Hello and welcome to HCM,
A warm spot over the knee suggests an inflammatory process.
Inflammation is usually associated with increase in temperature over the local area.
It is difficult to determine the origin of the spot- whether
soft tissue origin or blood vessel origin.
Is there past history of vascular disorder?
Onset of symptoms while sitting in reclining position suggests the relation of the pathology with pressure.
If yes, it could have vascular origin.
However clinical examination is required to make any diagnosis.
For vascular problems Doppler is usually advised.
Consult your doctor preferably surgeon for your problem.
Thanks and take care
Dr Shailja P Wahal