Structural testing of a passive polycentric knee joint with advanced functionalities designed and developed for patient-specific fitting

The activities of transfemoral amputees depend upon the prosthetic knee joint for rehabilitation, which must bear the required load. A patient-specific design of a passive polycentric four-bar knee joint is evaluated based on ISO-10328 and a maximum normal stress theory followed by weight compatibility and knee flexion–extension test during a gait cycle conducted with a trans-femoral amputee, where the maximum von Mises stress is found to be 260 MPa for test load conditions II as per ISO-based approach. However, it is observed to be 233 MPa in the case of a maximum normal stress theory approach. The developed knee joint has 12 different configurations, which are categorized into Groups A, B, and C configurations, representing a set of 4 configurations in each group based on changes in the length of vertical and horizontal links. The ISO-based approach prescribes a maximum load of 65 kg for all group configurations, whereas the maximum normal stress theory recommends to use for less than 100, 80, and 65 kg for Groups A, B, and C configurations, respectively. A prototype is developed using nylon-66, SS-304, and aluminium alloy-6061-T6 material, and it is fitted to a transfemoral amputee. The load-bearing and knee flexion–extension profile of the prosthetic knee joint is closely matched with that of the sound limb. The ISO-based analysis showed the increased factor of safety of the prosthetic knee joint in comparison with that of maximum normal stress theory, though the later is still found to be very safe to use.