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Investigations have begun to connect leg prosthesis mechanical properties and user outcomes to optimize prosthesis designs for maximizing mobility. To date, parametric studies have focused on prosthetic foot properties, but not explicitly longitudinal stiffness that is uniquely modified through shock-absorbing pylons. The linear spring function of these devices might affect work performed on the body center of mass during walking. This study observed the effects of different levels of pylon stiffness on individual limb work of unilateral below-knee prosthesis users walking at customary and fast speeds. Longitudinal stiffness reductions were associated with minimal increase in prosthetic limb collision and push-off work, but inconsistent changes in sound limb work. These small and variable changes in limb work did not suggest an improvement in mechanical economy due to reductions in stiffness. Fast walking generated greater overall center of mass work demands across stiffness conditions. Results indicate limb work asymmetry as the prosthetic limb experienced on average 61% and 36% of collision and push-off work, respectively, relative to the sound limb. A series-spring model to estimate residuum and pylon stiffness effects on prosthesis energy storage suggested that minimal changes to limb work may be due to influences of the residual limb which dominate the system response.

Introduction: Daily volume loss of residual limb is a condition that most prosthetic users face, negatively affecting their life. One of the consequences is the loss of contact between the residual limb and the socket, which modifies internal pressures. Objective: The aim of this study was to study how the loss of volume of the residual limb affects socket adjustment through measuring pressures inside the socket. Study design: The study design is prospective longitudinal. Materials and Methods: Four subjects with unilateral transtibial amputation, with at least 1 year of prosthetic use, and walking with a comfortable prosthesis participated in this study. The pressure between the socket and the subject's residual limb was measured with an FSocket System (Tekscan). Residual limb volume was measured before and after each test with two different methods: optical scanning (Structure Sensor, Occipital) and conical frustum model. Sanders' protocol for volume loss was followed (Sanders et al. J Rehabil Res Dev. 2012;49:1467-1478. Volume changes in the residual limb and socket internal pressures were analyzed. Results/Discussion: The pressure graph obtained is consistent with Sanders' volume graphs. The pressure distribution inside the socket is lost after 5 hours of use of the prosthetic device; this can be related to volume loss and alignment. The only area where the pressure increases is in the distal zone, given that once the prosthetic fit is lost, weight bearing is transferred to the socket's distal section (mean volume loss, intrasession −3%; mean pressure loss, intrasession −39%). Conclusions:The study suggests that a small change in the volume can cause a change in the distribution of pressures inside the socket, indicating that the prosthetic fit may be compromised. For patient follow-up, measuring pressure inside the socket could be a useful indicator of socket misfit. Clinical Relevance: Daily volume changes in the prosthesis can produce pressures that lead to pain, injuries, an inefficient gait, and prosthesis abandonment. Consequently, it is important to understand the behavior of the pressures inside the socket and the influence of the daily changes of volume on the socket adjustment to design better strategies and techniques of daily volume changes management. (