Plates form and function

PLATES: FORMS &
FUNCTIONS
 Dr. Gaurav Deshwar
 Junior resident III
 Department of
orthopaedics
 Sarojini Naidu
Medical College,
Agra

History
Plates for fixation of long bone fractures were first
recorded by Hansmann, of Heidelberg University,
Germany in 1886.One of his original plate sets is
seen below .Already then the instruments where
listed. the white label says: Attention Do not lose
anything.

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

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.

Principle of AO
 1. Anatomical Reduction.
 2. Stable internal fixation.
 3. Preservation of Blood supply
 4. Early active pain free mobilisation

Biomechanical Aspect of AO
Technique
 Neutralization Plate or Protection Plate
 Compression Plating
 Lag screw
 Tension Band Principle
 Intra Medullary Nailing
 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.

Plate : Form and Function
 To understand how changes in the design of
plates has evolved to meet the needs of the
patient
 To understand how you can use a plate in
several different ways to achieve different
types of fixation

Plate : Form
 DCP 4.5 narrow and broad types
 DCP 3.5
 LC-DCP 3.5 and 4.5
 LCP
 Reconstruction plate 3.5 and 4.5 mm
 Semitubular - 1/3rd Tubular Plate
 PC-FIX (Point contact fixator)
 LISS

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

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.

Tubular plates
 3.5 system - 1/3rd Tubular
 4.5 system - Semitubular
 Limited stability
 Collared hole
 Lateral malleolus
 Distal ulna / Olecranon
 Distal humerus

Reconstruction plates
 Deep notches between holes
 Accurate contouring in any
plane
 Pelvis
 Acetabulum
 Distal humerus
 Clavicle
 Olecranon

LCP – Locking Compression Plate

LCP
 Latest in the evolution
 “ Internal fixator ”
 Combination of
locking screw with
conventional screw
 Extraperiosteal
location of plate

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

 Traditional plating
techniques produced
stability by:
 Compression the plate
to the bone surface
 Engaging both
cortices.thereby
producing a rectangular
hoop with two bicortical
screws.

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

 Shown – LCP used as
internal fixator to bridge
multifragmentary
diaphyseal fracture zone.
 In this example :
 Locking compression plate
is used.
 Standard cortical and
cancellous screws are used
as a traditional plate.

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

Plate: Function
Each time a plate is used the surgeon
determines how a plate will function. Plates
can be used in four different ways:
 Neutralization/protection
 Compression
 Buttress
 Tension Band

Neutralization Plate
 A neutralization plate acts as a
""bridge". It transmits various
forces from one end of the bone to
the other, bypassing the area of the
fracture. Its main function is to act
as a mechanical link between the
healthy segments of bone above
and below the fracture. Such a
plate does not produce any
compression at the fracture site.

 A plate used with combination with lag
screw is also a neutralisation plate lag
screw produce compression and stability.
neutralisation plate merely protects the lag
screw, allowing mobilization of the
extremity. Lag screw generates forces of
3000 N.
 Term protection plate expresses the true
function.

it is crucial to use a plate that is long
enough so that at least three bicortical
screw can be inserted in to each main
fragment.

 The most common clinical application of
the neutralization plate is to protect the
screw fixation of a short oblique fracture, a
butterfly fragment or a mildly comminuted
fracture of a long bone, or for the fixation
of a segmental bone defect in combination
with bone grafting.

Compression plate
 A compression plate produces a locking
force across a fracture site to which it is
applied. The effect occurs according to
Newton's Third Law (action and reaction
are equal opposite). The plate is attached
to a bone fragment. It is then pulled
across the fracture site by a device,
producing tension in the plate. As a
reaction to this tension, compression is
produced at the fracture site across which
the plate is fixed with the screws. The

Role of compression
 Reduction of the space between the bone
fragments to decrease the gap to be bridged by
the new bone.
 Compaction of the fracture to force together the
interdigitating spicules of bone and increase the
stability of the construct.
 Protection of blood supply through enhanced
fracture stability.
 Friction, which at the fracture surfaces resists the
tendency of the fragments to slide under torsion or
shear. This is advantageous as plates are not
particularly effective in resisting torsion.

 Static compression between two fragments
maintained over several weak and does not
enhance bone resorption and necrosis.
 Interfragmentary compression leads to
absolute stability but has no direct influence on
bone biology or fracture healing.

METHODS OF ACHIEVING
COMPRESSION
 With tension devise
 By overbanding
 With dynamic compression principle (DCP/LC-
DCP)
 By contouring plate
 Additional lag screw thro plate

Compression with external devise
 it is recommended for fractures of the femur or
humeral shaft, when the gap to be closed
exceeds 1–2 mm, as well as for the
compression of osteotomies and nonunions.
 After fixation of the plate to one main
fragment, the fracture is reduced and held in
position with a reduction forceps. The tension
device is now connected to the plate and fixed
to the bone by a short cortex screw.and then
after comression another fragment is fixed to
plate.

Application of the articulated
tension device
 In oblique fractures the
tension device must be
applied in such a way
that the loose fragment
locks in the axilla if
compression is
produced.
 This figure
demonstrates the
tension device applied
in the wrong position

Compression with overbanding
 If a straight plate is
tensioned on a straight
bone, a transverse
fracture gap will open
up due to the eccentric
forces acting on the
opposite side.

 If the plate is slightly
prebent prior to the
application (a), the gap
in the opposite cortex
will disappear as
compression is built up
(b), so that finally the
whole fracture is firmly
closed and compressed
(c).

Compression plating
 Compression through plate
- DCP / LC-DCP

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.

 After insertion of one compressing screw,
it is only possible to insert one further
screw with compressing function in the
same fragment. Movement of the plate
pushes the first compression screw
against the side of the screw hole and
prevents further movement. When the
second screw is tightened, the first has to
be loosened to allow the plate to slide on
the bone, after which it is retightened.

 Screw holes
allow 1mm
compression
 Additional
compression
with 1 more
eccentric screw
before locking
first screw

The oval shape of the
holes allows 25°
inclination of the screws
in the longitudinal plane,
and up to 7° inclination in
the transversal plane

Contouring Plates
Straight plates often need to
be contoured prior to
application to fit the anatomy
of the bone. This is best done
with hand-held bending pliers,
the bending press, or bending
irons. Special flexible
templates are available that
can be modeled to the bone
surface. Repeated bending
back and forth should be
avoided, as this weakens the
plate.

Plate contouring steps
 Twisting the plate-The anteromedial surface of
the tibial shaft twists internally approximately
20° as it approaches the medial malleolus.
The first step of plate contouring is to twist the
plate so it matches the tibial surface upon
which it will lie.
If the plate is bent before it is twisted, the
process of twisting will alter the bend that has
been created.

 Matching the curvature
Depending upon the plate location, more or less
bending of the plate will be required to match the
contour of the intact (or reduced) bone. Much of the
medial tibial shaft is quite straight, so that little
bending is required. However, the distal medial
surface has a significant concavity, with a typical
radius of curvature of 20 cm as illustrated.
Such a 20 cm radius can be drawn on a sterile
drape and used as a template for plates to be used
in this location.

 Bending the plate
The plate can be bent with bending irons
alone, but it is preferable to bend with a
bending press, because the press gives more
control.
In either case, the bending is done in small
steps to produce a smooth contour. Contouring
only takes place over the distal 10-12 cm of
the plate. When finished, the plate should
match the 20 cm radius of curvature.

Buttress Plate
 A buttress is a
construction that resists
axial load by applying
force at 90° to the axis of
potential deformity
 Used in
metaphyseal/epiphyseal
shear or split fractures
 For application of a
buttress plate, the first
screw must be eccentric
to prevent sliding of the

Tension band principle
 Frederic Pauwels observed that a
curved, tubular structure under axial
load always has a compression side as
well as a tension side. Under vertical
pressure the curved femur creates a
tension force laterally and a
compression force medially A plate
positioned on the side of tensile forces
neutralizes them at the fracture site
provided there is cortical contact
opposite to this plate. In case of a
cortical defect, the plate will undergo
bending stresses and eventually fail
due to fatigue.

Dynamic and static tension band
 a) tension band principle on a
fracture of the patella. Upon
knee-flexion the distraction
forces are converted to
compression.
 In the olecranon fracture the
figure-of-eight wire loop acts
as a tension band upon
flexion of the elbow
 tension band principle at the
proximal humerus with an
avulsion of the greater
tubercle
 Tension band principle to the
medial malleolus example of
static tension band

Tension band principal
 The following prerequisites are essential:
 a) Bone or a fracture pattern that is able to
withstand compression.
b) An intact cortical buttress on the opposite
side of the tension band element.
c) Solid fixation that withstands tensile forces.

Antiglide Concepts
• In this model black plate is secured by three white
screws distal to the blue fracture line.
• The fracture is oriented such that displacement from
axial loading requires the proximal portion to move
to the left.
• The plate acts as a buttress against the
proximal portion, prevents it from “sliding”
and in effect prevents displacement from
an axial load.
• If this concept is applied to an intraarticular
fracture component it is usually referred to as a
buttress plate, and when applied to a diaphyseal
fracture it is usually referred to as an antiglide
plate.

Bone-implant composite
 Interdependence of bone and
implant in contributing to
stability
 Intact femur- support axial
load of 850 kg
 Transverse fracture of mid
shaft, with plate on lateral,
tension cortex – withstand
upto about 800 kg.
 Similar fixation with gap in
medial cortex will fail under a
load of about 60 kg
 Plated gap in shaft- buckle
under a 20 kg load.

 Fixation with an empty screw hole
directly leval with a single plane
fracture resulted in early fatigue
failure due to
 Movement
 Stress concentration at the weak
point.
 If a single plane fracture is
spilnted with a plate even with
axial interfragmentary
compression,the fracture will open
at the cortex oppsite to plate due
to elasticity of the plate.
 This instability is avoided by-lag
screw and prestressd by
overbending and by incorporate
bone graft medially.

Relative stability :
Biological osteosynthesis
 In multiplaner fracture
complex,use of technique to
achieve absolute rigid stability
can jeopardize the fragment
biology and failure of healing
and fixation. Application of
plate over top of wedge can
damage the vascularity.
 To avoid these complication of
absolute stability has
developed the concept of
relative stability.

 In such a fraacture if the
comminuted zone is bridged in a
manner that the main diaphyseal
fragments are:
 Aligned
 Correctly matched for rotation
 Out of length
 Undisturbed intermediate
fragments heal rapidly by
formation of external callus in
response to interfragmentary
motion.
 Addition of bone graft will ensure
rapid bone healing.

AO Organisation
☻ Philosophies and techniques of treatment will
change with time
☻ The philosophy that we exist to improve the
care given to our patients will last forever

Plates form and function

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