Screw & PlatesTraumas Team

Dept. of Orthopaedic SurgeryHasan Sadikin General HospitalMedical School of Padjadjaran UniversityBandung

Lag Screw

General AspectsScrew very efficient tool for fixation of a fracture by interfragmentary compression or for fixing a splinting device (e.g : plate, nail or fixator to bone)

The axial force produced by a screw results from rotating screw clockwise the inclined surfaces of its threads glide along a corresponding surface of the bone.

General AspectsThe undersurface of the screw head is spherical allowing a congruent fit to be maintained while tilting the screw, e.g., within a plate hole. The thread is asymmetrical. The dimensions shown are designed to offer a good relation between axial force & torque applied

B. These dimension result in an inclination of the thread which is self locking

General AspectsTwo force components are active one along the circumference of the thread one along the axis of the screwThe compression applied by a screw affects a comparatively small area of the bone by which it is surrounded a single intert=fragmentary lag screw does not prevent rotation between two fragments

Types of Bone ScrewsTwo basic types : cortical & cancellousCancellous bone screw- larger outer diameter- deeper thread- larger pitch- metaphyseal or epiphysealCortical bone screw- diaphysis

Shaft ScrewsCompression of an epi-metaphyseal fracture using a shaft screwThe thread pulls the opposite bone fragment towards the head of the screw.The shaft of the screw does not transmit any great axial force between the shaft & the surrounding bone.The length of the screw shaft must be chosen the threaded part lies fully within the opposite bone fragment.Washer is used to prevent the screw head sinking into cortex

Mode of application of a Fully Threaded lag ScrewTo act as a lag screw the cortex screw requires a gliding hole in the near(cis) and a threaded hole in the far (trans) cortexIn diaphyseal bone, shaft screws or fully threaded screws are used because partially threaded cancellous bone screws are difficult to remove after healing

Modes of failureScrews can fall because of axial pull out, bending forces, or both.Screws usually resist axial pull out rather well.Most screws are fairly weak in bending due to their small core diameter

Special Considerations of Screw InsertionA screw should not be tightened to the limits of its strength, but only about 2/3 of this allow resistance to any additional functional loading

Positioning of the Screw in Respect to the fracture PlaneA lag screw oriented perpendicular to the fracture plane ideal inclination in the absence of forces along the bone axisInclination half way between the perpendiculars to the fracture plane and to the long axis of the bone better suited to resisting compressive functional load along the bone long axis.

Lag screws in metaphyseal and epiphyseal regionsTo obtain anatomical reduction and absolute stability interfragmentary lag screws are mandatory in articular fractures.

New Trends in Screw Application : Internal Fixator with Locked ScrewsThe new technology of using the so-called internal fixators for biological internal fixation takes advantage of short, unicortical screws.The head of this screw is locked within the body of the fixator (plate) in a position perpendicular to the long axis of the fixator.

New Trends in Screw Application : Internal Fixator with Locked ScrewsShows the design & force components of a conventional screw as used for the DCP and LC-DCP. The screw acts by producing friction between the plate undersurface & the bone surface due to compression of the interface.Locked screws as used in newer implants. These are usually unicortical & work more like bolts than screws; the axial force produced by the screw is minimal. The screw provides fixation screw head is locked in a position perpendicular to the plate body.

Cancellous screwCortical Screw

Plates

IntroductionRigid fixation Vs Biological fixationRigid fixation with plates and screws has a firm place in fracture treatmentArticular fractures require anatomical reduction and stable fixation as callus formation is not desiredThe potential compromise of cortical blood supply is a major draw back of conventional plating

Dynamic compression plate (DCP) 3.5 & 4.5Functions :1. Compression2. Neutralization3. Tension band3 sizes :1. Broad DCP 4.5 femur & humerus2. Narrow DCP 4.5 tbia & humerus 3. DCP 3.5 forearm,fibula,pelvis & clavicle

Dynamic compression plate (DCP) 3.5 & 4.5

Dynamic compression plate (DCP) 3.5 & 4.5When the screw is inserted & tightenedMovement of the bone fragment relative to the plateCompression of the fracture

Technique of DCP application2 DCP drill guide : with an eccentric (load) hole with concentric (neutral) hole

Limited Contact Dinamic Compression Plate (LC-DCP) 3.5 & 4.5The new LC-DCP design reduces the area of contact between plate & bone & thereby interferes less with bone biology

Limited Contact Dinamic Compression Plate (LC-DCP) 3.5 & 4.5

Technique of LC-DCP application3 different modes :1. Compression2. Neutral3. Butress2 LC- DCP drill guides plate 3.5 & 4.5 LC-DCP universal drill guide neutral or eccentric position relative to the plate hole.

Technique of LC-DCP application

Tubular plates (4.5/3.5/2.7)1/3 tubular plate (3.5 version only) titanium / stainless steel 1.0 mm thick useful in areas with minimal soft tissue covering (e.g lat. malleolus, olecranon) Each hole is surrounded by a small collar Oval shape of each hole eccentric screw placement to produce fracture compressionSemitubular plate (4.5 system) less used

Tubular plates (4.5/3.5/2.7)

Reconstruction plate 3.5 & 4.5Deep notches between the holes allow accurate contouring on the flat as well as standard bendingOval holes allow dynamic compressionUseful in fractures of bone with complex 3-D geomtery (e.g pelvis & acetabulum, distal humersu, clavicle)Special instruments are available for the contouring of these plates.

Special plates Several special plates for specific locations have been developed

They are shaped anatomically corresponding to the site where they are to be applied

Classical Principles of Rigid Internal Fixation with PlatesInterfragmentary compression provides stability through friction, but has no direct influence on bone bridging or fracture healing4 ways to obtain interfragmentary compression with a plate :1. Compression with a tension device2. Compression with the dynamic compression principle (DCP / LC-DCP)3. Compression by contouring (overbending) the plate 4. Additional lag screws through plate holes

Rigid Fixation by Lag Screw & Neutralization (Protection) PlateThe traditional & quite effective way to rigidly fix a simple diaphyseal fracture is to use lag screws combined with a neutralization (protection) plate.In metaepiphyseal split fractures lag screw fixation often needs to be combined with a buttress plate to protect the screws from shearing forces.

Rigid Fixation by Lag Screw & Neutralization (Protection) Plate

Compression with the Tension DeviceIn transverse or short oblique fractures of the diaphysis, placement of a lag screw is not always possible best treated by intramedullary fixation (except in the forearm)Compression plate is used if nailing is impossible.

Compression with the Tension Device

Compression by Overbending

Contouring of PlatesStraight plates often need to be contoured prior to application to fit the anatomy of the bone.If this not done reduction will be lost esp. if no lag screws are placed across fractureRepeated bending back & forth should be avoided

Different functions of platesThe function assigned to a plate does not depend on its designPlate may also be used for other functions: buttressing, bridging, or to act as a tension band

Buttress PlateIn a metaphyseal / epiphyseal shear or split fracture fixation with lag screws alone may not be sufficient combined with a plate with buttress or antiglide functionIn plates with DCP holes, the screws should inserted in the buttress position

Tension Band PlateCriteria for a plate to act as a tension band:1. The fractured bone must be eccentrically loaded, e.g., femur 2. The plate must be placed on the tension side 3. The plate must be able to withstand the tensile forces 4. The bone must be able to withstand the compressive force which results from the conversion of distraction forces by the plate There must be a bony buttress opposite to the plate to prevent cyclic bending

Tension Band PlateA plate undertensionis much strongerthan underbending forces

Bridge PlatingIndicated in complex diaphyseal fracture patterns.Fixed to the 2 main fragments only, leaving the fracture zone untouched acts as an extramedullary splint.This concept combines adequate mechanical stability offered by the plate with uncompromised natural fracture biology to achieve rapid interfragmentary callus formation & fracture consolidation

Bridge Plating

Bridge Plating

Bridge Plating