Brief Answer:
Please give details and post actual photographs.

Detailed Answer:
Hi.
Thanks for your query, albeit short and specific.
Noted the history and understood the concerns.
Please give additional information for me to assist you better:
Since when is the boil present?
Over a knee cap is a rare site for boil - was there any injury over this area?
Please post clear and focused photos as these help sometimes for on-the-spot diagnosis.
Do you have any medicines at home? May be left over like antibiotics, anti-inflammatory.

Apply Liquid Povidone Iodine locally and may be a sterile bandage.
Give rest to this knee as movements do not allow early healing.

Awaiting for photos and your feedback.

Take care.
With Regards.

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