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Gait Posture. 2017 Jun;55:184-190. doi: 10.1016/j.gaitpost.2017.03.033. Epub 2017 Mar 31.

Soft tissue artifact causes significant errors in the calculation of joint angles and range of motion at the hip.

Author information

1
Department of Orthopaedics, University of Utah, 590 Wakara Way, Salt Lake City, UT 84108, USA.
2
Department of Orthopaedics, University of Utah, 590 Wakara Way, Salt Lake City, UT 84108, USA; Department of Bioengineering, University of Utah, 36 S. Wasatch Drive, Room 3100, Salt Lake City, UT 84112, USA.
3
Department of Orthopaedics, University of Utah, 590 Wakara Way, Salt Lake City, UT 84108, USA; Department of Physical Therapy, University of Utah, 520 Wakara Way, Suite 240, Salt Lake City, UT 84108, USA.
4
Department of Orthopaedics, University of Utah, 590 Wakara Way, Salt Lake City, UT 84108, USA; Department of Bioengineering, University of Utah, 36 S. Wasatch Drive, Room 3100, Salt Lake City, UT 84112, USA; Department of Physical Therapy, University of Utah, 520 Wakara Way, Suite 240, Salt Lake City, UT 84108, USA; Scientific Computing and Imaging Institute, University of Utah, 72 S. Central Campus Drive, Room 3750, Salt Lake City, UT 84112, USA. Electronic address: Andrew.Anderson@hsc.utah.edu.

Abstract

Soft tissue movement between reflective skin markers and underlying bone induces errors in gait analysis. These errors are known as soft tissue artifact (STA). Prior studies have not examined how STA affects hip joint angles and range of motion (ROM) during dynamic activities. Herein, we: 1) measured STA of skin markers on the pelvis and thigh during walking, hip abduction and hip rotation, 2) quantified errors in tracking the thigh, pelvis and hip joint angles/ROM, and 3) determined whether model constraints on hip joint degrees of freedom mitigated errors. Eleven asymptomatic young adults were imaged simultaneously with retroreflective skin markers (SM) and dual fluoroscopy (DF), an X-ray technique with sub-millimeter and sub-degree accuracy. STA, defined as the range of SM positions in the DF-measured bone anatomical frame, varied based on marker location, activity and subject. Considering all skin markers and activities, mean STA ranged from 0.3cm to 5.4cm. STA caused the hip joint angle tracked with SM to be 1.9° more extended, 0.6° more adducted, and 5.8° more internally rotated than the hip tracked with DF. ROM was reduced for SM measurements relative to DF, with the largest difference of 21.8° about the internal-external axis during hip rotation. Constraining the model did not consistently reduce angle errors. Our results indicate STA causes substantial errors, particularly for markers tracking the femur and during hip internal-external rotation. This study establishes the need for future research to develop methods minimizing STA of markers on the thigh and pelvis.

KEYWORDS:

Dual fluoroscopy; Gait models; Hip; Measurement errors; Skin markers; Skin motion artifact

PMID:
28475981
DOI:
10.1016/j.gaitpost.2017.03.033
[Indexed for MEDLINE]

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