Surgical Fixation of Fractures of the Distal Femur

James F. Kellam, BSc, MD, FRCSC, FACS, FRCSI

Stephen Warner, MD, PhD

Dr. Kellam or an immediate family member serves as a board member, owner, officer, or committee member of the American Academy of Orthopaedic Surgeons. Dr. Warner or an immediate family member serves as a paid consultant to or is an employee of DePuy, A Johnson & Johnson Company.

INTRODUCTION

Fractures of the distal femoral metaphysis still represent a significant challenge to the fracture surgeon.¹^,² The successful management of these fractures—either extra-or intra-articular—demands anatomic axial alignment with a precise reduction of the articular surface of this major lower extremity joint. The distal femur is defined by a square, the sides of which are the same length as the widest part of the distal femoral epiphysis in a child or the metaphysis in an adult (Figure 1). Any fracture that has its center inside this box is considered a distal femoral end segment fracture. The intra-articular fractures may involve a part of the joint (partial articular fractures) in which one component of the joint is separated from the remainder of the joint that is still attached to the shaft or a complete articular fractures in which no part of the fractured articular segment remains attached to the metaphysis and/or diaphysis of the femur.

FIGURE 1 In this illustration of the anteroposterior aspect of the distal end segment, the distal end segment is defined by a square, the sides of which are the same length as the widest part of the distal femoral epiphysis in a child or the metaphysis in an adult.

There are three major factors that make treatment of this fracture difficult:

The high-energy distal femoral fracture by nature has significant soft-tissue stripping, and approximately 50% of the intra-articular fractures are open. In addition, the distal end of the femur is covered more by tendinous structure than by muscle bellies, thus leading to a poor environment for bone healing because of the lack of extraosseous vascularity so common in the more proximal femur.¹^,²
The high-energy fracture patterns result in significant joint surface and metaphyseal fragmentation. This makes reduction difficult. It may also be impossible to reconstruct the articular surface, thus dooming the patient to early posttraumatic arthritis. This fragmentation in the metaphysis also contributes to the increased rate of delayed union and nonunion in these fractures.
With the increasing incidence of osteoporosis, fractures of the distal femur are becoming more common. Advancing age is associated with the development of osteoarthritis requiring total knee arthroplasty and potentially an increased number of periprosthetic fractures. These fractures are associated with their own set of problems, which make management of this injury difficult.³^,⁴^,⁵^,⁶^,⁷

PATIENT SELECTION

Contraindications

Contraindications for surgical fixation include a completely nondisplaced fracture of the joint or metaphysis in a healthy individual who could mobilize with cast immobilization. This is extremely uncommon but will rarely result in knee stiffness. The other contraindications would
be in individuals who are unfit for surgery and those who are nonambulators or significantly incapacitated such that they do not require their extremities for mobility. In the elderly patient with a multifragmented articular fracture in whom prolonged non-weight bearing will be difficult, consideration for total knee arthroplasty may be advisable.

PREOPERATIVE IMAGING

The first radiographs obtained for diagnostic purposes of distal femoral fractures are AP and lateral projections of the knee and the femoral shaft. It is imperative that adequate AP and lateral views centered on the knee be obtained. If the fracture is significantly displaced, these radiographs may be best performed after gentle traction and realignment has been performed. This will make the interpretation of the radiographs much easier. It is imperative to identify whether the fracture lines enter the joint, especially on the lateral projection, where coronal-plane fractures of the medial or lateral condyle (Hoffa fracture) must be ruled out.⁸ In high-energy open fractures, a significant number have occult or minimally displaced coronal-plane fractures. Full length radiographs of the femoral shaft are also required to assess the proximal femoral osteology.

Following reduction and immobilization with either a knee immobilizer or, more appropriately, tibial tubercle traction, a CT scan is indicated only if the surgeon’s interpretation of the plain radiographs is uncertain as to articular involvement. Axial cuts and their associated coronal and sagittal reformations are excellent to determine the various intra-articular fracture pattern extensions. Three-dimensional CT reconstructions of the distal end segment will be of help in the preoperative planning.

FIGURE 2 A, The illustration of the lateral aspect of the leg shows the joint-spanning external fixator. B, Intraoperative photograph demonstrates that it is imperative that the Schanz screws are placed outside of the proposed area for the surgical incisions for the fixation. (Courtesy of AO Archives and AO Principles of Operative Management of Fractures.)

PROCEDURE

Timing

Surgical timing for this fracture should be as soon possible given the constraints of a healthy resuscitated patient, an adequate understanding of the injury, appropriate surgical conditions, and skilled staff. These fractures are complex and require excellent preoperative planning and experienced surgical acumen. In a situation in which these conditions may not be met, consideration for joint-bridging external fixation is helpful as a method of stabilizing the patient’s soft tissues, aligning the fracture, providing comfort, and awaiting the appropriate surgical team. For open fractures, the degree of soft-tissue disruption and contamination will determine the place of internal fixation. If in doubt, it is best to use a joint-spanning external fixator and allow the soft tissues to “declare” their intent (Figure 2).

Room Setup/Patient Positioning

A radiolucent table should be used for the operation. It is best if the whole table top is radiolucent, but if not, the surgeon can check to make sure that adequate radiographs of the complete femur in both the AP and lateral planes can be obtained. This is essential to ensure axial alignment. The use of fluoroscopy is important, and the fluoroscope is usually placed opposite the injured leg. The surgical team and scrub technicians are on the same side as the surgeon. The patient is placed on the operating table in the supine position, and the use of a sterile triangle or bump placed proximal to the fracture to allow flexion of the knee (Figure 3, A) is mandatory (flexion of up to 60° is very helpful). Another option is to place the patient’s injured knee at the table break so that following draping,
the lower end of the operating table is flexed to allow the knee to flex to whatever degree is required (Figure 3, B). This also allows some reverse Trendelenburg positioning to help with the exposure and surgical access. This will reduce the pull of the gastrocnemius and abductor magnus, preventing genu recurvatum and shortening. If a roll is placed under the buttock, care must be taken to avoid a malreduction, as this will internally rotate the leg, resulting in a rotational malposition.

FIGURE 3 A, Intraoperative photograph of the lateral aspect of the leg shows the patient positioned on radiolucent table with C-arm from the side opposite the fractured limb. Note the roll under the thigh providing a force for indirect reduction along with manual traction. B, Intraoperative photograph of the anteroposterior aspect of the patient positioned on a regular operating table with the end flexed so as to allow access to the knee. (A, Courtesy of Steve Sims, MD, Charlotte, NC. B, Courtesy of Eric Johnson, MD, Los Angeles, CA.)

Special Instruments/Equipment/Implants

The first important aspect of this surgical procedure is the ability to obtain a reduction. If this is an intra-articular fracture, then the joint reduction must be anatomic. In order for this to be done, it is useful for the surgeon to have available multiple periarticular clamps of various throat sizes. These clamps should be pointed to get a good bite on the bone and minimize the soft-tissue disruption. For osteoporotic bone, the use of foot plates that can be attached to the ends of the reduction clamps will prevent the clamp from penetrating the weak metaphyseal cortical bone. A wide-throated clamp is usually used because of the width of the distal femoral metaphysis (Figure 4). The use of Kirschner wires (K-wires) as joysticks to manipulate fragments is also extremely helpful.

Implant choice begins with either cancellous or cortical screws of multiple sizes (2.7-to 6.5-mm screws). These are necessary for the stabilization of small and large intra-articular fragments. Presently, there is an increasing trend toward the use of 3.5-/4.0-mm screws for intra-articular stabilization. These screws provide more options for distal plate or nail interlock screw placement and may provide very good fixation due to their high pitch.

Currently, the most common plate is some form of a locking femoral condylar plate. The distal metaphyseal screw configuration is all round holes, allowing locked screw insertion so as to enhance the angular stability of the metaphyseal component of the construct. The shaft holes of these plates may have round locking holes or combination holes that can allow both locking and regular cortical screws so axial compression may be obtained if needed (Figure 5, A and B). Another advantage of the combination hole is the ability to modify fixation and to angle nonlocking screws to be able to better affect stabilization.

The addition of variable angled locking plates allows the locking screws to be angled to avoid prior implants such as the femoral implant of a total knee arthroplasty. Other implants for this region are retrograde femoral nails or fixed-angle devices such as the 95° blade plate or the dynamic condylar screw plate (Figure 5, C through E). The 95° angled devices are extremely appealing because with proper insertion, they allow reconstitution of the anatomic axis of the knee joint.⁹^,¹⁰^,¹¹^,¹² Double plating especially in osteoporotic bone is another possibility.¹³ For fixation with a retrograde femoral nail, the implant must provide several distal interlocking screw options at the most distal end of the nail. The distal interlocking screws should be multiplanar to maximize the fixation in the distal articular block.

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