1 Principles top
The patellofemoral 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 vertical patellar fractures to strive for anatomical reduction of the joint surface and stable fixation with interfragmentary compression.
Combination of techniques
In fragmentary partial articular sagittal fractures, lag screw fixation alone, following anatomical reduction, provides absolute stability of the main fragments.
The addition of a tension band is not necessary as the longitudinal integrity of the extensor mechanism is not disrupted. However, a cerclage wire may be added to fix any small fragment.
Historically 4.5 screws were used but have been found to be too large. Now it is more common to use 3.5 or 2.7 screws.
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.
With the knee in flexion, reduce the major fracture fragments using a pointed bone reduction forceps tenaculum.
Two K-wires are inserted through the planned screw trajectory with the fracture reduced
Insert two partially threaded cannulated lag screws over the K-wires.
Alternatively, a fully threaded screw may be inserted using the appropriate technique.
Anatomical restoration of the articular surface is verified by palpation if possible.
Fixation of small fragment with cerclage wire
Preliminarily fix the small fragment with bone reduction forceps.
Use a circular cerclage wire to secure its reduction after the lag screw insertion.