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) 88 per 100,000 per year knee OA (symptomatic) 240 per 100,000 per year Risk factors modifiable articular trauma occupation, repetitive knee bending muscle weakness large body mass metabolic syndrome login to view 1 more bullet non-modifiable gender login to view 1 more bullet increased age genetics race login to view 1 more bullet Etiology Pathophysiology pathoanatomy articular cartilage login to view 6 more bullets synovium and capsule login to view 7 more bullets bone login to view 4 more bullets Cell biology proteolytic enzymes matrix metalloproteases (MMPs) login to view 5 more bullets tissue inhibitors of MMPS (TIMPs) login to view 2 more bullets inflammatory cytokines login to view 5 more bullets Genetics inheritance non-mendilian genes potentially linked to OA vitamin D receptor estrogen receptor 1 inflammatory cytokines login to view 5 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 effect on walking distances pain at night or rest activity induced swelling knee stiffness mechanical instability, locking, catching sensation Physical exam inspection body habitus gait login to view 5 more bullets limb alignment effusion skin (e.g. scars) range of motion lack of full extension (>5 degrees flexion contracture) lack of full flexion (flexion <110 degrees) ligament integrity Imaging Radiographs recommended views weight-bearing views of affected joint optional views knee login to view 2 more bullets findings pattern of arthritic involvement login to view 1 more bullet characteristics login to view 5 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 approximately 97% higher than normal with reduced perfusion Treatment Nonoperative non-steroidal anti-inflammatory drugs indications login to view 1 more bullet technique login to view 4 more bullets outcomes login to view 1 more bullet tramadol indications login to view 1 more bullet technique login to view 2 more bullets outcomes login to view 1 more bullet rehabilitation, education and wellness activity indications login to view 1 more bullet technique login to view 3 more bullets outcomes login to view 1 more bullet weight loss programs indications login to view 1 more bullet technique login to view 1 more bullet outcomes login to view 1 more bullet bracing medial unloader for isolated medial compartment OA AAOS guidelines: moderate evidence for Radiofrequency ablation is safe and effective controversial treatments acupuncture login to view 1 more bullet viscoelastic joint injections login to view 1 more bullet glucosamine and chondroitin login to view 1 more bullet needle lavage login to view 1 more bullet lateral wedge insoles login to view 1 more bullet Orthobiologics (BMAC, PRP, etc.) login to view 2 more bullets Operative high-tibial osteotomy indications login to view 1 more bullet technique login to view 1 more bullet outcomes login to view 1 more bullet unicompartmental arthroplasty (knee) indications login to view 1 more bullet outcomes login to view 1 more bullet total knee arthroplasty indications login to view 2 more bullets techniques login to view 5 more bullets controversial treatments arthroscopic debridement or lavage login to view 1 more bullet arthroscopic meniscal debridement login to view 1 more bullet