BONE PLATES

Presented By:Dr Dipendra Maharjan1st yr Resident,Orthopaedics

AO PRINCIPLES

• In 1958, the AO formulated four basic principles which have become guideline for internal fixation– Anatomical reduction– Stable fixation– Preservation of blood supply– Early active mobilization

BONE PLATE

• Like an internal splints holding together the fractured end of a bone

• A load sharing device• General principle – anatomical reduction and stable

internal fixation• Two mechanical function– Transmits force from one end to another bypassing

fracture area– Holds the fracture ends while maintaining alignment of

the fragments

CLASSIFICATION

• Shape of the plate (semitubular plate)• Width of the plate (broad/Narrow)• Shape of the screw hole (Round hole plate)• Surface contact characteristics of the plate

(low contact)• Intended site of application (Condylar)

Contd…

• Classified into a group, according to their function– Neutralization plate– Compression plate– Buttress plate– Condylar plate

NEUTRALIZATION PLATE

• Transmits force from one end to another bypassing the fracture site

• Acts as a bridge• Function – mechanical link

between healthy segment of bone above and below fracture

• Does not produce compression• In combination with lag screw is

also neutralization plate

• If geometry permits, produce compression at fracture site

• Clinical application– To protect the screw fixation of a short oblique

fracture– Butter fragment–Mildly comminuted fracture of long bone– Fixation of segmental bone defect in combination

with bone graft

COMPRESSION PLATE

• Produce locking force across a fracture site

• Works as per Newton’s third law• Direction of compression is

parallel to plate• General principle – A plate is attached to a bone

fragment, pulled across the fracture site and tension is produces. As a reaction to this tension, compression is produced at the fracture site.

• ROLE OF COMPRESSION– Compaction of fracture to force together• Increase stability of the construct

– Reduction of the space between bone fragments– Protection of blood supply– Friction• Resists the tendency of fragment to slide under torsion

or shear force– Generates axial inter-fragmental compression• Fracture immobilization to that of neutralization plate

• Compression may be static or dynamic compression– Dynamic• A phenomenon by which a plate can transfer or modify

functional physiological force into compression force at fracture site

– Static• A plate applied under tension produces static

compression site, this compression exist constantly even when limb is at rest or functioning

DYNAMIC COMPRESSION PLATE• Two basic functions:– independent axial compression– the ability to place screws at different angles of

inclination. • There are three areas in which to place a

screw: – one at each end (eccentrically)– one in the middle (concentrically).

• The act of compression is accomplished through the merging of two eccentric circles to become concentric.

• A screw placed at the inclined plane moves the plate horizontally in relation to the bone until the screw head reaches the intersection of the two circles.

• At this point, the screw has optimal contact with the hole, ensuring maximal stability and producing axial compression of the bone and tension on the plate.

• The plate can be placed for depending on the insertion of the screw – neutralization– compression– buttressing,

• The DC plate can be modified for use and its use is based on fracture pattern and location

• Certain shortcomings of the DC plate have been discovered through the years. – interference with the periosteal blood supply

• plate-induced osteoporosis• sequestrum could form underneath the plate.

– a soft spot in fracture healing can occur • possibility of refracture

LIMITED CONTACT DYNAMIC COMPRESSION

• Modification that attempts to correct some of the design shortcomings of the DC plate.

• Based on work by Klaue and Perren, there are three main differences in design.– sides of the plate are inclined to form a trapezoidal cross section

interrupted by undercuts that form. • reduces the area of contact between the plate and the periosteal surface of

the bone, – the screw hole is made up of two inclined and one horizontal cylinder

• they meet at the same angle, permitting compression in both directions– stress is more equally distributed

• less deformation occurs at the screw holes when contouring

• The biomechanical uses and applications of the LCDC plate are the same as those for the DC plate.

Methods of achieving compression

• Self compressing plate– Converts torque applied to the screw head to a longitudinal

force which compresses the fractured bone ends– Screws and plates are designed to facilitate this conversion

• Tensioning device– Special tensioning device can be attached the bone plate

and adjacent bone cortex– Produce tension in the plate and compression force across

the fracture

• Eccentric screw placement– Eccentric means cirlce with different centre– Eccentric screw placement in a plate hole creates

considerable shear stress in the screw which is transmitted to the plate and can occasionally be used to produce interfragmental compression

– Inefficient technique, screw head may break

TENSION BAND

• When fuctional activity begins, physiological force which are normally destabilizing for a fracture, are converted to a stabilizing and active force by the same plate, which acts as a tension band.

• This band is used to create a small amount of compression, which results in partial closure of the discontinuity and compression of the spring on the same side as the band.

Buttress plate• Applies a force to the bone which is

perpendicular to the flat surface of the plate

• Main function:– Buttress weakened are of cortex– Protects from collapsing during

healing process– Designed with large surface area to

facilitate wider distribution of load– Used to maintain bone length or

support the depressed fracture fragment

• Commonly used in fixing epiphyseal and metaphyseal fracture

Bridging Plate

• Called bridge because its fixation is out of the main zone of injury at the end of the plate to avoid additional injury in comminuted zone

• Intended to maintain length and alignment of severly comminuted and segmental fracture

• Limits devitalization of fragments and thereby allows for a better healing enviroment

Condylar plate

• Has distinct mechanical function– Maintains the reduction of main intra-articular fragments– Rigidly fixes the metaphyseal components to diaphyseal

shaft, permitting early movement of the extremity• Functions as neutralization plate as well as buttress

plate. it does act as compression plate as well.• Fixed angle of the plate overcomes the coronal plane

instability and prevents consequent collapse.

SEMI-TUBULAR, ONE-THIRD TUBULAR, AND QUARTER-TUBULAR PLATES

• the first AO self-compression plate designed in the shape of a half-tube.• It provides compression through eccentrically placed oval plate holes.• Semi tubular plate:

– maintains its rotational stability with edges that dig into the side of the periosteum under tension.

– Its main indication is for tension resistance• The one-third tubular plate

– commonly used as a neutralization plate in the treatment of lateral malleolar fractures.

• The quarter-tubular plates – have been used in small bone fixation (e.g., in hand surgery).

RECONSTRUCTION PLATE• designed with notches in its side

so that it can be contoured in any plane

• mainly used in fractures of the pelvis, where precise contouring is important

• also be used for fixation of distal humerus and calcaneal fractures.

• relatively low strength, further diminished with contouring.

• offers some compression because of its oval screw holes.

ANGLED PLATES• developed in the 1950s for the fixation

of proximal and distal femur fractures. • They are a one-piece design with a U-

shaped profile for the blade portion and a 95° or 130° fixed angle between the blade and the plate.

• The shaft is thicker than the blade and can withstand higher stress.

• The forces applied in this area exceed 1200 lb/in. with the medial cortex exposed to compression combined with greater stress and the lateral cortex exposed to tension.

• The 130° Blade Plate– originally designed for fixation of proximal femur

fractures– has different lengths to accommodate different

fracture patterns. – The 4- and 6-hole plates are used for fixation of

intertrochanteric fractures, while the 9- to 12-hole plates are used for treatment of subtrochanteric fractures.

– It has been replaced for the most part by the dynamic hip screw, which allows for compression of the fragments.

• The 95° Condylar Blade Plate– designed for use with supracondylar and bicondylar

distal femur fractures– the length employed is also fracture specific– It can be used for subtrochanteric fractures where

more purchase on the fracture fragment can be gained with a sharper angled plate.

– the device is strong and provides stable fixation– The need for precise alignment in all three planes

demands careful preoperative planning and intraoperative radiographic control.

LOCKING COMPRESSIVE PLATE

• General principle:– Represents novel, bio-friendly approach to internal

fixation– it combines the principles of conventional plate

osteosynthesis for direct anatomical reduction with those of bridging plate osteosynthesis.

– The importance of the reduction technique and minimally invasive plate insertion and fixation relates to ensuring that bone viability is undisturbed.

• Is a symbiosis of various locking techniques of plate osteosynthesis

• Offers a versatile, easy to use and purposeful design to improve the surgical approach to fracture treatment

• Is a construct where screw with threaded head locked in a threaded hole in a bone plate

• The force are transferred from the bone to the fixator across the threaded-screw fixator connection

BIOMECHANICS• Might be considered as ultimate external fixator, with

minimal soft tissue dissection, wide screw spacing, locked screw and the plate functioning as the connecting bare, placed extremely close to the mechanical axis of the bone.

• Locked plate controls the axial orientation of the screw to the plate, enhancing the screw-plate-bone construct stability by creating a single beam construct

• Single beam construct is four times stronger than load sharing beam construct.

• Relative stability and secondary bone healing are the goals of LCP

ADVANTAGES

• Preserve biological intergrity• Resistance to infection• Locking the screw in the fixator abolishes – load transmission by friction, – minimizes bone contact, – increase stability, – eliminates the risk of loss of reduction

• Achieving fixation in osteopenic or pathologic bone

DISADVANTAGES

• Has no tactile feedback as to the quality of screw purchase into the bone

• Can maintain fracture reduction but not to obtain it• Locked screw will not pull the plate down on its own• Higher rate of fracture malalignment• Rigidity of locked screw plate construct• Inability to alter the angle of the screw within the

hole and still achieve a locked screw• Hardware removal is more difficult

SUMMARY

• The basic biomechanical functions of plates in fracture fixation have been discussed, as well as some of the major plate designs and examples of plates modified for use in specific anatomic areas.

• It is important to realize that specific design features of plates can be used to fulfill biomechanical needs based on the particularities of the fracture.

• Research in this area continues to improve fracture fixation techniques and instrumentation.

THANK YOU

REFERENCES

• The element of fracture fixation, 2nd Edition• Skeletal Trauma, 4th Edition