Orthopaedic Surgery - Patellar Tendon Rupture

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Basics

Patellar tendon rupture is an injury involving the portion of the knee extensor mechanism extending from the inferior pole of the patella to the tibial tubercle.

Complete rupture disrupts continuity between the quadriceps mechanism and the tibia, resulting in:

Loss of effective active knee extension.

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Epidemiology

Patellar tendon rupture most commonly affects:

Younger adults, often under approximately 40 years of age.

It occurs more frequently in:

Males

than females.

Quadriceps tendon rupture, by comparison, tends to occur in an older population.

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Risk Factors

Factors that weaken the patellar tendon increase susceptibility to rupture.

Important risk factors include:

Chronic patellar tendinopathy

Previous corticosteroid injection around the tendon

Systemic corticosteroid use

Anabolic steroid use

Chronic kidney disease requiring dialysis

Other systemic disorders that compromise collagen or tendon quality may also increase risk.

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Patellar Tendinopathy

Longstanding patellar tendinopathy may produce:

Degeneration

Microtearing

Reduced tensile strength

These changes can predispose the tendon to rupture during an otherwise tolerable load.

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Corticosteroids

Systemic corticosteroid exposure or local steroid injection can impair:

Collagen integrity and tendon healing

and may increase the risk of spontaneous or low-energy rupture.

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Etiology

Most acute ruptures occur during a traumatic event involving:

Powerful eccentric contraction of the quadriceps against resistance while the knee is flexed.

A typical mechanism is an attempt to prevent a fall or land from a jump while the quadriceps contracts forcefully.

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Mechanism of Failure

The extensor mechanism is suddenly loaded while elongated.

If the applied force exceeds the strength of the patellar tendon, the tendon may:

Tear through its midsubstance

or

Avulse from one of its bony attachments.

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Diagnosis

Diagnosis is primarily based on:

Mechanism of injury

Loss of active extension

Palpable tendon defect

and

Imaging when needed.

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Signs and Symptoms

Patients usually report:

Sudden anterior knee pain

Swelling

Difficulty walking

Inability to actively straighten the knee

The injured knee may demonstrate a patella positioned more proximally than the opposite side.

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Patella Alta

Disruption of the patellar tendon allows the intact quadriceps tendon to pull the patella:

Proximally.

This produces:

Patella alta, which may be visible clinically and radiographically.

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Extensor Mechanism Defect

A gap may be palpable:

Immediately distal to the patella

or elsewhere along the course of the tendon.

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Active Extension

Complete rupture usually produces:

Inability to actively extend the knee from a flexed position.

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Straight-Leg Raise

Patients with a complete disruption typically cannot perform a:

Straight-leg raise.

However, partial preservation of the retinaculum can occasionally permit some active extension despite a substantial tear.

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Pain and Effusion

Acute injuries are often associated with:

Substantial knee pain

Hemarthrosis or effusion

Painful range of motion

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Physical Examination

The examination should focus on determining whether the:

Extensor mechanism remains functionally continuous.

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Inspection

Assess for:

Swelling

Ecchymosis

Asymmetry of patellar height

Visible soft-tissue defect

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Palpation

Palpate the entire patellar tendon for:

Tenderness

A gap or defect

Discontinuity

The patella should be compared with the contralateral side for:

Proximal displacement.

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Active Knee Extension

Ask the patient to:

Actively extend the knee

and perform a:

Straight-leg raise.

Loss of extension or a substantial:

Extensor lag

suggests disruption of the extensor mechanism.

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Extensor Lag

An extensor lag means the patient cannot achieve full active extension despite having greater passive extension available.

This may indicate:

Partial or complete extensor mechanism dysfunction.

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Imaging

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Plain Radiographs

Initial radiographs generally include:

AP

and

Lateral views of the knee.

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Purpose of Radiographs

Radiographs help exclude:

Patellar fracture

Tibial plateau fracture

Other associated osseous injury

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Patella Alta on Radiographs

The classic radiographic finding is:

Patella alta

because the patella is no longer tethered distally by an intact patellar tendon.

Comparison with the opposite knee may occasionally help.

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MRI

MRI can directly demonstrate:

The site and extent of tendon disruption

Partial versus complete tear

Tendon retraction

Underlying degeneration

It can also identify associated:

Ligamentous

Chondral

or

Other intra-articular injuries.

MRI is particularly helpful when the diagnosis is uncertain clinically.

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Ultrasound

High-quality musculoskeletal ultrasound may also identify:

Tendon discontinuity and retraction

and can be useful when performed by an experienced operator.

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Pathological Findings

Degenerative changes may be present within the tendon surrounding the rupture.

These may include:

Collagen disorganization

Chronic tendinopathy

Mucoid or degenerative change

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Location of Tear

The tendon may rupture:

Through the midsubstance

At its attachment to the inferior pole of the patella

or

At its insertion on the tibial tubercle.

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Differential Diagnosis

The differential diagnosis includes other injuries that cause:

Acute anterior knee pain and loss of active extension.

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Quadriceps Tendon Rupture

Quadriceps tendon rupture produces disruption:

Above the patella

and may lead to:

Patella baja rather than patella alta.

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Patellar Fracture

A displaced patellar fracture can interrupt the:

Extensor mechanism

and produce a similar inability to perform a straight-leg raise.

Radiographs help distinguish the two.

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Patellar Dislocation

Acute patellar dislocation may cause:

Pain

Swelling

Apparent loss of active extension

but the extensor mechanism itself may remain structurally intact.

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Ligamentous Injury

ACL, PCL, or other ligament injuries can cause a large painful effusion.

This may produce:

Reflex quadriceps inhibition or “quadriceps shutdown”

which can mimic true extensor mechanism failure.

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Occult Tibial Plateau Fracture

A tibial plateau fracture can also produce:

Pain

Effusion

Inability to actively use the knee

without actual disruption of the patellar tendon.

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Treatment

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General Principles

A complete acute patellar tendon rupture generally requires:

Operative repair

to restore the extensor mechanism.

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Initial Management

Before definitive surgery, treatment includes:

Knee immobilization in full extension

Ice and swelling control

Analgesia

Protected ambulation

and

Orthopaedic referral.

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Weight Bearing

Patients may often:

Bear weight as tolerated

provided the knee is:

Locked in full extension in a brace or immobilizer.

Crutches may be used for comfort and stability.

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Partial Tears

Selected partial tears with:

Preserved active extension

and

An intact extensor mechanism

may occasionally be managed nonoperatively with immobilization and rehabilitation.

Complete tears generally require surgery.

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Physical Therapy

Postoperative rehabilitation is essential to restore:

Range of motion

Quadriceps strength

Gait

Functional knee control.

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Early Rehabilitation

Initial exercises commonly include:

Quadriceps sets

Straight-leg raises when permitted

Hip strengthening

Core strengthening

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Range of Motion

Controlled knee motion is introduced according to:

The strength of the repair

Tissue quality

Surgeon protocol

The goal is to restore motion while avoiding excessive tension across the healing tendon.

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Weight Bearing During Rehabilitation

Patients are commonly allowed:

Weight bearing as tolerated with the knee locked in extension

during the early postoperative period.

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Later Rehabilitation

After approximately:

6 weeks

many protocols gradually advance:

Knee flexion

Active range of motion

Progressive resistance exercises

Quadriceps strengthening

The exact timing is individualized.

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Medication

Analgesics may be used for:

Acute injury pain

and

Postoperative discomfort.

Anti-inflammatory medications may also be used when clinically appropriate.

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Surgery

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Indications

Surgical repair is generally indicated for:

Acute complete patellar tendon rupture.

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Timing

Early repair is preferred because it allows:

Restoration of normal patellar height

Preservation of tendon length

Easier approximation of the torn ends

Better functional recovery

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Surgical Technique

The exact repair depends on the location of the tear.

Options may include:

Direct tendon-to-tendon repair

Transosseous sutures through the patella

Suture-anchor fixation

Repair to the tibial tubercle

depending on the injury pattern.

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Repair Augmentation

When tissue quality is poor or the injury is chronic, repair may be augmented with:

Autograft

Allograft

Synthetic material

or other reinforcement techniques.

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Chronic Ruptures

Chronic patellar tendon ruptures are more difficult to treat because of:

Tendon retraction

Scarring

Patella alta

Poor tissue quality

They may require:

Reconstructive procedures rather than simple primary repair.

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Postoperative Protection

The repair may be protected using:

A hinged knee brace

or, less commonly,

An above-knee cast

for approximately:

6 weeks, depending on repair strength and surgeon preference.

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Follow-Up

The first postoperative review is commonly performed approximately:

7–14 days after surgery

for:

Wound assessment

Suture or staple removal when appropriate

Brace evaluation

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Ongoing Follow-Up

Patients are then commonly reviewed every:

4–6 weeks

while progressing toward:

Full range of motion

Quadriceps recovery

Return of normal gait

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Prognosis

Most patients undergoing:

Early repair of an acute rupture

achieve:

Good to excellent functional outcomes.

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Chronic Rupture Prognosis

Chronic tears have a less predictable outcome because reconstruction is technically more demanding.

Even so, operative reconstruction with appropriate augmentation generally provides better function than leaving a complete chronic rupture untreated.

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Complications

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Loss of Range of Motion

Postoperative stiffness may develop because of:

Immobilization

Scar formation

Protective rehabilitation

Controlled early motion helps reduce this risk.

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Extensor Weakness

Residual weakness may result from:

Quadriceps atrophy

Tendon elongation

Altered patellar height

Incomplete rehabilitation

Some patients retain a small:

Extensor lag.

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Re-Rupture

Although uncommon, the repaired tendon may fail again, particularly with:

Premature loading

Poor tendon quality

Noncompliance with rehabilitation

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Infection and Wound Problems

As with other open repairs, complications may include:

Superficial or deep infection

Delayed wound healing

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Patient Monitoring

Follow-up should assess:

Wound healing

Patellar height

Active knee extension

Extensor lag

Range of motion

Quadriceps strength

Gait

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Key Principle

Patellar tendon rupture is a disruption of the extensor mechanism between the inferior patella and tibial tubercle, typically occurring during a forceful eccentric quadriceps contraction against a flexed knee.

The characteristic findings are:

Patella alta, a palpable tendon defect, and inability to perform a straight-leg raise.

Complete acute ruptures are best treated with:

Early surgical repair followed by protected, progressive rehabilitation.