Distal Femur Fracture
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Direct answer
A distal femur fracture is a break of the femoral metaphysis and condyles just above the knee joint, and the AO classification sorts it by whether the articular surface is involved. Extra-articular patterns are fixed with a retrograde nail or a lateral locking plate, while articular fractures need anatomical reduction of the condyles and rigid fixation so that early knee movement is possible.
What you must remember
- Location: the fracture involves the distal femoral metaphysis and condyles above the knee, most often from high-energy trauma in young adults or a low-energy fall in osteoporotic older patients.
- AO type A: extra-articular fractures of the supracondylar region, with simple, wedge and complex subtypes.
- AO type B: partial articular fractures, where one condyle or a coronal or sagittal component is split off.
- AO type C: complete articular fractures, where the joint surface is separated from the shaft, usually with metaphyseal comminution.
- Hoffa fracture: a coronal fracture through a femoral condyle, most often lateral, that is easily missed on a plain AP film.
- Neurovascular risk: the popliteal artery lies directly behind the distal femur, so posterior displacement needs a pulse check before surgery.
- Articular reduction: the goal is a smooth joint surface, because step-off or malalignment drives post-traumatic arthritis.
A table of AO patterns and fixation
A 70-year-old woman falls from standing and has a supracondylar fracture with a displaced intra-articular component. The table links each AO group to the usual planning, and the same logic guides the choice between a nail and a plate. Examiners expect the AO group to be named before any implant is chosen.
| AO group | Pattern | Usual fixation |
|---|---|---|
| Type A | Extra-articular, supracondylar | Retrograde nail or lateral locking plate |
| Type B | Partial articular, including Hoffa-type coronal fractures | Lag screws to compress the fragment, with a buttress plate if needed |
| Type C | Complete articular with metaphyseal comminution | Dual plating, or distal femoral replacement in selected elderly patients |
Articular extension decides how precise the reduction must be, while metaphyseal comminution decides how strong the construct must be. A retrograde nail suits selected extra-articular patterns through a minimally invasive route, whereas a locking plate is preferred when a rigid construct must span comminuted bone. State the AO group first, then the implant, because that sequence is what the viva rewards.
Where the exam tries to catch you
Distal femur questions usually reward the candidate who asks about the joint surface before choosing an implant.
- Trap: using a retrograde nail for every supracondylar fracture. Correct: intra-articular extension or comminution usually calls for a plate that allows anatomical articular reduction.
- Trap: missing a Hoffa component on the AP view alone. Correct: oblique views and CT show coronal condylar fractures, which change the screw or buttress plan.
- Trap: operating without documenting distal pulses. Correct: the popliteal artery lies behind the femur, so pulses are checked and compared with the opposite limb before surgery.
Frequently asked questions
Which classification is used for distal femur fractures?
The AO/OTA classification is the one most often used for distal femur fractures. It grades them as extra-articular type A, partial articular type B and complete articular type C, with subgroups that describe the complexity of the pattern.
What is a Hoffa fracture of the femur?
A Hoffa fracture is a coronal fracture through a femoral condyle, most often lateral, and it counts as an articular injury. It needs recognition because it may require screw or buttress fixation, and it is easily missed on a plain AP radiograph.
When is a retrograde nail preferred over a locking plate for the distal femur?
A retrograde nail is preferred for selected extra-articular supracondylar patterns where a minimally invasive route suits the bone and soft tissue. A locking plate is preferred when the articular surface or the metaphysis is comminuted and a rigid construct is needed in the distal fragment.
What vascular injury must be checked in a distal femur fracture?
The popliteal artery lies directly behind the distal femur and is at risk when the fracture is displaced posteriorly. Distal pulses should be documented and compared with the opposite limb before surgery, and any suspected arterial injury needs urgent vascular review.
Why does articular step-off matter in distal femur fractures?
Articular step-off or malalignment at the knee surface leads to uneven load and early post-traumatic arthritis. This is why type B and C fractures are reduced anatomically and fixed rigidly, so that early knee movement can be started safely.