Procedures
Subjects were required to wear shorts and to walk without shoes.
Spherical, passive reflective markers (25 mm diameter) were attached directly to the skin of each subject’s bilateral lower extremities using double-sided adhesive tape.
All markers were placed in accordance with the VCM model on 15 points of bony landmarks, including the sacrum at the level of S2, bilateral anterior superior iliac spines (ASIS), lateral thighs, the axis of the knee joints, the shanks, lateral malleoli, heels, and the second metatarsal heads (Fig. 2).
The ASIS and sacral markers were also placed directly on the skin, not on the shorts.
After recording anthropometric measures such as leg length and pelvic width, markers were placed by Tester 1 following the defined protocol.
The subjects were instructed to walk at self-selected speed along a 10-m walkway and they practiced walking in
order to get familiar with the surroundings.
Then the movement of each joint was captured as the subject walked on the walkway at his or her own pace 5 times.
A single gait cycle of kinematic data was recorded for each trial.
All markers were then removed.
After 30 minutes, tester 1 checked that all traces of the marker placement on the subject’s skin had disappeared.
Tester 2 then repeated the placement of markers and data collection following identical procedures.
Subsequent test sessions were conducted in an identical manner for the same subjects on a second day within 2 weeks of the first session.
Each session was videotaped, to assist with interpretation of the data.
Prior to the study commencing, the two physical therapists practiced marker placement for a 3 month period.
When gait data is processed in VCM, a static trial that calculates the actual joint center and alignment of the axis prior to the dynamic trial, which calculates the gait variables.
In the static trial, the actual joint centers and axis of the lower limb joints are determined according to the anthropometric measures and the positional data of each marker and the Knee Alignment Device (KAD).
The KAD is a spring-loaded G-shaped clamp and has three standardsize fixed markers mounted on the tip of rods of equal
length placed at right angles in three-dimensional directions.
The kinematic data processed by VCM is shown as the angle between two segment axes projected into the related plane.