1 Principles topenlarge
Formerly, the angled blade plate was the proven work horse of distal femoral fracture surgery. In some countries this device is still the only implant available.
Blade plate usage follows the principles of restoration of the mechanical axis of the femur and compression of the fracture site if possible.
The advantage of the angled blade plate is that it allows the plate to be used as the reduction device. When the surgeon places the blade plate in the distal femoral articular block in the correct position, the restoration of the correct biomechanical axis is ensured. It is also useful in revision surgery of distal femoral fracture fixations, including previous intramedullary nail fixation. Finally it is an implant of choice for corrective osteotomies of the distal femur.
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, or blade plates. In order to avoid joint penetration, these devices should be placed parallel to both the patellofemoral and femorotibial joints planes.
The muscle attachments to the distal femur are responsible for the typical displacement of the distal articular block following a supracondylar fracture, namely shortening with varus and extension deformity. Shortening is due to the pull of the quadriceps and hamstring muscles, while the varus and extension deformity is caused by the unopposed pull of the adductors and gastrocnemius, respectively.
The popliteal vessels, the tibial nerve and the common peroneal nerve lie in close proximity to the posterior aspect of the distal femur. Because of this, vascular injuries occur in about 3% and nerve injuries in about 1% of fractures of the distal femur.
There are no significant arteries, veins, or nerves on the lateral side of the knee.
There may be bleeding from the lateral genicular arteries, which will need to be controlled using diathermy.
At the posterior aspect of the knee lie the popliteal artery, nerve and vein. It must be borne in mind that these structures can be damaged by the injury, or can be damaged by the surgeon during the reconstruction.
In the past two decades, experience has shown that maintenance of the
metaphyseal/diaphyseal soft-tissue attachments in comminuted fractures leads to
higher rates of union. There may be surgical enthusiastic about reducing and
performing lag screw fixation of small intermediate fragments on the medial
aspect of the distal femur. However, in doing so, disruption of the normal
healing process may result. Therefore, appropriate length, angulation and
rotation should be obtained but there is no need to reposition and fix every
small fragment in a comminuted fracture.
Provided the anatomical relationships of the main proximal and distal fragments are restored, and the biology of the comminuted metaphyseal zone is respected, satisfactory union is highly likely to occur.
It is very important to restore the biomechanical axis of the lower limb. The normal biomechanical axis follows a line from the center of the femoral head, through the center of the proximal tibia and then through the center of the ankle joint. This axis can be checked intraoperatively by using a piece of cable, such as the diathermy cord, to give an approximate estimate of the axis, as follows.
The biomechanical axis must be restored and care should be taken to ensure that there is no malrotation of the distal femur on the proximal femur.
If no traction table is used (i.e., using the freehand technique) the cable method may be used. In this technique, the electrocautery cord is held from the iliac spine across the patella to the cleft between the first and second toes. If rotation is correct, this cord will pass over the midline of the patella, and slightly medial to the tibial eminence.
Another method of assessing rotational reduction is to compare the cortical thickness above and below the fracture. If a shaft fracture is multifragmentary, the image intensifier cannot be used to compare cortical diameters on each side of the fracture.
Illustration of the longitudinal axes of the lower limb.
Choice of implant
For retrograde femoral nailing to achieve adequate fracture stabilization, the fracture should be at least 6 cm from the joint line to achieve distal locking with two transverse screws or a screw and a spiral blade. In contrast, more distal fixation can be achieved with plates, or locked fixators. For example the distal most screws in a LISS plate, or a condylar plate, may be subchondral.
The distal most fixation for various implants are:
- LISS plate: subchondral
- Condylar plate: subchondral
- 95° angled blade plate: 1.5 – 2 cm
- 95° dynamic condylar screws: 2 cm
- Retrograde intramedullary nail: 6 cm (for 2 locking screws, or one locking screw and a spiral blade)
2 Planning the plate insertion topenlarge
Preparation for correct positioning
Determine the correct blade plate position with the help of guide wires around the joint. Under image intensifier control, pass one guide wire lateral to medial along the tibio-femoral joint line (red). Pass a second guide wire over the anterior surface of the femur to indicate the plane of the patello-femoral joint (green).
The ideal position of the blade plate is shown by the yellow wire. Note that this is parallel to the red wire in the frontal plane (and thus leads to the appropriate varus/valgus) and is parallel to the green line on the end-on view on the femur. This latter parameter ensures that the plate is flush with the lateral cortex.
The ideal insertion point for the blade plate is shown on the diagram. The blade enters 1.5 cm above the distal end of the femur. It is possible to position the plate slightly more distally than with a dynamic condylar screw (DCS; 2 cm). The entry point for the blade plate is crucial. In terms of anterior/posterior placement the distal femoral condyle should be viewed from laterally. The distal femur is divided into thirds and the center of the blade plate entry site is at the junction of the anterior one third and middle one third.
Insert the third guide wire just distal to the intended place of plate
insertion. This guide wire is parallel to the distal femoral articular surface
in the frontal plane, is perpendicular to the lateral femoral cortex and
parallel to the plane of the patello-femoral joint.
Note: There is a cannulated variation of the blade plate which has a guide wire which runs through the blade itself. This cannulated blade makes insertion of the device in the correct axis easier. This technique is not shown here.
Plate length determination
Determine the plate length by measuring from the template.
It should be remembered that the medial aspect of the femur is angled 20°-25° inwards and 15 mm should be subtracted from the apparent length to ensure that the blade does not perforate the medial aspect of the femur.
Conventional templating has in the past been performed with plain x-rays. Many departments around the world now have digital pictures archiving communication systems (PACS). Some companies now provide digital templates to accommodate these systems.
3 Reduction and fixation of the articular block topenlarge
Reduction of the articular block
The chosen approach must adequately expose the articular surface of the distal femoral condyle. Reduction aids that are helpful include:
- A 5.0 mm or 6.0 mm Schanz pin in the medial and/or lateral femoral condyle to act as a joystick.
- Pointed reduction forceps, or large pelvic reduction clamps, to clamp from medial to lateral across the intercondylar split.
Pearl: combination of reduction aids
Attempts at reduction of the intercondylar split with the pointed reduction forceps alone are often unsuccessful, as rotational control of the femoral condyle is also needed. The use of the Schanz pin in conjunction with the pointed reduction forceps is therefore preferred.
Before definitive fixation is undertaken, more than one clamp is applied. Usually, one to two additional K-wires are inserted, either from medial to lateral, or lateral to medial.
If the K-wires are inserted from medial to lateral, they may either go through small stab incisions in the skin, or through the parapatellar retinaculum.
Definitive articular surface fixation
Screws may be placed along the periphery of the articular surface of the lateral femoral condyle going from lateral to medial to compress the intercondylar split.
These screws may be fully threaded 3.5 mm lag screws (shown with gliding hole), 6.5mm partially threaded lag screws, or 4.0/4.5 mm cannulated, partially threaded lag screws.
Insertion of screws in this manner leaves a „free zone“ of bone into which a laterally based plate system can be inserted (dotted circle).
This end-on view demonstrates the screw trajectories from lateral to medial.
On occasions, it is acceptable to insert screws through the articular surface, when no other option is available. These screws must be countersunk and recessed beneath the articular surface.
4 Reduction topenlarge
There are, in general, two basic methods to reduce the
metaphyseal/diaphyseal component of a distal femur fracture when utilizing a
blade plate. The method utilized depends on the fracture morphology. In the
first method, the fracture of the metaphysis undergoes a direct reduction and
then the blade plate is subsequently inserted. This might be done in a single
plane short spiral or oblique fractures.
In the second method, the blade plate is inserted into the correct position in the distal articular block of the femur. Then, after manual traction is used to restore the appropriate length and rotation, the bone is drawn down to the plate and the proximal screws are inserted. This type of reduction is very helpful in highly comminuted metaphyseal/diaphyseal fractures.
Direct reduction instruments include:
- Large pointed reduction forceps
- Bone repositioning forceps
- Bone hook
Indirect reduction techniques are:
- Manual traction (illustrated)
- External fixator/distractor
Pitfall: osteoporotic bone
In osteoporotic bone indirect reduction techniques, using the angled blade plate itself, may be preferable as attempts to reduce the fracture directly may cause severe comminution. Attempts to apply reduction clamps to osteoporotic bone will potentially crush the bone.
5 Preparing the channel topenlarge
Cutting the channel
To prepare for opening the entry site for the blade, three 4.5 mm holes are drilled in the cortex of the femoral condyle. They only need to penetrate 1 cm., except in young, harder bone, when the surgeon may need to drill almost the full depth of the chosen blade length. The central of the three holes lies at the center of the slot to be prepared, the other 2 holes are drilled on either side of the central hole.
A triple drill guide is available, but this has been designed for the proximal femur and use with 130° angled blade plates: this makes it a little cumbersome at the distal femur. It is easier to drill the holes freehand, as illustrated, using the 4.5 mm single drill sleeve, in an anteroposterior configuration. Drill them as parallel to the third guide wire as you can.
Connect the drill holes with a router
Take care not to damage or displace the guide wire. Then connect the drill holes with a router.
Round the proximal shoulder of the slot off with a chisel to enable the
plate to be seated fully on the bone.
It may be necessary to use the 4.5 mm drill to deepen the channel into the femoral condyles in the correct planes.
The seating chisel is meant to be driven exactly parallel to the guide wire
in both planes. The seating chisel is hammered into the distal femur with a
mallet. Particular in the young, the seating chisel “back-slapped” using the
slotted hammer. For each 15 mm of insertion this back-slapping should be
performed. Otherwise, the seating chisel will become jammed in the bone.
Repeatedly check parallelism with the guide wire.
In hard bone, it may become necessary to pre-drill the seating chisel track, but this requires great care to keep the 4.5 mm drill bit exactly parallel to the guide wire.
Seating chisel insertion
Insert the seating chisel through its guide into the distal femur. Use the slotted hammer to control the rotation of the seating chisel in the bone, so that the tongue of the guide lies in the anatomical long axis of the shaft.
An assistant may need to apply counter pressure on the medial side of the femur, especially if preliminary lag screw fixation of an intercondylar split has been performed.
6 Plate insertion topenlarge
Plate insertion by use of the holding device
Insert the blade plate using the blade plate holding device, fitted so that the shaft of the device is parallel with the blade.
The blade should follow the path of the seating chisel precisely and remain parallel with the guide wire. The first half of the blade plate should be able to be pushed manually into the bone along the previous path of the seating chisel. If this is not possible the surgeon should question whether a false path is being developed.
Take care to control the alignment of the blade plate to the longitudinal axis of the femur.
Maintain counter pressure on the medial side of the distal femur while inserting the plate.
Impaction of plate to the bone
As the plate comes to within 1.5 cm of the lateral femoral cortex, the blade plate holding device is removed. At this point the final insertion of the blade is performed the impactor.
Securing the plate to the distal femur
At least one additional screw is inserted into the distal femoral articular block. This provides sagittal plane stability.
7 Final reduction and fracture compression topenlarge
Reduction of metaphyseal component
The key concept in reduction of the metaphyseal component of the fracture, when using a blade plate, is that correct insertion of the blade into the distal femur allows the surgeon to use the plate to achieve the metaphyseal fracture reduction. When brought down to the femoral shaft the correct frontal plane alignment has been assured. The surgeon must then control for length and rotation. Length can be aided by manual traction. The sagittal plane deformity correction is determined by rotational control, using the slotted hammer, during seating chisel insertion. Small corrections of extension/flexion deformity can be achieved by moving the proximal end of the plate forwards or backwards on the lateral femoral cortex, but there is little room for maneuver.
Take care to restore the mechanical axis in all planes of the femur. Give consideration to fracture reduction in:
- Internal/external rotation
Secure the plate to the proximal femur with a Verbrugge clamp.
Articulated tension device
The articulated tension device is very useful to apply controlled
compression across the fracture site. It should be utilized when possible.
Metaphyseal compression can only be applied if there is some contact between
the main proximal and distal fragments after reduction. Throughout compression,
monitor the fracture zone carefully for any unwanted displacement.
It may not be used in situations of severe metaphyseal comminution and/or osteoporosis.
Now fix the plate to the proximal femur with at least 4 bicortical standard 4.5 mm screws.
8 Wound closure, assessment of alignment and knee stability topenlarge
Before wound closure, perform thorough irrigation of the knee wound, in
order to minimize the risk of infection and to remove any debris from the
End the procedure with the closure of the deep tissues and the skin.
Assessment of alignment and knee stability
Before the patient is moved from the fracture table, observe rotation of the leg clinically and compare it to the contralateral side.
With the femur now stable, it is possible to perform a thorough examination of the knee joint, in order to exclude associated ligamentous laxity.