The public health system will need to have adequate resources to meet a marked increase in demand for knee and hip replacements as the population continues to grow and age, researchers say.
An Otago University study that looked at hip and knee total joint replacement (TJR) procedures says the number of such surgeries rose by 6 per cent from 2006 and 2013.
But a growing population meant the per capita rate actually fell by 0.6 per cent.
The research, funded by Arthritis NZ and published in the NZ Medical Journal, found that the highest rate of public-funded joint replacement procedures was for those aged 75 to 84.
The next largest group was those aged 65 to 74.
Study principal investigator Dr Helen Harcombe says nearly one-third of New Zealanders over 65 are diagnosed with osteoarthritis, the most common reason for joint replacement surgery.
She says 14 per cent of the population is currently in this age group, a figure that is predicted to rise to 27 per cent by 2063.
"This means demand for TJR surgeries is likely to increase markedly in coming years and the public health system will need to be adequately resourced to meet future demand," she said.
The research also showed up geographically-based inequities in getting treatment.
Dr Harcombe said that even taking into account age and ethnicity, rates of TJR procedures varied between district health boards.
She said DHBs covering larger populations tended to have lower rates than smaller ones.
The three boards with the highest rates of TJRs were West Coast, Whanganui and South Canterbury.
The lowest rates were in Waitamata, Capital and Coast, and at the bottom of the table, Auckland.