An unusual case of knee locking

Area of Science:

• Orthopaedic Surgery
• Musculoskeletal Pathology
• Diagnostic Imaging

Background:

• Knee locking is a common orthopaedic emergency often caused by meniscal tears, ligament injuries, or loose bodies.
• Accurate diagnosis is crucial for effective treatment and patient outcomes.
• Magnetic resonance imaging (MRI) is a standard tool for evaluating internal knee derangements.

Observation:

• A patient presented with incapacitating left knee locking, initially suspected to be a lateral meniscal tear based on clinical and radiological findings.
• Standard MRI did not reveal the suspected meniscal tear.
• Diagnostic arthroscopy identified a 1-cm yellowish mass on the medial meniscus.

Findings:

• Histological examination confirmed the mass to be pigmented villonodular synovitis (PVNS).
• The patient's menisci and cruciate ligaments were otherwise intact.
• PVNS, a rare intra-articular tumor, was the cause of the knee locking.

Implications:

• This case underscores the importance of considering rare diagnoses like PVNS in cases of knee locking, especially when initial imaging is inconclusive.
• PVNS should be included in the differential diagnosis for unexplained knee locking.
• Prompt diagnosis and surgical intervention are essential for managing PVNS and restoring knee function.