What causes pain in knee osteoarthritis ?

Pain in knee OA is likely a heterogenous, multifactorial phenomenon that involves not only the disease process but also elements specific to patient psychosocial make-up and pain neurophysiology (Andrew et al., 2013). However, pain in OA of the knee is presumed to arise from a combination of the following mechanisms (Joern et al., 2010):

1. Osteophytic periosteal elevation
2. Vascular congestion of subchondral bone, leading to increased intraosseous pressure
3. Fatigue in muscles that cross the joint
4. Overall joint shortening
5. Joint effusion and stretching of the joint capsule
6. Torn menisci
7. Inflammation of the joint
8. Muscle spasm 
9. Rough or crunchy sensation
10. Central pain sensitization
11. Psychosocial factors