The Impact of Psychological Factors on Return to Sports after Anterior Cruciate Ligament Reconstruction: A Systematic Review

: The rehabilitation of those who have undergone anterior cruciate ligament reconstruction (ACL-R) is a complex process that involves many factors. Physical ability recovery is not the only factor in the return to sport; psychosocial factors such as anxiety, pain response, self-esteem, locus of control, and fear of re-injury also play an important role. A systematic search was conducted on the PubMed, Medline, Cochrane, CINAHL and Embase databases using the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). No randomized controlled trials (RCTs) were identiﬁed. The Methodological Index for Non-Randomized Studies (MINOR) was used to assess the quality of the identiﬁed non-RCT studies. A total of 308 studies were identiﬁed, of which 32 met the eligibility criteria. The results of these studies were obtained using the KOOS (ADL, Sport, QoL), ACL, TSK-11, K-SES, questionnaires/interviews, and other scales as instrumental approaches. This systematic review and meta-analysis revealed that psychological factors have a signiﬁcant inﬂuence on the post-anterior cruciate ligament reconstruction outcomes of athletes. Fear of re-injury and pain were the primary factors that limited return to sport, whereas self-efﬁcacy, psychological will, and age were associated with better functional outcomes and were essential for male and young patients. Clinicians should focus on both physical and psychological components to optimize rehabilitation.


Introduction
The reconstruction (ACL-R) of the anterior cruciate ligament (ACL) represents one of the most frequent procedures in sports medicine [1][2][3].Every year in Western countries, approximately 40 out of every 100,000 individuals undergo ACL-R [4].This is estimated to be 250,000 cases in Europe and the United States alone [5].ACL stabilizes the knee by preventing the tibia from sliding anteriorly in relation to the femur [6,7].The primary objectives of ACL-R are to enable a return to all pre-injury activities and to improve the health-related quality of life (HRQoL) of the patient by restoring the full biomechanics of the knee following injury [1].Despite the treatment, athletes who suffer an ACL injury do not successfully return to their pre-trauma level of activity.This is due to surgery, the psychological impact of the injury on the patient's life, and the patient's perception of the knee function [8,9].
Recent reviews have shown that only 54% of patients who have undergone ACL reconstruction are able to return to the same level of sports activity that they were participating in prior to the injury [10].Athletes who do not return to any competitive level are instead around 15% or 20% [11].
Psychological effects, such as anxiety, depression, and fear of reinjury, need to be considered along with the physical effects that are often experienced by patients' postserious sports injury [12,13].Studies have shown that the primary reason why return rates to competitive and amateur sports are low when there are no deficits or complications following ACL-R, is the fear of re-injury [14][15][16][17][18].
Fear and anxiety of a high degree can lead to a decreased adherence to the rehabilitation process [19].Having strong self-efficacy and low fear of a potential re-injury is essential for optimal rehabilitation following an ACL-R [20].Thus, a comprehensive analysis of the patient must include not only the traditional objective assessments from a medical point of view but also the psychological state of the individual.This should be the primary factor in determining the potential outcomes associated with resuming sports activities [21].The physical effects of ACL-R are described in numerous studies; however, there is not a large number of studies in the literature on the role that psychological components may have on an individual's ability to return to sport after the ACL-R intervention [11].
The aim of this systematic review was to evaluate the psychosocial factors associated with return to sport following anterior cruciate ligament reconstruction.

Materials and Methods
The preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines were employed to enhance the reporting of the review (Figure 1) [22].
psychological impact of the injury on the patient's life, and the patient's perception of the knee function [8,9].
Recent reviews have shown that only 54% of patients who have undergone ACL reconstruction are able to return to the same level of sports activity that they were participating in prior to the injury [10].Athletes who do not return to any competitive level are instead around 15% or 20% [11].
Psychological effects, such as anxiety, depression, and fear of reinjury, need to be considered along with the physical effects that are often experienced by patients' postserious sports injury [12,13].Studies have shown that the primary reason why return rates to competitive and amateur sports are low when there are no deficits or complications following ACL-R, is the fear of re-injury [14][15][16][17][18].
Fear and anxiety of a high degree can lead to a decreased adherence to the rehabilitation process [19].Having strong self-efficacy and low fear of a potential re-injury is essential for optimal rehabilitation following an ACL-R [20].Thus, a comprehensive analysis of the patient must include not only the traditional objective assessments from a medical point of view but also the psychological state of the individual.This should be the primary factor in determining the potential outcomes associated with resuming sports activities [21].The physical effects of ACL-R are described in numerous studies; however, there is not a large number of studies in the literature on the role that psychological components may have on an individual's ability to return to sport after the ACL-R intervention [11].
The aim of this systematic review was to evaluate the psychosocial factors associated with return to sport following anterior cruciate ligament reconstruction.

Materials and Methods
The preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines were employed to enhance the reporting of the review (Figure 1

Eligibility Criteria
The research question was formulated using a PICOS approach: Patient (P); Intervention (I); Comparison (C); Outcomes (O) and Study design (S) [23].

Eligibility Criteria
The research question was formulated using a PICOS approach: Patient (P); Intervention (I); Comparison (C); Outcomes (O) and Study design (S) [23].
The exclusion criteria included: non-validated studies, non-human studies, and studies with a treatment group of less than 10 patients.

Search
A systematic review was conducted in November 2020.A comprehensive search of the databases PubMed, Medline, Cochrane, CINAHL, and Embase databases was conducted from the inception to November 2020 with the English language constraint.The following keywords were used isolated and combined: anterior cruciate ligament; wounds and injuries; reconstructive surgical procedures; repairability; tears; lacerations; quality of life; fear; adaptation; psychological; self-efficacy; psychology; anxiety.All the keywords were searched isolated and combined with their MeSH terms.More studies were searched among the reference lists of the selected papers.

Study Selection and Data Collection
Two authors (FD and MB) initially conducted a search for the article using a previously described search strategy.All abstracts were read, after which the full article was reviewed if, after discussion between the two independent reviewers, it could not be unequivocally excluded based on the title and abstract.The full text of all papers not excluded based on abstract or title was evaluated.The number of articles excluded or included was registered and reported in a PRISMA flowchart (Figure 1) following the rules by Liberati et al. [24].

Quality Assessment
The Methodological Index for Non-Randomized Studies (MINORS) was used for quality assessment [25].This score consists of 12 items: clearly stated aim; inclusion of consecutive patients; prospective data collection; endpoints appropriate to study aim; unbiased assessment of study endpoint; follow-up period appropriate to study aim; <5% lost to follow up; prospective calculation of study size; adequate control group; contemporary groups; baseline equivalence of groups and adequate statistical analyzes.The reviewers individually evaluated these items.The MINORS items were scored 0 if not reported, 1 when reported but inadequate, and 2 when reported and adequate.The ideal global score was 20 for NRCTs.The simplicity of MINORS comprising only 12 items makes this item readily usable by both readers and researchers.The reliability of this score has already been demonstrated [25].Two reviewers independently evaluated (FD/MB) the potential risk of bias in the studies using the MINORS.

Data Synthesis and Analysis
Data were extracted and organized using Microsoft Excel.Relevant study characteristics extracted included study, year, design, location, aim, sport and sport participation level, sample age and size, instrument(s) or approach(s), social and/or contextual factor, and study result.Considering the heterogeneity of the included studies, only seven articles (Ardern et 2016)) [16,[26][27][28][29][30] were included in the meta-analysis.The calculation of the overall mean from studies (or cohorts) reporting a single mean using the inverse variance method for pooling was performed for the Knee Injury and Osteoarthritis Outcome Score (KOOS), which is divided into KOOS Sport and KOOS Quality of Life (QoL), Tampa Scale of Kinesiofobia-11 (TSK-11), Knee-Self Efficacy Scale (K-SES), and Anterior Cruciate Ligament Quality of Life (ACL QoL) scores.The K-SES is a self-administered questionnaire and consists of two subscales: knee self-efficacy present (present), consisting of 18 items, and knee self-efficacy future (future), consisting of 4 items.Patients rate each item on an 11-point Likert scale, ranging from 0 = not at all certain to 10 = very certain.The ACL-QOL score is a disease-specific patient-reported outcome measure that assesses patients with ACL-deficient and reconstructed knees.The ACL-QOL has demonstrated validity, responsiveness, and reliability.
The inverse variance weighting was used for pooling.To assess the heterogeneity between the studies, the I 2 statistic was used.Since the I 2 statistic was >50% [31], the random effect model was used.Meta-regression was performed to evaluate the correlation between the return to sport (KOOS Sport score) and psychological factors (KOOS QoL, TSK-11, K-SES, and ACL QoL scores).In all studies, p < 0.05 was considered statistically significant.All statistical analyses were performed using R software version i368 3.6.1.

Study Selection
According to the PRISMA protocol, a flow-chart diagram showing the selection process of the studies was reported (Figure 1).A total of 306 studies were found, to which articles identified through other sources (N = 2) were added, for a total of 308 selected articles.From these 308 studies, articles that were not in the English language (N = 4) and articles published before 2000 (N = 8) were excluded.From the total of 296, studies were excluded through the title, abstract, and the complete reading of the article, because they were not considered relevant to our objective (N = 245).Validated studies (N = 9) and non-human articles (N = 2) were not included.In addition, studies with <10 patients per treatment group were also excluded (N = 6).From the total of 45 final studies, those unavailable due to the absence of material were eliminated (N = 10).Finally, articles that did not have functional and psychological outcomes were excluded (N = 2).After this trial, 32 articles were eligible for this study.The research question was formulated using a PICOS approach (Table 1).
The level of sporting participation of the patients present in the review includes both amateur and elite sports (Table 3).The gender, the timing of surgery following injury, and the level of sport the athletes returned to may be associated with fear of re-injury following surgery.Webster et al. [33] 107 (62 men and 45 women) -2 football, netball, basketball, and soccer.
The meta-regression found a statistically significant correlation between the return to sport (KOOS Sports score) and three psychological factors (KOOS QoL, p = 0.0025; K-SES, p < 0.001; and ACL QoL, p < 0.001).As the KOOS Sports score increased, the value of the psychological scores increased (Figures 7-9).The meta-regression found a statistically significant correlation between the return to sport (KOOS Sports score) and three psychological factors (KOOS QoL, p = 0.0025; K-SES, p < 0.001; and ACL QoL, p < 0.001).As the KOOS Sports score increased, the value of the psychological scores increased (Figures 7-9).[26,27,41].
The meta-regression found a statistically significant correlation between the return to sport (KOOS Sports score) and three psychological factors (KOOS QoL, p = 0.0025; K-SES, p < 0.001; and ACL QoL, p < 0.001).As the KOOS Sports score increased, the value of the psychological scores increased (Figures 7-9).No statistically significant correlation between KOOS Sport and TSK-11 score was found (p = 0.7274).

Discussion
The cruciate ligament rupture represents one of the most common injuries in the athlete's population.The stability of the knee can only be effectively recovered following ACL-R reconstruction surgery [43] with the primary aim being to return to their pre-injury daily and sporting activities [6].
Engaging in physical activity on a regular basis has been associated with an enhanced quality of life, a reduction in depressive symptoms, and a decrease in obesity rates [46].Nonetheless, physical and psychological preparation to return to sport does not always coincide [51].Psychological factors have become increasingly recognized as important parameters for determining an athlete's ability to return to sports after surgery.In the study conducted by M. Xiao et al., psychological parameters were recorded using the ACL-Return to Sports Injury scale, Knee Self-Efficacy Scale (K-SES), and Tampa Scale of Kinesiophobia (TSK/TSK-11).[52] Another study by L. N. Erickson et al., to determine whether psychological readiness for sport and knee self-efficacy assessed early (3 months) after anterior cruciate ligament reconstruction is predictive of self-reported functional results, quadriceps strength, and knee mechanics during running upon return to sports training (6 months), used these two scores: ACL-RSI and K-SES [53].
In the last 25 years, subjective scales have been developed to assess the psychological aspect of an athlete's decision to return to physical activity and training [32,54].The ACL-RSI is considered to be highly correlated with the level of participation in physical activities prior to ACL reconstruction, due to its ability to evaluate the psychological readiness for returning to sports and leisure activities [27,38,47].
Existing studies have demonstrated that age constitutes a key factor for the early return to sport [41,55].Several studies have indeed shown that, compared to adults, teenagers have a stronger psychological profile, with greater awareness of their self-efficacy and greater motivation to achieve their goals [39,54,56].The organization of daily life, workrelated duties, family commitments, and the general lifestyle are only a few of the reasons explaining why adults are less likely to return to pre-injury sports [10, 15,32,43].Female patients reported worse KOOS than male patients, reporting that also gender could represent a co-leading factor [41,57].
In a meta-analysis of 2011 [15]., Ardern's reported that of 5770 participants (with a mean follow-up of 41.5 months), 82% had returned to some type of sports participation, 63% returned to their pre-injury level of participation, and 44% returned to competitive sports at the final follow-up.Moreover, Ardern and colleagues showed that psychological No statistically significant correlation between KOOS Sport and TSK-11 score was found (p = 0.7274).

Discussion
The cruciate ligament rupture represents one of the most common injuries in the athlete's population.The stability of the knee can only be effectively recovered following ACL-R reconstruction surgery [43] with the primary aim being to return to their pre-injury daily and sporting activities [6].
Engaging in physical activity on a regular basis has been associated with an enhanced quality of life, a reduction in depressive symptoms, and a decrease in obesity rates [46].Nonetheless, physical and psychological preparation to return to sport does not always coincide [51].Psychological factors have become increasingly recognized as important parameters for determining an athlete's ability to return to sports after surgery.In the study conducted by M. Xiao et al., psychological parameters were recorded using the ACL-Return to Sports Injury scale, Knee Self-Efficacy Scale (K-SES), and Tampa Scale of Kinesiophobia (TSK/TSK-11).[52] Another study by L. N. Erickson et al., to determine whether psychological readiness for sport and knee self-efficacy assessed early (3 months) after anterior cruciate ligament reconstruction is predictive of self-reported functional results, quadriceps strength, and knee mechanics during running upon return to sports training (6 months), used these two scores: ACL-RSI and K-SES [53].
In the last 25 years, subjective scales have been developed to assess the psychological aspect of an athlete's decision to return to physical activity and training [32,54].The ACL-RSI is considered to be highly correlated with the level of participation in physical activities prior to ACL reconstruction, due to its ability to evaluate the psychological readiness for returning to sports and leisure activities [27,38,47].
Existing studies have demonstrated that age constitutes a key factor for the early return to sport [41,55].Several studies have indeed shown that, compared to adults, teenagers have a stronger psychological profile, with greater awareness of their self-efficacy and greater motivation to achieve their goals [39,54,56].The organization of daily life, work-related duties, family commitments, and the general lifestyle are only a few of the reasons explaining why adults are less likely to return to pre-injury sports [10, 15,32,43].Female patients reported worse KOOS than male patients, reporting that also gender could represent a co-leading factor [41,57].
In a meta-analysis of 2011 [15]., Ardern's reported that of 5770 participants (with a mean follow-up of 41.5 months), 82% had returned to some type of sports participation, 63% returned to their pre-injury level of participation, and 44% returned to competitive sports at the final follow-up.Moreover, Ardern and colleagues showed that psychological factors such as fear of re-injury (19%), problems with the function of the reconstructed knee (13%), and fear of losing work with re-injury (11%) were the most cited personal reasons by participants for changing or ceasing postoperative sports participation.These findings may explain the discrepancy between satisfactory physical outcomes and the rate of return to sport.In 2014, another study by Ardern et al. [27] reported that the rate of return to some types of sport and pre-injury sport level after ACL-R was 81% and 65%, respectively.Instead, the rate of return to competitive sport after ACL-R was 55%.In this study, the authors concluded that these effects were also achieved by consideration and management of psychological factors, which are among the most useful modifiable elements in favor of patients' quality of life and return to sport.An example of an intervention that can help athletes return to sport after surgery involves the use of health coaching, motivational interviewing, and cognitive-behavioral strategies to address and manage factors that could impede such return, such as fear of re-injury and pain.
In the present study, the meta-analysis considered 7 of the 32 studies included in the systematic review.The results were consistent with existing research.It was observed that as KOOS sport levels increased, there was an increase in KOOS QoL, KSES, and ACL QoL, suggesting that a return to sport participation is associated with improved postoperative psychological functioning.At the same time, in fact, a reduction in KOOS QoL is accompanied by a decrease in KOOS sport, ACL QoL, and KSES.According to the results of the present study, it seems that the parameters of physical and psychological health are closely linked and influenced by each other.
A holistic rehabilitation experience with a robust psychological support system is an effective way to facilitate a successful return to sports.Participants in these studies have indicated that providing support throughout the recovery period can have a positive effect on confidence [34].Support to ACL patients should also come from teammates, coaches, and family members, but especially from medical personnel [40,50,58].
This study has some limitations.In some cases, participants who already returned to sport did not see the need to attend follow-up appointments, thinking that their progress was already satisfactory.On the other hand, patients who felt dissatisfied with their results preferred not to show up for follow-up [15,27,59].
Return to sport after ACL-R surgery is considered a key indicator of success.However, it is not possible to determine exactly whether patients with improved function are able to participate in sports activities or whether it is sports participation that leads to increased function [29,58,60].
The results of the reviewed studies indicate that to maximize the athlete's chances of regaining pre-injury performance levels, both their physical and psychological conditions should be addressed during rehabilitation [40,61,62].
Thus, to meet the desired therapeutic objectives, it is essential to identify and address any psychological and social impediments that may impede the patient's rehabilitation progress and that may affect the patient's decision to return to the same level of physical activity [47,63].

Conclusions
This systematic review and meta-analysis investigated the impact of psychological factors on patients' post-anterior cruciate ligament reconstruction.Indeed, our meta-analysis results support the notion that psychological and environmental influence patients' ability to resume sports activities following surgical ACL reconstruction (a positive correlation between KOOS sport and KOOS QoL, KSES, and ACL QoL was observed).
Hence, to support athletes' resumption of sport, clinicians should focus on not only the physical components but also strive to resolve all aspects of rehabilitation [48].
In order to reduce injury-related apprehension and bolster population self-efficacy in the future, research should investigate the efficacy of psychoeducation techniques [34].

Figure 8 .
Figure 8. Knee Injury and Osteoarthritis Outcome Score Quality of Life (KOOS QoL).

Figure 8 .
Figure 8. Knee Injury and Osteoarthritis Outcome Score Quality of Life (KOOS QoL).

Figure 8 .
Figure 8. Knee Injury and Osteoarthritis Outcome Score Quality of Life (KOOS QoL).

Figure 8 .
Figure 8. Knee Injury and Osteoarthritis Outcome Score Quality of Life (KOOS QoL).Figure 8. Knee Injury and Osteoarthritis Outcome Score Quality of Life (KOOS QoL).

Figure 8 .
Figure 8. Knee Injury and Osteoarthritis Outcome Score Quality of Life (KOOS QoL).Figure 8. Knee Injury and Osteoarthritis Outcome Score Quality of Life (KOOS QoL).

Table 2 .
Characteristics of the included studies.

Table 3 .
Characteristics of patients.