Distal femoral fractures represent one of the most complex and clinically significant orthopedic injuries in small animal practice. These fractures account for approximately 20–25% of all femoral fractures, frequently occurring secondary to high-energy trauma. Due to the anatomy of the distal femur, strong muscular forces, and the involvement of the stifle joint, these fractures require precise anatomical reconstruction and rigid fixation to ensure optimal long-term function.

The AO Vet classification system divides distal femoral fractures into three major categories based on involvement of the articular surface:

Type A – Extra-articular supracondylar or metaphyseal fractures
Type B – Partial articular fractures (unicondylar fractures)
Type C – Complete articular fractures (bicondylar T- or Y-type injuries)

Each type presents unique surgical challenges, and successful outcomes rely on adherence to core orthopedic principles—anatomic reduction, rigid internal fixation, and early joint motion.

1. Biomechanics and Pathophysiology

The distal femur is a biomechanically demanding region characterized by:

A large metaphyseal flare
Thin cortical bone distally
A broad articular surface with complex geometry
Strong caudal displacement forces produced by the gastrocnemius muscle
Close proximity to the patellofemoral mechanism

These factors contribute to fragmentation, displacement, and significant hematoma formation at the injury site. Without rigid internal fixation, malalignment, joint incongruity, and post-traumatic degenerative joint disease (DJD) are inevitable outcomes.

Conservative management is consistently ineffective and contraindicated in nearly all cases.

2. Classification: AO 3-3 (Distal Femur)

Type A – Extra-articular Fractures

These fractures occur through the metaphysis or supracondylar region without joint involvement.
Common patterns include transverse, short oblique, wedge, and complex supracondylar fractures.
In juveniles, these often correlate with Salter-Harris Type I or II injuries.

Type B – Partial Articular Fractures

Involve one condyle while the other remains attached to the diaphysis.
Typical pattern: sagittal unicondylar fracture (medial or lateral).

Type C – Complete Articular Fractures

Involve both condyles and detach the distal segment completely from the shaft.
These fractures are typically T- or Y-shaped, requiring staged reconstruction.

3. Surgical Objectives

1. Anatomic Reconstruction of the Articular Surface

Articular congruity is paramount. Even minor deviations lead to cartilage wear, instability, and early DJD. All intra-articular fractures (Type B and C) require direct visualization through arthrotomy and fixation under compression.

2. Rigid Stabilization

Fixation must withstand the powerful forces acting across the stifle and distal femur. Rigid constructs enable early joint motion and reduce the risk of implant failure.

3. Early Controlled Stifle Motion

Postoperative fibrosis is a major complication. PROM should begin as soon as tolerated to maintain joint mobility.

4. Fixation Techniques

A. K-wires / Transphyseal Pins

Indicated primarily for juvenile Salter-Harris Type I and II fractures.

Key principles:

Use smooth Kirschner wires or Steinmann pins to avoid growth arrest.
Place implants perpendicular to the physis and avoid crossing the articular surface.
Cross-pin or parallel pin configurations both provide acceptable stability.

These implants can migrate and thus require careful postoperative monitoring and early removal (2–6 weeks).

B. Lag Screws

Lag screws are mandatory for repairing intra-articular fractures.

Applications:

Unicondylar fractures (Type B)
Intercondylar component of T- or Y-fractures (Type C)
Large metaphyseal wedge fragments

Technical considerations:

Screws must be placed in true lag fashion.
Fully threaded cortical screws are preferred for metaphyseal bone to prevent stripping and provide higher shear resistance.
Screw heads must be positioned outside the weight-bearing surface or countersunk below the cartilage.

C. Bone Plates

Plates are essential for stabilizing metaphyseal and complete articular fractures (Type A3, Type C).

Plate types:

Reconstruction plates
“Hockey stick” or condylar plates
LCP (locking compression plate) systems
Specialty distal femoral plates in larger patients

Functions:

Neutralization after lag screw reconstruction
Buttress plating when the metaphysis is unstable
Bridging in severely comminuted metaphyseal fractures

Plate fixation provides superior resistance to bending and torsional loads and generally yields the best long-term prognosis.

5. Management of Specific Fracture Types

A. Physeal Fractures (Salter-Harris I/II)

Common in animals aged 4–11 months.

Reduction:

Must realign the epiphysis precisely to avoid patellar tracking abnormalities.
Reduction facilitated by flexing the stifle and extending the hock to relax the gastrocnemius.

Fixation:

2+ smooth K-wires in a crossed or parallel arrangement.
Avoid physis violation with threaded implants.

Prognosis:

Excellent with proper reduction and stabilization.

B. Partial Articular Fractures (Type B)

Surgical steps:

Arthrotomy for visualization
Anatomic reduction
Lag screw fixation
Neutralization plate when metaphyseal involvement is present

Prognosis depends on precision of articular reconstruction.

C. Complete Articular Fractures (Type C, T/Y Fractures)

These require a two-stage repair:

Condyle Reconstruction
- Reduce and compress the sagittal fracture using a transcondylar lag screw.
- Converts the fracture into a reducible supracondylar fracture.
Condyle-to-Shaft Fixation
- Achieved using multiple K-wires, transfixation pins, or a plate.
- Plate fixation provides superior stability and outcomes.

These fractures carry the highest risk of postoperative stiffness and require early PROM and careful follow-up.

6. Postoperative Management

NO external coaptation

Splints and casts lead to fibrosis, muscle contracture, and permanent restriction of stifle ROM.

Activity Restriction

Strict control for 4–6 weeks
Early controlled weight-bearing as tolerated

Rehabilitation

PROM should begin immediately or within a few days post-op.
Hydrotherapy may be introduced once the incision heals.

Implant Removal

Pins/K-wires: 2–6 weeks
Plates: Removed only if clinically indicated (soft tissue irritation, implant loosening), typically after bone union at ~4–6 months.

7. Expected Prognosis

With anatomic reconstruction and rigid fixation, prognosis is generally good to excellent, particularly for Type A and B fractures. Type C fractures have a more guarded prognosis due to joint involvement but still do well with precise reduction and early mobilization. Complications most commonly involve joint stiffness, implant migration, and degenerative joint changes.

Distal Femur Fracture Repair (AO 3-3)

1. What is the most common complication following distal femoral fracture repair?

The most frequent complication is postoperative joint stiffness due to fibrosis and delayed initiation of stifle motion. Early controlled PROM and avoidance of external coaptation are essential to prevent reduced range of motion.

2. When should K-wires or pins be used versus screws or plates?

K-wires/pins are indicated primarily for Salter-Harris I/II physeal fractures in juveniles.
Lag screws must be used for all partial or complete articular fractures (Type B and C).
Plates are used for metaphyseal, comminuted, or complete articular fractures requiring buttress or neutralization functions.
Adult metaphyseal fractures rarely achieve adequate stability with pins alone.

3. What is the recommended sequence for repairing T- or Y-type fractures (Type C)?

Anatomically reduce and compress the intercondylar sagittal fracture using a lag screw.
Convert to a supracondylar fracture.
Stabilize the condyles to the diaphysis using a plate or transfixation pins.
This staged approach provides stronger reconstruction and minimizes articular incongruity.

4. Is external fixation ever indicated for distal femur fractures?

Rarely. ESF does not provide sufficient rotational stability for most distal femoral injuries and complicates stifle mobilization. It may be considered only in severe open fractures where internal fixation is contraindicated.

5. How important is anatomical reduction of the articular surface?

It is critical. Even small incongruities (1–2 mm step-off) can lead to rapid osteoarthritis, altered patellar tracking, and long-term pain. Direct visualization via arthrotomy is required for accurate reduction.

6. What is the best plate type for distal metaphyseal fractures?

Options include:

Reconstruction plates for contouring
LCP distal femoral plates for locking support
“Hockey stick” plates for distal metaphyseal flare
The choice depends on fragment configuration, patient size, and surgeon preference.

7. When should physeal fractures be repaired openly versus closed?

Closed reduction may be attempted initially, but open reduction is preferred when:

Reduction is unstable
Soft tissue interposition prevents alignment
The epiphysis is rotated or displaced
Anatomical reduction cannot be confirmed radiographically

8. When should implants be removed?

Pins/K-wires: 2–6 weeks in juvenile animals (due to migration risk).
Plates: Only if clinically indicated—e.g., soft tissue irritation, loosening, or infection. Removal is typically considered after 3–6 months of healing.

9. Is postoperative external coaptation ever appropriate?

No. Splints and casts restrict stifle motion and dramatically increase the likelihood of fibrosis and permanent ROM deficits. A soft padded bandage may be used short-term for comfort only.

10. What postoperative rehabilitation protocol is recommended?

Begin PROM exercises within days of surgery (as tolerated).
Encourage early controlled weight-bearing to minimize stiffness.
Avoid high-impact activity for 6–8 weeks.
Hydrotherapy after incision healing improves joint mobility.

Distal Femur Fracture Repair (AO 3-3): Technical Surgical Overview for Veterinary Surgeons