This is a sequential, randomized, double-blind, placebo controlled, multiple dose, dose escalation study in subjects with OA knee pain (n=32; 8/cohort). In each cohort, subjects will be randomized 3:1 to receive SC AMG 403 or placebo once every 4 weeks for a total of 4 doses (Q28D x 4).

Inclusion Criteria:

• Diagnosed with knee OA as determined by ACR criteria: Knee pain and radiographic osteophytes and at least 1 of the following 2 items: Morning stiffness 30 minutes, Crepitus on motion, a VAS pain score of ≥ 30 mm for index knee at screening,

Exclusion Criteria:

• Weight of > 125 kg, Inflammatory arthropathy including secondary OA (eg, degenerative arthritis in patients with rheumatoid arthritis) as confirmed by a rheumatologist or investigator, Diagnosis of a condition other than knee OA that, in the investigator's opinion, may cause or affect pain or pain assessment in the index knee; these conditions may include but are not limited to radiculopathy or neuropathy, vasculopathy, fibromyalgia or active depression, Subjects taking neuromodulatory agents (antiepileptics or antidepressants) used as analgesic therapy for neuropathic pain