1 Principles topenlarge
The patello-femoral joint is biomechanically very stressed when the knee is loaded. Any compromise of the joint surface is likely to lead to degenerative joint disease. It is, therefore, highly desirable, in patellar fractures to strive for anatomical reduction of the joint surface and stable fixation.
In wedge or multifragmentary complete articular fractures, anatomical reduction of the joint surface in relation to all the fragments, combined with durable restoration of the integrity of the extensor mechanism is not commonly achievable.
Cerclage wiring draws the fragments together as anatomically as possible and permits controlled quadriceps rehabilitation in the medium to late healing phases. The joint surface commonly heals with some irregularity, predisposing to secondary degenerative joint disease.
An additional treatment goal is restoration of function of the knee extensor mechanism and allow early range of motion of the knee.
Combination of techniques
In fractures with several large fragments and disruption of the extensor mechanism, cerclage wiring may be used alone, or in combination with lag screw fixation, tension band wiring, or plating.
If cerclage wiring is used alone, it must be supplemented with a period of splintage or hinged knee bracing.
Verification of reduction
Anatomical reduction of the articular surface is monitored by palpating the joint from inside, as neither inspection nor the x-ray will reveal a minor step off. This will require creation of a small arthrotomy.
Nevertheless, an image intensifier or X-ray should always be available, so that the reduction can be checked in the AP and lateral planes if needed.
2 Patient preparation and approach topenlarge
This procedure is normally performed with the patient in a supine position with the knee flexed 30°.
For this procedure a mid-axial longitudinal approach is used.
3 Reduction and fixation topenlarge
The knee joint and fracture lines must be irrigated and cleared of blood clot and small debris to allow exact reconstruction.
Reduce the major fracture fragments using a pointed bone reduction forceps or tenaculum. Transverse fractures are more easily reduced with the leg in extension and sagittal fractures are more easily reduced with the leg in extension.
Verify the reduction by palpation of the retropatellar surface if possible.
Inserting the cerclage wire
Choose a wire of enough strength to withstand the tensile forces generated in the cerclage (1.0 – 1.25 mm diameter).
The wire should be as close as possible to the bone throughout its whole course both superiorly and inferiorly. The use of a curved large bore injection needle may be helpful.
The wire is then similarly threaded around the circumference of the body of the patella and its lower pole, as illustrated.
Loosely prepare the wire twist ensuring that each end of the wire spirals equally - the twist should not comprise one spiral around a straight wire.
Carefully tighten the wire while pulling away from the patella as the wires are twisted. Avoid over-tightening as this may distort the overall shape of the patella.
The wires should be twisted at least 5 times to prevent fixation failure. When stainless steel wires tighten they will lose the surface sheen and if tightened further the wire may break.
When the correct tension is achieved, twist and trim the wire ends.
Care should be taken finally to position the twisted wire into deeper soft-tissue muscle layers, if possible.
Verify the reduction by palpation of the retro patellar surface if possible.
The major fragment may additionally be fixed using a lag screw.