1. Clinical indications for locked plating—when and where?
AO Trauma Advanced Principles Course

2. Learning objectives
Compare indications for using locked and nonlocked plates.
Identify indications for the use of locked plating techniques vs conventional plating techniques.
Formulate the advantages of locked plates in special clinical circumstances, eg, osteoporosis.
Identify patient populations where plates are most useful.
Outline areas where locking compression plates may fail or may be used incorrectly leading to failure.

3. Absolute vs relative stability
Absolute stability
Relative stability
No callus formation
No fracture site resorption
Callus formation
Fracture site resorption
With absolute stability, primary bone union will occur through cutting cones crossing the fracture site. No callus is formed at the fracture site. The requirements to achieve absolute stability are anatomical reduction and compression across the fracture site. Preservation of blood supply is critical to the success of the technique.
With relative stability, ie, motion at the fracture site, initial resorption at the fracture site occurs. This is followed by the formation of callus. Requirements for achieving relative stability are the correct restoration of length, axis, and rotation at the fracture site. Anatomical reduction is not necessary. A degree of movement must occur at the fracture site. Preservation of the blood supply is critical.
Cutting cones

4. Indications for absolute stability
Articular fractures
Simple fractures of the diaphysis or metaphysis (Müller AO/OTA Classification type A)
Soft tissues must be in good condition because the technique usually requires open direct reduction
Articular fractures must be treated by anatomical reduction and early active mobilization of the joint. The articular surface is usually fixed using a direct surgical approach and compression is usually applied at the level of the joint.
Simple fractures of the diaphysis and metaphysis can be treated by indirect reduction and bridge plating using a MIPO technique but this approach should be reserved for experts. There is probably an increased risk of delayed union if bridging is used in these fractures.
Absolute stability only works if there is a good blood supply to the fracture site. Absolute stability can only be achieved by anatomical reduction and usually this involves open surgery. Hence, absolute stability techniques usually require good soft-tissue conditions to be successful.

5. Indications for relative stability
Multifragmentary fractures
Inability to achieve compression at the fracture site
Compromised soft tissues especially periosteal stripping
If multifragmentary fractures are treated using absolute stability techniques severe soft-tissue damage is inevitable and the risk of implant failure and fracture nonunion is high. Multifragmentary fractures are ideally treated with bridging techniques.
The risk of implant pull-out in osteoporotic bone is significantly less with locked internal fixators than with conventional plates and screws.

6. Optimize fixation
The strength and stability of a fixation performed using
the LCP can be altered by the following factors:
Number of screws
Poitioning of screws
Plate length
Callus formation requires a degree of controlled movement at the fracture site. There is debate as to the amount of movement that is desirable and generally speaking the more comminution there is, the more movement can be tolerated without the risk of nonunion.
How many screws should be used, what is the placement of those screws, and what should be the length of the plate are still matters for debate but the general principles are outlined in the following slides.

7. Screw placement Stoffel K et al (2003) Injury Working length
Moving first screw further from fracture site:
Increases the working length
Decreases axial load by 64%, decreases torsional rigidity by 36%
Increasing working length by leaving a single screw hole unfilled will decrease stability by 10%
Working length is the distance between two screws closest to the fracture site.
The number and placement of the screws can greatly affect the axial load and torsional rigidity of the plate-screw construct. As reported by Stoffel, in Injury, the working length between screws adjacent to the fracture site can significantly alter the mechanics of the plate-screw construct.
By moving the first screw further from the fracture site, you increase the working length, but decrease the axial load and torsional rigidity. Each screw hole that is between the fracture site and the placement of the first screw will decrease the stability by 10%.
Source:
Stoffel K, Dieter U, Stachowiak G, et al (2003) Biomechanical testing of the LCP—how can stability in locked internal fixators be controlled? Injury;34(2)B11–19.
Bridging length
Screw holes
6, 1
6, 3
6, 5

8. Screw number Stoffel K et al (2003) Injury
A 3rd screw increases axial stiffness, not torsional rigidity (only number of screws)
Decreases axial stiffness with 3rd screw closer to fracture gap
Number of screws
Screw holes
6, 2, 1
By the addition of a third screw, you can increase axial stiffness without increasing torsional rigidity.
Source:
Stoffel K, Dieter U, Stachowiak G, et al (2003) Biomechanical testing of the LCP—how can stability in locked internal fixators be controlled? Injury;34(2)B11–19.
6, 5, 4, 3, 2, 1
6, 4, 3
6, 5, 4, 3

9. Application principles—flexible or stiff?
Do you want absolute or relative stability?
How many screws and in what positions for relative stability?
The clinical application is always a question of how flexible or how stiff to make the plate-screw construct—absolute or relative stability?
With absolute stability you want fracture compression. This is usually obtained by a lag screw—occasionally by axial compression using the DCP part of the LCP hole.
For relative stability, you do not wish to achieve fracture compression, and the working length of the construct is usually large.
Stress dissipation
Stress concentration

10. Length of LCP—relative stability
Plate length should be at least 2 or 3 times fracture length [Gautier E, et al 2003]
Gautier and Sommer reported in Injury that the plate length should be at least 2 and preferably 3 times the fracture length. The plate screw density, ie, the number of screws versus the number of screw holes should be less than 0.5.
In the diagram shown, the plate screw density is 0.43 because it is a 14-hole plate with 6 screws.
The proximal part has 6 holes occupied with 3 screws for a density of 50%.
The fracture gap area has 4 screw holes with no screws, a density of 0, and the distal fragment has 3 out of 4 screw holes filled for a density of 75%. This appears to be an ideal ratio of both plate length and screw density for this particular fracture and fracture length; and the LCP applied as an internal fixator.
In general terms use longer plates when using an LCP as opposed to a DCP and leave more screw holes unfilled to achieve relative stability.
Source:
Gautier E, Sommer C (2003) Guidelines for the clinical application of the LCP. Injury; 34(2):B63–B76.

11. Avoid short “middle”
The problems seen in conventional plating when there is a very small gap at the fracture site, and all the strain is concentrated on a small area of the plate are also seen with the LCP when locking head screws are used. Because the link between the locking head screw and the plate is so secure the strain on the plate is even higher than with conventional plates and plate failure is a frequent occurrence.

12. If a single hole is left unfilled then all the strain is concentrated in one area and implant failure is likely.
If several holes are left unfilled, the strain is distributed over a larger area of the plate and implant failure is rare.
If a single hole is left unfilled you should probably use a lag screw if possible and go for an absolute stability construct.

13. Number of screws Per end segment:
Mechanical minimum 2, only in good bone
3 (or more) is recommended, particularly in osteoporosis, and to avoid failure
Leave empty holes at fracture
site (at least 2–3)
The number of cortices crossed by screws is still a matter of debate. If in doubt, stick to the old plating rule with a minimum of six cortices on either side of the fracture.

14. General Principles Stoffel K et al (2003) Injury
Upper extremity: 3 of 4 screws on either side (torsional)
Lower extremity: 2 of 3 screws on either side (axial)
Simple fracture (if relative stability is to be applied): omit screws on either side of fracture gap
Multifragmentary fracture:
Reduced working length
Long plate
1st screws inserted close to fracture gap
The number of screws to be inserted depends on the anatomical site of the fracture, the fracture anatomy, and the bone quality. The advice given above represents an average view and each fracture must be assessed individually to achieve an optimal construct.
Source:
Stoffel K, Dieter U, Stachowiak G, et al (2003) Biomechanical testing of the LCP—how can stability in locked internal fixators be controlled? Injury;34(2)B11–19.

15. Clinical indications for locked plating
Osteopenia/osteoporosis
Metaphyseal comminution or short metaphyseal fragment
Periprosthetic fractures
Special circumstance
Early unprotected weightbearing, eg, a noncompliant patient
Osteotomies
MIPO
Cut-out of screws is significantly less with locking head screws than conventional screws in osteopenia or fractures with metaphyseal comminution a short metaphyseal fragment.

16. Metaphyseal comminution with bone loss

17. Metaphyseal comminution with bone loss

18. Metaphyseal comminution with percutaneous plating

19. Metaphyseal comminution with percutaneous plating

20. Osteoporosis and metaphyseal comminution
LCPs are particularly useful for fractures in osteoporotic bone

21. 82-year-old female, 1 year postoperatively

22. Percutaneous plating of a femoral fracture in a child

23. Periprosthetic femoral fracture with metaphyseal comminution

24. 22-year-old male,193 cm, 137 kg T4 paraplegic
Bilateral Galeazzi fractures
Early unprotected weight bearing

25. Complex femoral neck/shaft fracture, osteopenia

26. MIPO with healing

27. Callus formation

28. Complications Failure to achieve reduction Screw heads “not locked”
Inability to remove screws
Too little or too much fixation
Penetration of joint surface by implant
Mixed techniques
Catastrophic failure

29. Which screw type for… Gautier E et al (2003) Dept of Orthop Surg
Monocortical
Excellent bone quality
Diaphyseal bone
Bicortical
Poor bone quality
If in any doubt always use bicortical screws.
Monocortical screws can be used, when bone quality is good, in the diaphysis of the bone. You cannot measure the optimal length of a monocortical screw during surgery because the screws are self-drilling and self-tapping. Monocortical screws were designed for blind-insertion through the aiming arm of the LISS. It is likely that the use of these screws will become less common with time. Additionally, they are more expensive than the bicortical screws.
In metaphyseal bone, where the bone quality is poor, bicortical screws should be used.
Source:
Gautier E, Sommer C (2003) Guidelines for the clinical application of the LCP. Dept of Orthop Surg; 34(2):B63–76.

30. Failure to achieve locking of the screw heads into the plate—cross threading
Cross threading of the screw heads into the plate is not uncommon. The risk of doing this can be reduced by careful use of the drill guide. Cross threaded screw heads may loosen, the screw may break, or the screw may never be removable. Great care should therefore be taken to prevent this complication which is caused by poor surgical technique.

31. Screws locked but not inserted in bone
When locking head screws are used, the tactile sense of screw placement, both for the quality of the bone and also the feel of the screw going from one cortex to the other is lost. The surgeon must ensure that the screws are correctly positioned.
It is often difficult to achieve this with image intensification and so particularly when starting to learn this technique the surgeon is advised to make a mini-incision down to the bone and ensure that the plate is correctly positioned on the bone.
In the example shown the axis of the plate and the axis of the bone are different. The plate will angle across the bone and it is likely that the proximal unicortical screws will achieve very poor grip.

32. Screws—penetration of the joint surface
Unforgiving cortical protrusion with articular erosion
Intraoperative error
Avascular collapse
When inserting a locking head screw, the surgeon will not have any idea that he has gone into the joint due to the lack of tactile feedback when using the torque limiting screw driver. It is therefore critical that screw length is accurately measured and that the measure is verified on image intensification particularly for the inexperienced surgeon.
Penetration of the humeral head is a potential complication when the PHILOS is used.

33. Periprosthetic distal femoral fracture

34. Postoperative x-rays

35. Screw pull-out and cut-out

36. Osteoporotic bone and working length Gautier E et al (2003) Dept of Orthop Surg
Sufficient working length
Good bone quality
Insufficient working length
The working length of monocortical screws depends on the thickness of the bone cortex.
In osteoporotic bone, monocortical screws do not have adequate fixation.
In osteoporotic bone the working length is very short and under torque the bone thread will quickly wear out leading to secondary displacement and instability.
One needs to increase the working length by placing bicortical screws in osteoporotic bone which leads to a much better torque resistance.
Source:
Gautier E, Sommer C (2003) Guidelines for the clinical application of the LCP. Dept of Orthop Surg; 34(2):B63–76.
Osteoporotic bone

37. Osteoporotic bone Gautier E et al (2003) Dept of Orthop Surg
LCP in a wave-like form
In osteoporotic bone, parallel placed locking head screws do not have the same holding power as locking head screws placed at different angles to each other. This can be achieved by bending the plate back and forth to make a wave-like form so that the screws can be inserted divergently and convergently in order to increase pull-out resistance.
Source:
Gautier E, Sommer C (2003) Guidelines for the clinical application of the LCP. Dept of Orthop Surg; 34(2):B63–76.

38. Final fixation
Final fixation with a plate with bicortical locking head screws.

39. Misapplication—failure to achieve reduction
Decorating bone with expensive implants does not necessarily mean that you have performed open reduction and internal fixation (ORIF).
Open internal fixation is not open reduction and internal fixation.
“OIF” instead of ORIF
No “R” = no Reduction

40. Misapplication—failure to achieve reduction
Tibial plateau: varus
A well secured plate will only allow the bone to heal in the position that it is placed.
The LCP has a very low incidence of secondary displacement of the fracture. The device will ensure that the fracture will unite in the same position as when the plate was applied hence the need for a good functional reduction is paramount if the implant is to be used successfully.

41. Failure to achieve reduction
Distal femur: valgus

42. Catastrophic failure
Discuss with the participants why this implant failed.
Possible reasons include: a failure to achieve reduction—the fracture was always in varus, osteopenia—even with the LCP some osteoporotic fractures are not fixable.

43. Catastrophic failure Osteoporotic bone Stiff constructs
Larger core diameter screws

44. Summary LCP can be used to achieve absolute or relative stability
Use longer plates leave more screw holes unfilled
Achieving a good functional reduction is critical before application of the plate
New complications occur due to lack of tactile feedback—ie, penetration of the joint, plates not actually on the bone
Plate design has evolved from standard plates to the dynamic compression plate to a low contact dynamic compression plate to the locking compression plate design. One of the advantages of this evolution of plate design is the reduction of plate compression on the periosteal blood supply, thus decreasing bone necrosis and infection.
Screw design has evolved from standard screws to the locking head screws.
Locking plates have a use in certain applications, but are technically demanding and require basic surgical principles with good reduction, stable fixation, and an understanding of how the plate is to be used.
We may encounter new complications with these implants if they are not correctly used. Furthermore they are quite costly and as such should be used for specific indications.