CASE 40 distal femur fractures

 

A 23-year-old rancher presents to the emergency department after being trampled by a bull. He complains of severe pain in his right leg with inability to flex or extend his knee and exquisite tenderness over his distal femur. He is neurovascularly intact otherwise and without open wounds. Radiographs are shown in Figure 6–43A and B.

 

 

 

Figure 6–43 A–B

 

What is the next step in evaluation of his injury?

1. CT with contrast

2. Ankle brachial index (ABI)

3. MRI left knee

4. Ligamentous examination

5. CT without contrast

 

Discussion

The correct answer is (E). It is most important to evaluate for the presence of an associated coronal split fracture (Hoffa fracture) extending into the articular surface. These fractures are often missed on plain radiographs as they are not easily appreciated. The incidence of a Hoffa fracture is 38% and, if missed, can cause malreduction and failure of fixation.

What screw orientation is most commonly needed when a Hoffa fracture is present?

1. Oblique screw from lateral to medial into the lateral femoral condyle

2. Anterior to posterior screw in the medial femoral condyle

3. Oblique screw from medial to lateral into the medial femoral condyle

4. Anterior to posterior screw into the lateral femoral condyle

5. Anterior to posterior screws into the medial and lateral femoral condyles

 

Discussion

The correct answer is (D). A Hoffa fracture is a coronal split through the distal femoral condyle. These are often missed on plain radiographs. When present, the fracture most commonly involves the lateral femoral condyle alone 80% of the time. This fracture requires an anterior to posteriorly oriented screw through the lateral femoral condyle.

What view is needed to decrease the incidence of a common hardware complication following submuscular plating?

1. Anterior–posterior view of knee

2. 25-degree internal rotation view of knee

3. Lateral view of knee

4. Sunrise view of knee

5. 10-degree external rotation view of knee

 

Discussion

The correct answer is (B). The slope of the distal femoral metaphysis is 25 degrees medially and 10 degrees laterally in the sagittal plane. When using a laterally based submuscular distal femoral plate it is important to obtain a 25-degree internal rotation view of the knee. This allows for visualization down the slope of the medial femoral cortex that will show protruding screws causing pain and irritation if the screws are too long. The AP and lateral views of the knee are also important for proper plate position intraoperatively.

What precludes the use of a retrograde intramedullary nail following a stable fracture, without signs of implant loosening, around a PCL-sacrificing total knee arthroplasty that occurred 3 weeks postoperatively?

1. Proximity to the femoral component

2. PCL-sacrificing design

3. Aseptic loosening of femoral component

4. Proximity of primary surgery

5. Cruciate-retaining design

 

Discussion

The correct answer is (B). This design precludes passage of an intramedullary nail through the distal femur. Consequently, treatment of distal femur fractures with this construct is limited to open reduction and internal fixation via plate fixation and antegrade intramedullary nailing. This injury does not show evidence of aseptic

loosening, and proximity to the index surgery does not play a role in implant choice. In fractures displaying hardware loosening or failure, the arthroplasty components must be exchanged for revision components. Cruciate-retaining designs do not have this same limitation.

 

Objectives: Did you learn...?

 

Importance of Hoffa fragment in distal femur fractures?

 

 

Importance of TKA design when treating periprosthetic distal femur fractures? Anatomic considerations of distal femur fractures?