Change in willingness for surgery and risk of joint replacement after an education and exercise program for hip/knee osteoarthritis: A longitudinal cohort study of 55,059 people

Belinda J Lawford; Ali Kiadaliri; Martin Englund; Kim L Bennell; Rana S Hinman; Michelle Hall; Andrea Dell’Isola

doi:10.1371/journal.pmed.1004577

. 2025 May 8;22(5):e1004577. doi: 10.1371/journal.pmed.1004577

Change in willingness for surgery and risk of joint replacement after an education and exercise program for hip/knee osteoarthritis: A longitudinal cohort study of 55,059 people

Belinda J Lawford ¹, Ali Kiadaliri ², Martin Englund ², Kim L Bennell ¹, Rana S Hinman ¹, Michelle Hall ³, Andrea Dell’Isola ^2,^*

Editor: Christelle Nguyen⁴

PMCID: PMC12061182 PMID: 40338890

Abstract

Background

Numerous studies report that education and exercise interventions can shift people’s willingness to undergo joint replacement surgery for osteoarthritis. We aimed to investigate whether becoming unwilling to undergo surgery following an education and exercise intervention for hip and knee osteoarthritis is associated with lower probability of receiving actual surgery.

Methods and findings

This was a register-based cohort study including people from the Swedish Osteoarthritis Register who underwent a 3-month education and exercise intervention for knee or hip osteoarthritis. Participants self-reported their willingness to have joint replacement surgery (‘yes’ or ‘no’) and were grouped based on their response pre- and post-intervention (always willing for surgery; became unwilling for surgery; never willing for surgery; became willing for surgery). Data on joint replacement surgery was obtained through the Swedish Arthroplasty Register. The probability and hazard of surgery occurring, as well as the mean time without surgery was calculated up to 5-years (primary outcome) and 9-years (secondary outcome) post-intervention. We adjusted for age, sex, body mass index (BMI), education, joint pain, quality of life, walking difficulties, number of prior visits with an orthopedic surgeon, prior joint surgeries in the knee or hip (other than joint replacement), and comorbidities.

55,059 people were included, 69% were female (N = 37,739), with a mean age 66years (standard deviation [SD] = 9.3), and a BMI of 27.5 (SD = 4.9). In total, 70% (N = 38,386) were never willing for surgery, 14% (N = 7,736) were always willing for surgery, 10% (N = 5,649) became unwilling for surgery, and 6% (N = 3,288) became willing for surgery. Compared to those who were always willing for surgery, participants who became unwilling had a 20% (95% confidence interval [CI]: 18, 22%) lower probability of having surgery by 5-years post-intervention. This corresponded to delaying surgery by 1.1 (95% CI: 1.0, 1.1) years. Compared to those who were always willing for surgery, the hazard of surgery occurring at 1-year post-intervention was lower in those who became unwilling (hazard ratio (HR) 0.5 [95% CI: 0.4, 0.5]), though was then higher at 5-years (HR 1.4 [95% CI: 1.2, 1.7]). Estimates remained stable from 5 to 9 years. Limitations of our study include the inability to account for all potential confounders, and to infer the contribution of the intervention to change in willingness for surgery due to the absence of a control group. Data were collected in Sweden, generalisability to other countries may be limited.

Conclusions

Becoming unwilling for joint replacement surgery following an education and exercise program for hip and knee osteoarthritis could reduce the number of joint replacement surgeries by 20% at 5 years post-intervention, with the possibility of maintaining most of this reduction up to 9 years post-intervention. Interventions that can shift willingness to undergo surgery may thus result in relevant delays and reductions in future joint replacements.

Author summary

Why Was This Study Done?

Each year, millions of hip and knee joint replacement surgeries are performed for osteoarthritis worldwide, incurring substantial healthcare costs.
First-line interventions like education and exercise interventions can shift self-reported willingness to undergo joint replacement surgery for osteoarthritis.
However, it remains unclear whether change in self-reported willingness for surgery results in a reduction in the actual number of surgeries occurring in the short, medium, and long-term.

What Did the Researchers Do and Find?

This was a register-based cohort study including 55,059 people from Sweden who underwent a 3-month education and exercise intervention for knee or hip osteoarthritis.
Participants self-reported their willingness to have joint replacement surgery (‘yes’ or ‘no’) and were grouped based on whether their willingness changed after completing the intervention.
People who became unwilling for surgery had a 20% lower probability of having actual surgery by 5-years after the intervention, compared to those who were always willing for surgery, corresponding to delaying the procedure by 1.8 years.

What Do These Findings Mean?

Shifting willingness for joint replacement surgery in people with osteoarthritis could delay joint replacement surgery and lead to a reduction in the number of surgeries, potentially contributing to substantial economic savings.
A simple question about willingness for surgery can be used as a proxy measure of progression to actual surgery in the short-medium term following an intervention, which could be used to help clinicians identify patients who may benefit from additional support to help them avoid or delay surgery in the future.
We were unable to account for all potential confounders, and, due to the absence of a control group, we cannot infer whether the education and exercise intervention, or something else, contributed to a change in willingness for surgery.

Belinda J Lawford and colleagues investigate whether becoming unwilling to undergo surgery following an education and exercise intervention for hip and knee osteoarthritis is associated with lower probability of receiving actual surgery.

Introduction

Osteoarthritis (OA) of the knee and hip is one of the leading causes of pain and disability worldwide [1]. Globally, healthcare expenditure for OA is substantial, predominantly driven by the costs associated with total joint replacement surgery [2]. Each year, > 1.2 million hip and knee joint replacements are performed in the US alone, incurring $20 billion USD in healthcare costs [2,3]. In 2023, 17,089 hip joint replacements and 16,549 knee joint replacements for OA were performed in Sweden (10.5M inhabitants) [4], costing approximately $462 million USD [5]. With the ageing population and rising prevalence of obesity and sedentary lifestyles, rates of joint replacement surgery are projected to increase in the coming decades [6,7]. However, joint replacement surgery may not be effective for everyone [8], particularly for knee joint replacement where 1 in 4 patients report unsatisfactory symptom improvement [9–11]. Additional cost savings could therefore be achieved by providing non-surgical management of OA to prevent or delay joint replacement.

Clinical guidelines overwhelmingly recommend non-surgical, non-pharmacological treatment as core components of OA management [12–15], in particular education and advice, exercise, and weight loss for people who have overweight or obesity. Exercise is recommended for all people with hip and knee OA, irrespective of age, comorbidity, pain severity, or disability [12–15], due to its potential to improve joint pain and physical function [16,17]. There is also evidence that education and exercise programs can reduce or delay the need for joint replacement surgery among people with knee and hip OA [18–21].

Among the many factors influencing uptake of joint replacement surgery in people with knee and hip OA, self-reported willingness to have surgery has been shown to be the strongest predictor [22]. Numerous studies have suggested that exercise interventions can shift willingness to undergo surgery for knee and hip OA [23–27], with up to 71% of participants no longer desiring surgery after participation [21,23]. However, it remains unclear whether change in self-reported willingness for joint replacement surgery results in a reduction in the number of surgeries occurring in the short, medium, and long-term. Such information can be used to support the validity and usefulness of self-reported outcome measures related to willingness for surgery and guide future research on OA management. Thus, the aim of this study was to use long-term cohort data to investigate whether becoming unwilling to undergo surgery following an education and exercise intervention for hip and knee osteoarthritis is associated with lower probability of receiving actual surgery.

Methods

Study design

This is a longitudinal observational register-based cohort study using data from the Swedish Osteoarthritis Register (SOAR). The SOAR was started in 2008 and currently includes data from more than 120,000 individuals who sought treatment for OA in primary healthcare in Sweden [28]. To be eligible for inclusion in SOAR, participants were required to receive a clinical diagnosis of OA from primary or secondary care in Sweden and agree to participate in an education and exercise program. People with joint pain caused by another disease (e.g., hip fracture, inflammatory joint disease, cancer) were not eligible.

This study is reported as per the Reporting of Studies Conducted using Observational Routinely-Collected Data (RECORD) guideline [29] (S1 Appendix). Analyses were planned upon conception of this study. Data-driven changes to analyses were performed in response to peer reviewer comments, including adding another secondary analysis to stratify outcomes by pain severity.

Education and exercise program

In Sweden, people with clinically confirmed OA can be referred by their healthcare provider to a publicly-funded education and exercise intervention, which is described in detail elsewhere [30,31]. Briefly, it comprises a mandatory education component (2 x 1-hour sessions) and a 3-month exercise component (up to 12 sessions with a physiotherapist) with the aim to improve participant ability to self-manage their OA. During education sessions, participants are provided with information about disease pathophysiology, the effectiveness and indication of OA treatments (including surgery, pharmacological management methods, and non-pharmacological management methods), benefits of exercise, self-management advice, and strategies around incorporating exercise into daily life. During the exercise component, participants receive a personalised program (based on individual needs, preferences, and level of physical function) to be completed three times per week, along with detailed exercise instructions. Participants provided data via an interview with a physiotherapist and self-reported questionnaire at the start (‘baseline’) and at the end (‘post-intervention’) of the program. At the first visit, the clinician and patient decided which was the most symptomatic joint to target in the intervention (knee or hip). In the case of OA affecting multiple joints, the most symptomatic joint was considered as the ‘index’ joint for the intervention. No major changes to this program were made during the timeframe of this study.

Study sample

This project was approved by the Ethical Review Authority Board in Sweden (original application 2019‒02570 and amendment 2020‒04460). As this was a registry study, no additional consent was required from the participants for the specific research questions investigated. All participants had already agreed to allow their data to be used for research purposes at the time of their inclusion in the registry.

The sample used in this study consisted of people recorded in the SOAR between January 2008 and December 2018 who underwent the education and exercise program for their knee or hip OA (N = 71,089). We excluded anyone who had not been living in Sweden over the 10 years preceding the intervention (to minimize the chance that they had previously received a joint replacement, N = 511; Fig 1), anyone who had already had knee or hip joint replacement surgery (N = 4,996), and anyone who did not report their willingness for surgery at post-intervention (N = 2,570). Although follow-up is intended to occur at 3-months, some participants provided follow-up data earlier or later than that (i.e., they finished the intervention early or late due to scheduling issues or other disruptions) or did not provide follow-up data at all (i.e., had dropped out of the intervention). As such, to enhance data quality and maximise the generalizability of the results to similar interventions, we excluded participants who did not provide post-intervention within a reasonable timeframe (i.e., we excluded anyone who provided data >1 month before or more than 2 months after the 3-month follow-up time point; N = 7,944).

Fig 1 — SOAR, Swedish Osteoarthritis Register.

Exposure

Willingness to undergo joint replacement surgery was self-reported via questionnaire using the question “Are your joint symptoms so severe that you wish to undergo surgery?” (‘Yes’ or ‘No’) collected pre- and post-intervention. We grouped participants into four categories based on their self-reported willingness pre- and post-intervention: YES-YES, always willing for surgery; NO-NO, never willing for surgery; YES-NO, became unwilling for surgery, and; NO-YES, became willing for surgery.

Outcome

Data relating to incident joint replacement surgery (i.e., the first joint replacement received by a person) for OA in either the hip or the knee was collected via the Swedish Arthroplasty Register. The register has a data completeness of 98%, covering nearly all the joint replacement surgeries performed in Sweden [4]. Our primary outcome was any joint replacement surgery due to OA up to five years post-intervention, as we assumed willingness for surgery was more likely to influence people’s decision closer to the time point at which it was collected. Incident joint replacement surgery up to 9 years was reported in a secondary analysis (limited at 9 years as it was the last time point where at least 1% of the population had usable data; i.e., they did not experience the outcome and were not censored). All participants were followed from the 3-month post-intervention date until they either had joint replacement surgery for OA, death, joint replacement for reasons other than OA (e.g., fractures, cancer), relocation outside Sweden, or 31st December 2018, whichever came first. We did not match the index joint with the joint being replaced because surgery prioritisation in patients with multiple joint OA is not solely symptom-based; for example, a surgeon may choose to operate on the hip before the knee for biomechanical reasons, even if the knee is more severely affected. Moreover, the intervention focuses on overall symptoms and self-management, which are transferable over multiple joints.

Confounders

Based on prior evidence and direct acyclic graphs to identify confounders, we considered age, sex, body mass index (BMI), education (as proxy for socioeconomic status), joint pain (both at baseline and post-intervention to capture both absolute pain and change during the intervention; measured on 11-point Numeric Rating Scale ranging from 0 [no pain] to 10 [worst possible pain]), quality of life (both at baseline and post-intervention; measured on the Eq5D), walking difficulties (both at baseline and post-intervention; recorded as ‘Yes’ or ‘No’), self-efficacy for pain (both at baseline and post-intervention; measured on Arthritis Self-Efficacy Scale), number of prior visits with an orthopedic surgeon in the year before the program, prior joint surgeries in the knee or hip (other than joint replacement), and comorbidities (Measured using Elixhauser score) as confounders [24,32–34]. All analyses were adjusted for confounders with the exception of self-efficacy for pain which was included as a confounder only in a secondary analysis. This was because the scale assessing self-efficacy for pain was no longer recorded from 2017 (i.e., all participants from 2017-2018 have the variable missing). Information about how each confounder variable was measured is included in S2 Appendix.

Statistical analysis

We used flexible parametric survival models based on restricted cubic splines (“stpm2” command in Stata [35]) to estimate the association between change in willingness to undergo surgery during the intervention and the hazard of undergoing total joint replacement in the 5- and 9-years post-intervention.

Considering the low prevalence of missing exposure data (94% of the sample has complete data) and the large sample size, no imputation of missing data was performed. We tested the assumption of proportional hazard using Wald test for testing the statistical significance of an exposure*time interaction (i.e., the effect of the exposure on the outcome varied over time) and by assessing model fit. Model fit (for degrees of freedom 1−5 for the main model and up to i-1 for the time varying factor where i is the degree of freedom of the main model) was assessed graphically by plotting the predicted cumulative hazard of models with and without time-varying factors against the Nelson-Aalen estimates and statistically by comparing the Bayesian information criterion (BIC) of the models with and without time varying coefficients (lower values indicate better fit). To choose the final model we used a parsimonious approach where the simplest model with the lowest BIC was selected [36].

The final model was adjusted for the confounders listed above. We then predicted standardised survival curves (using stpm2_standsurv command in Stata [37]), adjusted for all the listed confounders, under four counterfactual scenarios where all the participants are in the same willingness for surgery subgroup – i.e., never willing for surgery (Scenario 1), became willing for surgery (Scenario 2), became unwilling for surgery (Scenario 3) and always willing for surgery (Scenario 4). As we were interested in reducing the need for surgery, our main analysis compared the counterfactual scenario where everyone is willing for surgery at both pre- and post-intervention (always willing for surgery) with the scenario where people become unwilling for surgery. In a secondary analysis, we compared the counterfactual scenario where no one is willing for surgery at both pre- and post-intervention (never willing for surgery) with the scenario where people become willing for surgery. We contrasted these scenarios in terms of the following estimates:

(i) proportion of individuals who have not had joint replacement surgery (i.e., probability of survival and difference in probability of survival between subgroups);
(ii) hazard of receiving joint replacement surgery at a specific time point (i.e., instantaneous hazard of surgery per 1,000 people among those who have not yet had surgery at that time, and hazard ratios between subgroups), and;
(iii) mean time without having joint replacement surgery (i.e., restricted mean survival time and difference in mean survival time between subgroups).

We also conducted additional secondary analyses: (i) repeated the analysis extending the follow-up time up to 9 years; (ii) repeated the analysis with follow-up to 9 years stratified by the index joint (most symptomatic joint, knee or hip); (iii) repeated the analysis with follow-up to 9 years stratified by pain severity at baseline (pain above median considered severe and below median as mild), and; (iv) adjusted the main analysis for self-efficacy at baseline and post-intervention.

Results

In total, 55,059 individuals with hip (N = 17,216; 31%) or knee (N = 37,843; 69%) OA from the SOAR were included in this study (S3 Appendix). Most participants were female (N = 37,739; 69%), with a mean age 66.1 years (standard deviation [SD] = 9.3), and a BMI of 27.5 (SD = 4.9). At baseline, mean (SD) joint pain was 5.3 out of 10 (SD = 2.0) and reduced to 4.3 (SD = 2.3) at 3-month post-intervention.

More than two-thirds of participants (N = 38,386, 70%; Table 1) were never willing for surgery, 14% (N = 7,736) were always willing, 10% (N = 5,649) became unwilling, and 6% (N = 3,288) became willing. Compared to those who were always willing for surgery, those who became unwilling showed milder symptoms post-intervention and were more likely to have knee OA. The opposite was observed when comparing those who were never willing for surgery to those who became willing, in that those who became willing had more severe symptoms and were less likely to have knee OA.

Table 1. Demographics and sample characteristics (N = 55,059).

	Never willing for surgery	Became willing for surgery	Became unwilling for surgery	Always willing for surgery	Total
	N: 38,386	N: 3,288	N: 5,649	N: 7,736	N: 55,059
Sex, N (%)
Male	10,483 (27)	1,153 (35)	2,285 (40)	3,399 (44)	17,320 (32)
Female	27,903 (73)	2,135 (65)	3,364 (60)	4,337 (56)	37,739 (69)
Age (years), mean (SD)	66.2 (9.3)	66.8 (9.2)	65.0 (9.5)	65.9 (9.5)	66.1 (9.3)
Body mass index, mean (SD)	27.2 (4.8)	27.9 (4.9)	28.2 (4.9)	28.5 (5.1)	27.5 (4.9)
Education attainment, N (%)
0–9 years	11,914 (31)	1,156 (35)	1,982 (35)	2,914 (38)	17,966 (33)
10–14 years	14,387 (38)	1,258 (39)	2,263 (40)	3,176 (41)	21,084 (38)
>14 years	11,952 (31)	852 (26)	1,388 (25)	1,619 (21)	15,811 (29)
Affected joint, N (%)
Hip	11,132 (29)	1,345 (41)	1,566 (28)	3,173 (41)	17,216 (31)
Knee	27,254 (71)	1,943 (59)	4,083 (72)	4,563 (59)	37,843 (69)
Walking difficulties, N (%)
No	10,016 (26)	346 (11)	409 (7)	248 (3)	11,019 (20)
Yes	28,089 (74)	2,928 (89)	5,206 (93)	7,460 (97)	43,683 (80)
Pain at baseline^*, mean (SD)	4.9 (2.0)	5.8 (1.8)	6.3 (1.7)	6.8 (1.6)	5.3 (2.0)
Pain at follow-up^*, mean (SD)	3.7 (2.0)	6.3 (1.8)	4.2 (2.0)	6.5 (1.8)	4.3 (2.3)
Quality of life at baseline^£, mean (SD)	0.7 (0.2)	0.6 (0.2)	0.5 (0.2)	0.4 (0.3)	0.6 (0.2)
Quality of life at follow-up^£, mean (SD)	0.7 (0.1)	0.5 (0.2)	0.7 (0.2)	0.5 (0.3)	0.7 (0.2)
Pain self-efficacy^§, mean (SD)	67.2 (17.3)	61.3 (17.3)	55.6 (18.0)	49.6 (18.4)	63.3 (18.7)
Number of comorbidities^¥, N (%)
0	25,565 (67)	1,968 (60)	3,512 (62)	4,666 (60)	35,711 (65)
1	7,068 (18)	677 (21)	1,088 (19)	1,528 (20)	10,361 (19)
2	3,304 (9)	355 (11)	587 (10)	781 (10)	5,027 (9)
3 +	2,449 (6)	288 (8)	462 (9)	761 (10)	3,960 (7)
Comorbidity Elixhauser^¥ score (0–31), mean (SD)	0.6 (1.0)	0.8 (1.2)	0.7 (1.2)	0.8 (1.2)	0.6 (1.1)
Visited surgeon previous year, N (%)
No	35,137 (92)	2,814 (86)	4,777 (85)	6,199 (80)	48,927 (89)
Yes	3,249 (8)	474 (14)	872 (15)	1,537 (20)	6,132 (11)
Number of orthopaedic surgeon visits during the year prior to the intervention, mean (SD)	0.1 (0.4)	0.2 (0.5)	0.2 (0.5)	0.3 (0.6)	0.1 (0.4)

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SD: Standard Deviation

*Measured on 11-point Numeric Rating Scale ranging from 0 (no pain) to 10 (worst possible pain)

^£

Measured on the Eq5D; scores range 0-1.0 (higher values represent better quality of life)

^§

Measured on Arthritis Self-Efficacy Scale; scores range 10–100 (higher values represent better self-efficacy)

^¥

Measured using Elixhauser score, ranging 0–31 [38]

Primary analysis: Comparing those who were always willing for surgery to those who became unwilling, up to 5 years post-intervention

The cumulative number of surgeries for each year post-intervention within each subgroup is presented in S4 Appendix. Among those who became unwilling for surgery, the probability of having undergone surgery by 1- and 5-years post-intervention was 23% (95% CI: 22, 24%) and 20% (95% CI: 18, 22%) lower, respectively, than those who were always willing for surgery (Table 2 and Fig 2). For those who became unwilling for surgery, the hazard of having surgery at 1-year post-intervention was half that of those who were always willing for surgery (hazard ratio 0.5 [95% CI: 0.4, 0.5]; Table 3 and Fig 2). At 3-years post-intervention, the hazard of surgery occurring was similar in both subgroups (1.1 [95% CI: 1.0, 1.2]), and, at 5-years, was higher among those who became unwilling for surgery (1.4 [95% CI: 1.2, 1.7]). Over 5-years, becoming unwilling for surgery was associated with surgery occurring 1.1 (95% CI: 1.0, 1.1) years later than those who were always willing for surgery (Table 4 and Fig 2).

Table 2. Adjusted^* proportion of participants who had not had surgery following the intervention.

Years post-intervention	Proportion, % (95% CI)	Proportion, % (95% CI)	Proportion difference, % (95% CI)	Proportion, % (95% CI)	Proportion, % (95% CI)	Proportion difference, % (95% CI)
	Always willing for surgery	Became unwilling for surgery	Became unwilling VS always willing	Never willing for surgery	Became willing for surgery	Became willing VS Never willing
1	71 (70, 72)	94 (94, 95)	23 (22, 24)	98 (97, 98)	78 (77, 79)	−20 (−21, −18)
2	62 (60, 63)	86 (85, 87)	24 (23, 26)	93 (93, 93)	69 (67, 70)	−24 (−26, −23)
3	57 (56, 58)	80 (79, 81)	23 (21, 25)	89 (89, 90)	64 (63, 66)	−25 (−26, −23)
4	55 (53, 56)	76 (75, 77)	22 (20, 23)	86 (86, 87)	62 (60, 64)	−24 (−26, −22)
5	53 (51, 54)	73 (72, 74)	20 (18, 22)	84 (83, 84)	60 (59, 62)	−23 (−25, −21)
6	52 (50, 53)	70 (69, 72)	19 (17, 21)	82 (81, 82)	59 (58, 61)	−22 (−24, −20)
7	51 (49, 52)	68 (66, 70)	18 (15, 20)	80 (79, 80)	59 (57, 61)	−21 (−23, −19)
8	50 (48, 51)	66 (64, 68)	16 (14, 19)	78 (77, 79)	58 (56, 60)	−20 (−22, −18)
9	49 (47, 51)	64 (62, 66)	15 (13, 18)	76 (75, 77)	57 (55, 59)	−19 (−21, −17)

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CI: confidence interval

*Adjusted by: age, sex, body mass index (BMI), education, joint pain (both at baseline and post-intervention), quality of life (both at baseline and post-intervention) walking difficulties (both at baseline and post-intervention), number of prior visits with an orthopedic surgeon in the year before the intervention, prior joint surgeries in the knee or hip (other than joint replacement), and comorbidities.

‘Always willing for surgery’ = indicated they were willing for surgery both before and after the intervention. ‘Became unwilling for surgery’ = indicated they were willing for surgery before the intervention, but unwilling after. ‘Never willing for surgery’ = indicated they were unwilling for surgery both before and after the intervention. ‘Became willing for surgery’ = indicated they were unwilling before the intervention, but willing after.

Fig 2 — Lines represent point estimates, shaded areas represent the 95% Confidence Intervals of the estimates. TJR, total joint replacement. Lines represent point estimates, shaded areas represent the 95% Confidence Intervals of the estimates. TJR = total joint replacement. *Adjusted by: age, sex, body mass index (BMI), education, joint pain (both at baseline and post-intervention), quality of life (both at baseline and post-intervention) walking difficulties (both at baseline and post-intervention), number of prior visits with an orthopedic surgeon in the year before the intervention, prior joint surgeries in the knee or hip (other than joint replacement), and comorbidities. ^Number of joint replacement surgeries per 1000 people among those who had not already had surgery at that time-point). ‘Always willing for surgery’ = indicated they were willing for surgery both before and after the intervention. ‘Became unwilling for surgery’ = indicated they were willing for surgery before the intervention, but unwilling after. ‘Never willing for surgery’ = indicated they were unwilling for surgery both before and after the intervention. ‘Became willing for surgery’ = indicated they were unwilling before the intervention, but willing after*.

Table 3. Adjusted* hazard of having surgery^ following the intervention.

Years post-intervention	Hazard (95%CI)	Hazard (95%CI)	Hazard ratio (95%CI)	Hazard (95%CI)	Hazard (95%CI)	Hazard ratio (95%CI)
	Always willing for surgery	Became unwilling for surgery	Became unwilling VS always willing	Never willing for surgery	Became willing for surgery	Became willing VS never willing
1	206 (195, 218)	95 (88, 103)	0.5 (0.4, 0.5)	45 (43, 47)	182 (170, 195)	4.0 (3.7, 4.4)
2	97 (91, 103)	79 (74, 84)	0.8 (0.7, 0.9)	45 (43, 47)	85 (78, 92)	1.9 (1.7, 2.1)
3	56 (51, 61)	60 (55, 64)	1.1 (1.0, 1.2)	38 (36, 39)	47 (41, 53)	1.2 (1.1, 1.4)
4	38 (33, 42)	47 (43, 52)	1.3 (1.1, 1.5)	32 (30, 33)	30 (25, 36)	0.9 (0.8, 1.1)
5	28 (24, 33)	39 (35, 45)	1.4 (1.2, 1.7)	28 (26, 30)	22 (17, 27)	0.8 (0.6, 1.0)
6	23 (19, 27)	35 (30, 40)	1.5 (1.2, 1.9)	25 (24, 27)	17 (13, 22)	0.7 (0.5, 0.9)
7	19 (16, 23)	31 (27, 37)	1.6 (1.3, 2.1)	24 (22, 26)	14 (11, 19)	0.6 (0.4, 0.8)
8	17 (14, 20)	29 (24, 34)	1.7 (1.3, 2.2)	22 (20, 24)	12 (9, 16)	0.5 (0.4, 0.7)
9	15 (12, 19)	27 (23, 32)	1.8 (1.4, 2.3)	21 (19, 23)	11 (8, 15)	0.5 (0.4, 0.7)

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CI: confidence interval

^Number of joint replacement surgeries per 1,000 people among those who had not already had surgery at that time point)

Table 4. Adjusted* amount of time without surgery (mean survival time) and average time surgery can be delayed (difference in mean survival time) following the intervention.

Years post-intervention	Mean survival time (years)	Mean survival time (years)	Difference in mean survival time (years)	Mean survival time (years)	Mean survival time (years)	Difference in mean survival time (years)
	Always willing for surgery	Became unwilling for surgery	Became unwilling VS always willing	Never willing for surgery	Became willing for surgery	Became willing VS never willing
1	0.8 (0.8, 0.9)	1.0 (1.0, 1.0)	0.2 (0.1, 0.2)	1.0 (1.0, 1.0)	0.9 (0.9, 0.9)	−0.1 (−0.1, −0.1)
2	1.5 (1.5,1.5)	1.9 (1.9, 1.9)	0.4 (0.4, 0.4)	2.0 (2.0, 2.0)	1.6 (1.6, 1.7)	−0.3 (−0.4, −0.3)
3	2.1 (2.1, 2.1)	2.7 (2.7, 2.8)	0.6 (0.6, 0.7)	2.9 (2.9, 2.9)	2.3 (2.3, 2.3)	−0.6 (−0.6, −0.6)
4	2.7 (2.6, 2.7)	3.5 (3.5, 3.6)	0.9 (0.8, 0.9)	3.8 (3.8, 3.8)	2.9 (2.9, 3.0)	−0.8 (−0.9, −0.8)
5	3.2 (3.2, 3.3)	4.3 (4.2, 4.3)	1.1 (1.0, 1.1)	4.6 (4.6, 4.6)	3.6 (3.5, 3.6)	−1.1 (−1.1, −1.0)
6	3.7 (3.6, 3.8)	4.9 (4.9, 5.0)	1.3 (1.2, 1.3)	5.4 (5.4, 5.4)	4.1 (4.0, 4.2)	−1.3 (−1.4, −1.2)
7	4.2 (4.1, 4.3)	5.6 (5.6, 5.7)	1.4 (1.3, 1.5)	6.2 (6.3, 6.2)	4.7 (4.6, 4.8)	−1.5 (−1.6, −1.4)
8	4.7 (4.6, 4.8)	6.3 (6.2, 6.4)	1.6 (1.5, 1.7)	7.0 (7.0, 7.0)	5.3 (5.2, 5.4)	−1.7 (−1.8, −1.6)
9	5.2 (5.1, 5.3)	7.0 (6.9, 7.1)	1.8 (1.6, 1.9)	7.8 (7.7, 7.8)	5.9 (5.7, 6.0)	−1.9 (−2.2, −1.8)

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Secondary analysis: Comparing those who were never willing for surgery to those who become willing, up to 5-years post-intervention

Among those who became willing for surgery, the probability of having undergone surgery at 5-years post-intervention was 23% (95% CI: 21, 25%) higher than those who were never willing for surgery (Table 2 and Fig 2). This corresponded to surgery occurring an average of 1.1 (95% CI: 1.0, 1.1) years earlier (Table 4 and Fig 2).

Secondary analysis: Long-term outcomes up to 9-years post-intervention

Among those who became unwilling for surgery, the probability of having undergone surgery at 9-years post-intervention was 15% (95% CI: 13, 18%) lower than those who were always willing for surgery (Table 2). This corresponded to surgery occurring an average of 1.8 (95% CI: 1.6, 1.9) years later (Table 4). The opposite trend was observed when comparing those who became willing for surgery to those who were never willing, who had a 19% (95% CI: 17, 21%) higher probability of having undergone surgery (Table 2), corresponding to surgery occurring an average of 1.9 (95% CI: 1.8, 2.1) years earlier (Table 4).

Secondary analysis: Differences between hip and knee OA

Overall trends were similar between those with knee and hip OA. However, compared to people with knee OA, the magnitude of differences between subgroups in terms of probability and hazard of surgery occurring, as well as amount of time without surgery, was greater in those with hip OA (e.g., among those with hip OA, those who became unwilling for surgery had a 23% [95% CI: 19, 26%] lower probability of having surgery at 5 years than those who were always willing, compared to 17% [95% CI: 14, 19%] among those with knee OA; S5-S8 Appendices).

Secondary analysis: Differences between those with severe and mild pain at baseline

Overall trends were similar to those observed in the main analysis. However, people with more severe pain had a higher probability of undergoing surgery than those with milder pain, resulting in a larger difference in probability when becoming unwilling (among those with severe pain, those who became unwilling for surgery had a 26% [95% CI: 23, 29%] lower probability of having surgery at 5 years than those who were always willing, compared to 16% [95% CI: 13, 18%] among those with mild pain; S9 Appendix).

Secondary analysis: Adjustment for self-efficacy

Results did not change when adjusting for arthritis self-efficacy, except for a decrease in precision due to the reduced sample size (S10 Appendix).

Discussion

The aim of this study was to investigate whether becoming unwilling to undergo surgery following a 3-month education and exercise intervention for hip and knee osteoarthritis is associated with lower probability of receiving actual surgery. We found that becoming or remaining unwilling to have joint replacement surgery could delay the procedure by more than 1 year and lead to a 20% reduction in surgeries 5 years after the intervention; with the possibility that this is maintained up to 9 years after the intervention.

We found that, for all subgroups, the hazard of surgery (for anyone who had not already had surgery at that time point) peaked around 1-year post-intervention and then declined, becoming similar between all subgroups by 3-years post-intervention. This reflects prior work [39,40,41] which also found that the rate of progression to surgery declines around 3-years after a conservative management program for people with hip and knee OA. This may be because most people who are eligible and willing for surgery tend to have it early (within the first 3 years after an intervention, particularly in publicly funded healthcare systems) [39,40,41]. This also helps explains why the hazard of surgery at 5-years post-intervention were higher in those who became unwilling for surgery than those who were always willing for surgery (i.e., a larger proportion of those who were always willing had already undergone surgery in the first 3-years, and had not ‘survived’ to 5-years post-intervention). In the years after the intervention, symptom progression as well as underutilization of self-management strategies (which may contribute to diminishing effects on symptoms) [42,43] may have also contributed to reconsideration about willingness for surgery. To minimise risk of surgery reconsideration in the months and years following an intervention, longer interventions, additional contact with care providers, booster sessions, or re-completion of the education and exercise intervention might be necessary [27,44].

Our findings suggest that a simple question about willingness for surgery can be used as a proxy measure of progression to surgery in the short-medium term following an intervention. As such, researchers and clinicians should consider using such an outcome to evaluate the effectiveness of OA management interventions. This may also help clinicians identify those who remain willing for surgery post-intervention, and may therefore benefit from additional interventions to help them avoid or delay surgery in the future. However, there is some variability in the way in which participant willingness for surgery has been measured. In our study, participants were asked “Are your joint symptoms so severe that you wish to undergo surgery?”, responding either ‘Yes’ or ‘No’, which is similar to some prior work [45]. Other studies have used slightly different questions and/or outcome scales (e.g., 5-point Likert scales) [23,24]. The best way in which to measure willingness to undergo surgery, and detect changes in willingness, needs further investigation.

Our work has implications for clinical practice. Our findings suggest that shifting willingness for joint replacement surgery in people eligible for an education and exercise intervention could delay joint replacement surgery and lead to fewer surgeries (>20% reduction over 5 years). This could potentially contribute to substantial economic savings. There are numerous factors that influence change in willingness for surgery. Multiple studies report that education, exercise, and/or weight loss interventions can reduce willingness for surgery [23–27]. People who experience improvement in symptoms (e.g., self-reported pain and physical function, and arthritis self-efficacy) [24,46,47], do not have walking difficulties [48], are younger [24], have lower pain at baseline [24,47], and complete the entire treatment program (i.e., attend the final appointment) [24] are more likely to be, or become, unwilling for surgery. Given that our estimates are adjusted for change in symptoms, the actual impact of an intervention aimed at changing willingness for surgery may result in an even larger reduction in actual surgeries, as many participants are likely to experience improvements in symptoms after the intervention. Our secondary analysis also showed that targeting those with severe pain at baseline may result in an even greater reduction in surgeries in the future. However, clinicians should be aware that people with more severe pain still have a higher probability of undergoing surgery than those with milder pain (as shown by our secondary analysis) and therefore may need additional support to manage their condition, maintain quality of life, and avoid low-value care [49], even if their willingness for surgery changes. Other factors, such as having peers or family members who have had a joint replacement, interaction with a surgeon, and receiving a recommendation for surgery, may also play a role in willingness for surgery. It is also important to acknowledge that changing willingness for surgery can be challenging – only 42% of participants in our cohort who were originally willing for surgery at baseline became unwilling at post-intervention.

Our findings have implications for future research. Further work is needed to evaluate the potential mechanisms by which education and exercise interventions can contribute to changes in willingness for surgery, as well as the characteristics of those who do and do not change their willingness. Future research should also evaluate new cost-effective ways of further shifting surgery willingness, such as through use of tools like decision aids [50] or predictive tools (which provide personalised information about the likelihood in improvement after surgery, based on the participant’s age, sex, and baseline symptoms) [45].Finally, future research should use qualitative methods to explore the perceptions and experiences of those that became unwilling for surgery, including why their beliefs changed and what support is important to maintain this change in willingness in the long-term.

Our study has strengths and limitations. One strength of our approach is the use of a large sample of real-world data. However, some unknown and unobserved confounders – such as social factors, risk-taking behaviours, duration of symptoms, total number of joints affected – are likely to be present and thus causality cannot be determined. Furthermore, due to the absence of a control group, we cannot infer whether the intervention, or something else (e.g., undergoing other treatments during the study period), contributed to the shifts in willingness to undergo surgery. We did not account for the variability introduced by different hospitals, where varying protocols, resources, and local hospital culture can influence the probability of a patient receiving surgery. Ignoring these clustering effects may lead to a biased association between willingness for surgery status and the probability of receiving actual surgery. Moreover, we did not account for variability in attendance at the education and exercise program. However, prior work using data from the SOAR has suggested that attendance is only minimally associated with symptoms [51] and outcomes [52]. While it is highly likely that the self-reported willingness to undergo surgery impacted the hazard of receiving the operation in the short term (1–2 years), caution is needed when inferring causality for longer periods. We excluded participants who did not provide data at post-intervention, however missing data accounted for less than 5% of the total sample and is therefore unlikely to have created significant bias. As our data were collected in a clinical setting, there was some variability in the precise time point at which follow-up data was collected. We did not distinguish whether participants received joint replacement surgery to their index joint or to another affected joint (e.g., a person with both hip and knee OA might have nominated their knee as their index joint, but later undergone joint replacement surgery for their hip). However, we do not believe this introduces bias as, of those who underwent joint replacement surgery, 97% of individuals with knee OA and 90% of those with hip OA received the joint replacement on their index joint. Finally, our data were collected in a Swedish healthcare setting and in people who were eligible for an education and exercise intervention, where that intervention is publicly funded and requires minimal to no out-of-pocket costs to participate. As such our results may not be generalisable to other countries with different healthcare systems and cultures.

In conclusion, we found that becoming unwilling for joint replacement surgery following an education and exercise program for hip and knee osteoarthritis could reduce the number of joint replacement surgeries by 20% at 5 years post-intervention, with the possibility of maintaining most of this reduction up to 9 years post-intervention.

Ethics committee approval

Supporting information

S1 Appendix. RECORD statement.

(PDF)

pmed.1004577.s001.pdf^{(115.6KB, pdf)}

S2 Appendix. List of confounders included in the analyses.

(PDF)

pmed.1004577.s002.pdf^{(176.4KB, pdf)}

S3 Appendix. Demographics and sample characteristics.

(PDF)

pmed.1004577.s003.pdf^{(113.4KB, pdf)}

S4 Appendix. Cumulative number of joint replacement surgeries from 1 to 9 years after the intervention (N = 55,059).

(PDF)

pmed.1004577.s004.pdf^{(137.3KB, pdf)}

S5 Appendix. Adjusted differences in proportion of participants who had not had surgery following the intervention, categorized by knee and hip osteoarthritis.

(PDF)

pmed.1004577.s005.pdf^{(123.9KB, pdf)}

S6 Appendix. Adjusted differences in hazard of having surgery following the intervention, categorised by knee and hip osteoarthritis.

(PDF)

pmed.1004577.s006.pdf^{(122KB, pdf)}

S7 Appendix. Adjusted difference in average time surgery can be delayed following the intervention, categorised by knee and hip osteoarthritis.

(PDF)

pmed.1004577.s007.pdf^{(112.2KB, pdf)}

S8 Appendix. Adjusted (A) proportion of participants who had not had surgery; (B) hazard of having surgery, and; (C) average time surgery can be delayed following the intervention, categorized by knee and hip osteoarthritis.

(PDF)

pmed.1004577.s008.pdf^{(511.4KB, pdf)}

S9 Appendix. Adjusted proportion of participants with severe and mild pain who had not had surgery following the intervention.

(PDF)

pmed.1004577.s009.pdf^{(155.7KB, pdf)}

S10 Appendix. Adjusted (A) proportion of participants who had not had surgery, and; (B) hazard of having surgery following the intervention, when adjusting for self-efficacy.

(PDF)

pmed.1004577.s010.pdf^{(513.5KB, pdf)}

Data Availability

The dataset of this includes data from the Swedish Osteoarthris Register, Swedish Drug Register, National Patient Register and Swedish Arthroplasty register, provided to the researchers through a restricted-access agreement that prevents sharing the dataset with a third party or publicly. Individual-level data of patients included in this paper after deidentification are considered sensitive and will not be shared. However, the individual-level data are accessible to authorized researchers after ethical approval and application to https://bestalladata.socialstyrelsen.se/bestalla-microdata-for-statistikandamal/ (contact: registerservice@socialstyrelsen.se) and https://etjanst.halsodatabestallning.vgregion.se/ (contact: regionalvardanalys@vgregion.se).

Funding Statement

Greta and John Kock foundation, The Swedish Research Council (dnr: 2022−01507).

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51.Battista S, Kiadaliri A, Jönsson T, Gustafsson K, Englund M, Testa M, et al. Factors associated with adherence to a supervised exercise intervention for osteoarthritis: data from the Swedish osteoarthritis registry. Arthritis Care Res (Hoboken). 2023;75(10):2117–26. doi: 10.1002/acr.25135 [DOI] [PubMed] [Google Scholar]
52.Dell’Isola A, Jönsson T, Ranstam J, Dahlberg LE, Ekvall Hansson E. Education, home exercise, and supervised exercise for people with hip and knee osteoarthritis as part of a nationwide implementation program: data from the better management of patients with osteoarthritis registry. Arthritis Care Res (Hoboken). 2020;72(2):201–7. doi: 10.1002/acr.24033 [DOI] [PubMed] [Google Scholar]

PLoS Med. 2025 May 8;22(5):e1004577. doi: 10.1371/journal.pmed.1004577.r001

Author response to Decision Letter 0

19 Sep 2024

PLoS Med. doi: 10.1371/journal.pmed.1004577.r002

Decision Letter 0

Alexandra Tosun

23 Sep 2024

Dear Dr Lawford,

Thank you for submitting your manuscript entitled "Association between change in willingness for joint replacement surgery after an education and exercise program for hip/knee osteoarthritis and probability of receiving actual surgery: A longitudinal cohort study of 55,059 people" for consideration by PLOS Medicine.

Your manuscript has now been evaluated by the PLOS Medicine editorial staff and I am writing to let you know that we would like to send your submission out for external peer review.

However, before we can send your manuscript to reviewers, we need you to complete your submission by providing the metadata that is required for full assessment. To this end, please login to Editorial Manager where you will find the paper in the 'Submissions Needing Revisions' folder on your homepage. Please click 'Revise Submission' from the Action Links and complete all additional questions in the submission questionnaire.

Please re-submit your manuscript within two working days, i.e. by Sep 25 2024.

Once your full submission is complete, your paper will undergo a series of checks in preparation for peer review. Once your manuscript has passed all checks it will be sent out for review.

Feel free to email me at atosun@plos.org or us at plosmedicine@plos.org if you have any queries relating to your submission.

Kind regards,

Alexandra Tosun, PhD

Associate Editor

PLOS Medicine

PLoS Med. 2025 May 8;22(5):e1004577. doi: 10.1371/journal.pmed.1004577.r003

Author response to Decision Letter 0

23 Sep 2024

PLoS Med. doi: 10.1371/journal.pmed.1004577.r004

Decision Letter 1

Alexandra Tosun

21 Nov 2024

Dear Dr Lawford,

Many thanks for submitting your manuscript "Association between change in willingness for joint replacement surgery after an education and exercise program for hip/knee osteoarthritis and probability of receiving actual surgery: A longitudinal cohort study of 55,059 people" (PMEDICINE-D-24-03148R1) to PLOS Medicine. The paper has been reviewed by subject experts and a statistician; their comments are included below and can also be accessed here: [LINK]

As you will see, the reviewers are supportive of the manuscript and have provided valuable comments and questions, as well as suggestions to improve the exploration of the data. After discussing the paper with the editorial team and an academic editor with relevant expertise, I'm pleased to invite you to revise the paper in response to the reviewers' comments. We plan to send the revised paper to some or all of the original reviewers, and we cannot provide any guarantees at this stage regarding publication.

When you upload your revision, please include a point-by-point response that addresses all of the reviewer and editorial points, indicating the changes made in the manuscript and either an excerpt of the revised text or the location (eg: page and line number) where each change can be found. Please also be sure to check the general editorial comments at the end of this letter and include these in your point-by-point response. When you resubmit your paper, please include a clean version of the paper as the main article file and a version with changes tracked as a marked-up manuscript. It may also be helpful to check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper.

We ask that you submit your revision by Dec 12 2024. However, if this deadline is not feasible, please contact me by email, and we can discuss a suitable alternative.

Don't hesitate to contact me directly with any questions (atosun@plos.org).

Best regards,

Alexandra

Alexandra Tosun, PhD

Associate Editor

PLOS Medicine

atosun@plos.org

-----------------------------------------------------------

Comments from the reviewers:

Reviewer #1: A very interesting manuscript! This paper examines associations between self-reported surgery willingness before and after an exercise program and receipt of surgery after participation in this program (as a related note, the title was a bit weird. You're not looking at an association between a change in surgery willingness and the /probability/ of receiving surgery, but /whether/ the patient actually receives the surgery). One major strength of the study is the registry-based design that captures a population-level patient experience; choices for patient inclusion/exclusion made sense. Another strength is empirical confirmation of "surgery unwillingness" being associated with being less likely to go through with a surgery and more importantly, the authors' attempt at quantifying the extent to which this occurs. However, I do have some comments regarding the statistical analysis in the manuscript, which as is, was not entirely satisfactory.

Given that the intent wasn't to make the most accurate predictions, but rather to understand any association between receipt of this intervention/status of the intervention and the outcome, why not simply use all identified confounders in the modeling? I didn't understand what the variable selection process was trying to achieve. Even if certain variables such as sex might not have a statistically significant association with receipt of surgery, why not include them in the model so you can say that it was adjusted for? (along those lines, it actually looks like there's an association between sex and patient segmentation in terms of willingness before/after the intervention). As an aside, in the figures, you mentioned that survival curves were estimated based on the adjusted models. Does this specifically mean that for the four curves, these are for the four patient segments, marginalizing over the distribution of all confounders of all patients in each category?

Regarding the causal inference, the use of counterfactuals was certainly interesting from a real world perspective, but causal assumptions did not appear to be mentioned at all beyond assuming that all possible confounders have been accounted for (which is unrealistic here). Is a causal model being asserted, and if so, what is the causal estimand of interest? Does it accurately reflect some yes/no pairs canceling with no/yes pairs? The phrasing regarding "causal framework using counterfactual scenarios" appears in the discussion section, without sufficient justification for use of causal methods or formal evaluation of assumptions in the methodoloy. If you are going to use a causal analysis, it would have been helpful to actually do this formally. As for the actual assumptions themselves, I find it hard to believe that comparing the real-life yes/yes vs. yes/no is truly causal where everything has been accounted for. With that said, despite use of causal methodology and estimation of causal effects, results are phrased in terms of associations/as if you aren't trying to exploit causal inference methodology - this is fine, but just kind of discordant given what the methodology might imply.

An interesting aspect of your data is that there were more no/yes discordant pairs than yes/no discordant pairs, which makes sense. However, it might be of scientific interest to examine what might be associated with each of these types of patients (i.e., what is associated with a patient going from willing to unwilling to undergo surgery?), as well as examine patients who go "the wrong way" in terms of the intervention. Given that the intervention was designed to reduce patient willingness to undergo surgery, why did many of them go from unwilling to willing after the intervention? This might be of potential interest. I found it surprising that the actual results from your regression modeling was not presented at all - I strongly recommend you provide adjusted hazard ratios for your model, as you would be able to answer these types of questions. For instance, a clinician may be interested in whether there might be any potential associations based on age - are older or younger adults more/less likely to undergo surgery, especially considering that the recovery period after the operation may represent a larger burden for older adults? In general, displaying results from regression models would allow readers to understand whether certain other variables might also be associated with differential time to surgery (I'm particularly interested in a model account for all potential confounders assessed, not one based on some likelihood-based variable selection criteria).

As some final minor issues, there is some weirdness in the way results are reported. For instance, it is not clear what "hazard rate" means in line 246 (i.e., do you simply mean the hazard of surgery?).

Reviewer #2: This is a very interesting and relevant research that should be accepted if the authors addressed the following important comments:

-This paper seems to have been written by methodologists for methodologists. It is not so much accessible for the average reader with little quantitative skills, especially in survival analysis and parametric modelling. The reporting is pretty indigestible, even for an applied medical statistician. The grouping should be described in an easier way, with of course a formal description in the methods section and then the use of a reader-friendly wording. For example (but feel free to use any other relevant wording): Never considered surgery vs NO-NO, always planned surgery vs YES-YES, ultimately refused surgery vs YES-NO, or ultimately accepted surgery vs NO-YES . Moreover, the numbers presented in tables should never be repeated in the text, which should only report a digest of the main messages. The figure titles are too technical: Use footnotes to describe the technical elements, including what adjustments have been made, but don't use such hard-core titles that will put off reviewers and readers. In the text wording such as "The hazard rate (i.e., instantaneous risk of surgery for anyone who had not already had surgery at that time point) at 1-year post-intervention among those who responded YES-NO was half of that of 245 those responding YES-YES (hazard ratio 0.5 [95% CI 0.4-0.5]; Table 3; Figure 1)." is really not reader-friendly. Why not writing " the risk of surgery for anyone initially accepting but then refusing surgery at 1-y post-inter was half the risk estimated among patients still willing to undergo surgery…" or something like that?

-One key ignored methodological aspect is the clustering of data by hospital facilities: it is possible that patients attending a surgical place could be influenced by the local clinical/surgical team for or against surgery. So we cannot rule out a cluster effect. The analyses are not accounting for the multilevel nature of the used data. However, this is my experience that conducting multilevel flexible survival analysis is incredibly computer-intensive, and too often with big data, the statistical software (R or Stata) tends to crash. The authors should therefore either consider to model the clustering (Multilevel mixed-effects parametric survival analysis: Estimation, simulation, and application - Michael J. Crowther, 2019 (sagepub.com)) or discuss the potential implications of ignoring this clustering in the limitations section.

-It is unclear whether the willingness to undergo surgery is related to the severity of the symptoms experienced, and therefore the length-of-time with a high level of OA limitations. It could be that patients suffering from severe pain and functional limitations would want surgery to alleviate their symptoms; and vis-versa for those with lower or more recent OA symptoms. The authors are already adjusting for pain levels at baseline and post-intervention, but table 1 is clearly showing that the level of post-intervention pain is the highest in the YES-YES and NO-YES groups. Does it deserve further discussions? It would be dangerous for any care provider to wrongly use this article to reduce arthroplasty provision and related funding based on the overall message of this research and ignoring the specificities of the YES-YES and NO-YES groups. This requires more discussion.

-Minor comments:

*The term "incident joint replacement". What does it mean? This is non-reader friendly. Does it refer to the concept of incidence ratio, but then the concept of person-year is very briefly mentioned. Clarify, but make sure to use some wordings that are simple and accessible for all readers.

*Consider reporting a flow diagram graph rather than appendix 1.

*The number of comorbidities categories is ridiculously large, simplify to 0,1,2 3+

*In the figures, the concept "end of intervention" is difficult to grasp. Consider a more reader-friendly labelling.

Reviewer #3: This is an interesting paper that reports on secondary analyses of population based registry data for people seeking care for OA and people receiving total joint arthroplasty (TJA) in Sweden. The primary question is whether participation in a 3-month education and exercise intervention results in a change in patient willingness to undergo TJA and the relationship of pre-post willingness to subsequent receipt of TJA at 5 and 9 years follow-up. The statistical approaches used to link and analyse the data are sound, addressing potential confounders. The authors acknowledge the limitations of a single yes/no measure of willingness before and after a brief 3-month intervention as causally related to subsequent rates of TJA, yet the simplicity of the approach is compelling. Importantly, the authors found that those who converted from yes i want surgery to no i do not want surgery were less likely to receive a TJA during follow-up... in the short term specifically...compared to the yes-yes group.

My main concerns regarding the study relate to the time lag from the education/exercise intervention and receipt of surgery, and thus the causal relationship, if any. The results are hypothesis generating at best. But, the results are provocative with respect to the potential role of improved OA symptom management to reduce symptoms/improve function in helping stem growing demand for TJA for OA. That said, I have some suggestions to improve the interpretability of the findings to readers and also clarify the extent to which potential confounders have been accounted for.

Abstract: it would be helpful to clarify that all patients presenting for OA care in Sweden are provided the 3-month education and exercise intervention.

Introduction: Lines 74-76- I am not sure what the sentence that begins with "Further, joint replacement..." The sentence appears redundant - please revisit/clarify.

Methods:

Please clarify what changes, if any, were introduced to the education/exercise OA intervention over the 10-year time period of this study. Please also explain why the willingness question was introduced, and justify why a simple yes/no versus Likert scale was used as the measure of willingness.

Confounders:

To what extent was the selection of confounders informed by prior literature on the factors that influence willingness to consider TJA? Prior work has identified social network factors and other social health determinants as key to determining people with OA's perceived candidacy for surgery, perceptions of the risks and benefits of surgery, and perceived OA severity, all of which relate to willingness - please comment more explicity on how these factors were incorporated into analyses.

Was the overall burden of OA considered - i.e., the total number of joints affected?

Results:

Table 1 is very informative - there are expected differences across the groups with respect to confounders controlled for (sex, education attainment, measures of OA symptom severity), yet the results do not help the reader to understand the role of controlling for these differences on the outcomes of interest. For example, what was the effect of controlling for a prior surgeon visit? I think that greater clarity regarding a) which variables were controlled for in which analysis - e.g., footnotes in figures and tables - and mention of the effect of controlling for key confounders on the results, would help readers interpret the results and also plan for future studies to confirm or refute the findings.

Discussion:

Overall, the discussion is well-written and addresses methodological limiations inherent in secondary cohort analyses. However, as noted above, I think the discussion regarding the potential mechanisms by which the intervention resulted in changes in willingness to consider TJA, or not, could be strengthened considerably, building on prior work regardiing factors that influence the willingness construct. From the paper, it appears the primary mechanism considered was change in OA symptoms and improvement in arthritis coping / self-efficacy, which I agree may have played a role. But what about speaking with peers who had undergone TJA previously? What about interactions with surgeons, recommendations for surgery received during the intervention? Greater description of what the intervention entails, and whether surgery is explicitly discussed, and the opportunity for group discussion among patients, would be helpful in this respect.

Page 20, line 322 states that "...symptom progression as well as poor adherence to self-management strategies may have contributed to reconsideration about willingness for surgery." Could you please explain what is meant by "poor adherence" to therapy? how might this be related to change in willingness if not due to progression of symptoms?

Figures and Tables:

Please clarify variables controlled for in the various models in footnotes.

Was the overall burden of OA considered - i.e., the total number of joints affected?

Reviewer #4: Dear Author,

It was a pleasure to review your manuscript.

Well done on pursuing this research topic and using such meticulous methodology and statistical analyses. Congratulations on the amazing results and please consider my comments in the attachments and amend the manuscript accordingly.

Kind regards,

Candice

Any attachments provided with reviews can be seen via the following link: [LINK]

--------------------------------------------------------- ---

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PLoS Med. 2025 May 8;22(5):e1004577. doi: 10.1371/journal.pmed.1004577.r005

Author response to Decision Letter 1

6 Jan 2025

Attachment

Submitted filename: PLOS Medicine response to reviewer comments_v6.docx

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PLoS Med. doi: 10.1371/journal.pmed.1004577.r006

Decision Letter 2

Alexandra Tosun

13 Feb 2025

Dear Dr. Dell'Isola,

Thank you very much for re-submitting your manuscript "Association between change in willingness for joint replacement surgery after an education and exercise program for hip/knee osteoarthritis and future joint replacement surgery: A longitudinal cohort study of 55,059 people" (PMEDICINE-D-24-03148R2) for review by PLOS Medicine.

Thank you for your detailed response to the editors' and reviewers' comments. I have discussed the paper with my colleagues, and it has also been seen again by three of the original reviewers. The changes made to the paper were mostly satisfactory to the reviewer. As such, we intend to accept the paper for publication, pending your attention to the reviewers' and editors' comments below in a further revision. When submitting your revised paper, please once again include a detailed point-by-point response to the editorial comments.

The remaining issues that need to be addressed are listed at the end of this email. Any accompanying reviewer attachments can be seen via the link below. Please take these into account before resubmitting your manuscript:

[LINK]

In revising the manuscript for further consideration here, please ensure you address the specific points made by each reviewer and the editors. In your rebuttal letter you should indicate your response to the reviewers' and editors' comments and the changes you have made in the manuscript. Please submit a clean version of the paper as the main article file. A version with changes marked must also be uploaded as a marked up manuscript file. Please also check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper.

Please note, when your manuscript is accepted, an uncorrected proof of your manuscript will be published online ahead of the final version, unless you've already opted out via the online submission form. If, for any reason, you do not want an earlier version of your manuscript published online or are unsure if you have already indicated as such, please let the journal staff know immediately at plosmedicine@plos.org.

We ask that you submit your revision within 1 week (Feb 20 2025). However, if this deadline is not feasible, please contact me by email, and we can discuss a suitable alternative.

Please do not hesitate to contact me directly with any questions (atosun@plos.org). If you reply directly to this message, please be sure to 'Reply All' so your message comes directly to my inbox.

We look forward to receiving the revised manuscript.

Sincerely,

Alexandra Tosun, PhD

Associate Editor

PLOS Medicine

plosmedicine.org

***Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.***

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Comments from Reviewers:

Reviewer #1: The authors have satisfactorily addressed all of my comments. With that said, I now have a minor quibble with respect to a change made due to a comment from the second reviewer. Specifically, hazards are not risks - I would simply call a hazard a hazard - it is the instantaneous rate of failure given that a patient had not yet failed at that time. Neither are hazards unconditional rates, which was my original comment.

The manuscript is sound and interesting, but I would strongly recommend simply using the term "hazard."

Reviewer #3: Thank you for the extensive rewriting and attention to addressing prior questions and concerns. I have no additional issues to consider.

Reviewer #4: Dear Authors,

Thank you very much for considering my comments and recommendations!

I am happy with the way that you had addressed my comments/recommendations and know that this revised manuscript will be a meaningful contribution to our wider research and health professional community.

Kind regards,

Candice

Any attachments provided with reviews can be seen via the following link:

[LINK]

------------------------------------------------------------

Requests from Editors:

GENERAL

1) Please confirm that your abstract complies with our requirements, including providing all the information relevant to this study type https://journals.plos.org/plosmedicine/s/submission-guidelines#loc-abstract

2) Please ensure that all abbreviations are defined at first use throughout the text.

3) Please review your text for claims of novelty or primacy (e.g. 'for the first time') and remove this language (e.g. line 401). In addition, please check that any use of statistical terms (such as trend or significant) are supported by the data, and if not please remove them.

4) Where data points are discrete, please ensure that they are depicted in the figures as discrete data and not as a continuous line.

5) Statistical reporting: Please separate upper and lower bounds with commas instead of hyphens as the latter can be confused with reporting of negative values. Please revise throughout the manuscript.

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Please include the ethics statement from lines 522-526 in the Methods section of your manuscript.

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1) Please include basic participant characteristics in the Methods and Findings section (e.g. sex, age, BMI).

2) l.58ff: Please ensure that you include the statistical definitions (e.g. 95% CI, HR, etc.) for each set of brackets. Please revise throughout the Abstract and the main text.

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4) Please ensure that all numbers presented in the abstract are present and identical to numbers presented in the main manuscript text.

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1) Please clarify in the Methods and Results section how joint paint, quality of life, pain self-efficacy and number of comorbidities were measured (i.e. what scale/tool was used, as done below Table 1).

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PLoS Med. 2025 May 8;22(5):e1004577. doi: 10.1371/journal.pmed.1004577.r007

Author response to Decision Letter 2

15 Mar 2025

Attachment

Submitted filename: PLOS Medicine response to reviewer comments2_v1.docx

pmed.1004577.s016.docx^{(49.1KB, docx)}

PLoS Med. doi: 10.1371/journal.pmed.1004577.r008

Decision Letter 3

Alexandra Tosun

18 Mar 2025

Dear Dr Dell'Isola,

On behalf of my colleagues and the Academic Editor, Christelle Nguyen, I am pleased to inform you that we have agreed to publish your manuscript "Association between change in willingness for joint replacement surgery after an education and exercise program for hip/knee osteoarthritis and future joint replacement surgery: A longitudinal cohort study of 55,059 people" (PMEDICINE-D-24-03148R3) in PLOS Medicine.

I appreciate your thorough responses to the reviewers' and editors' comments throughout the editorial process. We look forward to publishing your manuscript, and editorially there are only a few remaining points that should be addressed prior to publication. We will carefully check whether the changes have been made. If you have any questions or concerns regarding these final requests, please feel free to contact me at atosun@plos.org.

Please see below the minor points that we request you respond to (line numbers according to Marked Up Manuscript):

* Title: If you agree, we suggest shortening the title to: Change in willingness for joint replacement surgery after an education and exercise program for hip/knee osteoarthritis: A longitudinal cohort study of 55,059 individuals

* Abstract, l.80, please change to: ‘was then higher at 5-years (HR 1.4 [95% CI: 1.2, 1.7])’. Please ensure that you include the abbreviation for Hazard Ratio in the preceding brackets.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

S1 Appendix. RECORD statement.

(PDF)

pmed.1004577.s001.pdf^{(115.6KB, pdf)}

S2 Appendix. List of confounders included in the analyses.

(PDF)

pmed.1004577.s002.pdf^{(176.4KB, pdf)}

S3 Appendix. Demographics and sample characteristics.

(PDF)

pmed.1004577.s003.pdf^{(113.4KB, pdf)}

S4 Appendix. Cumulative number of joint replacement surgeries from 1 to 9 years after the intervention (N = 55,059).

(PDF)

pmed.1004577.s004.pdf^{(137.3KB, pdf)}

S5 Appendix. Adjusted differences in proportion of participants who had not had surgery following the intervention, categorized by knee and hip osteoarthritis.

(PDF)

pmed.1004577.s005.pdf^{(123.9KB, pdf)}

S6 Appendix. Adjusted differences in hazard of having surgery following the intervention, categorised by knee and hip osteoarthritis.

(PDF)

pmed.1004577.s006.pdf^{(122KB, pdf)}

S7 Appendix. Adjusted difference in average time surgery can be delayed following the intervention, categorised by knee and hip osteoarthritis.

(PDF)

pmed.1004577.s007.pdf^{(112.2KB, pdf)}

(PDF)

pmed.1004577.s008.pdf^{(511.4KB, pdf)}

S9 Appendix. Adjusted proportion of participants with severe and mild pain who had not had surgery following the intervention.

(PDF)

pmed.1004577.s009.pdf^{(155.7KB, pdf)}

S10 Appendix. Adjusted (A) proportion of participants who had not had surgery, and; (B) hazard of having surgery following the intervention, when adjusting for self-efficacy.

(PDF)

pmed.1004577.s010.pdf^{(513.5KB, pdf)}

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Submitted filename: PMEDICINE-D-24-03148_R1_15Nov.pdf

pmed.1004577.s012.pdf^{(952.1KB, pdf)}

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Submitted filename: PLOS_PMEDICINE-D-24-03148R1_Reviewer Response.docx

pmed.1004577.s013.docx^{(17.9KB, docx)}

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Submitted filename: PLOS Medicine response to reviewer comments_v6.docx

pmed.1004577.s015.docx^{(146.1KB, docx)}

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Submitted filename: PLOS Medicine response to reviewer comments2_v1.docx

pmed.1004577.s016.docx^{(49.1KB, docx)}

Data Availability Statement

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PERMALINK

Change in willingness for surgery and risk of joint replacement after an education and exercise program for hip/knee osteoarthritis: A longitudinal cohort study of 55,059 people

Belinda J Lawford

Ali Kiadaliri

Martin Englund

Kim L Bennell

Rana S Hinman

Michelle Hall

Andrea Dell’Isola

Roles

Abstract

Background

Methods and findings

Conclusions

Author summary

Introduction

Methods

Study design

Education and exercise program

Study sample

Fig 1. Reasons for participant exclusion.

Exposure

Outcome

Confounders

Statistical analysis

Results

Table 1. Demographics and sample characteristics (N = 55,059).

Primary analysis: Comparing those who were always willing for surgery to those who became unwilling, up to 5 years post-intervention

Table 2. Adjusted* proportion of participants who had not had surgery following the intervention.

Fig 2. Adjusted* (A) Proportion of participants who had not had surgery; (B) hazard^ of having surgery, and; (C) difference in amount of time surgery is delayed# following the intervention.

Table 3. Adjusted* hazard of having surgery^ following the intervention.

Table 4. Adjusted* amount of time without surgery (mean survival time) and average time surgery can be delayed (difference in mean survival time) following the intervention.

Secondary analysis: Comparing those who were never willing for surgery to those who become willing, up to 5-years post-intervention

Secondary analysis: Long-term outcomes up to 9-years post-intervention

Secondary analysis: Differences between hip and knee OA

Secondary analysis: Differences between those with severe and mild pain at baseline

Secondary analysis: Adjustment for self-efficacy

Discussion

Ethics committee approval

Supporting information

Data Availability

Funding Statement

References

Author response to Decision Letter 0

Decision Letter 0

Alexandra Tosun

Roles

Author response to Decision Letter 0

Decision Letter 1

Alexandra Tosun

Roles

Author response to Decision Letter 1

Decision Letter 2

Alexandra Tosun

Roles

Author response to Decision Letter 2

Decision Letter 3

Alexandra Tosun

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

Similar articles

Cited by other articles

Links to NCBI Databases

Table 2. Adjusted^* proportion of participants who had not had surgery following the intervention.

Fig 2. Adjusted* (A) Proportion of participants who had not had surgery; (B) hazard^ of having surgery, and; (C) difference in amount of time surgery is delayed^# following the intervention.