Thanks for all these additional details.
Well, it could be related with lipoma, which is a subcutaneous, benign fatty growth.
These are firm (but usually they are movable) growths that can develop at any place on the body. They are very common and they are not cancerous or concerning. Occasionally they can cause discomfort.
Other possibility could be Epidermoid cyst. Usually, these are benign nodules that can occur anywhere on the body as well. Sometimes these can become inflamed and infected. As you don't have associated pain in thigh, so it doesn't sound to be infected.
From my clinical experience, i can say that it is not related with any serious issue. This is most likely benign cause and would not develop into serious issue. We come across such cases, in routine clinical practice.
It can be co-incidence that knee pain has started at the same time.
The most common cause for knee pain is- Arthritis, knee joint is most commonly involved joint in rheumatic diseases.
It could also be related with Tendinitis, It is the inflammation of the tendon in knee. Medical name for this condition is Patellar tendinitis.
This condition is treated with Ice packs, immobilization with a knee brace as needed, rest, and anti inflammatory medications.
You should take help from physical therapist. Physical therapy includes various modalities like - Short wave diathermy, Infra red , Wax therapy ,these will help you a lot.
Also exercise programs can rehabilitate the tissues in and around the involved tendon.
Please consult your doctor for clinical checkup and get appropriate management. If required, they may send you to Orthopedician for further management.
I hope this helps.
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