Orthopaedic Surgery - Patellar Fracture

Basics

A patellar fracture is a fracture involving the patella, or kneecap.

Because the patella forms part of the knee extensor mechanism, fracture displacement may disrupt continuity between the:

Quadriceps tendon

Patella

and

Patellar tendon.

Loss of extensor mechanism continuity can result in inability to actively extend the knee.

Classification

Patellar fractures are commonly classified according to fracture pattern.

Typical patterns include:

Vertical

Transverse

Stellate or comminuted

Superior or inferior pole

The degree of displacement, articular incongruity, and integrity of the extensor mechanism are also clinically important.

Pediatric Sleeve Fracture

In children, the characteristic injury is the:

Patellar sleeve fracture.

In this injury, a sleeve of:

Cartilage and periosteum

is avulsed from the developing patella, often together with the:

Patellar tendon.

Because much of the avulsed tissue is not ossified, the fracture may be difficult to identify on plain radiographs.

A clue is:

Patella alta

without an obvious large bony fragment.

For this reason, pediatric sleeve fractures are easily missed.

Epidemiology

Patellar fractures occur in:

Both males and females

and across a broad age range.

Incidence

Patellar fractures account for approximately:

1% of all skeletal fractures.

Risk Factors

The major risk factor is:

Direct blunt trauma to the anterior knee.

A classic mechanism is a:

Dashboard injury during a motor vehicle collision.

Etiology

Patellar fractures may result from:

Direct trauma

or

Indirect force through the extensor mechanism.

Direct Trauma

A direct blow to the patella, especially with the knee flexed, can produce:

Comminuted

Stellate

or other fracture patterns.

The exact pattern depends partly on:

Direction and magnitude of the impact

and

Degree of knee flexion.

Indirect Injury

A sudden, powerful eccentric contraction of the quadriceps against a flexed knee may generate enough force to produce a:

Transverse fracture

or

Patellar pole avulsion.

Fracture in Compromised Bone

Patellar fracture can also occur in structurally weakened bone, including after:

Total knee arthroplasty

Osteolysis

or

Patellar tendon graft harvest during ACL reconstruction.

Associated Injuries

Patellar fracture may occur with other significant injuries, including:

Femoral shaft fracture

Knee ligament injury

Other injuries caused by high-energy trauma

Diagnosis

Signs and Symptoms

Typical symptoms include:

Acute anterior knee pain

Swelling

Difficulty walking

and, in displaced injuries,

Inability to actively straighten the knee.

Physical Examination

The examination should determine both:

Fracture characteristics

and

Whether the extensor mechanism remains functional.

Swelling and Tenderness

Typical findings include:

Localized patellar tenderness

Anterior knee swelling

Hemarthrosis

Straight-Leg Raise

The ability to perform a:

Straight-leg raise

is an important test of extensor mechanism continuity.

Inability to perform the test raises concern for:

Displaced patellar fracture

Quadriceps tendon rupture

or

Patellar tendon rupture.

Palpable Defect

A gap may occasionally be:

Visible or palpable

across the patella or extensor mechanism.

Extensor Mechanism

The clinician should assess whether the patient can:

Actively extend the knee against gravity.

An intact retinaculum may sometimes preserve active extension despite a patellar fracture, so imaging remains important.

Imaging

Plain Radiographs

Standard imaging includes:

AP

and

Lateral radiographs.

Axial or Tangential Views

Axial or sunrise views can be particularly useful for identifying:

Vertical fractures

Marginal fractures

Articular incongruity

These views should be obtained only when clinically safe and tolerable.

CT

CT is not routinely required for a straightforward isolated patellar fracture.

It can be useful when there is:

Complex comminution

Uncertain fracture morphology

Need for detailed surgical planning.

MRI

MRI is rarely necessary for an isolated fracture but may help evaluate:

Cartilage injury

Retinacular injury

Associated ligamentous injury

Occult pediatric sleeve injury

Pathological Findings

Common associated findings include:

Hemarthrosis

and, in displaced fractures,

Disruption of the extensor mechanism.

The articular surface may also be damaged depending on the fracture pattern.

Differential Diagnosis

Important alternatives include:

Quadriceps tendon rupture

Patellar tendon rupture

Patellar dislocation

Posterior cruciate ligament injury

Osteochondral injury

Treatment

General Principles

Treatment is determined primarily by:

Fracture displacement

Articular congruity

Integrity of the extensor mechanism

Degree of comminution

Nondisplaced Fractures

Nondisplaced or minimally displaced fractures with an intact extensor mechanism can often be treated:

Nonoperatively.

Treatment usually involves:

A cast, brace, or splint with the knee in extension.

Follow-Up of Nonoperative Fractures

Close radiographic follow-up is important because a fracture that is initially well aligned may:

Displace during healing.

Weight Bearing

Many patients treated nonoperatively may:

Bear weight as tolerated with the knee locked in extension, depending on stability and pain.

Range of Motion

Range-of-motion exercises are introduced progressively once sufficient stability and healing are present.

Prolonged immobilization should be minimized when safe because it may contribute to:

Knee stiffness

Quadriceps atrophy

Displaced Fractures

Displaced fractures are generally treated with:

Open reduction and internal fixation, particularly when the extensor mechanism is disrupted.

Surgery allows:

Restoration of articular congruity

Restoration of extensor mechanism continuity

Earlier rehabilitation

Medication

Pain can be treated with:

Acetaminophen

and other appropriate analgesics.

NSAID use may be individualized based on fracture-healing considerations and patient comorbidities.

Short-term opioid medication may be used for:

Severe acute postoperative or fracture pain when necessary.

Surgery

Indications

Operative treatment is generally indicated for:

Significant fracture displacement

Articular step-off that cannot be accepted

Loss of extensor mechanism continuity

Open fracture

Displaced osteochondral or pole fragments

Tension-Band Fixation

Traditional fixation for a transverse patellar fracture uses:

Parallel Kirschner wires

with a:

Tension-band construct.

The construct converts tensile forces at the anterior patella into:

Compression across the fracture during knee flexion.

Cannulated Screw Fixation

Tension-band principles may also be applied using:

Parallel cannulated screws

with a tension-band construct.

This may provide stronger fixation and reduce some wire-related problems in selected fractures.

Stellate and Comminuted Fractures

Comminuted fractures may require:

Additional cerclage fixation

Multiple screws

Plates

or other modern fixation constructs.

The goal is to preserve as much viable patella and articular surface as possible.

Distal Pole Fractures

Small, nonreconstructible inferior-pole fragments were historically treated with:

Partial excision and patellar tendon repair.

Current treatment increasingly favors:

Fragment-preserving fixation when feasible

because preservation of patellar length and the extensor mechanism generally improves function.

Patellectomy

Partial or total patellectomy should be reserved for:

Rare, severely comminuted fractures that cannot be reconstructed.

Loss of patellar bone reduces:

Quadriceps mechanical efficiency

and may weaken knee extension.

Open Fractures

Open patellar fractures require:

Prompt irrigation and debridement

Appropriate antibiotics

and

Stable fixation when possible.

Every effort should be made to preserve:

Viable patellar bone

and

Extensor mechanism continuity.

Rehabilitation

Physical therapy is important after both operative and nonoperative treatment.

Goals include:

Restoring range of motion

Preventing stiffness

Rebuilding quadriceps strength

Normalizing gait

Returning to function

Prognosis

Nondisplaced fractures treated appropriately generally have a:

Good prognosis.

Displaced fractures also have favorable outcomes when:

Anatomic or near-anatomic alignment is restored

and

Stable fixation permits rehabilitation.

Elderly Patients

Older patients with displaced fractures and disruption of the extensor mechanism generally benefit from:

Operative restoration of continuity, provided they are suitable surgical candidates.

Complications

Nonunion and Malunion

Fracture healing may occasionally result in:

Nonunion

or

Malunion.

This may cause persistent:

Pain

Weakness

Extensor dysfunction

Refracture

Refracture can occur, particularly after:

Premature return to activity

or in the setting of compromised bone.

Symptomatic Hardware

Prominent wires or other fixation devices may cause:

Anterior knee pain

Soft-tissue irritation

and sometimes require:

Hardware removal.

This is one of the more common problems after traditional tension-band fixation.

Post-Traumatic Arthritis

Damage to the patellar articular surface may lead to:

Patellofemoral osteoarthritis.

Risk increases with:

Comminution

Residual articular incongruity

Cartilage loss

Extensor Mechanism Weakness

Quadriceps strength decreases as:

More of the patella is lost

Articular anatomy becomes more disrupted

or

Patellar height and mechanics become abnormal.

This is one reason preservation of the patella is preferred whenever possible.

Knee Stiffness

Prolonged immobilization or postoperative scarring may result in:

Loss of flexion

Arthrofibrosis

Early controlled motion helps reduce this risk when fixation is sufficiently stable.

Patient Monitoring

Serial clinical and radiographic follow-up should assess:

Fracture alignment

Healing

Extensor function

Range of motion

Hardware position

Radiographs are often repeated at approximately:

4–6-week intervals

until satisfactory union is demonstrated.

Key Principle

Patellar fracture management is determined primarily by fracture displacement and integrity of the extensor mechanism.

Stable, nondisplaced fractures with preserved active extension can often be treated with:

Immobilization in extension and progressive rehabilitation.

Displaced fractures or fractures that interrupt the extensor mechanism generally require:

Operative fixation with preservation of as much patellar bone and articular surface as possible.