Transient medial patellar dislocation: injury patterns at US and MR imaging

Area of Science:

• Orthopedics
• Radiology
• Sports Medicine

Background:

• Medial patellar dislocation is uncommon, often resulting from iatrogenic injury after lateral retinacular release surgery.
• Trochlear groove dysplasia is a predisposing anatomical factor for patellar instability.

Observation:

• A case of transient medial patellar dislocation in a 19-year-old patient with trochlear groove dysplasia and no surgical history is presented.
• Clinical presentation, ultrasound (US), and magnetic resonance (MR) imaging findings were analyzed.

Findings:

• Ultrasound demonstrated an acute injury with complete avulsion of the lateral patellar retinaculum at its patellar insertion.
• MR imaging confirmed a complete tear of the lateral patellar retinaculum and revealed bone contusions in the medial femoral condyle and lateral patella.
• The observed injury pattern of soft tissue restraints significantly differs from typical lateral patellar dislocations.

Implications:

• This case highlights a distinct mechanism of medial patellar dislocation, emphasizing the role of trochlear dysplasia and lateral retinacular integrity.
• Understanding these unique injury patterns is crucial for accurate diagnosis and appropriate management of patellar dislocations, especially in cases without a clear surgical history.
• Advanced imaging modalities like US and MR are vital for characterizing the extent of soft tissue and bone injury in these unusual dislocations.