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Healthcare budgets are constrained and there are perennial concerns about the potential mismatch between health-care need and the provision of publicly-funded services. Ageing populations1 and technological advances2 are increasing pressures on healthcare budgets and the prioritisation of healthcare services can be required.3 One area that is likely to be affected by these pressures is total joint replacement (TJR) surgery. The most common reason for TJR surgery in New Zealand is osteoarthritis (OA)4 that is not responding adequately to conservative treatment. OA has a high prevalence among older adults5,6 with 29% of New Zealanders aged over 65 years diagnosed with this condition.7 This is important to consider as, currently in New Zealand, those aged over 65 years comprise 14% of the population but this is predicted to increase to 27% in 2063.8 Therefore, demand for TJR will likely increase substantially. In New Zealand, hip TJR surgery (including privately-funded procedures) has already increased between 1999 and 2013 by 75%; there was a corresponding 158% increase for knee TJR surgery.6 However, despite these increases, concerns have been raised that the provision of these procedures may not be expanding sufficiently to keep up with increases in clinical need or population changes.9Publicly-funded healthcare in New Zealand is provided by 20 District Health Boards (DHBs) \"responsible for providing or funding the provision of health services in their district\".10 In New Zealand, prioritisation scoring tools are used to determine access to publicly-funded TJR surgery. This should ensure equitable access across the country. However, Derrett et al (2009)11 found a lack of equity between DHBs in the provision of elective hip and knee TJR (2000 to 2005), and an analysis of New Zealand newspaper articles and Parliamentary questions from 2000-2006 found thataccess inequities remained a persistent theme (p.57).12 Although there has been an increase in funding for TJR surgery in New Zealand in recent years it is not clear whether that has translated into increased rates of surgical provision. Additionally, any increases in provision of TJR should be equitable with regard to geographic and demographic determinants such as place of residence, age, sex, ethnicity and socioeconomic deprivation.13 This paper examines publicly-funded elective hip and knee TJR surgery provision among DHBs in New Zealand from 2006-2013. The aims of this study are to: describe changes in rates of publicly-funded hip and knee TJR surgery nationally between 2006 and 2013, investigate whether national rates vary according to age, sex, ethnicity, small-area deprivation and rurality, and determine whether the provision of publicly-funded hip and knee TJR surgery is equitable across DHBs in New Zealand. MethodsThis study examined New Zealand hospital discharge data for publicly-funded hip and knee TJR surgery from 2006-2013. Ethical approval for the study was received from the University of Otago Human Ethics Committee (Reference number D13/253). Relevant hospital discharge data was obtained from the Ministry of Healths National Minimum Dataset (NMDS).14 The NMDS is a national collection containing publicly-funded hospital discharges and some privately-funded hospital discharges. Data was obtained for patients with at least one publicly-funded hip or knee TJR procedure who were discharged between 1 January 2006 and 31 December 2013. This time period was chosen as similar work on this topic11 analysed data up until the end of 2005, and 2013 data was the latest available at the time this study commenced. The variables obtained from the NMDS included the International Classification of Diseases version 10 (ICD10) clinical code, age at discharge, sex, domicile code, ethnicity, type of admission, diagnosis type, event dates and the principal health service purchaser. As well as waiting list admissions, arranged admissions defined asa planned admission where: the admission date is less than seven days after the date the decision was made by the specialist that the admission was necessary14 were also included as these were likely to capture urgent sub-acute OA patients. Acute admissions and injury admissions (primary diagnosis code within ICD10 S00-T98)15 were excluded as were those under 20 years of age at time of surgery and overseas residents. Hip and knee TJR surgeries were identified using the clinical codes in the 3rd edition of the Australian Modification of ICD10.15 The specific procedures included were: total arthroplasty of hip, total arthroplasty of knee, total arthroplasty of knee with bone graft to femur or to tibia, total arthroplasty of knee with bone graft to femur and tibia and total replacement arthroplasty of patellofemoral joint of knee. Hemiarthroplasty of the knee was also included because indications for this are similar to TJR and their popularity may vary across the country. Revisions of hip and knee joint replacements were not included as the aim was to focus on primary procedures. Records with missing or historic domicile codes that could not be forward-mapped were excluded as these could not be analysed by DHB, area-level deprivation or rurality. Self-identified ethnicity data collected at the patients health event was obtained from the NMDS. The recording of at least one ethnicity is mandatory, and two additional ethnic group codes may be recorded.14 As the DHB-level denominator data was only available by prioritised ethnicity, this approach was used in our analyses with estimates obtained for M1ori, Pacific, Asian and Other ethnicity groupings. Prioritisation follows a Statistics New Zealand (SNZ) algorithm with the end result being each person associated with only one ethnic group.16 M1ori ethnicity has the highest priority, meaning that people who identified as both M1ori and any other ethnicities are classified as M1ori. For example, those who identify as both M1ori and Pacific are classified as M1ori. Pacific ethnicity is given the next highest priority with those who identify as Pacific and any other ethnicity (apart from M1ori) being classified as Pacific.The New Zealand Deprivation Index (NZDep2006) is asmall-area index of relative socio-economic deprivation17 (p.S7) derived from 2006 Census data. The NZDep scale runs from one (an area in the least deprived 10% of small areas) to 10 (in the 10% most deprived small areas). The 1:1 mapping between domicile codes available in the NMDS and Census area units used by SNZ enabled NZDep to be assigned to each TJR discharge record. Rurality was also derived from domicile codes by 1:1 mapping with SNZs Census area units and SNZs Urban/Rural Profile Classification.18 The seven categories of the Urban/Rural profile were categorised for analysis as: Main Urban (described as beingvery large and centred on a city or main urban centre minimum population of 30,000),18 Other Urban which consisted of Satellite Urban (201cdefined as urban areas (other than main urban areas) where 20 percent or more of the usually resident employed populations workplace address is in a main urban area18and Independent Urban (defined as for Satellite Urban but <20 percent with a main urban area workplace), and Rural comprising the four rural profiles (Rural Areas with a High Urban Influence, Rural Areas with a Moderate Urban Influence, Rural Areas with a Low Urban Influence and Highly Remote Areas). Denominator data were sourced from SNZ, and restricted to those aged 20 years and above. Annual resident population estimates by year, ethnicity, sex, age group and DHB region for 2006-2013 were calculated by SNZ. Usually resident population counts from the 2006 Census were used for calculations involving rurality and deprivation. In 2010 the Southern DHB was created from a merger of two DHBs (Otago and Southland); for this study we combined data from those DHBs and considered them as the Southern DHB throughout the period analysed. Crude rates per 100,000 person years (py) were calculated and presented alongside exact Poisson 95% Confidence Intervals (CIs). Age-standardised rates (ASRs) were calculated using direct standardisation and five-year age groups. Ten five-year age groups (<45, 45-4980-84, 85+) were used for sex and ethnicity ASRs. Denominator data for deprivation and rurality ASRs was not available disaggregated by age for those over 65 years so these ASRs were calculated using age groups <45, 45-49, 50-54, 55-59, 60-64, 65+ years. Age- and ethnicity-standardised rates (AESRs) by DHBs were calculated in a similar way using four prioritised ethnic groups: M1ori, Pacific, Asian and Other. Linear trends in rates were analysed using Poisson regression. Pitmans variance ratio test was used to compare the distribution of AESRs by DHB over time. Analyses were carried out using Stata/SE (version 13.1).19ResultsOf the 74,784 procedures obtained from the NMDS for people with at least one publicly-funded hip or knee TJR and a date of discharge between 2006 and 2013, 62,907 (84.1%) met the inclusion criteria. Figure 1 details the exclusions. Of these 62,907 publicly-funded primary hip or knee TJR procedures, 2% were bilateral joint replacements giving a total of 64,222 primary hip or knee joints replaced (Table 1).Figure 1:Table 1:Publicly-funded primary total hip and knee joint replacement procedures in those aged 20 years and over, 2006-2013 by District Health Board (DHB). District Health Board Overall N Bilateral % Population* Overall Crude Rate** (95% CI) Ranking/20*** Auckland 3,472 1.8 330,660 131.3 (126.9, 135.7) 20 Bay of Plenty 4,373 1.9 149,663 365.2 (354.5, 376.2) 5 Canterbury 6,781 2.5 367,993 230.3 (224.9, 235.9) 16 Capital and Coast 3,001 5.4 211,259 177.6 (171.3, 184.0) 19 Counties Manukau 5,636 2.8 318,674 221.1 (215.3, 226.9) 17 Hawke's Bay 2,703 0.2 109,900 307.4 (296.0, 319.3) 11 Hutt Valley 1,918 5.3 100,735 238.0 (227.5, 248.9) 15 Lakes 1,827 1.4 71,043 321.5 (306.9, 336.6) 9 Mid Central 2,719 1.2 118,968 285.7 (275.1, 296.6) 12 Nelson Marlborough 3,015 2.4 102,653 367.1 (354.2, 380.5) 4 Northland 2,987 1.8 112,131 333.0 (321.2, 345.1) 8 South Canterbury 1,460 0.3 41,890 435.7 (413.6, 458.6) 3 Southern 4,734 2.7 222,008 266.5 (259.0, 274,2) 14 Tairawhiti 889 0.1 31,134 356.9 (333.8, 381.2) 7 Taranaki 2,013 1.3 79,248 317.5 (303.8, 331.7) 10 Waikato 5,757 1.4 256,493 280.6 (273.4, 287.9) 13 Wairarapa 866 0.9 29,839 362.8 (339.0, 387.8) 6 Waitemata 6,274 2.0 378,591 207.1 (202.1, 212.3) 18 West Coast 871 0.6 24,241 449.1 (419.8, 480.0) 1 Whanganui 1,611 0.8 45,012 447.4 (425.8, 469.8) 2 Total 62,907 2.1 3,102,133 253.5 (251.5, 255.5) *Population = Average DHB population for 2006-2013 of those aged 20 years and over. ** Rate/100,000 person years. ***Ranking is from highest to lowest overall crude rate for the 20 DHBs.Nationally, the number of publicly-funded hip and knee TJR procedures increased by 19.5% from 7,053 in 2006 to 8,429 in 2013 (Table 2) while the rate increased by only 10.7%. The rate peaked in 2007 at 263/100,000 py before decreasing (2008-2011) and returning to 261 and 262/100,000 py in 2012 and 2013 respectively. Although there was a statistically significant increase in the rates from 2006 onwards (p-value <0.001), there is no evidence to suggest a linear change in the rates from 2007 onwards (p-value=0.2).Table 2: Publicly-funded hip and knee total joint replacement procedures in New Zealand for those aged 20 years and over from 2006-2013 by year. Discharge Year Denominator Number Rate* 95% CI 2006 2982345 7,053 236.5 (231.0, 242.1) 2007 3015800 7,943 263.4 (257.6, 269.2) 2008 3046505 7,535 247.3 (241.8, 253.0) 2009 3083845 7,934 257.3 (251.7, 263.0) 2010 3124770 7,745 247.9 (242.4, 253.4) 2011 3158140 7,950 251.7 (246.2, 257.3) 2012 3185125 8,318 261.2 (255.6, 266.8) 2013 3220535 8,429 261.7 (256.2, 267.4) *Rate/100,000 person years of those aged 20 years and over.From 2006 to 2013 inclusive, the highest rate of publicly-funded hip and knee TJR procedures was for those aged 75-84 years at the time of surgery (1,063/100,000 py) followed by those aged 65-74 (907/100,000 py), with the lowest rate among those aged less than 55 years (45/100,000 py) (Table 3). ASRs were significantly higher for females (260/100,000 py) than for males (246/100,000 py).Table 3: Publicly-funded primary hip and knee total joint replacement procedures for those aged 20 years and over for 2006-2013 by socio-demographic characteristics. Denominator* N Annual crude rate (95% CI)** ASR*** (95% CI) Overall 3,102,133 62,907 253.5 (251.5, 255.5) -- -- -- Age group (years) <55 2,066,311 7,405 44.8 (43.8, 45.8) -- -- -- 55-64 474,338 14,939 393.7 (387.4, 400.0) -- -- -- 65-74 311,123 22,581 907.2 (895.4, 919.2) -- -- -- 75-84 183,611 15,611 1062.8 (1046.2, 1080.0) -- -- -- 85+ 66,751 2,371 444.0 (426.3, 462.2) -- -- -- Sex Female 1,612,114 34,075 264.2 (261.4, 267.0) 259.7 (257.0, 262.5) Male 1,490,019 28,832 241.9 (239.1, 244.7) 246.2 (243.4, 249.1) Prioritised Ethnicity M1ori 366,255 5,793 197.7 (192.7, 202.9) 303.1 (294.8, 311.5) Pacific 158,319 1,809 142.8 (136.3, 149.6) 224.2 (213.4, 235.0) Asian 327,923 1,259 48.0 (45.4, 50.7) 93.8 (88.2, 99.3) Other**** 2,249,636 54,046 300.3 (297.8, 302.9) 258.3 (256.1, 260.4) Rurality Main Urban Area 2,037,012 40,003 245.5 (243.1, 247.9) 258.6 (256.1, 261.1) Other Urban Area 399,417 14,672 459.2 (451.8, 466.7) 361.6 (355.7, 367.5) Rural 362,802 8,230 283.6 (277.5, 289.8) 295.9 (289.4, 302.3) NZDep 1-3 (least deprived) 785,292 13,314 211.9 (208.3, 215.6) 219.6 (215.9, 223.4) 4-7 1,136,757 26,780 294.5 (291.0, 298.0) 279.9 (276.6, 283.3) 8-10 (most deprived) 877,113 22,806 325.0 (320.8, 329.3) 342.0 (337.6, 346.5) *Uses 2006-2013 resident population estimates for all except Rurality and NZDep comparisons which use 2006 usuallyresident Census counts. **Rate/100,000 person years (226520 year-olds).***Age-standardised rate. ****The numerator of those classified as other ethnicity includes those with ethnicity recorded as Dont Know, Refused to answer, Response unidentifiable or Not Stated to align with denominator.The crude TJR rate of 300/100,000 py was highest among those categorised as Other ethnicity (ie those not identifying as M1ori, Pacific or Asian). M1ori had the second highest crude rate (198/100,000 py). However, M1ori had the highest ASR of procedures (303/100,000 py) followed by those of Other and Pacific ethnicities (258 and 224/100,000 py respectively). Those of Asian ethnicity had a substantially lower ASR (94/100,000 py). Differences in crude and ASRs between prioritised ethnic groups were all statistically significant.Rates were highest for people living in Other Urban Areas (ie urban areas other than those classified as centred on a city or main urban centre) with a crude rate of 459/100,000 py and an ASR of 362/100,000 py). This ASR was significantly higher than the ASR for those in Rural (296/100,000 py) and Main Urban Areas (259/100,000 py).There was a clear linear relationship between TJR procedure rates and socio-economic deprivation, with people that lived in the most deprived three deciles (deciles 8-10) having a significantly higher ASR (342/100,000 py) than those in deciles 4-7 (280/100,000 py) and similarly those who lived in the least deprived deciles (deciles 1-3) had a substantially lower ASR again (220/100,000 py).Of the 20 DHBs, 10 had increases in their age- and ethnicity-standardised rate (AESR) of TJR procedures between the periods 2006-07 to 2012-13, one was unchanged and nine had a reduced rate (Figure 2). Of the eight largest DHBs by population, five had an increase in AESR: Bay of Plenty (31%), Auckland (22%), Waitemata (25%), Canterbury (19%) and Counties Manukau (7%). Southerns AESR remained unchanged and Capital Coasts and Waikatos fell by 7% and 22% respectively. In contrast, AESRs fell between the periods 2006-07 to 2012-13 in seven of the 12 smaller DHBs: West Coast, Wairarapa, Tairawhiti, South Canterbury, Taranaki, Hawkes Bay and Northland. However, in 2012-13, the six smallest DHBs by population (with the exception of South Canterbury) had AESRs higher than five of the six DHBs with the largest populations. Five of the eight largest DHBs (Auckland, Canterbury, Capital and Coast, Southern and Waikato) were below the New Zealand average of 261/100,000 py in 2012-13 as were three of the smallest DHBs (Hawkes Bay, Taranaki and South Canterbury). To assess whether the variation in AESRs by DHB had changed over time, the standard deviation of DHBs AESRs for 2006-07 was compared with that from the rates for 2012-13. Excluding one outlier (West Coast), there was no statistically significant difference over time (ratio of standard deviations 1.13, (95% CI 0.70, 1.82), p=0.6).Figure 2: Age- and ethnicity-standardised rates of publicly-funded hip and knee total joint replacements per 100,000 person-years by District Health Board from 2006-2013.There were also variations by DHB for those in the most deprived deciles. For those in the most deprived three deciles, considering the eight years of the study combined, the ASRs varied from 236/100,000 py (Auckland) to 514/100,000 py (South Canterbury) (results not shown). Again, the smaller DHBs had greater provision within this group of the population, with the five smallest DHBs by population having ASRs of at least 400/100,000 pys, a rate which was not reached for the most deprived deciles in any of the other larger DHBs.DiscussionThis study demonstrates that national rates of publicly-funded elective hip and knee TJR procedures have not increased beyond their 2007 peak. Higher rates were observed in older adults, females, those not living in Rural or Main Urban Areas and those living in areas of greater social deprivation. Rates varied between DHBs, even when age- and ethnicity-standardised. In general, there were higher rates of the provision of publicly-funded hip and knee TJR procedures among the smallest DHBs in New Zealand compared with the largest population DHBs in 2012-13.A strength of this study was the use of consistently collected data for the entire New Zealand population. A limitation is that domicile was obtained from the National Health Index database which is updated when patients present at their DHB and therefore may no longer reflect the domicile as it was at the time of surgery for all participants. This study is restricted to publicly-funded procedures, therefore it does not consider the overall provision of TJR surgery&#

Summary

Abstract

Aim

This study examines equity in the provision of publicly-funded hip and knee total joint replacement (TJR) surgery in New Zealand between 2006 and 2013 to: 1) investigate national rates by demographic characteristics; 2) describe changes in national rates over time; and 3) compare rates of provision between District Health Boards (DHBs).

Method

Hospital discharge data for people aged 20 years or over who had at least one hip or knee TJR between 2006 and 2013 was obtained from the Ministry of Healths National Minimum Dataset.

Results

Higher TJR rates were observed among those aged 75-84 years, females, those of M1ori ethnicity, those not living in rural or main urban areas and those in the most deprived socio-economic groups. TJRs increased from 7,053 in 2006 to 8,429 in 2013, however the rate was highest in 2007. In 2012-13, age-ethnicity-standardised rates varied between DHBs from 196 to 419/100,000 person years, with larger DHBs having lower rates than smaller DHBs.

Conclusion

There was evidence of geographic inequity in TJR provision across New Zealand. Despite increased numbers of procedures, rates of publicly-funded TJR surgery are barely keeping up with population increases. Reasons behind differences in provision should be examined.

Author Information

Helen Harcombe, Lecturer, Preventive and Social Medicine, University of Otago, Dunedin; Gabrielle Davie, Senior Research Fellow, Preventive and Social Medicine, University of Otago, Dunedin; Sarah Derrett, Associate Professor, Preventive and Social Medicine, University of Otago, Dunedin; Haxby Abbott, Research Associate Professor, Department of Surgical Sciences, University of Otago, Dunedin; David Gwynne-Jones, Associate Professor, Department of Surgical Sciences, University of Otago, Dunedin.

Acknowledgements

Correspondence

David Gwynne-Jones, Department of Surgical Sciences, University of Otago, Great King Street, Dunedin.

Correspondence Email

david.gwynne-jones@otago.ac.nz

Competing Interests

All authors report grants from Arthritis New Zealand during the conduct of the study; Dr Abbott was supported by a Sir Charles Hercus Health Research Fellowship from Health Research Council of New Zealand during the conduct of the study.

- - Rice DP, Fineman N. Economic implications of increased longevity in the United States. Annu Rev Public Health. 2004;25:457-73. Okunade AA, Murthy VNR. Technology as a major driver of health care costs: a cointegration analysis of the Newhouse conjecture. J Health Econ. 2002 Jan;21:147-59. Ministry of Health. Targeting more elective operations. Improved access to elective surgery. Ministry of Health; 2011; Available from:http://www.health.govt.nz/system/files/documents/publications/targeting-electives-health-target.pdf. The New Zealand Joint Registry Fifteen Year Report January 1999 to December 2013. 2014 [30 January 2014]; Available from: http://www.nzoa.org.nz/system/files/NZJR2014Report.pdf. Buckwalter JA, Saltzman C, Brown T. The impact of osteoarthritis: implications for research. Clin Orthop Relat Research. 2004 Oct:S6-15. Hooper G. The aging population and the increasing demand for joint replacement. NZMJ. 2013;126. Ministry of Health. Regional results from the 2011-2014 New Zealand Health Survey. 2015 [30 October 2015]; Available from: http://www.health.govt.nz/publication/regional-results-2011-2014-new-zealand-health-survey. Statistics New Zealand. 2013 Census QuickStats about people aged 65 and over. 2015; Available from: www.stats.govt.nz. Gwynne-Jones D. Quantifying the demand for hip and knee replacement in Otago, New Zealand. NZMJ. 2013 Jun 28;126:7-17. Ministry of Health. District health boards. [Accessed 30 January 2015]; Available from: http://www.health.govt.nz/new-zealand-health-system/key-health-sector-organisations-and-people/district-health-boards. Derrett S, Bevin TH, Herbison P, Paul C. Access to elective surgery in New Zealand: considering equity and the private and public mix. Int J Health Plann Manage. 2009 Apr-Jun;24:147-60. Derrett S, Cousins K, Gauld R. A messy reality: an analysis of New Zealands elective surgery scoring system via media sources, 2000-2006. Int J Health Plann Manage. 2013 Jan-Mar;28:48-62. Derrett S, Paul C, Herbison P, Williams H. Evaluation of explicit prioritisation for elective surgery: a prospective study. J Health Serv Res Policy. 2002 Jul;7 Suppl 1:S14-22. National Health Board. National Minimum Dataset (Hospital Events) Data Dictionary. Wellington: Ministry of Health; 2014. NCCH (National Centre for Classification in Health). The International Statistical Classification of Diseases and Related Health Problems, Tenth Revision, Australian Modification (3rd edn). Sydney: NCCH, Faculty of Health Sciences, The University of Sydney; 2002; Available from: http://meteor.aihw.gov.au/content/index.phtml/itemId/270546. Allan J. Review of the measurement of ethnicity. Statistics New Zealand; 2001 [2 September 2015]; Available from: http://www.stats.govt.nz/browse_for_stats/population/census_counts/review-measurement-of-ethnicity/classifications-and-issues.aspx. Salmond CE, Crampton P. Development of New Zealands Deprivation Index (NZDep) and its uptake as a national policy tool. Can J Public Health. 2012;103(Suppl 2):S7-S11 page S7. Statistics New Zealand. Defining urban and rural New Zealand. [Accessed 14 August 2015]; Available from: http://www.stats.govt.nz/browse_for_stats/Maps_and_geography/Geographic-areas/urban-rural-profile/defining-urban-rural-nz.aspx. StataCorp. Stata Statistical Software: Release 13: College Station, TX: StataCorp LP; 2013. Blackett J, Carslaw A, Lees D, et al. The impact of the 6-month waiting target for elective surgery: a patient record study. NZMJ. 2014 Nov 7;127:45-53. Synergia Limited. 2008. A review of the elective services orthopaedic major joint and ophthalmology cataract initiatives: A report prepared for the Ministry of Health. Wellington: Ministry of Health. Hooper G, Lee AJ, Rothwell A, Frampton C. Current trends and projections in the utilization rates of hip and knee replacement in New Zealand from 2001 to 2026.NZMJ. 2014 Aug 29;127:82-93. Ministry of Health. Annual update of key results 2013/14: New Zealand Health Survey. Wellington: Ministry of Health; 2014. Singleton N, Buddicom E, Vane A, Poutawera V. Are there differences between Maori and non-Maori patients undergoing primary total hip and knee arthroplasty surgery in New Zealand? A registry-based cohort study. NZMJ. 2013 Aug 2;126:23-30. Cormack D, Harris R. Issues in monitoring M1ori health and ethnic disparities: an update. Te R014dp016b Rangahau Hauora a Eru P014dmare: Wellington. 2009. Ministry of Health. About the electives programme. [Accessed 2 Sept 2015]; Available from: http://www.health.govt.nz/our-work/hospitals-and-specialist-care/elective-services/about-electives-programme- -

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Healthcare budgets are constrained and there are perennial concerns about the potential mismatch between health-care need and the provision of publicly-funded services. Ageing populations1 and technological advances2 are increasing pressures on healthcare budgets and the prioritisation of healthcare services can be required.3 One area that is likely to be affected by these pressures is total joint replacement (TJR) surgery. The most common reason for TJR surgery in New Zealand is osteoarthritis (OA)4 that is not responding adequately to conservative treatment. OA has a high prevalence among older adults5,6 with 29% of New Zealanders aged over 65 years diagnosed with this condition.7 This is important to consider as, currently in New Zealand, those aged over 65 years comprise 14% of the population but this is predicted to increase to 27% in 2063.8 Therefore, demand for TJR will likely increase substantially. In New Zealand, hip TJR surgery (including privately-funded procedures) has already increased between 1999 and 2013 by 75%; there was a corresponding 158% increase for knee TJR surgery.6 However, despite these increases, concerns have been raised that the provision of these procedures may not be expanding sufficiently to keep up with increases in clinical need or population changes.9Publicly-funded healthcare in New Zealand is provided by 20 District Health Boards (DHBs) \"responsible for providing or funding the provision of health services in their district\".10 In New Zealand, prioritisation scoring tools are used to determine access to publicly-funded TJR surgery. This should ensure equitable access across the country. However, Derrett et al (2009)11 found a lack of equity between DHBs in the provision of elective hip and knee TJR (2000 to 2005), and an analysis of New Zealand newspaper articles and Parliamentary questions from 2000-2006 found thataccess inequities remained a persistent theme (p.57).12 Although there has been an increase in funding for TJR surgery in New Zealand in recent years it is not clear whether that has translated into increased rates of surgical provision. Additionally, any increases in provision of TJR should be equitable with regard to geographic and demographic determinants such as place of residence, age, sex, ethnicity and socioeconomic deprivation.13 This paper examines publicly-funded elective hip and knee TJR surgery provision among DHBs in New Zealand from 2006-2013. The aims of this study are to: describe changes in rates of publicly-funded hip and knee TJR surgery nationally between 2006 and 2013, investigate whether national rates vary according to age, sex, ethnicity, small-area deprivation and rurality, and determine whether the provision of publicly-funded hip and knee TJR surgery is equitable across DHBs in New Zealand. MethodsThis study examined New Zealand hospital discharge data for publicly-funded hip and knee TJR surgery from 2006-2013. Ethical approval for the study was received from the University of Otago Human Ethics Committee (Reference number D13/253). Relevant hospital discharge data was obtained from the Ministry of Healths National Minimum Dataset (NMDS).14 The NMDS is a national collection containing publicly-funded hospital discharges and some privately-funded hospital discharges. Data was obtained for patients with at least one publicly-funded hip or knee TJR procedure who were discharged between 1 January 2006 and 31 December 2013. This time period was chosen as similar work on this topic11 analysed data up until the end of 2005, and 2013 data was the latest available at the time this study commenced. The variables obtained from the NMDS included the International Classification of Diseases version 10 (ICD10) clinical code, age at discharge, sex, domicile code, ethnicity, type of admission, diagnosis type, event dates and the principal health service purchaser. As well as waiting list admissions, arranged admissions defined asa planned admission where: the admission date is less than seven days after the date the decision was made by the specialist that the admission was necessary14 were also included as these were likely to capture urgent sub-acute OA patients. Acute admissions and injury admissions (primary diagnosis code within ICD10 S00-T98)15 were excluded as were those under 20 years of age at time of surgery and overseas residents. Hip and knee TJR surgeries were identified using the clinical codes in the 3rd edition of the Australian Modification of ICD10.15 The specific procedures included were: total arthroplasty of hip, total arthroplasty of knee, total arthroplasty of knee with bone graft to femur or to tibia, total arthroplasty of knee with bone graft to femur and tibia and total replacement arthroplasty of patellofemoral joint of knee. Hemiarthroplasty of the knee was also included because indications for this are similar to TJR and their popularity may vary across the country. Revisions of hip and knee joint replacements were not included as the aim was to focus on primary procedures. Records with missing or historic domicile codes that could not be forward-mapped were excluded as these could not be analysed by DHB, area-level deprivation or rurality. Self-identified ethnicity data collected at the patients health event was obtained from the NMDS. The recording of at least one ethnicity is mandatory, and two additional ethnic group codes may be recorded.14 As the DHB-level denominator data was only available by prioritised ethnicity, this approach was used in our analyses with estimates obtained for M1ori, Pacific, Asian and Other ethnicity groupings. Prioritisation follows a Statistics New Zealand (SNZ) algorithm with the end result being each person associated with only one ethnic group.16 M1ori ethnicity has the highest priority, meaning that people who identified as both M1ori and any other ethnicities are classified as M1ori. For example, those who identify as both M1ori and Pacific are classified as M1ori. Pacific ethnicity is given the next highest priority with those who identify as Pacific and any other ethnicity (apart from M1ori) being classified as Pacific.The New Zealand Deprivation Index (NZDep2006) is asmall-area index of relative socio-economic deprivation17 (p.S7) derived from 2006 Census data. The NZDep scale runs from one (an area in the least deprived 10% of small areas) to 10 (in the 10% most deprived small areas). The 1:1 mapping between domicile codes available in the NMDS and Census area units used by SNZ enabled NZDep to be assigned to each TJR discharge record. Rurality was also derived from domicile codes by 1:1 mapping with SNZs Census area units and SNZs Urban/Rural Profile Classification.18 The seven categories of the Urban/Rural profile were categorised for analysis as: Main Urban (described as beingvery large and centred on a city or main urban centre minimum population of 30,000),18 Other Urban which consisted of Satellite Urban (201cdefined as urban areas (other than main urban areas) where 20 percent or more of the usually resident employed populations workplace address is in a main urban area18and Independent Urban (defined as for Satellite Urban but <20 percent with a main urban area workplace), and Rural comprising the four rural profiles (Rural Areas with a High Urban Influence, Rural Areas with a Moderate Urban Influence, Rural Areas with a Low Urban Influence and Highly Remote Areas). Denominator data were sourced from SNZ, and restricted to those aged 20 years and above. Annual resident population estimates by year, ethnicity, sex, age group and DHB region for 2006-2013 were calculated by SNZ. Usually resident population counts from the 2006 Census were used for calculations involving rurality and deprivation. In 2010 the Southern DHB was created from a merger of two DHBs (Otago and Southland); for this study we combined data from those DHBs and considered them as the Southern DHB throughout the period analysed. Crude rates per 100,000 person years (py) were calculated and presented alongside exact Poisson 95% Confidence Intervals (CIs). Age-standardised rates (ASRs) were calculated using direct standardisation and five-year age groups. Ten five-year age groups (<45, 45-4980-84, 85+) were used for sex and ethnicity ASRs. Denominator data for deprivation and rurality ASRs was not available disaggregated by age for those over 65 years so these ASRs were calculated using age groups <45, 45-49, 50-54, 55-59, 60-64, 65+ years. Age- and ethnicity-standardised rates (AESRs) by DHBs were calculated in a similar way using four prioritised ethnic groups: M1ori, Pacific, Asian and Other. Linear trends in rates were analysed using Poisson regression. Pitmans variance ratio test was used to compare the distribution of AESRs by DHB over time. Analyses were carried out using Stata/SE (version 13.1).19ResultsOf the 74,784 procedures obtained from the NMDS for people with at least one publicly-funded hip or knee TJR and a date of discharge between 2006 and 2013, 62,907 (84.1%) met the inclusion criteria. Figure 1 details the exclusions. Of these 62,907 publicly-funded primary hip or knee TJR procedures, 2% were bilateral joint replacements giving a total of 64,222 primary hip or knee joints replaced (Table 1).Figure 1:Table 1:Publicly-funded primary total hip and knee joint replacement procedures in those aged 20 years and over, 2006-2013 by District Health Board (DHB). District Health Board Overall N Bilateral % Population* Overall Crude Rate** (95% CI) Ranking/20*** Auckland 3,472 1.8 330,660 131.3 (126.9, 135.7) 20 Bay of Plenty 4,373 1.9 149,663 365.2 (354.5, 376.2) 5 Canterbury 6,781 2.5 367,993 230.3 (224.9, 235.9) 16 Capital and Coast 3,001 5.4 211,259 177.6 (171.3, 184.0) 19 Counties Manukau 5,636 2.8 318,674 221.1 (215.3, 226.9) 17 Hawke's Bay 2,703 0.2 109,900 307.4 (296.0, 319.3) 11 Hutt Valley 1,918 5.3 100,735 238.0 (227.5, 248.9) 15 Lakes 1,827 1.4 71,043 321.5 (306.9, 336.6) 9 Mid Central 2,719 1.2 118,968 285.7 (275.1, 296.6) 12 Nelson Marlborough 3,015 2.4 102,653 367.1 (354.2, 380.5) 4 Northland 2,987 1.8 112,131 333.0 (321.2, 345.1) 8 South Canterbury 1,460 0.3 41,890 435.7 (413.6, 458.6) 3 Southern 4,734 2.7 222,008 266.5 (259.0, 274,2) 14 Tairawhiti 889 0.1 31,134 356.9 (333.8, 381.2) 7 Taranaki 2,013 1.3 79,248 317.5 (303.8, 331.7) 10 Waikato 5,757 1.4 256,493 280.6 (273.4, 287.9) 13 Wairarapa 866 0.9 29,839 362.8 (339.0, 387.8) 6 Waitemata 6,274 2.0 378,591 207.1 (202.1, 212.3) 18 West Coast 871 0.6 24,241 449.1 (419.8, 480.0) 1 Whanganui 1,611 0.8 45,012 447.4 (425.8, 469.8) 2 Total 62,907 2.1 3,102,133 253.5 (251.5, 255.5) *Population = Average DHB population for 2006-2013 of those aged 20 years and over. ** Rate/100,000 person years. ***Ranking is from highest to lowest overall crude rate for the 20 DHBs.Nationally, the number of publicly-funded hip and knee TJR procedures increased by 19.5% from 7,053 in 2006 to 8,429 in 2013 (Table 2) while the rate increased by only 10.7%. The rate peaked in 2007 at 263/100,000 py before decreasing (2008-2011) and returning to 261 and 262/100,000 py in 2012 and 2013 respectively. Although there was a statistically significant increase in the rates from 2006 onwards (p-value <0.001), there is no evidence to suggest a linear change in the rates from 2007 onwards (p-value=0.2).Table 2: Publicly-funded hip and knee total joint replacement procedures in New Zealand for those aged 20 years and over from 2006-2013 by year. Discharge Year Denominator Number Rate* 95% CI 2006 2982345 7,053 236.5 (231.0, 242.1) 2007 3015800 7,943 263.4 (257.6, 269.2) 2008 3046505 7,535 247.3 (241.8, 253.0) 2009 3083845 7,934 257.3 (251.7, 263.0) 2010 3124770 7,745 247.9 (242.4, 253.4) 2011 3158140 7,950 251.7 (246.2, 257.3) 2012 3185125 8,318 261.2 (255.6, 266.8) 2013 3220535 8,429 261.7 (256.2, 267.4) *Rate/100,000 person years of those aged 20 years and over.From 2006 to 2013 inclusive, the highest rate of publicly-funded hip and knee TJR procedures was for those aged 75-84 years at the time of surgery (1,063/100,000 py) followed by those aged 65-74 (907/100,000 py), with the lowest rate among those aged less than 55 years (45/100,000 py) (Table 3). ASRs were significantly higher for females (260/100,000 py) than for males (246/100,000 py).Table 3: Publicly-funded primary hip and knee total joint replacement procedures for those aged 20 years and over for 2006-2013 by socio-demographic characteristics. Denominator* N Annual crude rate (95% CI)** ASR*** (95% CI) Overall 3,102,133 62,907 253.5 (251.5, 255.5) -- -- -- Age group (years) <55 2,066,311 7,405 44.8 (43.8, 45.8) -- -- -- 55-64 474,338 14,939 393.7 (387.4, 400.0) -- -- -- 65-74 311,123 22,581 907.2 (895.4, 919.2) -- -- -- 75-84 183,611 15,611 1062.8 (1046.2, 1080.0) -- -- -- 85+ 66,751 2,371 444.0 (426.3, 462.2) -- -- -- Sex Female 1,612,114 34,075 264.2 (261.4, 267.0) 259.7 (257.0, 262.5) Male 1,490,019 28,832 241.9 (239.1, 244.7) 246.2 (243.4, 249.1) Prioritised Ethnicity M1ori 366,255 5,793 197.7 (192.7, 202.9) 303.1 (294.8, 311.5) Pacific 158,319 1,809 142.8 (136.3, 149.6) 224.2 (213.4, 235.0) Asian 327,923 1,259 48.0 (45.4, 50.7) 93.8 (88.2, 99.3) Other**** 2,249,636 54,046 300.3 (297.8, 302.9) 258.3 (256.1, 260.4) Rurality Main Urban Area 2,037,012 40,003 245.5 (243.1, 247.9) 258.6 (256.1, 261.1) Other Urban Area 399,417 14,672 459.2 (451.8, 466.7) 361.6 (355.7, 367.5) Rural 362,802 8,230 283.6 (277.5, 289.8) 295.9 (289.4, 302.3) NZDep 1-3 (least deprived) 785,292 13,314 211.9 (208.3, 215.6) 219.6 (215.9, 223.4) 4-7 1,136,757 26,780 294.5 (291.0, 298.0) 279.9 (276.6, 283.3) 8-10 (most deprived) 877,113 22,806 325.0 (320.8, 329.3) 342.0 (337.6, 346.5) *Uses 2006-2013 resident population estimates for all except Rurality and NZDep comparisons which use 2006 usuallyresident Census counts. **Rate/100,000 person years (226520 year-olds).***Age-standardised rate. ****The numerator of those classified as other ethnicity includes those with ethnicity recorded as Dont Know, Refused to answer, Response unidentifiable or Not Stated to align with denominator.The crude TJR rate of 300/100,000 py was highest among those categorised as Other ethnicity (ie those not identifying as M1ori, Pacific or Asian). M1ori had the second highest crude rate (198/100,000 py). However, M1ori had the highest ASR of procedures (303/100,000 py) followed by those of Other and Pacific ethnicities (258 and 224/100,000 py respectively). Those of Asian ethnicity had a substantially lower ASR (94/100,000 py). Differences in crude and ASRs between prioritised ethnic groups were all statistically significant.Rates were highest for people living in Other Urban Areas (ie urban areas other than those classified as centred on a city or main urban centre) with a crude rate of 459/100,000 py and an ASR of 362/100,000 py). This ASR was significantly higher than the ASR for those in Rural (296/100,000 py) and Main Urban Areas (259/100,000 py).There was a clear linear relationship between TJR procedure rates and socio-economic deprivation, with people that lived in the most deprived three deciles (deciles 8-10) having a significantly higher ASR (342/100,000 py) than those in deciles 4-7 (280/100,000 py) and similarly those who lived in the least deprived deciles (deciles 1-3) had a substantially lower ASR again (220/100,000 py).Of the 20 DHBs, 10 had increases in their age- and ethnicity-standardised rate (AESR) of TJR procedures between the periods 2006-07 to 2012-13, one was unchanged and nine had a reduced rate (Figure 2). Of the eight largest DHBs by population, five had an increase in AESR: Bay of Plenty (31%), Auckland (22%), Waitemata (25%), Canterbury (19%) and Counties Manukau (7%). Southerns AESR remained unchanged and Capital Coasts and Waikatos fell by 7% and 22% respectively. In contrast, AESRs fell between the periods 2006-07 to 2012-13 in seven of the 12 smaller DHBs: West Coast, Wairarapa, Tairawhiti, South Canterbury, Taranaki, Hawkes Bay and Northland. However, in 2012-13, the six smallest DHBs by population (with the exception of South Canterbury) had AESRs higher than five of the six DHBs with the largest populations. Five of the eight largest DHBs (Auckland, Canterbury, Capital and Coast, Southern and Waikato) were below the New Zealand average of 261/100,000 py in 2012-13 as were three of the smallest DHBs (Hawkes Bay, Taranaki and South Canterbury). To assess whether the variation in AESRs by DHB had changed over time, the standard deviation of DHBs AESRs for 2006-07 was compared with that from the rates for 2012-13. Excluding one outlier (West Coast), there was no statistically significant difference over time (ratio of standard deviations 1.13, (95% CI 0.70, 1.82), p=0.6).Figure 2: Age- and ethnicity-standardised rates of publicly-funded hip and knee total joint replacements per 100,000 person-years by District Health Board from 2006-2013.There were also variations by DHB for those in the most deprived deciles. For those in the most deprived three deciles, considering the eight years of the study combined, the ASRs varied from 236/100,000 py (Auckland) to 514/100,000 py (South Canterbury) (results not shown). Again, the smaller DHBs had greater provision within this group of the population, with the five smallest DHBs by population having ASRs of at least 400/100,000 pys, a rate which was not reached for the most deprived deciles in any of the other larger DHBs.DiscussionThis study demonstrates that national rates of publicly-funded elective hip and knee TJR procedures have not increased beyond their 2007 peak. Higher rates were observed in older adults, females, those not living in Rural or Main Urban Areas and those living in areas of greater social deprivation. Rates varied between DHBs, even when age- and ethnicity-standardised. In general, there were higher rates of the provision of publicly-funded hip and knee TJR procedures among the smallest DHBs in New Zealand compared with the largest population DHBs in 2012-13.A strength of this study was the use of consistently collected data for the entire New Zealand population. A limitation is that domicile was obtained from the National Health Index database which is updated when patients present at their DHB and therefore may no longer reflect the domicile as it was at the time of surgery for all participants. This study is restricted to publicly-funded procedures, therefore it does not consider the overall provision of TJR surgery&#

Summary

Abstract

Aim

This study examines equity in the provision of publicly-funded hip and knee total joint replacement (TJR) surgery in New Zealand between 2006 and 2013 to: 1) investigate national rates by demographic characteristics; 2) describe changes in national rates over time; and 3) compare rates of provision between District Health Boards (DHBs).

Method

Hospital discharge data for people aged 20 years or over who had at least one hip or knee TJR between 2006 and 2013 was obtained from the Ministry of Healths National Minimum Dataset.

Results

Higher TJR rates were observed among those aged 75-84 years, females, those of M1ori ethnicity, those not living in rural or main urban areas and those in the most deprived socio-economic groups. TJRs increased from 7,053 in 2006 to 8,429 in 2013, however the rate was highest in 2007. In 2012-13, age-ethnicity-standardised rates varied between DHBs from 196 to 419/100,000 person years, with larger DHBs having lower rates than smaller DHBs.

Conclusion

There was evidence of geographic inequity in TJR provision across New Zealand. Despite increased numbers of procedures, rates of publicly-funded TJR surgery are barely keeping up with population increases. Reasons behind differences in provision should be examined.

Author Information

Helen Harcombe, Lecturer, Preventive and Social Medicine, University of Otago, Dunedin; Gabrielle Davie, Senior Research Fellow, Preventive and Social Medicine, University of Otago, Dunedin; Sarah Derrett, Associate Professor, Preventive and Social Medicine, University of Otago, Dunedin; Haxby Abbott, Research Associate Professor, Department of Surgical Sciences, University of Otago, Dunedin; David Gwynne-Jones, Associate Professor, Department of Surgical Sciences, University of Otago, Dunedin.

Acknowledgements

Correspondence

David Gwynne-Jones, Department of Surgical Sciences, University of Otago, Great King Street, Dunedin.

Correspondence Email

david.gwynne-jones@otago.ac.nz

Competing Interests

All authors report grants from Arthritis New Zealand during the conduct of the study; Dr Abbott was supported by a Sir Charles Hercus Health Research Fellowship from Health Research Council of New Zealand during the conduct of the study.

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Healthcare budgets are constrained and there are perennial concerns about the potential mismatch between health-care need and the provision of publicly-funded services. Ageing populations1 and technological advances2 are increasing pressures on healthcare budgets and the prioritisation of healthcare services can be required.3 One area that is likely to be affected by these pressures is total joint replacement (TJR) surgery. The most common reason for TJR surgery in New Zealand is osteoarthritis (OA)4 that is not responding adequately to conservative treatment. OA has a high prevalence among older adults5,6 with 29% of New Zealanders aged over 65 years diagnosed with this condition.7 This is important to consider as, currently in New Zealand, those aged over 65 years comprise 14% of the population but this is predicted to increase to 27% in 2063.8 Therefore, demand for TJR will likely increase substantially. In New Zealand, hip TJR surgery (including privately-funded procedures) has already increased between 1999 and 2013 by 75%; there was a corresponding 158% increase for knee TJR surgery.6 However, despite these increases, concerns have been raised that the provision of these procedures may not be expanding sufficiently to keep up with increases in clinical need or population changes.9Publicly-funded healthcare in New Zealand is provided by 20 District Health Boards (DHBs) \"responsible for providing or funding the provision of health services in their district\".10 In New Zealand, prioritisation scoring tools are used to determine access to publicly-funded TJR surgery. This should ensure equitable access across the country. However, Derrett et al (2009)11 found a lack of equity between DHBs in the provision of elective hip and knee TJR (2000 to 2005), and an analysis of New Zealand newspaper articles and Parliamentary questions from 2000-2006 found thataccess inequities remained a persistent theme (p.57).12 Although there has been an increase in funding for TJR surgery in New Zealand in recent years it is not clear whether that has translated into increased rates of surgical provision. Additionally, any increases in provision of TJR should be equitable with regard to geographic and demographic determinants such as place of residence, age, sex, ethnicity and socioeconomic deprivation.13 This paper examines publicly-funded elective hip and knee TJR surgery provision among DHBs in New Zealand from 2006-2013. The aims of this study are to: describe changes in rates of publicly-funded hip and knee TJR surgery nationally between 2006 and 2013, investigate whether national rates vary according to age, sex, ethnicity, small-area deprivation and rurality, and determine whether the provision of publicly-funded hip and knee TJR surgery is equitable across DHBs in New Zealand. MethodsThis study examined New Zealand hospital discharge data for publicly-funded hip and knee TJR surgery from 2006-2013. Ethical approval for the study was received from the University of Otago Human Ethics Committee (Reference number D13/253). Relevant hospital discharge data was obtained from the Ministry of Healths National Minimum Dataset (NMDS).14 The NMDS is a national collection containing publicly-funded hospital discharges and some privately-funded hospital discharges. Data was obtained for patients with at least one publicly-funded hip or knee TJR procedure who were discharged between 1 January 2006 and 31 December 2013. This time period was chosen as similar work on this topic11 analysed data up until the end of 2005, and 2013 data was the latest available at the time this study commenced. The variables obtained from the NMDS included the International Classification of Diseases version 10 (ICD10) clinical code, age at discharge, sex, domicile code, ethnicity, type of admission, diagnosis type, event dates and the principal health service purchaser. As well as waiting list admissions, arranged admissions defined asa planned admission where: the admission date is less than seven days after the date the decision was made by the specialist that the admission was necessary14 were also included as these were likely to capture urgent sub-acute OA patients. Acute admissions and injury admissions (primary diagnosis code within ICD10 S00-T98)15 were excluded as were those under 20 years of age at time of surgery and overseas residents. Hip and knee TJR surgeries were identified using the clinical codes in the 3rd edition of the Australian Modification of ICD10.15 The specific procedures included were: total arthroplasty of hip, total arthroplasty of knee, total arthroplasty of knee with bone graft to femur or to tibia, total arthroplasty of knee with bone graft to femur and tibia and total replacement arthroplasty of patellofemoral joint of knee. Hemiarthroplasty of the knee was also included because indications for this are similar to TJR and their popularity may vary across the country. Revisions of hip and knee joint replacements were not included as the aim was to focus on primary procedures. Records with missing or historic domicile codes that could not be forward-mapped were excluded as these could not be analysed by DHB, area-level deprivation or rurality. Self-identified ethnicity data collected at the patients health event was obtained from the NMDS. The recording of at least one ethnicity is mandatory, and two additional ethnic group codes may be recorded.14 As the DHB-level denominator data was only available by prioritised ethnicity, this approach was used in our analyses with estimates obtained for M1ori, Pacific, Asian and Other ethnicity groupings. Prioritisation follows a Statistics New Zealand (SNZ) algorithm with the end result being each person associated with only one ethnic group.16 M1ori ethnicity has the highest priority, meaning that people who identified as both M1ori and any other ethnicities are classified as M1ori. For example, those who identify as both M1ori and Pacific are classified as M1ori. Pacific ethnicity is given the next highest priority with those who identify as Pacific and any other ethnicity (apart from M1ori) being classified as Pacific.The New Zealand Deprivation Index (NZDep2006) is asmall-area index of relative socio-economic deprivation17 (p.S7) derived from 2006 Census data. The NZDep scale runs from one (an area in the least deprived 10% of small areas) to 10 (in the 10% most deprived small areas). The 1:1 mapping between domicile codes available in the NMDS and Census area units used by SNZ enabled NZDep to be assigned to each TJR discharge record. Rurality was also derived from domicile codes by 1:1 mapping with SNZs Census area units and SNZs Urban/Rural Profile Classification.18 The seven categories of the Urban/Rural profile were categorised for analysis as: Main Urban (described as beingvery large and centred on a city or main urban centre minimum population of 30,000),18 Other Urban which consisted of Satellite Urban (201cdefined as urban areas (other than main urban areas) where 20 percent or more of the usually resident employed populations workplace address is in a main urban area18and Independent Urban (defined as for Satellite Urban but <20 percent with a main urban area workplace), and Rural comprising the four rural profiles (Rural Areas with a High Urban Influence, Rural Areas with a Moderate Urban Influence, Rural Areas with a Low Urban Influence and Highly Remote Areas). Denominator data were sourced from SNZ, and restricted to those aged 20 years and above. Annual resident population estimates by year, ethnicity, sex, age group and DHB region for 2006-2013 were calculated by SNZ. Usually resident population counts from the 2006 Census were used for calculations involving rurality and deprivation. In 2010 the Southern DHB was created from a merger of two DHBs (Otago and Southland); for this study we combined data from those DHBs and considered them as the Southern DHB throughout the period analysed. Crude rates per 100,000 person years (py) were calculated and presented alongside exact Poisson 95% Confidence Intervals (CIs). Age-standardised rates (ASRs) were calculated using direct standardisation and five-year age groups. Ten five-year age groups (<45, 45-4980-84, 85+) were used for sex and ethnicity ASRs. Denominator data for deprivation and rurality ASRs was not available disaggregated by age for those over 65 years so these ASRs were calculated using age groups <45, 45-49, 50-54, 55-59, 60-64, 65+ years. Age- and ethnicity-standardised rates (AESRs) by DHBs were calculated in a similar way using four prioritised ethnic groups: M1ori, Pacific, Asian and Other. Linear trends in rates were analysed using Poisson regression. Pitmans variance ratio test was used to compare the distribution of AESRs by DHB over time. Analyses were carried out using Stata/SE (version 13.1).19ResultsOf the 74,784 procedures obtained from the NMDS for people with at least one publicly-funded hip or knee TJR and a date of discharge between 2006 and 2013, 62,907 (84.1%) met the inclusion criteria. Figure 1 details the exclusions. Of these 62,907 publicly-funded primary hip or knee TJR procedures, 2% were bilateral joint replacements giving a total of 64,222 primary hip or knee joints replaced (Table 1).Figure 1:Table 1:Publicly-funded primary total hip and knee joint replacement procedures in those aged 20 years and over, 2006-2013 by District Health Board (DHB). District Health Board Overall N Bilateral % Population* Overall Crude Rate** (95% CI) Ranking/20*** Auckland 3,472 1.8 330,660 131.3 (126.9, 135.7) 20 Bay of Plenty 4,373 1.9 149,663 365.2 (354.5, 376.2) 5 Canterbury 6,781 2.5 367,993 230.3 (224.9, 235.9) 16 Capital and Coast 3,001 5.4 211,259 177.6 (171.3, 184.0) 19 Counties Manukau 5,636 2.8 318,674 221.1 (215.3, 226.9) 17 Hawke's Bay 2,703 0.2 109,900 307.4 (296.0, 319.3) 11 Hutt Valley 1,918 5.3 100,735 238.0 (227.5, 248.9) 15 Lakes 1,827 1.4 71,043 321.5 (306.9, 336.6) 9 Mid Central 2,719 1.2 118,968 285.7 (275.1, 296.6) 12 Nelson Marlborough 3,015 2.4 102,653 367.1 (354.2, 380.5) 4 Northland 2,987 1.8 112,131 333.0 (321.2, 345.1) 8 South Canterbury 1,460 0.3 41,890 435.7 (413.6, 458.6) 3 Southern 4,734 2.7 222,008 266.5 (259.0, 274,2) 14 Tairawhiti 889 0.1 31,134 356.9 (333.8, 381.2) 7 Taranaki 2,013 1.3 79,248 317.5 (303.8, 331.7) 10 Waikato 5,757 1.4 256,493 280.6 (273.4, 287.9) 13 Wairarapa 866 0.9 29,839 362.8 (339.0, 387.8) 6 Waitemata 6,274 2.0 378,591 207.1 (202.1, 212.3) 18 West Coast 871 0.6 24,241 449.1 (419.8, 480.0) 1 Whanganui 1,611 0.8 45,012 447.4 (425.8, 469.8) 2 Total 62,907 2.1 3,102,133 253.5 (251.5, 255.5) *Population = Average DHB population for 2006-2013 of those aged 20 years and over. ** Rate/100,000 person years. ***Ranking is from highest to lowest overall crude rate for the 20 DHBs.Nationally, the number of publicly-funded hip and knee TJR procedures increased by 19.5% from 7,053 in 2006 to 8,429 in 2013 (Table 2) while the rate increased by only 10.7%. The rate peaked in 2007 at 263/100,000 py before decreasing (2008-2011) and returning to 261 and 262/100,000 py in 2012 and 2013 respectively. Although there was a statistically significant increase in the rates from 2006 onwards (p-value <0.001), there is no evidence to suggest a linear change in the rates from 2007 onwards (p-value=0.2).Table 2: Publicly-funded hip and knee total joint replacement procedures in New Zealand for those aged 20 years and over from 2006-2013 by year. Discharge Year Denominator Number Rate* 95% CI 2006 2982345 7,053 236.5 (231.0, 242.1) 2007 3015800 7,943 263.4 (257.6, 269.2) 2008 3046505 7,535 247.3 (241.8, 253.0) 2009 3083845 7,934 257.3 (251.7, 263.0) 2010 3124770 7,745 247.9 (242.4, 253.4) 2011 3158140 7,950 251.7 (246.2, 257.3) 2012 3185125 8,318 261.2 (255.6, 266.8) 2013 3220535 8,429 261.7 (256.2, 267.4) *Rate/100,000 person years of those aged 20 years and over.From 2006 to 2013 inclusive, the highest rate of publicly-funded hip and knee TJR procedures was for those aged 75-84 years at the time of surgery (1,063/100,000 py) followed by those aged 65-74 (907/100,000 py), with the lowest rate among those aged less than 55 years (45/100,000 py) (Table 3). ASRs were significantly higher for females (260/100,000 py) than for males (246/100,000 py).Table 3: Publicly-funded primary hip and knee total joint replacement procedures for those aged 20 years and over for 2006-2013 by socio-demographic characteristics. Denominator* N Annual crude rate (95% CI)** ASR*** (95% CI) Overall 3,102,133 62,907 253.5 (251.5, 255.5) -- -- -- Age group (years) <55 2,066,311 7,405 44.8 (43.8, 45.8) -- -- -- 55-64 474,338 14,939 393.7 (387.4, 400.0) -- -- -- 65-74 311,123 22,581 907.2 (895.4, 919.2) -- -- -- 75-84 183,611 15,611 1062.8 (1046.2, 1080.0) -- -- -- 85+ 66,751 2,371 444.0 (426.3, 462.2) -- -- -- Sex Female 1,612,114 34,075 264.2 (261.4, 267.0) 259.7 (257.0, 262.5) Male 1,490,019 28,832 241.9 (239.1, 244.7) 246.2 (243.4, 249.1) Prioritised Ethnicity M1ori 366,255 5,793 197.7 (192.7, 202.9) 303.1 (294.8, 311.5) Pacific 158,319 1,809 142.8 (136.3, 149.6) 224.2 (213.4, 235.0) Asian 327,923 1,259 48.0 (45.4, 50.7) 93.8 (88.2, 99.3) Other**** 2,249,636 54,046 300.3 (297.8, 302.9) 258.3 (256.1, 260.4) Rurality Main Urban Area 2,037,012 40,003 245.5 (243.1, 247.9) 258.6 (256.1, 261.1) Other Urban Area 399,417 14,672 459.2 (451.8, 466.7) 361.6 (355.7, 367.5) Rural 362,802 8,230 283.6 (277.5, 289.8) 295.9 (289.4, 302.3) NZDep 1-3 (least deprived) 785,292 13,314 211.9 (208.3, 215.6) 219.6 (215.9, 223.4) 4-7 1,136,757 26,780 294.5 (291.0, 298.0) 279.9 (276.6, 283.3) 8-10 (most deprived) 877,113 22,806 325.0 (320.8, 329.3) 342.0 (337.6, 346.5) *Uses 2006-2013 resident population estimates for all except Rurality and NZDep comparisons which use 2006 usuallyresident Census counts. **Rate/100,000 person years (226520 year-olds).***Age-standardised rate. ****The numerator of those classified as other ethnicity includes those with ethnicity recorded as Dont Know, Refused to answer, Response unidentifiable or Not Stated to align with denominator.The crude TJR rate of 300/100,000 py was highest among those categorised as Other ethnicity (ie those not identifying as M1ori, Pacific or Asian). M1ori had the second highest crude rate (198/100,000 py). However, M1ori had the highest ASR of procedures (303/100,000 py) followed by those of Other and Pacific ethnicities (258 and 224/100,000 py respectively). Those of Asian ethnicity had a substantially lower ASR (94/100,000 py). Differences in crude and ASRs between prioritised ethnic groups were all statistically significant.Rates were highest for people living in Other Urban Areas (ie urban areas other than those classified as centred on a city or main urban centre) with a crude rate of 459/100,000 py and an ASR of 362/100,000 py). This ASR was significantly higher than the ASR for those in Rural (296/100,000 py) and Main Urban Areas (259/100,000 py).There was a clear linear relationship between TJR procedure rates and socio-economic deprivation, with people that lived in the most deprived three deciles (deciles 8-10) having a significantly higher ASR (342/100,000 py) than those in deciles 4-7 (280/100,000 py) and similarly those who lived in the least deprived deciles (deciles 1-3) had a substantially lower ASR again (220/100,000 py).Of the 20 DHBs, 10 had increases in their age- and ethnicity-standardised rate (AESR) of TJR procedures between the periods 2006-07 to 2012-13, one was unchanged and nine had a reduced rate (Figure 2). Of the eight largest DHBs by population, five had an increase in AESR: Bay of Plenty (31%), Auckland (22%), Waitemata (25%), Canterbury (19%) and Counties Manukau (7%). Southerns AESR remained unchanged and Capital Coasts and Waikatos fell by 7% and 22% respectively. In contrast, AESRs fell between the periods 2006-07 to 2012-13 in seven of the 12 smaller DHBs: West Coast, Wairarapa, Tairawhiti, South Canterbury, Taranaki, Hawkes Bay and Northland. However, in 2012-13, the six smallest DHBs by population (with the exception of South Canterbury) had AESRs higher than five of the six DHBs with the largest populations. Five of the eight largest DHBs (Auckland, Canterbury, Capital and Coast, Southern and Waikato) were below the New Zealand average of 261/100,000 py in 2012-13 as were three of the smallest DHBs (Hawkes Bay, Taranaki and South Canterbury). To assess whether the variation in AESRs by DHB had changed over time, the standard deviation of DHBs AESRs for 2006-07 was compared with that from the rates for 2012-13. Excluding one outlier (West Coast), there was no statistically significant difference over time (ratio of standard deviations 1.13, (95% CI 0.70, 1.82), p=0.6).Figure 2: Age- and ethnicity-standardised rates of publicly-funded hip and knee total joint replacements per 100,000 person-years by District Health Board from 2006-2013.There were also variations by DHB for those in the most deprived deciles. For those in the most deprived three deciles, considering the eight years of the study combined, the ASRs varied from 236/100,000 py (Auckland) to 514/100,000 py (South Canterbury) (results not shown). Again, the smaller DHBs had greater provision within this group of the population, with the five smallest DHBs by population having ASRs of at least 400/100,000 pys, a rate which was not reached for the most deprived deciles in any of the other larger DHBs.DiscussionThis study demonstrates that national rates of publicly-funded elective hip and knee TJR procedures have not increased beyond their 2007 peak. Higher rates were observed in older adults, females, those not living in Rural or Main Urban Areas and those living in areas of greater social deprivation. Rates varied between DHBs, even when age- and ethnicity-standardised. In general, there were higher rates of the provision of publicly-funded hip and knee TJR procedures among the smallest DHBs in New Zealand compared with the largest population DHBs in 2012-13.A strength of this study was the use of consistently collected data for the entire New Zealand population. A limitation is that domicile was obtained from the National Health Index database which is updated when patients present at their DHB and therefore may no longer reflect the domicile as it was at the time of surgery for all participants. This study is restricted to publicly-funded procedures, therefore it does not consider the overall provision of TJR surgery&#

Summary

Abstract

Aim

This study examines equity in the provision of publicly-funded hip and knee total joint replacement (TJR) surgery in New Zealand between 2006 and 2013 to: 1) investigate national rates by demographic characteristics; 2) describe changes in national rates over time; and 3) compare rates of provision between District Health Boards (DHBs).

Method

Hospital discharge data for people aged 20 years or over who had at least one hip or knee TJR between 2006 and 2013 was obtained from the Ministry of Healths National Minimum Dataset.

Results

Higher TJR rates were observed among those aged 75-84 years, females, those of M1ori ethnicity, those not living in rural or main urban areas and those in the most deprived socio-economic groups. TJRs increased from 7,053 in 2006 to 8,429 in 2013, however the rate was highest in 2007. In 2012-13, age-ethnicity-standardised rates varied between DHBs from 196 to 419/100,000 person years, with larger DHBs having lower rates than smaller DHBs.

Conclusion

There was evidence of geographic inequity in TJR provision across New Zealand. Despite increased numbers of procedures, rates of publicly-funded TJR surgery are barely keeping up with population increases. Reasons behind differences in provision should be examined.

Author Information

Helen Harcombe, Lecturer, Preventive and Social Medicine, University of Otago, Dunedin; Gabrielle Davie, Senior Research Fellow, Preventive and Social Medicine, University of Otago, Dunedin; Sarah Derrett, Associate Professor, Preventive and Social Medicine, University of Otago, Dunedin; Haxby Abbott, Research Associate Professor, Department of Surgical Sciences, University of Otago, Dunedin; David Gwynne-Jones, Associate Professor, Department of Surgical Sciences, University of Otago, Dunedin.

Acknowledgements

Correspondence

David Gwynne-Jones, Department of Surgical Sciences, University of Otago, Great King Street, Dunedin.

Correspondence Email

david.gwynne-jones@otago.ac.nz

Competing Interests

All authors report grants from Arthritis New Zealand during the conduct of the study; Dr Abbott was supported by a Sir Charles Hercus Health Research Fellowship from Health Research Council of New Zealand during the conduct of the study.

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