DOS Kongressen 2014 ·
211
Acceptable agreement between Inertia-based
Measurement Unit and Optical Motion Capture
System applied in quantitative measurement of
physical function in patients
Inger Mechlenburg, Peter Bo Jørgensen, Henrik Sørensen, Dennis B Nielsen,
Bernd Grimm, Kjeld Søballe
Orthopaedic Research, Aarhus University Hospital; Section of Sports, Aarhus
University; ATRIUM Medical Center, AHORSE Foundation, The Netherlands
Background:
There is need for valid objective measures of physical function
when outcome after orthopaedic or rehabilitation interventions are evaluated.
Purpose / Aim of Study:
The aim of this study was to validate an Inertia-based
Measurement Units (IMU) against an Optical Motion Capture System (OMCS).
Materials and Methods:
Ten patients (eight females), mean age 28 (16-43)
years with hip dysplasia were tested. The test battery included four lower ex-
tremity performance measures: sit-stand-sit (STS), stair climbing (SC), block
stepping test (BST) and counter movement jump (CMJ). We applied an IMU
(Micro Strain Inertia-Link) and recorded data at 100 Hz. Kinematic data were
recorded at 240 Hz with an 8-camera ProReflex MCU 1000 OMCS. Rotations
were measured as range between highest and lowest value. Agreement between
the two systems was analyzed and presented with Limits of Agreement (LOA)
(mean difference ±1.96 x SD).
Findings / Results:
Overall, the agreement between the results acquired by
the IMU and the OMCS was acceptable. LOA for rotations in the frontal plane in
degrees for STS were 3.7±15.4 in ascending and 3.3±11.1 in descending. For
SC, LOA for rotations in the sagittal plane were 2.2±6.9 deg in ascending and
-3±5.8 deg in descending. LOA for rotations in the sagittal plane at the BST
were -0.7±5.3 deg in ascending and -1.2±5.9 deg in descending. LOA for ver-
tical translation for CMJ were -0.6±5.5 cm. There were systematic differences
between the IMU and OMCS in SC (mean diff 2.2 deg p=0.03 and mean diff -3
deg p<0.01 respectively).
Conclusions:
The IMU showed acceptable agreement with OMCS when ap-
plied in test of physical function in patients. There is a clear perspective for
clinicians to apply the IMU in the evaluation of orthopaedic or rehabilitation in-
terventions.
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