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    Biomechanics

    Weak Correlation between the Normalized Symmetry Index and Other Symmetry Measures in Patients following an Anterior Cruciate Ligament Reconstruction

    (D-137) Weak Correlation between the Normalized Symmetry Index and Other Symmetry Measures in Patients following an Anterior Cruciate Ligament Reconstruction

    Friday, October 13, 2023
    9:30 AM – 10:30 AM PDT
    Location: Exhibit Hall - Row D - Poster # 137

      Presenting Author(s)

    • Jenna Qualter

      Undergraduate Research Assistant
      Virginia Polytechnic Institute and State University
      Sagamore Beach, Massachusetts, United States

      • Co-Author(s)

    • GB

      Garret Burks, PhD

      Postdoctoral Scholar
      Virginia Polytechnic Institute and State University, United States

      • Primary Investigator(s)

    • Robin Queen

      Professor
      Virginia Polytechnic Institute and State University, United States

    Introduction::

    Limb asymmetry is commonly used in the assessment of patients with an anterior cruciate ligament reconstruction (ACLR) to identify performance deficits between limbs and assist in return-to-activity decisions.2,4  Asymmetry can be evaluated by symmetry indices such as the Normalized Symmetry Index (NSI)1, Limb Symmetry Index (LSI)2,4,  Absolute Symmetry Index (ASI)5, and the Symmetry  Index (SI)6. The current standard for evaluating symmetry is ambiguous and appears to underestimate performance deficits.3,7 The NSI was recently developed as a universal index and compared with other symmetry metrics, however, no determination of the relationships between these measures was made. This study aims to determine the correlation between the NSI and other symmetry measures. Based on the differences between the conventional symmetry formulas, we hypothesize that the NSI will not be highly correlated with any other symmetry metric.



    Materials and Methods::

    To determine the correlations, symmetry measures for each index were calculated using data collected from 22 young adult athletes following an ACLR and 22 control participants with no known injury during a stop-jump task. A 10-camera marker-based motion capture system was used to collect kinematic data at 120 Hz (Qualisys, Goteborg, Sweden). Ground reaction force data was collected using embedded force plates at 2400 Hz (AMTI, Watertown, MA). The absolute value of the NSI was compared to the corresponding values of the LSI, ASI, and SI for peak vertical ground reaction force (vGRF), peak knee extension moment (KEM), and frontal plane knee range of motion (KROM) using a Pearson correlation coefficient. A statistical analysis was completed with MATLAB (MathWorks, Natick, Massachusetts) at an alpha level of 0.05.   



    Results, Conclusions, and Discussions:: The results of this study demonstrate that the absolute value of the NSI is only weakly correlated with the LSI, ASI, or SI (Table 1, Figure 1). The NSI showed a weak correlation to the LSI, ASI, and SI for frontal plane KROM.  A moderate correlation was found across all metrics for peak vGRF and peak KEM with peak KEM demonstrating the highest correlation. 

    This study examines the correlation between the NSI and other standard symmetry measures in patients following an ACLR and healthy controls across multiple dependent variables. The study results highlight the need for a robust measure of symmetry like the NSI that can be used across various types of data. Further, the results reveal that the NSI is only weakly correlated with other symmetry indices when evaluated on multiple data types. Thus, the reported values of the NSI cannot be directly compared to symmetry values reported in literature. The weak correlations between the NSI and other standard symmetry indices in patients following an ACLR demonstrates the need for further guidelines regarding the use of symmetry indices and associated symmetry thresholds that inform clinical decision-making. For example, the threshold for symmetry used for the NSI must be defined differently than the standard 10% symmetry difference based on normative data from hop distance that is historically used for other metrics3. To effectively use the NSI in clinical decision-making processes, the metric must be utilized to assess symmetry, and appropriate symmetry standards must be developed. Better standards of functional symmetry must be defined for all metrics to confidently compare reported symmetry values. Defining a standard for healthy levels of symmetry specific to each dependent variable is an important step in establishing better rehabilitation objectives and return-to-activity requirements for the clinical assessment of patients recovering from an ACLR.


    Acknowledgements (Optional): :

    References (Optional): :

    1.         Queen R, Dickerson L, Ranganathan S, Schmitt D. A novel method for measuring asymmetry in kinematic and kinetic variables: The normalized symmetry index. Journal of Biomechanics. 2020/01/23/2020;99:109-531.


    2.         Zwolski C, Scmitt L, Thomas S, Hewett T, Paterno M. The Utility of Limb Symmetry Indices in Return-To-Sport Assessment in Patients With Bilateral Anterior Cruciate Ligament Reconstruction. The American Journal of Sports Medicine. 2016; 44(8): 2030-2037.


    3.         Barber-Westin S, Noyes F. Factors Used to Determine Return to Unrestricted Sports Activities After Anterior Cruciate Ligament Reconstruction. Arthroscopy: The Journal of Arthroscopic and Related Surgery. 12/2011;27(12)1697-1705.


    4.         Gokeler A, Welling W, Benjaminse A, Lemmink K, Seil R, Zaffagnini S. A critical analysis of limb symmetry indices of hop tests in athletes after anterior cruciate ligament reconstruction: A case control study. Orthopaedics and Taumatology: Surgery & Research. 10/2027;103(6):947-951.


    5.         Herzog W, Nigg BM, Read LJ, et al. Asymmetries in ground reaction force patterns in normal human gait. Med Sci Sports Exerc 1989; 21: 110–114.


    6.         R.O. Robinson, W. Herzog, B.M. Nigg. Use of force platform variables to quantify the effects of chiropractic manipulation on gait symmetry. J. Manip. Physiol. Ther., 10 (1987), pp. 172-176.


    7.         Wellsandt E, Failla M, Snyder-Mackler L. Limb Symmetry Indexes Can Overestimate Knee Function After Anterior Cruciate Ligament Injury. Journal of Orthopedic & Sports Physical Therapy. 04/30/2017;47(5)334-338.