The Relationship Among Pain, Intrinsic Capacity, and Fear of Movement in Patients with Knee Osteoarthritis: A Moderated Network Analysis

Abstract

Objective

To investigate the relationship between intrinsic capacity (IC) and fear of movement, and to clarify how pain modified the relationship between IC and fear of movement at the symptom-level in patients with knee osteoarthritis (KOA).

Methods

In this cross-sectional observational study, 452 patients with KOA were recruited from a tertiary hospital in China. All participants completed validated self-report questionnaires to assess IC, pain, and fear of movement. Symptom-level network visualization and centrality analyses were conducted via moderated network analysis. The Johnson-Neyman technique was further applied to verify and quantify statistically significant moderated network edges.

Results

In the network, “somatic focus” was identified as the most central symptom (Expected Influence = 1.71), with the strongest association observed between “somatic focus” and “vision” (r = 0.62). Johnson-Neyman analysis revealed that pain significantly moderated the relationship between IC and fear of movement, including the edge between “psychological well-being” and “somatic focus” (t = −3.241, p < 0.01), and between “cognition” and “activity avoidance” (t = −2.740, p < 0.01). Additionally, higher pain strengthened the positive association between “avoidance beliefs” and “somatic focus” (t = 4.574, p < 0.001).

Conclusion

Higher pain levels were associated with weaker relationships between selected intrinsic capacity domains and fear-of-movement dimensions. Targeted interventions integrating improved IC and pain management may represent a viable strategy to reduce fear of movement in patients with KOA, which requires confirmation in future longitudinal and intervention studies.

Introduction

Knee osteoarthritis (KOA) is a highly prevalent and debilitating musculoskeletal condition characterized by progressive damage to the cartilage, subchondral bone, synovium, and surrounding soft tissues of the knee joint.¹ Primary KOA usually develops through a multifactorial degenerative process involving age-related, biomechanical, metabolic, and genetic factors, whereas secondary KOA develops in association with identifiable predisposing conditions, such as previous trauma, structural deformity, or other underlying joint disorders.^2–4 Recent epidemiological estimates indicate that approximately 374.74 million people worldwide live with KOA.⁵ Knee pain is the cardinal manifestation of the disease and remains the most commonly reported symptom among affected patients.¹ Notably, KOA is an irreversible disease with a substantial global health burden. Current pharmacological treatments for KOA merely alleviate pain and cannot cure the disease.⁶ The progression of KOA may ultimately lead to chronic pain and disability.⁷

The European League Against Rheumatism has emphasized that exercise represented the most extensively investigated and robustly endorsed nonpharmacological core intervention for KOA, a recommendation supported by the strongest level of evidence.⁸ A meta-analysis including 21 studies with 3266 participants reported that only 13% of patients with KOA achieved ≥150 min per week of moderate-to-vigorous physical activity in bouts of ≥10 min.⁹ Fear of movement, also referred to as kinesiophobia, could constitute a key barrier to attaining sufficient exercise in patients with KOA. Fear of movement was described as an excessive and irrational fear of engaging in physical movements and activities.¹⁰ This concern resulted from both the expectation of pain and a perceived susceptibility to painful injury or reinjury during exercise.¹⁰ A systematic review reported that high levels of fear of movement were associated with increased disability and poorer quality of life.¹¹ Fear of movement has been linked impaired postural control, altered neuromuscular function, reduced joint position sense, and poorer functional performance.^12–16 Considering the adverse effects of fear of movement on knee function and quality of life, it is crucial to address fear of movement in patients with KOA.

In patients with KOA, fear of movement often perpetuates functional decline by limiting rehabilitative activity. Intrinsic capacity (IC) emerges as a promising target to disrupt this vicious cycle, with its established role in sustaining functional independence closely linked to a novel role in mitigating psychological barriers to movement. IC is defined as the composite of inherent physical and mental capacities, as well as their interaction with relevant environmental factors.¹⁷ As a positive attribute, IC embodies a dynamic reserve of physiological and psychological resources that underpin adaptive responses to health challenges, facilitate rehabilitation, and sustain functional independence.¹⁸ This conceptualization marks a pivotal shift from traditional disease-centered frameworks to a proactive, strengths-based paradigm. Epidemiological evidence indicated that robust IC correlated with reduced disability risk, improved survival, and enhanced quality of life among older adults.^19,20 A randomized controlled trial has reported that interventions targeting the core domains of IC—cognition, locomotion, vitality, and psychological well-being—effectively reduce fear of movement in patients with KOA.²¹

According to the conservation of resources theory, individuals continuously seek to obtain, preserve, and develop valued personal resources, and the loss of resources or the possibility of losing them causes maladaptive psychological reactions.²² IC is a multifaceted resource cluster.¹⁷ Evidence has shown that deficits in specific IC domains, such as cognition and psychological well-being, are associated with higher levels of fear of movement.^23,24 Pain is a potent stressor that directly depletes energetic and functional resources while heightening the threat of further resource loss,²⁵ which may moderate the association between IC and fear of movement. However, the extent of this moderation remains unclear. Node-level (symptom-to-symptom) analysis can address this limitation by identifying the specific high-centrality IC and fear of movement nodes whose modification is critical for maximally disrupting the network. In contrast to conventional mediation approaches, network analysis is more adept at capturing micro-level or node–specific symptom interactions, and moderated network models enable effective investigation of moderating variables.^26,27 One major benefit of using moderated network models in conjunction with Johnson-Neyman probing is that they measure how a continuous moderator (pain in our study) modifies the strength of each symptom-symptom connection throughout its entire range.²⁶

To examine these symptom-level relationships, we employed moderated network analysis to illustrate how IC and pain interactively affect fear of movement at the micro-level in patients with KOA. Relative to traditional moderation models that only use total scale scores, this method yields higher analytical precision and supports targeted interventions by pinpointing the most critical symptom links. We put forward the following hypotheses: (1) patients with robust IC exhibit lower levels of fear of movement; (2) pain moderates the relationship between IC and fear of movement.

Methods

Study Design and Participants

From July 2025 to January 2026, this cross-sectional study enrolled patients with clinically and radiologically diagnosed KOA via convenience sampling method from a tertiary hospital in Shandong province, China. The inclusion criteria were as follows: (1) aged above 45 years; (2) diagnosed with primary KOA of Kellgren-Lawrence grade II or III; (3) stable medical condition permitting participation in study assessments and capacity to provide informed consent. The exclusion criteria were: (1) a history of knee surgery; (2) a history of knee joint trauma; (3) secondary or inflammatory arthritis; (4) other conditions causing pain.

The study was conducted in accordance with the Declaration of Helsinki. All participants provided informed consent prior to enrollment, and the study was approved by the ethics committee of Shandong Provincial Hospital (SWYX: NO. 2025–454).

Procedures

After eligibility screening and obtaining informed consent, participants were invited to a private setting. Participants filled out a paper questionnaire in accordance with their preferences while being guided by the researcher. Throughout the assessment, strict privacy protections were implemented, and participants were reminded that they could withdraw from the study at any time. A total of 460 eligible participants were identified, and all provided written informed consent. Of the 460 returned questionnaires, eight (1.74%) contained missing data and were excluded from the analyses. Specifically, five questionnaires had missing data for the fear of movement measure, and three had missing data for the intrinsic capacity measure. The final sample size was 452, corresponding to a response rate of 98.26%.

Sample Size

Our network model contained 11 nodes, requiring estimation of 11 threshold parameters and 55 pairwise association parameters ([11 × (11–1)]/2), for a total of 66 parameters.²⁸ Based on previous network analysis studies, an empirical recommendation of approximately 3–5 participants per estimated parameter was adopted to guide sample-size planning,^29,30 indicating a recommended sample size of 198–330. There was sufficient power for stable network estimate in the final sample (N = 452).

Measures

Demographic and Clinical Characteristics

Demographic and clinical data were obtained from a self-report questionnaire, including age, sex, body mass index (BMI), educational level, residence, marital status, duration of pain, disease history, smoking history, and drinking history.

Pain

Pain intensity was assessed using an 11-point numerical rating scale (NRS), where 0 represented no pain and 10 indicated the worst possible pain at the moment of evaluation.³¹ In the patients with bilateral KOA, knee pain on the more painful side was evaluated.

Fear of Movement

Fear of movement was measured by the Tampa Scale for Kinesiophobia-11 (TSK-11). The TSK-11 consisted of 11 items divided into three dimensions: somatic focus, activity avoidance, and avoidance beliefs.³² The TSK-11 had a total score between 11 and 44, with each item ranging from 1 to 4. The higher the score, the higher the fear of movement level of the patients with KOA. The Cronbach’s α of the TSK-11 in the present sample was 0.911.

Intrinsic Capacity

Intrinsic capacity (IC) was assessed using the Integrated Care for Older People Screening Tool (ICOPES). This tool incorporated seven domains: cognition, locomotion, vitality, vision, hearing, psychological well-being, and medication usage, which was developed in conjunction with the Integrated Care for Older People framework.¹⁷ Each domain was given a score between 0 and 1 (0 = preserved; 1 = impaired), and the range of total score was from 0 to 7. A lower total score denoted a higher level of IC.

Statistical Analysis

IBM SPSS 27.0 was used to manage the data. Moderated network analysis was carried out in R 4.4.3. P-values ≤0.05 were regarded as significant. We proceeded in three steps.

First, we assessed sample characteristics using descriptive statistics. Continuous variables were presented as mean (standard deviation [SD]), whereas categorical variables were reported using frequencies (percentages).

Subsequently, moderated network models were constructed using the “modnets” package (version 0.9.0). We adopted the hierarchical Least Absolute Shrinkage and Selection Operator approach for variable selection to improve model interpretability.³³ A sequence of λ values was evaluated, and the model was selected according to the Akaike Information Criterion (AIC). All variables were mean-centered to ensure comparability across variables with different scales. Network structure and moderation effects were conducted via the fitNetwork function, with pain serving as a moderator for the associations between IC nodes and fear of movement nodes. This function applied nodewise regression, a technique employing univariate regression models to estimate structure and infer network connections.³⁴ The network was visualized with PlotNet function under an “AND” rule for edge inclusion, retaining only edges that in both nodewise regressions achieved a significant main or interaction effects at P<0.05. Considerable main (non-interaction) effects between two nodes were indicated by solid edges, whereas considerable moderating by pain was indicated by dashed edges. Edge thickness was correlated with the size of the regression coefficients. Analysis employed case-dropping bootstrap methods using the bootNet function with 500 bootstrap repetitions to assess network stability and ensure the robustness of the network model.²⁸

Finally, pathways exhibiting significant moderation effects (indicated by dashed edges in the network) were further explored using the Johnson–Neyman technique via the interactions package. The specific range, direction, and magnitude of pain’s moderating effect in the association between IC and fear of movement could be described.

Results

Sample Characteristics

A total of 452 patients with KOA were analyzed (mean age 64.05 years, SD 7.09), most were female (77.2%), primary and below educational level (52.7%), rural residence (66.8%), and married (95.6%). Detailed characteristics were presented in Table 1.

Table 1.

Sample Characteristics of Patients with KOA (N = 452)

Characteristics	Mean (SD)/n (%)
Age (years)	64.05 (7.09)
Sex
Male	103 (22.8%)
Female	349 (77.2%)
BMI (kg/m2)	24.77 (3.65)
Educational level
Primary and below	238 (52.7%)
Secondary	146 (32.3%)
Tertiary or above	68 (15.0%)
Residence
Urban	58 (12.8%)
County	92 (20.4%)
Rural	302 (66.8%)
Marital status
Married	432 (95.6%)
Divorced/Widowed	20 (4.4%)
Smoking history
No	415 (91.8%)
Yes	37 (8.2%)
Drinking history
No	410 (90.7%)
Yes	42 (9.3%)
Duration of pain (years)	4.94 (4.57)
Heart disease
No	379 (83.8%)
Yes	73 (16.2%)
Diabetes
No	368 (81.4%)
Yes	84 (18.6%)
Hypertension
No	232 (51.3%)
Yes	220 (48.7%)
Kellgren-Lawrence grade
II	248 (54.9%)
III	204 (45.1%)
Symptomatic knee laterality
Left knee	178 (39.4%)
Right knee	122 (27.0%)
Bilateral knees	152 (33.6%)
IC	2.50 (1.34)
TSK-11	23.71 (8.04)
NRS	3.40 (1.36)

Notes: Data presented as mean (SD) continuous variables and n (%) for categorical variables.

Abbreviations: BMI, body mass index; IC, Intrinsic Capacity; TSK-11, the Tampa Scale for Kinesiophobia-11; NRS, Numerical Rating Scale.

Moderated Network Model

Variable selection and nodewise adjacency matrices were detailed in Tables S1 and S2. The regression coefficients with 95% confidence intervals (CIs) for all interaction terms across varying levels of pain was exhibited in Figure S1. Figure 1 consisted of ten subfigures, each corresponding to a distinct predictor variable and displaying the estimated model coefficients along with 95% CIs. In the estimated moderated network model (Figure 2), the top three nodes with the highest expected influence (EI) encompassed “somatic focus” (EI = 1.71), “psychological well-being” (EI = 0.90), and “activity avoidance” (EI = 0.78). Centrality indices were shown in Figure S2. Regarding the relationships between IC and fear of movement nodes, the strongest estimated association was observed between “somatic focus” and “vision” (r = 0.62), followed by “activity avoidance” and “cognition” (r = 0.42), and “somatic focus” and “vitality” (r = 0.40). Bootstrap analyses based on case-dropping resampling confirmed the stability of network edge weights and centrality indices (Figure 3), with a correlation stability (CS) coefficient of 0.70 for expected influence centrality. Notably, pain significantly moderated three pathways: the somatic focus (TSK2)-psychological well-being (IC6) pathway, the activity avoidance (TSK3)-cognition (IC1) pathway, and the avoidance beliefs (TSK1)-somatic focus (TSK2) pathway.

Figure 1.

Plot displaying estimated model coefficients and confidence intervals. An effect is considered statistically significant if the confidence interval does not contain zero.

Abbreviations: IC, Intrinsic Capacity; TSK, the Tampa Scale for Kinesiophobia; M, Pain.

Figure 2.

Moderated network analysis visualization.

Abbreviations: IC, Intrinsic Capacity; TSK, the Tampa Scale for Kinesiophobia.

Figure 3.

Case-dropping bootstrap assessment of network stability. The x-axis represents the proportion of cases retained in each bootstrap subsample. The y-axis shows the average correlation of edge weights between the subsampled networks and the original full-sample network. Red lines denote interaction-term edges, and green lines denote pairwise edges. A correlation coefficient ≥ 0.25 is considered acceptable.

Moderation Effect Analysis

Johnson–Neyman plots (Figure 4) clarified the effects of pain on key associations, between “psychological well-being (IC6)” and “somatic focus (TSK2)”, “cognition (IC1)” and “activity avoidance (TSK3)”, as well as “avoidance beliefs (TSK1)” and “somatic focus (TSK2)”. Specifically, the association between “psychological well-being (IC6)” and “somatic focus (TSK2)” was significant at low pain levels but turned non-significant once pain exceeded a threshold of 5.08 ((b = −0.994, 95% CI: −1.597 to −0.391, t = −3.241, p < 0.01); Similarly, the association between “cognition (IC1)” and “activity avoidance (TSK3)” was significant under low pain levels but became non-significant once pain exceeded a threshold of 4.09 (b = −0.771, 95% CI: −1.324 to −0.218, t = −2.740, P < 0.01). In contrast, the positive associations between “avoidance beliefs (TSK1)” and “somatic focus (TSK2)” became strengthened as pain increased (b = 0.312, 95% CI: 0.178 to 0.446, t = 4.574, P < 0.001).

Figure 4.

Johnson–Neyman plots. (A) Estimated effect of “psychological well-being (IC6)” × pain on “somatic focus (TSK2)”. (B) Estimated effect of “avoidance beliefs (TSK1)” × pain on “somatic focus (TSK2)”. (C) Estimated effect of “cognition (IC1)” × pain on “activity avoidance (TSK3)”.

Abbreviations: IC, Intrinsic Capacity; TSK, the Tampa Scale for Kinesiophobia.

Discussion

This study investigated the relationship between IC and fear of movement in patients with KOA, with a particular focus on the moderating effect of pain. To the best of our knowledge, this was the first study to adopt a moderated network analysis to elucidate such symptom-level relationships, providing original and perceptive results. Our results demonstrated that pain significantly moderated the relationship between IC and fear of movement in patients with KOA.

Patients with KOA who had higher IC showed lower fear of movement, as we identified several edges of IC associated with fear of movement. This finding supported Hypothesis 1 and was in line with the results of several prior empirical studies.^21,35 Robust IC means that patients with KOA possess a larger reserve of psychological and physiological resources, including cognitive function, motor ability, visual and auditory function, and psychological status.^17,18 Patients with better cognitive function can more effectively understand disease-related knowledge, master self-management skills, and accurately perceive the value and safety of early functional exercise.³⁶ A randomized controlled trial demonstrated that cognitive behavioral therapy effectively reduced fear of movement by modifying maladaptive beliefs through cognitive restructuring, suggesting that cognitive processes may play an important role in the management of kinesiophobia.³⁷ Patients with impaired motor function have insufficient ability to carry out daily activities.³⁸ They may fear (re)injury or pain during exercise, resulting in fear of movement. Compared with patients with visual OR hearing impairment, patients with normal vision and hearing can rely on intact sensory perception to accurately assess the surrounding environment, maintain body balance and avoid potential risks during exercise.^39,40 These challenges may reduce confidence in movement and could contribute to fear of movement, although direct evidence supporting this mechanism remains limited. Anxiety is one psychological factor closely associated with fear of movement. Patients in a long-term state of emotional tension and hypersensitivity are more likely to generate excessive worries about exercise-related discomfort, joint pain and potential injury.⁴¹ The increased emotional vulnerability further heightens their psychological vigilance toward exercise.

The moderating role of pain in the relationship between IC and fear of movement demonstrated that higher pain levels weakened the protective effect of psychological well-being on somatic focus, as well as the protective effect of cognition on activity avoidance, thereby supporting Hypothesis 2. Previous studies have reported an association between greater pain intensity and central sensitization in patients with osteoarthritis.⁴² Patients with central sensitization frequently experience multiple somatic symptoms, including fatigue, headache, sleep disturbances, mood alterations, and gastrointestinal complaints.⁴³ Based on these findings, we speculate that central sensitization may represent one potential factor contributing to the observed association between higher pain levels and greater somatic focus. However, this proposed explanation was not directly examined in the present study, and additional research is warranted to clarify these underlying mechanisms. As pain intensity increases, the vicious cycle developed between pain and activity avoidance.⁴⁴ Under intense pain stimulation, even patients with KOA and intact cognitive function tend to develop activity avoidance behavior. Although no interventions were implemented in the present study, previous studies have suggested that multi-component intervention strategies involving aerobic exercise, muscle strength training, balance training and gait training can be adopted to improve patients’ physical function and intrinsic capacity.^45,46 In addition, joint health education, weight management, physiotherapy, and pain cognitive education can be implemented to alleviate pain,⁴⁷ especially in patients with moderate to severe pain.

Notably, pain also moderated the internal structure of fear of movement. At higher levels of pain, we observed an amplification effect: the positive associations between avoidance beliefs and somatic focus became stronger as pain increased. This aligns with the notion that higher pain intensity is associated with greater fear of movement.⁴⁸ When pain is low, patients may leverage their personal internal and external resources to cope with pain avoiding fear of movement. But as pain increases, these resources may become depleted. Patients perceive an inability to control pain and exhibit excessive focus on pain symptoms, which leads them to avoid and escape pain-inducing activities.⁴⁹ Strengthen pain management in patients with KOA, evaluate pain intensity at the individual level, select and optimize analgesic regimens based on different pain levels, and promote patients to perform active functional exercise.

Analyzed from the indicators of network centrality, TSK2 (somatic focus), IC6 (psychological well-being), and TSK3 (activity avoidance) occupy core positions in the network model and exert a stronger influence on other symptoms. Their prominent network positions suggest that they may represent clinically relevant symptoms worthy of further investigation in future longitudinal and intervention studies.

While these findings are meaningful, several limitations should be acknowledged. First, this was a cross-sectional design, which cannot clarify the causal relationships among symptoms or determine whether the moderating effect of pain persists over time. Reciprocal relationships among these variables are also plausible. A longitudinal study is therefore needed to explore these causal dynamics and verify the stability of pain-related moderation effects. Second, the findings should be interpreted within the context of the study population and may not be generalizable beyond the characteristics of the participants included in this study. Recruitment from a single center using convenience sampling, together with the predominance of female participants, may limit the external generalizability of the study findings. Third, this study relied on self-report questionnaires to assess intrinsic capacity, fear of movement, and pain among patients with KOA, which may introduce recall bias and social desirability bias. Future research may combine self-reported data with objective biological indicators or behavioral assessments.

Conclusion

Pain moderates the relationship between IC and fear of movement in patients with KOA. Patients with sufficient IC reserve and low pain intensity report significantly lower fear of movement, and pain strengthens the linkage between avoidance beliefs and somatic focus. These findings identify symptom-level associations among IC, pain, and fear of movement that may help generate hypotheses for future longitudinal and intervention studies.

Funding Statement

This study was supported by Shandong Provincial Natural Science Foundation (grant number: ZR2025QC2117Z) and the Incubation Foundation of Shandong Provincial Hospital (grant number: 2024FY044).

Ethics Approval and Consent to Participate

All participants provided informed consent prior to enrollment, and the study was approved by the ethics committee of Shandong Provincial Hospital (SWYX: NO. 2025-454).

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

Dr Zeping Yan reports Support for the manuscript from the Incubation Foundation of Shandong Provincial Hospital, Shandong Provincial Natural Science Foundation, during the conduct of the study. The authors declare no competing interest.