The knee x-rays show a lytic area in the proximal tibia with pathological fracture.

The patient had metastatic deposits in the proximal tibia from lung carcinoma and underwent internal fixation.

The most common primary malignancies metastasizing to the bone are carcinoma of the breast, bronchus, prostate, kidney and thyroid.

Reference: Grainger & Allison’s Diagnostic Radiology, 6th Edition.