Elsevier

Gait & Posture

Volume 66, October 2018, Pages 83-87
Gait & Posture

Full length article
Contributors to knee loading deficits during gait in individuals following anterior cruciate ligament reconstruction

https://doi.org/10.1016/j.gaitpost.2018.08.018Get rights and content

Highlights

  • Deficits in kinematics and kinetics are present during gait 3 months post-ACLr.

  • GRF, shank angular velocity and knee flexion relate to knee extensor moment in gait.

  • Asymmetries in posterior GRF and knee flexion predict knee extensor deficits.

Abstract

Background

Altered gait mechanics following anterior cruciate ligament reconstruction (ACLr) are commonly reported in the surgical limb 2–3 months post-surgery when normalization of gait is expected clinically. Specifically, deficits in knee extensor moment during loading response of gait are found to persist long-term; however, the mechanisms by which individuals reduce sagittal plane knee loading during gait are not well understood.

Research question: This study investigated between limb asymmetries in knee flexion range of motion, shank angular velocity, and ground reaction forces to determine the strongest predictor of knee extensor moment asymmetries during gait.

Methods

Thirty individuals 108 ± 17 days post-ACLr performed walking gait at a self-selected speed and peak knee extensor moment, peak vertical and posterior ground reaction force, and peak anterior shank angular velocity were identified during loading response. Paired t-tests compared limbs; Pearson's correlations determined associations between variables in surgical and non-surgical limbs; and stepwise linear regression determined the best predictor of knee extensor moment asymmetries during gait.

Results

Reduced vertical and posterior ground reaction forces and shank angular velocity were strongly associated with reduced knee extensor moment in both limbs (r = 0.499-0.917, p < 0.005). Less knee flexion range of motion was associated with reduced knee moment in the surgical limb (r = 0.358, p < 0.05). Additionally, asymmetries in posterior ground reaction force and knee flexion range of motion predicted asymmetries in knee extensor moment (R2 = 0.473, p < 0.001).

Significance

Modulation of kinetics and kinematics contribute to decreases in knee extensor moments during gait and provide direction for targeted interventions to restore gait mechanics.

Introduction

Clinically, restoration of gait mechanics following anterior cruciate ligament reconstruction (ACLr) is expected by 2–3 months post-surgery [1,2]. However, despite concentrated efforts to normalize gait, biomechanical studies consistently report the presence of altered mechanics in the surgical limb. Decreased knee flexion range of motion (ROM) and extensor moments during loading response of gait are observed throughout rehabilitation [[3], [4], [5], [6], [7]]. Moreover, despite improvements over time, between limb asymmetries in knee extensor moment continue to exceed the minimal clinically important difference 2 years after surgery [8]. These alterations have been attributed to the progression of knee joint osteoarthritis in an already vulnerable population [9,10]. Given the repetitive nature of gait and its importance in daily activities, it is important to ameliorate these impairments in early rehabilitation post-ACLr.

While many studies have quantified deficits in knee mechanics following ACLr, the mechanisms by which individuals reduce sagittal plane knee loading is not well understood. Altered knee mechanics are commonly reported during loading response, a time at which individuals are loading the limb and transitioning to single limb stance [11]. At 3–5 months post-ACLr, deficits of up to 4 degrees in knee flexion ROM and up to 50% in knee extensor moment have been reported [4,5,12,13]. Following initial contact, during loading response, rapid knee flexion of 15 degrees and eccentric knee extensor control are required to decelerate and progress the body over the stance limb [11]. This is accomplished using heel rocker mechanics in unimpaired gait and is characterized by rapid forward progression of the shank over the heel immediately after ground contact [11]. The presence of decreased shank angular velocity in the surgical limb along with decreased knee flexion ROM suggests that individuals may alter kinematics during the heel rocker mechanism to reduce extensor loading [7,14]. This is supported in part by a recent study that found that 57.5% of the variance in knee extensor moment deficits in individuals 3 months post-ACLr were explained by shank angular velocity deficits during loading response [7].

In addition to altering joint and segment kinematics, it is conceivable that individuals modulate ground reaction forces (GRFs) to limit sagittal plane knee loading. Sagittal plane joint moment calculations are influenced by GRF magnitude in both vertical and anteroposterior directions [15]. To date, no study has evaluated vertical GRFs during gait in early rehabilitation following ACLr. However, between limb differences in vertical GRFs loading rate in individuals 4 years post-ACLr suggest that individual alter GRFs following surgery [16]. It is not known if these alterations are present during early rehabilitation or if they contribute to reduced knee extensor moments. Following initial contact, the posterior GRF helps to slow forward momentum of the body and allows the stance limb to achieve weight-bearing stability [11]. Posterior GRFs are reflective of braking forces and are resisted by the knee extensors in loading response. As no previous work has investigated anteroposterior GRFs, it is not known if individuals modulate these forces to reduce sagittal plane knee loading following ACLr. While alterations in kinematics that explain decreased sagittal plane loading of the knee are well documented, a critical understanding of how individuals modulate GRFs in early rehabilitation is lacking.

A comprehensive understanding of the mechanical factors that relate to reduce knee loading during gait in individuals following ACLr is needed to develop interventions to target these deficits. Identifying deficits early in rehabilitation and developing targeted interventions is crucial for long-term joint health. The primary purpose of this study was to investigate the mechanics associated with reduced knee extensor moments by determining the strongest predictor of knee extensor moment asymmetries during gait following ACLr from between limb asymmetries in kinematics and ground reaction forces. To do this, we determined if there were differences between limbs in these variables, as well as the relationship of these variables to knee extensor moments in each limb. It was hypothesized that between limb asymmetries in knee range of motion, vertical and posterior ground reaction force, or shank angular velocity would be predictive of between limb asymmetries in knee extensor moment.

Section snippets

Methods

Thirty individuals 108 ± 17 days post-ACLr were enrolled (Table 1). Three participants reported previous ACLr to the contralateral (n = 1) and ipsilateral knee (n = 2) of greater than 4 years. Those with a history of ACLr had returned to pre-surgical levels of physical activity prior to re-injury. Participants were included in the study if they were between the ages of 14–50, 10–20 weeks status-post ACLr, and currently participating in physical therapy. Participants were excluded if they had a

Results

All data were reported as mean (SD). On average, the surgical limb exhibited reduced knee extensor moment (-0.135(0.224) Nm/kg; p = 0.003), knee flexion ROM (-4.1(4.1) degrees; p < 0.001), posterior GRF (-0.020(0.036) BW; p = 0.005), and shank angular velocity (-16.6(30.6) degrees/second; p = 0.006) compared to the non-surgical limb (Table 2). Vertical GRF did not differ between limbs (-0.032(0.096) BW; p = 0.079).

In the surgical limb, strong positive correlations were found between knee

Discussion

These data are consistent with the literature during early rehabilitation highlighting deficits in knee extensor loading in the surgical knee during loading response of gait [4,5,7]. Self-reported knee pain during testing and IKDC scores suggest that participants were progressing typically [21]. On average, knee extensor moments were 26% smaller in the surgical compared to the non-surgical limb. Only 7 out of 30 participants exhibited knee extensor moment ratio symmetry between limbs

Conclusion

This study concurrently highlights between limb differences in sagittal plane knee loading, ROM, posterior GRF, and shank angular velocity at a time when gait is expected to be normalized post-ACLr. Reduced vertical and posterior GRFs and shank angular velocity were strongly associated with reduced knee loading in both limbs. Less knee flexion ROM was associated with reduced knee loading only in the surgical limb. Further, asymmetries in posterior GRF and knee ROM predicted asymmetries in knee

Conflicts of interest

None.

Acknowledgements

This study was approvedby the Institutional Review Board of the Health Sciences Campus of the University of Southern California. This research was supported in part by grant # K12 HD0055929 from the National Institutes of Health (NIH). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIH.

References (21)

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The authors would liketo acknowledge CATZ Physical Therapy and Sports Performance Center for their support and assistance with this study.

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