Distal Femur Fracture

Distal femur fractures involve the distal metaphysis and femoral condyles above the knee.

They occur in two major populations:

• Young patients after high energy trauma
• Older osteoporotic patients after low energy falls

These fractures are challenging because of:

• Metaphyseal comminution
• Short distal fragments
• Osteoporotic bone
• Articular involvement
• Coronal plane Hoffa fragments
• Strong deforming forces

The gastrocnemius pulls the distal fragment posteriorly, creating an apex posterior deformity. Adductor forces can contribute to varus or shortening.

AO/OTA classification

Distal femur = 33

33A: Extraarticular

The articular surface is intact.

• A1 simple
• A2 metaphyseal wedge
• A3 metaphyseal multifragmentary

33B: Partial articular

Part of the articular surface remains attached to the shaft.

• B1 lateral condyle sagittal fracture
• B2 medial condyle sagittal fracture
• B3 coronal plane fracture, commonly called a Hoffa fracture

33C: Complete articular

The entire articular block is separated from the shaft.

• C1 simple articular and simple metaphyseal component
• C2 simple articular component with metaphyseal comminution
• C3 multifragmentary articular fracture.

Patients present with severe distal thigh or knee pain and inability to bear weight.

Look for:

• Deformity
• Extensive swelling
• Knee haemarthrosis
• Open wounds
• Skin tenting
• Associated patellar injury

Because of proximity to the popliteal artery, document:

• Distal pulses
• Capillary refill
• Motor function
• Sensation

Repeat vascular examination after reduction.

High energy fractures may accompany knee ligament injuries that are not immediately obvious.

Obtain AP and lateral radiographs of the distal femur and knee, including adequate views of the whole femur.

CT knee: strongly useful for intra articular fractures and identifies coronal plane Hoffa fragments that can be missed on standard radiographs.

CTA is indicated when vascular injury is suspected.

Nonoperative treatment

Nonoperative treatment has a limited role.

Consider a hinged knee brace for:

• Stable nondisplaced fracture
• Nonambulatory patient
• Patient whose operative risk is prohibitive.

Prolonged immobilisation produces stiffness, muscle loss and complications of immobility and should be avoided where possible.

Temporary external fixation

Use spanning external fixation when:

• The patient is physiologically unstable
• Severe swelling or soft tissue injury prevents definitive internal fixation
• Open contamination requires repeated debridement
• Temporary restoration of length and alignment is required.

Operative principles

The sequence in an articular fracture is:

• Reconstruct the joint surface
• Restore the condylar block
• Restore femoral length, alignment and rotation
• Connect the reconstructed articular segment to the shaft

Avoid varus alignment.

Lateral locking plate

A precontoured lateral locking plate is useful for:

• Metaphyseal comminution
• Osteoporotic bone
• Intra articular fractures
• Very distal fractures

The construct should provide adequate working length and avoid unnecessarily dense locking screw placement that creates an excessively stiff construct and contributes to nonunion.

Medial comminution with poor cortical support can require additional medial fixation.

Retrograde intramedullary nail

Useful for:

• Extraarticular fractures
• Simple articular fractures after independent fixation of the joint split
• Selected periprosthetic fractures with an open femoral component box

The distal segment must be large enough to accept sufficient locking fixation.

Hoffa fracture

A coronal plane femoral condyle fracture is inherently unstable and should usually undergo anatomical reduction and screw fixation, often supplemented with a buttress plate in large or unstable fragments.

Nonoperative management of a displaced Hoffa fracture produces poor articular results.

Severe osteoporotic fracture

In an elderly patient with extreme comminution, severe bone loss or a nonreconstructible articular surface, distal femoral replacement may permit immediate stable reconstruction and early weight bearing.

It is a major arthroplasty procedure and should not replace reconstructive fixation when satisfactory osteosynthesis is achievable.

Rehabilitation

Stable fixation should permit early knee motion.

Prolonged knee immobilisation leads rapidly to arthrofibrosis.

Weight bearing depends on construct stability, fracture morphology and bone quality. Increasingly robust constructs can permit early weight bearing in selected patients.

Complications

Major complications are:

• Nonunion
• Varus collapse
• Implant failure
• Infection
• Knee stiffness
• Post traumatic osteoarthritis
• Malalignment