1 Principles topenlarge
Compression plating is useful in two-part fracture patterns, where the bone fragments can be compressed. When the obliquity is sufficient, a lag screw should be used to add additional stability of the fracture. This should be inserted through the plate. This may not be possible, depending upon the fracture orientation and plate position. The objective of compression plating is to produce absolute fracture stability, abolishing all interfragmentary motion.
Make an “axilla”
The plate should be attached first to the fragment that will allow an “axilla” to be created between fracture surface and the plate.
Dynamic compression principle
Compression of the fracture is usually produced by eccentric screw placement at one or more of the dynamic compression plate holes. These holes are shaped like an inclined and transverse cylinder. The screw head slides down the inclined cylinder as it is tightened, the head forcing the plate to move along the bone, thereby compressing the fracture.
The stability of a plate fixation can be greatly enhanced by inserting a lag screw across the fracture, through the plate after primary axial compression has been achieved.
The screw holds only in the far cortex, but glides in a gliding hole in the near cortex.
The illustrated screw is a “shaft” screw, with threads only at its distal end. The shaft portion, with the same outside diameter as the threads, slides more freely in the near cortex gliding hole than a fully threaded screw, which may also be used. It is important that the near cortex hole be as large as the thread diameter.
It is crucial to use a plate that is long enough on each side of the fracture. Plate length is more important for ensuring stability than is the number of screws.
2 Plate position topenlarge
The humerus has an anterolateral, a posterior, and a medial surface to each of which a plate can be applied. The location of the fracture will determine where the surgeon chooses to apply a plate to the humerus. The position of the plate is selected according to fracture location, and the length of proximal and distal main segments.
The location should allow sufficient plate length on both proximal and distal segments, with a minimum of 4 holes for each.
An anterolateral plate fits well from very proximally to the distal fifth of the humerus.
The posterior surface is difficult to access proximally and is best suited for middle and distal third fractures. Once a location for the plate has been selected, the surgical approach is determined by that location. For proximal fractures, an anterolateral plate location and anterolateral surgical exposure are usual. For distal fractures, a posterior plate location is preferred. This area can be accessed with either a posterolateral, or a posterior, approach. In the central portion of the humerus, the plate can be applied to the anterolateral, lateral, or posterior surfaces, with the approach dependent on the preferred plate location.
The medial surface is generally reserved for complex reconstructive procedures.
An anterolateral approach is chosen for proximal and middle third fractures, and allows supine patient positioning.
The lateral approach can also be used, particularly if the most proximal part of the humerus need not be exposed.
Distally, the plate may lie deep to the radial nerve.
A posterior approach will generally be chosen for more distal fractures.
It is important to protect the radial nerve and its accompanying vessels in the spiral groove. Typically, a posterior plate must be placed underneath the radial nerve, to gain proximal bone anchorage.
(a) It is possible to extend an anterolateral approach to access the posterior surface of the distal humerus.
(b) It is mandatory to record accurately in the operation record the exact relationship of the radial nerve to the plate - either by a precise drawing, or by recording the plate hole numbers (counted from proximal to distal) where the nerve lies. This will reduce the risk of accidental nerve damage if the plate should ever need to be removed.
3 Reduction topenlarge
Reduction should begin with limb realignment. This manipulative reduction takes advantage of soft tissue tension. Traction on the distal humerus restores bone length and tension in the soft tissues, and realigns the axis. Rotation must also be corrected.
Interposed soft tissue may interfere with bone contact. If so, this will need to be cleared by direct exposure, preserving as much soft tissue attachment as possible.
Oblique fractures are inherently unstable, so that an external fixator or a distractor may be necessary to maintain length. Such devices minimize soft tissue injury if manual reduction is relied upon while the plate is being attached.
Reduction by external fixator or distractor
Use of an external fixator or distractor is recommended. The two pins should be inserted outside the planned plate location. Complete reduction may require additional correction of angulation or rotation. Folded linen bolsters under the fracture often help.
Pointed reduction forceps
Reduction forceps will interfere with plate application for A2 fractures. However, they may be placed through the plate hole of the intended lag screw position, while the mobile shaft fragment is moved into the “axilla” between the plate and the other fragment. Next, the plate is attached to the mobile fragment, and then the forceps can be removed.
4 Contouring the plate topenlarge
Fitting the plate to the bone
If possible, the plate should be positioned so that it lies directly over the distal end (as shown here) or the proximal end of an oblique or short spiral fracture. This position is best if the surgeon wishes to place a lag screw through the plate perpendicular to the fracture. Furthermore, when attached first to the fragment with which the plate makes an acute angle, the sharp end of the opposite bone fragment can be compressed securely into the "axilla" formed by the plate and the bone, to gain stable preloaded fixation.
Depending on the planned plate location, some contouring of the plate is likely to be necessary. This is true distally, posteriorly, and also on the anterolateral surface centrally.
A malleable template can guide contouring for more complex surfaces, at proximal or distal zones.
Overbending the plate
Even with oblique fractures, the plate should be slightly overbent (more convex) so that it does not fit perfectly on the bone. This causes the cortex opposite the plate (trans cortex) to be compressed first, as the eccentrically placed plate screws are tightened. With further tightening, the near surface of the fracture (cis cortex) also becomes compressed. A short, convex “overbend” can be made with the handheld bending pliers, or bending irons.
Pitfall: Fracture opening opposite plate
When a transverse or short oblique fracture is compressed with a plate that is not overbent, compression will first be exerted at the cortex under the plate (cis cortex), and will cause gapping of the cortex opposite the plate (trans cortex). This gapping, and its consequent associated micromotion, can be prevented by overbending the plate to achieve compression of the opposite side first.
An alternative solution can be to insert a lag screw through the plate, across the fracture plane, as discussed below. This technique will also prevent gapping and micromotion.
In single plane fractures, such as this example, micromotion results in excessive strain of the healing tissues at the fracture site and also risks plate fatigue failure if union is slow.
5 Plate fixation topenlarge
Planning for a lag screw
Since the screw will be applied through the plate, the proposed location of the screw and its chosen hole must be considered before applying the plate. The center of the plate should lie over the fracture site.
Exceptionally, a lag screw will be inserted outside the plate for an A2 fracture. In this case the plate functions in neutralization mode. Unfortunately, attempts to place such a screw for short oblique fractures often fail mechanically, and also disrupt local soft tissues.
When a lag screw is inserted through the plate, either the hole nearest the plate center, or the adjacent hole will be used. This hole must be positioned appropriately (neither too proximal nor too distal) to allow ideal placement of the screw centrally across the fracture plane. The lag screw is usually inserted after the plate has been secured to both fracture fragments.
Application of the plate
No periosteal stripping should be done, either for plate fixation, or screw placement, but there must be adequate soft tissue exposure to provide sufficient area for the plate.
The plate should be positioned over the fracture so that four holes can be used in each of the proximal and distal fragments. Often, a slightly longer plate is necessary, so that 4 bicortical screws can be inserted into each fragment.
It is often helpful to hold the plate to the bone with one well-placed screw in order to confirm that it is contoured correctly.
Drilling for first screw
Remembering the desired plate position, drill a pilot hole approximately 8 mm away from the fracture. Its depth should be measured and then the thickness of the plate added to determine screw length. Its depth can alternatively be measured through the plate. Now tap if non-selftapping screws will be used.
Application of the plate with a first screw
Attach the plate with one screw to the pre-drilled fragment. Do not tighten the screw completely at this stage. Check plate fit and alignment, and proceed with fracture reduction. Bring the other fragment into position in the 'axilla' between the plate and the fracture surface, and check the reduction and plate alignment.
If satisfactory, proceed to drill the other fragment, using the eccentric (load) drill guide.
Insert second screw eccentrically
A second screw is inserted eccentrically into this fragment, leaving empty the hole for the planned lag screw.
Confirm that the fracture surfaces are reduced, and that both ends of the plate fit satisfactorily.
Tighten screws to compress fracture
Tighten both screws alternately, watching carefully to see that the reduction is maintained and compressed satisfactorily.
6 Add lag screw topenlarge
Drill pilot hole
Drill a pilot hole as perpendicular as possible to the fracture plane. Aim to pass the drill through the center of the fracture plane.
Press the universal drill guide into the plate hole and confirm position and angle. Drill both cortices with an appropriate drill bit, 3.2 mm for large fragment plates, 2.5 mm for small fragment plates.
Overdrill the gliding hole
Using an appropriate drill bit, 4.5 mm for large fragment screws, 3.5 mm for small fragment screws, enlarge the pilot hole in the near (cis) cortex.
Tap the hole
Tap the hole in the far (trans) cortex with an appropriately sized tap (exception: self-drilling screws).
Insert lag screw
The lag screw is now inserted.
Before tightening the lag screw fully, the axial compression has to be released slightly to allow additional interfragmentary compression.
The loosened screw is retightened after tightening of the lag screw.
Insert remaining screws
The remaining screws are then inserted. Screws closest to the fracture site are inserted first.
The humerus has a thin cortex and may be osteoporotic, in which case it may be safer to fill all the screw holes. In the past, the broad plate has been recommended to allow staggered screw holes. This is not necessary, but the screws should be inserted divergently to achieve this effect on the far cortex.