Background and objectives: There are no reports on articular stress distribution during walking based on any computed tomography (CT)-finite element model (CT-FEM). This study aimed to develop a calculation model of the load response (LR) phase, the most burdensome phase on the knee, during walking using the finite element method of quantitative CT images. Materials and Methods: The right knee of a 43-year-old man who had no history of osteoarthritis or surgeries of the knee was examined. An image of the knee was obtained using CT and the extension position image was converted to the flexion angle image in the LR phase. The bone was composed of heterogeneous materials. The ligaments were made of truss elements; therefore, they do not generate strain during expansion or contraction and do not affect the reaction force or pressure. The construction of the knee joint included material properties of the ligament, cartilage, and meniscus. The extensor and flexor muscles were calculated and set as the muscle exercise tension around the knee joint. Ground reaction force was vertically applied to suppress the rotation of the knee, and the thigh was restrained. Results: An FEM was constructed using a motion analyzer, floor reaction force meter, and muscle tractive force calculation. In a normal knee, the equivalent stress and joint contact reaction force in the LR phase were distributed over a wide area on the inner upper surface of the femur and tibia. Conclusions: We developed a calculation model in the LR phase of the knee joint during walking using a CT-FEM. Methods to evaluate the heteromorphic risk, mechanisms of transformation, prevention of knee osteoarthritis, and treatment may be developed using this model.

This study aimed to evaluate the mechanism of progression involved in knee osteoarthritis (OA). We used the computed tomography-based finite element method (CT-FEM) of quantitative X-ray CT imaging to calculate and create a model of the load response phase, wherein the greatest burden is placed on the knee joint while walking. Weight gain was simulated by asking a male individual with a normal gait to carry sandbags on both shoulders. We developed a CT-FEM model that incorporated walking characteristics of individuals. Upon simulating changes owing to a weight gain of approximately 20%, the equivalent stress increased extensively in both medial and lower leg aspects of the femur and increased medio-posteriorly by approximately 230%. As the varus angle increased, stress on the surface of the femoral cartilage did not change significantly. However, the equivalent stress on the surface of the subchondral femur was distributed over a wider area, increasing by approximately 170% in the medio-posterior direction. The range of equivalent stress affecting the lower-leg end of the knee joint widened, and stress on the posterior medial side also increased significantly. It was reconfirmed that weight gain and varus enhancement increase knee-joint stress and cause the progression of OA.

Patients with knee osteoarthritis can significantly affect the function of the knee joint in terms of joint range and mobility and have a stereotypical pattern of knee stiffness during gait, caused by an increased resistance in the muscles and soft tissues during the stance phase of knee joint movement. Smoothness in movement, such as during walking and running, is assumed to be attained by adulthood; however, disruptions in gait pattern due to injury or performance enhancement can alter the smoothness of the movement, and this is often quantified in terms of "jerk". A higher jerk value is linked with a decrease in smoothness. However few have reported to evaluate the smoothness of the knee joint movement during walking in patients with knee osteoarthritis. The purpose of the present study was to quantify the smoothness of the knee joint movement during walking in people with knee osteoarthritis. Patients were classified as having early or severe knee osteoarthritis. There were eight patients in each group (16 knees; three males, five females). The normalized angular jerk was calculated as an indicator of the walking knee joint smoothness in each of the four periods of the stance phase. Two-way ANOVA was performed to compare the smoothness of knee joint movement between groups and between each period of the stance phase. The angular change in the sagittal plane of those with severe knee osteoarthritis was smaller than that of those with early knee osteoarthritis in all periods of the stance phase. Normalized angular jerk did not significantly differ between groups in all periods. In both groups, the normalized angular jerk in the sagittal plane was significantly larger in the mid-stance and terminal stance periods than in the early stance and pre-swing periods. Only in patients with severe knee osteoarthritis, there was a significantly larger jerk in the frontal plane in the mid-stance period. The present results revealed that the smoothness of joint movement decreases during the single leg supporting phase of the stance phase in the frontal plane with severe knee osteoarthritis, although there is no difference in smoothness of joint movement according to the severity of knee osteoarthritis The instability during single leg support due to increase of the knee joint load and destruction cause the impaired smoothness of the knee joint movement.

Background and Objectives: The purpose of this study was to compare the side-to-side differences in knee joint movement and moment for the degree of pain in the walking stance phase in patients with bilateral knee osteoarthritis (KOA) of comparable severity. We hypothesized that knee joint movement and moment on the side with strong pain were lower compared with the side with weak pain. Materials and Methods: We included 11 patients diagnosed with bilateral severe KOA. In all patients’ left and right knees, the Kellgren–Lawrence radiographic scoring system grade was level 4, and the femorotibial angle and knee range of motion were equivalent. Following patients’ interviews with an orthopedic surgeon, we performed a comparative study with KOA with strong pain (KOAs) as the strong painful side and KOA with weak pain (KOAw) as the weak painful side. Data for changes in bilateral knee joint angles in three dimensions during the stance phase and bilateral knee sagittal and frontal moments exerted in the early and late stance phases were extracted from kinematics and kinetics analyses. Results: Three-dimensional joint movements in the knee joint were not significantly different in all phases between KOAs and KOAw. Knee extensor moment in the early stance phase in KOAs was significantly smaller than that in KOAw. Knee abductor moment in the early and late stance phase was not significantly different between KOAs and KOAw. Conclusions: Although we found no difference in joint motion in bilateral knee joints, knee extensor moment on the side with strong pain was decreased. In patients with bilateral severe KOA, it was suggested that the magnitude of knee pain contributed to the decrease in knee joint function.

Elucidating the sway and changes in the acceleration of center of mass (COM) during walking is important for effective gait training and rehabilitation. The objective of this study was to verify the improvement in gait before and after total knee arthroplasty (TKA) from COM sway and the changes in the acceleration of COM during the stance phase of walking. This study included 13 patients (1 male and 12 females) with medial knee osteoarthritis who were hospitalized for TKA. The COM sway during the stance phase of walking was evaluated using root mean square (RMS) normalized by walking speed, and the changes in acceleration were further verified. Lateral and vertical RMS showed significant differences between preoperative and postoperative states and demonstrated low values after TKA. The lateral acceleration at the latter part of the early stance phase demonstrated a significant difference between preoperative and postoperative states. A significant difference was also observed in the lateral acceleration in the late stance phase between the two groups. Improvement in pain and alignment after TKA reduced the lateral sway of COM and the changes in acceleration during the gait stance phase, which is speculated to lead to improvement in gait and prevention of falls.