Introduction

The prevalence of problematic outcomes following total knee arthroplasty (TKA) is alarmingly high, in spite of indicators of surgical success [22, 38]. In fact, one in eight patients reported moderate-to-severe pain 1 year after surgery despite an absence of clinical or radiographic abnormalities [4], and post-surgical symptoms may be a heavy burden for up to 30 % of patients after TKA [35]. Considering the exponential increase in TKA and potential revision procedures, this is becoming a major concern not only for patients, but also for health care providers and researchers [27].

Research efforts have therefore focused on the evaluation of factors associated with unsatisfactory outcomes after TKA [27]. Besides demographic factors such as age, sex, and body weight, psychological variables might also play an important role as determinants of problematic health outcomes after TKA [23, 24]. Such psychological factors strongly influence pain perceptions, rehabilitation compliance, and patient outcomes especially after orthopaedic surgeries requiring extensive rehabilitation such as total joint arthroplasty. Early recognition of patients exhibiting psychological distress, fear-avoidance behaviour, or unfavourable personality traits can be used to improve preoperative risk stratification for poor rehabilitation or surgical outcomes [16]. In this light, converging evidence suggests that pain disability derives not only from pain severity, but rather from patients’ interpretation and adjustment to their own pain [6]. Kinesiophobia [26], a maladaptive strategy that causes the avoidance of physical activity because of pain-related fear [9], is gaining increasing attention since it may lead to illness behaviour and subsequently create a vicious cycle of pain and disability [29]. The influence of kinesiophobia has been initially suggested to play a role on post-surgery recovery time [9, 37], and recently, its impact has been explored also on the final outcome after TKA [14].

However, caution should be exercised when interpreting the results of the available studies, given their small sample size, nonparametric analyses, failure to adjust for any covariates, and failure to adjust for multiple analyses, all of which increase the likelihood of false-positive findings [6]. To this regard, preoperative depression and anxiety have also been shown to be associated with increased pain 1 year after TKA [4]. It remains unclear if kinesiophobia may confer a risk also when considering depression and anxiety as covariate [6]. Pain-related fear of movement may be an overlapping or unique risk factor for problematic TKA outcomes. From a clinical perspective, the distinctiveness may have important implications because it could help to identify which of these factors should be key targets for psychosocial interventions designed to improve TKA outcomes [31]. Thus, despite a growing body of the literature [8] suggesting that certain psychological variables might predispose patients to untoward pain-related outcomes after TKA, the role of kinesiophobia and in particular its correlation with other psychological and physical factors still needs to be explored.

The aim of this study was to prospectively evaluate a large cohort of patients to analyse the role of physical factors and psychological aspects, and the intercorrelation among depression, anxiety, and kinesiophobia. The hypothesis was that kinesiophobia represents an independent factor influencing the results obtained after TKA.

Materials and methods

The study was approved by the Internal Review Board and Hospital Ethics Committee (Prot. 0032215) of the Rizzoli Orthopaedic Institute (Bologna, Italy), and informed consent was obtained from all patients.

All patients who underwent primary TKA between January 2011 and September 2014 and accepted to participate were included in this study and prospectively evaluated. Patients were excluded if they were unable to complete the questionnaires independently because of emotional, cognitive, or language barriers. The same surgical technique, with a medial parapatellar approach, was used in all the examined patients, who underwent the same rehabilitation programme during their hospital stay.

Two hundred and fifty-five patients were enrolled for the study. During the study period, 10 patients were excluded because of TKA on the opposite knee (n = 3), TKA infection (n = 1), or for other medical reasons not related to their TKA (n = 6). Two patients refused to answer to the follow-up questionnaires, and 43 were lost at follow-up. Consequently, 200 patients were included in the study analysis. This cohort presented a mean age of 65.7 ± 9.1 years. Of these patients, 134 were women and 66 men, with a mean BMI of 28.2 ± 4.1. The mean number of joints presenting pain in the 200 patients evaluated was 2.7 ± 2.2, with a mean history of 8.2 ± 8.0 years of symptoms. Patient education level ranged from elementary school (71 patients), middle school (59 patients), high school (58 patients), and university degree (12 patients).

The basal evaluation included the assessment of pain and function on 0–10 numeric rating scales. Moreover, patients completed the SF-12 (both Physical and Mental Health subscales forming a multipurpose short-form survey with 12 questions, derived from the SF-36, to quantify the overall health-related quality of life) [36], State-Trait Anxiety Inventory—STAI: in particular, we evaluated the Trait Anxiety Scale— T-Anxiety, focusing on relatively stable aspects of “anxiety proneness” including general states of calmness, confidence, and security, with higher scores indicating greater anxiety [21]. BDI (Beck Depression Inventory) was used for the self-assessments of depression symptoms [28]. Finally, the Tampa Scale for Kinesiophobia was administered (TSK, both Activity Avoidance—TSK1 and Harm—TSK2 subscales) [30]. TSK [32] is a widely used questionnaire for assessing pain beliefs and pain-related fear of movement/reinjury in the musculoskeletal field [30]. The 13-item version of the original 17-item questionnaire was used, with higher scores representing stronger fear-avoidance beliefs in two subscales: TSK1 (a belief that activities causing pain should be avoided) and Harm—TSK2 (a belief that pain is a sign of body damage).

Pain, function, and SF-12 subscales were used to evaluate the improvement at 12-month follow-up. At 1 year, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC, a validated scale designed to reflect the problems experienced by individuals with lower limb deficiencies) [1] was used to evaluate the overall TKA results. This composite questionnaire includes five questions about pain, two about stiffness, and 17 about the degree of difficulty in daily life activities. Higher scores of these subscales indicate greater difficulty.

The first analysis phase involved the evaluation of the improvement over time in terms of pain, function, and SF-12. The second phase focused on the correlation of kinesiophobia with the scores obtained at 12-month follow-up. Other factors that may have influenced the results after TKA were also explored, such as sex, age, BMI, education level, and number of painful joints and years of symptoms’ duration before surgery. Finally, a multivariate analysis was performed to test whether these factors influenced the outcome correlation with kinesiophobia, or whether kinesiophobia represented an independent factor influencing TKA results.

Statistical analysis

All continuous data were expressed in terms of mean and standard deviation of the mean, and the categorical data were expressed as frequency and percentages. The Kolmogorov–Smirnov test was performed to test the normality of continuous variables. The paired t test was performed to assess the differences at different follow-up times. The ANOVA test was performed to assess the differences between groups of continuous, normally distributed and homoscedastic data, and the Mann–Whitney test was used in all other cases. The Spearman rank correlation was used to assess the correlation between continuous data. The Kendall tau correlation was used to assess the correlation between ordinal data. Finally, to answer to the study hypothesis and confirm whether kinesiophobia is an independent factor influencing the final outcome regardless of the other variables, the patient characteristics and psychological scores that were found significant at the univariate analysis were used for a multivariate analysis with the general linear model (GLM) to confirm their influence on the outcome. For all tests, p < 0.05 was considered significant.

All statistical analyses were performed using SPSS v.19.0 (IBM Corp., Armonk, NY, USA).

Results

The analysis of the outcome after TKA showed a significant improvement of pain from 6.5 ± 2.3 to 2.2 ± 2.6 (p < 0.0005), function improved from 2.7 ± 2.2 to 7.6 ± 2.1 (p < 0.0005), while SF-12 scores for Physical and Mental Health subscales increased from 30.9 ± 6.4 to 46.4 ± 9.6 and from 46.4 ± 12.2 to 52.2 ± 10.5, respectively, at the 12-month follow-up (both p < 0.0005).

The analysis on the influence of kinesiophobia on the measured outcomes was performed separately for the two TSK subscales. TSK1 was correlated with WOMAC results at 12 months (p = 0.005, ρ = 0.197) (Fig. 1), whereas no correlation was documented between TSK2 and any outcome scores. Age was found to correlate with TSK1 values (p = 0.018, ρ = 0.167). The analysis of the other factors that may have influenced TKA outcome showed that WOMAC results were also influenced by sex (women 15.9 ± 16.9, men 10.1 ± 12.4; p = 0.004), and a correlation was also found with STAI (p = 0.002, ρ = 0.222) and BDI (p < 0.0005, ρ = 0.307). Moreover, SF-12P results were correlated with TSK1, STAI, and BDI (p = 0.023, ρ = −0.160; p = 0.013, ρ = −0.199; p = 0.002, ρ = −0.213, respectively). Other parameters that may have influenced TKA results, such as age, BMI, education level, and number of painful joints and years of symptoms’ duration before surgery, did not correlate with the clinical outcome in our series.

Fig. 1
figure 1

Correlation between TSK1 and WOMAC results at 12-month follow-up (p = 0.005, ρ = 0.197): higher levels of kinesiophobia correlated with a worst functional outcome after TKA

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Finally, to test the hypothesis on the influence of kinesiophobia on the final outcome, a multivariate analysis was performed. This analysis included all the factors found to correlate with the clinical outcome in the univariate analysis and confirmed the importance of BDI (p = 0.006, partial η 2 = 0.038), TSK1 (p = 0.011, partial η 2 = 0.033), and sex (p = 0.048, partial η 2 = 0.020), while age and STAI were not confirmed. Finally, further analysis documented the synergic interaction of BDI and TSK1, which together presented an even stronger correlation (p < 0.0005, partial η 2 = 0.111) with the outcome measured through the WOMAC score 12 months after TKA (Fig. 2).

Fig. 2
figure 2

Synergic interaction of BDI and TSK1: patients with higher levels of both kinesiophobia and depression presented a worst outcome measured with WOMAC score 12 months after TKA

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Discussion

The most important finding of the present study was that kinesiophobia affects TKA outcome, independently from other psychological and physical variables.

This finding adds to a growing body of the literature suggesting that certain psychological variables might predispose patients to untoward pain-related outcomes after TKA. In particular, pain-related fears may lead to hypervigilance towards body sensations, such as touch or movement, and to the avoidance of certain behaviours [9], and the amplification of these cognitive and behavioural disorders may impede recovery. These patients have difficulties in not focusing on the painful or threatening stimulus, which intensifies fear of pain and further increases the attention paid to the stimulus causing an overall higher perception of the experience of pain [7]. In fact, MRI evaluation documented higher degrees of activity not only in brain processing areas, but also in areas related to attention, anticipation, and emotional aspects of pain [19]. These psychological processes may also influence pain modulation through neurophysiological processes, interfering with descending pain-inhibitory systems, facilitating neuroplastic changes in the spinal cord, and finally promote pain sensitization [18, 31]. This further sustains activity avoidance due to pain-related fears, which may lead to functional disability after TKA.

Kinesiophobia has been reported to influence the post-acute phase in terms of hospitalization and patient recovery [5, 9, 25, 33, 37], but it has also been found to be a significant predictor of chronic pain persisting more than 3 months. At this stage, pain can be considered chronic since it exceeds typical healing time often becoming a disorder on its own, which can perpetuate functional disability [6]. The impact on TKA results has been recently confirmed by a systematic review of the literature; however, the available studies present small- to medium-sized cohorts, and analyses have not been often adjusted for other relevant confounders [6]. Kinesiophobia might not make a unique contribution to problematic health outcomes following TKA, and depression or anxiety could potentially covary with kinesiophobia or confound associations under investigation. In fact, previous reports suggested that also patients with preoperative anxiety and depressive symptoms had worse outcome after TKA and were less satisfied than patients without anxiety or depressive symptoms [10, 15, 17]. Faller et al. [13] reported that preoperative depression scores predicted post-operative scores of a measure of functional difficulties at 3 and 12 months following TKA, as confirmed by other studies showing that depression [3, 4, 15] is related to fewer improvements in pain and function after joint replacement.

Thus, it is mandatory to measure and include as covariates in the model predicting chronic pain other psychological constructs known to be related (such as anxiety and depression), as shown by a previous study where pain catastrophizing (another disorder where pain is perceived as abnormally harmful) lost significance after further inclusion of depression in the model [6]. In fact, we currently lack sufficient evidence to conclude which risk factor(s) among the many related psychological constructs (e.g. kinesiophobia, anxiety, and depression) contribute uniquely to chronic pain after TKA [6]. Moreover, there could be an interplay among psychological aspects. For example, depression and catastrophizing have been shown to be significantly intercorrelated [11]. If pain is perceived as harmful, pain-related fear may develop, which may lead to the avoidance of certain behaviours, hypervigilance towards bodily sensations such as movement or touch, and finally cause idleness, disability, and depression [34]. Depression prolongs the experience of pain and therefore the amplification of cognitive and behavioural disorders (such as pain catastrophizing and kinesiophobia), thus creating a vicious cycle of disability and pain that may impede recovery and affect the treatment outcome [9]. Therefore, we believed it was important to include measures of both kinesiophobia and depression in our analysis, as well as the other variables that could contribute to the final result after TKA, as suggested by the literature.

Many other variables have been actually investigated in observational studies as risk factors associated with the presence of chronic pain after TKA [2, 20]: the severity and prognosis of postoperative pain have been associated, besides with psychological factors including anxiety, depression, pain catastrophizing, also with demographic factors, such as age, sex, and body weight, and clinical factors such as preoperative pain, etc. [23]. However, while particular variables may be consistently associated with poor pain outcomes, gauging the extent of their influence is important to determine the priority for intervention. To this regard, Lewis et al. [27] performed a systematic review and meta-analysis to determine the stronger independent predictors of persistent pain after TKA. There was little impact on the outcomes when the moderating effects of primary patient diagnosis and type of surgery were evaluated, suggesting the results are robust across the population presenting for TKA. Several clinical and psychosocial factors were consistently associated with long-term pain, while patient characteristic, biomechanical, and perioperative variables had limited influence. In particular, the analysis underlined six preoperative factors that had a significant effect: greater number of pain sites and higher levels of preoperative pain; higher levels of catastrophizing, depression, and anxiety; and poorer levels of preoperative function.

Thus, in this study, the role of kinesiophobia was assessed together with all these factors in a multivariate analysis of a large patient population undergoing TKA and followed prospectively at 1 year of follow-up. The analysis confirmed the importance of kinesiophobia together with depression, which were independently correlated to the final outcome and presented a synergic interaction, showing together an even stronger predictive value for TKA results. Many other factors, demographic, social, psychological, and physical, may also play a role for the final outcome, and the fact that we could not analyse all possible variables represents a limitation of the study. However, the main factors documented by the previous literature have been considered, thus supporting the strength and novelty of the study findings.

Kinesiophobia is an important risk factor for chronic pain following TKA surgery, which is of marked clinical interest given that this variable can be measured prior to surgery and is potentially modifiable. This is a key aspect especially for these orthopaedic patients where post-operative movement is both an outcome measure as well as a necessary component of the rehabilitation process to optimize the overall results. To this regard, an interesting finding is that the highest correlation between kinesiophobia and results was found for the subscale of the score focused on the avoidance of movement, in agreement with the findings of Doury-Panchout et al. [9], and activity avoidance may jeopardize both rehabilitation and final recovery. Thus, this could be the focus for targeted treatments. Monticone et al. [29] performed a randomized controlled trial on 110 patients followed up for 6 months and found that a home-based programme using functional exercises for the management of kinesiophobia was effective in improving disability and quality of life after TKA. This kind of maladaptive cognition may be effectively managed, and the consequent pain perception and activity avoidance could be positively influenced as well [35].

These findings are of clinical relevance because they show the impact of kinesiophobia, and suggest the possibility of adopting co-interventions: conventional biomedical treatments and cognitive-behavioural treatment may synergically contribute at improving symptoms, having overcome the fear of physical activity, and in the end might also improve patient recovery and final outcome after TKA. The next steps in this research line should involve studies on the potential analgesic effects of kinesiophobia- and depression-reducing interventions such as cognitive-behavioural therapy [32] at different time points before or after TKA [12]. Such psychological interventions should be considered and targeted for individuals scheduled for surgery, to identify patients at risk and overcome dangerous barriers to full recovery after TKA.

Conclusions

Kinesiophobia is a factor influencing the outcome after TKA, independently from other psychological and physical variables. This risk factor may affect TKA results, especially in women, and might have a further synergic interaction with depression in terms of lower surgical outcome. Screening for individuals at risk of pain-related fear of movements should be performed for a proper preoperative assessment of problematic outcomes, as well as for targeting interventions to prevent the onset of chronic pain and disability and improve the results of patients at risk undergoing TKA.