1 Principles topenlarge
Bridge plating uses the plate as an extramedullary splint, fixed to the two main fragments, and leaving the intermediate fracture zone untouched. Anatomical reduction of intermediate fragments is not necessary. Furthermore, their direct manipulation would risk disturbing their blood supply. If the soft-tissue attachments to the fragments are preserved and the fragments are relatively well aligned, healing is unimpaired.
Alignment of the main shaft fragments can be achieved indirectly with the use of traction and the support of indirect reduction tools, or indirectly via the implant.
Mechanical stability, provided by the bridging plate, is adequate for gentle functional rehabilitation and results in satisfactory indirect healing (callus formation). Occasionally, a larger wedge fragment might be approximated to the main fragments with a lag screw.
Bridge plate insertion
Bridge plates can be inserted either with an open exposure that respects soft-tissue attachments to the fracture, or using a minimally invasive (MIO) approach that leaves the soft tissues intact over the fracture site. In this latter case, incisions are made proximally and distally, and the plate is inserted through a submuscular tunnel. This requires image intensifier monitoring.
Consideration must be given to fracture reduction in:
- internal/external rotation
Reduction can be performed with a single reduction tool (e.g., large distractor), or by combining several steps (for example fracture table +/- external fixator, +/- reduction via the implant, etc.) to achieve the final reduction.
The preferred method depends on the fracture and soft-tissue injury pattern, the chosen stabilization device and the experience and skills of the surgeon.
If a large fragment has separated from the fracture zone and impaled the adjacent muscle, direct reduction of that fragment may be required.
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.
Lag screw fixation of small metaphyseal fragments is to be avoided, as this will interfere with their blood supply and often does not add significant biomechanical stability to the final fracture fixation construct.
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.
The radiological landmarks of the center of the femoral head, the center of the knee and the center of the ankle joint should all be in line if the mechanical axis of the femur is correct.
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.
This illustration shows 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 DCS fixation to the distal fragment topenlarge
Preparation for correct positioning
Determine the correct position for the DCS 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 knee to indicate the plane of the patello-femoral condyles (green).
The ideal position of the DCS is shown by the yellow wire. Note that it is inserted parallel to both the red wire in the frontal plane and is parallel to the green line on the end-on view on the femur. This latter orientation ensures that the plate comes to lie flush with the lateral cortex.
The ideal entry point for the DCS is shown on the diagram. The guide wire for the DCS is positioned at 2 cm proximal to the distal end of femur. On the lateral view, the distal femur is divided into thirds and the DCS entry site is located at the junction of the anterior and middle thirds.
Insert the guide wire at the chosen entry site of the DCS. Insert the guide wire under image intensifier control all the way across the femur. Check the position of the guide wire carefully to ensure it has been correctly positioned, with the parallelism already described.
Correct depth of guide-wire insertion
The depth of guide-wire insertion is crucial. Remember that the cross section of the distal femoral condylar mass is trapezoidal and slopes markedly on the medial side. The tip of the guide wire should just engage the medial cortex, and so will appear short of the medial condylar cortex on the AP intensifier image.
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 and the DCS will cause pain and possibly heterotopic ossification. 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.
Screw length measurement
Next, slide the direct measuring device over the guide wire and determine guide-wire insertion depth and, thereby, the length of the DCS required.
After assembling the DCS triple reamer and setting the reamer to the correct depth, ream the hole for the DCS over the guide wire.
Preliminary DCS insertion
After tapping, insert the DCS over the guide wire so that its outer end is still visible 2-3 mm outside the lateral cortex of the distal femur. Align the T-handle with the vertical axis of the distal femoral articular block.
Pearl: do not tap the track in osteoporotic bone
Do not tap the track of the DCS in osteoporotic bone.
Detach the T-handle and slide in the plate submuscularly from distal to proximal.
The plate is pushed from distal to proximal along the naturally preexisting potential tunnel beneath the vastus lateralis. If there is a continuous contact of the plate tip with the bone while pushing it proximally, there is no need preliminarily to create a tunnel.
Plate and screw combination
Insert the T-handle through the barrel of the plate and reconnect it to the screw. This can be challenging and may temporarily tilt the distal femoral articular block. It may be helpful to make an incision over the proximal end of the plate at this point to gain control of both ends of the plate. This will allow for easier connection of the plate to the screw.
In order for the barrel to slide over the screw the T-handle should be parallel, on the lateral view, to the long axis of the distal fragment.
Final plate impaction
Disconnect the T-handle from the screw.
Use the impactor to bring the plate down to the bone with the barrel sliding over the screw shank.
The compression screw may be used to couple the DCS to the plate.
A cancellous screw can then be inserted into the most distal screw hole of the plate to prevent rotation of the main distal fragment around the axis of the DCS.
Pearl: do not use compression screw in osteoporotic patients
Do not use the compression screw in osteoporotic patients – it can cause the DCS thread to strip out from the soft cancellous bone of the medial femoral condyle.
3 Reduction topenlarge
Closed reduction is aided by:
- Complete anesthetic muscle relaxation of the patient
- A bolster posterior to the supracondylar region to prevent
- Manual traction
- Use of the femoral distractor, or external fixator
- Percutaneous instruments (e.g., colinear clamp as illustrated)
4 Plate fixation to proximal fragment topenlarge
Verification of reduction
Under image intensifier control, the preliminary reduction is checked again with respect to axial alignment, length and, to a degree, rotation.
Insertion of first screw into proximal fragment
Make stab incisions over the proximal fragment according to the planned final screw placement.
Control the mid-lateral plate position using two blunt Hohmann retractors placed ventrally and dorsally around the femoral shaft.
If the overall reduction is found to be satisfactory, insert the first cortical screw in the distal part of the proximal main fragment, without fully tightening. This still allows for the plate position to be finely tuned.
Pearl: final reduction
If the lateral position prior to the insertion of the second screw is inadequate, use sterile bolsters to aid correction.
Be cautious not to malalign the articular block as this will make application of the plate to the proximal femur difficult.
Insertion of second screw into proximal fragment
Confirm the mid-lateral plate position using two Hohmann retractors introduced through a second incision over the proximal plate portion, or by palpation.
Once the most proximal screw is fully inserted, the more distal screw in the proximal fragment is finally tightened.