summary Knee osteoarthritis is degenerative disease of the knee joint that causes progressive loss of articular cartilage. Diagnosis can be made with plain radiographs of the knee. Treatment is observation, NSAIDs, tramadol and corticosteroids for minimally symptomatic patients. Knee arthroplasty is indicated for progressive symptoms with severe degenerative disease. Epidemiology Incidence hip OA (symptomatic) login to view 1 more bullet knee OA (symptomatic) login to view 1 more bullet Risk factors modifiable login to view 6 more bullets non-modifiable login to view 6 more bullets Etiology Pathophysiology pathoanatomy login to view 20 more bullets Cell biology proteolytic enzymes login to view 15 more bullets Genetics inheritance login to view 1 more bullet genes potentially linked to OA login to view 8 more bullets Classification Kellgren & Lawrence (based on AP weightbearing XRs) Grade 0 No joint space narrowing (JSN) or reactive changes Grade 1 Possible osteophytic lipping + doubtful JSN Grade 2 Definite osteophytes + possible JSN Grade 3 Moderate osteophytes + definite JSN + some sclerosis + possible bone end deformity Grade 4 Large osteophytes + marked JSN + severe sclerosis + definite bone end deformity Presentation History identify age, functional activity, pattern of arthritic involvement, overall health and duration of symptoms Symptoms function-limiting knee pain login to view 1 more bullet pain at night or rest activity induced swelling knee stiffness mechanical login to view 1 more bullet Physical exam inspection login to view 10 more bullets range of motion login to view 2 more bullets ligament integrity Imaging Radiographs recommended views login to view 1 more bullet optional views login to view 3 more bullets findings login to view 8 more bullets Studies Histology loss of superficial chondrocytes replication and breakdown of the tidemark fissuring cartilage destruction with eburnation of subchondral bone subchondral marrow edema associated with higher intraosseus pressure than adjacent normal bone login to view 1 more bullet Treatment Nonoperative non-steroidal anti-inflammatory drugs login to view 9 more bullets tramadol login to view 7 more bullets rehabilitation, education and wellness activity login to view 8 more bullets weight loss programs login to view 6 more bullets bracing login to view 2 more bullets Radiofrequency ablation is safe and effective controversial treatments login to view 13 more bullets Operative high-tibial osteotomy login to view 6 more bullets unicompartmental arthroplasty (knee) login to view 4 more bullets total knee arthroplasty login to view 9 more bullets controversial treatments login to view 4 more bullets