Recognition of a chronic Pellegrini-Stieda lesion prevents unnecessary acute trauma work-up. MRI is indicated only when clinical findings suggest ongoing MCL insufficiency or additional internal derangement despite the chronic appearance of the ossification.
Learning card
Old Pellegrini-Stieda lesion
Ali Talib ·
The case
Curvilinear or crescent-shaped ossification adjacent to the medial femoral condyle at the proximal attachment of the medial collateral ligament (MCL). The ossification is well corticated, indicating a chronic healed lesion. No surrounding soft tissue swelling or acute fracture.
Why this case matters
Evidence of previous MCL injury.
Associated medial compartment osteoarthritis.
Valgus instability if clinically suspected.
Additional chronic post-traumatic ossifications around the knee.
Differentiate from an acute avulsion fracture.
Anatomy you must name
The Pellegrini-Stieda lesion represents post-traumatic ossification or calcification at the femoral attachment of the superficial medial collateral ligament. It develops weeks to months after an MCL injury due to heterotopic ossification during healing.
The clinical decision
No universally accepted classification exists.
Differentiate:
- Acute MCL avulsion (non-corticated fragment)
- Pellegrini-Stieda lesion (mature corticated ossification)
- Pellegrini-Stieda syndrome (radiographic lesion accompanied by medial knee pain and restricted motion)
Protocol & reporting checklist
An incidental chronic Pellegrini-Stieda lesion requires no treatment. If the patient has persistent medial knee pain or instability, correlate with the clinical examination and consider MRI to assess the MCL and associated ligamentous or meniscal injuries.
Pitfalls
✔ Describe the location of the ossification.
✔ State whether the lesion is mature/corticated or appears acute.
✔ Evaluate the medial joint space for osteoarthritis.
✔ Assess for associated fractures or ligamentous avulsion.
✔ Recommend MRI only if symptoms suggest persistent ligament injury or instability.
Management implication
- Mistaking a chronic Pellegrini-Stieda lesion for an acute avulsion fracture.
- Assuming the radiographic finding explains current knee pain.
- Missing associated ligamentous injuries in the acute setting.
- Confusing it with soft tissue calcification from other causes (e.g., calcific tendinopathy or heterotopic ossification elsewhere).
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