- The distal femur has unique geometry in three planes: axial, sagittal, and coronal. A thorough appreciation of this anatomy is critical to obtaining an anatomic reduction of fractures and for appropriate placement of precontoured plates and periarticular screws.
- In the axial plane, the distal femur is trapezoidal, with a lateral slope of 10 degrees and a medial slope of 25 degrees. The lateral condyle projects anteriorly relative to that of the medial condyle at an angle of 10 degrees. In the coronal plane, the medial condyle extends further distally than does the lateral condyle, resulting in an average lateral distal femoral angle of 81 degrees (Fig. 21-1).1,2
Radiographic Anatomy and Preoperative Imaging
- AP and lateral plain film radiographs are obtained in order to appreciate the extent of coronal and sagittal plane deformity. Figure 21-2 demonstrates the shortening and recurvatum deformity typical of distal femur fractures, which occurs secondary to the unopposed pull of the extensor mechanism and gastrocnemius.
- In addition to orthogonal radiographs of the knee, the entire femur should be imaged to assess for proximal fractures or extension, retained previous hardware, or associated bony deformity. The presence of any of these situations may alter the anticipated surgical treatment plan.
- The presence of an intercondylar fracture line indicates that a preoperative CT scan is necessary to properly assess for associated coronal split condylar fractures (“Hoffa fragments,” Figs. 21-3 and 21-4). The incidence of these injuries in the setting of an intercondylar fracture on plain films is 38%, and they are easily missed in the absence of a CT scan.3
Intraoperative Positioning and Imaging—Plating and Retrograde Nailing
- The patient is positioned supine on a radiolucent table with the C-arm positioned opposite the injured extremity. A bump should be placed under the hip and buttock to aid with imaging and rotational alignment during the procedure (Fig. 21-5).
- Prior to draping, fluoroscopic images of the contralateral femur should be obtained to aid with intraoperative assessment of rotation. A perfect AP of the knee is first obtained, and then the C-arm is directed proximally to obtain a corresponding true AP of the hip, allowing the contour of the lesser trochanter to be used as a guide for comparison (specifically, rotation) (Fig. 21-6). Positioning the C-arm for obtaining an AP intraoperative fluoroscopic image.
The surgeon must ensure that quality AP (Fig. 21-6) and lateral (Fig. 21-7) intraoperative fluoroscopic images can be obtained prior to beginning the case. Additionally, several additional fluoroscopic images may be employed intraoperatively to verify the accuracy of fracture reduction and positioning of hardware, especially screws. Ensuring that correct AP and lateral views can be obtained becomes critically important when assessing fracture reduction and placement of implants. For retrograde nailing of metaphyseal and metadiaphyseal fractures where isthmal fit of the nail will not occur, nail starting point and trajectory must be correct; otherwise, a translational or angular deformity may occur during nail placement.
- AP of the knee: Obtained by ensuring that the lateral aspect of the tibia bisects the proximal fibula and that the patella is centered over the femoral condyles (Fig. 21-8). Alternatively, the surgeon can obtain a perfect lateral image and then rotate the C-arm 90 degrees for the corresponding AP image.
- Lateral of the knee: obtained by superimposing the posterior aspects of the medial and lateral femoral condyles. The lateral femoral condyle extends further anterior compared to the medial femoral condyle; these landmarks should be used when determining appropriate placement of plates (Fig. 21-9). Blumensaat’s line represents the anterior and proximal extent of the intercondylar notch and is a critical landmark for nail starting point and plate/screw placement (Figs. 21-10 and 21-11).