hi sir/madam, Thanks for your question on Healthcare Magic. There are possibily 3 main causes- Musculoskeletal pain:- Crepitus, recognized by a popping or cracking sound in the knee, or arthritis, an autoimmune disease that affects the joints in the hip, knee, or ankle. If a muscle, tendon, or ligament is strained, for example, during a fall, any pain will be musculo-skeletal. Night cramps, compartment syndrome, and stress fractures are also musculoskeletal problems. Vascular pain:- Causes include peripheral arterial disease (PAD), deep vein thrombosis (DVT), cellulitis, infections, varicose veins, and varicose eczema, where pain is accompanied by discoloration of the skin. Neurological pain:- Conditions include restless leg syndrome (RLS) in which the legs twitch uncontrollably, neuropathy, or nerve damage, and sciatic nerve pain. Neurological pain can be present even when resting. Hope i was helpful. Have a healthy day.