Trends in incidence and prevalence of osteoarthritis in the United Kingdom: findings from the Clinical Practice Research Datalink (CPRD)

Open AccessPublished:March 14, 2020DOI:https://doi.org/10.1016/j.joca.2020.03.004

      Summary

      Objective

      This study aimed to explore the incidence and prevalence of OA in the UK in 2017 and their trends from 1997 to 2017 using a large nationally representative primary care database.

      Design

      The UK Clinical Practice Research Datalink (CPRD) comprising data on nearly 17.5 million patients was used for the study. The incidence and prevalence of general practitioner diagnosed OA over a 20 years period (1997–2017) were estimated and age-sex and length of data contribution standardized using the 2017 CPRD population structure. Cohort effects were examined through Age-period-cohort analysis.

      Results

      During 1997–2017, there were 494,716 incident OA cases aged ≥20 years. The standardised incidence of any OA in 2017 was 6.8 per 1000 person-years (95% CI 6.7 to 6.9) and prevalence was 10.7% (95% CI 10.7–10.8%). Both incidence and prevalence were higher in women than men. The incidence of any-OA decreased gradually in the past 20 years at an annual rate of −1.6% (95%CI -2.0 to −1.1%), and the reduction speeded up for people born after 1960. The prevalence of any-OA increased gradually at an annual rate of 1.4% (95% CI 1.3–1.6%). Although the prevalence was highest in Scotland and Northern Ireland, incidence was highest in the East Midlands. Both incidence and prevalence reported highest in the knee followed by hip, wrist/hand and ankle/foot.

      Conclusion

      In the UK approximately one in 10 adults have symptomatic clinically diagnosed OA, the knee being the commonest. While prevalence has increased and become static after 2008, incidence is slowly declining. Further research is required to understand these changes.

      Keywords

      Introduction

      Osteoarthritis (OA) is one of the commonest long-term conditions, causing significant impairment of physical function. It can affect several joints which may further compound functional impairment and participation restriction. In the absence of any cure, the burden of OA is increasing globally with an estimated 28% of the older population (>60 years) having OA
      • Symmons D.
      • Mathers C.
      • Pfleger B.
      . The 2017 Global Burden of Disease (GBD) report ranked hip and knee OA as the 11th highest contributor to global disability and the 23rd highest cause of disability adjusted life years (DALYs)
      • James S.L.
      • Abate D.
      • Abate K.H.
      • Abay S.M.
      • Abbafati C.
      • Abbasi N.
      • et al.
      Global, regional, and national incidence, prevalence, and years lived with disability for 354 diseases and injuries for 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017.
      . Increasing life expectancy and the ageing population are expected to make OA the fourth leading cause of disability by 2020
      • Woolf A.D.
      • Pfleger B.
      Burden of major musculoskeletal conditions.
      and a significant increase in DALYs has already been noted from 2007 to 2017.
      • James S.L.
      • Abate D.
      • Abate K.H.
      • Abay S.M.
      • Abbafati C.
      • Abbasi N.
      • et al.
      Global, regional, and national incidence, prevalence, and years lived with disability for 354 diseases and injuries for 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017.
      Whilst DALYs provide useful data on disease burden, accurate information on changing incidence and prevalence of a disease provides an alternative picture to help guide effective preventive and management planning. To date, very few studies have examined trends of OA incidence and prevalence using national representative cohort data. The lack of such information creates challenges in reliable estimation of the burden of OA. Worldwide, the estimated incidence of OA has varied from a low of 14.6 per 1000 person-years in Canada
      • Rahman M.M.
      • Cibere J.
      • Goldsmith C.H.
      • Anis A.H.
      • Kopec J.A.
      Osteoarthritis incidence and trends in administrative health records from British columbia, Canada.
      to a high of 40.5 per 1000 person-years in the UK
      • Yu D.
      • Jordan K.P.
      • Bedson J.
      • Englund M.
      • Blyth F.
      • Turkiewicz A.
      • et al.
      Population trends in the incidence and initial management of osteoarthritis: age-period-cohort analysis of the Clinical Practice Research datalink, 1992–2013.
      . Only three countries have reported increasing trends of the incidence of OA, whereas none has published prevalence trend data. In Sweden, age-standardized hospitalization rates due to hip and knee OA increased from 1998 to 2014
      • Kiadaliri A.A.
      • Rinaldi G.
      • Lohmander L.S.
      • Petersson I.F.
      • Englund M.
      Temporal trend and regional disparity in osteoarthritis hospitalisations in Sweden 1998–2015.
      and in Canada crude incidence rates increased during 2000–2008 from 11.8 to 14.2 per 1000 person-years in men, and from 15.7 to 18.5 person-years in women
      • Rahman M.M.
      • Cibere J.
      • Goldsmith C.H.
      • Anis A.H.
      • Kopec J.A.
      Osteoarthritis incidence and trends in administrative health records from British columbia, Canada.
      . However, one UK study using the Clinical Practice Research Datalink (CPRD) reported no change in trends of incidence of physician-diagnosed OA (1992–2013)
      • Yu D.
      • Jordan K.P.
      • Bedson J.
      • Englund M.
      • Blyth F.
      • Turkiewicz A.
      • et al.
      Population trends in the incidence and initial management of osteoarthritis: age-period-cohort analysis of the Clinical Practice Research datalink, 1992–2013.
      . Seven years of consultation data till 2010 reveals nearly 8.75 million people in the UK had visited any health facility for treatment of OA, and by 2035, 8.3 million people in the UK aged 45 years or over could have symptomatic knee OA.
      Primary care is the usual first point of contact for someone with symptomatic OA. The UK CPRD is a primary care database that represents the community burden in better ways than hospital (secondary care) records and allows evaluation of the trends of incidence and prevalence over time. However, these estimates depend on the nature of consultation, the coding system and other individual factors. While the incidence measures the aetiological impact of OA, the prevalence measures the disease burden to inform health resource requirements. Although there have been some incidence and prevalence studies from the UK
      • Yu D.
      • Jordan K.P.
      • Bedson J.
      • Englund M.
      • Blyth F.
      • Turkiewicz A.
      • et al.
      Population trends in the incidence and initial management of osteoarthritis: age-period-cohort analysis of the Clinical Practice Research datalink, 1992–2013.
      ,
      • Prieto-Alhambra D.
      • Judge A.
      • Javaid M.K.
      • Cooper C.
      • Diez-Perez A.
      • Arden N.K.
      Incidence and risk factors for clinically diagnosed knee, hip and hand osteoarthritis: influences of age, gender and osteoarthritis affecting other joints.
      ,
      • Jordan K.P.
      • Jöud A.
      • Bergknut C.
      • Croft P.
      • Edwards J.J.
      • Peat G.
      • et al.
      International comparisons of the consultation prevalence of musculoskeletal conditions using population-based healthcare data from England and Sweden.
      , they have given inconsistent results through use of different definitions and sampling methods. Therefore, the recent trend and natural history of OA in UK primary care remains largely unknown.
      This study aimed to explore both the incidence and prevalence of OA (overall and joint specific) in the UK during the period 2017 and their trends during 1997–2017 using a large nationally representative primary care database.

      Methods

      This was a descriptive study using longitudinal primary care database of the UK.

       Source population

      The CPRD is a large database of general practice electronic medical records that is generalisable to the wider UK population. As of 31st December 2017, the CPRD contained data on 17,480,766 individuals from 736 general practices. Recording of ailment is mandatory for every visit and there is no limit on the number of diagnoses entered. The database contains information on symptoms, diagnoses, prescriptions, referrals, tests, immunisations, life style factors, information on medical staff, health promotion activities, management and quality outcome framework indicators
      • Herrett E.
      • Gallagher A.M.
      • Bhaskaran K.
      • Forbes H.
      • Mathur R.
      • van Staa T.
      • et al.
      Data Resource Profile: Clinical Practice Research Datalink (CPRD).
      . Substantial research has been undertaken to examine the validity and completeness of the CPRD and has provided satisfactory results
      • Khan N.F.
      • Harrison S.E.
      • Rose P.W.
      . More details about the database can be found at https://cprd.com/primary-care. This study was approved by the independent scientific advisory committee for CPRD research (protocol reference: 19_030 R). No further ethical permissions were required for the analyses of these anonymized patient level data.

       Study population

      CPRD data available for patients registered from 1st January 1997 until 31st December 2017 was used for the study. Inclusion criteria were individual records with: (1) people aged 20 years or more during each study year of 1997–2017; (2) active registration for at least 12 months with the up-to-standard practice prior to the study start date (determined by CPRD database standards); and (3) data quality flagged as ‘acceptable’ in the database.

       Case definition of OA

      Incident OA was defined as the first diagnosis of OA within each study year. Prevalent OA was defined as having an OA diagnosis by 1st July of each study year. We used Read codes: a medical coding system of clinical terms used by national health services (NHS), UK
      • Booth N.
      What are the Read Codes? Health Libr Rev (II).
      . The available Read code list (www.keele.ac.uk/mrr) to identify people with a General Practitioners (GP) diagnosed OA was adapted according to our inclusion and exclusion criteria. We used the exact list but excluded two OAs (acromio-clavicular and sterno-clavicular joints), because of the possible low accuracy of diagnosis at these joints and the expected incidence is very low. The codes obtained from the given website was previously matched with ICD-10 codes (Musculoskeletal disorder chapter)
      • Jordan K.P.
      • Jöud A.
      • Bergknut C.
      • Croft P.
      • Edwards J.J.
      • Peat G.
      • et al.
      International comparisons of the consultation prevalence of musculoskeletal conditions using population-based healthcare data from England and Sweden.
      . Even though not all OA joint codes have been validated, a recently published article shows the positive predictive value (PPV) for Read codes for hip OA in people aged 60 and over was nearly 80% and suitable for research purposes
      • Ferguson R.J.
      • Prieto-Alhambra D.
      • Walker C.
      • Yu D.
      • Valderas J.M.
      • Judge A.
      • et al.
      Validation of hip osteoarthritis diagnosis recording in the UK clinical practice research datalink.
      . The Read codes for OA (N05…) used in the study was further screened by two independent GPs before the use (Appendix 1).
      The index date was defined as the date of the first diagnosis of OA recorded in the database. Patients meeting the following criteria were excluded from both incidence and prevalence estimation: (1) any recording of joint diseases (rheumatoid arthritis, psoriatic arthritis, systemic lupus erythematosus, ankylosing spondylitis, septic arthritis, spondyloarthropathy or crystal disease and human parvovirus B19 infection) before or within 3 years after the index date; (2) any record of specific non-OA diagnosis (soft-tissue disorders, other bone/cartilage diseases) at the same joint in the 12 months before or after the recorded OA consultation; and (3) any history of joint injury within 1 year prior to the index date. In the absence of a recording of OA during the study year, any recording of joint replacement was taken as a proxy measure of OA.

       Estimation of incidence and prevalence

      The annual incidence rate for OA was defined as the number of incident (new) OA cases between 1st January and 31st December, divided by the number of person-years at risk for each calendar year from 1997 to 2017. Person-years of follow-up were calculated for eligible people at risk (i.e., no previous diagnosis of OA) from the latest of 1st January to the earliest date of transfer-out, last data collection, incident diagnosis of OA, death or 31st December of the study year. The annual prevalence of OA was calculated by dividing the number of people ever diagnosed with OA at 1st July of each calendar year, by the total number of eligible people in the population at the same time point of the calendar year.

       Statistical analysis

      The incidence and prevalence for each year from 1997 to 2017 were standardised according to age (5 years band), sex and length of data contribution (observation period) using the CPRD population structure in the year 2017 as reference. This method of adjustment for the observation period has been used previously
      • Kuo C.-F.
      • Grainge M.J.
      • Mallen C.
      • Zhang W.
      • Doherty M.
      Rising burden of gout in the UK but continuing suboptimal management: a nationwide population study.
      . The length of data contribution of each patient was defined as the period from the up to standard date for participants to 1st July of each calendar year for prevalence and 1st January of each calendar year for incidence. Up to standard date is always later the registration date. The length of data contribution was then categorised in four groups 0–3 years, 4–6 years, 7–9 years and ≥ 10 years. Standardization by length of data contribution was done because higher estimates were observed for longer lengths of data contribution (Supplementary fig S1). For 1997, no data contribution was seen for ≥ 10 years (Supplementary Figs. S1 and S2). Because, even though the first registration date with the database was traced back before 1987, the up to standard practice data started recording in 1988, which is acceptable as a quality data, as per CPRD. For sex specific estimation, only age and length of data contribution standardisation was done. Age-sex standardized incidence and prevalence of OA in 2014 were calculated for all 13 regions of the UK and plotted using choropleth maps in QGIS software (V.3, Open source)
      QGIS Geographic Information System
      Open Source Geospatial Foundation Project.
      . The prevalence and incidence for the UK region after 2014 could not be estimated adequately because of lack of information from the East Midlands region from 2015 onwards.
      Age-sex and length of data standardized trends (overall and sex specific) of the incidence and prevalence of OA were calculated for any-OA, joint specific and unspecified OA for 1998–2017. Unspecified OA cases are coded as ‘unspecified’ in the database without any mentioning of the site involved. We computed the incidence and prevalence across each age group for both sexes only for the year 2017. The 95% confidence interval (CIs) were derived based on the assumption of a Poisson distribution for the observed cases. The trends were tested using Joinpoint regression analysis
      • Kim H.-J.
      • Fay M.P.
      • Feuer E.J.
      • Midthune D.N.
      Permutation tests for joinpoint regression with applications to cancer rates.
      with Joinpoint software (Version 4.6.0.0)
      . Bayesian Information Criterion (BIC) was used to identify the ‘join points’, which describes the significant change across the trend line and best-fit data series. Using BIC, a maximum of three joinpoints were selected. Annual percentage changes (AAPC) for each segment and average AAPC for the entire study period were calculated at the significance level of 0.05 using the empirical model
      • Clegg L.X.
      • Hankey B.F.
      • Tiwari R.
      • Feuer E.J.
      • Edwards B.K.
      Estimating average annual percent change in trend analysis.
      . Additional, trend analysis of joint pain incidence was done using the same database. Details are provided in Supplementary Fig. S8.
      Both incidence and prevalence trends were modelled as a function of age at diagnosis, period (year of diagnosis) and birth (year of birth) cohort. To assess the cohort effect, age-period-cohort (A-P-C) analysis was undertaken
      • Keyes K.M.
      • Utz R.L.
      • Robinson W.
      • Li G.
      What is a cohort effect? Comparison of three statistical methods for modeling cohort effects in obesity prevalence in the United States, 1971–2006.
      . For visual clarity incidence and prevalence were aggregated in 5-year age groups for period and birth cohort graphs. The A-P-C analysis was performed in R using the package ‘Epi’ and ‘APC’
      • Carstensen B.
      • Plummer M.
      • Laara E.
      • Hills M.
      Epi package for epidemiological analysis in R.
      • Carstensen B.
      Demography and epidemiology: age-Period-Cohort models in the computer age.
      • Nielsen B.
      Apc: an R package for age-period-cohort analysis.
      . Statistical analyses were performed using STATA (SE v 15, STATA corp, Texas) and R(V 5.2, R software, Austria).
      ,
      • StataCorp
      Stata Statistical Software: Release 12.

      Results

       Incidence and prevalence

      In 2017, the total person-years of follow up for any-OA was 1,495,497 with 10,147 incident OA cases, and the incidence was 6.8 per 1000 person-years (95% CI 6.7 to 6.9 per 1000 person-years). The incidence was higher in women (8.1; 95% CI 7.9 to 8.3) than in men (5.5; 95% CI 5.3 to 5.7 per 1000 person-years). The age-specific incidence in 2017 shows that OA was very rare in people less than 30 years of age. The incidence was 0.08 per 1000 person-years in both sexes which increased gradually with age and peaked at 75–79 years at 27 per 1000 person-years (95% CI 23.5 to 29.8 per 1000 person-years) in women and 18 per 1000 person-years (95% CI 15.4 to 20.6 per 1000 person-years) in men [Fig. 1(A)].
      Fig. 1
      Fig. 1Age specific incidence (A) and prevalence (B) of OA in 2017.
      Of 1,690,618 eligible individuals in 2017, 181,464 had a recorded diagnosis of any-OA. The prevalence in 2017 was 10.8% (95% CI: 10.7–10.9%) which was higher in women (12.8%; 95% CI 12.8–12.9%) than men (8.6%; 95% CI 8.5–8.7%) across all age groups. The prevalence increased sharply at age 40–44 years in women and 45–49 years in men. In both men and women, the increasing trend continued until age group of >80 years, reaching the peak of 47% for women and 35% for men [Fig. 1(B)].
      The joint-specific OA incidence (per 1000 person-years) in 2017 was highest for knee (2.3; 95% CI 2.2 to 2.4) followed by hip (1.1; 95% CI 1.1 to 1.2), wrist and hand (0.65; 95% CI 0.6 to 0.7) and ankle and foot (0.2; 95% CI 0.2 to 0.2). The incidence of unspecified OA was 5.2 per 1000 person-years (95% CI 5.1 to 5.3). All joint-specific incidence rates were higher in women than in men. The detailed distribution across age in both men and women is given in Supplementary Fig. S3. In descending order, the overall prevalence according to joint site in 2017 was; knee (2.9%, 95% CI 2.7–2.9%), hip (1.5%, 95%CI 1.4–1.5%), wrist or hand (0.5%, 95%CI 0.5–0.5%) and ankle or foot (0.3%, 95% CI 0.3–0.3%). The prevalence of unspecified OA was 7.6% (95%CI 7.5–7.6%). The distribution of joint site and unspecified OA across the sex is provided in Supplementary Fig. S4.

       Temporal trends of incidence and prevalence

      The incidence (both crude and standardised) of any OA decreased over time during the study period, changing from 9.5 per 1000 person-years (95% CI 9.4 to 9.7 per 1000 person-years) to 6.8 per 1000 person-years (95% CI 6.7 to 6.9 per 1000 person-years) (Table I). Similar trends were seen in both women and men [Fig. 2(A)]. The incidence of OA in men declined from 8.0 per 1000 person-years (95% CI 7.8 to 8.3 per 1000 person-years) in 1997 to 5.5 per 1000 person-years (95% CI 5.3 to 5.7 per 1000 person-years) in 2017, whereas in women the incidence reduced from 11.5 per 1000 person-years (95% CI 11.2 to 11.7 per 1000 person-years) to 8.1 per 1000 person-years (95%CI 7.9 to 8.3 per 1000 person-years). Joinpoint analysis identified two points of changes in overall trend at 2002 and 2005. The AAPC was −1.6% (95% CI -2.0 to −1.1%), indicating a slight decline in the incidence since 1998. Women (−1.9.1%; 95% CI -2.2 to −1.6%) had a higher decline in rates compared to men (−1.5%; −1.1 to −1.9%). No change in trend was observed for ankle and foot and wrist and hand sites. Whereas, unspecified OA trend was on decline, while OA at knee and hip showed slightly increasing trend. Details of joint specific incidence trends are given in Supplementary Fig. S5 and sex wise distribution is given in supplementary table S1.
      Table ICrude and standardized incidence and prevalence of OA in the UK from 1997 to 2017
      YearIncidence (per 1000 person-years)Prevalence (%)
      Person-YearCasesCrude Incidence [95% CI]Age-sex standardized [95% CI]Age-sex-LOD standardized [95% CI]Eligible populationCasesCrude

      Prevalence [95% CI]
      Age-sex standardized [95% CI]Age-sex-LOD standardized [95% CI]
      19971,321,48712,2969.30 [9.14–9.47]9.17 [9.00–9.34]5,711,501195,3623.42 [3.40–3.44]6.15 [6.11–6.19]
      19981,509,15914,8179.81 [9.66–9.97]9.05 [8.89–9.20]9.50 [7.43–12.67]5,781,677215,1133.72 [3.70–3.74]7.20 [7.16–7.24]8.23 [8.06–8.40]
      19991,831,97117,2169.39 [9.26–9.54]8.87 [8.73–9.01]9.69 [9.00–10.37]5,848,216234,8354.01 [3.98–4.03]7.41 [7.37–7.45]8.47 [8.39–8.55]
      20002,262,73220,5999.10 [8.98–9.22]8.97 [8.84–9.11]9.61 [9.31–9.92]5,896,329255,2644.32 [4.30–4.35]7.41 [7.37–7.44]8.94 [8.88–9.00]
      20012,534,40123,6159.31 [9.19–9.43]9.20 [9.07–9.32]9.36 [9.15–9.57]5,900,383276,0914.77 [4.74–4.80]7.87 [7.83–7.90]9.08 [9.03–9.13]
      20022,858,23726,5979.30 [9.19–9.41]9.37 [9.25–9.49]9.64 [9.44–9.84]5,862,771296,4455.05 [5.02–5.08]7.98 [7.95–8.01]9.27 [9.22–9.32]
      20033,046,69229,3589.63 [9.52–9.74]9.63 [9.51–9.74]10.00 [9.81–10.19]5,788,957317,6115.48 [5.45–5.51]8.19 [8.16–8.22]9.47 [9.42–9.52]
      20043,247,17532,54310.02 [9.91–10.13]10.06 [9.95–10.17]10.42 [10.23–10.61]5,705,620339,7185.95 [5.92–5.98]8.55 [8.52–8.58]9.77 [9.73–9.82]
      20053,317,48433,0939.97 [9.86–10.08]10.15 [10.04–10.26]10.33 [10.15–10.52]5,615,033363,5346.47 [6.43–6.52]9.06 [9.03–9.09]10.21 [10.16–10.26]
      20063,346,59830,8409.21 [9.11–9.31]9.39 [9.29–9.50]9.55 [9.37–9.72]5,467,107378,7996.92 [6.90–6.94]9.44 [9.42–9.47]10.62 [10.57–10.66]
      20073,374,99330,2368.95 [8.88–9.06]9.15 [9.04–9.25]9.49 [9.32–9.65]5,294,313388,7087.34 [7.30–7.38]9.73 [9.71–9.76]10.64 [10.60–10.68]
      20083,381,82430,2618.94 [8.84–9.05]9.20 [9.10–9.30]9.59 [9.44–9.74]5,112,496398,0037.78 [7.74–7.82]10.07 [10.04–10.10]10.91 [10.87–10.95]
      20093,362,70129,3878.73 [8.63–8.83]8.99 [8.89–9.10]9.36 [9.22–9.50]4,924,529405,4028.23 [8.20–8.26]10.35 [10.32–10.38]10.91 [10.88–10.95]
      20103,314,62027,1338.18 [8.09–8.28]8.42 [8.32–8.52]8.74 [8.62–8.87]4,689,058403,3438.60 [8.56–8.64]10.54 [10.51–10.57]10.93 [10.90–10.96]
      20113,235,50526,1008.06 [7.96–8.16]8.30 [8.20–8.40]8.48 [8.36–8.59]4,421,201398,4349.01 [8.96–9.06]10.69 [10.66–10.72]10.94 [10.91–10.97]
      20123,196,39224,7277.73 [7.64–7.83]7.95 [7.85–8.05]8.10 [7.90–8.30]4,165,371391,6919.40 [9.36–9.44]10.76 [10.73–10.79]10.87 [10.84–10.90]
      20133,030,31723,4097.72 [7.62–7.82]7.87 [7.77–7.97]7.94 [7.84–8.05]3,812,788374,2989.82 [9.78–9.86]10.87 [10.84–10.90]10.90 [10.87–10.93]
      20142,758,06521,1137.65 [7.55–7.75]7.74 [7.64–7.85]7.75 [7.65–7.86]3,314,992337,16810.17 [10.14–10.20]10.96 [10.93–10.99]10.95 [10.92–10.98]
      20152,360,85217,6907.49 [7.38–7.60]7.52 [7.41–7.63]7.51 [7.40–7.62]2,761,702290,02010.50 [10.47–10.53]10.94 [10.90–10.97]10.93 [10.90–10.96]
      20161,889,58713,5407.16 [7.04–7.28]7.18 [7.06–7.30]7.17 [7.05–7.29]2,100,061223,94810.66 [10.63–10.69]10.96 [10.93–11.00]10.95 [10.92–10.99]
      20171,495,49710,1466.78 [6.67–6.93]6.78 [6.67–6.93]6.78 [6.67–6.93]1,690,618181,46410.77 [10.72–10.82]10.77 [10.72–10.82]10.77 [10.72–10.82]
      AAPC (%)494,716−1.6[-2.0 to −1.1]1.4 [1.3 to 1.6]∗
      Age-sex and length of data contribution (LOD) standardization was done using 2017 CPRD population as standard population. For 1997, LOD standardisation was not calculated because of absence of data for ≥ 10 years (See Supplementary Figs. S1 and S2).
      IR: Incidence Rate; CI: Confidence Interval; AAPC: Annual Average Percentage Change; ∗P-value.
      Fig. 2
      Fig. 2Trends of standardized incidence (A) and prevalence (B) between 1998 and 2017.
      In contrast, prevalence increased from 1998 to 2017 (Table I). The age and length of data standardised rates were found to rise in both men and women across the years. The overall prevalence of people with any OA in 2017 was found to increase to 10.7% from 8.2% in 1998, 1.3 times increase in prevalence over this period [Fig. 2(B)]. The average annual percentage change was 1.4% (95% CI 1.3–1.6%) for any OA, whereas among women it was a 1.6% (95% CI 1.4–1.8%) and in men a 1.3% (95% CI 1.1–1.4%) change each year. The prevalence of OA in joint-specific OA in 2017 also increased from 1998 except for ankle and foot. Details are given in Supplementary Fig. S6 and sex wise distribution is given in supplementary table S2. The additional analysis on trends of incidence of joint pain recorded in the CPRD shows a sudden increase in the trends after 2003 (Supplementary Fig. S8).

       Geographic distribution

      In 2014, the East Midlands and the North East had the highest incidence rates of OA of 12.6 per 1000 person-years and 11.7 per 1000 person-years respectively. Lowest incidence rates were seen in Northern Ireland and South East England [Fig. 3(A)]. The prevalence of any OA varied from one region to another within the UK. In 2014 the highest age and sex standardised prevalence were in Scotland, West Midlands and Northern Ireland ranging from 7% to 9%. The prevalence ranged from 3% to 5% in the Southern region [Fig. 3(B)].
      Fig. 3
      Fig. 3Geographic variations in the incidence (A) and prevalence (B) of OA in the UK in 2014.

       Cohort effects

      The incidence was found to decline according to the birth cohorts. For people in the same age group, those born later were less likely to have OA than those born earlier (Fig. 4). The reduction speeded up gradually after 1960, particularly for people aged 20–40 years, suggesting a potential aetiological change after 1960 that led to people being less likely to develop OA. In contrast, prevalence increased gradually by age but remained almost constant for people born after 1960. The plot of distribution of incidence and prevalence across the age groups for different periods of birth is provided as supplementary material (Supplementary Figs. S7(A) & S7(B)).
      Fig. 4
      Fig. 4Age-period-cohort analysis of trend of OA (1997–2017) incidence (A) and prevalence (B) in the UK.

      Discussion

      This study confirms a high burden of OA in the UK with a current (year 2017) prevalence of 10.7% and incidence of 6.8 per 1000 person-years in people aged 20 and over. The prevalence of OA has increased at a rate of 1.4% per year since 1998, whereas the incidence is declining at a rate of −1.6% per year. Geographically, the prevalence and incidence of OA are not uniformly distributed. Scotland, Northern Ireland and West Midlands had higher prevalence compared to the rest of the country, whereas, the incidence was higher in East midlands and North-Eastern regions.
      The standardised incidence of OA in 2013 estimated from CPRD among people aged 45 years or more was 6.3 per 1000 person-years
      • Yu D.
      • Jordan K.P.
      • Bedson J.
      • Englund M.
      • Blyth F.
      • Turkiewicz A.
      • et al.
      Population trends in the incidence and initial management of osteoarthritis: age-period-cohort analysis of the Clinical Practice Research datalink, 1992–2013.
      . In another study, Yu et al. reported the standardised rates of any OA incidence in 2010 as 8.6 per 1000 person-years among persons aged 15 years or more in a UK regional administrative database
      • Yu D.
      • Peat G.
      • Bedson J.
      • Jordan K.P.
      Annual consultation incidence of osteoarthritis estimated from population-based health care data in England.
      . According to the literature, the prevalence of OA among people aged 45 years and over varies between 20% and 35%
      • Brennan-Olsen S.L.
      • Cook S.
      • Leech M.T.
      • Bowe S.J.
      • Kowal P.
      • Naidoo N.
      • et al.
      Prevalence of arthritis according to age, sex and socioeconomic status in six low and middle income countries: analysis of data from the World Health Organization study on global AGEing and adult health (SAGE) Wave 1.
      ,
      • Dillon C.F.
      • Rasch E.K.
      • Gu Q.
      • Hirsch R.
      Prevalence of knee osteoarthritis in the United States: arthritis data from the Third National Health and Nutrition Examination Survey 1991-94.
      . Our estimated prevalence among people aged 45 years or more using the entire CPRD database was nearly 23%. Global burden of disease reports the prevalence of knee and hip was 7.3% and musculoskeletal disease profile report from the NHS shows the prevalence in 2015–16 was nearly 12%
      • James S.L.
      • Abate D.
      • Abate K.H.
      • Abay S.M.
      • Abbafati C.
      • Abbasi N.
      • et al.
      Global, regional, and national incidence, prevalence, and years lived with disability for 354 diseases and injuries for 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017.
      ,. Comparing the incidence and prevalence across studies is very difficult because of the wide differences in study population, case definition, database quality and standardisation methods
      • Rahman M.M.
      • Cibere J.
      • Goldsmith C.H.
      • Anis A.H.
      • Kopec J.A.
      Osteoarthritis incidence and trends in administrative health records from British columbia, Canada.
      ,
      • Dillon C.F.
      • Rasch E.K.
      • Gu Q.
      • Hirsch R.
      Prevalence of knee osteoarthritis in the United States: arthritis data from the Third National Health and Nutrition Examination Survey 1991-94.
      ,
      • Parsons S.
      • Ingram M.
      • Clarke-Cornwell A.M.
      • Symmons D.P.M.
      A HEAVY BURDEN: The occurrence and impact of musculoskeletal conditions in the United Kingdom today.
      . Values similar to our prevalence estimates have been reported in the UK by Jordan et al.
      • Jordan K.
      • Clarke A.M.
      • Symmons D.P.M.
      • Fleming D.
      • Porcheret M.
      • Kadam U.T.
      • et al.
      Measuring disease prevalence: a comparison of musculoskeletal disease using four general practice consultation databases.
      using a database with better recording pattern, as the GPs from this region actively participate in musculoskeletal research.
      • Jordan K.
      • Porcheret M.
      • Kadam U.T.
      • Croft P.
      The use of general practice consultation databases in rheumatology research (editorial),.
      These differences should not affect comparisons within the study such as, incidence by age and sex. The increase in incidence and prevalence of OA with age and in women supports existing epidemiological evidence
      • Litwic A.
      • Edwards M.H.
      • Dennison E.M.
      • Cooper C.
      Epidemiology and burden of osteoarthritis.
      . The sudden rise of both prevalence and incidence at age of 40 years in women has been explained through biological sex hormone changes and also has been reported uniformly in previous studies
      • Doherty M.
      Risk factors for progression of knee osteoarthritis.
      ,
      • Spector T.D.
      • Campion G.D.
      Generalised osteoarthritis: a hormonally mediated disease.
      . The incidence pattern with age also concurs with previous studies in the UK and other countries.
      • Yu D.
      • Jordan K.P.
      • Bedson J.
      • Englund M.
      • Blyth F.
      • Turkiewicz A.
      • et al.
      Population trends in the incidence and initial management of osteoarthritis: age-period-cohort analysis of the Clinical Practice Research datalink, 1992–2013.
      ,
      • Parsons S.
      • Ingram M.
      • Clarke-Cornwell A.M.
      • Symmons D.P.M.
      A HEAVY BURDEN: The occurrence and impact of musculoskeletal conditions in the United Kingdom today.
      In both sexes, the prevalence and incidence of ‘unspecified’ OA was high compared to reported joint-specific OA, a finding also reported by Yu et al.
      • Yu D.
      • Peat G.
      • Bedson J.
      • Jordan K.P.
      Annual consultation incidence of osteoarthritis estimated from population-based health care data in England.
      Such ‘unspecified’ reporting reflects the recording pattern in primary care, though whether the term ‘unspecified’ is a substitute to record multiple joint involvement, remains unclear. The higher burden of knee and hip OA in this study reflects consultation behaviour, for example a preference to seek advice for large joint rather than small joint problems. There is wide variation in reported prevalence of OA at individual joint sites. Again, this could indicate different methods of ascertainment, and whether diagnosis is purely clinical or based on presence of radiographic OA changes. Also the findings are likely to underrepresent true prevalence and incidence, as more than 12% of people with hip OA never consult GPs about their condition, even if it is symptomatic.
      • Ferguson R.J.
      • Prieto-Alhambra D.
      • Walker C.
      • Yu D.
      • Valderas J.M.
      • Judge A.
      • et al.
      Validation of hip osteoarthritis diagnosis recording in the UK clinical practice research datalink.

       Trends of incidence and prevalence

      Surprisingly, there was an overall slow decline in incidence rates for any-OA since 1998. Yu et al. found no change in trends of incidence physician-diagnosed OA for the period 1997–2013 among people aged 45 years or more
      • Yu D.
      • Jordan K.P.
      • Bedson J.
      • Englund M.
      • Blyth F.
      • Turkiewicz A.
      • et al.
      Population trends in the incidence and initial management of osteoarthritis: age-period-cohort analysis of the Clinical Practice Research datalink, 1992–2013.
      . One other population-based study in the US found no increase in trends of radiographic knee OA during the period 1974–1994 after adjusting for body mass index (BMI) change
      • Nguyen U.-S.D.T.
      • Zhang Y.
      • Zhu Y.
      • Niu J.
      • Zhang B.
      • Felson D.T.
      Increasing prevalence of knee pain and symptomatic knee osteoarthritis: survey and cohort data.
      . The Joinpoint analysis reveals a slight rise in incidence from 2000 to 2004 followed by a slow decline. We found significant increase in rate for knee and hip joint-specific incidence, but the ‘unspecified’ OA rate was declining, indicating possible improvement in clinical coding. Perhaps the increase in trend of ‘joint-pain’ after the year 2005 partially explains the gap (Supplementary Fig. S6) if physicians became more prone to report symptoms rather than a specific diagnosis. We observed a nearly 1.3 times increase in standardized prevalence of OA from 1998 to 2017, with an annual percentage increase of 1.4%. Globally, contribution of OA to the total prevalent cases has increased by 8.5% from 1990 to 2017 and in the UK the prevalence has increased from 6.3% in 1990–7.7% in 2017
      • James S.L.
      • Abate D.
      • Abate K.H.
      • Abay S.M.
      • Abbafati C.
      • Abbasi N.
      • et al.
      Global, regional, and national incidence, prevalence, and years lived with disability for 354 diseases and injuries for 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017.
      . The increase in prevalence with the slow declining incidence rate is surprising. Especially, the increased prevalence trend could be because of the cumulative nature of the longitudinal database from electronic health records. CPRD is a dynamic database with people moving in and out of the database at any time point, which changes the eligible population every year. Also, we found the prevalence trend is becoming stable since 2008, which partially explains the effect of declining incidence.
      Age-period-cohort effects, length of data contribution and the participation of practices in the CPRD database influence the incidence estimates
      • Kuo C.-F.
      • Grainge M.J.
      • Mallen C.
      • Zhang W.
      • Doherty M.
      Rising burden of gout in the UK but continuing suboptimal management: a nationwide population study.
      ,
      • Jordan K.
      • Clarke A.M.
      • Symmons D.P.M.
      • Fleming D.
      • Porcheret M.
      • Kadam U.T.
      • et al.
      Measuring disease prevalence: a comparison of musculoskeletal disease using four general practice consultation databases.
      . Our age-period-cohort analysis shows a strong cohort effect in incidence among people born after the 1960s. It suggests that people born after this period may expose less to physically very demanding occupations such as coal-mining, farming and certain heavy industrial work because of change in patterns of occupation in the UK since 1960s including the mining activities

      Long-term trends in UK employment: 1861 to 2018 - office for national statistics. https://www.ons.gov.uk/economy/nationalaccounts/uksectoraccounts/compendium/economicreview/april2019/longtermtrendsinukemployment1861to2018. Accessed July 10, 2019.

      . We standardised for the length of data contribution period to eliminate the problem of prevalent cases for OA for robust incidence estimates. In contrast, prevalence remained almost unchanged in people born after 1960s (Fig. 4), indicating the treatment of this condition may remain same.

       Geographical distribution

      Scotland and the middle region of England and had higher incidence rates in 2014 compared to the rest of the UK
      • Yu D.
      • Jordan K.P.
      • Bedson J.
      • Englund M.
      • Blyth F.
      • Turkiewicz A.
      • et al.
      Population trends in the incidence and initial management of osteoarthritis: age-period-cohort analysis of the Clinical Practice Research datalink, 1992–2013.
      . The reasons for regional variation could be differences in practice areas, socio-economic conditions, lifestyles and health seeking behaviours. Interestingly, higher prevalence in the Northern region largely matches the obesity distribution in the Northern region of the UK compared to the South.

       Limitations of the study

      In addition to the highlighted caveats on coding of the diseases and data contribution, a few more limitations do exist. The case definition relied on the clinical diagnosis by the general practitioners without requiring demonstration of structural OA on imaging. However, concordance between symptoms and radiographic OA (the usual way to assess structural OA) is variable and often poor, depending on the joint site being assessed
      • Hunter D.J.
      • Guermazi A.
      • Roemer F.
      • Zhang Y.
      • Neogi T.
      Structural correlates of pain in joints with osteoarthritis.
      . Patient-centred outcomes rather than imaging changes are key determinants of disability and burden of disease, and the National Institute for Health and Care Excellence (NICE) recommends that a purely clinical diagnosis is sufficient and that imaging should be reserved for specific situations such as atypical clinical features or rapid progression of symptoms

      Osteoarthritis - NICE CKS. https://cks.nice.org.uk/osteoarthritis#!topicsummary. Accessed October 21, 2018.

      . Coding of joint specific OA in a consultation database is always controversial. The index date reflects the date of allocation of Read codes for OA and does not reflect disease onset or the date of diagnosis. However, the date of allocation of a Read code for OA would be expected to be within a few months of the date of diagnosis
      • Ferguson R.J.
      • Prieto-Alhambra D.
      • Walker C.
      • Yu D.
      • Valderas J.M.
      • Judge A.
      • et al.
      Validation of hip osteoarthritis diagnosis recording in the UK clinical practice research datalink.
      . We did not perform a validation study for the OA definitions used in this study, therefore the results are open to misclassification bias. Caution must be taken when comparing the prevalence and incidence of this study with that reported in other studies. However, we believe this will not affect the internal validity, such as prevalence and incidence by age and gender, and temporal trends of OA/joint pain in the past 20 years in the UK as they all were based on the same Read codes to define the disease. Furthermore, because our estimates are based on GP consultations for symptomatic regional joint pain, and not all people with symptomatic OA will consult their GP, these data may underestimate the true community prevalence and incidence of symptomatic OA. Unlike other chronic conditions, OA is not included in Quality and Outcome Framework (QOF) by the NHS in 2004. QOF is an incentivising program, which rewards GP practices in England for quality delivery of primary care including the diagnosis and recording of conditions. Therefore, the prevalence and incidence might have been underestimated. In addition, the exclusion criteria used in our study might have led to underestimation of the burden. Also, health care accessibility might influence the estimation. CPRD might have the duplication of people, because of the movement of patients from one practice area to other and being recorded with new unique identifier. However, we assume, the rate of migration might be similar in both OA group and ‘at-risk’ population. Even though, the method of standardising by length of data observation has been used previously for calculating trends using electronic health records, some residual confounding by length of data observation might still exist. Another limitation is the geographical presentation of the estimates, which needs cautious interpretation because of the non-uniform practices involved in the database.

      Conclusion

      One in 10 adults aged 20 years or more in the UK has GP-diagnosed OA and the knee was the leading site. The incidence of GP-diagnosed OA is declining, but the prevalence is rising slowly in the UK. A cohort effect was observed, that is, within the same age groups people born after 1960s had lower incidence than those born earlier. If it is a real change in trend or change in recoding and reporting pattern needs to be studied. Also, further research is necessary to understand these temporal trends in OA.

      Contributor and guarantor information

      SS, WZ and MD conceived and designed the study. SS and WZ acquired the data. SS performed the analysis and CC, AS and WZ supervised the statistical analysis. SS, AS, CM, CC, WZ, CFK and MD interpreted the results. SS and WZ drafted the manuscript. All authors contributed to the critical revision of the manuscript for important intellectual content. WZ, CC and MD supervised the study. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.

      Competing interests

      This study had no financial competing interests.
      The authors declare that they have no conflict of interest.

      Funding

      This work was supported by Versus Arthritis [grant numbers 20777 , 21595 ] formerly Arthritis Research UK; The University of Nottingham Vice-Chancellor Scholarship and Beijing Joint Care Foundation Scholarship . CM is funded by National Institute for Health Research (NIHR) - Research Professorship ( NIHR-RP-2014-04-026 ), the NIHR Collaborations for Leadership in Applied Health Research and Care West Midlands and the NIHR School for Primary Care Research . The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care.

      Role of the funding sources

      The sponsors did not participate in the design and conduct of the study; collection, management, analysis, and interpretation of the data; or preparation, review, or approval of the manuscript and the decision to submit the manuscript for publication.

      Studies involving humans or animals

      No direct participant recruitment was done for the study. This study was approved by the independent scientific advisory committee for CPRD research (protocol reference: 19_030 R).

      Acknowledgements

      We would like to thank the University of Nottingham , UK and Beijing Joint Care Foundation , China for financially supporting the research. The authors would like to acknowledge Keele University's Prognosis and Consultation Epidemiology Research Group who have given us permission to utilise the Code Lists (©2014).

      Data sharing statement

      We used anonymised data on individual patients on which the analysis, results, and conclusions reported in the paper are based. The CPRD data is not distributable under licence. However, the relevant data can be obtained directly from the agency (https://www.cprd.com/). The codes developed for the analysis can be available upon a valid request.

      Appendix A. Supplementary data

      The following is the Supplementary data to this article:

      Appendix 1.

       Read codes for Osteoarthritis

      Tabled 1
      Read CodeName of the condition
      N05zJ00Osteoarthritis NOS, of hip
      N053512Hip osteoarthitis NOS
      N05z511Hip osteoarthritis NOS
      N053500Localised osteoarthritis, unspecified, pelvic region/thigh
      N051500Localised, primary osteoarthritis of the pelvic region/thigh
      N052500Localised, secondary osteoarthritis of pelvic region/thigh
      N054500Oligoarticular osteoarthritis, unspecified, of pelvis/thigh
      N05z500Osteoarthritis NOS, pelvic region/thigh
      Nyu2E11[X] Unilateral secondary coxarthrosis
      Nyu2200[X]Other dysplastic coxarthrosis
      Nyu2300[X]Other post-traumatic coxarthrosis
      Nyu2100[X]Other primary coxarthrosis
      Nyu2E00[X]Other secondary coxarthrosis
      Nyu2400[X]Other secondary coxarthrosis, bilateral
      N051900Primary coxarthrosis, bilateral
      N05zL00Osteoarthritis NOS, of knee
      N05z611Knee osteoarthritis NOS
      N053600Localised osteoarthritis, unspecified, of the lower leg
      N05z600Osteoarthritis NOS, of the lower leg
      N051600Localised, primary osteoarthritis of the lower leg
      N052600Localised, secondary osteoarthritis of the lower leg
      N054600Oligoarticular osteoarthritis, unspecified, of lower leg
      N053611Patellofemoral osteoarthritis
      N05zM00Osteoarthritis NOS, of tibio-fibular joint
      Nyu2511[X] Unilateral primary gonarthrosis
      N051B00Primary gonarthrosis, bilateral
      Nyu2811[X] Unilateral secondary gonarthrosis
      Nyu2800[X]Other secondary gonarthrosis
      Nyu2700[X]Other secondary gonarthrosis, bilateral
      Nyu2500[X]Other primary gonarthrosis
      N052C00Post-traumatic gonarthrosis, unilateral
      N05zN00Osteoarthritis NOS, of ankle
      N05z700Osteoarthritis NOS, of ankle and foot
      N05zU00Osteoarthritis NOS, of IP joint of toe
      N05zT00Osteoarthritis NOS, of lesser MTP joint
      N05zS00Osteoarthritis NOS, of 1st MTP joint
      N05zR00Osteoarthritis NOS, of other tarsal joint
      N05zP00Osteoarthritis NOS, of subtalar joint
      N05z712Foot Osteoarthritis NOS
      N05zQ00Osteoarthritis NOS, of talonavicular joint
      N053700Localised osteoarthritis, unspecified, of the ankle and foot
      N051700Localised, primary osteoarthritis of the ankle and foot
      N051E00Localised, primary osteoarthritis of toe
      N052700Localised, secondary osteoarthritis of the ankle and foot
      N05z713Toe osteoarthritis NOS
      N05z711Ankle osteoarthritis NOS
      N054700Oligoarticular osteoarthritis, unspecified, of ankle/foot
      Nyu2900[X]Other primary arthrosis of first carpometacarpal joint
      N051C00Primary arthrosis of first carpometacarpal joints, bilateral
      Nyu2A00[X]Other post-traumatic arthrosis/1st carpometacarpal joint
      Nyu2B00[X]Other 2ndry arthrosis/1st carpometacarpal joints, bilaterl
      N053400Localised osteoarthritis, unspecified, of the hand
      N051400Localised, primary osteoarthritis of the hand
      N05011Heberden's node
      N052400Localised, secondary osteoarthritis of the hand
      N05z412Thumb osteoarthritis NOS
      N050700Heberden's node with arthropathy
      N054400Oligoarticular osteoarthritis, unspecified, of hand
      N050112Bouchard's node
      N05zH00Osteoarthritis NOS, of DIP joint of finger
      N050300Bouchard's node with arthropathy
      N05zG00Osteoarthritis NOS, of PIP joint of finger
      N05z311Wrist osteoarthritis NOS
      N05z400Osteoarthritis NOS, of the hand
      N051D00Localised, primary osteoarthritis of the wrist
      N05z411Finger osteoarthritis NOS
      N05zE00Osteoarthritis NOS, of wrist
      N05zF00Osteoarthritis NOS, of MCP joint
      N050100Generalized OA of hand
      N06z311Wrist arthritis NOS
      N051800Localised, primary osteoarthritis of other specified site
      N051.00Localised, primary osteoarthritis
      N051z00Localised, primary osteoarthritis NOS
      N051000Localised, primary osteoarthritis of unspecified site
      N052.00Localised, secondary osteoarthritis
      N052z00Localised, secondary osteoarthritis NOS
      N052800Localised, secondary osteoarthritis of other specified site
      N050000Osteoarthritis and allied disorders
      N054.00Oligoarticular osteoarthritis, unspecified
      N054900Oligoarticular osteoarthritis, unspecified, multiple sites
      Nyu2.00[X]Arthrosis
      Nyu2000[X]Other polyarthrosis
      N054000Oligoarticular osteoarthritis, unspec, of unspecified sites
      N05z000Osteoarthritis NOS, of unspecified site
      N05..00Osteoarthritis and allied disorders
      N054800Oligoarticular osteoarthritis, unspecified, other spec sites
      N05z.00Osteoarthritis NOS
      N053z00Localised osteoarthritis, unspecified, NOS
      N053800Localised osteoarthritis, unspecified, of other spec site
      N05zz00Osteoarthritis NOS
      N053000Localised osteoarthritis, unspecified, of unspecified site
      N05..11Osteoarthritis
      N05z800Osteoarthritis NOS, other specified site
      N054z00Osteoarthritis of more than one site, unspecified, NOS
      N06z.11Arthritis
      N050500Secondary multiple arthrosis
      N050400Primary generalized osteoarthrosis
      N050Z00Generalized OA NOS
      N050200Generalised OA Multiple sites
      N050.00Generalised OA
      NOS- ‘not otherwise specified.
      We did not include acromio-clavicular and sterno-clavicular joint OA because of the possible accuracy of diagnosis at these joints and the expected incidence is very low.

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