Lower limb amputee gait characteristics on a specifically designed test ramp: Preliminary results of a biomechanical comparison of two prosthetic foot concepts.

BACKGROUND: For demanding activities in daily life, such as negotiating stairs, ramps and uneven ground, the functionality of conventional prosthetic feet ("Daily Life Feet" - DLF) is often limited. With the introduction of microprocessor-controlled feet (MPF) it was expected that the functional limitations of DLF might be reduced. The purpose of the present study was to investigate biomechanical gait parameters with DLF and MPF when walking on a specifically designed ramp involving abruptly changing inclination angles as a scenario reflecting typical situations related to walking on uneven ground.

RESEARCH QUESTION: The specific aim of the study was to answer the research question if the advanced adaptability of MPF to different ground slopes would lead to more natural motion patterns and reduced joint loading compared with DLF feet.

METHODS: A specifically designed ramp was installed within a gait lab. During downward motion on this ramp biomechanical parameters - ground reaction forces, joint moments and joint angles were obtained both with DLF and MPF used by four transtibial amputees. A control group of 10 non-amputees (NA) was measured with for comparison.

RESULTS: The NA group managed the ramp element with the abruptly changing inclination with a specific ankle joint adaptation. Compared to DLF the MPF considerably improved the ankle adaptation to the abruptly changing inclination which was reflected by a significantly increased stance phase dorsiflexion which was comparable to the NA group. The peak value of the knee extension moment on the prosthetic side was significantly increased with DLF, whereas it was almost normal with MPF (DLF: 0.71 ± 0.13 Nm/kg, MPF: 0.42 ± 0.12 Nm/kg, NA: 0.36 ± 0.07 Nm/kg, p < 0.05 and p < 0.01). The external knee adduction moment was generally reduced for the transtibial amputees and did not show differences between foot designs.

SIGNIFICANCE: The adaptable ankle joint motion of the MPF is a crucial requirement for a more natural motion pattern and leads to a reduction of sagittal knee joint loading on the prosthetic side.