Brief Answer:
Age related change and not always a disease related finding

Detailed Answer:
Hi,
Aortic Knuckle is a finding on Chest Xray only.
The aortic knuckle represents the left lateral edge of the aorta that arises out of left ventricle, as it arches backwards over the left main bronchus, and pulmonary vessels. The contour of the descending thoracic aorta can be seen in continuation from the aortic knuckle.
Prominent aortic knuckle is an age related change. Long term Hypertensive patients and long term cardiac pathology this aorta vessel is seen prominent on the left side to the sternum.
But yes displacement or loss of definition of the lines can indicate disease, such as aneurysm or adjacent lung consolidation.
Please see your doctor to treat blood pressure, CT scan to check for aneurysm.

Good luck.

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