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A 37-year-old female pedestrian who had been hit by a car sustained a comminuted supracondylar fracture of the left distal femur with an intercondylar extension. On initial review of the patient's radiographs, a minimal step-off of the anterior cortex of the lateral femoral condyle was not seen (Figs. 1A and 1B). CT more clearly delineated a coronal plane fracture of the lateral condyle and the extension of the intercondylar fracture (Fig. 1C).

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Fig. 1A. —37-year-old woman who had been hit by automobile while walking. Anteroposterior radiograph shows comminuted supracondylar and intercondylar fracture of distal femur with medial displacement and overriding femoral shaft (arrows).

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Fig. 1B. —37-year-old woman who had been hit by automobile while walking. Lateral radiograph shows minimal step-off (arrow) of anterior cortex of articular surface of lateral femoral condyle.

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Fig. 1C. —37-year-old woman who had been hit by automobile while walking. Axial CT scan acquired with 1-mm collimation shows coronally oriented fracture (arrows) through lateral femoral condyle.

The imaging evaluation of distal femoral fractures is based primarily on conventional radiographs. Supracondylar distal femoral fractures may be classified as extraarticular, unicondylar, or bicondylar, and the fractures may have an intercondylar extension [1, 2]. About 40% of intercondylar fractures have an associated coronal plane, or a “Hoffa,” fracture, (Nork SE, unpublished data) which is a marker of high-energy blunt trauma [3, 4]. Although occasionally bicondylar, the Hoffa fragments are more commonly unicondylar and usually originate from the lateral femoral condyle [3, 4]. Overall, Hoffa fractures are rare [1, 4], and, considering the plane and location of fracture, it is not surprising that they are often overlooked on conventional radiographs [3].

Because these injuries result from high-energy trauma, one should also exclude other associated injuries of the pelvis and hip (acetabular fractures, femoral neck and shaft fractures, and posterior hip dislocations), patella and tibial plateau fractures, popliteal vessel injuries, and ligamentous disruptions of the knee [1, 2].

Patients with distal femoral fractures do not routinely require CT. However, the presence of a supracondylar fracture with intraarticular extension suggests that there may be an occult associated coronal-plane Hoffa fracture. In our experience, CT is extremely helpful in characterization of complex intraarticular fractures of the distal femur. Twenty-five percent of Hoffa's fractures associated with supracondylar femur fractures are not diagnosed in patients in whom only conventional radiographs are obtained (Nork SE, unpublished data).

Preoperative recognition of an associated Hoffa fracture affects surgical planning. Fragment displacement may occur during placement of an angled blade plate or its seating chisel, and if unrecognized, postoperative displacement may necessitate a second surgery [3]. In our experience, more than half of radiographically occult Hoffa fragments required an intraoperative change in the hardware selection and technique for fixation.