36 Distal Femur Fractures
Introduction
Distal femur fractures comprise various injury patterns ranging from high-energy trauma to low-energy fragility fractures. High-energy injuries may occur in either young or old patients, while low-energy fractures tend to occur in the elderly population, or patients who have previously sustained spinal cord injuries. Furthermore, with increasing incidence of arthroplasty being performed, these fractures may be periprosthetic above a total knee arthroplasty (TKA), below a total hip arthroplasty (THA), or interprosthetic between a THA and TKA.
I. Preoperative
History and physical examination
A detailed history and physical examination can offer key insights that can help guide the treating physician when deciding on an appropriate treatment strategy. Specific areas to focus on include the following:
Patient age and medical comorbidities.
Mechanism of injury.
Previous surgical procedures (especially around the hip or knee).
Preinjury ambulatory status.
Any history of spinal cord injury.
Associated injuries.
Assessing neurologic function distally (motor and sensory).
Assessing skin for any signs of open injury or traumatic arthrotomy.
Anatomy
It is important to understand the normal anatomy of the distal articular block, as well as deformities of the articular block in relation to the shaft. Preoperative imaging of the contralateral femur taken with fluoroscopy can help establish normal articular morphology, coronal alignment, femoral length, and rotational alignment of the femur.
Articular anatomy:
The articular block of the distal femur is trapezoidal (the posterior width of the distal femur is wider than the anterior width; see ▶ Fig. 36.1c ).
Fig. 36.1 (a–c) Illustration of the trapezoidal shape of the articular surface of the distal femur.
This must be taken into account when restoring the articular anatomy and placing lateral plate fixation.
Coronal deformity alignment (varus–valgus alignment; ▶ Fig. 36.1a ):
Normal femoral shaft is oriented 7 to 11 degrees of valgus in relation to the articular surface. It is designated as the anatomic lateral distal femoral angle (aLDFA) = 79 to 83 degrees.
The fracture deformity is related to the location of the fracture with respect to the adductor tubercle.
Sagittal alignment (▶ Fig. 36.1b ):
Normal posterior distal femoral angle (PDFA) is 79 to 87 degrees. This is represented by the angle formed by a line drawn along the axis of the femoral shaft and a line drawn between the anterior and posterior points where the femoral condyle meets the metaphysis.
There is typically an extension (apex posterior) deformity through the fracture site.
Deformity is due to the pull of the gastrocnemius muscle.
Length and rotation:
Both can be assessed in comparison to the contralateral side.
Length can be measured with a radiolucent ruler overlaid on the opposite femur.
Rotation can be matched with the lesser trochanter profile views of the opposite femur, ensuring similar rotational profile of the knee.
Mechanical axis of the femur and extremity:
The native femur has a lateral distal femoral mechanical axis of typically 88 degrees. It is important to keep this relationship in mind during preoperative planning and intraoperatively.
Matching the mechanical axis to the contralateral limb is often beneficial for comminuted fracture patterns.
Imaging
Conventional radiology:
Anteroposterior and lateral radiographs of the knee.
Full-length orthogonal imaging of the femur.
Computed tomography—two-dimensional imaging with reconstruction views is useful for identifying the following:
Coronal plane articular fragments.
Intra-articular extension.
Intercondylar comminution.
Classification
The AO/OTA fracture classification is the most useful for guiding treatment (see ▶ Fig. 36.2 ).
Fig. 36.2 Schematic depictions of the AO/OTA classification.
Type A—extra-articular fractures (supracondylar).
Type B—partial articular fractures are typically unicondylar, and can be either medial or lateral condyle fractures:
Type B1—lateral condyle.
Type B2—medial condyle.
Type B3—isolated coronal fracture (“Hoffa’s” fragment).
Type C—complete intercondylar (Note: Any type C pattern may also be associated with a coronal plane articular fracture).
Type C1—simple intercondylar fracture line with no metaphyseal comminution.
Type C2—simple intercondylar fracture line with metaphyseal comminution.
Type C3—comminuted intercondylar fracture with metaphyseal comminution.
II. Treatment
Initial management
Initial management should consist of gross realignment of the limb and application of a stabilizing device:
Well-padded long leg splint.
Knee immobilizer.
Hinged knee brace if the definitive treatment will be nonoperative.
The purpose of immobilization is to facilitate patient care, mobilization, and pain control.
There is rarely a role for skeletal traction, as this usually exacerbates the deforming forces.
Definitive management
Operative versus nonoperative management:
Distal femur fractures are typically treated surgically.
There may be occasions when medical comorbidities preclude surgical treatment:
i. Medically ill patients where the risks of anesthesia and blood loss outweigh benefit.
ii. Severely debilitated, nonambulatory patients.
iii. Paraplegic or spinal cord injured patients.
Nonoperative management should consist of a well-padded brace or knee immobilizer.
Evaluate neuropathic or spinal cord injury patients on a weekly or biweekly basis to ensure there is no skin or soft-tissue compromise. Impending open fractures or threatened skin should be considered indications for surgical intervention in these patients.
Surgical approaches and fixation techniques—Preoperative imaging should be scrutinized and the preoperative plan should be determined prior to the OR. Patient positioning and implants will depend on the type of fixation strategy that is planned. Furthermore, based on whether or not articular reduction will be required may affect the ultimate surgical approach chosen.
Extra-articular fractures (AO/OTA type A):
Extra-articular fractures may be treated with either plate fixation or intramedullary nail.
Intramedullary nails:
i. If there is space distally for multiple points of fixation in the intramedullary nail (▶ Fig. 36.3 ).
Fig. 36.3 Postoperative radiograph demonstrating anatomic alignment of a distal supracondylar fracture treated with a retrograde intramedullary nail.
ii. Multiplanar interlocking screws distally may improve stability.
The same reduction techniques as outlined later may be used in order to position the fragments appropriately for nail fixation. Blocking screws may also be used during and after nail placement to prevent later displacement of the fracture fragments. The surgical approach for this procedure is the same as for a retrograde femoral nail.
Lateral plate fixation:
i. Reduction techniques can be either direct or indirect.
ii. Simple fracture patterns may be fixed with lag screws and a lateral neutralization plate.
iii. Supracondylar fractures with metaphyseal comminution may best be treated with a bridge plating technique (Refer Chapter 4, Biomechanics of Internal Fracture Fixation).
iv. A lateral approach is typically sufficient for reduction and fixation.
Partial articular fractures (AO/OTA type B):
Type B1 bridge lateral condyle fracture—lateral buttress plate fixation.
i. If a lateral approach is used, then the reduction is assessed using radiographic assessment of the articular surface and alignment.
ii. If the anterolateral approach is used, then the joint surface is directly visualized and reduced anatomically
Type B2 bridge medial condyle fracture—medial buttress plate fixation.
i. This is typically the only fracture pattern that requires a medial approach to the distal femur.
ii. A standard anteromedial approach to the femur is used, elevating the vastus medialis muscle.
Type B3 bridge articular fracture in the coronal plane (Hoffa’s fracture).
i. Anteromedial or anterolateral approach to assess the joint surface.
ii. The fragment may be provisionally reduced with a variety of pointed reduction clamps and Kirschner’s wires (K-wires).
iii. Fixation with headless compression screws or mini/small fragment screws countersunk beneath the articular surface. Two to three screws are typically used, and should be placed in a divergent orientation for maximal stability.
Complete articular fractures (AO/OTA type C):
The first priority in fixation of type C fractures is restoration of the articular congruity.
Reduction and provisional fixation can be achieved with smooth K-wires, bone clamps, large periarticular clamps, or Steinmann’s pins (often used as joysticks in the femoral condyles).
Fragment-specific fixation should be performed with threaded K-wires or interfragmentary screws (either mini fragment, or small fragment fixation).
Think about the ultimate fixation construct, to ensure that the interfragmentary screws are not in the path of the primary fixation construct.
Following reduction of the articular surface, fixation proceeds in a similar fashion to type A fractures.
The implant of choice is typically a fixed-angle device. Examples include the following:
i. Blade plates.
ii. Condylar sliding-barrel plates.
iii. Distal femur locking plates.
iv. Intramedullary nail for select simple articular fracture patterns.
When reducing the articular surface to the shaft, the following parameters should be considered (imaging of the contralateral femur can provide the surgeon with a template):
i. Overall length of the femur.
ii. Alignment of the mechanical axis of the limb (e.g., varus/valgus alignment).
iii. Flexion/extension of the distal femur.
iv. Rotation of the articular block with respect to the shaft.
Surgical approach:
Regardless of specific surgical approach used, the patient is typically positioned supine. The lateral decubitus position may be used to facilitate proximal exposure; however, distal joint work and alignment are more difficult in the lateral position.
Supine bridge a bump under the hip may or may not be used.
i. If a bump is used, it is more difficult to obtain intraoperative imaging to compare length and rotation with the contralateral side.
ii. The use of a bump, however, facilitates proximal exposure if a long plate is required that extends toward the vastus ridge.
The entire hindquarter is prepped into the sterile field.
If a tourniquet is used, a sterile tourniquet is preferred.
Lateral approach:
i. Preferred for type A and simple type C fractures that do not require direct visualization of the articular cartilage.
ii. As illustrated in ▶ Fig. 36.4 (posterior line), the incision is centered laterally over the distal femur.
Fig. 36.4 Standard incisions for direct lateral and anterolateral approaches to the distal femur.
iii. Split the iliotibial band in line with its fibers.
iv. Reflect the vastus lateralis muscle anteriorly to expose the distal femur.
v. Care should be taken to leave a cuff of muscle attached to the posterior intermuscular septum in order to prevent profunda perforator vessels from retracting into the posteri- or compartment during the approach.
Anterolateral approach:
i. Facilitates direct visualization of the joint surface.
ii. Useful for complex intra-articular fractures (OTA C2, C3, and select displaced C1).
iii. As depicted in ▶ Fig. 36.4 (anterior line), the incision is curvilinear from lateral toward midline.
iv. Perform a lateral parapatellar arthrotomy to directly visualize the articular cartilage of the distal femur and patellofemoral joint.
Either incision may be extended proximally as far as desired. Many plate fixation systems have percutaneous targeting jigs that allow for minimally invasive proximal fixation through cannulas that minimize soft-tissue dissection proximally.
Modification when the primary implant is an intramedullary nail:
i. Use the anterolateral approach as necessary for joint reduction and fixation.
ii. Alternatively, an anterior knee incision can be performed with a medial or lateral arthrotomy to access the joint.
iii. Continue the parapatellar arthrotomy distally to gain access for the starting point of a retrograde femoral nail.
Reduction, hardware construct, and fixation strategy:
The first step is obtaining an anatomic reduction of the articular block through direct or indirect visualization.
Simple (minimally displaced or nondisplaced) articular fractures:
i. Reduction may be assessed on fluoroscopic imaging without a full anterolateral approach and arthrotomy.
ii. Large bone clamps may be placed through percutaneous stab incisions.
iii. Reduction can be temporarily held with K-wires until interfragmentary lag screws are placed orthogonal to the fracture line (▶ Fig. 36.5 ).
Fig. 36.5 Anteroposterior knee radiograph 6 months postoperatively that demonstrates multiple mini- and small-fragment interfragmentary screws used to reduce the components of the articular block in a 20-year-old male patient. The metaphyseal comminution above the distal segment was bridged with the lateral locking plate, and notable medial callus is seen.
Complex intra-articular fractures:
i. Coronal fractures should be reduced first:
Anterior to posterior directed interfragmentary (countersunk) lag screws.
Typically 2.0-, 2.7-, or 3.5-mm diameter screws.
Divergent on lateral fluoroscopy.
ii. Intercondylar fragments should then be reduced and provisionally held with K-wires and/or large bone clamps.
iii. Interfragmentary screws should be placed from a lateral to medial orientation, and should be placed in the periphery of the condyle in order to avoid later placement of lateral plate construct.
The implant of choice is typically a distal femoral locking plate.
i. Additional options are listed above.
ii. There are numerous options by multiple manufacturers, all of which can be applied using the same fundamental concepts.
iii. Following articular reduction (or if there is no intra-articular extension), the articular block must then be reduced to the shaft.
iv. Simple fracture patterns in patients with adequate bone stock:
Femur is exposed, fracture reduced, clamped, and absolute stability may be obtained with multiple small fragment or large fragment lag screws orthogonal to the fracture line.
The lateral plate subsequently functions as a neutralization plate for the construct (▶ Fig. 36.6 ).
Fig. 36.6 Postoperative anteroposterior radiograph of a type B extraarticular fracture above a total knee arthroplasty with a long spiral component into the shaft that was treated with lag screws and lateral plate neutralization.
v. Metaphyseal comminution or poor bone quality:
Bridge the metaphyseal region with the lateral plate construct.
The working length of the particular fracture characteristics must be taken into consideration, and screw placement must be modulated to minimize the risk of creating too stiff of a construct.
vi. Plate length. Comminuted fractures are often treated by a bridge plating technique with longer plates, fewer screws proximally, and more screws in the articular segment.
vii. Plate placement:
Most plating systems offer an optional targeting arm. Affix the jig to the plate and slide the plate underneath the vastus lateralis muscle to position it on the lateral aspect of the femur.
Plate position is confirmed via fluoroscopy.
Most plates are designed to sit on the anterior aspect of the distal femoral condyle. Due to the trapezoidal nature of the distal femur, care should be taken to avoid placement of the plate too posterior on the lateral condyle, as doing so may increase the risk of medialization, or “golf club deformity” of the distal segment.
Most plates contain a distal screw hole designed to restore the anatomic axis of the femur. When inserted, this screw should be approximately parallel to the joint line. This should be placed first, and sets the coronal alignment.
viii. Pin the most proximal hole in the plate to the shaft:
The sagittal deformity (typically extension through the fracture site) should be corrected during this step.
Towel bumps or percutaneous Schanz pins (placed in the distal and proximal segment placed orthogonal to one another) allow for control of the extension deformity.
ix. The distal shaft segment is then reduced to the plate with a cortical screw:
If the plate is a straight, then it should sit on the anterolateral cortex of the femur.
Some plates have a built-in 11-degree twist, which allows the plate to sit on the direct lateral surface of the femur when the fracture is correctly reduced.
Cortical screws can be used for fixation to the femoral shaft if the precontoured plate matches the reduced femur.
However, if the plate is not in contact with the lateral cortex of the femur when the reduction otherwise matches the contralateral limb, consider insertion of locking screws in the shaft segment (▶ Fig. 36.7 ). This strategy prevents drawing the femoral shaft toward the plate and creation of a medial translational (“golf club”) deformity of the articular block.
Fig. 36.7 One-year postoperative images in a patient who has no pain, knee range of motion of 0 to 120 degrees, and is full weight bearing who had plate fixation locked off the bone laterally to prevent medial displacement of the distal articular block.
x. An electrocautery cord may be stretched from the center of the femoral head to the center of the ankle to provide a gross assessment of overall limb alignment (▶ Fig. 36.8 ). Comparison to the contralateral limb provides a template for the patient’s native alignment.
Fig. 36.8 Intraoperative fluoroscopic views of the hip, knee, and ankle demonstrating a neutral mechanical axis.
xi. Once the alignment is acceptable, the distal segment of the plate is filled with locking screws. Oblique views of the medial condyle can be taken to assess screw length.
Long screws in this position may be symptomatic postoperatively.
Complications
Nonunion is the most common complication, with reports ranging in the literature from 3 to 24%.
There are few prospective studies describing nonunion rates, but the existing literature suggests that nonunion risk is dependent on the following:
i. Fracture type.
ii. Type of implant used.
iii. Screw configuration (generally recommended to skip one to two holes proximal to fracture between screws).
iv. Obesity.
v. Open fracture:
Nonunion treatment—typically repaired with a plate or nail fixation. Distal femoral replacement is a less commonly used treatment option.
Malunion occurs in up to one-third of patients, and may be due to rotational deformity, angular deformity, or a medialization of the distal articular block.
Knee stiffness—physical therapy may be of benefit to regain motion faster and prevent contracture.
Infection rates are low in closed injury, but are as high as 7% in open fractures.
Post-traumatic arthritis is uncommon.
Rehabilitation
Postoperative bracing (knee immobilizer or hinged knee brace) is optional. There is no evidence that bracing improves clinical outcomes.
Non-weight-bearing (touchdown weight bearing) for 6 to 12 weeks for most young adults with intra-articular fractures.
Weight bearing in geriatric patients is controversial. Recent reports have shown improved outcomes with immediate weight-bearing protocols in patients with extra-articular or periprosthetic fractures in patients older than 65 years.
Early active range of motion as tolerated.
Outcomes
Functional and radiographic outcomes demonstrate 85 to 90% excellent results.
Outcomes are poor when complicated by nonunion, stiffness, or infection.
Patients require second procedures at reported rates from 16 to 25%.
The majority of evidence reports similar outcomes between locking plates and intramedullary nails.
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