Are preoperative psychological factors associated with chronic postoperative pain after total knee arthroplasty: a systematic review

Abstract

Purpose

• To examine whether psychological factors are associated with chronic postoperative pain ≥12 months after total knee arthroplasty (TKA), given that ∼10% of patients report persistent pain despite otherwise successful surgery, and psychological influences are proposed contributors.

Methods

• A systematic review was conducted following PRISMA guidelines, including adults undergoing primary or revision TKA with postoperative pain assessed at a minimum of one year. Searches were performed in MEDLINE and Embase. Risk of bias was evaluated using the Newcastle–Ottawa scale. The protocol was registered with PROSPERO (CRD42024620401). Due to substantial heterogeneity in the studies, findings were synthesised narratively.

Results

• Thirty-seven studies met eligibility criteria. Twelve psychological factors were assessed across studies, most frequently depressive symptoms, pain catastrophising, and anxiety. Results were inconsistent, and no psychological factor showed a reproducible association with long-term postoperative pain across studies. Expectations were the only factor consistently associated with pain outcomes, while self-efficacy showed no association. Other factors, such as kinesiophobia and psychological distress, were examined in too few studies to support firm interpretation. Most studies demonstrated a moderate risk of bias, primarily due to reliance on self-reported measures and lack of non-exposed comparison cohorts.

Conclusion

• Substantial heterogeneity across studies limits firm conclusions regarding the influence of psychological factors on chronic postoperative pain one year after TKA. Patient expectations may play a meaningful role, whereas self-efficacy appears unrelated. Overall, most patients experienced pain improvement regardless of psychological profile. Standardised assessment methods are needed to clarify these associations and guide clinical practice.

Introduction

Total knee arthroplasty (TKA) is generally considered a successful treatment for severe degenerative conditions of the knee (1), and the proportion of patients undergoing a TKA is thought to be increasing (2, 3). Nevertheless, the literature reports that about 10% of patients experience dissatisfaction and persistent pain after surgery (4, 5). Persistent pain after TKA may cause patients to seek options for a reoperation in the hope of relief. For each revision procedure, there seems to be incremental risk of complications (6), sometimes resulting in more pain contrary to expectation. Therefore, the study of factors that increase the risk of dissatisfaction or chronic postoperative pain is of great relevance.

The development of chronic postoperative pain is thought to arise from a combination of factors, including inflammatory responses, nerve injury, and peripheral or central sensitisation (7). Several psychological traits have also been suggested as contributing factors to postoperative pain (8, 9, 10, 11, 12, 13) and shown to be linked to prolonged opioid use (14, 15, 16). This is reflected in the biopsychosocial model, which explains that chronic postoperative pain results from complex interactions between biological, psychological, and social factors (17). Several different psychological factors have been proposed in the literature as potential explanations for postoperative pain following TKA (18, 19, 20). These include pain catastrophising, kinesiophobia, and symptoms of depression and anxiety. These factors have been suggested to influence pain through behavioural, emotional, and cognitive pathways that may affect recovery and rehabilitation outcomes (18, 20). In addition, it has been suggested that psychological factors may influence pain perception through central nervous system mechanisms, including altered processing of nociceptive input and changes in pain-related brain activity, which may contribute to the maintenance of pain over time (17, 19, 21).

Consequently, several studies have examined psychological factors’ potential role in the development of chronic postoperative pain (8, 9, 10, 22, 23).

However, to our knowledge, no systematic review exists that exclusively focuses on psychological factors as potentially significant for chronic postoperative pain at least 1 year postoperatively in patients receiving a TKA. A synthesis of current knowledge has the potential to provide a deeper understanding. This will be of importance for surgeons and patients who can use this information during surgical decision-making and to manage expectations. The aim of this study was to report a systematic review of the literature regarding associations between psychological factors and chronic postoperative pain following TKA.

Method

This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and was registered with the Prospective Register of Systematic Reviews (PROSPERO). According to the Danish National Committee on Health Research Ethics’ guidelines, no ethical approval was required for this review. AI assistance tools (Copilot) were used for grammar checking and text rephrasing.

The study was structured according to the population, intervention, comparison, and outcome (PICO) framework with the following research question: are there associations between psychological factors and chronic postoperative pain in TKA patients?

Search strategy

The medical databases MEDLINE and Embase were searched using free wording and Medical Subject Headings (MeSH) related to psychological factors, postoperative pain, and TKA. The search was conducted on 24 October 2024, and an updated search was conducted on 11 March 2026, resulting in one additional study. All extracted literature was stored in the electronic database Covidence (24).

Eligibility

Study participants had to be >18 years old, have undergone a primary or revision TKA, and be followed up with pain assessment at least 12 months after surgery. The studies had to report on one or more preoperative factors concerning psychological disorders’ association with postoperative pain. We restricted the search to only include observational studies, excluding case reports, as we believed that observational studies were better suited for assessing risk factors and long-term outcomes. We included all original studies published in English, regardless of publication year or geography to maximise the inclusion of relevant evidence.

Data selection

Articles were selected for screening if they reported on the risk of developing postoperative pain in an exposed group. Chronic postoperative pain was defined as i) knee-specific pain, ii) pain not improving compared with the preoperative state, and iii) persisting pain >1 year after surgery. The pain should be patient-reported, and therefore, the literature that only reported on the use of pain medication was not selected for screening. The exposed group was defined as patients with a specified psychological factor (e.g. catastrophising or anxiety). Studies reporting only global measures of mental health (e.g. mental component summary scores from generic health questionnaires) were not included, as these do not capture specific psychological constructs, which were the focus of this review. In addition, studies concerning patients with a severe psychotic disorder (e.g. schizophrenia) under pharmacological treatment with antipsychotics were not included.

Two reviewers independently screened all titles and abstracts for inclusions to full-article reading. Potential disagreements were discussed among the reviewers until consensus was reached. The final number of articles was reached after full-text screening.

Data analysis

The risk of bias was evaluated using the scoring system Newcastle–Ottawa scale (NOS) for cohort and case–control studies. The quality of the studies was assessed using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) tool.

Due to a substantial heterogeneity among the included studies, a meta-analysis was deemed inappropriate. Instead, a narrative synthesis was conducted, and key findings were summarised in tabular form. Odds ratios and risk ratios were extracted as primary effect sizes. If these were not available, alternative metrics reported by the study were used. When provided, 95% confidence intervals were recorded to assess precision.

Results

Our systematic search resulted in 1,335 studies from MEDLINE (n = 569) and Embase (n = 766). After removing duplicates (n = 446) and applying eligibility criteria (n = 852), 37 full-text articles were considered appropriate for inclusion (Fig. 1).

Figure 1.

PRISMA flow diagram illustrating the study selection process.

Study characteristics

The studies reported on a total number of 17,258 TKA patients (15,581 primary and 1,677 revision). On average, 61% of the participants were females and the mean or median age ranged from 63 to 73 years. Studies were published between 2003 and 2025 and originated from 12 different countries. The follow-up period ranged from 1 year (n = 28) to 5 years (n = 6). All study characteristics are presented in Supplementary Table 1 (see section on Supplementary materials given at the end of the article).

Twelve different psychological factors were investigated. The most frequently examined factors were depressive symptoms (n = 21) followed by catastrophising (n = 16) and anxiety (n = 16),

Postoperative pain was assessed using nine different measuring tools: the Western Ontario and McMaster Universities Osteoarthritis Index (the WOMAC pain subscale) (25) (n = 13), a visual analogue scale (VAS) (n = 7), a numerical rating scale (NRS) (n = 6), the Brief Pain Inventory (BPI) scale (26) (n = 3), the Knee Injury and Osteoarthritis Outcome Score (KOOS pain subscale) (n = 3) (27), the Knee Society Score (the pain component of the KSS) (28) (n = 1), the McGill Pain Questionnaire (MPQ) (29) (n = 1), and the Oxford Knee Score (the pain component of the OKS) (30) (n = 1). Three studies used a single question to categorise patients into pain groups.

Psychological factors

Detailed results for all studies are provided in Supplementary Tables 2, 3, 4, 5.

Depressive symptoms

Twenty-one studies investigated preoperative depressive symptoms as a potential factor for postoperative pain following TKA, including one study examining patients who had undergone a revision TKA (23, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50). Eleven identified statistically significant association with increased postoperative pain, while thirteen found no association. Effect sizes were generally small to moderate. Note that some studies found associations only under specific conditions, such as type of pain measurement (daily vs nightly (31)), pain severity (average vs severe (36)), or at particular follow-up times (2 vs 5 years (34)). Studies reporting statistically significant associations had a median sample size of 202 (range: 32–4,234) compared with studies reporting non-significant findings (median = 260 (range: 83–7,139)).

The studies that found an association had follow-up periods of 1 (n = 9) and 5 years (n = 2). Those that did not find an association had follow-up periods of 1 year (n = 8), 2 years (n = 1), 3 years (n = 1), 46 months (n = 1), and 5 years (n = 2). For revision TKAs, an association was found when follow-up was done at 2 years; however, this association ceased after 5 years (34).

In seven studies, the Hospital Anxiety and Depression Scale (HADS) (51) was used as a psychological assessment tool, of which six studies dichotomised between anxiety and depression and one study was based on the total HADS score. In addition, the studies used the following assessment tools: the Patient Health Questionnaire (52) (n = 4), the Beck Depression Inventory (53) (n = 3), the Center for Epidemiological Studies Depression Scale (CES-D) (54) (n = 2), the Patient-Reported Outcomes Measurement Information System for Depression (55) (PROMIS – Depression) (n = 1), the Hamilton Depression Rating Scale (HDRS) (56) (n = 1), diagnostic codes (n = 1), the Geriatric Depression Scale (GDS) (57) (n = 1), and an existing clinical diagnosis (n = 1).

Despite several studies finding an association, a slight majority did not identify a significant association between preoperative depressive symptoms and postoperative pain, and results were further limited by substantial variation in follow-up duration and measurement methods.

Catastrophising

Sixteen studies investigated preoperative pain catastrophising as a factor in the development of postoperative pain (31, 35, 41, 43, 44, 45, 49, 58, 59, 60, 61, 62, 63, 64, 65, 66). Eight studies found a positive association, while nine studies found no association. The studies showed small-to-moderate effect sizes. Studies with an association had a median sample size of 117 (range: 32–442), whereas studies reporting no associations had a median of 100 (range: 32–288). One study reported a significant relationship between pain catastrophising and nightly pain, but no association was observed when looking at global daily pain (31).

The studies that found a positive association did follow-ups at 1 (n = 7) and 2 years (n = 1). The studies that did not find an association did follow-ups at 1 (n = 6) and 5 years (n = 2). Fourteen studies used the Pain Catastrophizing Scale (PCS) (67) to evaluate pain catastrophising, and two used the Coping Strategies Questionnaire (68).

The studies’ findings were evenly divided, and even with similar assessment tools and follow-ups, no clear consensus on pain catastrophising emerged.

Anxiety

Sixteen studies examined potential associations between preoperative anxiety and postoperative pain following TKA, including one study that additionally examined revision TKAs (23, 34, 35, 36, 37, 39, 40, 42, 43, 44, 45, 46, 47, 50, 58, 69). Eight studies found a positive association, nine studies found no association, and one study found a negative association. Effect sizes were low to moderate. Studies reporting significant associations generally had larger sample sizes (median: 220 (range: 116–7,139)) compared with studies reporting non-significant findings (median: 166 (range: 83–349)). Overall, the strength and direction of associations between preoperative anxiety and postoperative pain varied across studies. Some studies found that anxiety was associated with postoperative pain under specific conditions, such as pain severity group (36) or follow-up duration (1 vs 5 years) (44). No association was observed for revision TKA (34).

The studies that reported a positive association had a follow-up period of 1 (n = 7) and 5 years (n = 1). The studies that did not report an association had follow-up periods of 1 year (n = 5), 5 years (n = 3), and 46 months (n = 1). The study that found a negative association had a 1-year follow-up.

Eight studies used the HADS to assess anxiety. Of these, seven reported dichotomising the scores between anxiety and depression, while the remaining study did not specify whether dichotomisation was applied. In addition, the studies used the State-Trait Anxiety Inventory (STAI) (70) (n = 5), the Generalised Anxiety Disorder (GAD) scale (71) (n = 1), PROMIS anxiety instruments (55) (n = 1), and the Mayo Clinic’s H-ICDA codes (34).

Considerable variation existed across studies in terms of measurement tools and follow-up duration, which limits the comparability of findings between the studies. Consequently, there is no clear consensus regarding the role of anxiety, as studies reporting an association and those reporting no association were nearly evenly distributed.

Kinesiophobia, expectations, self-efficacy, and psychological distress

Kinesiophobia was examined as a potential factor associated with postoperative pain in four studies. Two studies found an association between kinesiophobia and postoperative pain 1 year after TKA, but not after 3 years (72). Studies reporting an association had a median sample size of 88 (range: 75–101). Three studies found no association, all with a follow-up period of 1 year (49, 61, 66) and sample sizes with a median of 101 (range: 79–116). The Tampa Scale of Kinesiophobia (TSK) (73) was used as the assessment tool in all four studies. One study found an association only when looking at the TSK-1 subscale, but not when looking at the TSK-2 subscale (40).

Four studies investigated patients’ preoperative expectations, and all four studies found an association (sample size median: 156 (range: 75–288)) (43, 45, 49, 74). In addition, one study found no association but only when using at different measurement tool (CEQ) (sample size: 146). Higher (more positive) preoperative expectations were consistently associated with lower levels of pain postoperatively. All studies assessed pain 1 year after surgery; however, different approaches were used to evaluate expectations. Tilbury et al. (74) applied both the Credibility/Expectancy Questionnaire (CEQ) (75) and the Hospital for Special Surgery (HSS) expectations scale (76), while Sullivan et al. (49) used a brief questionnaire comprising four items addressing expectations. Rice et al. (43) and Carrier et al. (45) both employed a single-item numerical scale asking patients how much knee pain they expected to experience after surgery.

Self-efficacy was examined in three studies (41, 44, 47). No significant association was found in any of these studies. Sample sizes had a median of 260 (range: 220–346), and postoperative pain was assessed at 1 (n = 2) and 5 years (n = 1) following TKA. Self-efficacy was measured using the Arthritis Self-Efficacy Scale (77) (n = 1) and the Pain Self-Efficacy Questionnaire (78) (n = 2).

Psychological stress was investigated in three studies (23, 79, 80). One study, with a sample size of 682, found an association with postoperative pain at both 1 and 2 years; however, when examining the change in pain from baseline to follow-up, no difference was found between the two groups (80). Two studies found no association at one year (median sample size of 159 (range: 116–202)) (23, 79). Psychological stress was measured using the Mental Health (MH) subscale from the Short Form-36 (SF-36) (81), the Perceived Stress Scale (PSS) (82), and HADS.

The correlating effect sizes for kinesiophobia, self-efficacy, and psychological stress were generally small. Studies examining expectations had moderate effect sizes. All findings were based on a limited number of studies, and for several of the factors, different measurement tools were used for both exposure and outcomes, increasing heterogeneity across studies.

Additional factors

Five additional factors were investigated in the included studies: i) type D personality (negative affectivity and social inhibition) (61), ii) pessimistic explanatory style (83), iii) illness perception (36), iv) Borderline Personality Organization (BPO) (84), and v) perceived injustice (66).

All additional factors were found to be associated with postoperative pain for TKA patients but not for revision patients (83). The median sample size was 159 (range: 79–783), and the effect sizes were moderate in all studies. However, each factor was only investigated in one single study. As these findings have not been confirmed by further research, the evidence is insufficient to support any definitive conclusions.

Risk of bias

All studies were evaluated for risk of bias using the Newcastle–Ottawa scale (NOS) for cohort studies. The scale assesses three main domains: selection (maximum of 4 points), comparability (maximum of 2 points), and outcome (maximum of 3 points). Low numbers correspond to a higher risk. Thirty studies were rated as having a moderate risk of bias (4–6 points), and seven studies were rated as having a low risk of bias (7–9 points) (median: 6 (range: 4–7)). Most studies lost points due to the absence of a non-exposed cohort, reliance on self-reported measurement tools, and insufficient reporting of either the amount or description of participants lost to follow-up. Detailed risk-of-bias assessments are presented in Supplementary Table 6.

Discussion

The aim of this systematic review was to investigate the association between psychological factors and chronic postoperative pain at least one year after receiving a TKA. The review synthesised evidence from 36 studies, examining 12 different preoperative psychological factors’ association with chronic pain following TKA. The most frequently studied factors, depression, anxiety, and catastrophising, all showed inconsistent results. Kinesiophobia and self-efficacy were found not to be associated with postoperative pain, and psychological stress was inconclusive. Expectations, along with all additional psychological factors examined, showed associations with postoperative pain, but these results were based on few studies, making the evidence insufficient for a definitive conclusion. Across the included studies, effect sizes were generally small to moderate, although reporting methods varied considerably, limiting direct comparison.

Previous studies have described similar results regarding the association between expectations and postoperative pain. In a meta-analysis by Laferton et al., a small but robust positive association between positive preoperative expectations and better postoperative outcomes in TKA and THA patients was reported (85). This association may partly be explained by placebo and nocebo effects. Colloca and Barsky (86) describe how expectations are shaped by previous treatment experiences, verbal information from healthcare professionals, and social observation. They note that these positive expectations can activate the placebo effect, improving clinical outcomes, whereas negative expectations may trigger the nocebo effect and lead to poorer outcomes. However, some studies argue that expectation fulfilment, rather than baseline expectations, is the key determinant of patient satisfaction (87). This is an important nuance when considering how clinicians should approach and work with patient expectations. Recognising this nuance, intervention studies have explored how actively shaping expectations may serve as a valuable clinical tool. Tolk et al. found that patients who received preoperative education aimed at fostering realistic expectations reported significantly higher satisfaction levels (88). Realistic expectations are inherently more likely to be fulfilled than overly optimistic ones. This suggests that implementing clinical pathways designed to promote realistic patient expectations may improve overall outcomes and warrants further investigation.

The heterogeneity across studies likely contributed to the conflicting results regarding associations. This was apparent in the use of various measurement tools used for estimating postoperative pain and psychological factors, differences in the time from surgery to pain assessment (ranging from 1 to 5 years), variations in sample sizes, and differences in statistical methods and included confounders (Supplementary Tables 2, 3, 4, 5). Variation in the number of psychological factors examined may also have influenced the results. Seventeen of the studies investigated only one psychological factor, 14 of which found an association with pain. By analysing only one psychological factor, the predictive value may have been overestimated, as confounding or interacting effects of co-occurring psychological variables are not considered. This may be particularly important for psychological factors since they often co-occur and share symptom domains.

Previous systematic reviews have investigated the association between a variety of factors and postoperative pain, across many surgical fields (89, 90, 91, 92, 93, 94, 95). Unlike our findings, some reported associations between one or more psychological factors and postoperative pain (89, 90, 92, 95, 96). However, these reviews did not focus exclusively on psychological factors as predictors, as done in our review. In one meta-analysis examining patients undergoing breast surgery, they found that higher preoperative anxiety, depression, and catastrophising were weak but statistically significant predictors of postoperative pain up until 12 months after surgery (89). Likewise, Petrucci et al. found that anxiety and depression were associated with worse back pain, but not leg pain following lumbar spine surgery (90).

Previous narrative analyses report a large discrepancy between included studies similar to our findings. Giusti et al. reported wide variations in significance rates for depression, trait anxiety, and catastrophising, while kinesiophobia and self-efficacy showed no association with postoperative pain (91). Hinrichs-Rocker et al. observed correlations with depression, psychological vulnerability, and stress, but other factors, such as anxiety and self-control, remained inconclusive (92).

Specifically, for TKA patients, Lewis et al. reported an association between catastrophising and persistent pain, contrary to the findings of our study (93). This difference may relate to follow-up time. Our review examined pain at >1 year postoperatively, whereas Lewis et al.’s review considered outcomes >3 months postoperatively. Although they argued that catastrophising was not influenced by the length of the follow-up period, this is contradicted by another systematic review by Vissers et al. (94). The authors found evidence that catastrophising predicts pain after TKA only in follow-ups shorter than 1 year (94).

Similarly, Brander et al. (42), Wylde et al. (44), and Bierke et al. (35) all found early postoperative associations for depression or anxiety, which resolved with extended follow-up.

Another explanation for this inconsistency of our findings with those of Lewis et al. (93) may be study numbers. Lewis et al. reported on only three studies examining pain catastrophising, in contrast to our 16 included studies. This discrepancy may be explained by differences in search strategies and publication year.

Vissers et al. similarly found conflicting evidence regarding the effect of psychological factors in THA patients (94). In contrast, O’Connor et al.’s systematic review suggested a possible link between preoperative depression/anxiety and postoperative pain in THA patients (95). Discrepancies such as these in the conclusions of systematic reviews may arise from differences in search methods, inclusion criteria, or analytical approaches.

Limitations

A strength of this review is the highly specific PICO question, focusing exclusively on preoperative psychological factors, postoperative pain assessed >1 year after surgery, and the use of patient-reported outcomes exclusively rather than using many additional exposure measurements. This resulted in a comprehensive yet highly targeted search, aimed at identifying comparable exposures and outcomes. Despite this approach, considerable heterogeneity was observed across studies regarding measurement tools for exposures and outcomes, effect measures, statistical analyses, and adjustments for confounding variables. This heterogeneity limits the generalisability of the findings and is considered a limitation. The methodological heterogeneity prevented us from conducting a meta-analysis, as the results could not be meaningfully quantified without compromising validity.

In general, none of the included studies were at high risk of bias, which is an advantage. The majority were judged to have a moderate risk of bias according to the NOS criteria.

All study participants were TKA patients who were considered representative of the general population undergoing TKA surgery. However, one study required participants to have moderate-to-high levels of pain catastrophising prior to surgery (a score of 16 or higher on the PCS (range: 0–52)) (41). This inclusion criterion may introduce a degree of selection bias, as the extent to which pain catastrophising serves as a predictive factor for poor outcomes could potentially be underestimated due to this selection limitation.

Twenty-five studies only included a single cohort and therefore could not be awarded points for item 2 under the selection domain (‘Selection of the non-exposed cohort’), as this item exclusively address studies with two cohorts. Whether this should be considered a limitation is debatable, as this criterion emphasises how the unexposed group is selected rather than whether it is present or not.

The studies used validated patient-reported questionnaires to assess the exposure (n = 34) and outcome (n = 36), which have been tested and approved for use in research. However, self-reported questionnaires may still be susceptible to recall bias and social desirability bias. A few of the studies used unvalidated, ad hoc instruments.

Most of the included studies managed to adjust for important confounders, such as age, sex, and preoperative pain (n = 33). The sample sizes for included studies were generally high, and most studies included more than 100 participants (n = 29).

Sixteen studies had lost more than 20% of their included participants at follow-up. Of these, loss to follow-up was considered likely to have introduced bias in four cases.

Our narrative assessment did not suggest the presence of publication bias, as several studies also reported no association between at least one psychological factor and chronic pain. However, the potential influence of publication bias should not be disregarded. Non-significant findings are sometimes underreported, and studies with non-significant associations may face challenges in getting published. This could have led to an overestimation of the strength of the associations observed.

Importantly, only a minority of the included studies reported conducting a priori power calculations or provided sufficient information to assess whether they were adequately powered. Likewise, few studies clearly reported whether they achieved their predefined sample size targets. Several studies had relatively small to moderate sample sizes, suggesting that many of these studies were likely underpowered. However, without formal power calculations, this assumption is difficult to verify. Consequently, it remains unclear whether statistically non-significant findings reflect a true absence of association or insufficient statistical power, increasing the risk of type II errors. Therefore, conclusions based on these results should be interpreted with appropriate caution.

No backward or forward citation searching of the included studies was conducted. This decision was made to maintain a transparent and reproducible search process, as our search strategy was designed to capture all relevant studies. We acknowledge that this approach may have missed additional studies not covered in the selected databases.

This review focused on specific psychological constructs rather than general mental health. While this approach enabled detailed examination of discrete psychological factors, it may have excluded broader aspects of mental well-being that could influence postoperative pain outcomes, which can be considered as a limitation. Examining the research of the predictive value of general mental health status alongside specific psychological constructs may provide additional insights into the multifaceted relationship between preoperative psychological factors and postoperative pain.

GRADE

The included studies were generally of good methodological quality within their respective designs, with adequate sample sizes, relevant study populations, and low-to-moderate risk of bias, as well as a low risk of indirectness in relation to the PICO question. However, the overall GRADE assessment was low due to substantial inconsistency in measurement methods and outcomes (97) and the observational nature of the studies, which lowers the evidence level (Table 1). Publication bias was not indicated in the studies, but the possibility cannot be excluded because of insufficient information in the studies. Although the individual studies were relatively well conducted, the inconsistency reduces confidence in the overall body of evidence and suggests that the true effect may differ from what the studies reported.

Table 1.

Summary of the grade of evidence for each outcome according to the GRADE approach.

GRADE
Factor	Depression	Catastrophising	Anxiety	Kinesiophobia	Expectations	Psychological distress	Self-efficacy
Study design	Observational study	Observational study	Observational study	Observational study	Observational study	Observational study	Observational study
Patients, n	13,624	3,151	11,668	463	792	1,331	801
Risk of bias	Moderate risk of bias	Moderate risk of bias	Moderate risk of bias	Moderate risk of bias	Moderate risk of bias	Moderate risk of bias	Moderate risk of bias
Inconsistency	High risk of inconsistency	High risk of inconsistency	High risk of inconsistency	High risk of inconsistency	Low risk of inconsistency	High risk of inconsistency	High risk of inconsistency
Indirectness	Low risk of indirectness	Low risk of indirectness	Low risk of indirectness	Low risk of indirectness	Low risk of indirectness	Low risk of indirectness	Low risk of indirectness
Imprecision	Moderate risk of imprecision	Moderate risk of imprecision	Moderate risk of imprecision	Moderate risk of imprecision	Moderate risk of imprecision	Moderate risk of imprecision	Moderate risk of imprecision
Publication bias	Insufficient information	Insufficient information	Insufficient information	Insufficient information	Insufficient information	Insufficient information	Insufficient information
Quality	Low	Low	Low	Low	Moderate	Low	Low

Perspective

Despite indications from previous research, this study did not confirm that psychological factors influence chronic postoperative pain after TKA, due to inconclusive results and substantial variability observed across studies. More methodologically rigorous and comparable studies are needed to support evidence-based guidelines. Without such alignment, the field will remain fragmented and difficult to translate into clinical practice.

Implementing psychological interventions prior to TKA may improve postoperative outcomes, but current evidence is mixed. Szeverenyi et al. reported that psychosocial interventions reduced postoperative pain in orthopaedic patients, with stronger effects in acute surgery than in elective procedures (98). However, these results were based on pain measured one month postoperatively, making it uncertain whether the same effect applies to chronic postoperative pain.

A meta-analysis by Liu et al. examined the effect of cognitive behavioural therapy (CBT) in TKA patients (99). The study found that CBT reduced kinesiophobia but did not improve pain or knee function. In contrast, Rojas Marcos et al. reported that psychosocial interventions reduced postoperative pain in nine of 15 studies (100). However, both analyses were based primarily on follow-up periods shorter than 12 months.

In conclusion, it remains difficult to determine whether psychological interventions have a positive effect on long-term postoperative pain, as there is a lack of studies focusing on the longitudinal impact of such interventions.

It is important to note that while several studies found statistically significant associations between psychological factors and postsurgical pain, the clinical relevance of these was often considered to be limited. For studies reporting mean differences, the observed effects were generally smaller than the MCID, suggesting that the differences would not be perceived as clinically meaningful by patients. In addition, the majority of the studies reporting unstandardised regression coefficients indicated that very large changes in psychological scores would be required to reach MCID thresholds. Overall, these findings highlight the importance of emphasising that statistical significance alone should not be interpreted as evidence of clinically important effects.

We observed substantial heterogeneity across included studies. Future research should aim to standardise measurement tools for both predictors and outcomes, prioritising validated instruments in accordance with COSMIN guidelines to ensure reliability, validity, and responsiveness (101).

The HADS and the PCS are commonly used in TKA research and have been evaluated using COSMIN standards, although PROMIS-D has demonstrated superior ratings compared with HADS (102, 103, 104). Consistent use of such instruments to assess depressive symptoms, anxiety, and pain catastrophising may reduce heterogeneity. Similarly, validated instruments should be used for pain assessment, with clear specification of whether pain is measured unidimensionally (e.g. numerical rating scale (105)) or multidimensionally. For knee-specific multidimensional assessment, KOOS has been recommended (106). When using multidimensional instruments, reporting subscale scores rather than just total scores is encouraged to enhance interpretability and comparability (107). Finally, we recommend sufficiently large sample sizes to enable robust statistical modelling, allowing adjustment for covariates, and to reduce the risk of type II errors.

Finally, we would like to emphasise that all included studies, evaluating pain development, reported an improvement, even when a psychological factor was present. Although the degree of improvement varied, these findings suggest that a TKA generally alleviates pain regardless of psychological status. Therefore, patients should not be excluded from surgery solely due to the presence of psychological factors. In addition, 13 of our included studies assessed changes in the psychological status following TKA. Nine of these reported an improvement, suggesting beneficial effects on psychological well-being and pain.

Conclusion

This review could not confirm or rule out that psychological factors contribute to chronic postoperative pain >1 year after TKA surgery, largely due to substantial heterogeneity and inconsistent findings across studies. This highlights the need for more standardised research to improve comparability. Expectations were the only factor consistently associated with postoperative pain, while self-efficacy consistently showed no association. However, both were based on few studies, limiting the validity. Across studies, patients generally experienced pain improvement after surgery regardless of preoperative psychological status, indicating that a TKA can alleviate pain even when preoperative psychological factors are present.

ICMJE Statement of Interest

The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the work reported.

Funding Statement

Open access funding provided by Copenhagen University, research funds of the University Hospital of Copenhagen, and health donations were used for the salary of the first author. The funders had no influence on the concept or execution of this study or manuscript.

Author contribution statement

JH designed the study and was responsible for data collection, data analysis, and drafting of the manuscript and further editing. JTH assisted in investigation and data collection. MMP and AO reviewed and edited the manuscript.