1. Evolution of plate design and function
Author: Michael Gardner
Reviewer: Michael Gardener
Reviewed: 2018
AO Trauma Advanced Principles Course

2. Learning objectives
Describe a spectrum of fixation methods using different plate types
Discuss the role of conventional implants and new techniques
Identify indications for the use of locked screw fixation (internal fixator)
Outline the mechanics of locking head screw and plate constructs
Evaluate key outcome publications
Teaching points:
Clearly identify the progressive relationship between plate evolution and bone healing understanding.

3. Original AO Principles (1958)
Anatomical reduction
Rigid fixation with fracture compression:
Stable internal fixation
Preservation of blood supply and soft tissues
Early active pain-free mobilization
In the beginning in 1958, AO formulated four principles for the treatment of fractures. This concept was applied expecting better results in the surgical treatment of fractures.
Reference:
Müller ME, Allgöwer M, Schneider R, et al (1991) Basic aspects of Internal Fixation. Manual of Internal Fixation. 3rd ed. Berlin Heidelberg New York Tokyo: Springer-Verlag, 2.

4. AO Principles today Reduction: restore anatomical relationship
Fixation: absolute or relative stability
Depends mainly on fracture pattern
Preservation of blood supply to bone tissues and bone
Early and safe mobilization
After more than 50 years, the four principles are almost the same, having withstood the test of time.
References:
Rüedi TP, Buckley RE, Moran CG. AO Principles of Fracture Management. 2nd ed. Stuttgart, New York: Thieme Verlag; 2007:vol

5. Lag screw Most effective way to create interfragmentary compression
Requires:
Simple fracture pattern
Sufficient obliquity
Anatomical reduction

6. Historical implants
In this slide, the lecturer should make a slight remark about the history of surgical fracture treatment; for instance osteosynthesis with wires as shown in the first photo.
Looking for more stability, the surgeons utilized different tools like the screws in the middle photo.
Then plates were employed to provide even more stability. Different types of plates could not standardize the results of osteosynthesis, leading to the evolution of different forms and designs (third photo).
Plates differed not only in form but also in material (bottom photo).

7. Coapteur created by Robert Danis (1880–1962)
In this slide the lecturer should give an exact account of the importance of the design of the holes of the plate.
The Coapteur created by Robert Danis provides axial compression.

8. Round-hole plate (1958)
Axial compression can only be obtained using the external compression device
Be aware that round-hole plates are still used in some developing countries.
The axial compression obtained using the external compression device is significantly more than using the oval hole of the dynamic compression plate (DCP). The external compression device is frequently used in the treatment of nonunions and is also used in osteotomies.

9. Absolute stability obtained by lag screws and external compression device
Classical AO technique. Note the use of cerclage wires as reduction tools. Such a technique will inevitably result in significant soft-tissue stripping but good results can still be obtained with meticulous surgical technique in the presence of good soft tissues.
Open
reduction
Rigid
fixation
No callus,
direct healing

10. Dynamic compression plate (DCP)
“Still—don’t forget”
The design of the holes in the plate permitted axial compression without the external compressor.
Only 1 mm of compression can be obtained with each DCP screw inserted in an eccentric position. The external compressor is still therefore invaluable if more compression is required.
Dynamic compression plate (DCP)
External tension device

11. Compression plate Absolute stability Direct healing
Transverse or oblique 2-part fractures
Screws compress plate to bone
Axial compression can only be achieved using the DCP if the fracture is simple transverse or short oblique. In short oblique fractures the plate must be fixed to the bone such as to create an axilla between the plate and bone into which the second fragment can be drawn.

12. Compression plate
Axial compression can only be achieved using the DCP if the fracture is simple transverse or short oblique. In short oblique fractures the plate must be fixed to the bone such as to create an axilla between the plate and bone into which the second fragment can be drawn.

13. Other fracture line compression techniques
Wedge fragment:
Open reduction
Rigid fixation
Lag screws and neutralization
Comminution:
Open reduction
Lag screws
Bone graft
Both may require substantial soft-tissue disruption
If there was such comminution that lag screw fixation could not be obtained, the classical technique involved the use of bone grafting on the contralateral surface to the plate to speed union.

14. Limited contact DCP (LC-DCP)
1991
The LC-DCP was the first attempt to reduce the contact area between the plate and bone. Initially, it was manufactured in titanium only but is now available in stainless steel.
Limited contact dynamic compression plate (LC-DCP)
Bridge plate using LC-DCP

15. Plate pressure—necrosis
Compression of plate to bone has a biological consequence
DCP, no undercuts
LC-DCP, partial undercuts to reduce plate “footprint”
Studies have shown that the blood supply under a fixed dynamic compression plate showed poor periosteal blood supply leading to bone necrosis and absorption with a potential for delayed union and infection.
The low-contact DCP was developed to reduce the plate-bone contact, leaving the periosteal blood supply less disturbed with less bone necrosis.

16. Plate design Gradual evolution of plate design
Minimize detrimental effects on bone
DCP
LC-DCP
PC-FIX
PC-FIX, point contact fixator

17. Plate function
The same plate can have different biomechanical functions

18. Plate function Compression Protection neutralization
Buttress, antiglide, and blade plate
Tension band
Bridging plate
All plates should be applied with respect to preservation of soft tissues—”biological plating”

19. Neutralization plate
Resists torsion, bending, and shear forces on fractures fixed with interfragmentary lag screw(s)
Also known as PROTECTION plate

22. Absolute
stability
The neutralization plate, also known as a PROTECTION plate, protects the lag screw by limiting bending and torsion at the fracture site.

23. Buttress mode Used when fracture will only displace one direction
“Pushes” fragment the opposite way:
Where would you push with your thumb?
Often metaphyseal fractures and “B”-type fractures (partial articular)

24. Example of buttress effect of the plate on a tibial plateau fracture
Example of buttress effect of the plate on a tibial plateau fracture. The plate will resist displacement by the axial loading.

26. Antiglide mode
High shear-angle fracture
Noncomminuted apex

27. Antiglide mode
Create axilla with plate

28. Antiglide mode
Antiglide screw

29. Bridge plating Relative stability
This is relative NOT ABSOLUTE stability.

30. Bridge plating Restore length Restore angular alignment
Restore rotational alignment
Respect fragment biology
Can be biologically friendly.

31. Relative stability heals with callus.

32. Tension band plating
Placed on the tension side of an eccentrically loaded bone
Load is applied:
Convex (tension) side would normally distract
Plate prevents this
Concave side compresses instead
Requires intact medial cortex
Converts tension into compression

33. Tension band plating

34. Tension band plating Plate placed medially
Cannot resist distractive forces
Will fail

35. Spectrum of stability No motion Absolute stability Some motion
Relative stability
Excessive motion
No stability
Compression
Neutralization
Buttress
Tension band
Bridge

36. Locking screws Conventional screws Locking screws Conventional plates
Screws compress against bone
Bone-plate friction creates stability
Screw heads thread into plate
Angular stable (locked) construct
Screws attach to bone
No bone-plate contact or friction required for stability
The interface between a locking head screw and the plate will not loosen. Interfragmentary compression is not possible using locking head screws, nor is compression of the plate to the bone.
Shear = lateral deformation produced in a body by an external force, expressed as the ratio of the lateral displacement between two points lying in parallel planes to the vertical distance between the planes.
Conventional screws create compression between the plate and the screw. The plate is compressed onto the bone and it is this friction that conveys stability to the fracture site.
Locking head screws put the plate under shear. There is a space between the bone and the plate. No compression of the plate onto the bone is achieved. Screw loosening does not occur at the screw-plate interface.

37. Combination holes in locking compression plate (LCP)
Allow a single plate to be used for multiple functions in different fracture fragments
Dynamic compression unit (DCU)
Locking head screw
The desire to have the option to create interfragmentary compression, also the characteristics of the internal fixators led to the design of the combination of holes: compression and lock.
Threaded side of combination hole

38. LCP—combination holes
Screws
Conventional
Self-tapping, locking
Self-drilling, self-tapping, and locking
Screw-plate interaction
Conventional screws perform the same function as conventional plates. If a conventional screw is used, then the plate will be compressed onto the bone and so part of the biological advantage of the plate is lost.
Self-tapping locking head screws are the conventional locking head screws and are usually inserted bicortically.
Self-drilling, self-tapping locking head screws are for monocortical insertion only. They come in a standard length for use in the diaphysis.
It is important to note that the length of the metaphyseal screws in the less invasive stabilization system (LISS) needs to be calculated in advance using the x-ray.

39. LCP use As a conventional plate, using conventional screws
The LCP can be used either as a conventional plate or an internal fixator.
The use of conventional screws through the oval “DCP” holes allows the use of lag screws and also axial compression through the dynamic compression unit (oval side of the combination hole).
Lab studies have shown that the locking compression plate when used with locking head screws is superior for fracture fixation in poor bone quality or osteoporotic bone. Using conventional screws for compression with absolute stability and additional locking head screws, results in a higher pull-out strength and overall strength in osteoporotic bone.
Good bone quality with interfragmentary compression  absolute stability

40. LCP use
For poor bone quality, using conventional and locking head screws
The LCP can be used either as a conventional plate or an internal fixator.
The use of conventional screws through the oval “DCP” holes allows the use of lag screws and also axial compression through the dynamic compression unit (oval side of the combination hole).
Lab studies have shown that the locking compression plate when used with locking head screws is superior for fracture fixation in poor bone quality or osteoporotic bone. Using conventional screws for compression with absolute stability and additional locking head screws, results in a higher pull-out strength and overall strength in osteoporotic bone.
Initial reduction and stability achieved with conventional screws FIRST, protected by locking screws SECOND

41. LCP use Bridging plating  relative stability
The LCP can be used either as a conventional plate or an internal fixator.
The use of conventional screws through the oval “DCP” holes allows the use of lag screws and also axial compression through the dynamic compression unit (oval side of the combination hole).
Lab studies have shown that the locking compression plate when used with locking head screws is superior for fracture fixation in poor bone quality or osteoporotic bone. Using conventional screws for compression with absolute stability and additional locking head screws, results in a higher pull-out strength and overall strength in osteoporotic bone.
As an internal fixator, using locking head screws if poor quality bone

42. Locked plating—indications
Osteoporosis
Short metaphyseal/articular segment
Periprosthetic fractures
Minimally invasive plating:
Bridge plating can be done with standard plates
Conventional bridge plating
Locked bridge plating

43. Summary Outer surface Mechanics: Round holes Oval holes DCP
DCU on both ends of the hole LC-DCP
Round hole with thread for locked screws (LISS)
Combination hole LCP
Plate design has evolved from conventional plates to dynamic compression plates to low-contact dynamic compression plates (LC-DCP) to locking compression plates (LCP) with locking head screws.
The locking compression plate, as an internal fixator/noncontact plate, does not compress the periosteum and results in undisturbed blood supply, no bone necrosis under the plate, callus formation/bone healing under the plate, and reduced risk of infection.

44. Summary Under surface Biology Complete contact plate-bone cortex
Round holes
Oval holes DCP
DCU on both ends of the hole LC-DCP
Round hole with thread for locked screws LISS
Combination hole LCP
Complete contact plate-bone cortex
Limited contact plate-bone cortex
Plate design has evolved from conventional plates to dynamic compression plates to low-contact dynamic compression plates to locking compression plates with locking head screws.
The locking compression plate, as an internal fixator/noncontact plate, does not compress the periosteum and results in undisturbed blood supply, no bone necrosis under the plate, callus formation/bone healing under the plate, and reduced risk of infection.

45. Take-home messages Plate name ≠ plate function
Any plate can be used in many ways
Plate function is dependent upon:
Design
Method of application

46. Take-home messages Evolution of plates: mechanics  biology
Plating comminuted fractures:
Bridging
Biological: “gardener” versus “carpenter”
Locked plating:
Osteoporosis; short end segments
Plate design has evolved from conventional plates to dynamic compression plates to low-contact dynamic compression plates to locking compression plate with locking head screws.
The locking compression plate, as an internal fixator/noncontact plate, does not compress the periosteum and results in undisturbed blood supply, no bone necrosis under the plate, callus formation/bone healing under the plate, and reduced risk of infection.