1 Principles topenlarge
Long oblique (A2) fractures can often be reduced and held with lag screws, but the durability of fixation is inadequate, and the protection of a neutralization plate is needed.
It is crucial to use a plate that is long enough on each side of the fracture. Plate length is more important than the number of screws for ensuring stability.
Lag screw fixation may be tenuous. Be cautious handling the fracture during plate application. It is important to contour the plate to fit the bone perfectly so that tightening its screws does not displace the fracture.
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 good for proximal and middle third fractures, and allows easier patient positioning. The lateral approach can also be used, particularly if the most proximal humerus needs not be exposed. Distally, the plate may lie under the radial nerve. If a small open fracture wound is present, the approach is made separately. Only if there is a large wound, after debridement, should the surgeon consider using the wound itself, with its necessary extensions, for plate insertion.
A posterior approach will generally be chosen for more distal fractures, although it is possible to extend an anterolateral approach to access the posterior surface of the distal humerus. It is important in a posterior approach to remember the radial nerve and its accompanying vessels which lie posteriorly in the spiral groove.
(a) Typically, the posterior plate must be placed underneath the radial nerve, to gain proximal bone anchorage.
(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.
Traction with external fixator or distractor
Traction can be maintained with an external fixator or distractor. 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
Definitive reduction and fracture apposition is best done with bone forceps. Pointed reduction forceps are usually preferred. As the fracture is reduced, an anatomical alignment should be obtained before the forceps are tightened. It may be necessary to readjust to achieve this. If soft tissues have been preserved, the reduction may be difficult to assess.
The clamp is applied perpendicularly to the fracture plane. Its position will mimic that of an appropriately placed lag screw. The clamp should be placed near, but not exactly, where the planned lag screw will be inserted.
The clamp may also interfere with plate application if it lies within the planned plate position. A lag screw placed near the clamp, but outside the plate location may maintain the reduction, and allow clamp removal before the plate is applied.
4 Contouring the plate topenlarge
Fitting the plate to the bone
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. Sometimes twisting the plate around the shaft of the humerus provides a better fit, and allows a longer plate.
Contouring is aided by a stable provisional reduction with a clamp or lag screws and a malleable template that can easily be shaped to the bone surface. The template is then used as a guide to shaping the plate to fit the bone.
Use care to avoid fracture displacement while contouring the plate.
It is not necessary to contour the plate if locking head screws are to be used.
5 Lag screw fixation topenlarge
Planning for lag screw
The lag screw should be placed centrally across the plane of the fracture, and perpendicularly to it. For longer spiral fractures a second lag screw will increase stability. Plan lag screw location so that, if possible, the screw heads are outside the chosen area for the plate.
Drill gliding hole
Use a 4.5 mm or 3.5 mm drill (according to screw size) to create a gliding hole, located centrally across the fracture plane, away from the fracture line, and angled perpendicularly to the fracture plane, at the chosen location.
Using an appropriate drill sleeve, drill through the near (cis) cortex.
Drill the pilot hole for the thread
Insert an appropriately sized drill sleeve through the gliding hole to contact the far cortex. Drill through this with the appropriate drill for the pilot hole, 3.2 mm for large fragment screw, 2.5 mm for small fragment screws.
Deep countersinking is often unwise for the thin humeral cortex although shallow countersinking reduces the risk of fissure fracture beneath the screw head. This requires careful surgical judgement. Measure the length of the screw and tap, if necessary. Insert the screw, tightening it carefully. For longer spiral fractures, a second screw is inserted in an appropriate location and orientation, using a similar technique. Both screws should be perpendicular to the fracture plane at the site where they are inserted. Each hole should pass through the middle of the fracture spike, or of the fracture plane of the other fragment.
6 Plate fixation topenlarge
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 sufficient to provide an area for the plate.
The plate should be centered over the fracture, and long enough to allow four holes for bicortical screws in each of the proximal and distal fragments.
Rather than clamping the plate to the bone, 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.
Be careful not to displace the fracture, as initial lag screws may lack strength. If possible, leave a reduction clamp across the fracture during plate application.
Insert remaining screws
Confirm that contouring of the plate is appropriate and that its position is satisfactory.
Then insert the rest of the screws in neutral positions using either the universal, or appropriate LC-DCP, guide. Screws closest to the fracture site are placed first.
The humerus has a thin cortex and may be osteoporotic, in which case it may be more secure 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 (trans) cortex.