Stair stepping motion is important in daily living, similar to gait. In this study, we did a Kinematic Analysis of total knee arthroplasty during stair-stepping. A total of 20 patients implanted with Bi-Surface 5PS were assessed. The Bi-Surface knee is a posterior-cruciate substitute prosthesis with a unique ball-and-socket joint in the mid-posterior portion of the femoral and tibial components. This joint functions as a posterior stabilizing cam mechanism and as a load-bearing surface in flexion. Patients were examined during stair-stepping motion using a 2-dimensional to 3-dimensional registration technique. The kinematic pattern in step up was a medial pivot, in which the level of anteroposterior translation was very small. In step down, the kinematic pattern was neither pivot shift nor rollback. From minimum to maximum flexion, anterior femoral translation occurred slightly. However, it became clear in this study that the joint's stability during stair-stepping was affected by the design of the femorotibial joint rather than Post/Cam engagement.

Total Knee Arthroplasty (TKA) has been widely performed and successful clinical outcomes have been achieved for the patients with knee osteoarthritis which is generally known to cause ADL problem. Clinical and radiographic evaluations are commonly used when evaluating postoperative outcomes, among which kinetic analysis and gait analysis are considered essential to investigate the more detailed effect of the treatment. There is a controversy whether performing TKA on both knees simultaneously is appropriate in treating patients with bilateral knee osteoarthritis, in terms of the speed and effectiveness of gait recovery. In this study, we reviewed the significance of performing simultaneous bilateral TKA, by the results of preoperative and postoperative gait analysis.

Materials and Methods: Total of eight patients, all female and diagnosed of bilateral knee osteoarthritis, were treated with TKA and reviewed. Mean age was 70 years old (60–74). For prosthesis, we used Scorpio NRG PS, and ADVANCE, with cementation for all. No patella was replaced. Some had unilateral TKA, and some were treated bilaterally as needed. We examined distance factors (step length and step width), gait velocity, and gait barycentric factors (single-support phase and Ratio of center of gravity maximum values). We performed the analysis preoperatively, postoperatively at 1 month, 3 months, and 6 months. We used the floor pressure gauge (NITTA CORPORATION) and the three-dimensional motion analysis device (DITECT Co. Ltd) for the analysis.

Results: During the six-month follow-ups, six cases were unilateral TKA and two were treated bilaterally. Increase in step length was seen in the unilateral cases, and it decreased in the bilateral cases. Step width decreased in five cases, two cases showed no change, and increased in one case. Gait velocity had increased in all cases. Single-support phase was close to 1 for all the cases. Ratio of center of gravity maximum values, which indicates the movement of centroid during ambulation, the ratio went up for unilateral cases while it showed no change in the bilateral cases.

Discussion: Quantitative studies of gait analysis have reported that gait condition had improved after TKA. However, some reported that the gait impairment had remained. Unilateral TKA group showed gait restoration, whereas gait abnormality in either leg was seen in the bilateral group. Gait analysis is effective in determining whether surgeons should perform unilateral TKA or bilateral TKA to the patients with bilateral knee osteoarthritis. Among the gait analysis factors, we consider that Ratio of center of gravity maximum values shows effectively the improvement of the treated knee, gait, and the condition of contralateral knee.