1. PLATES AND
SCREWS:
An Overview
Presented by :
Dr. REM
KUMAR RAI

2. SCREW : BRIEF OVERVIEW

3. 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)

4. Screw: Parts
 4 functional parts
 Head
 Shaft
 Thread
 Tip
shank

5. Head: Function
 1. Means for applying torque with a
screwdriver
 2. Acts as a stop (the undersurface) i.e.
countersunk

6. Head: Recess Types
 1. Slotted
 2. Cruciate
 3. Philips
 4. Hex/ Allen
 5.Torx (eg Stardrive of Synthes)

7. Head: Countersink
 Undersurface of head
 Conical
 Hemispherical
 Morse-cone (steep): locking plates

8. Screw: Shaft/ Shank
 Smooth link
 Almost not present in standard cortex screw
 Present in cortical SHAFT SCREW or
cancellous screw

9. Screw: Run out
 Transition between shaft and thread
 Site of most stress riser
 Screw break
 Incorrectly centered hole
 Hole not perpendicular to the plate

10. 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

11. 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

12. Screw: Pitch and Lead
 Distance between the adjacent threads
 Cortex screw : small pitch 1.75mm
 Cancellous screw: large pitch
 Pitch also determines the lead
 Lead :distance advanced in a complete turn
 Equals pitch in single threaded screw
 Greater M.A. if smaller lead

13. Screw: Thread Diameter
 Diameter across the
maximum thread
width
 Affects the pull out
strength
 Cancellous have
larger thread
diameter

14. 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

15. 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

16. 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

17. Screw: 4.Trochar Tip
 Like self tapping
 Displaces the bone as it advances
 Malleolar screw
 Schanz screws
 Locking bolts for IMIL

18. Screw: 5.Self drilling self
tapping
 Like a drill bit
 In locked internal fixator plate hole
 Pre-drilling not required
 Good purchase in osteoporotic and
metaphyseal area

19. Locking Screws vs
Cortical Screws
Creates Fixed Angle Generates
Friction/Compression
4.4mm Core Dia. 3.5mm Core Dia.
5.0 mm Locking Screw 4.5 mm Cortical Screw

20.  Bending stiffness proportional to the core
diameter
 Pull out strength is proportional to the size of
the thread
 Cannulated screws have less bending
stiffness

21. Machine and Wood Screws
 Wood
 Used in wood
 Large threads , usually tapered
 Pilot hole is small
 Elastic force from deformation of wood
 Machine
 Used in metals
 Pilot hole matches the size of the screw
core
 Tapped
 Elastic force from deformation of the
screw itself

22.  Tensile strength is directly proportional to the
squared core diameter d2
 Pull out strength is depends on the outer
diameter
 Shear strength is directly proportional to the
cubed core diameter d3.

23. 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
 2:phalanx

24.  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

25.  Cannulated screws
 3.0
 4.0
 4.5
 6.5
 7.0
 7.3

26.  Locking screws synthes
 2.4mm
 3.5mm
 4.0mm
 5.0mm
 7.3mm

27. 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.

28. 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

29. Special Screws
 Herbert Screw
 Dynamic Hip Screw
 Malleolar Screw
 Locking bolt
 Interference screw
 Suture anchor
 Acutrak screw
 Pedicle screw

30. Herbert Screw
 Specialized to achieve
interfragmentary compression
 Headless
 Threads at both ends
 Pitch differential between the
leading and trailing threads
 Compression by the difference in
thread pitch
 Coarser pitch moves a greater
distance with each turn than does
the finer pitch

31. Clinical application:Lag Screw
 Used to compress fracture fragments
 Use to hold plates on bone
 Threads only engage far cortex
 Can be achieve with:
- Partially threaded screw
- Fully threaded with over drilling near cortex

32. Clinical Application:
Positional Screw

33. Lag Screw
PartiallyThreaded cancellous screw
Threads must be completely across the fracture to
achieve compression and purchase far cortex if
possible

35. PLATES
Introduction :
 Bone plates are like internal splints
holding together the fractured ends of a
bone.

36. Mechanical functions of
plate
1. Transmit forces from one end to another,
bypassing and thus protecting the area of
fractures.
2. Holds the fracture ends together in
alignment throughout the healing process.

37. 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

38. 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.

39. 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

40. Special Plates
 T Plates
 T&L Buttress plates
 LateralTibial head buttress plates
 Condylar buttress plate
 Narrow lenthening plates
 Broad Lengthening plate
 Spoon plate
 Clover leaf plate

41. 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.

42. The Neutralization Plate
 Lag screws:
 compression and
initial stability
 Plate:
 protects the screws
from bending and
torsional loads

43. NEUTRALIZATION PLATE

44. COMPRESSION PLATE
• produces a locking force across a
fracture site
• Newton's Third Law (action and
reaction are equal opposite)
• plate is attached to a bone fragment
then pulled across the fracture site by a
device, producing tension in the plate
• direction of the compression force is
parallel to the plate

45. COMPRESSION
Static: does not change with
time
Dynamic: periodic partial
loading & unloading due to
functional activity
1. Tension Band wiring
2. Tension Band Plating

46. BONE UNDER
COMPRESSION
• Superior stability – Utilization of
physiological forces
• Improved milieu for bone healing
• Early mobilization

47. DCP (Dynamic Compression
Plate):
Principle :
- a self compression
plate due to the
special geometry
of screw holes
which allow the
axial compression.

48. Dynamic compression principle: screw head slides down the
inclined plate hole as it is tightened, with the head forcing the
bone-screw to move towards the fracture, thereby compressing the
fracture

49. • Screw hole and the
spherical gliding
principle.
• Axial compression result
from the an interplay
between screw hole
geometry and eccentric
placement of the screw in
the screw hole.

50. The shape of the holes of the dynamic compression
plate allows inclination of the screws in a transverse
direction of +7° and in a longitudinal direction of
25°.

51. 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 compression
4. Usage of two lag screws in the main fragments
for axial compression
5. Compression of several fragments individually
in comminuted fractures
6. Application as a buttress plate in articular area

52. Shortcomings of DCP :
1. Flat under surface.
2. Inclination upto 25°
3. Plate hole distribution (extended middle
segment)

53. The structure of a limited-
contact dynamic
compression plate
1.Structured
undersurface
2.Undercut screw holes
3.Trapezoid cross
section
LC-DCP

54. 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.

55.  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

56.  The trapezoid cross section of the plate
results in a smaller contact area between
plate and bone.
 The plate holes are uniformaly spaced,
which permits easy positioning of the plate.
 Undercuts plate holes; undercut at each end
of the plate hole allows 40 tilting of screws
both ways along the long axis of the plate.
Lag screw fixation of short oblique fractures
is thereby possible.

57. Sizes of DCP
Name 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 LCDCP
Name 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

58. 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.

59. • The fixation to the
bone should begin
in the middle of the
plate, i.e. 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.
BUTTRESS PLATE

60. 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

61. Wave Plating :
Wave Plating for
non union

62. ADDITIONAL PRINCIPLES OF PLATE
FIXATION
 The engineering principle of the tension band is
widely used in fracture fixation. It applies to the
conversion of tensile forces to compression
forces on the convex side of an eccentrically
loaded bone.

63. Reconstruction Plates :
 Can be bent and twisted in two dimensions.
 Decrease stiffness than DCP.
 Should not be bent more than 15°.
 Used were the exact and complex contouring is
required. eg. Pelvis, Distal Humerus, Clavicle.

64. 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.

65. One Third Tubular Plates :
 Plates have the form of one third of the
circumference of a cylinder.
 Low rigidity (1mm thick).
 Oval holes – Axial compression can be achieved.
 Uses – Lateral malleolus, distal ulna,
metatarsals.

66. 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.

67. 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)

68. LCP: internal external
fixator

69. 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

70. Unicortical Fixation
Conventional
Plating
SmallSmall
LoadLoad
SmallSmall
LoadLoad
Screws have
single point of
fixation
Screws have
two points of
fixation
Locked Plating

71. Principle of internal fixation
using LCP :
1. 1st
reduced the # as anatomical as possible
2. Cortical screw should be used 1st
in a fracture
fragment
3. 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

73. 6. Osteoporotic bones bicortical screws should
be used.
7. In the comminuted # screw holes close to
the fracture should be used to reduce stain.
8. In the fracture with small or no gap the
immediate screw holes should be left
unfilled to reduced the strain.

75. Indications :
1. Osteoporotic #
2. Periprosthetic #
3. Multifragmentry #
4. Delayed change from external fixation to internal
fixation.
Advantages :
1. Angular stability
2. Axial stability
3. Plate contouring not required
4. Less damage to the blood supply of bone
5. Decrease infection because of submuscular technique
6. Less soft tissue damage

76. HOW MANY SCREWS ?
 Hands-on experience suggests that, in the
humerus, screws grip seven cortices on each side of
the fracture ; in the radius and the ulna, five; in the
tibia, six, and in the femur, seven.
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

77. HOW CLOSE TO THE FRACTURE SITE?
 A screw, as a result, should not be placed
closer than one centimeter from the fracture
line.

78. Timing of Plate Removal,
Recommendations for removal of
plates in the lower limb :
 Bone / Fracture
 Time after implantation in months
 Malleolar fractures
 8-12
 The tibial pilon
 12-18
 The tibial shaft
 12-18
 The tibial head
 12-18

79.  The femoral condyles
 12-24
 The femoral shaft: Single plate, Double Plate
 24-36
 From month 18, in 2 steps ( Interval 06 months)
 Pertrochanteric and femoral neck fractures Upper extremity
 12-18
 Optional
 Shaft of radius / ulna
 24-28
 Distal radius
 8-12
 Metacarpals
 4-6

81. DIFFERENT AO SCREWS
LARGE STANDARD SCREWS. 4.5 mm Cortex Screw
6.5 mm Cancellous Screw
Malleolar Screw 4.5
CANNULATED SCREW
SYSTEM
6.5 Cannulated Screw
4.0 mm Cannulated
Screw
3.5 Cannulated Screw
SMALL FRAGMENT SCREW 3.5 mm Cortical Screw
4.0 Canceleous Screw
-Partially Threaded.
-Fully Threaded
MINI SCREW 2.7 mm Cortex Screw
2.0 mm Cortex Screw
1.5 mm Cortex Screw

82. Screw Core
diam
eter
Threa
d
diame
ter
Pitch Drill
bit for
glidin
g
hole
Drill
bit for
thread
hole
Tap
diame
ter
Large
Standa
rd
Screws
7mm
Cancello
us
Screw
4.5m
m
7mm 2.75m
m
4.5m
m
7mm
6.5mm
cancello
us
screw
3.5m
m
6.5m
m
2.7mm 3.2m
m
4.5m
m
6.5m
m
4.5mm
cancello
us
screw
4.5m
m
3.1m
m
1.75m
m
3.2m
m
4.5m
m
4.5mm
cortical
3mm 4.5
mm
1.75m
m
4.5m
m
3.2m
m
4.5m
m

83. Small
Fragme
nt
Screws
3.5mm
cancello
us screw
2.5m
m
3.5m
m
1.25m
m
2.7m
m
3.5m
m
4mm
Cancello
us screw
1.9m
m
4mm 1.75m
m
2.5m
m
4mm
3.5mm
Cortex
Screw
2.4m
m
3.5m
m
1.25m
m
3.5m
m
2.5m
m
3.5m
m
Mini
Fragme
nt
Screws
2.7mm
Cortex
Screw
1.9m
m
2.7m
m
1mm 2.7m
m
2mm 2.7m
m
2mm
Cortex
Screw
1.3m
m
2mm 0.6mm 2mm 1.5m
m
2mm
1.5mm
Cortex
Screw
1mm 1.5m
m
0.5mm 1.5m
m
1.1m
m
1.5m
m