Basic principles of plating

Updated: May 27, 2021


1. Introduction


Plating modalities Plates may be applied in various modes according to the function required. These include:

  • Protection (neutralization)

  • Compression

  • Bridging

  • Buttress (antiglide)

NB: The terminology may be confusing; these names refer to the mode in which the plates are applied and are not specific to a particular plate.

Plate designs

Various plate designs are available. These may be larger or smaller, thicker, or thinner as appropriate to various anatomic sites and the loads to which they will be subjected. The holes in the plate may be designed for locking screws, non-locking screws or either, and designed to facilitate dynamic compression. Some plates are designed to have reduced contact area on the bone. Reconstruction plates are designed to be easier to contour in complex anatomic locations. There are plates designed for many specific anatomic locations.


Plate contouring

The plate must fit the shape of the bone. The midshaft of many long bones is straight so plates applied to these regions may not need to be contoured. Towards the metaphysis most bones show a flare so plates applied in these regions usually need to be contoured. The use of a flexible template can facilitate plate contouring. Where locking screws are used, the bone-plate construct remains stable even if the plate is not in direct contact with the bone. Therefore, contouring does not to be so accurate.

Anatomic plates are pre-contoured to fit the region they are designed for, but beware that this is for an average patient and they may still need to be adjusted to fit individual patients.


2. Protection (neutralization) plates


Function A protection plate neutralizes bending and rotational forces to protect a lag screw fixation. This is equally true of plates with locking or non-locking screws.




Application Reduce the fracture and fix the fracture with one or more lag screws.

The appropriately contoured plate is applied to the bone and screws inserted in a neutral mode. Depending of the plate design, bone quality, implant availably, and surgeon's preference, fixed angle locking head screws, variable angle locking head screws or non-locking screws may be inserted. It is not necessary to fill every hole, if enough screws are inserted to obtain sufficient hold to maintain the reduction until the fracture heals.

3. Compression plating


Function The plate produces compression at the fracture site to provide absolute stability.

Application (transverse fractures) Reduction

If possible, the fracture is reduced and temporarily fixed with clamps. Place the forceps such that it will not interfere with the planned plate position.


Pre-contouring

If the plate is exactly contoured to the anatomically reduced fracture surface, there will be some gapping of the far cortex, when the plate is tensioned by tightening the load screw.


The solution to this problem is to “over-bend” the plate so that its center stands off 1-2 mm from the anatomically reduced fracture surface. The overbend should lie directly over the fracture line. When the first screw is inserted, slight gapping of the cortex will occur directly underneath the plate. After fixation is complete, the plate will be in contact with the bone throughout its length, but it is acting as a spring, providing compression at the far cortex.


Screw insertion

The prebent plate is fixed to one of the main fragments with a screw in compression mode. A reduction forceps is placed on the opposite fragment to hold it in the reduced position against the plate. The screw is not fully tightened.


A screw is inserted in compression mode in the opposite fragment. To maintain reduction, it is recommended to tighten the screws gradually by alternating between the two sides.


If after insertion of the two compression screws there remains a fracture gap, a third screw can be inserted in compression mode on either side. Before this screw is tightened, the compression screw already placed in the same fragment needs to be loosened. After the third screw is fully tightened, the first screw is re-tightened and additional screws are inserted in neutral mode.


Application (oblique fractures) In oblique fractures, place and fix the plate with one or more screws inserted in neutral mode to create an axilla with one of the bone segments.




Insert a screw in compression mode into the second fragment. This drives the second fragment into the axilla and compresses the fracture.

If the plate is applied in an oblique fracture without creating an axilla, as the fracture is compressed, the fracture may displace. If the fracture pattern and location does not allow the plate to be applied so that an axilla is created, it may be better to apply a lag screw and a neutralization plate.


An interfragmentary lag screw can in some case be inserted thought the plate for additional compression.


Articulated tension device As an alternative to obtaining compression using screws inserted in dynamic compression mode, the articulated tension device may be used to provide mechanical compression prior to fixation with screws inserted in neutral mode. The device may also be used to create distraction.

Compression

Reduce the fracture approximately and attach a plate securely to one fragment. Anchor the device to the bone with a screw inserted through the articulated footplate and insert the hook on the device into the hole at the end of the plate. As the tensioning screw is then tightened, the two limbs of the device are pulled together, and compression is achieved at the fracture site.


Distraction

To distract the fracture, the hook of the device is placed against the plate end and the tensioning screw on the device turned anti-clockwise.


Application in oblique fractures

In oblique fractures, the plate should be applied to create an axilla following the same principle as described above for dynamic compression plates.


Screws are inserted into the second segment in neutral mode and the device removed.


4. Bridge plate


Function Bridge plating techniques are used for multifragmentary long bone fractures where intramedullary nailing or conventional plate fixation is not suitable. The plate provides relative stability by fixation of the two main fragments, achieving correct length, alignment, and rotation. The fracture site is left undisturbed and fracture healing by callus formation is promoted.


Conventional vs locking head screws Either conventional or locking head screws may be used. The advantages of locking head screws compared to conventional screws are:

  • They provide more stability in osteoporotic bone by reducing the risk of screw pullout and over tightening of the screws

  • Well reduced fractures stay reduced

  • Unicortical screws may be used

  • The plate does not need to be perfectly contoured to the bone

  • As the plate is not pressed against the bone, the periosteum is not compromised

Extent of surgical approach To leave the fracture site as undisturbed as possible, bridge plates are often inserted through a minimally invasive approach. Screws are either inserted through a limited approach, only exposing the plate sufficiently for screw insertion, or through small stab incisions.


The least surgical disturbance to the fracture site occurs when a minimally invasive percutaneous technique is used for plate insertion.


Reduction Reduce and secure the main proximal and distal fragments in correct length, alignment and rotation. This is typically achieved using indirect reduction techniques such as:

  • Temporary external fixation

  • Reduction devices

  • Traction

This will allow manipulation of the main fragments into correct position without opening the fracture site, thus minimizing further damage to the blood supply.


Especially with multifragmentary fractures, the use of an external fixator, or distractor, can provide alignment and temporary stability for bridge plating without disturbing the soft tissues at the fracture zone. Proximal and distal pins should be inserted carefully in order not to interfere with the later plating procedure. zone may facilitate reduction.


Working length Long plates with a long working length allow the distribution of bending stresses over a long segment of the plate and the stress per unit area is correspondingly low. This prevents high stress over the fracture site and reduce the risk of plate failure. Long plates also allow for a long lever arm which reduce the risk of screw pullout. Fix the plate to the bone using either conventional screws inserted in neutral mode or locking head screws.



5. Buttress (antiglide) plate


Function Buttress plates are often used to supplement lag screw fixation of metaphyseal shear or split fractures in the metaphyseal regions. The lag screws may be inserted either through or outside of the buttress plate.


Application Reduce and fix the fracture with one or more lag screws following standard technique. A washer may be used in osteoporotic bone


Contour the plate with a slight pre-bend, that is, there should be a small gap between the central part of the plate and the bone.


Apply the plate and press it firmly against the bone by inserting a standard bicortical screw in the hole closest to the fracture in buttress mode.


Secure the buttress plate with additional bicortical screws inserted in neutral mode.

Source : AO

https://surgeryreference.aofoundation.org/orthopedic-trauma/adult-trauma/basic-technique/basic-principles-of-plating

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