Biomedical Engineering Reference
In-Depth Information
undergone unilateral hip-arthroplasty for the first time and presented no other physi-
cal or cognitive conditions. The group was composed of four women and seven men,
the mean age was 69
±
±
15 years, mean weight was 81
20 Kg, and mean height was
172
9cm.
All subjects were equipped with sensor nodes similarly to the in-lab data collection.
They were then asked to walk by themselves along a 10-meter walkway at a comfortable
speed, twice. The walkway was marked with black tape on the floor. The time and
number of steps taken to complete the walkway were recorded.
This procedure took place on the day the patient was discharged from the hospital,
and a few months later, when the patient came back for a follow-up evaluation. The
average number of days spent at the ward after surgery was 4
±
±
1 day. The time between
baseline and follow-up measurements was 108
15 days. All patients employed a walk-
ing aid during baseline measurements, six used two crutches and five used a walker with
wheels. During follow-up measurements six patients used one crutch and five patients
walked without any aiding device.
Patients filled out an EQ-5D TM health questionnaire (Swedish version) approximately
two weeks before surgery, and soon after their follow-up session. The EQ-5D TM is
a standardized instrument for measuring health outcome, developed by the EuroQol
Group (www.euroqol.org). The English version of the questionnaire, validated for Ire-
land, is shown in Figure 3. Each answer is given a value from 1 to 3, lower values
indicate better health.
±
3.3
Observational Gait Analysis
The time, Tm , and number of steps, NumSteps , taken to complete the 10-meter walk
test were used to compute average speed, Speed =10 /Tm (m/s), and average step
length, StepLeng =10 /N umSteps (m). In addition, step length was normalized by
the patient's height. These variables were used as reference for the improvement of the
patient, under the assumption that average speed and step length should increase as the
patient recovers.
3.4
MOCAP Gait Analysis
Gait normality and symmetry measures were calculated from the 3D kinematic data.
The normality index used for the kinematic data was the GPS and the MAP [18]. How-
ever, the mean value was removed from all curves before calculating the score, and foot
progression was not used because it was not available in the reference data set. Remov-
ing the curves' mean values makes the normalcy measure more robust to offset errors,
while preserving the shape and range of the curves.
The reference data set was an ensemble of 34 randomly selected adult subjects pre-
senting no known pathologies, previously acquired at the clinical gait lab at Sahlgren-
ska University Hospital, Gothenburg, Sweden. Joint angle curves were calculated for
each individual and normalized to stride time. The ensemble average of the normalized
curves was used as a reference curve.
Each MAP component, Eq. 1, was calculated as the RMS difference between the
reference curve, C ref , and the subject's curve, C subj ,where N is the number of points
 
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