Subjects
The subjects included 7 female volunteer OA patients (age: 68.4 ± 7.8 years; height: 151.2 ± 8.4 cm; weight: 61 ± 7.8 kg; mean ± standard deviation). All subjects were diagnosed with bilateral osteoarthritis of the knee and had a favorable course with conservative management. The grade determined by the Modified Kellgren and Lawrence Scale for all subjects was 1 or 2. The Japanese Orthopedics Association grade was 85.7 ± 6.7 for the right side and 80.0 ± 5.0 for the left side. The passive knee joint flexion angle was 130.0 ± 10.0° for the right side and 126.4 ± 14.1° for the left side. All subjects were able to walk independently.
Prior to the start of the study, a detailed description of its purpose was provided and informed consent was obtained. The present study was performed in accordance with the Declaration of Helsinki and the protocol was approved by the Ethics Committee of Kosei General Hospital.
Experimental setting
Stairs which all of the 7 OA patients could ascend were constructed in order to measure various movement parameters during forward descending (FD) and backward descending (BD) movements. The stairs used in the present study had three steps with a tread width of 30 cm and a riser height of 10 cm, 15 cm or 20 cm. The stairs were made to match the size and the height of the force plate placed beneath the staircase, which consisted of right and left parts (Figure 1). During the experiment, a non-slip mat was placed on the force plate so that none of the stairs were in contact with each other [9]. The force plate level was reset to the zero base line to eliminate the weight of the stair.
In addition, a handrail was installed beside the force plate to prevent falls and to secure the safety of the subjects, who were allowed to lightly touch it in case of pain or instability (but using it for pushing and pulling was not allowed). The handrail was mounted at the same level as the subject's greater trochanter and 10 cm away from the body.
Experimental apparatus and tasks
This study used a 3-dimensional motion analysis system comprising a VICON512 infrared position sensor (6 cameras; Oxford Metrics, UK) and a force plate (Kistler, Switzerland) with sampling frequencies set at 120 and 1080 Hz.
Infrared reflection markers were attached to 12 areas on each subject: top of the head; left and right acromion; left and right greater trochanters; lateral epicondyles of both knees; left and right lateral malleoli; left and right fifth metatarsal heads; and left inferior angle of the scapula (left/right-differentiation markers).
Each subject was asked to start in a static standing position at the top of the stairs, and began descending on a signal. The subject performed either FD or BD movement at a self-selected speed to reflect the subject's natural descending pattern. For safety reasons, the risers were installed starting from the lowest riser in the order of height and the subjects were instructed to first perform the FD movement. Three measurements were made under each condition. Each time riser height was changed, and a rest interval of about 3 min was provided. The study was conducted barefoot in order to mirror normal activities in Japanese homes.
The subjects were also given a written questionnaire to determine their preference in the descending method.
Data extraction and interpretation
ARMO software (Gsport Inc. Japan) was used for data extraction and interpretation. During the period when a subject descended the stair with the support leg holding the body weight (descending support phase), the peak values of the following data were extracted: maximum knee joint force (KJF-Max), knee flexion angle, knee extension moment, ankle dorsal flexion angle, ankle plantar flexion moment, hip flexion angle, and hip extension moment. In addition, the peak value of the knee joint force (KJF-LR) was extracted during the shock-absorbing phase when the leading leg landed (loading response phase). Joint moment and joint force were normalized to body weight. The points for data extraction during FD and BD movements for angle are shown in Figure 2, for moment in Figure 3, and for joint force in Figure 4.
While the leading leg was defined as the affected leg in this study, for patients with bilateral osteoarthritis of the knee, the leg providing more comfort in the descending support phase was defined as the support leg. Based on inverse dynamics, joint force was obtained by the summation of muscle tensions generated by all muscle groups surrounding the knee joint using the Newton-Euler equations of motion [10]. Paired t-tests were conducted to compare the values extracted in both descending methods for each riser height. P values less than 5% were considered significant.