1 Principles topenlarge
The B1-type distal femoral fractures are characterized either by a simple, or complex, fracture line into the articular surface. As with any articular injury, anatomical restoration of the joint surface must be obtained. This is generally best done under direct vision, with clamp application, provisional fixation and then lag screw fixation.
The surgeon must bear in mind that the strong axial loading forces, as well as varus/valgus stress in the knee joint can tend to displace fragments. With vertical fracture lines, in particular, screw fixation alone may not be sufficient, and a buttress plate should be added.
Anatomy of the distal femur
The distal femur has a unique anatomical shape. Seen from an end-on view, the lateral surface has a 10° inclination from the vertical, while the medial surface has a 20–25° slope. A line drawn from the anterior aspect of the lateral femoral condyle to the anterior aspect of the medial femoral condyle (patellofemoral inclination) slopes approximately 10°. These anatomical details are important when inserting screws. In order to avoid joint penetration, screws should be inserted parallel to the patellofemoral and femorotibial joint planes.
In B1-type fractures with a vertical fracture line, a buttress plate is necessary to counteract the vertical shear forces. The buttress plate prevents proximal displacement of the fragment by axial forces.
The buttress plate is added to enhance the stability and to avoid axial load on the fracture, especially in osteoporotic bone.
2 Joint debridement topenlarge
Remove the intraarticular hematoma and rinse the joint thoroughly with Ringer lactate solution.
3 Reduction topenlarge
Reduce the fragment using a periosteal elevator and a ball-spiked pusher (illustrated), or a dental pick.
Skin incision for pointed reduction forceps placement
Make a medial stab incision for the placement of the pointed reduction forceps.
Temporary fixation with K-wire insertion
Hold the final reduction using a large pointed reduction forceps. Make sure to place the pointed reduction forceps not too posterior as compression across the intercondylar notch would tend to tilt the fragment.
Secure the reduction with one, or more, temporary K-wires. Make sure that the K-wire does not conflict with the planned screw track.
Check of reduction
The quality of the reduction is confirmed radiographically.
4 Insertion of K-wires for cannulated screws topenlarge
In general, the screws are inserted at points along the midshaft axis of the femur (dashed line). The area distal to the Blumensaat’s intercondylar roof line must be avoided in order not to violate the notch. In addition, the area of the lateral knee recess should be avoided.
If you need to insert a screw in the area distal to the Blumensaat’s intercondylar roof line, make sure to direct the screw anteriorly, in order to avoid the intercondylar notch.
Insertion of guide-wires
Insert the appropriate guide-wires for 7.3 mm cannulated screws, or, alternatively, 4.5 mm cannulated screws. Depending on the size of the fragment, 2 to 4 screws are necessary.
Guide-wire position check
Use the image intensifier to make sure that the tips of the guide wires just penetrate the far cortex.
In good bone stock, you may now remove the pointed reduction forceps. Otherwise, leave the pointed reduction forceps in place until all screws have been inserted.
Pitfall: too long a guide wire
It is important to remember that the distal femur tapers from the posterior to the anterior. Therefore, if a straight AP view is obtained, the guide wire can appear to be inside the bone. If it appears to be outside the bone, it is most likely too long. In order to assess the exact length of the guide wire obtain an AP view with 30° internal rotation of the lower extremity.
In this illustration, internal rotation by 30° reveals that the guide wire length was chosen inappropriately.
5 Cannulated screw insertion topenlarge
Screw length determination
Determine the appropriate screw lengths using the dedicated measuring device.
Predrilling is usually not necessary.
If it is planned to use a plate it is helpful to slightly countersink the head of the most proximal screw. Manually insert the screws of appropriate length over the guide-wire.
Washers are helpful if plate application is not planned, and always in osteoporotic bone.
The temporary K-wire can now be removed.
Pearl: use temporary K-wire for further screw insertion
If you have used an appropriate K-wire size for temporary fixation of the fracture, you can now insert an additional cancellous screw further to enhance stability.
6 Insertion of buttress plate topenlarge
To enhance the stability and to avoid axial load on the fracture (especially in osteoporotic bone) a buttress plate is needed to prevent cranial displacement of the fragment.
Insertion of first screw
All types of 4.5mm plates can be applied. Although a condylar LCP can be utilized, a simple slightly undercontoured 4.5 mm narrow plate is sufficient, as shown here.
Apply the plate to the lateral aspect of the distal femur. To press the plate firmly to the femur, insert a standard cortical screw just proximal to the fracture line. Perform drilling, screw length measurement, and tapping, as usual.
Final screw insertion
Secure the plate with at least 2 more bicortical cortical screws proximal to the first screw.
Additional 4.5 mm screws are optionally inserted in the distal aspect of the plate.
Alternative: lag screws through plate
Distal partially threaded cannulated cancellous screws can be inserted in lag mode through the plate. This is an alternative to inserting independent lag screws outside of the plate.
Check of implant position
Check the osteosynthesis, using the image intensifier in at least two planes.
7 Wound closure top
Irrigate all wounds copiously. Insert an intraarticular suction drain. Close the joint and the iliotibial tract using absorbable sutures. Close the skin and subcutaneous tissue in the routine manner.
Pearl: post-ORIF examination of knee joint stability under anesthesia
With the femur now stable, it is possible to perform a gentle examination of the knee joint to exclude associated ligamentous laxity, but be extremely careful testing with valgus stress.