Quantification of Triple Single-Leg Hop Test Kinematic Parameters using Inertial Sensors: A Validated Method for Functional Assessments after Knee Injury

  • Author / Creator
    Ahmadian, Niloufar
  • Severe knee injuries such as anterior cruciate ligament and meniscus tears, can have a serious effect on the lives of young athletes. Consequences may include an inability to return to previous levels of activity, an increased risk of re-injury or contralateral injury upon return to sport (RTS), and early-onset osteoarthritis. Horizontal hop tests are commonly used to monitor functional performance after a youth sport-related knee injury and assess it prior to RTS. Traditionally, the symmetry of total distance hopped, or time to hop a set distance, between injured and uninjured limbs is expressed as a limb symmetry index (LSI). However, clinical decisions based upon LSIs may be misleading, as kinematic and kinetic deficiencies of lower limbs may exist independent of symmetrical hop performance.
    Despite providing robust data about kinematic features of movement, motion-capture systems used for research-based purposes are not compatible with typical clinical environments given that they are expensive, and require specialized operators and lengthy data post-processing. Therefore, an alternative measurement system that can reveal robust in-depth kinematic details of functional tests, including hopping tests, is required in clinical research settings.
    This research aimed to: (1) develop a methodology for kinematic measurements during horizontal hop tests using a wearable system of inertial measurement units (IMUs), (2) validate the accuracy and precision of the estimated knee and ankle angles, initial and terminal contact instants, and foot forward progression along the hops against a reference motion-capture system, and (3) evaluate the applicability of this system in a clinical research environment during triple single leg hop (TSLH) test to highlight kinematic differences between injured and uninjured leg groups during hopping, with clinically relevant outcome measures.
    First, a system of 3 IMUs was applied on the dominant leg of 10 able-bodied participants while each performed two TSLH trials. Foot-ground initial contact (IC) and terminal contact (TC) instants were calculated based on kinematic features of foot and shank-mounted accelerometers and gyroscopes recordings. 3D knee and ankle angles were calculated using the strap-down integration method. Further, anterior foot trajectory during the TSLH was calculated by double integration of gravity-free foot acceleration and implementation of velocity correction techniques. The errors of these estimated quantities were calculated in comparison to the joint angles and temporospatial parameters obtained with a motion-capture system. Secondly, a system of 3 IMUs per limb was applied to 22 youth with a sport-related unilateral intra-articular knee injury and 10 uninjured youth while each performed two trials of TSLH bilaterally. All estimated kinematic parameters were compared side-to-side and between the leg groups of injured and uninjured individuals, using Wilcoxon signed-rank test and Wilcoxon rank-sum test, respectively. Additionally, Spearman’s correlation was assessed between temporospatial parameters and all subscales of Knee Injury and Osteoarthritis Outcome Score (KOOS) within the injured group. Finally, the LSIs of kinematic parameters were compared between injured and uninjured groups, using Wilcoxon rank-sum test (α=0.05).
    Overall (for all the 10 able-bodied participants, all hop phases, all anatomical planes), root-mean-square (RMS), and range of motion (ROM) error medians were below 2.3 and 3.2 degrees for knee and ankle angles, and correlation coefficient medians of IMU-based and camera-based joint angles exceeded 0.92 for both joints. IC and TC instants were estimated with median errors less than 2 ms and 11 ms, respectively, while individual hop distances and total TSLH progression were estimated with median relative errors less than 4.5% and 2.5% of camera-based recordings. During the third flying phase, knee sagittal ROM was significantly smaller (p=0.009) for the injured side of the injured group, compared to the uninjured group. Additionally, the knee ROM symmetry indices were significantly smaller (p=0.017) for the injured group compared to the uninjured group. Concurrently, injured participants demonstrated significant side-to-side differences (p=0.008) on ankle ROM, with the uninjured side showing greater ROM. Furthermore, all hop distances and the second flying time of TSLH were moderate- to strongly correlated with KOOS Symptom and Function in Daily Living scores (r>0.4).
    In conclusion, a novel method of detailed kinematic monitoring in clinical research environments was introduced for horizontal hop tests based on a wearable system of IMUs. This system has the appropriate accuracy and precision to reveal kinematic differences between hopping strategies adopted by injured limbs with acute knee injuries and uninjured limbs.

  • Subjects / Keywords
  • Graduation date
    Spring 2020
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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