On the Possibility of Achieving Near-Normal Swing Phase of Walking with Passive Single-Axis and Polycentric Knees: A Simulation Approach

Introduction: A new passive polycentric knee called IITM polycentric knee (IPK), where IITM stands for the authors' institution, namely, Indian Institute of Technology Madras, was designed to provide better functionality at a reduced cost. The design of the knee was based on stance phase stability criteria and toe clearance during the swing phase for users in developing countries to handle uneven terrain. The present study features a simulation-based dynamic analysis of a passive single-axis knee (SAK) and IPK to understand the swing phase behavior of the IPK with respect to SAK. This study aims at understanding the advantages and disadvantages of the IPK against a passive SAK to improve its design criteria and enable further development to provide better functionality to the existing passive SAK users. Methods: Lower-limb models of a normal leg and prosthetic legs with SAK and IPK were created, their swing phases were simulated, and gait parameters were analyzed. The passive knees in the present study have only frictional damping and no active knee moments, implying the requirement of compensatory strategies for forward progression of the swinging leg. The required frictional damping at the knee joint to obtain near-normal knee motion and the compensations required while using the SAK and IPK were obtained by simulation. The lower-limb dynamics obtained from the simulations was analyzed to understand the performance of the SAK and IPK during swing. Results: This study shows that the IPK is superior to an SAK in terms of achieving knee extension in preparation for stance, even without an extension assist and with lower hip effort. The peak hip power during swing with the IPK was 58.7% less than with the SAK. A negative heel clearance was found in terminal swing with the IPK, which demands a compensatory strategy for foot clearance during the swing and shows the necessity for inclusion of a heel clearance parameter in the design of polycentric knees. Conclusions: The present work focuses on the swing behavior comparison of passive single-axis and polycentric knees. The study provides insight into the compensatory strategies required to achieve successful forward progression of the swinging leg with both types of knees. The analysis shows the potential for a well-designed passive polycentric knee to be a costeffective alternative to achieve near-normal swing during walking.