1 INTRODUCTION

The current management of young, active patients after anterior cruciate ligament reconstruction (ACLR) is failing as wide variation in outcomes persist in this population. The incidence of second ACL injury after ACLR and return to sport (RTS) is as high as 25%–33% in these young patients.1-3 Conversely, the ability to return to pre-injury level of activity following ACLR may be as low as 65% with only 55% able to return to competitive levels of sports.4 Collectively, these data indicate that reliable, successful outcomes are not consistently achieved in this population.

One factor that contributes to variation in outcome is a lack of consistent, standardized, evidence-based criteria to evaluate readiness for an athlete to safely RTS after ACLR. In 2011, Barber–Westin and Noyes highlighted the inconsistent use of standard measures in a systematic review that reported only 35% of current published articles described the use of objective criteria, 32% only used the time from surgery and 40% failed to provide any criteria to determine readiness to return to unrestricted sports participation.5 More recently, Burgi et al.6 reported in a scoping review that 85% of studies used the time from surgery as an RTS criteria and 42% used time as the only criteria to determine readiness to return athletes to sport. When objective criteria are used, a focus remains on impairment level assessments, such as lower extremity strength and performance on functional hop testing.7-9 More recent data from Toole et al.10 and Welling et al.11 highlighted in current practice, as few as 11%–14% of young patients met current, impairment-based RTS criteria at 6–9 months post-ACLR, indicating inconsistent achievement of current discharge criteria before returning to the high-level sport in this population. Furthermore, there is some question if the current RTS criteria are sufficient to appropriately identify readiness to safely return to sport.7, 12

Beyond impairment-based factors, patient-level contextual factors have been identified as an important domain to consider before RTS after ACLR. Fear of reinjury,13-18 psychological readiness to return to sport,7, 19, 20 and patient confidence17 have all been investigated in patients after ACLR and before RTS. Specifically, confidence has been reported to be higher in patients who successfully return to sport after ACLR compared with those who fail to RTS.7, 21 While associations between these contextual measures, impairment-level deficits and ability to return to activity have been reported, the association of patient-level contextual factors with the ability to meet current RTS criteria and rates of second ACL injury have yet to be determined.

The purpose of this analysis was to identify the associations among knee-related confidence, ability to meet current RTS criteria, and future risk of second ACL injury. The tested hypothesis was two-fold: (1) participants with high knee-related confidence at the time of medical clearance for sports participation after ACLR would have a greater likelihood of meeting all RTS criteria and; (2) these participants would also present with a higher likelihood of second ACL injury after RTS.

2 METHODS 2.1 Participants

This analysis was a subset of a large, prospective, longitudinal, observational cohort study (level of evidence: 2) that recruited participants from local orthopedic practices, physical therapy clinics, and the sports medicine community. One hundred and fifty-nine participants (112 females and 47 males) with a mean age of 17.2 ± 2.6 years old, were included in this analysis. The participants were (1) between 13 and 27 years old, (2) underwent primary ACLR (3) participated in rehabilitation and were released to return to pivoting/cutting sport by their physician and rehabilitation specialist, and (4) intended to return to a Level I/II22 pivoting and cutting sport after completion of rehabilitation. Rehabilitation progression and the decision for clearance to sports participation were not controlled by this study. Exclusion criteria included failure to attempt to RTS, a history of low back or lower extremity injury or surgery (beyond ACL injury) that required the care of a physician in the past year, a concomitant ligament injury (beyond Grade I medial collateral ligament injury) in the involved limb, or skeletally immaturity as defined by an ACLR procedure that was modified due to open epiphyseal plates in the tibia or femur. All participants, and guardians when required, provided written consent and assent approved by the Institutional Review Board of Cincinnati Children's Hospital Medical Center. At the time of medical clearance for sports participation (return to sport, RTS), participants were enrolled in the prospective study, completed a RTS testing session, and were tracked for the occurrence of second ACL injury for the subsequent 2 years.

2.2 RTS testing session

Within 4 weeks of medical clearance for sports participation (8.4 ± 2.6 months after ACLR), each subject participated in a RTS assessment. The assessment included standard measures most commonly used to assess readiness to RTS by clinicians, inclusive of patient-reported function, lower extremity strength, and functional hop testing.

2.2.1 Patient-reported outcome measures

Each patient completed the quality of life subscale of the Knee injury and Osteoarthritis Outcome Score (KOOS-QOL) subscales. Each item is scored from 0 to 4 and the subscale is scored on a 0–100 score, with 100 indicating no limitations in knee-related function. Two confidence groups were created based on responses to the KOOS Quality of Life subscale Question 3 (QOL3), which asked “How much are you troubled with lack of confidence in your knee?” All participants who responded “never” (QOL3 = 0) were classified as having knee-related confidence (Confident group) and all participants who responded “mildly,” “moderately,” “severely,” or “extremely” (QOL3 ≥ 1) were classified as lacking knee-related confidence (Lacking Confidence group).

The second patient-reported outcome measure was the International Knee Documentation Committee subjective knee form (IKDC).23 The IKDC is both reliable and valid in patients after ACL reconstruction, and it has been validated in a population of young athletes.23, 24 The IKDC reports patient perspectives on knee-related symptoms, daily function, and sports activities and is commonly used with patients following ACLR. The IKDC score is placed on a 0–100 scale with 100 representing a perfect score of a patient with a high knee.25

2.2.2 Strength assessment

Quadriceps strength was evaluated on each participant using a maximum voluntary isometric contraction (MVIC) on an isokinetic dynamometer (Biodex Medical Systems) using previously described methods.26 Participants were stabilized using static straps, in a seated position with 90° of hip flexion, and 60° of knee flexion with the knee joint center aligned with the dynamometer axis of rotation. Following a practice trial, participants executed three maximum effort knee extension trials for 5 seconds with a 15 seconds rest between trials. Peak torque of the three trials was recorded and the average was used to calculate limb symmetry index (LSI: involved limb peak torque/uninvolved limb peak torque × 100%) with a score of less than 100% indicating weakness on the involved limb.

2.2.3 Functional hop testing

Each participant completed four single-leg hop tests27 as a means to assess physical performance in a closed kinetic chain. These hop tests are commonly used clinically as an RTS measure following ACLR,9 in part due to their ease in administration and low resource demand. The single-leg hop tests were administered sequentially, beginning with the single hop for distance and followed by the triple hop for distance, the triple cross over hop for distance, and then the 6-m timed hop. Each participant completed one practice trial on each limb and then executed two trials on each limb (randomized order) for the test. The average of the two test trials was calculated and used for data analysis. In addition, limb symmetry index (LSI) for distance hop tests was calculated by dividing involved limb performance by uninvolved limb performance and multiplying by 100%. As the timed hop test is the only test where a lower score represented better performance, LSI was calculated by dividing uninvolved limb performance by involved limb performance and multiplying by 100%. Collectively, an LSI of less than 100% indicated worse performance in the involved limb.

2.3 Injury tracking

Each participant reported intent to RTS at the time of medical release to RTS and RTS testing. From this point, each participant was tracked for 24 months following the RTS testing to determine incidence of a second ACL injury to either the ipsilateral or contralateral limb and level of sports participation. Tracking was executed through communication during regularly attended longitudinal follow-up assessments of the parent study, in addition to phone or email contact every 2–4 weeks over the 24-month period to assess the incidence of second ACL injury. Within the 24-month observation period after RTS, 35 patients suffered a second ACL injury.

2.4 Statistical analysis

Mean, standard deviations, and frequencies were calculated to describe the study sample's characteristics. Unpaired t-tests were used for all between-group comparisons of demographic data and performance on RTS measures. The χ2 test analyses were initially used to compare the percent differences for meeting RTS measures and suffering a second ACL injury between the Confident and Lacking Confidence groups at the time of RTS. To test the primary hypothesis of the study, successfully passing each RTS measure was defined, a priori, as more than or equal to 90% LSI on strength and functional performance test assessments and a score of more than or equal to 90 on the IKDC. Participants were classified as pass RTS criteria (scored 90 or above on all six RTS tests) or fail RTS criteria (scored below 90 on any of the RTS tests). A cut-off value of 90 was selected as recent evidence has suggested a minimum of 90% LSI and 90/100 on IKDC is recommended for RTS criteria.28-30 Crude odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to determine the likelihood of Confident participants also successfully passing RTS criteria. To test the second hypothesis, χ2 test analyses were used to compare the percent differences of those sustaining a second ACL injury between the Confident and Lacking Confidence groups. Crude ORs and 95% CIs were calculated to determine the likelihood of Confident participants meeting current RTS criteria or suffering a second ACL injury in the 24 months after RTS after ACLR.

3 RESULTS

At the time of RTS, the average age of the 159 participants was 17.2 ± 2.6 years old. Demographic data are displayed in Table 1. At the time of medical release to sports participation, 60 (37.7%) participants were classified as Confident. The remaining 99 (62.2%) participants were classified as Lacking Confidence. The Confident group was slightly younger than the Lacking Confidence group; however, there were no other demographic or time to RTS differences between groups (Table 1). With respect to the ability to RTS, all study participants reported a plan to return to pre-injury level of participation as measured by the Tegner Activity scale. At the time of RTS testing, there was no difference in the proportion of patients in the Confident group that initially returned to an equal or higher level of activity (52/60; 86.7%) compared with the Lacking Confidence group (80/99; 80.2%) (p = 0.34). Similarly, there was no difference in the age of the patients who returned to an equal or greater pre-injury level of activity (17.1 ± 2.3 years) compared to those who decreased their activity level at the time of RTS. (18.0 ± 3.4 years) (p = 0.07).

Table 1. Demographic data between the confident and lacking confidence groups Total (n = 159) Confident (n = 60) Lacking confidence (n = 99) p value Age (in years) 17.2 (2.6) 16.7 (2.0) 17.6 (2.8) 0.03 Height (in cm) 168. 9 (9.3) 169.4 (9.6) 168.5 (9.2) 0.55 Weight (in kg) 68. 9 (14.4) 68.5 (13.1) 69.2 (15.2) 0.79 Time from Surgery to RTS Testing (in months) 8. 4 (2.6) 8.4 (2.4) 8.4 (2.7) 0.94 Note: All values represent mean (± standard deviation). Abbreviation: RTS, return to sport.

Comparison of performance at the time of RTS between the Confidence groups demonstrated that those in the Confident group presented with superior functional, strength, and patient-reported performance on all RTS measures (p < 0.05) (Table 2). Within the entire cohort, 42 (26.4%) of the participants passed all RTS criteria and 117 (73.6%) participants failed to meet at least one of the RTS criteria. The group that successfully passed all RTS criteria was significantly younger (p = 0. 005) than the fail group, but there were no differences in height, weight, or time from surgery to RTS testing.

Table 2. Raw data comparing RTS performance between confident and lacking confidence groups Total (n = 159) Confident (n = 60) Lacking confidence (n = 99) p value Hop testing (LSI in %) Single leg hop 947 (6. 2) 96.0 (5.7) 93.9 (6.3) 0. 047 Triple hop 95.4 (6. 6) 96.7 (6.1) 94.5 (6.8) 0. 047 Triple crossover hop 95.1 (8. 1) 97.2 (7.2) 93.7 (8.4) 0. 010 Times hop 97.1 (7. 3) 99.0 (6.9) 95.9 (7.4) 0. 011 Quadriceps strength (LSI in %) Isometric QI at 60° knee flexion 89.0 (16.4) 93.6 (14. 7) 86. 2 (16. 7) 0. 005 Patient-reported outcomes (0–100) IKDC (0–100) 88.8 (10.2) 94.4 (5.8) 85.3 (10.7) <0. 001 KOOS-Pain 92.6 (8.4) 97.2 (3.8) 89.8 (9.2) <0. 001 KOOS-Symptoms 85.5 (13.4) 92.9 (7.3) 81.0 (14.3) <0. 001 KOOS-ADL 97.3 (5.4) 99.0 (2.7) 96.3 (6.4) 0. 002 KOOS-Sport 85.5 (13.7) 92.6 (8.4) 81.2 (14.5) <0. 001 KOOS-QOL 72.1 (18.7) 87.8 (13.4) 62.6 (14.6) <0. 001 Note: All values represent mean (± standard deviation). Abbreviations: ADL, activities of daily living; IKDC, International knee documentation committee subjective rating form; KOOS, Knee Osteoarthritis Outcome Survey; LSI, Limb symmetry index; QI, Quad Index; QOL, quality of life.

In the 24 months following RTS, 35 participants (22.0%) sustained a second ACL injury, including 27 female patients and 8 male patients. Sixteen (10.0%) sustained an ipsilateral graft rupture and 19 (11.9%) sustained a contralateral ACL injury. The participants who sustained a second ACL injury were significantly younger than those that did not suffer a second ACL injury (p = 0.003) but had similar height (p = 0.51), weight (p = 0.23), and time from surgery to RTS testing (p = 0.94). (Table 3).

Table 3. Demographic data Total (n = 159) Second ACL Injury (n = 35) No second ACL injury (n = 124) p value Pass RTS criteria (n = 42) Fail RTS criteria (n = 117) p value Age (in years) 17.2 (2.6) 16.1 (1.3) 17.5 (2.7) 0.003 16.3 (1.4) 17.6 (2.8) 0.005 Sex: Female (%) 112 (70.4%) 27 (77.1%) 85 (68.5%) 0.33 30 (71.4%) 82 (70.1%) 0.87 Height (in cm) 168.9 (9.3) 167.9 (10.6) 169.1 (9.0) 0.51 167.5 (8.0) 169.4 (9.8) 0.26 Weight (in kg) 68.9 (14.4) 66.3 (14.5) 69.7 (14.4) 0.23 66.4 (11.1) 69.8 (15.4) 0.18 Time from Surgery to RTS Testing (months) 8.4 (2.6) 8.5 (2.9) 8.4 (2.5) 0.94 8.5 (2.4) 8.4 (2.7) 0.79 Note: All values represent mean (±standard deviation). Abbreviations: ACL, anterior cruciate ligament; RTS, return to sport.

When examining the association between knee-related confidence and passing RTS criteria, a higher proportion of Confident participants successfully passed all RTS criteria (27/60; 45.0%) compared to only 15.2% (15/99) in the Lacking Confidence group (p = 0. 001). Figure 1 Confident participants were five times more likely to pass RTS criteria (OR = 4.59; 95% CI:2.16, 9.71) (p < 0.001). With respect to second ACL injury, a higher percentage of participants in the Confident group sustained a second ACL injury (19/60; 31.7%) compared with those in the Lacking Confidence group (16/99; 16.2%) (p = 0.02), with Confident participants being over two times more likely to suffer a second ACL injury (OR = 2.40; 95% CI:1.21, 5.20) (p = 0.02). Figure 2 When examining the smaller cohort of patients who met all 6 RTS criteria (n = 42), 40.7% (11/27) of those patients who reported “confidence” suffered a second ACL injury while only 6. 7% (1/15) of those “lacking confidence” despite achieving all six RTS criteria suffered a second ACL injury. Figure 3 Those patients who met all six RTS criteria and self-reported knee confidence were 10 times more likely to suffer a second ACL injury (OR = 9.6; 95% CI:1.1, 84.2) (p = 0.02) than those who met RTS criteria but lacked confidence. Finally, when examining the remaining 124 participants who did not suffer a second ACL injury, there was no difference in the proportion of Confident patients who maintained pre-injury level of activity (21/41; 51.2%) compared with the proportion of Confident patients in the group that failed to maintain pre-injury level of activity for 12 months post-RTS (39/83; 47.0%) (p = 0.66).

Ability to meet all six RTS criteria at medical discharge after ACLR split by self-reported confidence. ACLR, anterior cruciate ligament reconstruction; RTS, return to sport [Color figure can be viewed at wileyonlinelibrary.com] Incidence of second ACL injury after ACLR and RTS split by self-reported confidence. ACLR, anterior cruciate ligament reconstruction; RTS, return to sport [Color figure can be viewed at wileyonlinelibrary.com] Distribution of second ACL Injury by meeting RTS criteria and confidence. ACL, anterior cruciate ligament; RTS, return to sport [Color figure can be viewed at wileyonlinelibrary.com] 4 DISCUSSION

The purpose of this study was to identify the associations among knee-related confidence, the ability to meet current RTS criteria, and subsequent second ACL injury risk. Consistent with the stated hypothesis, participants with higher knee-related confidence at the time of return to sports participation after ACLR had a greater likelihood to pass RTS criteria. Confident participants in both the cohort who met all RTS criteria and the sample, at large, were more likely to sustain a second ACL injury in the first 24 months after RTS. These data indicate modifiable patient-centered contextual factors after ACLR and RTS may play a role in predicting a patient's success in returning to high-level sports participation after ACLR.

The associations between modifiable patient-centered contextual factors, such as fear, self-efficacy, and confidence and ability to RTS after ACLR are reported in the literature14, 15, 31 Specifically, patients with high self-reported fear on the Tampa Scale for Kinesiophobia (TSK-11) at the time of RTS, typically had more significant strength impairments and more frequently did not return to sporting activities15, 18 Similarly, lower pain catastrophizing and higher knee self-efficacy scores early in rehabilitation were associated with a greater likelihood to meet impairments level goals at 12 weeks post-ACLR.13 These data are consistent with the findings of this study, which also demonstrate higher limb symmetry scores with hop testing and quadriceps femoris strength and higher PRO scores in participants with self-reported Confidence compared with those Lacking Confidence. Collectively, these data demonstrate the potential relationship between self-reported contextual factors and ability to achieve impairment level goals and ability to RTS.

Fewer studies have explored the relationship between self-reported psychological factors and future ACL injury. One study reported a relationship between self-reported fear and second ACL injury. In a pilot study, Paterno et al.18 reported self-reported fear after ACLR may predict a greater risk of suffering an ipsilateral graft failure in the first 24 months after ACLR and RTS, however, no other studies have confirmed this relationship of fear of reinjury and subsequent second ACL injury after ACLR and RTS. A second contextual factor often reported in the ACLR literature is psychological readiness to RTS as measured by the ACL-return to sport index (ACL-RSI).32 The ACL-RSI is a 12 item questionnaire that is reported to assess an athlete's emotions, confidence in performance, and risk appraisal after ACLR. Analyses comparing psychological readiness to RTS based on the ACL-RSI score and abnormal kinematics and kinetics during gait,33 functional hop testing,34 and quadriceps femoris strength35 have been reported in the literature. Two studies have reported the relationship between psychological readiness to return to sport and second ACL injury after ACLR. McPherson et al.36 reported a population of younger patients (<20 years) who sustained a second ACL injury after ACLR and RTS has a significantly lower psychological readiness to return to sports scores when compared with young patients who did not suffer a second ACL injury after RTS. In a second analysis, McPherson et al.37 reported patients who went on to suffer a second ACL injury after ACLR and RTS failed to show improvement in their ACL_RSI score between surgery and 12 months post-surgery and had significantly lower change scores when compared to patients who did not go onto suffer a second ACL injury after RTS. Collectively, these studies begin to demonstrate the association between self-reported contextual factors such as fear and readiness to return to sport after ACLR and future ACL injury after RTS.

Despite the rising prevalence of reports on modifiable contextual factors following ACLR, no studies have specifically looked at the relationship of knee-related confidence and outcome after ACLR. Interestingly, these data indicated high knee-related confidence predicted an increased likelihood of meeting all six impairment and functional level RTS criteria, including strength, hop testing, and IDKC scores. Prior work has reported associations between psychological readiness to RTS and various impairment-level measures,7, 14, 15 however these data appear to be the first to examine the correlation with ability to successfully achieve all 6 RTS measures.

With respect to second ACL injury, no prior studies have reported the association between knee-related confidence and second ACL injury rates. Interestingly, these data suggest patients with high knee-related confidence are at greater risk of second ACL injury, especially if they have already met current RTS criteria. Mechanistically, the concept of a relationship between high knee-related confidence and second ACL injury may be related to the intensity of play upon RTS. Considering high confidence may identify future ACL injury risk, this factor may need to be incorporated within a dynamic evaluation of both impairment level and contextual factors before release to RTS. If athletes present with residual impairments and altered movement patterns previously identified as high-risk factors38, 39 in addition to high knee-related confidence, there would appear to be a gap between actual functional ability and perceived confidence and ability to resume pre-injury level of activity. Increased rehabilitation may be needed to address both modifiable risk factors and the disconnect between function and knee-related confidence before release to RTS in an effort to reduce second ACL injury risk. Initial work has begun to investigate the efficacy of such intervention on modifiable contextual factors, and future work will continue to be needed to refine and validate the efficacy of these treatments.7, 40

4.1 Limitations

This study is not without limitations. The current standard of care suggests criterion values of more than 90 for “passing” RTS criterion,10, 29, 30 however, recent evidence has questioned if limb symmetry values are sufficient to assess readiness to RTS.41 Future work needs to address the relationship of knee-related confidence and other contextual factors with known high-risk variables related to second ACL injury and readiness to RTS. A second limitation of the study relates to generalizability to a more heterogeneous sample. These patients, by design, represented a very high-risk sample of subjects with the potential to sustain a second ACL injury as they were young (10–25 years old) and active as they all intended to return to pivoting and cutting sports. It is unknown if these findings also apply to potentially higher risk subgroups, such as female athletes and potentially lower risk subgroups such as older or less active subjects. Future studies must critically evaluate these metrics in more diverse populations to determine the generalizability of these results. A third limitation is related to the absence of an assessment related to the frequency and intensity of play. With the knowledge that increased confidence is associated with future ACL injury risk, future work needs to objectively assess these factors to determine their relationship to future ACL injury risk. A fourth limitation may be the dichotomization of confidence based on the KOOS scale. Our choice to explore the differences between patients with no concerns with knee-related to confidence compared with patients with any level of concern with knee-related confidence may limit the ability to appreciate the effect of varying levels of confidence on the outcome. Future studies, with larger samples, should explore this question more directly. Finally, rehabilitation was not controlled in these subjects as the primary aim was to determine the relationship between the ability to meet RTS and future outcome. Future studies designed to identify optimal interventions to improve outcomes must focus on the effect of unique interventions on outcomes.

5 CONCLUSION

Young athletes after ACLR, who report high knee-related confidence at the time of RTS, are more likely to demonstrate more optimal physical function as indicated by meeting all RTS criteria; however, they are also more likely to sustain a second ACL injury within the 24 months after RTS. Current RTS measures may be insufficient to accurately identify patient risk for second ACL injury after ACLR and RTS. Future work must consider how the inclusion of psychosocial measures, such as knee-related confidence into impairment level RTS criteria may help improve outcomes for this patient population.

ACKNOWLEDGMENTS

The authors thank the staff at the Division of Sports Medicine and the Sports and Orthopaedic Team in the Division of Occupational and Physical Therapy at Cincinnati Children's Hospital Medical Center for their contribution to this study.

AUTHOR CONTRIBUTIONS

Mark Paterno made significant contributions to research design, acquisition, and analysis/interpretation of data. He also drafted the article and approved the final version. Staci Thomas made significant contributions to research design, acquisition, and analysis/interpretation of data. She also revised and approved the final version. Karen Thatcher made significant contributions to the analysis/interpretation of data. She also contributed to the draft and revisions of the approved final version. Laura Schmitt made significant contributions to research design, acquisition, and analysis/interpretation of data. She also revised and approved the final version. All authors have read and approved the final version to be published.

REFERENCES

1Paterno MV, Rauh MJ, Schmitt LC, Ford KR, Hewett TE. Incidence of second ACL injuries 2 years after primary ACL reconstruction and return to sport. Am J Sports Med. 2014; 42(7): 1567- 1573. 2Wiggins AJ, Grandhi RK, Schneider DK, Stanfield D, Webster KE, Myer GD. Risk of secondary injury in younger athletes after anterior cruciate ligament reconstruction: a systematic review and meta-analysis. Am J Sports Med. 2016; 44(7): 1861- 1876. 3Lai CCH, Feller JA, Webster KE. Fifteen-year audit of anterior cruciate ligament reconstructions in the Australian Football League from 1999 to 2013: return to play and subsequent ACL injury. Am J Sports Med. 2018; 46: 3353- 3360. 4Ardern CL, Taylor NF, Feller JA, Webster KE. Fifty-five percent return to competitive sport following anterior cruciate ligament reconstruction surgery: an updated systematic review and meta-analysis including aspects of physical functioning and contextual factors. Br J Sports Med. 2014; 48: 1543- 1552. 5Barber-Westin SD, Noyes FR. Factors used to determine return to unrestricted sports activities after anterior cruciate ligament reconstruction. Arthroscopy. 2011; 27(12): 1697- 1705. 6Burgi CR, Peters S, Ardern CL, et al. Which criteria are used to clear patients to return to sport after primary ACL reconstruction? A scoping review. Br J Sports Med. 2019; 53(18): 1154- 1161. 7Ardern CL. Anterior cruciate ligament reconstruction-not exactly a one-way ticket back to the preinjury level: a review of contextual factors affecting return to sport after surgery. Sports Health. 2015; 7(3): 224- 230. 8Ardern CL, Webster KE, Taylor NF, Feller JA. Return to sport following anterior cruciate ligament reconstruction surgery: a systematic review and meta-analysis of the state of play. Br J Sports Med. 2011; 45(7): 596- 606. 9Kvist J. Rehabilitation following anterior cruciate ligament injury: current recommendations for sports participation. Sports Med. 2004; 34(4): 269- 280. 10Toole AR, Ithurburn MP, Rauh MJ, Hewett TE, Paterno MV, Schmitt LC. Young athletes after anterior cruciate ligament reconstruction cleared for sports participation: how many actually meet recommended return-to-sport criteria cutoffs? J Orthop Sports Phys Ther. 2017: 1- 27. 11Welling W, Benjaminse A, Seil R, Lemmink K, Zaffagnini S,