Introduction
Of all femoral fractures, approximately 4-7% are distal femur fractures (Kolmert, 1982). There is a bimodal distribution, with young patients with high energy trauma and elderly patients with low-energy falls. Approximately 85% of these fractures occur in patients over fifty years old (Shewring, 1992). The incidence of supracondylar fracture after total knee arthroplasty is approximately 1%.
Anatomy
The normal anatomic axis of the distal femur is 6 to 7 degrees of valgus in a male and 8 to 9 degrees in a female. The lateral cortex of the femur has a 10 degree slope, and the medial cortex slopes 25 degrees. This is important when using plates as fixation. Also important is the three-dimensional anatomy of the notch and condyles. When placing lag screws from lateral to medial under fluoroscopic guidance, one must stay posterior to Blumensat's line which represents the anterior border of the femoral notch. Straying posterior to Blumensat's line places the ACL and PCL at risk.
Classification
The AO/OTA system is a commonly used classification system. Distal femur fractures are designated as "33".
33A Extra-articular
33A1 Simple metaphyseal component
33A2 Wedge fracture in metaphyseal region
33A3 Complex metaphyseal involvement
33B Partial articular
33B1 Partial articular fracture of the lateral condyle in the sagittal plane
33B2 Partial articular fracture of the medial condyle in the sagittal plane
33B3 Partial articular fracture of medial or lateral femoral condyle in the frontal plane---Hoffa fracture
33C Complete articular 33C1 Supracondylar / intercondylar femur fracture with simple metaphyseal and articular fractures
33C2 Supracondylar / intercondylar femur fracture with complex metaphyseal component and simple articular split
33C3 Supracondylar / intercondylar femur fracture with complex articular fragments
Presentation
Patients are typically unable to ambulate. They have severe pain, swelling, and varying amounts of deformity above the knee. Patients may present with vascular and neurologic compromise.
Diagnosis
A thorough neurovascular exam is essential along with a spine and extremity exam. AP and lateral x-rays of the femur alone often are not adequate for the assessment of distal femur fractures. Dedicated AP, lateral, and oblique x-rays of the knee better define complex fracture patterns often found in these fractures. The proximal femur should be included in order to rule out a hip fracture, which might influence the type of internal fixation. When significant comminution exists, the appropriate length of the femur is difficult to determine. Therefore full length x-rays of the contralateral femur allows measurement of the femur length. CT scans are not routinely necessary; however, if there is any question regarding the interpretation of the x-rays or if the fracture involves the joint surface, CT with sagittal and coronal reconstructions is useful. CT better delineates fracture patterns and articular involvement. Nork et al (2005) found that 38% supracondylar-intercondylar distal femoral fractures had an associated coronal plane fracture, many of which were undiagnosed on radiographs and discovered on CT imaging.
Treatment
Operative indications:
- Displaced distal femur fracturesNonoperative indications:
- Nondisplaced or incomplete fractures
- Impacted, stable fractures in elderly patients
- Comorbidities that preclude operative fixation
The timing of surgery often depends on the type of injury. Open fractures require urgent debridement. If the surgeon feels that adequate debridement has occurred, and the patient is stable, it is acceptable to perform fixation at that time. If debridement is not adequate external fixation can be applied. Fracture patterns dictate the type of fixation. Extra-articular fractures do not involve the joint surface and may be treated with either anterograde or retrograde intramedullary nailing if the distal femoral segment is large enough to place a distal interlocking screw. Intra-articular fractures require joint visualization, reduction, and fixation of the joint surface. Intra-articular fractures that are isolated unicondylar fractures are uncommon, but most can be repaired with lag screw fixation alone. Intra-articular fractures that leave both condyles detached from the proximal femur are more challenging and require fixation of the joint surface and then the proximal and distal femur segments.
Complications
Nonunion (6%)
Malunion
Infection (3%)
Knee stiffness
Outcomes
The outcome of operative treatment is favored over non-operative management. The outcomes are likely dependent on patient age, comorbidities, degree of comminution, and condition of the soft-tissues.
Bibliography
1. Kolmert L, Wulff K. Epidemiology and treatment of distal femoral fractures in adults. Acta Orthop Scand 1982;53:957-962.
2. Nork SE, Segina DN, Aflatoon K. The association between supracondylar-intercondylar distal femoral fractures and coronal plane fractures. J Bone Joint Surg Am 2005;87:564-569.
3. Shewring DJ, Meggitt BF. Fractures of the distal femur treated with the AO dynamic condylar screw. J Bone Joint Surg Br 1992;74:122-125.
