Orthopaedic Surgery - Osteochondritis Dissecans of the Knee

Basics

Osteochondritis dissecans (OCD) of the knee is a disorder of the subchondral bone and overlying articular cartilage in which a localized segment of subchondral bone becomes abnormal and may eventually separate from the surrounding bone.

The process can lead to:

Cartilage injury

Fragment instability

Loose-body formation

Secondary osteoarthritis

The knee is the most commonly affected joint, although OCD can also occur in the:

Elbow, particularly in throwing athletes and gymnasts

and

Ankle, where lesions may be associated with recurrent instability or trauma.

Age at Presentation

OCD occurs most commonly during the:

Second decade of life

but can also occur in younger children and adults.

Lesions that develop before skeletal maturity are referred to as:

Juvenile OCD

whereas lesions in skeletally mature patients are generally considered:

Adult OCD.

Healing potential is better when the growth plates remain open.

Older adolescents and adults are less likely to heal with nonoperative treatment alone.

Common Locations

The classic location is the:

Posterolateral aspect of the medial femoral condyle, accounting for approximately 65% of lesions.

Other reported sites include:

Inferocentral lateral femoral condyle – approximately 30%

Patella – approximately 2%

Lateral femoral trochlea – approximately 2%

Central trochlea – less than 1%

Lateral tibial plateau – less than 1%

Epidemiology

OCD is uncommon.

Historical incidence has been estimated at approximately:

10 cases per 100,000 population.

It is more common in:

Males

than females.

Bilateral Disease

Approximately:

8–30% of patients

may have bilateral lesions.

For this reason, the contralateral knee should be considered during clinical and radiographic evaluation.

Risk Factors

Potential risk factors include:

High levels of sports participation

Repetitive mechanical stress

Abnormal mechanical axis

Discoid meniscus

Generalized ligamentous laxity

Obesity

Abnormal intraosseous blood supply

Genetics

Familial clustering has been reported.

However, most cases do not follow a clearly established Mendelian inheritance pattern.

Etiology

The exact cause is probably multifactorial.

Proposed contributing mechanisms include:

Repetitive microtrauma

Subchondral ischemia

Abnormal biomechanics

Altered vascular supply

Genetic susceptibility

Repeated loading may impair the integrity of the subchondral bone, eventually compromising the overlying cartilage.

Diagnosis

Diagnosis is based on:

History

Physical examination

Radiographs

and often

MRI.

Signs and Symptoms

Early lesions commonly present with:

Insidious, activity-related knee pain.

The pain may be vague and poorly localized.

Late Symptoms

As the lesion becomes unstable, patients may develop:

Swelling

Catching

Locking

Mechanical clicking

These symptoms may indicate:

Fragment instability or loose-body formation.

History

Important questions include:

Duration of symptoms

Activity-related pain

Participation in repetitive or high-impact sports

Episodes of swelling

Locking or catching

Previous knee injury

Previous treatment

Physical Examination

A complete knee examination should be performed.

Range of Motion

Assess:

Flexion

Extension

and any:

Painful or mechanical restriction.

Tenderness

Localized tenderness may be present over the involved femoral condyle.

Effusion

Joint effusion should be graded as:

Mild

Moderate

or

Large.

Effusions are more common when the lesion is unstable or when there is significant cartilage irritation.

Meniscal Examination

The McMurray test can be used to assess for associated meniscal pathology.

Ligament Examination

The Lachman test should be performed to assess for ACL injury when appropriate.

Gait

An:

Antalgic gait

may be present.

Muscle Atrophy

Chronic symptoms may lead to:

Quadriceps or thigh atrophy.

Contralateral Knee

Because bilateral lesions are not uncommon, the opposite knee should be examined.

Imaging of the contralateral side may be considered when clinically appropriate.

Imaging

Plain Radiographs

Initial radiographs commonly include:

AP

Lateral

Tunnel

Merchant or patellofemoral views

Tunnel View

The tunnel view is commonly obtained with the knee flexed approximately:

45°

and improves visualization of the posterior femoral condyles, where classic OCD lesions frequently occur.

Merchant View

The Merchant or patellofemoral view helps assess uncommon OCD lesions involving the:

Trochlea

or

Patella.

Bilateral Imaging

Bilateral radiographs can be obtained when there is concern for:

Contralateral involvement.

Physeal Status

The growth plates should be evaluated carefully.

Open physes are generally associated with:

Better healing potential and a more favorable prognosis.

Early Radiographic Findings

Early lesions may appear as:

A localized area of radiolucency or subchondral irregularity.

Late Radiographic Findings

Chronic or more advanced lesions may demonstrate:

Subchondral cysts

Sclerotic margins

Fragmentation

Separation of the osteochondral fragment

A prominent sclerotic rim may indicate reduced healing potential.

Radiographic Healing

Healing is suggested by:

Resolution of radiolucency

Progressive incorporation of the lesion

Disappearance of cystic or fragmentary changes

MRI

MRI is particularly useful for:

Characterizing the lesion

Assessing stability

Measuring lesion size

Evaluating cartilage

Detecting loose bodies

Identifying associated knee pathology

MRI Findings

Important features include:

Bone marrow edema

Lesion dimensions

Subchondral cysts

Fluid beneath the fragment

Articular cartilage defects

Loose bodies

MRI Classification

A commonly used MRI staging system includes:

Stage I

There is:

Small or poorly defined signal alteration without clear lesion margins.

Stage II

The OCD fragment has:

Well-defined margins

but there is:

No fluid between the fragment and underlying bone.

Stage III

Fluid is:

Partially visible between the fragment and underlying bone.

This raises concern for partial instability.

Stage IV

Fluid:

Completely surrounds the fragment.

This strongly suggests instability.

Stage V

The fragment is:

Displaced.

MRI Signs of Instability

Features associated with an unstable lesion include:

A high-signal line greater than approximately 5 mm between the lesion and underlying bone

A homogeneous high-signal area greater than approximately 5 mm beneath the lesion

A focal articular-surface defect greater than approximately 5 mm

A high-signal line extending through the subchondral plate into the lesion

Fluid Behind the Fragment

A high-signal fluid line behind the fragment is particularly concerning for:

Loss of attachment and instability.

It is also commonly seen in lesions that fail nonoperative treatment.

MRI Accuracy

MRI is highly sensitive for detecting instability.

However, specificity is lower in skeletally immature children because:

Normal developmental vascularity and ossification patterns may mimic instability.

Thus, MRI findings should be interpreted together with:

Age, symptoms, radiographs, and clinical course.

Pediatric Considerations

In children younger than approximately 7 years, irregularities of the distal femoral ossification center may resemble OCD.

These normal developmental variants should not be mistaken for pathological lesions.

Pathological Findings

Pathology may show:

An osteochondral fragment composed of articular cartilage with attached abnormal or necrotic subchondral bone.

If separation progresses, the fragment may become unstable and eventually detach.

Differential Diagnosis

Stress Fracture

Stress injury may cause activity-related pain but often has a different imaging pattern.

Some stress fractures present more acutely.

ACL Injury

ACL injury is suggested by:

Instability

and

A positive Lachman test.

Normal Ossification Variant

Young children may have physiologic irregularity of the distal femoral epiphysis that resembles OCD on radiographs.

Meniscal Injury

Meniscal tears may produce:

Locking

Catching

Joint-line pain

and a:

Positive McMurray test.

Osteonecrosis

Spontaneous or secondary osteonecrosis of the knee may enter the differential diagnosis, particularly in adults.

Potential risk factors include:

Corticosteroid exposure

Alcohol use

Other causes of impaired bone blood supply

Treatment

General Principles

Treatment depends on:

Age

Physeal status

Lesion size

Location

Stability

Symptoms

Radiographic stage

Favorable Lesions

The lesions most likely to heal without surgery are:

Small

Stable

Covered by intact cartilage

and present in:

Skeletally immature patients with open physes.

Unstable Lesions

An unstable or detached lesion generally requires:

Operative treatment, regardless of skeletal maturity.

Nonoperative Treatment

Conservative management is preferred initially for many stable lesions that present before physeal closure.

Very small lesions may sometimes be treated with:

Observation and activity modification alone.

Three-Phase Nonoperative Protocol

A structured three-phase treatment approach can be used.

Phase 1: Initial Protection

During approximately the first 6 weeks, treatment may include:

Knee immobilizer or cast

Unloader brace

Crutch-assisted or protected weight bearing

The patient should become:

Pain-free before progressing.

Radiographs are generally repeated at the end of this phase.

Phase 2: Rehabilitation

From approximately 6–12 weeks:

Weight bearing is progressively increased as tolerated

Immobilization is discontinued

Physical therapy begins

The focus is on:

Knee range of motion

Quadriceps strengthening

The patient should remain pain-free before further activity progression.

Repeat radiographs may be obtained.

Phase 3: Return to Activity

Beginning around:

3 months

activity is gradually advanced under supervision.

Impact Restrictions

High-impact and shear-loading activities should remain restricted until the patient has:

No pain

No swelling

Improving imaging findings

and has remained symptom-free for a sustained period.

Repeat MRI

MRI may be repeated when:

Healing is uncertain

Symptoms persist

Instability is suspected

Return to sport is being considered

Failed Nonoperative Treatment

If the lesion progresses, symptoms recur, or imaging demonstrates instability, immobilization may be resumed or surgery may be considered.

Surgery

Surgery is recommended for:

Detached lesions

Unstable lesions

Displaced fragments

Relative Surgical Indications

Surgery may also be considered for:

Symptomatic patients approaching physeal closure who fail conservative treatment

Stable lesions that show no healing after approximately 6–9 months

Arthroscopic Drilling

Drilling is most appropriate for:

Stable lesions with intact articular cartilage.

Mechanism of Drilling

Small channels are created through or around the lesion to stimulate:

Revascularization and bone healing.

Techniques include:

Transarticular drilling

and

Retrograde drilling through the epiphysis.

Drilling Outcomes

Historical series report healing in approximately:

85% of patients with open physes

and

75% of patients with closed physes.

Factors Associated With Failure

Less favorable results have been associated with:

Atypical lesion location

Multiple lesions

Underlying medical disorders

Skeletal maturity

Fragment Reduction and Fixation

Unstable but salvageable fragments may be:

Reduced anatomically and fixed.

Bone Grafting

If there is subchondral bone loss, the crater may be filled with:

Autologous bone graft

before or during fragment fixation.

Fixation Options

Possible implants include:

Headless compression screws

Conventional screws

Osteochondral plugs

MRI-compatible implants are preferred when future MRI surveillance is anticipated.

Chronic Loose Fragments

Longstanding detached fragments may have:

Poor vascularity

Altered shape

Poor healing potential

and may not be suitable for fixation.

Unsalvageable Lesions

If the fragment cannot be preserved, treatment is based on the size of the residual defect.

Marrow Stimulation

For smaller defects, options include:

Drilling

Abrasion arthroplasty

Microfracture

These techniques stimulate marrow-derived cells and produce:

Fibrocartilage repair tissue.

Osteochondral Plug Transplantation

Autologous or allograft osteochondral transplantation may be used for:

Moderate-sized defects, particularly those unsuitable for simple marrow stimulation.

Historically, lesions under approximately:

2 cm in diameter

have often been considered for osteochondral plug techniques.

Autologous Osteochondral Transfer

Healthy osteochondral plugs are harvested from a low-load portion of the patient’s knee and transplanted into the defect.

This restores:

Subchondral bone and hyaline cartilage.

Osteochondral Allograft

Larger defects may be reconstructed using:

Fresh osteochondral allograft tissue.

This avoids donor-site morbidity but introduces considerations related to:

Graft availability and incorporation.

Autologous Chondrocyte Implantation

Autologous chondrocyte implantation may be considered for:

Large cartilage defects

particularly in:

Skeletally mature patients.

Cartilage cells are harvested, cultured, and later implanted into the defect.

Follow-Up

Stable lesions treated nonoperatively require close surveillance to determine whether they are:

Healing

Remaining unchanged

or

Becoming unstable.

Imaging Follow-Up

Serial radiographs or MRI may be obtained approximately every:

3–6 months

depending on symptoms, lesion characteristics, and treatment.

Prognosis

Small, stable, nondisplaced lesions in patients with:

Open growth plates

have the best prognosis and often heal.

Poor Prognostic Factors

Less favorable outcomes are associated with:

Skeletal maturity

Large lesions

Unstable lesions

Displaced fragments

Sclerotic margins

Failure of prolonged conservative treatment

Long-Term Outcome

Large or unstable lesions that fail to heal may result in:

Persistent symptoms and early degenerative osteoarthritis.

Complications

Potential complications include:

Persistent OCD despite treatment

Nonunion of a repaired fragment

Progression from stable to unstable lesion

Loose-body formation

Loss or displacement of fixation hardware

Failure or displacement of osteochondral plugs

Overgrowth or hypertrophy of cartilage repair tissue

Secondary osteoarthritis

Patient Monitoring

Patients should be monitored for:

Pain

Effusion

Mechanical symptoms

Range of motion

Quadriceps strength

Radiographic healing

Development of instability

Return to impact sports should occur only after clinical and imaging evidence suggests satisfactory healing.

Key Principle

Osteochondritis dissecans of the knee is a subchondral bone disorder that may secondarily compromise the overlying articular cartilage.

The most important treatment determinants are:

Skeletal maturity and lesion stability.

Small, stable lesions in patients with open physes often heal with protected activity and rehabilitation, whereas:

Unstable, detached, displaced, or persistently symptomatic lesions usually require surgical treatment.