Plates and screws in orthopaedics

1. SCREWS AND PLATES
PRESENTOR:Dr. ARUN RAVINDRAN.
MODERATOR:Dr.RAMESH PERUMAL.

2. SCREWS:
• Powerful element that converts rotation into linear motion.
• Four functional parts: Head, Shaft, Thread, Tip.

3. HEAD:
RECESS , COUNTERSINK.
•Recess in the head to attach the screw driver.
5 types of screw Head Recess.
1)single slot head.
2) Cruciate head/Frearson screw head: Two slots at right angles
more contact area.
3) Philips Head: screw driver cams out if the screw stalls; avoids the damage
to screw head.

4. 4) Hexagonal head: good connection with screw & good lateral
guidance that allows blind insertion and removal.
5) Torx-type head socket: causes minimum stress and least
deformation of socket.

5. Countersink
• Under surface of the head.
• Can be conical or hemispherical.

6. SHAFT:
• Smooth transitional zone between the head & the thread.
Run out: it is a zone of transition between shaft & thread.
Point of stress concentration.
screw may break at run out if it incorrectly centered over
the hole.

7. THREAD
• It makes purchase of screw with bone.
core diameter: it is the narrowest/root diameter of screw
weakest part of screw.
The smaller the core diameter,
greater the tendency to shear off during insertion and removal.
• Thread diameter: represents outside diameter of screw.
larger the thread diameter, greater the resistanrce to pull out.

8. • Pitch: distance between two adjacent threads.
A cortical screw with fine threads has small pitch, whereas a
cancellous screw with a coarse thread has larger pitch.
The stronger the bone(cortex) the smaller the pitch; weaker the
bone (cancellous) the larger the pitch.
Purchase: resistance between screw and bone interface.

9. • Lead: Distance travelled by screw in one complete turn.
• Thread depth: Half of difference between thread and core diameter.

10. TIP
• Simple tip: (non tapping): smooth conical tip and needs a tool Tap to
make channel for passage of screw Eg: NST cortical screw.
• Self tapping: having cutting “flutes” for creating a channel. Eg: ST
cortical screw.
• Self drilling & self tapping:screws tip make a drill hole and also cuts
channel for passage of screw.eg: locking screw.

11. Corkscrew tip: used in cancellous screws. It forms its own thread by
compressing the thin walled trabecular bone
Trocar tip: it does not produce a true tread but rather displaces the
bone as it advances.Eg: malleolar screw, schanz screw.

12. Machine screws & wood screws:
Wooden screw Machine screw
Threads large small
Tip Self taping Non self taping
Tap Not needed Needed

14. Self tapping screws
• Screws which can make threads through bone over which it
advances.
• It can inserted into a predrilled hole without tapping a thread.
Thread forming screws (by plastic elastic deformation)
• ST screws
Thread cutting screws (cuts its threads)

15. Non self Tapping screw
• It is incapable of cutting threads in bone.
• Eg: Non self tapping cortical screws.
• A special instrument called Tap is used for cutting threads in bone.
• After tapping, we can insert NST screws into pre drilled hole.
• Advantage : higher percentile of applied torque is converted to
effective tensile force.

16. Fully threaded & Partially threaded screws
• Cortical & cancellous screws are fully or partially threaded.
Cortical screw Cancellous screw
Fully threaded Lag screw Placement screw
Partially threaded (Shaft
screw)
Lag screw Lag screw

17. Lag screw
• Lag screw is a technique of insertion and not a screw.
• It pulls the fragments together and achieve compression b/w two
bone fragments.
• A lag screw must freely glide/over drilled through near cortex &
engage/purchase only the far cortex.
• Whenever a screw crosses a fracture line,it should be inserted as lag
screw.
• The holding strength of lag screw increases as the distance from the
fracture line at the far cortex to the screw is longest.
• Two small screws produce more stable fixation than one large screw.

18. LAG SCREW

19. • Partially threaded cortical & cancellous screw with long shaft (shaft
screws) act as lag screws.
• The unthreaded portion engage the near cortex and threaded portion
engages the far cortex

20. Cannulated screws
• Used for precise insertion in metaphyseal or epiphyseal site over
guide wire.
• Large cannulated screws are used to fix
fractures of femoral neck, femoral condyle,
tibial plateau.
Small cannulated cancellous screw used for distal radius
Distal humerus &scaphoid bone fracture.
For cancellous bone,cannulated screws should be
Selfcutting & Self tapping.

21. Locking screws:
• Is a bone screw with threads on undersurface or countersink of the
head.
• On tightening ,it lock in matching threads in plate hole and get axially
and angularly stable.
• It does not produce compression b/w plate and bone but it resists pull
out forces.

22. Locking screws
Locking screws Conventional
screws
pitch Large and coarse smaller
Core diameter large small
tip ST & SD ST Same
thread shallower

23. Herbert screw:
• Cannulated headless screw.
• No head. Threads at both ends ie leading end (3mm) and trailing
end(3.9mm) with differential pitch.
• Provide interfragmentary compression.
• Uses: for scaphoid fractures.
capitellum fractures.
Radial head fractures.
Talus fractures.
small joint arthrodesis.

24. Acutrak screw
• A fully threaded, headless, cannulated screw.
• Differential pitch, i.e. greater pitch at tip and smaller pitch at head
end causes lag effect.
• Provides interfragmentary compression.
• Can be used in place of Herbert screw.

25. DHS sliding screw & DHS compression screw
• A cannulated headless screw with lag effect.
• Provides interfragmentary compression.
• Screw dimensions are as:
screw length: 50-130 mm
core diameter: 8 mm
Thread length: 22mm
Thread diameter: 12.5mm

26. • Shaft is rectangular with rounded corner in transverse section that fits
in similar slot of barrel of DHS plate.
• It prevents the rotation of screw in barrel and finally stabilize the
fracture.
• DHS compression screw: it compress the distal fragment of fracture
over proximal one.
length : 36mm
diameter: 4mm

27. Malleolar screw:
• Cortical screw
• Solid screw
• Partially threaded
• Trocar tipped
• 4.5 mm diameter
• 4mm cancellous screw now taken its place.

28. Other functions of screws:
• Anchor screw : act as an anchor to hold wire or suture material
Eg: TBW in proximal humerus fracture.
Poller screw: used for redirection of nail during IM nailing.
Eg: nailing in proximal tibia fracture.

29. Drill Bit measurements

30. BONE PLATES

31. Bone plates:
• Internal splints holding together the fracture ends of a bone.
• TWO mechanical functions:
1)Transfer forces from one end to other end of bone & thus
protecting the fracture site.
2)Maintain alignment of bone.

32. History:
• SHERMAN plate is the first scientific plate in history of orthopaedic
hardware.
• In 1958, AO devised a family of plates for long bone fractures.
• In 1969, the dynamic compression plate was developed.
• In 1994 LC DCP was created.

33. CLASSIFICATION ON THE BASIS OF FUNCTION
1.COMPRESSION PLATING
2.PROTECTION (NEUTRALIZATION) PLATING
3.BUTTRESS PLATING
4.TENSION BAND PLATING
5.BRIDGE PLATING
6.CONDYLAR PLATING

34. COMPRESSION PLATING
• Produce locking force/compression force across a fracture site.
• If fracture reduced anatomically, plate partialy shares load until
fracture heals.
• If fracture not reduced anatomically, entire load will shared by plate
implant failure occur.
Two types of compression: Static compression:-plates applied under
tension produces static compression.it constantly exerts compression
either limb is resting or functional.
• Dynamic compression : plate can modify the physiological
destabilizing forces to compressive forces.
• IMPLANT used: DCP,LCDCP

35. DCP:
• Three main types:
.

37. Dynamic compression principle:

38. Order of application of screw:
First apply centric screw by the one side of fracture.- (1mm displacement)
Second eccentric screw by the other side of fracture-( 2mm displacement)
if fracture gap still remains, a third eccentrically placed screw may be inserted.
Before this screw is tightened, the first screw has to be loosened to allow the plate to
slide.
After that, first screw is tightened again

39. The oval shape of the hole allows 25 deg inclination of the screws in the
longitudinal plane and upto 7 deg inclination in transverse plane

40. LC DCP: Low contact DCP
• DCP has direct contact with bone. So some degree of osteoporosis develops
(stress shielding).
• To avoid this,AO develops LC-DCP.
• Used for transverse and short oblique fracture.

42. Neutralization/Protection Plate
• A Plate used in combination with a lag screw is a protection plate.
• It countering the torsional,bending,shearing forces that tend to
disrupt the screw.
• Lag screw provides interfragmentary compression & stability.
• The plate protects lag screw and provides mobility in extremity.

43. • It used in oblique fracture, long spiral fracture, butterfly fragment.
• Implants used: DCP,LCP

44. BUTRESS PLATING:
• A cancellous lag screw can produce compression force in cancellous
bone surface of fractures which passing through metaphyseal-
epiphyseal ends (periarticular surfaces).
• This fixation is insufficient to resist the axial forces to joint surfaces
during weight bearing.
• It is necessary to apply a long plate extending to diaphysis from meta-
epiphyseal area.
• Such a plate act as buttress plate

45. BUTRESS PLATING:
• It strengthen the weakened area of cortex and prevents bone from
collapsing during healing process.
• The large surface area of plate facilitate wider distribution of loads.
• Must be firmly anchored to main fragment.
• Fixation should begin in middile of plate i.e. closest to the fracture
site on the shaft.
• It applies force to the bone which is perpendicular to flat surface of
plate.
• Implants: T or L shaped implants
• Used for peri or intraarticular metaphyseal fracture.

47. CONDYLAR PLATING
• It used mainly in intraarticular distal femoral fractures.
• Two mechanical function:
1) maintains reduction of major intra articular
fragments & restoring anatomy of joint.
2) fixes the metaphyseal component to diaphyseal
shaft, permitting early movement of extremity.
it act as both neutralisation and buttress plate.

48. BRIDGE PLATING:
• A neutralization plate act as a bridge plate.
• Transmits forces from one end of the bone to other, bypassing the
fracture.
• Act as a mechanical link b/w healthy segments of bone.
• Does not produce compression at fracture site.
• Implants: LCP, DCP
• Used in comminuted fractures.

49. Tension Band Plating:
• It converts tensile force into compressive force
• After fracture reduction, the opposite cortex must provide a bony
buttress to prevent cyclic bending & failure of fixation.
• A strong plate to withstand the
tensile strength.
Plate placement on the tension
side (lateral side)

50. TUBULAR PLATES
• These plates are actually a part of metallic cylindrical tube.
• Mainly used in bridging & neutralization mode.
• Used in lateral malleoli,distal ulna fractures.

52. LOCKING COMPRESSION PLATE:
• Rounded holes with threads makes the basis of locked plate
• The threaded holes receives threaded
conical head of the screw & as the screw
tightened in the plate hole, the thread locks
fixed-angle construct is formed.
COMBI HOLE : Threaded hole combines with
smooth oval hole.
it provides self compression and locking
Mechanism.

53. LCP
• LCP has no contact with periosteum.
• It provides relative stability.
• It allows maximum blood supply
to allow rapid indirect healing through callus formation.
• It provides 6 biomechanical functions
of a non locking plates.
Plate length: at least 3 times of fracture length.
Placement of screw: Farthest screw first & alternate
placement.

54. LCP
• Prerequistie: Fracture should be completely reduced.
• Indications: osteoporotic fracture.
comminuted metaphyseal fracture.
Intra articular fracture.
Two kinds of locking plates:1) Fixed angle locking plates:
Here, the screw inserted at a predetermined angle to the hole.
This is achieved by drilling a pilot hole through a sleeve that is screwed in the
plate hole.
The predetermined angle of threaded hole may cause difficulty in
metaphyseal and periarticular fixations. Here, we use shorter locked screw.

55. Variable angle plates:
• Multidirectional angular stability allows screws to be locked in the
plate hole at a desired angle.
• Expanding washers , clips allows a screw to be put in the preffered
direction.

56. Reconstruction plates:
• These plates can be molded manually according to contour of bone
having fracture.
• Use: Bridging & Neutralization
• Types: 1) Simple Recon plates: screws2.5mm,3.5mm,4.5mm.
2)Locking Recon Plates: screw 3.5mm, 4.5mm.
3)Various shaped Recon Plates: Y-shapedRecon Plates.

57. Varaiable Regional Plates

59. THANK YOU