Distal Femoral Fractures

Abstract

Distal femur fractures are increasing injuries in our environment, due to their close relationship with the aging of the population. The diagnosis and treatment of these injuries have evolved in recent years, and the availability of new tools allows us to improve the results of our patients. Techniques such as dual nail-plate or plate-plate fixation emerge as an option in complications and complex fractures, and augmentation with PMMA may be an option in very low-density bones. To use these new techniques, anatomical knowledge, especially of the medial aspect of the femur, is essential. Many recent publications have studied the use of minimally invasive techniques with safe pathways. Throughout the following pages, we give a glimpse of the novelties in the treatment of these fractures, and we review the classic concepts.

1. Introduction

Although distal femur fractures represent <1% of all fractures, an increase in their incidence has been observed in relation to the aging of the population [1, 2, 3]. Studies completed in developed countries show a general incidence rate of distal femur fractures that ranges between 4.7 and 8.7 fractures per 100,000 patients per year [1, 2, 3].

These types of fractures have a bimodal distribution. There is a peak in young adults, often men, which decreases until the age of 50 in relation to high-energy polytrauma. This peak has been progressively decreasing in direct relation to the development of safety mechanisms in vehicles and currently represents a low fraction of all fractures [2]. As a result of high-energy injury mechanisms, percentages of open fractures close to 20% have been reported, especially in relation to traffic accidents and occupational accidents, and the presence of a high-energy distal femoral fracture should aware us of associated injuries [4]. A common mechanism in traffic accidents associated with this group of age is the “dashboard injury” in which the patella strikes the knee like a wedge between the femoral condyles. This pattern is associated with a higher risk of additional fractures in the ipsilateral extremity, particularly in patella, tibia and fibula, hip, and acetabulum, as well as non-orthopaedic injuries as damage in trunk and skull [4].

These fractures have a high mortality rate in the set of a high-energy trauma at 30 days, 6 months, and 1 year which are 1%, 2%, and 3%, respectively [5].

From the age of 60, we found an increase in mortality for both sexes with a female predominance in relation to low-energy trauma that could be comparable to hip or femoral shaft fractures in the elderly. The overall incidence rate in people over 60 years of age is 43 per 100,000 patients per year in men and 217 in women [5]. In this population group, the mortality rate at 30 days, 6 months and 1 year amounts to 8%, 26%, and 35%, respectively, and this increase is related to the age of the patient and their comorbidities [5].

Due to the high number of knee replacements performed, another type of distal femur fractures consisting of periprosthetic fractures is standing out. Due to their biological and mechanical characteristics, they constitute a clearly differentiated subgroup. The frequency of periprosthetic fractures of the distal femur after total knee arthroplasty is reported to be between 0.3 and 5.5% for primary knee arthroplasties and up to 30% after a revision procedure [6, 7]. In these patients, the annual mortality rate is 15% [5].

Extra-articular supracondylar fractures are the most frequent fractures, followed by partial articular fractures and complex supra-intercondylar fractures [3].

2. Anatomy

There have been proposed different descriptions to define the limits that involve the distal femur, but one of the most used is to define the distal femur as a square segment with a side distance equivalent to the space between both epicondiles (Figure 1).

Figure 1.

Segment that defines the distal femur.

This segment is particularly relevant for several reasons as follows:

• It is part of the knee joint, and injuries to it will affect its mechanics and kinematics.

• Together with the proximal tibia, it constitutes the segment of the lower extremity that is most affected by malunion, so a nonanatomical reduction will modify the axes of the extremity in a higher degree.

• It is a joint whose stability and congruence depend on several elements, highlighting the ligamentous complexes, the menisci and the extensor apparatus of the knee. The repair and preservation of these structures are essential to preserve the function of the knee, and many injuries to the distal femur will compromise them.

If we focus on the shape, we see that the diaphysis of the distal femur widens into a cone shape with a trapezoidal projection corresponding to the medial and lateral condyles [8, 9]. The medial femoral condyle is larger and extends distally compared to the lateral femoral condyle [10]. For this reason, the anatomical axis of the distal femur, which is formed between the distal joint line and the diaphyseal axis, has 6–11° of valgus (Figure 2) [10, 11]. The lateral and medial cortex are inclined about 25° and 10°, respectively, in the axial plane toward the midline, which will condition the insertion of osteosynthesis material in this area. The posterior halves of the condyles are posterior to the posterior cortex of the femur [12].

Figure 2.

Angles of the distal femur.

Between both condyles is the intercondylar fossa. Each of the faces contributed by the condyles to this groove constitutes the insertion of the cruciate ligaments, the one offered by the lateral condyle for the anterior and the medial one for the posterior. The point anterior to the proximal insertion of the anterior cruciate ligament corresponds to the distal point of Blumensaat’s line and is the entry portal for the retrograde intramedullary nail (Figure 3).

Figure 3.

Entry point for distal femoral nailing and its relation to the anterior cruciate ligament. In yellow the Blumensaat’s line.

The medial and lateral collateral ligaments emerge from the medial and lateral epicondyles, respectively.

Surrounding the femur, we find a large part of the muscles that contribute to the mobility of the lower extremity, causing in cases of fracture the displacement of the bone fragments and conditioning deformity depending on the place of the fracture (Figure 4):

• Quadriceps and hamstrings favor shortening.

• The adductors help shortening and can promote varus disaxation, especially if there is metaphyseal comminution.

• The gastrocnemius causes a deformity with posterior apex of the distal fragment that can compromise the neurovascular bundle 11.

Figure 4.

Deformity forces in distal femoral fractures.

The position of the vascular bundle in the distal femur favored ruling out approaches other than the anterior and lateral ones (Figure 5). Recently, thanks to the evolution in surgical knowledge of the area, the development of anatomical materials, and the need to improve fixation in these complex fractures, medial approaches to the distal femur with proximal extension have been developed. To be able to carry them out, abundant studies have been completed on cadavers for percutaneous techniques and with a special interest in the Hunter’s canal. Interesting is the study by Maslow that focuses on seeing how far the femoral artery passes from the anterior to the posterior area of the femur, describing a mean distance from the adductor tubercle to the femoral artery of 23.2 cm and 14.3 cm at the level of the anterior border and posterior femur, respectively. This would allow us to use percutaneous plates using this safety distance. In open surgery, the location of the geniculate artery allows us to control it to unhook the package and favor access. The descending geniculate artery originates at a mean of 10.8 cm from the adductor tubercle [13]. It should always be kept in mind that the intraoperative position may vary in relation to the trauma.

Figure 5.

Distal femoral anatomy in sagittal anatomical images.

Knowledge of this vascular anatomy will also allow us to play with the implantation of cerclages in safe areas or choose the best approaches to access risk areas.

3. Diagnosis

The diagnosis of a distal femur fracture is usually clear in most cases, finding young patients with high-energy trauma with obvious deformity or older patients with less deformity, but with pain and ecchymosis that facilitate the diagnosis, which is easily confirmed on a two-plane radiological test. Basic radiological studies should include simple radiographs of the total femur to rule out the presence of acetabular, hip, femoral diaphyseal, patella, and hip dislocation or fractures. If there is excessive shortening or deformity, traction views can help the study [14]. In those situations, with partial fractures, especially in the coronal planes, the diagnosis is complicated. In these cases, functional limitation and hemarthrosis should lead us to a joint injury that will force us to perform oblique radiographs to confirm the injury (Figure 6). In many cases, performing a CT will allow us to complete the diagnosis and will provide us with information on the complex three-dimensional structure of the distal femur, especially in trauma with joint comminution.

Figure 6.

Coronal shear fracture is seen on an oblique view.

The use of MRI is generally restricted when chondral, tendon, meniscal, and ligamentous injuries associated with trauma are suspected. It is especially useful in knee instabilities and injuries of the extensor apparatus since they frequently accompany high-energy trauma.

We must also know the vascular status of the limb and suspect an injury in the presence of any of the four signs of vascular injuries, such as pulsatile hemorrhage, expanding hematoma, palpable thrill/audible murmur, or a pulseless limb. When these four signs are present, immediate surgical exploration is warranted. In patients with one of the four signs, an ankle-brachial index is recommended. If this is greater than 0.9, a clinical follow-up can be carried out without further studies. If it is less than or equal to 0.9, arteriography or Doppler ultrasound should be performed [15].

4. Fracture classification

Currently, the AO/OTA classification (Figure 7) is the most widely used classification in clinical practice and research, since it allows the use of an alphanumeric coding system that facilitates data storage and provides a hierarchy of severity [16]. Code 33 is designated for the location of this fracture. In addition, these fractures are divided into extra-articular (type A), partial articular or unicondylar (type B), and intra-articular (type C) [10]. Subgroups from 1 to 3 provide information on the degree of comminution in types A and C fractures. In type B fractures, however, the subgroups refer to the pattern of the fracture; type B1 are sagittal fractures of the lateral condyle, type B2 are sagittal fractures of the medial condyle, and type B3 are coronal fractures known as Hoffa’s fractures, described in 1907 and usually affect the lateral condyle [17].

Figure 7.

AO classification.

5. Management

The results published in recent years lead us to consider that distal femur fractures are always surgical, except in limited cases, due to the high mortality associated with conservative management and the number of complications, such as knee stiffness, inadequate alignment, consolidation delays, soft tissue problems, and prolonged hospitalization [18, 19].

There are few exceptions to this rule, more related to the patient than to the fracture itself. In recent years, the following situations have been described that may be considered relative contraindications, since even in these cases surgery may be beneficial: very high-surgical risk that prevents anesthesia, non-displaced fractures, non-ambulant patients, and irreversible spinal cord injuries [10, 20].

The fundamental objectives of surgery will be to achieve a good reduction of the joint surfaces, maintain the length of the femur, as well as alignment and rotation; achieving knee stability that allows rapid mobilization [9]. Stabilization in the sagittal plane with rotation of the condyles, unlike stabilization in the frontal plane, represents a challenge for the surgeon [21].

In high-energy fractures with comminution and shortening, unstable fractures, open fractures, fractures with vascular injury, or in the context of damage control orthopedics in polytraumatized patients, the use of a temporary external fixator will be useful until surgery is performed. Trans-skeletal traction can be useful for short waiting periods, but it is in disuse due to the limitation it entails for the management and care of hospitalized patients.

6. Fracture fixation and approaches

In most distal femur fractures, we will opt for a radiolucent table position, with supports and pads that allow correcting the deformity of the fracture (Figure 8). We must count on the elevation of the knee to angle the beam of rays and achieve correct orthogonal projections. It is also essential to allow access to the contralateral limb and hips, to compare length and rotation between limbs. To control screw lengthening, we should consider distal femoral angulations shown in Figure 2 to angulate the x-ray beam to fit both angles.

Figure 8.

Reduction of deformity in distal femoral fractures.

Another point of concern is rotation adjustment. In complex, distal femoral fractures are challenging. We have several tools to confirm this rotation: use of lesser trochanter, clinical rotation, and femoral cortex reduction, but the use of the lesser trochanter profile seems to be useful and reliable [22].

There are different approaches that will allow us to treat injuries of the distal femur.

In extra-articular or simple partial articular fractures, we can choose minimally invasive techniques, through lateral approaches or nailing techniques.

In case of complex joint injuries, joint exposure is necessary. In these cases, we can opt for parapatellar approaches, among which the external one is the most used, or techniques such as the TARPO approach, Swashbuckler, Olerud extensible anterior, and window approaches that allow us greater control of the joint fragments. If we need to provide medial support to prevent varus collapse, medial approaches will be necessary. On many occasions, especially in open fractures, we must adapt our approach to the underlying situation and minimize the damage to healthy structures by repairing the damaged ones (Figure 9).

Figure 9.

Extensile modified lateral approach in a patient with a bone defect and a complete injury of the extensor mechanism.

To achieve a proper fracture fixation, we must always follow certain principles that allow us to achieve good results in any situation. For this reason, we must follow a strategy that must consist of gradually reducing the complexity of the injury: we will begin by reconstructing the joint block, to later neutralize and fix the metaphyseal area.

The distal femur is going to be subjected to torsional forces and a lot of axial load, which will condition a high varus stress [21]. If we anticipate long consolidation times, sometimes a lateral plate does not tolerate the situation and suffers from fatigue, and the use of medial plates or intramedullary nails with or without a lateral plate will provide additional fixation that will improve our results (Figure 10) [23].

Figure 10.

Distal comminuted fracture treated with a lateral plate. Failed fixation was rescued with a double plate fixation.

We are going to face special situations, in which the complexity of the injury is going to force us to increase our fixation to prevent early collapse. Perhaps the osteoporotic fracture is today our battle horse, with fragile bones that prevent the adequate purchase and load transmission to the implant, leading to early failure and limiting the mobility of patients who require early loading. In these cases, the use of PMMA (Figure 11) to improve the bone-screw interface will give us a plus that can solve extreme cases [24].

Figure 11.

PMMA augmentation in a distal complex femoral fracture.

In the case of type B fractures (partial joints), total stability is required, for which interfragmentary compression would be necessary, normally with compression screws; to which another buttress plate can be added (Figure 12) [14]. As specific indications for the use of locked plates, we find comminution and poor bone stock [25].

Figure 12.

Hoffa fracture fixed with interfragmentary compression and neutralization plate.

Distal femoral replacement involves resection of the supracondylar segment of the femur and replacement with a rotational hinge knee system [26]. The main objective of the treatment when treating distal femoral fractures is to allow full weight bearing as soon as possible, restore patient mobility and function, and reduce hospital stays and the rate of death and medical complications. Some studies indicate that the difference between the costs of the different types of treatment is negligible if the total cost of care is considered; days of hospitalization, rehabilitation, and indirect costs [26, 27, 28, 29]. We must consider distal femoral replacement in non-reconstructible cases (Figure 13) to prevent hardware failure and in periprosthetic fractures without a bone stock for fixation. The two major problems with distal femoral replacement are infection and surgical stress on the patient. We should select our patients properly because the rescue of a distal femoral replacement in an old patient would be catastrophic, and the optimization of the physiological status is mandatory to prevent complications.

Figure 13.

Situations where a DFR could be an option.

Periprosthetic fractures constitute a greater challenge, since the presence of the implant limits bone metabolism and its consolidation capacity, increases the infection rate, we generally work on stiffer knees and, furthermore, the use of retrograde nails is not always possible. In the case we select a locking nails as the method of tratment, it is essential to use as many locking screws in the distal fragment as possible to improve purchase and prevent complications [30].

In these cases, we must be meticulous, study the loads to which the fracture will be subjected, assume long consolidation times, and achieve fixations that are sufficiently rigid to allow early loading (Figure 14), while being careful with soft tissue dissection to prevent postoperative complications.

Figure 14.

Rigid bone-plate construct to fix a distal femoral periprosthetic fracture.

7. Complications

Nonunion is the most frequent cause of reoperation in distal femur fractures [31]. Improvements in outcomes have been reported, probably due to “biologic approaches” and implant developments with nonunion rates of 6% [32]. Among the factors that lead to nonunion are metaphyseal comminution, especially medially, malalignment, poor bone quality, and comorbidities that reduce the adequate vascular supply of the bone, such as smoking, diabetes or vascular disease, and inadequate fixation with devices that are too rigid or plates that are too short [31, 33, 34]. Cases of non-septic nonunions in patients with good bone stock should be treated by revision of the implant and bone grafting. In special cases, resorbable methyl methacrylate or tricalcium phosphate cements can be added to “augment” fixation screws in the condylar fragment. Currently, the rate of cure, nonunion, and reoperation is similar between the different fixation methods [18].

Malalignment together with medial comminution are the main factors that predict nonunion [35]. The metaphyseal location with a predominance of cancellous bone predisposes to comminution of the fracture site, even with low-energy trauma. This leads to failure of the constructs with a varus collapse, especially if a lateral fixed angle plate is used [14]. In case of medial comminution greater than 2 cm, it is recommended to add a medial support by means of a “strut allograft,” a support plate medial or intramedullary nailing [31, 36]. It should be added that misalignment greater than 5–10 degrees can affect the biomechanics of the knee, conditioning the compartmental overload of the knee [37].

Deep infection rates of around 2.7% have been reported, considerably low when compared to those reported in the 1960 literature [14, 34, 38]. This complication requires meticulous debridement, culture, and appropriate antibiotic therapy. If the fracture allows, it may be appropriate to remove the fixation material. An infection with abscess formation should be “packed open” and some authors recommend the use of vacuum-assisted close therapy, but this point is controversial in the set of an infection [14, 37]. They are generally treated for 3–12 weeks with specific antibiotic therapy [27]. Given implant loosening and recalcitrant infection, removal of the implant and external fixation should be considered. Lower rates of infection have been shown with minimally invasive approaches than with open approaches [39].

Knee stiffness is the most common complication resulting from the initial trauma and surgical exposure. The effect of both is multiplied by prolonged immobilization depending on the surgical technique, which is why early mobilization is necessary, mainly in the case of intra-articular fractures.

8. Conclusions

Distal femoral fractures are challenging, and we should differentiate the two most common types of injuries: younger patients with high-energy fractures with comminution, which should be addressed with dual fixation to prevent varus stress and nonunion, and femoral fractures in the elderly, where the use of augmentation may solve purchase fixation and prevent failure while favoring early weight bearing.

Conflict of interest

The authors declare no conflict of interest.