Hi and welcome to HCM.
Warm sensation can be sign of inflammation but it doesnt seem likely in your case. There can be vascular or neurogenic vasodilatation which doesnt mean anythong. Just wait for few more days and see its progression. if it persist you should do rtg lumbar spine
and doppler ultrasounds to evaluate blood vessels in this area. Till that you can apply some cold
compresses and keep your leg elevated. Wish you good health.