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, 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 main fragment using a periosteal elevator and a ball-spiked pusher (illustrated) first. Then insert the smaller fragment using a dental pick. Take care to reduce it anatomically to ensure smooth joint surface.
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.
Option: absorbable pins
Optionally, the small intermediate fragment may first be fixed by absorbable pins, before final reduction of the main condylar fragment.
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 Lag screw insertion topenlarge
Drill screw hole
Make a small 1.2 cm incision over the lateral femoral condyle. The incision should go through the iliotibial band.
Create a pilot hole using a 3.2 mm drill bit in the direction of the eventual screw insertion.
Determine appropriate screw length
Insert a depth gauge into the hole, to determine the appropriate screw length. Generally, a screw is chosen which is 5-10 mm short of the medial cortex.
Remove the depth gauge and tap for the 6.5 mm cancellous bone screw under image intensifier control. In all but the densest cancellous bone of young athletes, tap only the near fragment – the screw itself will normally create its own thread in the cancellous bone of the far fragment.
Insert the 6.5 mm partially threaded cancellous bone screw and fully tighten. In the case illustrated, the partially threaded screw will have 32 mm of thread, as opposed to 16 mm of thread.
Note: a washer may be used particularly in osteoporotic patients.
Additional screw insertion
Insert 1 or 2 additional screws in a similar manner, and remove the K-wire.
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 could 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.