Quantification of pelvic soft tissue artifact in multiple static positions

doi:10.1016/j.gaitpost.2013.10.001

Gait & Posture

Volume 39, Issue 2, February 2014, Pages 712-717

https://doi.org/10.1016/j.gaitpost.2013.10.001 Get rights and content

Highlights

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This study describes soft tissue artifact at pelvis in static positions.
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ASIS markers are more susceptible to STA than PSIS markers.
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Marker displacement at ASIS was highly associated with hip flexion angle.

Abstract

Soft tissue artifact (STA) has been identified as the most critical source of error in clinical gait analysis. Multiple calibration is a technique to reduce the impact of STA on kinematic data, which involves several static calibrations through the range of motion of the joint of interest. This study investigated how skin markers at the pelvis were displaced in relation to anatomical body landmarks in multiple static calibration positions. The magnitude and direction of the pelvic marker displacement was assessed in nine different body positions including 90° and 45° hip flexion, maximum hip extension, and pelvic tilt in 20 healthy young adults. ASIS markers were found to be more susceptible to relative displacement than PSIS markers, with displacement particularly evident in positions where the hip was flexed (up to 17 mm). A strong correlation was found between the hip flexion angle and marker displacement (r² = 0.70). While the estimated impact of pelvic STA on gait kinematics was relatively small, the findings suggest that activities with large hip flexion would cause larger STA with a greater impact on pelvic kinematics. The skin surface located over the ASIS differed by a mean of 17 mm between standing and supine positions, which could affect the inter-ASIS distance and the location of hip joint center (HJC) by up to 20 mm and 10 mm, respectively.

Introduction

Gait analysis has been used in treatment decision-making or outcome assessment of pathological conditions, and the accuracy of the data is of critical interest. Soft tissue artifact (STA) refers to the movement of surface markers associated with deformation of subcutaneous tissues due to muscle contraction, skin movement and inertial effects. It has been identified as the most critical source of error within predictive models in clinical gait analysis [1].

The most commonly used biomechanical models within clinical gait analysis use the position of anatomical landmarks identified by skin-mounted markers in conjunction with geometrical equations to estimate the location of joint centers, track the motion of the underlying bone during walking, and calculate joint kinematics [2], [3]. The location of pelvic markers is critical in these hierarchical models as the pelvic segment is the origin of the kinematic chain and errors within this segment propagate to all distal segments.

There have been efforts to quantify STA or tracking true bone movement, using bone pins [4], [5], external fixators [6], X-ray or fluoroscopy [7], [8], [9], or MRI [10]. Although many studies have investigated STA of the thigh, shank, or foot [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], knowledge of STA at the pelvis is particularly scarce. Despite its potential significance, investigations of pelvic STA are limited, perhaps due to the practical and ethical considerations associated with those investigative techniques particularly around the pelvis. Only one study was found to have quantified STA at the pelvis, using bone pins in the S1 vertebrae [14]. Significant STA was noted in a sit-to-stand task (over 35 mm) and gait (over 25 mm). Although the presence of pelvic STA was identified, its detailed characteristics and effects on pelvis kinematics remain unknown.

Double calibration is one technique previously used to reduce the impact of STA on kinematic data. Double calibration procedures typically involve two static calibrations at end-range positions of the joint of interest as a reference [15]. Knee STA was effectively reduced with this technique compared to single calibration [13], [16].

The current study aimed to investigate how skin-mounted pelvic markers were displaced in relation to anatomical bony landmarks in multiple static calibration positions, and the corresponding influence on the pelvic angles in healthy young adults. The magnitude and direction of static STA at the pelvis was assessed, and the relationship between the STA and the position of adjacent joints was examined. The impact of STA on the pelvic angles in static positions and gait and the location of hip joint center (HJC) were also evaluated.

Section snippets

Procedures

A sample of convenience of 20 healthy adults (12 male, 28.6 ± 3.8 years, 171.2 ± 9.0 cm, 67.2 ± 12.3 kg, and BMI: 22.8 ± 2.7) participated in this study in a single Three-hour testing session. Eligible participants were those who (1) were aged between 18 and 40 years, (2) had no lower extremity fracture or injury in the last 6 months, (3) had no history of conditions that affect walking, (4) had a BMI between 18 and 30. Ethical approval was gained from human ethics committees, and participants provided

Marker displacement

Table 1 shows the total number of participants who were tested in each testing position and the number in whom marker displacement was identified. ASIS markers were displaced more frequently than PSIS markers. Displacement was more frequent when the hip was in a flexed position. Notably, displacement of the ASIS marker locations was detected for all participants between the standing and supine positions.

Marker displacement distance represented the absolute distance between the location of a

Discussion

This study investigated how skin-mounted pelvic markers moved relative to their underlying bony landmarks in multiple static calibration positions. Soft tissue artifact at the pelvis was statically quantified as the marker displacement distance and direction in relation to the underlying bone in various body positions. The mean marker displacement was less than 5 mm in most positions. Marker displacement was detected in a high proportion of cases where the hip was in flexion. The displacement

Conclusion

Evidence of relative displacements of the pelvic markers with respect to their bony landmarks was shown in multiple calibration positions. ASIS markers were more susceptible to displacement than PSIS markers, particularly in hip flexion positions. Although the estimated impact of pelvic STA on gait kinematics was relatively small, a larger influence was observed in position which involved 90° hip flexion (up to 6°). Inter-ASIS distance measured in supine was found to be smaller than the

Conflict of interest statement

None of the authors have any financial or personal relationships with other people or organizations that could inappropriately influence this work.

Acknowledgements

Authors would like to thank the Australian Federal Government and the University of Melbourne (Faculty of Medicine, Dentistry and Health Sciences) for the scholarship funding supports.

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Thirteen individuals with mild-to-moderate symptomatic and radiographic hip OA and seventeen healthy, age-matched controls performed a standardized STS task. Data were acquired using a three-dimensional motion capture system. The primary outcome measures were task duration, sagittal and frontal plane trunk, pelvis, and hip joint angles, and sagittal and frontal plane trunk and hip joint moments. Comparisons of lower-limb measures were between the most affected side in the hip OA group and a randomly chosen limb for the control group, termed the index limb, prior to and following lift-off from the chair.
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^☆: This research was supported by International Postgraduate Research Scholarship and Melbourne International Research Scholarship funded by the Australian Federal Government and the University of Melbourne.

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Quantification of pelvic soft tissue artifact in multiple static positions☆

Highlights

Abstract

Introduction

Section snippets

Procedures

Marker displacement

Discussion

Conclusion

Conflict of interest statement

Acknowledgements

J Biomech

Hum Mov Sci

Hum Mov Sci

J Biomech

Clin Biomech (Bristol, Avon)

Clin Biomech

Clin Biomech (Bristol, Avon)

J Biomech

Clin Biomech (Bristol, Avon)