Distal femur fracture

AO/OTA 33A

Extra-articular supracondylar

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A fracture just above the knee. The gastrocnemius, arising from the back of the condyles, tilts the distal fragment into extension (apex posterior), where its sharp end can threaten the popliteal vessels.

Mechanism

Bimodal: high-energy injuries in the young; falls in elderly women, increasingly around knee replacements (periprosthetic).

Clinical findings

Swollen, deformed knee; check distal pulses and ankle–brachial index.
Open wounds are common in the young.

Imaging

AP and lateral of the knee and the whole femur.
CT (with reconstructions) for any articular involvement: coronal (Hoffa) fractures are easy to miss.
Ankle–brachial index or CT angiography if pulses are reduced.

AP and lateral of the knee and full femur; CT for every fracture that might enter the joint (look for a coronal Hoffa fragment).

Classification

33A: Extra-articular.
33B: Partial articular: one condyle (B1 lateral, B2 medial, B3 coronal = Hoffa).
33C: Complete articular: the joint is separated from the shaft.

Types shown in 3D

33A1: Extra-articular, simple. Gastrocnemius tilts the distal fragment into extension.
33A3: Extra-articular, multifragmentary metaphysis (here a wedge).
33B1: Partial articular, lateral condyle (sagittal split). Lag screws ± buttress plate.
33B2: Partial articular, medial condyle.
33B3: Hoffa fracture: coronal split of the posterior condyle (usually lateral). Easily missed on X-ray; fix with anterior-to-posterior screws.
33C1: Complete articular, simple (T or Y): the condyles are split from each other and from the shaft.

Treatment

Extra-articular (33A): Lateral locking plate (bridging) or a retrograde intramedullary nail. Restore length, alignment and rotation.
Articular (33B/C): Anatomical reduction and absolute stability of the joint surface (lag screws), then bridge the metaphysis to the shaft with a lateral locking plate. Hoffa fragments need anterior-to-posterior screws.
Elderly / periprosthetic: Locking plate, retrograde nail, combined plate + nail, or a distal femoral replacement when the bone is too poor to fix.

Aftercare

Early knee motion; protected weight bearing for 6–12 weeks depending on the pattern.

Complications

Malalignment (valgus, recurvatum)
Knee stiffness
Non-union of the metaphysis
Post-traumatic arthritis