Australian Pain Society Poster Abstract, Melbourne, April 13-16, 2025

Title: FIFTY PERCENT OF PEOPLE HAVE NO PAIN 12-MONTHS AFTER A TOTAL KNEE REPLACEMENT FOR OSTEOARTHRITIS

Authors: Johns, N^1,2,5; Naylor, J³; McKenzie, D¹; Brady, B⁴; Olver, J¹

Affiliations: 1 Epworth Monash Rehabilitation Medicine Research Unit, Richmond, Victoria, Australia; 2. Peninsula Health, Subacute, Rehabilitation, Frankston, Victoria, Australia; 3 Whitlam Orthopaedic Research Centre, Liverpool, NSW, Australia; 4 Physiotherapy Department & Department of Pain Medicine, Liverpool Hospital, Sydney NSW, Australia; 5 The Rehabilitation Medicine Group, Melbourne, Australia

Background and aims

There is a high expectation from consumers that a total knee replacement (TKR) to treat osteoarthritis will eliminate pain, but the exact percentage of those who achieve this is mostly unknown. Without this knowledge, it is challenging for clinicians to help in setting realistic expectations from surgery and post-operative rehabilitation. The aims of this study are to investigate (i) the percentage of people who are pain-free at 3-, 12- and 36-months post-surgery and (ii) the percentage who stay or become pain-free at 12- and 36-months.

Methods

This is a retrospective analysis of data from a large Australian study (EPOC, HREC approved) that followed participants with osteoarthritis for 3-years after they had a total knee replacement.  The presence of pain was investigated using the Oxford Knee Pain Subscale Score which has scores ranging from 0 (most severe pain) to 28 (pain-free) across 7 categorical questions (Harris et al., Qual Life Res, 2013). The pain subscale questions capture the experiences of walking for 30 minutes, standing from a chair, limping, night knee pain, pain interference and feeling the knee might ‘give way’.  Relative risks for becoming pain-free were calculated using Poisson regression with robust standard errors using Stata/BE 18.5 Software.

Results

At 3-months post-TKR, 151 of 1034 participants (14.6%) were pain-free, at 12-months 517 of 1034 participants (50.0%) were pain-free and at 36-months, 300 of the 721 participants (41.6%) were pain-free.  A greater majority of participants who were pain-free at 3-months post-TKR, remained pain-free at 12-months compared to those with pain at 3-months who became pain-free: 122/151 (80.8%) versus 395/883 (44.7%), relative risk = 1.8 (95% confidence interval 1.6 – 2.0, p<0.001). Again, a greater majority of those who were pain-free at 12-months remained pain-free at 36-months compared to those with pain at 12-months who became pain-free: 216/369 (58.5%) versus 84/352 (23.9%), relative risk = 2.5 (95% confidence interval 2.0 – 3.0, p<0.001).

Conclusion

Almost 45% of participants with pain persisting at 3-months became completely pain-free by 12-months post-surgery. The low percentage of only 14.6% of participants being pain-free at 3-months but improving to 50% at 12-months is consistent with the Australian Orthopaedic Association National Joint Registry Annual Report, 2021, (accessed online) finding that only 28% of people were completely pain-free at 6-months post-TKR, (measured using a numerical rating scale). There is an advantage to being pain-free at either 3- and 12-months as it increases the likelihood of remaining pain-free at 12- and 36- months respectively. As treatment was not recorded after 3-months, it is not possible to speculate what led to the changes, but clinicians and recipients of knee replacements should be alert to the possibility that, despite persisting pain, they can still become pain-free after 3-months has elapsed.