Locking compression plate: configuration, indication, advantages and biomechanics, fixed angle and variable angle lock plates

1. Seminar on
LCP: Configuration, Indication,
Advantages and Biomechanics
Moderator : Dr Jishnu Prakash Baruah
(Assistant professor)
Presenter : Dr Himashis Medhi
(PG student)

2. Learning objectives
• Locking plates
• Types
• Biomechanics
• Indications and contraindications
• Advantages and disadvantages

3. Introduction
 LIFP
 One stable system
 Less Screw Loosening
 Angular and axial stability
 Rigid construct

4. LCP
• “Combi hole”
• Compression and locking
mechanism
• Advantages of 
conventional + locking
plate
• 3 alternatives modes

5. Locking screws
• Threaded or locking head
• Thicker core diameter
• Smaller thread pitch
• Angularly stable construct
• Preserved periosteal blood supply
• Accurate plate contouring not required

6. • Threads of screw & plate must match
• Threaded drill guide
• Prevent cross threading

7. Types of locking screws
Self-tapping
• Monocortical or bicortical
• Taping Not necessary
Self-drilling
• Only monocortical
• Tapping and predrilling not
necessary

8. Locking mechanisms
Fixed-angle locking plates
• Screw head locked in chamber by
threaded locknut
• Double-threaded screw
• Identical pitch  prevents
compression

9. Variable-angle locking plates
 Expansion ring PEEK insert set in plate
Up to 10◦ clearance
 Locknut covers spherical screw head
 Up to 15◦ clearance
 The screw head is
threaded but is spherical

10. Pros and cons
Fixed angle
 Unidirectional  Avoids
Screw crossing
 No joint penetration
 Screw directions provide
maximum support to joint
Variable angle
 Circumvents obstacles
 Adapts to different # types
 Weaker resistance to
bending load
 Thicker implant-undesirable
near joint

11. Undersurface of locked plate
 “Scalloped” underserface
 Uniform stiffness
 Prolonged fatigue life
 Plate–bone contact
“footprint” reduced
 Undercuts 40o longitudinal
and 7o transverse

12. LCP- Modes
Conventional plating with absolute
stability
• Combi-hole  conventional
compression plate.
• Remaining holes  conventional
screws or locking
• Locking screws  osteoporotic
bone
• Locking screws can’t compensate
for length of plate

13. Bridge plating with relative stability
 Without anatomical reduction at
each fracture line
 Allows controlled micromotion
 Working length increases
 rigidity of construct decreases
 Forces distributed over larger
length of plate fatigue failure
less likely

14. Combination fixation
• Segmental fractures - absolute
stability for a simple component
• Conventional screws can
interfragmentary compression
• Bridging for the rest of the fracture
• Lag first, lock second
• Conventional screws are all used
before locking screws

15. Special plates
• Special plates for specific
locations
• They are shaped anatomically
• Dynamic compression possible
(eg, Proximal humerus, distal
radius, distal femur, and
proximal tibia)
• Locking and dynamic
compression

16. Biomechanics of locked plate
Ex fix vs LIFP
 “Internal external fixators”
 Single beam construct
 Less dependent on bone quality
and anatomic anchoring region
 Plate ~ Connecting bar, placed
close to bone stability

17. Conventional plate
 Stability from plate bone contact
 Screw head free to tilt
 Requires bicortical hold for stability
Locking plate
 Load distributed to all screws
 No screw toggle
 Unicortical purchase ensures stability

18. Conventional plateLocking plate

19. Bending load
Conventional plate
 Screws get oriented parallel
to load applied
 Sequential pullout
Locking plate
 screws overcome bone’s
resistance to shear forces
 En bloc pullout

20. Axial load
Locking plate
 locking screw resists shearing
along its entire length.
 Failure of compressive strength of
bone
Conventional plate
 Shearing effect only on
proximal side of screw.

21. Unicortical screw
 Requires strong anchorage
 Inefficient in metaphyseal bone
 Screw working length~no of threads
engaged
 Weaker against torsional loads
 Decreased damage to endosteal blood
supply

22. Far cortex locking
• Far cortex locking - parallel
interfragmentary compression
• Symmetrical callus
• Fixed angle but flexible
• Reduces stiffness by 80-88%
• Collar segment-support during
overload

23. Plate length and working length
 Plate length based on intended
biomechanical behaviour at # site
Relative stability
 Comminuted #
 Plate length- 2-3x fracture length
Absolute stability
 Simple transverse #
 Plate length- 8-10x fracture length

24. Working length
 Distance between two firmly
fixed points on either side of
the fracture
 Bending open construct-
weak.
 Bending close construct-
strong
 Plate working length  length
of plate not filled by screws

25. Number of screws and cortices
Simple fractures
 At least 2 screws per main fragment with purchase of
at least 3 cortices
Comminuted fractures
 At least 2 screws per main fragment with purchase of
at least 4 cortices

26. Position of screws in relation to fracture focus
Simple fractures
 Recommended – leave 3-4 holes
free at # zone
 Increases system’s elasticity
 ( ‘‘biological’’ synthesis)
 Avoid excessive stress on the
small part of the implant

27. Comminuted fractures
 Screws placed near the focus
 The fixation has adequate
stiffness, while avoiding
excessive stress on the implant

28. Osteoporotic bone
Problem?
 Conventional plating - high failure rate
 Sequential screw loosening and migration.
 Low resistance to pull out
Locking plate
• All screws have to pull out together with
plate
• Smaller pitch of screws allowing more
threads to grasp thinner cortices

29. LISS
 Preshaped plates
 Locking ,self drilling self tapping
screws
 Small incision (using jig )
 Plate and wire position checked
radiologically before insertion

30. MIPO
 Small incisions & little
dissection /stripping of
soft tissue
 Conventional and locking
plates can be used
 Preservation of osseous
and soft tissue vascularity
 Relative stability

31. Advantages
 Preserves blood supply
 Rapid bone healing
 Less infection
 Less intra-op blood loss
 Small incision-better
cosmetics & less pain.
Disadvantages
 Complicated technique
 Expensive reduction tools
 Excessive demand on implant
 Axial and rotational
malalignment

32. Indications of locking plate
 Complex periarticular #
 Intra-articular #
 Short, extraarticular metaphyseal #
 Periprosthetic #
 Fixation of corrective ostcotomies
 Malunions, non-unions and failed
fixation
 Pathological bones

33. Contraindications
Can be used in any plating situation
Unnecessary to fix
 Simple dialphyseal fracture
 Pelvic and acetabular fractures
 Fractures around ankle
 Metastatic diaphyseal # treatable with IM nails

34. Advantages
 Improved stability  angular and axial
 Preservation of fracture biology & periosteal BS
 Higher union rates
 Lower infection rates
 Scope of screw angulation
 Less Screw Loosening
 Accurate plate contouring not required

35. Disadvantages
• Tactile recognition for bone quality absent
• Predetermine Screw length
• Can maintain reduction but can’t obtain it
• Skin impingement
• Fracture malalignment
• Plate Breakage
• Difficult implant removal

36. Locked Plate removal
Why ?
 No role after bone healing
 Possibility of corrosion
 Inflammatory reactions
 Implant bothering patient
mechanically

37. Locked Plate removal
Removal is difficult
 Callus growing into holes
 Longer skin incision than initial sx
 Overtightening - cold welding
 Osteointegration
Fan blade effect
 Removal of last locking screw or tightening
of first inserted locking screw may rotate
the plate
 Plate steadied with K wire
 Loosen all the screws remove one by one

38. Thank you