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Published in final edited form as: Clin Biomech (Bristol). 2019 May 25;68:104–108. doi: 10.1016/j.clinbiomech.2019.05.031

The Association of Psychological Readiness to Return to Sport after Anterior Cruciate Ligament Reconstruction and Hip and Knee Landing Kinematics

Christopher V Nagelli 1, Kate Webster 2, Stephanie Di Stasi 3,4, Samuel C Wordeman 4, Timothy E Hewett 1,5,6,7
PMCID: PMC6708489  NIHMSID: NIHMS1531577  PMID: 31195246

Abstract

Background:

Anterior cruciate ligament tears have a negative psychological impact on athletes. Currently, it is not clear if psychological readiness to return to sport has an impact on an athlete’s landing biomechanics. Thus the purpose of the study is to investigate whether there is an association of psychological readiness to return to sport and single-leg landing biomechanics.

Methods:

Athletes with an anterior cruciate ligament reconstruction (n=18) completed the Anterior Cruciate Ligament-Return to Sport after Injury scale to measure psychological readiness to return to sport, knee strength testing, and a single-leg landing task. A multivariate linear regression model was built for the involved and uninvolved limb based on sagittal and frontal plane knee and hip range of motion. Significance was set at p<0.05.

Findings:

Knee extensor/flexor strength testing showed significant differences (p<0.05) between involved and uninvolved limbs. Nearly 40% of the variance in psychological readiness scores (p=0.025) can be accounted for by the involved limb’s frontal plane hip and knee range of motion. Knee frontal plane range of motion was the only significant factor, and the standardized coefficients indicate that greater knee frontal plane range of motion and lower hip frontal plane range of motion were associated with higher psychological readiness. No other associations were found between psychological readiness and sagittal or frontal plane sing-leg biomechanics of the involved or uninvolved limbs.

Interpretation:

Greater psychological readiness to return to sport is associated with the involved limb’s frontal plane knee and hip range of motion during a single-leg landing biomechanics.

Keywords: Anterior cruciate ligament, ACL-reconstruction, psychological impact, landing biomechanics, ACL-Return to Sport Scale

1.0. INTRODUCTION

Injury to the anterior cruciate ligament (ACL) is a devastating event in the career of an athlete. Immediately after injury, the athlete is confronted with a loss of a season in their respective sport, a long, difficult recovery ahead, and a possible reduction in performance following a return to sport (RTS). Current clinical standards of care address the ligamentous instability of the knee and residual functional and muscular impairments through ACL reconstruction (ACLR) and post-operative rehabilitation, respectively. However, this current medical paradigm does not directly address the psychological impact of the injury. The recent large cohort studies that investigated the rate of RTS of athletes with ACLR indicates that treating the localized knee injury may not be enough. A large meta-analysis of nearly 70 articles and approximately 8000 athletes found that only 65% of athletes return to the pre-injury level of sport at a mean follow-up of nearly 3.5 years despite recovering normal knee function after ACLR.(Ardern et al., 2014b) Further, nearly two-thirds of athletes do not return to preinjury level of sports participation one year after ACLR.(Ardern et al., 2013b; Ardern et al., 2010) Therefore, contextual factors other than the functional and muscular performance of knee after ACLR may be relevant and need to be addressed during recovery and rehabilitation.

The impact of psychological factors following ACL injury and ACLR has been highlighted in the literature.(Ardern et al., 2014a; Ardern et al., 2012, 2013a; Ardern et al., 2013b; Chmielewski et al., 2008; Hartigan et al., 2013; Kvist et al., 2005) Athletes who demonstrate positive psychological factors such as motivation, confidence, and a lower fear are more likely to return to sport more quickly and to their preinjury level of participation.(Ardern et al., 2013a; Lentz et al., 2012a) In contrast, for athletes who do not return to sport or to the same level of sports participation, fear of re-injury is cited as one of the most common reasons for a reduction or cessation in sports participation.(Ardern et al., 2011) These same athletes also demonstrate characteristics of elevated pain related fear of movement, quadriceps weakness, and reduced self-reported knee function.(Hartigan et al., 2013; Lentz et al., 2015) Importantly, athlete who reported fear of injury can potentially limit functional recovery, but post-operative rehabilitation can mitigate this fear over time.(Chmielewski et al., 2008) However, fear is a prominent psychological response at the time that athletes resume sports participation.(Ardern et al., 2013a) The current understanding of psychological factors is limited to its impact on recovery (Chmielewski et al., 2008; Morrey et al., 1999), self-reported function (Chmielewski et al., 2011; Hartigan et al., 2013), and return to sport rates (Ardern et al., 2014a; Ardern et al., 2014b; Ardern et al., 2013b; Kvist et al., 2005) Currently, it is not known if psychological factors are associated with landing biomechanics in athletes with ACLR.

Altered sagittal and frontal plane biomechanical and neuromuscular control at the hip and knee are persistent in athletes following ACLR.(Delahunt et al., 2012a; Delahunt et al., 2012b; Paterno et al., 2010) Prospective biomechanical-epidemiological studies have reported that lower sagittal plane kinematics and greater frontal plane kinematics at the hip and kinee during a jump-landing task off of a 31 cm tall box are associated with a greater risk of primary and secondary ACL injury.(Hewett et al., 2005; Paterno et al., 2010) In light of this evidence, contemporary rehabilitation protocols emphasize addressing movement patterns in these planes of movement in order to prepare athletes to return to sport. Specifically, athletes are trained to avoid stiff landing patterns (without knee and hip bend) and a frontal plane collapse of the knee during dynamic activities. The significant gap in literature is whether psychological readiness to RTS is associated with sagittal and frontal plane movements of the knee and hip. Exploring and understanding this association may help further develop interventions for athletes who are returning to activity after sport but struggling with confidence in their knee. Therefore, the purpose of this study was to determine the association between psychological preparedness and sagittal and frontal plane single-leg landing biomechanics following ACLR at the time that athletes return to sport. The hypothesis tested was that a higher psychological readiness to return to sport of athletes with ACLR would be associated with lower sagittal and frontal plane hip and knee joint range of motion of the involved and uninvolved limbs during a single-leg landing task.

2.0. METHODS

2.1. Study Participants

Eighteen athletes (n=18) from a larger study were included in this study. The athletes who completed strength testing, the psychological preparedness scale, and the biomechanics testing were included in this investigation. For this study, we defined an athlete as an individual who at least participates in cutting, pivoting, and jumping sports recreationally. Basic demographics and anthropometries of the cohort are provided in Table 1. Written informed consent was obtained from all athletes, and parental permission was obtained for athletes under 18 years of age prior to any study related procedures. The study was approved by the Institutional Review Board at The Ohio State University. All the athletes received a hamstring autograft during ACLR and the surgery was performed by the same three fellowship trained sports medicine surgeons within Department of Sports Medicine. The athletes were approximately 9 months (8.5±4.2 months) from ACLR at the time of testing.

Table 1:

Demographics of athletes (Mean±SD)

Subjects (males/females) Age (yrs) Height (cm) Weight (kg)
18 (9/9) 20±7.4 170±7.05 72.7±14.0
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2.2. Measurement of Knee Strength, Psychological Preparedness, and Biomechanics

Bilateral isokinetic knee extension and flexion strength testing was conducted at 60 degrees/second using a dynamometer (Biodex Medical Systems, Shirley, NY, USA) for each athlete. The athletes completed 2 sets of 5 reps on each limb of knee isokinetic strength testing. The Anterior Cruciate Ligament Return-To-Sport after Injury (ACL-RSI) scale was used to measure psychological preparedness in the athletes with ACLR cohort. The scale was created around three specific psychological responses hypothesized to be related to sport resumption, confidence in one’s ability, emotion, and risk appraisal.(Webster et al., 2008) The ACL-RSI scale was completed by all athletes independently and prior to participation in the biomechanics testing. There are a total of 12 questions on the ACL-RSI outcome survey and each question is scaled from 0-100. A score of 100 on a question indicating that the athletes is fully confident, not at all afraid, or fully relaxed; while a score of 0 indicating that the athlete is not confident at all, extremely afraid, or not at all relaxed. Therefore, the lower the score on the survey the more fearful, lack of confidence, or unprepared the athlete reported. Reliability and validity of the ACL-RSI scale were previously demonstrated and are excellent.(Webster et al., 2008) Subsequently, the athletes underwent biomechanical analysis of a single-leg landing task of both the involved and uninvolved limbs using a 12 infrared camera, three-dimensional motion analysis system (Raptor 12 cameras, Motion Analysis Corporation, Santa Rosa, CA, USA). The athletes were first outfitted with 55 retro-reflective markers in a modified Helen Hayes configuration as described previously.(Bates et al., 2017) They were then given instructions on how to complete the single-leg landing task. Prior to data collection, the athletes were asked to complete 2-3 practice trials to demonstrate their understanding and capability of task. Directly afterwards, the athletes completed 3 single-leg landing tasks on both their involved and uninvolved limbs from a 31 cm box onto two embedded force plates (Bertec 6090, Bertec Corp, Columbus, OH, USA) during which data were recorded. A trial was deemed successful if the athlete was able to drop off the box unilaterally, land on a single limb, and regain control without foot adjustment from its initial landing position. The marker position data was sampled at 240 frames per second, and ground reaction forces for each limb were collected at a rate of 1200 Hz.

2.3. Data Analysis

Sagittal and frontal plane single-leg landing kinematics were analyzed using customized software. Gaps within marker position data that were within 25 consecutive frames during the single-leg landing task were filled using a cubic spline function in Cortex (Cortex version 4.1, Motional Analysis Corporation, Santa Rosa, CA, USA). Data were exported to Visual 3D (C-motion Inc. Germantown, MD, USA) in which customized static models scaled to the athlete’s anthropometries was created. The marker position data and the ground reaction force data were low-pass filtered using a bi-directional Butterworth filter at 12Hz and 50 Hz, respectively. Hip joint center was determined using anatomical indices. Joint angles from the first 500 milliseconds after initial contact were calculated. It was operationally defined that the first 500ms is the landing phase after observing the variability of individual landing techniques (i.e. fluctuations in COM, small balance recovery during landing, etc). Initial contact (0% stance) was defined as the frame of data in which the vertical component of the ground reaction force exceeded 10 Newtons. The kinematic data was calculated in Visual 3D and Matlab (Mathworks Inc., Natick, MA, USA) using Cardan-Euler sequence for local coordinate systems and inverse dynamics, respectively.

Sagittal and frontal plane range of motion of the hip and knee were defined as the difference between minimum and the maximum angle during the first 500 milliseconds. The hip and knee joint range of motion were averaged over the 3 single-leg landings. Average peak isokinetic knee extensor and flexor strength normalized to the athlete’s mass (kg) and the average limb symmetry index (LSI=(injured limb peak knee extensor or flexion torque /uninjured limb peak knee extensor or flexion torque)*100). The ACL-RSI scales from each athlete were totaled and averaged with a highest possible score being 100. Separate linear regression models for each involved and uninvolved limbs for the sagittal and frontal planes were used to determine the association of psychological readiness to RTS and single-leg landing biomechanics. ACL-RSI scores was the dependent variable. Average hip and knee range of motion were entered into the models separately first and then together. A paired t-test was used to evaluate the difference in mean peak knee extensor and flexor torque in the injured and uninjured limb. Statistical significance was set at P<0.05.

3.0. RESULTS

Isokinetic knee extensor and flexor testing showed significant differences between injured and uninjured limbs in peak extensor (UNINV: 2.53(.58) Nm/kg; INV: 2.27(.53) Nm/kg; p=0.016; Fig. 1) and flexor (UNINV: 1.25(.25) Nm/kg; INV: 1.13(.25) Nm/kg; p=0.010; Fig. 2) torque. The average LSI for the cohort was 91.2(20.0).

Fig. 1:

Fig. 1:

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Differences in peak knee extension torque between the uninvolved and involved limbs of the ACLR cohort. *Denotes a significant difference.

Fig. 2:

Fig. 2:

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Differences in peak knee flexion torque between the uninvolved and involved limbs of the ACLR cohort. *Denotes a significant difference.

The average ACL_RSI score for the athletes with ACLR was 66.7(22.5). The involved limb’s average sagittal range of motion for the hip and knee are 50.0°(9.6°) and 26.4°(9.2°), respectively. The involved limb’s average frontal plane knee and hip range of motion are 16.4°(6.4°) and 6.4°(2.6°), respectively (Fig. 3). The uninvolved limb’s average sagittal plane knee and hip joint range of motion are 52.1°(10.4°) and 28.0°(8.6°), respectively (Fig. 4). The uninvolved limb’s average frontal plane knee and hip joint range of motion are 6.8°(2.8°) and 16.6°(5.0°), respectively (Fig. 4). The involved and uninvolved limb’s regression model which included the respective limb’s sagittal plane knee and hip range of motion accounted for only 14% (p=0.318) and 15% (p=0.286) of the variance in ACL-RSI scores and no significant factors (Table 2). The involved limb’s regression model which included frontal plane knee and hip range of motion accounted for nearly 40% of the variance in ACL-RSI scores (p=0.025) in the regression model (Table 3). Frontal plane knee range of motion was the only significant factor, and the standardized coefficients indicate that greater frontal plane knee range of motion was associated with higher ACL-RSI scores. The uninvolved limb’s regression model accounted for only 8% of the variance in ACL-RSI scores (p=0.509). In addition, there were no significant factors with the uninvolved limb’s regression model (Table 3).

Fig. 3:

Fig. 3:

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A scatter plot of Involved Limb Joint Range of Motion s vs ACL-RSI Scores.

Fig. 4:

Fig. 4:

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A scatter plot of Uninvolved Limb Joint Range of Motion s vs. ACL-RSI Scores

Table 2:

Results of Linear Regression Analysis to Understand Association of ACL-RSI scores and Sagittal Plane Knee Range of Motion

Independent Variable Standardized Coefficients P-value R2 P-value of Model
Involved Limb 0.142 0.318
Knee Sagittal Plane Range of Motion (degrees) 0.522 0.146
Hip Sagittal Plane Range of Motion (degrees) −0.456 0.201
Uninvolved Limb 0.154 0.286
Knee Sagittal Plane Range of Motion (degrees) −0.340 0.463
Hip Frontal Plane Range of Motion (degrees) 0.637 0.178
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Table 3:

Results of Linear Regression Analysis to Understand Association of ACL-RSI scores and Frontal Plane Knee Range of Motion

Independent Variable Standardized Coefficients P-value R2 P-value of Model
Involved Limb 0.389 0.025*
Knee Frontal Plane Range of Motion (degrees) 0.802 0.007
Hip Frontal Plane Range of Motion (degrees) −0.485 0.081
Uninvolved Limb 0.0861 0.509
Knee Frontal Plane Range of Motion (degrees) −0.283 0.271
Hip Frontal Plane Range of Motion (degrees) −0.066 0.792
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4.0. DISCUSSION

The purpose of the study was to determine if there is an association of psychological readiness to return to sport and sagittal and frontal plane hip and knee joint single-leg landing mechanics. Contrary to the a priori tested hypothesis, the results of the study indicate that greater frontal plane knee range of motion was associated with psychological preparedness and more confidence to return to sport. We also found that sagittal plane range of motion at the hip and knee was not associated with psychological preparedness to return to sport. This may be attributed to the single-leg landing task which with its successful completion results in a large amount of sagittal plane movement. However, these results still have clinical implications for athletes returning back to sport following ACLR. As previously mentioned, the evidence in the literature indicates that a more positive psychological response to injury and a lower reported level of fear of re-injury is associated with a higher rate of return sport.(Ardern et al., 2013a; Lentz et al., 2012b) A recent study by Paterno and colleagues on clinical factors that predict a second ACL injury after ACLR and a return to sport found that one of the profiles for high-risk athletes includes: young athletes (less than 19 years of age), triple hop for distance greater than 1.34 times body weight, triple hop for distance limb symmetry index greater than 98.5%, female sex, and high knee-related confidence.(Paterno et al., 2017) This high-risk group of athletes was 5 times more likely to suffer a second ACL injury.(Paterno et al., 2017) Importantly, the greater psychological preparedness or confidence of the athletes with ACLR does necessarily indicate a reduction of risk for further knee injury within this group.

In addition, some recent evidence has specifically evaluated a greater fear of re-injury in this particular athlete population and its association to poor outcomes following ACLR. Trigsted and colleagues evaluated thirty-six females with a history of ACLR for a relationship between fear of re-injury and jump-landing biomechanics and muscle activation.(Trigsted et al., 2018) They found that individuals who reported higher fear of re-injury demonstrated lower peak knee, hip, and trunk flexion along with greater motion in the frontal plane during a bilateral drop vertical jump task which is a validated ACL-injury assessment tool.(Hewett et al., 2005; Trigsted et al., 2018) In a separate study, Paterno et al. investigated whether fear was related to functional performance measures and risk of second ACL injury after ACLR and return to sport.(Paterno et al., 2018) The patients in this small cohort who reported greater self-reported fear at the time of return of sport were 4 times more likely to report lower levels of activity, 7 times more likely to have a hop limb symmetry lower than 95%, and 6 times more likely to have quadriceps strength symmetry lower than 90%.(Paterno et al., 2018) The patients who went on to sustain a second ACL injury within the ipsilateral limb had reported a significantly greater fear or injury than the patients who didn’t sustain another ACL injury.(Paterno et al., 2018) The ACL-RSI scale was developed to measure the athlete’s emotion, confidence, and risk appraisal upon return to sport following ACLR. While there are questions within the scale that refer directly to the emotion of fear in these athletes, the scale as a whole encompasses a number of emotions. Interestingly, the questions that received the lowest average scores for this cohort were: (1) are you fearful of re-injuring your knee by playing your sport? (56.6(31.9)) and (2) are you afraid of accidentally injuring your knee by playing your sport? (52.7(30.2)). This demonstrates a fear of re-injury is still a prominent emotion amongst a cohort of athletes regardless of their psychological preparedness. The majority of data indicates that some form of psychological readiness to RTS or fear of movement/re-injury measurement should be incorporated into evidence-based return to sport criteria. Recent research has taken the necessary first step in intervening in this cohort of athletes by identifying factors that contribute to an athlete’s psychological readiness to RTS after ACLR.(Webster et al., 2018)

There are some limitations within the current study. The smaller sample size and single graft source may limit the generalizability of the results of this study. The present study also collected 3 data collection trials after the athletes performed practical trials to accustom them to the task. Future studies will focus on not allowing athletes any practice trials but rather an explanation of the task. This will prevent any learning effect that may be occurring after the practice trials are successfully done. In addition, peak knee extensor and flexor torques were reported because of its impact on single-leg landing tasks.(Ithurburn et al., 2015) The recovery of quadriceps and hamstring strength in the ACLR limb could influence an athlete’s confidence in dynamic tasks such as single-leg landing. We found the average LSI for this cohort to be 91.2(20.0). A healthy population with no prior knee injury typically demonstrates quadriceps and hamstrings LSI within the range of 80-100%.(Ostenberg et al., 1998) Furthermore, a unilateral landing task from a 31 cm tall box does not provide an opportunity for compensatory landing strategies by reliance on the uninjured limb. The physical demand of a single-leg task likely requires greater confidence in the injured limb. Finally, our study focused on the sagittal and frontal plane SLD biomechanics and our future investigations will also include the transverse plane.

5.0. CONCLUSION

The results from the present study indicates an association between psychological readiness to RTS and frontal plane hip and knee joint range of motion during a single-leg landing task for athletes with ACLR. Notably, a greater psychological preparedness was associated with greater frontal plane knee range of motion and lower frontal plane hip range of motion within the involved limb. This regression model explained nearly 40% of the variability in ACL-RSI scores. The same association was not found in the uninvolved limb. The results of this initial study indicate further inquiry into the association between psychological readiness to RTS and landing biomechanics. The impact of psychological readiness to return to sport should be considered when athletes are returning to activity following ACLR. Researchers and clinicians should be that either a greater or lower psychological readiness to RTS may impact how the athletes move.

Highlights:

  • Anterior cruciate ligament tears has a negative psychological impact on athletes

  • Psychological readiness to return to sport is related with hip and knee kinematics

  • Understanding the association of psychology and biomechanics will improve care

ACKNOWLEDGEMENTS

We would like to acknowledge the researchers and staff at The Ohio State University for their support with data collection. Additionally, we acknowledge support from the National Institute of Arthritis and Musculoskeletal and Skin Diseases: T32AR56950 for CVN and R01AR056259 and R01AR055563 to TEH and from the Sports Physical Therapy Section of the American Physical Therapy Association.

Footnotes

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