecular bone

Inadequate for cortical bone

Screw: 4.Trochar Tip

Like self tapping Displaces the bone as it

advances Malleolar screw Schanz screws Locking bolts for IMIL

Screw: 5.Self drilling self tapping

Like a drill bit In locked internal

fixator plate hole Pre-drilling not

required Flute Good purchase in

osteoporotic and metaphyseal area

Locking Screws vs Cortical Screws

Creates Fixed Angle Generates Friction/Compression

4.4mm Core Dia. 3.5mm Core Dia.

5.0 mm Locking Screw4.5 mm Cortical Screw

Bending stiffness proportional to the core diameter

Pull out strength is proportional to the size of the thread

Cannulated screws have less bending stiffness

AO/ASIF Screws: Types

Cortical Fully threaded Shaft screw 1.5:phalanx *drill bit 1.1 mm 2.7: mc and phalanx *bit:2.0 3.5: Radius/ Ulna/ Fibula/

Clavicle*bit:2.5 4.5: Humerus/ Tibia/ femur *bit:3.2

AO/ASIF Screws

• Cortical screws:– a machine type– Smaller threads– Lower pitch– Large core diameter– Smaller pitch higher

holding power– greater surface area of

exposed thread for any given length

– better hold in cortical bone

AO/ASIF Screws

• Cancellous screws:– a wood type– core diameter is less– the large threads– Higher pitch– Greater surface are for purchase– Untaped pilot hole– Pilot hole equals the core diameter– lag effect option with partially

threaded screws – theoretically allows better fixation in

soft cancellous bone.

Cancellous Fully threaded

Cannulated or Non- cannulated Partially threaded

16mm or 32 mm Cannulated or Non-cannulated

4.0, drill bit 2.5mm humeral condyle

6.5 drill bit 3.2mm tibial and femoral condyle

MALLEOLAR SCREW: - smooth shaft - partially threaded - trephine tip : no tapping

needed - was designed as lag screw for

malleoli fixation NOW small cancellous screws preffered

- distal humerus and lesser trochanter - size : 25mm – 75 mm

Cannulated screws 3.0 4.0 4.5 6.5 7.0 7.3

Special Screws

Locking bolt Herbert Screw Dynamic Hip

Screw Malleolar

Screw Interference

screw Acutrak screw

Pedicle screw

Suture anchor

Headless Screws

Herbert screw bridging a scaphoid fracture

Acutrak screw

Bioabsorbable Screws

The most common materials used are polylactic acid (PLA), poly-L-lactic acid (PLLA), and polyglycolic acid.

Advantages of bioabsorbable screws

• Does not interfere with MRI.• Does not interfere with future revision surgery if needed.• Decreased incidence of graft laceration.• Does not need implant removal

Disadvantages of bioabsorbable screws

• Major disadvantage is screw failure during insertion. Special screw drivers that span the entire length of screw reduce incidence of screw breakage.• Foreign body reaction may be seen in some.

Function or mechanism.

Neutralization screws – neutralizes forces on the plate in plate fixation.

Lag screws – For inter-fragmentary compression.

Reduction screw – To reduce displaced fracture by pushing or pulling.

Position screw – Holds two fragments in position without compression. Eq. Syndesmotic screw

Anchor screw – Acts as an anchor for wire or suture. In tension band wiring

Locking head screw – In locking plates Locking screw – In interlocking nails Poller screw – To guide the nail path in

interlocking nailing of fractures close to the bone ends.

TAP To cut threads in bone of same size as

the screw to facilitate insertion Flutes : to clear the bone debris Two turns forward and half turn

backward recommended to clear debris Used with sleeve Done manually Power tapping NOT recommended For cancellous bone : short and wide

thread , slightly smaller dia than screw

For cortical screws : - as fixation screw : both cortices - as lag screw : only far cortex For cancellous screw: - only near cortex - sometimes in young patients

tapping entire screw length needed

LAG SCREW TECHNIQUE :

- to achieve interfragmentary compression

- this technique is used if a screw is to be inserted across a # , even through a plate.

- screw has no purchase in near fragment, thread grips the far fragment only

-achieved either with screw with shaft or fully threaded screw

Positioning of screws:

-max. interfragmentary compression :

placed in middle of fragment, right angle to fracture plane

- max. axial stability: right angle to long

axis of bone

Thank You