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Nonlinear Modeling with Cavitation Phenomenon of a Novel Shock Absorber for above-Knee Prosthesis

The shock wave of ground reaction forces during walking and running is suggested as a primary etiological agent in some conditions, such as degenerative joint disease, prosthetic joint loosening, plantar fasciitis or muscle tears. This study proposes a novel shock absorber design with an adjustable automatic smooth tuning range of the damping coefficient and rapid rebounds after impact loads, equipped in the above-knee prosthesis tibia section without any electronic devices. This absorber is also capable of automatic locking-out and releasing for stance and heel-strike phases without manual switching. It absorbs the impact load of the ground reaction force at each heel strike and adapts itself to the input force speed, feasible for patients to tolerate a wide range of athletic and inert situations. This study constructs a high order nonlinear dynamic model for its pressure-sensitive plunger and check valve systems and considers the cavitation phenomenon during speedy fluid flows. Simulation results show that both the damper resistant force and the damping coefficient reduce as the ground reaction force velocity increases, providing a desirable tendency of diminishing shock wave influences on the biological musculoskeletal system.