Jean-Claude G. D’Alleyrand
Theodore T. Manson

Bony Anatomy

The femoral diaphysis is straight in the AP plane, with an apex anterior bow in the sagittal plane and its epiphyses rotated with respect to one another in the transverse plane.
- This rotation, or version, can vary quite a bit between patients, and some modest side-to-side variability may exist between the femora of individuals.¹
- There is also variability in the morphology of the greater trochanter between individuals, which can have implications on intramedullary rod placement from a trochanteric starting point.
The gold standard for treating femoral shaft fractures is by means of intramedullary rodding.
- This can be done in antegrade fashion, from either the piriformis or trochanteric starting points, or in retrograde fashion from a starting point at the junction between the trochlea and intercondylar notch.

Radiographic Anatomy

Preoperative Imaging

Imaging of a femoral shaft fracture is straightforward, requiring only standard radiographic technique. Specifically, one should use orthogonal, true AP, and lateral views, using the patella as the rotational reference, taking care to move the x-ray emitter and cassette, not the limb, when changing between views. Due to the length of the adult femur, it is important that the radiographer orient the cassette obliquely, such that the thigh forms a hypotenuse running diagonally across the cassette, so that a maximum amount of femur is captured on each image. This limits the chances of missing or underevaluating a mid-diaphyseal fracture.
Adequate radiographic imaging includes an AP pelvis and orthogonal views of the entire femur. An incompletely sedated patient may not tolerate the positioning needed for quality radiographs, and there is evidence that radiography alone is insufficient to evaluate for an associated femoral neck fracture.² With few exceptions, evaluation of a femoral shaft fracture should include a fine-cut CT through the femoral neck. Fractures that involve the distal one-third of the diaphysis may extend into the knee joint or have an unidentified, noncontiguous intra-articular fracture; thus, a CT scan of the knee should be considered for these injuries.

Radiographic Evaluation of Intramedullary Fixation Start Points

Piriformis Starting Point

On an AP view, the piriformis start point appears as an L-shaped radiodensity, in line with the medullary canal and approximately 2 to 3 cm distal to the proximal border of the femoral neck (Fig. 20-1A). On the lateral view, the piriformis fossa is visualized by following the slope of the posterior femoral neck. As the contour of the neck slopes obliquely posteriorly and distally, the cortical surface flattens out for a few millimeters before continuing its oblique course toward the lesser trochanter. The apex between this flattened section and the posterior cortex of the neck is the piriformis fossa (Fig. 20-1B). The trajectory of a piriformis nail is in line with the medullary canal of the femur; thus, the guidewire should be aligned with the center of the canal on both views prior to insertion into the femur (Fig. 20-2A and B).

Gardner1e-ch020-image001a — Figure 20-1 **A and B:** Piriformis starting point. *Curved line*: Contours of piriformis fossa. *Solid circle*: Starting points.

Gardner1e-ch020-image001b — Figure 20-1 **A and B:** Piriformis starting point. *Curved line*: Contours of piriformis fossa. *Solid circle*: Starting points.

Gardner1e-ch020-image002a — Figure 20-2 **A and B:** Piriformis guidewire. Starting point and trajectory keep the wire in line with the medullary canal on AP and lateral views.

Gardner1e-ch020-image002b — Figure 20-2 **A and B:** Piriformis guidewire. Starting point and trajectory keep the wire in line with the medullary canal on AP and lateral views.

Trochanteric Starting Point

The morphology of the greater trochanter varies between individuals. In order to obtain an optimal AP view for a trochanteric starting point, the C-arm should be rotated such that the anteromedial and posteromedial edges of the greater trochanter are superimposed. The guidewire is then placed on the superior tip of the trochanter, aiming for the center of the canal at the level of the lesser trochanter (Fig. 20-3A). Many surgeons will actually start this guidewire slightly medial to the tip of the trochanter, especially with more proximal fractures to resist varus deformity caused by too lateral of a starting point.
The lateral view of the trochanteric starting point is obtained by rotating the C-arm until the femoral head, neck, greater trochanter, and shaft are all collinear, or at least as collinear as allowed by the patient’s morphology. Delineation of the femoral neck is enhanced by adding cephalic tilt to the C-arm (Figs. 20-3B and 20-9B). Rather than focusing on a “one-third, two-thirds” starting point as is recommended in most technique guides, it is more important to consider the position of the implant with respect to the femoral head and neck. By obtaining a perfect lateral image, and bisecting the head and neck with the path of the guidewire (Fig. 20-3B), the surgeon ensures that the nail will be in a position to allow the safest possible placement of fixation into the femoral head, if needed. Where that trajectory traverses the greater trochanter is irrelevant, and it often bisects the trochanter, rather than being at the junction of the anterior one-third and posterior two-thirds. The trajectory of the guidewire should be aiming down the center of the proximal diaphysis. At times, the proximal femoral morphology is such that the starting point must be slightly off of the head-neck axis in order to allow the nail to easily pass through the diaphyseal canal.
Prior to locking the proximal aspect of a trochanteric nail, it is vital that the surgeon obtain a perfect lateral of the head and neck, ensuring that they are collinear with each other, and that the head-neck axis is perfectly superimposed with both the nail and the radiolucent jig (Fig. 20-3C). Even a small amount of rotation of the nail, such that the jig is noticeably anterior or posterior to the nail on this view, will cause the head fixation to deviate from the head-neck axis, thus increasing the chance of penetration into the joint.