Orthopaedic Surgery - Knee Supracondylar Fracture

Basics

A supracondylar fracture of the knee is a fracture involving the metaphyseal region of the distal femur, just proximal to the femoral condyles.

These injuries are also commonly referred to as distal femur fractures.

Fractures may remain extra-articular or extend into one or both femoral condyles and the knee joint.

Because the distal femur contributes directly to knee alignment, joint congruity, and lower-extremity mechanics, accurate reduction and stable fixation are important.

Classification

The AO/ASIF classification divides distal femoral fractures into three major groups.

Type A: Extra-Articular Fractures

The fracture does not involve the articular surface.

A1

Simple extra-articular fracture.

A2

Metaphyseal wedge fracture.

A3

Comminuted metaphyseal fracture.

Type B: Partial Articular or Unicondylar Fractures

A portion of the articular surface remains connected to the femoral shaft.

B1

Lateral condyle fracture.

B2

Medial condyle fracture.

B3

Frontal-plane fracture involving the posterior femoral condyle.

Type C: Complete Articular Fractures

The articular block is completely separated from the femoral shaft.

C1

Simple articular fracture combined with a simple metaphyseal fracture.

C2

Simple articular fracture with metaphyseal comminution.

C3

Articular comminution with a complex distal femoral fracture pattern.

Epidemiology

Distal femur fractures are less common than femoral shaft fractures but represent an important subgroup of femoral injuries.

Some series report that they account for up to approximately 30% of femoral fractures, depending on the population studied.

Age Distribution

A bimodal distribution is typical.

Younger Patients

Patients younger than approximately 35 years usually sustain these fractures through high-energy mechanisms.

Young men are affected more often in this group.

Older Patients

Patients older than approximately 50 years more commonly sustain distal femoral fractures after low-energy trauma.

Older women are disproportionately affected because of:

Osteopenia, osteoporosis, and increased fall risk.

Pediatric Population

Most pediatric distal femoral supracondylar fractures occur in adolescents.

In younger skeletally immature patients, fractures may involve the distal femoral physis.

Risk Factors

Important risk factors include:

Osteopenia, osteoporosis, advanced age, previous fragility fractures, and increased fall risk.

Etiology

The mechanism varies according to age.

Younger Adults

Common causes include:

Motor vehicle collisions, falls from height, and other high-energy trauma.

Older Adults

The typical mechanism is a low-energy fall, often with the knee flexed.

Periprosthetic Fracture

Distal femoral fracture may occur as a complication around a total knee arthroplasty.

The pattern depends on implant position, bone quality, and whether the prosthesis remains stable.

Pediatric Injury

In children, injury is usually traumatic.

Physeal fractures may exit through the metaphysis on the compression side, producing a pattern resembling a Salter-Harris type II injury.

Associated Injuries

High-energy distal femoral fractures may occur with:

Acetabular fracture, hip dislocation, femoral neck fracture, femoral shaft fracture, ligamentous knee injury, tibial plateau fracture, tibial shaft fracture, and vascular injury.

Diagnosis

Signs and Symptoms

Typical findings include:

Severe pain, focal tenderness, swelling, bruising, deformity, and inability to bear weight or walk.

Physical Examination

A complete musculoskeletal and neurovascular examination is essential.

Inspection

Assess for:

Deformity, swelling, ecchymosis, skin tenting, wounds, and evidence of an open fracture.

Neurovascular Examination

Document distal:

Pulses, capillary refill, motor function, and sensation.

Special attention should be paid to:

Peroneal nerve function and distal arterial perfusion.

Knee Examination

A complete ligamentous examination may be difficult because of pain and instability.

A more detailed examination can often be performed after fracture stabilization.

Pathophysiology and Deformity

Muscle forces commonly produce characteristic displacement.

Shortening

Muscle spasm may cause overlap of the fracture fragments and apparent shortening of the femur and limb.

Sagittal Deformity

The gastrocnemius originates from the distal femur and may pull the distal fragment posteriorly.

This often creates:

Anterior displacement of the proximal shaft and an apex-anterior deformity.

Coronal Deformity

The adductor muscles may pull the distal segment into varus alignment.

Imaging

Knee Radiographs

Obtain:

AP and lateral radiographs of the knee and distal femur.

Oblique Views

Oblique views may be useful when:

Intercondylar or articular extension is suspected.

Trauma Imaging

In high-energy trauma, additional imaging may be required.

Pelvis

An AP pelvis radiograph helps identify associated pelvic or proximal femoral injury.

Hip and Entire Femur

AP and lateral views of the:

Hip and entire femur

should be obtained when clinically indicated to exclude associated proximal fractures.

Vascular Imaging

If the distal vascular examination is abnormal or uncertain, further vascular assessment may be required.

Modern evaluation commonly uses:

CT angiography, although formal angiography may be used in selected circumstances.

CT

CT is particularly useful for:

Complex articular fractures, severe comminution, and operative planning.

It can define the number, size, and position of intra-articular fragments.

Pediatric Imaging

Standard trauma radiographs should be obtained.

Stress views may occasionally be considered when an occult physeal injury is suspected, although advanced imaging may be preferable in many situations.

The distal femoral physis remains visible until adolescence and is normally several millimeters thick.

Differential Diagnosis

Important alternative or associated diagnoses include:

Soft-tissue contusion, major knee ligament injury, patellar fracture, proximal tibial fracture, and tibial plateau fracture.

Treatment

General Principles

Treatment aims to restore:

Articular congruity, limb length, coronal and sagittal alignment, rotational alignment, and knee stability.

For intra-articular fractures, anatomical reconstruction of the joint surface is particularly important.

Nondisplaced or Impacted Fractures

Selected stable fractures may be managed with:

A splint, cast, or functional fracture brace.

Close radiographic surveillance is required because displacement can occur.

Skeletal Traction

Skeletal traction may occasionally be used:

Temporarily in medically unstable patients or when immediate fixation is not possible.

It is now less commonly used as definitive treatment.

External Fixation

External fixation is useful for:

Severe open fractures, extensive soft-tissue injury, temporary damage-control stabilization, or unstable polytrauma patients.

A spanning fixator may cross the knee initially.

Once soft tissues improve, conversion to internal fixation may be considered.

Operative Treatment

Most displaced closed distal femoral fractures are treated surgically.

The goals are:

Stable fixation, restoration of alignment, and early knee motion.

Pediatric Treatment

In skeletally immature patients, stable physeal injuries may sometimes be treated with:

Closed reduction and casting.

Displaced or unstable fractures may require:

Percutaneous pinning or open reduction and internal fixation.

Care must be taken to minimize damage to the distal femoral physis.

Activity

Initially, the injured extremity is generally kept non-weight bearing.

Weight bearing is advanced gradually once healing progresses.

Progression

Limited or toe-touch weight bearing may be started in selected cases once:

Fixation is stable, callus is developing, and pain is decreasing.

Progressive full weight bearing generally follows clinical and radiographic evidence of union.

Physical Therapy

Early rehabilitation is important after stable fixation.

Range of Motion

Knee motion should begin as soon as soft tissues and fixation permit.

This reduces the risk of arthrofibrosis.

Strengthening

Therapy emphasizes:

Quadriceps and hamstring activation and strengthening.

Gait Training

As weight bearing progresses, therapy advances to:

Walker or crutch use, gait retraining, balance, and progressive resistance exercises.

Healing Time

Early radiographic healing commonly becomes apparent by approximately 2–3 months.

Complete union may require approximately 4–6 months, depending on fracture severity and patient factors.

Medication

Pain control may include:

Acetaminophen and short-term opioid analgesics when necessary.

The effect of NSAIDs on fracture healing remains debated, so their use may be limited in selected patients at risk for impaired union.

Surgery

Indications

Common operative indications include:

Open fracture, displacement, vascular compromise, irreducibility, multiple injuries, ipsilateral lower-extremity fractures, and unstable intra-articular injury.

Relative Contraindications

Relative reasons to delay or modify surgery include:

Active local infection, severe medical instability, or exceptionally poor bone quality.

Fixation Options

Possible implants include:

Locked plates, fixed-angle plates, condylar plates, intramedullary nails, external fixation, and selected arthroplasty constructs.

Plate Fixation

Modern distal femoral plates are available in multiple shapes and designs.

They can be used for:

Simple fractures, comminuted fractures, osteoporotic fractures, and periarticular injuries.

Minimally Invasive Plating

Some plates can be inserted through limited incisions and passed submuscularly, reducing disruption of fracture-site blood supply.

Locked Plates

Locked plates are particularly useful in:

Osteoporotic bone and metaphyseal comminution, where conventional screw purchase may be limited.

Intramedullary Nailing

Intramedullary nails can stabilize selected extra-articular or simple articular distal femoral fractures.

They may be inserted:

Antegrade or retrograde.

Retrograde nails are commonly used for fractures closer to the knee.

External Fixation

External fixation is most commonly used as a temporary stabilizing measure when:

Soft tissues are severely damaged or the patient is physiologically unstable.

Distal Femoral Replacement

In selected elderly patients with:

Severe osteoporosis, unreconstructable comminution, preexisting advanced knee arthritis, or failed fixation, distal femoral replacement may be considered.

Periprosthetic Distal Femur Fracture

Treatment depends on:

Fracture location, implant design, available distal bone stock, and whether the knee prosthesis is stable.

Stable Prosthesis

When the implant is well fixed, treatment may include:

Locked plating or retrograde intramedullary nailing, depending on fracture pattern and implant compatibility.

Loose Prosthesis

If the femoral component is loose or the fracture is too distal for reliable fixation, revision arthroplasty or distal femoral replacement may be required.

Pediatric Considerations

Closed reduction with percutaneous pin fixation can produce good results in displaced pediatric fractures when appropriate.

If the fracture remains unstable, open reduction and internal fixation may be necessary.

Postoperative Immobilization

In some pediatric cases, the knee may be immobilized in slight flexion, historically around 10°, until early healing is visible.

Immobilization duration is individualized, commonly around several weeks.

Follow-Up

Early Monitoring

Patients should be monitored carefully after injury for:

Neurovascular deterioration, progressive swelling, and compartment syndrome of the thigh.

Prognosis

Outcome depends primarily on:

Fracture complexity, degree of articular damage, soft-tissue injury, age, bone quality, and quality of reduction.

Simple fractures generally have better outcomes than extensively comminuted intra-articular injuries.

With appropriate treatment, many patients achieve good to excellent function.

Periprosthetic Fracture Prognosis

Modern fixation, including appropriately selected intramedullary nails or locked plates, can provide favorable midterm results in periprosthetic fractures when the prosthesis remains stable.

Complications

Knee Stiffness

Arthrofibrosis is one of the most common complications.

Risk increases with:

Severe trauma, intra-articular injury, prolonged immobilization, and delayed rehabilitation.

Infection

Infection may occur, particularly in:

Open fractures, extensive soft-tissue injury, and major reconstructive procedures.

Nonunion

Failure of union is associated with:

Comminution, bone loss, poor fixation, infection, smoking, severe osteoporosis, and compromised biology.

Malunion

Healing with abnormal alignment may cause:

Varus, valgus, flexion, extension, rotational deformity, limb shortening, or altered gait.

Loss of Fixation

Mechanical failure may result from:

Poor bone quality, inadequate fixation, premature loading, or severe fracture comminution.

Post-Traumatic Arthritis

Intra-articular fractures may damage the articular cartilage and lead to:

Progressive degenerative arthritis of the knee.

Risk is greater when joint congruity cannot be restored.

Compartment Syndrome

Although less common than in the leg, compartment syndrome of the thigh can occur after major distal femoral trauma.

It requires urgent recognition and treatment.

Physeal Injury

In children, injury to the distal femoral growth plate is particularly important because this physis contributes substantially to lower-extremity growth.

Complications may include:

Growth arrest, angular deformity, and leg-length discrepancy.

Limb-Length Discrepancy

Significant discrepancy may require procedures such as:

Contralateral epiphysiodesis, femoral shortening, or ipsilateral femoral lengthening, depending on remaining growth and projected inequality.

A discrepancy greater than approximately 2.5 cm may become clinically important.

Patient Monitoring

Patients are usually reassessed within the first several weeks after definitive treatment and then periodically, often approximately monthly during active healing.

Monitoring should include:

Pain, tenderness, range of motion, alignment, neurovascular status, and serial radiographs.

Radiographic Healing

Follow-up imaging should demonstrate:

Progressive callus formation, maintenance of alignment, stable implants, and eventual bridging union.

Weight-Bearing Progression

Limited weight bearing may begin when:

Good callus formation is visible, fixation is stable, and fracture-site tenderness has substantially decreased.

Full weight bearing should be advanced according to clinical and radiographic healing rather than time alone.