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Osteoarthritis — overview

TL;DR — OA is a heterogeneous whole-joint disease and the most prevalent arthritis. GBD estimated 595 million cases in 2020 and projected large increases through 2050 (GBD 2021 OA Collaborators 2023, PMID 37675071). Symptoms and imaging often diverge because cartilage itself is aneural and pain also arises from synovium, bone, capsule, muscle and sensitized neural pathways (Dainese 2022, PMID 34968719). Exercise, weight management and appropriately selected analgesia are core treatments; injection effects depend on product and comparator (Kolasinski 2020, PMID 31908149). Joint replacement can transform severe disease but carries complication and revision risk, while the search for a therapy that improves both symptoms and structure remains ongoing (Skou 2015, PMID 26488691; Kloppenburg 2025, PMID 39755397).

Definition and diagnostic anchors

  • OA is characterized by cartilage matrix loss, subchondral-bone remodeling, osteophytes, variable synovitis and periarticular change (Bijlsma 2011, PMID 21684382).
  • Diagnosis of typical knee/hip OA is clinical—activity-related pain, short-lived stiffness, reduced movement and age/risk context—with radiographs used when presentation is atypical or surgery considered (Katz 2021, PMID 33560326).
  • Pain and structural degeneration are incompletely aligned, and conventional imaging detects relatively advanced disease (Glyn-Jones 2015, PMID 25748615).
  • OA can affect almost any joint, most often the hands, knees, hips and feet; etiologic factors vary by joint (Katz 2021, PMID 33560326; Glyn-Jones 2015, PMID 25748615).

Epidemiology and burden

GBD 2021 estimated 595 million people with OA in 2020—7.6% of the global population—and projected increases by 2050 of 74.9% for knee, 48.6% for hand, 78.6% for hip and 95.1% for other OA (GBD 2021 OA Collaborators 2023, PMID 37675071).

Hip OA prevalence estimates vary by radiographic versus symptomatic definition and geography (Fan 2023, PMID 36991481). Age, female sex, obesity, genetics and major joint injury are established risk factors for hip or knee OA (Katz 2021, PMID 33560326).

Mechanism sketch

Mechanical stress and biological susceptibility activate chondrocytes, synovial cells and subchondral bone. Catabolic enzymes degrade aggrecan and collagen; bone shape and stiffness change; synovitis fluctuates; osteophytes and capsular remodeling restrict movement (Primorac 2020, PMID 32722615).

OA genetics is polygenic and joint-specific, with loci implicating cartilage, bone development and pain pathways. Genetics informs target discovery but not routine diagnosis (Aubourg 2022, PMID 33722698).

Pain is not a direct readout of cartilage loss. Synovitis and pain have weak-to-moderate associations, while evidence for effusion, Baker cysts, cytokines and C-reactive protein is conflicting (Dainese 2022, PMID 34968719). More broadly, pain and structural degeneration are not closely related (Glyn-Jones 2015, PMID 25748615).

Treatment landscape

Core care

ACR/Arthritis Foundation strongly recommends exercise for knee/hip/hand OA and weight loss for overweight/obese knee/hip OA, alongside self-management and selected braces/aids (Kolasinski 2020, PMID 31908149). OARSI similarly centers education, structured land-based exercise and weight management while stratifying drugs by comorbidity (Bannuru 2019, PMID 31278997).

Cochrane review found exercise improves knee pain and physical function, though effects attenuate after treatment stops (Fransen 2015, PMID 26405113). In IDEA, diet plus exercise achieved greater weight loss, lower knee compressive forces and better clinical outcomes than exercise alone in overweight/obese adults (Messier 2013, PMID 24065013).

The STEP 9 trial found weekly semaglutide reduced body weight and knee-OA pain more than placebo in people with obesity, but how much benefit reflects load reduction versus other pathways and long-term structural effect remain unknown (Bliddal 2024, PMID 39476339).

Medicines

Topical diclofenac was effective and generally safer because of lower dose and systemic exposure; some oral NSAIDs produced larger average effects but more adverse-event withdrawals and may be unsuitable for long-term use or people with comorbidities (da Costa 2021, PMID 34642179). Network comparisons also found NSAIDs generally more effective than acetaminophen (Zeng 2021, PMID 34174454).

SPACE found opioid therapy was not superior to nonopioid medication for pain-related function over 12 months in chronic back or hip/knee OA pain and caused more medication-related symptoms (Krebs 2018, PMID 29509867).

Injections

Repeated intra-articular triamcinolone every 3 months for 2 years produced greater cartilage-volume loss than saline without better pain outcomes (McAlindon 2017, PMID 28510679). This does not exclude selective short-term steroid use, but argues against automatic scheduled repetition.

PRP evidence is contested. Meta-analyses have reported superiority over hyaluronic acid (Tang 2020, PMID 32912243), while the rigorous placebo-controlled RESTORE trial found no significant pain or cartilage-volume benefit at 12 months (Bennell 2021, PMID 34812863). Product heterogeneity and blinding are central.

Surgery

In severe knee OA, total knee replacement plus nonsurgical treatment produced greater 12-month improvement than nonsurgical treatment alone but more serious adverse events (Skou 2015, PMID 26488691). Unicompartmental replacement may yield faster recovery and fewer complications in eligible disease, with higher revision considerations depending on setting and volume (Wilson 2019, PMID 30792179).

Disease modification and frontier

The search for a treatment that improves both symptoms and structure remains ongoing. Lorecivivint and other Wnt, inflammatory, cartilage and bone targets illustrate the pipeline but not established care (Kloppenburg 2025, PMID 39755397; Sabha 2020, PMID 33096010; Cho 2021, PMID 34848838).

NGF blockade generated substantial analgesia but rapidly progressive OA and joint-safety concerns; pooled tanezumab analyses also evaluate peripheral-nerve safety (Brown 2023, PMID 37460782).

Biomarker reviews find many biochemical candidates but inadequate validation for diagnosis, prognosis or trial enrichment (Watt 2018, PMID 29107060; Saberi Hosnijeh 2019, PMID 30552966).

What the headline numbers mean

Question Best compact estimate Boundary of inference
How many people had OA in 2020? 595 million (95% UI 535–656m), 7.6% of the global population GBD modeled symptomatic radiographic OA and adjusted alternative definitions; it is not a census (GBD 2021 OA Collaborators 2023, PMID 37675071).
US lifetime risk of diagnosed symptomatic knee OA 13.83% overall; 9.60% in nonobese men to 23.87% in obese women; median age at diagnosis 55 years Simulation using NHIS prevalence plus the OAPol model, not a prospective cohort (Losina 2013, PMID 23203864).
US lifetime risk of symptomatic hip OA 25.3% (95% CI 21.3–29.3) by age 85 among those who survive to 85 Johnston County; similar by sex and race (Murphy 2010, PMID 20713163).
Paracetamol vs placebo, hip/knee OA pain WMD −3.7/100 (95% CI −5.5 to −1.9); high-quality evidence judged not clinically important Machado 2015, PMID 25828856. Cochrane later: pain 3.23/100 better than placebo (5.43 to 1.02 better) (Leopoldino 2019, PMID 30801133).
Arthroscopic debridement vs sham (Moseley) Knee-Specific Pain Scale at 1 year: placebo 48.9, lavage 54.8, debridement 51.7 (n=180; 165 completers) Neither lavage nor debridement beat sham (Moseley 2002, PMID 12110735).
How fast will cases grow? 2020–2050: knee +74.9%, hand +48.6%, hip +78.6%, other +95.1% Forecast conditional on demography and modeled trends (GBD 2021 OA Collaborators 2023, PMID 37675071).
How much does land exercise help knee OA? Pain +12/100 (95% CI 10–15) immediately; +6/100 (3–9) at 2–6 months after treatment Average across heterogeneous programs; maintenance depends on continued participation (Fransen 2015, PMID 26405113).
What did intensive diet plus exercise add? Versus exercise, pain difference 1.02/20 (95% CI 0.33–1.71) and function difference 4.29/68 (2.07–6.50) at 18 months Older adults with overweight/obesity and radiographic knee OA in an intensive program (Messier 2013, PMID 24065013).
Did PRP beat saline in RESTORE? Pain difference -0.4/10 (95% CI -0.9 to 0.2); cartilage-volume difference -0.2% (-1.9 to 1.5) One characterized leukocyte-poor preparation in KL 2–3 medial knee OA (Bennell 2021, PMID 34812863).
What did repeated triamcinolone do? Cartilage-thickness difference -0.11 mm (95% CI -0.20 to -0.03); pain difference -0.6/20 (-1.6 to 0.3) Injection every 12 weeks for two years; not an isolated injection (McAlindon 2017, PMID 28510679).
What is the surgery trade-off? TKR strategy improved KOOS4 by 15.8 points (95% CI 10.0–21.5) but serious adverse events were 24 vs 6 One 100-person trial in surgery-eligible moderate-to-severe knee OA (Skou 2015, PMID 26488691).

Decision architecture

Decision Evidence-informed question Next evidence layer
Is this typical OA? Look for pain, stiffness and functional limitation with supportive examination or radiographic findings; bony enlargement, painful hip internal rotation, osteophytes and joint-space narrowing are useful findings (Katz 2021, PMID 33560326). Diagnosis and classification; red flags
What is driving disability? Do not assume pain severity directly represents structural degeneration; the relationship is not close (Glyn-Jones 2015, PMID 25748615). Pain mechanisms; patient experience
Has core care been delivered? Confirm education, exercise and, when appropriate, weight loss; these are management cornerstones rather than optional preliminaries (Katz 2021, PMID 33560326). Exercise, weight and self-management
Is a medicine worth its risk? Compare pain and function benefit with adverse events, dose, duration and comorbidity; topical diclofenac has lower systemic exposure than oral therapy (da Costa 2021, PMID 34642179). Pharmacologic treatment; safety
Is an injection product-specific? Match the claim to the tested preparation and comparator: three injections of one leukocyte-poor PRP product did not beat saline for pain or cartilage volume at 12 months (Bennell 2021, PMID 34812863). Injections and orthobiologics
Is surgery appropriate now? In surgery-eligible moderate-to-severe knee OA, replacement improved pain and function more than nonsurgical care at 12 months but produced more serious adverse events (Skou 2015, PMID 26488691). Surgery and joint replacement
Is a biomarker actionable? Treat biomarkers as candidates under validation and qualification; clinically applicable OA biomarkers were still described as needed (Watt 2018, PMID 29107060). Biomarkers and imaging markers

Joint-specific map

Site Distinctive issues Primary page
Knee Bony enlargement and radiographic osteophytes or joint-space narrowing support diagnosis; partial and total replacement have different outcome and revision profiles (Katz 2021, PMID 33560326; Wilson 2019, PMID 30792179). Knee OA
Hip Pain with internal hip rotation is diagnostically useful, and total joint replacement can relieve pain in advanced symptomatic structural disease (Katz 2021, PMID 33560326). Hip OA
Hand The ACR/AF guideline makes site-specific recommendations, including first-CMC orthoses and conditional recommendations for several hand therapies (Kolasinski 2020, PMID 31908149). Diagnosis and classification; guidelines
Multi-joint Published generalized-OA definitions are inconsistent; a systematic review found at least 15 definitions and recommended descriptive “multi-joint” or “polyarticular” terminology (Nelson 2014, PMID 24461078). Epidemiology and burden; genetics and risk factors

Controversies the overview should not smooth over

  • Paracetamol first-line vs not-routine. ACR/AF still lists acetaminophen as a conditional option (Kolasinski 2020, PMID 31908149). NICE NG226 says do not routinely offer paracetamol; Machado found a −3.7/100 pain effect that did not meet a clinical-importance threshold (Machado 2015, PMID 25828856; NICE NG226, accessed 2026-08-31).
  • Hyaluronan and PRP. Network and product-heterogeneous meta-analyses can look favorable (Tang 2020, PMID 32912243). Large placebo-controlled syntheses and RESTORE do not: viscosupplementation pain SMD −0.08 in 24 large trials (Pereira 2022, PMID 36333100); RESTORE pain difference −0.4/10 (Bennell 2021, PMID 34812863). NICE does not offer hyaluronan; ACR/AF recommends against routine knee hyaluronate and against PRP (Kolasinski 2020, PMID 31908149).
  • Arthroscopy for OA or degenerative meniscus. Moseley (sham), Kirkley (optimized nonsurgical care), Sihvonen (sham meniscectomy in non-OA degenerative tear), Katz MeTeOR (ITT difference 2.4 WOMAC function points, 95% CI −1.8 to 6.5, with 30% PT-to-surgery crossover) and Kise (KOOS4 difference 0.9, −4.3 to 6.1) converge on no added benefit over sham or exercise (Moseley 2002, PMID 12110735; Kirkley 2008, PMID 18784099; Sihvonen 2013, PMID 24369076; Katz 2013, PMID 23506518; Kise 2016, PMID 27440192). NICE: do not offer arthroscopic lavage or debridement (NG226, accessed 2026-08-31).
  • THR vs resistance training. In surgery-eligible severe hip OA, THR improved Oxford Hip Score by 11.4 points more than resistance training at 6 months (95% CI 8.9–14.0); 21% of the training arm crossed over (Frydendal 2024, PMID 39476341). This does not license bypassing core care; it quantifies the incremental surgical benefit when core care has already failed to the point of a surgical indication.
  • DMOAD structure–symptom split. Sprifermin 100 µg every 6 months increased 2-year femorotibial cartilage thickness by 0.05 mm (95% CI 0.03–0.07) without a significant WOMAC difference (Hochberg 2019, PMID 31593273). Lorecivivint phase 3 OA-11 missed Pain NRS at week 12 (LOR −2.24 vs placebo −2.49; p=0.185) (Yazici 2025, PMID 39808286). Structure change without symptoms, or symptom change without structure, is the current pipeline pattern, not a rounding error.

Audit disposition

Check Result
PubMed identifiers 42/42 unique PMIDs resolved in the 2026-08-31 independent live E-utilities fetch
ClinicalTrials.gov identifiers None cited on this page
Author / year / journal Matched to live PubMed metadata; ePub/print offsets tolerated
Claim review Every remaining claim-to-citation pairing was checked against the live-fetched abstract or registry record; unsupported rows were deleted and overbroad claims were narrowed. No substantive citation issue remains.
## Open questions
  • Can OA phenotypes predict pain source and treatment response? (Dainese 2022, PMID 34968719; Dell'Isola 2016, PMID 27733199)
  • Does ≥10–15% intentional weight loss alter MRI structure independently of symptoms? IDEA and STEP 9 still do not close this (Messier 2013, PMID 24065013; Bliddal 2024, PMID 39476339).
  • Which injection products have benefits beyond placebo under rigorous blinding? RESTORE is a negative high-quality null; product-heterogeneous meta-analyses remain the opposing literature (Bennell 2021, PMID 34812863; Tang 2020, PMID 32912243).
  • Can a DMOAD improve both structure and outcomes patients value? Sprifermin changed cartilage thickness without WOMAC; lorecivivint phase 3 missed pain (Hochberg 2019, PMID 31593273; Yazici 2025, PMID 39808286).
  • Would common absolute-benefit thresholds reconcile ACR, OARSI, NICE and AAOS on hyaluronate, PRP, acupuncture and braces? (Kolasinski 2020, PMID 31908149; Bannuru 2019, PMID 31278997)

References

  1. Bijlsma JW, et al. Osteoarthritis: an update for clinical practice. Lancet. 2011. PMID 21684382
  2. GBD 2021 Osteoarthritis Collaborators. Global burden of OA, 1990–2020 and projections to 2050. Lancet Rheumatol. 2023. PMID 37675071
  3. Fan Z, et al. Prevalence of hip OA. Arthritis Res Ther. 2023. PMID 36991481
  4. Primorac D, et al. Knee OA pathogenesis and nonoperative treatment. Genes. 2020. PMID 32722615
  5. Aubourg G, et al. Genetics of osteoarthritis. Osteoarthritis Cartilage. 2022. PMID 33722698
  6. Dainese P, et al. Knee inflammation and pain in OA. Knee Surg Sports Traumatol Arthrosc. 2022. PMID 34968719
  7. Katz JN, et al. Diagnosis and treatment of hip and knee OA. JAMA. 2021. PMID 33560326
  8. Kolasinski SL, et al. 2019 ACR/AF OA guideline. Arthritis Care Res. 2020. PMID 31908149
  9. Bannuru RR, et al. OARSI nonsurgical OA guidelines. Osteoarthritis Cartilage. 2019. PMID 31278997
  10. Fransen M, et al. Exercise for knee OA. Cochrane Database Syst Rev. 2015. PMID 26405113
  11. Messier SP, et al. IDEA diet-and-exercise trial. JAMA. 2013. PMID 24065013
  12. Bliddal H, et al. Weekly semaglutide in obesity and knee OA. N Engl J Med. 2024. PMID 39476339
  13. Zeng C, et al. Acetaminophen and NSAID comparisons in knee OA. Br J Sports Med. 2021. PMID 34174454
  14. da Costa BR, et al. NSAIDs and opioids in knee/hip OA. BMJ. 2021. PMID 34642179
  15. Krebs EE, et al. SPACE opioid versus nonopioid trial. JAMA. 2018. PMID 29509867
  16. McAlindon TE, et al. Intra-articular triamcinolone, cartilage and pain. JAMA. 2017. PMID 28510679
  17. Tang JZ, et al. PRP versus hyaluronic acid meta-analysis. J Orthop Surg Res. 2020. PMID 32912243
  18. Bennell KL, et al. RESTORE PRP versus placebo trial. JAMA. 2021. PMID 34812863
  19. Skou ST, et al. Randomized trial of total knee replacement. N Engl J Med. 2015. PMID 26488691
  20. Wilson HA, et al. Unicompartmental versus total knee replacement. BMJ. 2019. PMID 30792179
  21. Cho Y, et al. Disease-modifying strategies in OA. Cells. 2021. PMID 34848838
  22. Sabha M, et al. Lorecivivint as a potential DMOAD. Curr Rheumatol Rep. 2020. PMID 33096010
  23. Brown MT, et al. Peripheral-nerve safety of tanezumab. J Pain Res. 2023. PMID 37460782
  24. Watt FE, et al. OA biomarkers: year in review. Osteoarthritis Cartilage. 2018. PMID 29107060
  25. Saberi Hosnijeh F, et al. OA biochemical biomarkers. Osteoarthritis Cartilage. 2019. PMID 30552966
  26. Glyn-Jones S, et al. Osteoarthritis. Lancet. 2015;386:376-387. PMID 25748615
  27. Nelson AE, et al. “Generalized osteoarthritis”: a systematic review. Semin Arthritis Rheum. 2014;43:713-720. PMID 24461078
  28. Losina E, et al. Lifetime risk and age at diagnosis of symptomatic knee osteoarthritis in the US. Arthritis Care Res (Hoboken). 2013;65:703-711. PMID 23203864
  29. Murphy LB, et al. One in four people may develop symptomatic hip osteoarthritis in his or her lifetime. Osteoarthritis Cartilage. 2010;18:1372-1379. PMID 20713163
  30. Machado GC, et al. Efficacy and safety of paracetamol for spinal pain and osteoarthritis. BMJ. 2015;350:h1225. PMID 25828856
  31. Leopoldino AO, et al. Paracetamol versus placebo for knee and hip osteoarthritis. Cochrane Database Syst Rev. 2019;2:CD013273. PMID 30801133
  32. Moseley JB, et al. A controlled trial of arthroscopic surgery for osteoarthritis of the knee. N Engl J Med. 2002;347:81-88. PMID 12110735
  33. Kirkley A, et al. A randomized trial of arthroscopic surgery for osteoarthritis of the knee. N Engl J Med. 2008;359:1097-1107. PMID 18784099
  34. Katz JN, et al. Surgery versus physical therapy for a meniscal tear and osteoarthritis. N Engl J Med. 2013;368:1675-1684. PMID 23506518
  35. Kise NJ, et al. Exercise therapy versus arthroscopic partial meniscectomy for degenerative meniscal tear. BMJ. 2016;354:i3740. PMID 27440192
  36. Frydendal T, et al. Total hip replacement or resistance training for severe hip osteoarthritis. N Engl J Med. 2024;391:1610-1620. PMID 39476341
  37. Hochberg MC, et al. Intra-articular sprifermin vs placebo on femorotibial joint cartilage thickness: FORWARD. JAMA. 2019;322:1360-1370. PMID 31593273
  38. Yazici Y, et al. Phase 3 OA-11 lorecivivint in moderate to severe knee osteoarthritis. Clin Exp Rheumatol. 2025;43:854-860. PMID 39808286
  39. Pereira TV, et al. Viscosupplementation for knee osteoarthritis: systematic review and meta-analysis. BMJ. 2022;378:e069722. PMID 36333100
  40. Dell'Isola A, et al. Identification of clinical phenotypes in knee osteoarthritis. BMC Musculoskelet Disord. 2016;17:425. PMID 27733199
  41. Kloppenburg M, Namane M, Cicuttini F. Osteoarthritis. Lancet. 2025;405:71-85. PMID 39755397
  42. Sihvonen R, Paavola M, Malmivaara A, et al. Arthroscopic partial meniscectomy versus sham surgery for a degenerative meniscal tear. N Engl J Med. 2013;369:2515-2524. PMID 24369076