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 central (abdominal) obesity, dyslipidemia (high triglycerides and low-density lipoproteins), high blood pressure, and elevated fasting glucose levels. non-modifiable gender females >males increased age genetics race African American males are the least likely to receive total joint replacement when compared to whites and Hispanics Etiology Pathophysiology pathoanatomy articular cartilage increased water content alterations in proteoglycans eventual decrease in amount of proteoglycans collagen abnormalities organization and orientation are lost binding of proteoglycans to hyaluronic acid synovium and capsule early phase of OA mild inflammatory changes in synovium middle phase of OA moderate inflammatory changes of synovium synovium becomes hypervascular late phases of OA synovium becomes increasingly thick and vascular bone subchondral bone attempts to remodel forming lytic lesion with sclerotic edges (different than bone cysts in RA) bone cysts form in late stages osteophytes form through the pathologic activation of endochondral ossification mediated by the Indian hedgehog (Ihh) signaling molecule Cell biology proteolytic enzymes matrix metalloproteases (MMPs) responsible for cartilage matrix digestion examples stromelysin plasmin aggrecanase-1 (ADAMTS-4) tissue inhibitors of MMPS (TIMPs) control MMP activity preventing excessive degradation imbalance between MMPs and TIMPs has been demonstrated in OA tissues inflammatory cytokines secreted by synoviocytes and increase MMP synthesis examples IL-1 IL-6 TNF-alpha Genetics inheritance non-mendilian genes potentially linked to OA vitamin D receptor estrogen receptor 1 inflammatory cytokines IL-1 leads to catabolic effect IL-4 matrilin-3 BMP-2, BMP-5 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 often an increased adductor moment to the limb during gait antalgic gait associated with knee arthritis knee is maintained in flexion shortened stride length compensatory toe walking 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 sunrise view PA view in 30 degrees of flexion findings pattern of arthritic involvement medial and/or lateral tibiofemoral, and/or patellofemoral characteristics joint space narrowing osteophytes eburnation of bone subchondral sclerosis subchondral cysts Studies Histology loss of superficial chondrocytes replication and breakdown of the tidemark fissuring cartilage destruction with eburnation of subchondral bone Treatment Nonoperative non-steroidal anti-inflammatory drugs indications first line treatment for all patients with symptomatic arthritis technique Non-steroidal anti-inflammatory drugs (first choice) topical and oral NSAIDS recommended selection should be based on physician preference, patient acceptability and cost duration of treatment based on effectiveness, side-effects and past medical history outcomes AAOS guidelines: strong evidence for tramadol indications treatment option for patients with symptomatic arthritis technique weak opioid mu receptor agonist good evidence for mid term (8-13 weeks) improvement in pain and stiffness over placebo outcomes Prior AAOS guidelines recommended its use, but newer guidelines do NOT recommend its routine use rehabilitation, education and wellness activity indications first line treatment for all patients with symptomatic arthritis technique self-management and education programs combination of supervised exercises and home program have shown the best results these benefits lost after 6 months if exercises are stopped outcomes AAOS guidelines strong evidence for weight loss programs indications patients with symptomatic arthritis and BMI > 25 technique diet and low-impact aerobic exercise outcomes AAOS guidelines: moderate evidence for bracing medial unloader for isolated medial compartment OA AAOS guidelines: moderate evidence for Radiofrequency ablation is safe and effective controversial treatments acupuncture AAOS guidelines: strong evidence against viscoelastic joint injections AAOS guidelines: strong evidence against glucosamine and chondroitin AAOS guidelines: strong evidence against needle lavage AAOS guidelines: moderate evidence against lateral wedge insoles AAOS guidelines: moderate evidence against Orthobiologics (BMAC, PRP, etc.) Bone marrow aspirate concentrate has higher concentration of IL-1ra than both leukocyte poor and rich PRP PRP has better outcomes than Hyaluronic Acid Operative high-tibial osteotomy indications younger patients with medial unicompartmental OA technique valgus producing proximal tibial oseotomy outcomes AAOS guidelines: limited evidence for unicompartmental arthroplasty (knee) indications isolated unicompartmental disease outcomes TKA have lower revision rates than UKA in the setting of unicompartmental OA total knee arthroplasty indications symptomatic knee osteoarthritis failed non-operative treatments techniques cruciate retaining vs. crucitate sacrificing implants show no difference in outcomes patellar resurfacing no difference in pain or function with or without patella resurfacing lower reoperation rates with resurfacing drains are not recommended controversial treatments arthroscopic debridement or lavage AAOS guidelines: strong evidence against arthroscopic meniscal debridement AAOS guidelines: inconclusive evidence