Bone Contusion Patterns of the Knee: MRI as a Footprint of Injury Mechanism

A practical radiology review of Bone Contusion Patterns of the Knee: MRI as a Footprint of Injury Mechanism, focused on imaging findings, differential diagnosis, reporting points, and high-yield teaching pearls.

• General Concept
• Bone marrow edema = injury footprint
• Distribution → predicts mechanism + soft tissue injury

Mechanisms

• Compression
• Direct blow
• Avulsion traction

1. Pivot Shift Injury (ACL injury pattern)

• Pattern
• Posterolateral tibial plateau
• Lateral femoral condyle (midportion)
• ± posterior medial tibial plateau (contrecoup)
• Mechanism
• Valgus + rotation + deceleration
• Tibial anterior subluxation → impaction
• Associated Injuries
• ACL tear (classic)
• Posterior horn meniscus tears (lat > med)
• MCL injury
• Posterolateral capsule / arcuate complex injury
• Osteochondral impaction
• Key Signs
• Deep lateral femoral sulcus (>2 mm)
• Femoral bruise position → flexion degree

2. Dashboard Injury (PCL injury pattern)

• Pattern
• Anterior proximal tibia
• ± posterior patella
• Mechanism
• Posterior force on flexed knee
• Tibia driven posteriorly
• Associated Injuries
• PCL tear (classic)
• Posterior capsule rupture
• Patellar fracture / osteochondral injury
• Possible hip injury

3. Hyperextension Injury

• Pattern
• “Kissing contusions”
• Anterior tibia
• Anterior femoral condyle
• Medial if valgus added
• Mechanism
• Hyperextension → anterior impaction
• Associated Injuries
• ACL ± PCL tears
• Meniscal injury
• Posterior capsule disruption
• Popliteal artery injury (severe)
• Posterolateral complex injury
• Gastrocnemius injury

4. Clip Injury (Valgus contact)

• Pattern
• Lateral femoral condyle (large)
• Medial femoral condyle (small, avulsion)
• Mechanism
• Direct valgus blow (slight flexion)
• Associated Injuries
• MCL injury spectrum
• Grade I: edema only
• Grade II: partial tear
• Grade III: complete tear

With more flexion

• ACL tear
• Medial meniscus tear
• → O’Donoghue triad

5. Lateral Patellar Dislocation

• Pattern
• Inferomedial patella
• Anterolateral femoral condyle
• Mechanism
• Internal femoral rotation + quad contraction
• Patella dislocates laterally
• Associated Injuries
• MPFL tear (most important)
• Medial retinaculum injury
• Osteochondral injury (patella / LFC)
• Joint effusion
• Key Differentiation

Pivot shift

• Patellar dislocation → anterior LFC edema
• Pivot shift → posterior/central LFC + PL tibia

Converting the pattern into an impression

Pivot-shift example: Bone contusions involve the terminal sulcus of the lateral femoral condyle and posterolateral tibial plateau. The distribution is compatible with a pivot-shift mechanism. There is a complete anterior cruciate ligament tear and an associated posterior horn lateral meniscal tear.

Lateral patellar dislocation example: Matching bone contusions are present at the medial patellar margin and anterolateral femoral condyle. The medial patellofemoral ligament is torn at its femoral attachment. No displaced patellar osteochondral fragment is identified. The report should relate the contusion pattern to the mechanism while documenting ligaments, menisci, and osteochondral surfaces separately.