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Gait Posture. 2014 Sep;40(4):545-8. doi: 10.1016/j.gaitpost.2014.06.013. Epub 2014 Jul 2.

A 3D mathematical model to predict spinal joint and hip joint force for trans-tibial amputees with different SACH foot pylon adjustments.

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Department of Physical Therapy and Assistive Technology, National Yang Ming University, Taipei, Taiwan, ROC.
Rehabilitation Center, Taipei Veterans General Hospital, Taiwan, ROC.
Department of Physical Therapy, Chang Gung University, Taoyuan, Taiwan, ROC.
Department of Biomedical Research, Mackay Memorial Hospital, Tamshui, Taipei County, Taiwan.
Department of Physical Therapy and Assistive Technology, National Yang Ming University, Taipei, Taiwan, ROC. Electronic address:


A solid-ankle cushioned heel (SACH) foot is a non-joint foot without natural ankle function. Trans-tibial amputees may occur toe scuffing in the late swing phase due to a lack of active dorsiflexion. To address this problem, clinical guidelines suggests shortening the pylon to produce a smooth gait. However, this causes a leg length discrepancy, induces asymmetry in the hip joint, and causes an overload of L5/S1 joint force. Therefore, this study aimed to investigate the influence of different prosthesis pylons on the hip joint and L5/S1 joint forces. Ten subjects were recruited using leg length for normalisation. Four different pylon reductions (0%, 1%, 2%, and 3%) were used for gait analysis. A Vicon system and force plates were used to collect kinematic data and ground reaction force, respectively. The software package MATLAB was used to create a mathematical model for evaluating the symmetry and force of the hip joint and the low back force of the L5/S1 joint. The model was validated by the correlation coefficient (CC=0.947) and root mean square (RMS=0.028 BW). The model estimated that the 1% group had a symmetrical hip joint force and a lower L5/S1 joint force in the vertical direction. This study indicates that a 1% pylon shortening on a SACH prosthesis is appropriate for a trans-tibial amputee.


Gait analysis; Low back force; Mathematic model; SACH foot; Trans-tibial amputee

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