In OA patients, gait is disturbed by knee pain and deformity. However, improvement of knee function alone is not sufficient to improve gait. It is very important to assess gait oscillation, including the function of the trunk. In this study, we assessed the difference in gait oscillation during gait and stair-stepping in OA patients and healthy adults as a control group. Acceleration in the anterior direction in the sacral region during gait and stair-down and in the lateral region in the sacral region during stair-down was greater in healthy adults than in OA patients. The ratio of the center of gravity maximum values was greater for the sacral region than for the dorsal vertebral region. This is more obvious in healthy adults than in OA patients. From these findings, we considered that gait and stair-stepping might be performed mainly on the pelvic girdle more in healthy adults than in OA patients. On the other hand, acceleration in the anterior direction in the dorsal vertebral region during stair-stepping was greater in OA patients than in healthy adults. The ratio of the center of gravity maximum values during stair-stepping was greater in OA patients than in healthy adults. Turcot reported that the knee OA patients increase trunk flexion angle and decrease knee flexion moment during stair-stepping, and they compensate for stair-stepping motion with anteroposterior movement of the upper trunk [
15]. Therefore, we considered that gait oscillation in the anterior direction might increase more in OA patients than in healthy adults during stair-stepping. Acceleration in the lateral direction in the dorsal vertebral region during stair-stepping was greater in OA patients than in healthy adults. The ratio of the center of gravity maximum values was smaller in healthy adults than in OA patients. From these findings, we considered that gait oscillation in the lateral direction during stair-stepping might increase more in OA patients than in healthy adults. To perform suitable transfer of center of gravity to the supporting lower limb, the reinforcement of a hip joint abductor and the trunk function by exercise therapy are very important. The single-support phase was close to 1 during gait and stair-stepping in healthy adults and OA patients. The single-support time was largely the same during gait and stair-stepping in healthy adults. On the other hand, the single-support time was longer during stair-stepping than during gait in OA patients. From these findings, we considered that gait and stair-stepping exercise were slower in OA patients and that this might relieve their knee pain. Therefore, the single-support phase may be close to 1 for gait and stair-stepping in OA patients. OA is thought to be caused by degenerative changes in articular cartilage and secondary proliferative changes in cartilage and bone, resulting in pain, joint deformity, and functional disorders with aging. Klitgaad reported that muscle mass, muscle strength, and muscle contractility decline with age [
16]. Judge reported older adults take shorter steps, spend more time in single support, and walk with their pelvis rotated anteriorly, hip slightly flexed, and toes pointing out [
17]. Therefore, in OA patients, not only knee function, but also influence by aging have to be considered. However, we reported the assessment of gait oscillation in elder OA patients that received unilateral TKA [
13]. The values of gait oscillation were different between healthy adults and elder patients after TKA, but gait and stair-stepping were performed mainly on the pelvic girdle. Gait oscillation seemed to show the same tendency. We consider that, according to gait oscillation, the influence of aging may be small.
There were some limitations to our study. The small number of patients weakens the statistical power of the results. Further investigation with a larger sample size is needed to obtain more clinical data. The participants significantly differed in the percentage of each sex within each group. There was no significant difference in the data between male and female for either OA patients or for healthy adults. However, detection power was small. A further limitation was that there was a difference in subjects’ ages. Since the OA patients were older than the healthy adults, the influence of age may have to be considered. In addition, standard error of measurements may have decreased the generalizability of this study. Despite these limitations, the present study contributes to our current understanding of gait oscillation.