A 44 yo male presents with knee pain for one year.  Pain is progressive and recently became severe. He reports no trauma.  On exam strength and range of motion are intact.  There is no redness over the joint.  An x-ray is shown.  What's the diagnosis?  Scroll down for answer.

Answer:  Malignancy

The plain film has a lytic lesion in the anterior tibial metaphysis, shown with MRI below

• Differential diagnosis for xray finding includes primary bone malignancy, metastatic disease, benign tumor, cyst, and osteomyelitis
• Malignant bone tumors are primarily a disease of young people (age 10-40)

• CT / MRI are helpful in diagnosis and often can be done as an outpatient
• Orthopedics consultation is warranted
• Screening for metastatic disease, leukemia, lymphma may be appropriate
• This 44 yo male had a high grade myxoid and spindle cell sarcoma consistent with peripehral nerve sheath tumor
• There are dozens of both benign and malignant bone tumors, but the three most common types are:

1. Rhabdomyosarcoma - often a painless mass
2. Osteosarcoma - most common pediatric bone tumor, found in long bone metaphases during growth spurts, pain with activity
3. Ewing's sarcoma - an aggressive malignancy, 25% will have metastatic disease at time of diagnoisis, "onion peel" appearance on plain film

Tintinalli et al.  Tintinalli’s Emergency Medicine: A Comprehensive Study Guide.  8th Ed.  New York:  McGraw hill Education, 2016. Print