1 Principles top
Retrograde nail fixation relies on maintenance of the fracture viability in the metaphyseal / diaphyseal component of the fracture. This is made possible through closed reduction techniques and results in high union rates and low infection.
Malreductions (external rotation/valgus) can be common without careful scrutiny of intraoperative technique and radiographic control. The articular surface should be addressed by direct vision and standard interfragmentary compression. Careful insertion of the nail must ensure that the articular surface reconstruction is not disrupted. Retrograde nailing of complete articular fractures requires great surgical skill and experience, if disaster is to be avoided. In expert hands it can produce adequate results, but the occasional use of the retrograde nail in complete articular fractures is fraught with risks.
Reamed versus unreamed nailing
Reamed nailing allows the use of larger diameter implants and may therefore provide greater initial stability. It carries a greater risk of a large entry hole causing articular cartilage damage, but reduces the risk of disrupting the fixation of intraarticular fractures.
Fat embolization, or articular reaming debris, may be concerns with reaming.
In elderly patients with osteoporotic femoral canals, no, or only minimal, reaming may be required because the canal is capacious.
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.
Muscle forces acting on the fracture fragments often determine the pattern of displacement of a fracture. Traction alone can restore the normal length of the bone, but may exaggerate the axial malalignment, instead of correcting it.
Positioning aid to assist reduction
The distal femoral fracture can be reduced by flexing the knee to reduce the muscle force of the gastrocnemius muscle.
A supporting pad can be used to help to correct a recurvatum deformity.
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.
Before interlocking, the correct position of the nail and the rotation of the femur must be verified. Not only must the biomechanical axis be restored, but 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.
Illustration of the longitudinal axes of the lower limb.
AO teaching video: Distal femoral nail
2 Patient preparation top
This procedure may be performed with the patient in one of the following positions:
4 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 condyles. Reduction aids which 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 to clamp from medial to lateral across an intercondylar split.
Pearl: combination of reduction aids
Attempts at reduction of an intercondylar split with the pointed reduction forceps alone (2) 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 helpful.
Before definitive fixation is inserted, the fracture is clamped. Usually, one to two 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 medial parapatellar retinaculum.
Definite articular surface fixation
Screws may be placed along the periphery of the articular surface of the lateral femoral condyle, going from lateral to medial, in order to compress the intercondylar split.
These screws may be fully threaded 3.5 mm lag screws (with gliding holes, as shown), 6.5mm partially threaded lag screws, or 4.0/4.5 mm cannulated, partially threaded lag screws.
This end-on view demonstrates the screw trajectory from lateral to medial. Such screw placement allows for insertion of the retrograde nail, without implant conflict.
On occasion, it is acceptable to insert screws through the articular surface when no other options are available. These screws should be countersunk and recessed beneath the articular surface.
5 Reduction top
A variety of techniques can be used to aid the reduction of the distal femur.
For most fractures, manual traction is satisfactory. In some cases, more sophisticated reduction techniques have to be used such as:
- Schanz screw
- Bone hook
- Pointed reduction forceps
- Colinear clamp
depending on the metaphyseal fracture configuration.
The fracture reduction may be achieved by longitudinal traction applied to the upper tibia.
It is useful to have a small sandbag just behind the hip joint to prevent external rotation. This will make subsequent alignment of the distal femoral condyles easier to orientate.
Alternatively, a carbon triangle can be used.
Direct reduction with a bone hook may be helpful in securing anatomical alignment. Careful insertion and manipulation must be performed in order to minimize soft-tissue trauma and to prevent injury to the femoral artery.
Depending on the fracture morphology, reduction of the distal femur can also be achieved using a colinear clamp.
One or more monocortical Schanz screws can be helpful for providing direct control of displaced main fragments. It is superior to external reduction maneuvers.
6 Opening the medullary canal topenlarge
Localization of entry point
It is very important to perform every step of the procedure of locating the entry point under image intensifier guidance. On the AP view, center the guide wire exactly in the middle of the intercondylar notch. On the lateral view it should be located in the extension of the Blumensaat’s intercondylar roof line.
The entry point for the nail is in line with the axis of the medullary canal, just below the crest of the intercondylar notch. The correct position is therefore located anterior and lateral to the proximal attachment of the posterior cruciate ligament.
On the lateral view, the entry point must be at the anterior tip of the Blumensaat’s intercondylar roof line. There is no “safe zone” posterior to this line. Take care not to start the entry point posterior to the Blumensaat’s line, in order to avoid damage to the cruciate ligaments when reaming.
The x-ray shows the desired 30° flexion of the knee joint. With less flexion the tibial plateau hinders the guide wire insertion. With more flexion the articular surface is in danger and the patella is in the way.
Insert the guide wire into the medullary canal, as far as approximately 12-14 cm proximal to the fracture zone.
Opening of the canal
To open the medullary canal, push the protection sleeve and drill sleeve over the guide wire into the notch. Open the medullary canal carefully to a depth of approximately 30 mm using the cannulated drill bit.
Pearl: use of pointed reduction forceps
Use the pointed reduction forceps to protect the lag screw fixation and avoid secondary displacement during reaming.
Then remove the drill bit, protection sleeve, and guide wire.
Irrigate the knee joint carefully to remove all drilling debris.
7 Poller screw (blocking screw) topenlarge
The concept of a poller screw is based on the principle that the malalignment induced by oblique, proximal and distal fractures can be counteracted by the nail-directing effect of the screw. Therefore, its position should aim to counteract the anticipated displacement of the fracture. Most often, it is therefore inserted in the short side in the distal fragment. If there is a wide canal, two screws can be inserted, one on either side of the path of the nail. It is technically challenging to insert the poller screw in the exactly correct position. On one hand, the screw should prevent reaming in the undesired location. On the other hand, it should not impede the reaming process, or nail insertion.
It is better to insert the poller screw prior to reaming and, in cases of unreamed nailing, prior to nail insertion, in order to provide adequate contact between the nail and the screw. If the poller screw is inserted after reaming, the path of the nail is already set and the poller screw may not function. A small fracture screw, or a locking screw, can be used as a poller screw, depending on the local anatomy.
The reaming process in the presence of the poller screw must be performed very carefully in order not to damage the reamer tip.
The most frequent indication for poller screws is an oblique fracture which
would tend to shift when the axial knee blow technique is used to close any
fracture gap, or when the patient is mobilized.
See also: Stedtfeld HW, Mittlmeier T, Landgraf P et al (2004) The Logic and Clinical Applications of Blocking Screws. J. Bone Joint Surg. Am. 86:17-25, 2004.
Insertion of poller screw
The poller screw should be located according to the direction of the initial fracture displacement. Therefore, in a medial displacement, the fracture will try to displace medially even after the reduction and a poller should be placed lateral to the proposed nail track.
If there is a wide canal, or a very unstable situation, a blocking screw can be placed on each side of the proposed nail path.
8 Choice of implant topenlarge
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)
Variations in surgical preferences exist with regard to the optimal length of a retrograde nail for treatment of a distal femoral fracture.
Determine nail length using a guide wire
If reaming was performed, the maximal length of the nail is determined by comparing a second identical length guide wire to the one that has been inserted. The correct placement of the tip of the guide wire in the proximal canal should be assessed using an image intensifier. A second guide wire must be positioned in contact with the articular surface of the distal femur. This must also be verified by image intensifier.
It is desirable to use the longest nail possible in the femur to prevent latent risk of periimplant fractures.
A radiographic ruler may also be used to determine the length of the femoral nail.
The ruler should lie in the center of the distal end of the femur at the roof of the intercondylar notch and along the center of the medullary canal.
It is important to measure the medullary diameter at the mid portion of the femur, which represents the narrowest segment of the medullary canal (isthmus).
The inner cortical edge should touch the inner numbered disk of a ruler aperture. In the illustration an inner cortical diameter of 14 mm is shown.
Consideration for special situations
Multifragmentary fractures, or open fractures with bone loss
In multifragmentary fractures, or in open fractures with bone loss, it is safer to perform preoperative planning on the uninjured leg.
Narrow medullary canal
In some cases, when the medullary is very narrow, it might be necessary to ream.
9 Reaming topenlarge
Sequential reamer size increase
After the tissue protector has been introduced, the reamer shaft, fitted with the initial reamer head is inserted over the guide wire. Usually, reaming begins with a nine-millimeter, end-cutting medullary reamer.
Sequential reaming is performed with increments of 0.5 mm each.
As soon as “chatter” can be felt and heard, the inner cortex has been reached.
Reaming must be performed to one or two increments above the planned nail diameter, in order to allow a smooth nail insertion. For example, for a nail diameter of 10 millimeters, reamer heads of up to 10.5, or 11, millimeters diameter are used. If a very tight fit of the reamer can be felt before the desired reaming size is reached, consider a smaller diameter nail than previously planned.
Pitfalls: eccentric and overaggressive reaming
Eccentric reaming can cause weakening of the adjacent cortex, which may interfere with healing, or even cause a fatigue fracture.
Trapping of reamer by slow spinning
If the reamer gets trapped while reaming, it must be gently removed by the most senior surgeon because breakage of the reamer tip in this situation can be a devastating complication.
Heat necrosis by over-forceful reaming
Reaming with excessive force should be avoided because it is likely to cause heat necrosis of the femoral cortex. This applies especially for narrow midshaft canals (9 mm or less in diameter).
Rapid thrusting/systemic fat embolization
Care should be taken only to use sharp reamers, to advance the reamers slowly and to allow sufficient time between reaming steps for the intramedullary pressure to normalize. Rapid thrusting of the reamer may increase further the intramedullary pressure. The image demonstrates fat extrusion during reaming in a human cadaver specimen with a window in the proximal section.
High intramedullary pressures may cause pulmonary embolization of medullary fat, which in turn may lead to pulmonary dysfunction (images show echocardiographic examples of fat embolization through the right atrium).
10 Nail insertion topenlarge
During nail insertion, it is important that the assistant apply traction to the lower extremity, in order to prevent shortening and/or angulation of the distal main fragment. In order to prevent this complication, which is very difficult to correct later, repeated image intensifier assessments are required.
Drive the nail gently into the distal fragment. This can often be performed manually. If required, gentle hammer taps are usually sufficient to ensure proper advancement. Insert the nail until it just passes deep to the cartilage surface.
Take care in osteoporotic oblique and multifragmentary distal femoral fractures not to shorten the femur by impacting the bone ends too firmly together.
11 Distal locking options topenlarge
It is important to perform the distal locking first. If proximal locking is done first, the surgeon will no longer be able to perform final corrections to length.
Distal locking is performed by using the appropriate aiming device attached to the insertion handle.
It is preferable to use at least two distal locking options for all distal femoral fracture types. When two distal locking options are used it is not possible to perform dynamic distal locking. Dynamic locking can only be achieved by using the proximal dynamic locking hole.
12 Distal locking with screws topenlarge
Distal aiming device
After verifying the correct position of the distal end of the nail under image intensifier control, the distal aiming device may be attached to the insertion handle.
Pearl: use of guide wire to determine position of nail end
Insert a guide wire through the small hole of the aiming device to determine the position of the nail end.
For correct measurements of locking screw length the drill sleeve must be pressed onto the bone surface at all times.
Gentle pressure can be applied to the tip of the drill sleeve to maintain its correct position.
The sites of the skin and fascial incisions for the drill bit and the distal locking screws may be determined after the drill sleeve assembly has been inserted into the holes of the aiming device. The length of each locking screw is read from the calibrated drill bit. The correct length is confirmed using image intensifier control.
Verification of locking screw placement
In all cases, obtain final x-rays in two planes in order to check the exact locking screw placement. If the normal tight coupling between the nail and the insertion guide has been altered, the screws might have been placed either anterior or posterior to the nail.
Pitfall: too long a locking screw
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 locking screws appear to be inside the bone. If they appear to be outside the bone, they are most likely too long and will invariably cause pain and possibly heterotopic ossification. In order to assess the exact length of the locking screws an AP view can be obtained with 30° internal rotation of the lower extremity.
Internal rotation by 30° reveals that an inappropriate screw length was chosen.
13 Intraoperative radiological assessment topenlarge
Assessment of rotation
Compare the profile of the lesser trochanter with that of the contralateral leg (lesser trochanter shape sign), holding the leg so that the patella faces anteriorly on both sides.
Before positioning the patient, store the profile of the lesser trochanter of the intact opposite leg (patella facing anteriorly) in the image intensifier.
The illustration shows the lesser trochanteric profile of the intact opposite side.
In cases of malrotation, the lesser trochanter is of a different profile when compared to that of the contralateral leg.
Take care to assess rotation with the patella facing directly anteriorly.
Matching of the lesser-trochanter shape
After distal locking, achieve correction by using the handle of the nail insertion device. The distal main fragment can be rotated in relation to the proximal main fragment.
14 Proximal locking top
The first proximal locking screw is inserted in the anteroposterior plane. A radiolucent x-ray table is essential. Care must be taken in preoperative planning so that adequate image intensifier views of the proximal femur can be obtained in both the AP and the lateral planes before the operation begins.
The thickness of the subcutaneous tissue, especially in obese patients, can make this procedure technically demanding.
It is extremely difficult to perform lateral to medial proximal locking with a long retrograde femoral nail. This is due to the difficulty in positioning the image intensifier around the proximal femur.
Drilling of screw hole
Proximal AP locking has to be performed by the freehand method. After you have verified the correct position of the distal end of the nail under the image intensifier, visualize the shape of the proximal locking hole.
Then, bring the image intensifier into a strict AP position at 90° to the nail. The proximal static holes must project a perfect circle and the tip of a scalpel is projected into the center of the hole.
Make a skin incision and bluntly dissect the muscle.
Place the radiographic projection of the tip of the drill bit as centered as possible into the hole image. Start drilling but assess the position of the tip of the drill bit repeatedly, with the drill temporarily uncoupled.
Maintaining lower extremity position
While drilling the locking hole, the assisting surgeon must prevent the leg from moving, in order not to miss the target hole.
Pearl: radiolucent drill
If available, a radiolucent angled drill can be used as described in distal locking of antegrade nailing for femoral shaft fractures (click here for the description).
Determine the appropriate screw length with a depth gauge and insert the AP locking screw. Take care to prevent an oblique insertion of a locking screw because it can become trapped between the firm cortex of the proximal femur and the nail.
Second locking screw
Depending on the fracture pattern, use either one or two proximal locking screws.
The question as to whether a second locking screw in the long nail should be used must be decided by the surgeon on a case-to-case basis.
In a short nail and a very wide medullary canals a second locking screw should be used. In this case the second screw should be inserted perpendicular to the first one.
Pearl: secure screw using a suture
If the contact between the screw driver and the locking screw is lost, the screw may move within the soft tissue and become extremely hard to capture. To prevent this time-consuming complication, lasso the locking screw with a strong absorbable suture.
15 Insertion of end cap topenlarge
An end cap must be used. The length of the head of the end cap depends on the final relationship of the nail end to the intercondylar notch of the distal femur.
In distal femoral fractures, the nail just passes the condylar surface resulting in the need for a 0 mm end cap. By no means should the end cap project distal to the subchondral region.
Introduce the end cap using a hexagonal screwdriver.
Verification of end cap placement
Tighten the end cap with the screw driver. Verify using image intensifier control and palpation that the end cap has been fully inserted into the nail and does not project from the bone.
16 Wound closure, assessment of alignment and knee stability top
Before the wound closure, perform thorough irrigation of the knee wound in order to minimize the risk of infection and to remove any debris from the joint.
End the procedure with the closure of the tendon (as necessary), the deep tissues and the skin.
A suction drain may be inserted intraarticularly, when indicated.
Assessment of alignment and knee stability
Before the patient is moved from the fracture table, observe rotation of the leg clinically and compared it to the contralateral side.
Pearl: post-ORIF examination of knee joint stability under
With the femur now stable, it is possible to perform a thorough, but gentle, examination of the knee joint to determine any associated ligamentous laxity.