Chondral & Osteochondral Injury, Ankle

Julia Crim, MD

TERMINOLOGY

Definitions

Osteochondral lesion (OCL): Umbrella term for focal injury of articular cartilage and underlying bone
- Preferred term, does not indicate chronicity or stage
Osteochondral injury: Term used for acute/subacute lesions
Osteochondritis dissecans (OCD): Chronic osteochondral lesion
Multiple staging systems used
Berndt and Harty staging system most widely accepted staging system
- Stage 1: Subchondral bone bruise, injury to overlying cartilage
- Stage 2: Crescentic fracture line, stable or partly detached
- Stage 3: Detached osteochondral fragment, in situ
- Stage 4: Detached osteochondral fragment, displaced from donor site
- Stage 5 (later addition to classification, some classify this as 2A): Cystic degeneration of osteochondral fragment
Most important features to orthopedic surgeon are lesion size and stability

IMAGING FINDINGS

General Features

Location
- Talus: Most commonly posteromedial or anterolateral
- Tibial plafond: Variable location
Morphology
- Lateral talar OCL: Usually shallow flake of avulsed bone and overlying cartilage
- Medial talar OCL: Usually deep, rounded lesion due to compression

Radiographic Findings

Bowl-shaped fracture line exiting at joint surface
Rounded bony defect at articular surface
Cyst-like lucency beneath articular surface
Thin flake of bone from subchondral bone plate

MR Findings

MR arthrogram findings correlate reliably with Berndt and Harty surgical staging
Stage 1: Cartilage abnormality, bone marrow edema
Stage 2: Curved fracture line below cartilage (cartilage may normalize)
Stage 3: Arthrographic contrast extends below unstable fragment
Stage 4: Bone defect, may or may not see displaced fragment
Stage 5: Cyst-like area of low signal T1WI, high signal T2WI
- Enhances with IV contrast due to fibrinous material filling “cyst”
- Poor prognostic indicator for healing

CT Findings

CT arthrography: Similar to MR, but does not detect bone marrow edema

DIFFERENTIAL DIAGNOSIS

Subchondral Cyst due to Arthritis

Mimics cystic degeneration of OCL
Roughly spherical shape rather than bowl shape
Osteophytes, nonuniform cartilage thinning also present
- Cartilage thins along lines of stress

Erosion due to Inflammatory Arthritis

Usually less sharply marginated
First erosions occur in bare area (margins) of joint
Uniform cartilage loss usually present

Avascular Necrosis

Subchondral bone marrow abnormality with serpentine margin
Cartilage normal until subchondral collapse occurs

PATHOLOGY

General Features

Etiology
- Talus lesions due to inversion ankle injury
- Tibial plafond injury: Impaction injury, due to inversion or axial load
- May be single traumatic episode or chronic, repetitive trauma
Associated abnormalities
- Talus OCL: Always associated with lateral collateral ligament injury
- Tibial OCL: Lateral collateral injury or syndesmosis injury

CLINICAL ISSUES

Presentation

Most common signs/symptoms: Pain, clicking, locking

Natural History & Prognosis

May heal spontaneously
Complications: Collapse of articular surface, intraarticular loose bodies

Treatment

Drilling chondroplasty
Osteochondral allograft

SELECTED REFERENCES

1. De Smet AA et al: Value of MR imaging in staging osteochondral lesions of the talus (osteochondritis dissecans): results in 14 patients. AJR Am J Roentgenol. 154(3):555-8, 1990

2. Berndt AL et al: Transchondral fractures (osteochondritis dissecans) of the talus. J Bone Joint Surg Am. 41-A:988-1020, 1959

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