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The development of artificial prosthetic lower limbs aims to improve patient’s mobility while avoiding secondary problems resulting from the use of the prostheses themselves. The residual limb is a pressure-sensitive area where skin injuries and pain are more likely to develop. Requirements for adequate prosthetic limbs have now become urgent to improve amputee’s quality of life. This study aims to understand how socket design parameters related to geometry can influence pressure distribution in the residual limb. A finite element model was developed to simulate the mechanical loading applied on the residual limb of a below-knee amputee while walking. A sensitivity analysis to socket initial geometry, scaling the socket downward in the horizontal plane, was performed. Recordings include stress levels on the skin and in the residual limb deep soft tissues. Peak stress was reduced by up to 51% with a limited reduction of the socket size. More important scale reduction of the residual limb would lead to possible negative effects, such as stress concentrations in sensitive areas. This result confirms the interest of the prosthetist to develop a well-fitting socket, possibly a little smaller than the residual limb itself, in order to avoid residual limb mobility in the socket that could cause friction and stress concentrations. Non-homogeneous geometrical reductions of the socket should be further investigated.

Background Prosthetic rehabilitation improves the overall quality of life of patients, despite discomfort and medical complications. No quantitative assessment of prosthesis-patient interaction is used in routine protocols and prosthesis quality still results from the manufacturer's know-how. Objective Our objective is to investigate whether pressure can be a relevant factor for assessing socket adequacy. Methods A total of 8 transtibial amputee volunteers took part in this experimental study. The protocol included static standing and 2 minutes walking tests while the stump-to-socket interface pressures were measured. Questionnaires on comfort and pain were also conducted. Results During static standing test, maximum pressures were recorded in the proximal region of the leg, with a peak value reaching 121.1 ± 31.6 kPa. During dynamic tests, maximum pressures of 254.1 ± 61.2 kPa were recorded during the loading phase of the step. A significant correlation was found between the pain score and static maximum recorded pressure (r= 0.81). Conclusions The protocol proposed and evaluated in this study is a repeatable, easy-to-set quantified analysis of the patient to socket interaction while standing and walking. This approach is likely to improve feedback for prosthesis manufacturers and consequently the overall design of prostheses.

Finite element analysis (FEA) has been widely used to study foot biomechanics and pathological functions or effects of therapeutic solutions. However, development and analysis of such foot modeling is complex and time-consuming. The purpose of this study was therefore to propose a method coupling a FE foot model with a model order reduction (MOR) technique to provide real-time analysis of the dynamic foot function. A generic and parametric FE foot model was developed and dynamically validated during stance phase of gait. Based on a design of experiment of 30 FE simulations including four parameters related to foot function, the MOR method was employed to create a prediction model of the center of pressure (COP) path that was validated with four more random simulations. The four predicted COP paths were obtained with a 3% root-mean-square-error (RMSE) in less than 1 s. The time-dependent analysis demonstrated that the subtalar joint position and the midtarsal joint laxity are the most influential factors on the foot functions. These results provide additionally insight into the use of MOR technique to significantly improve speed and power of the FE analysis of the foot function and may support the development of real-time decision support tools based on this method.

In 2005, the number of lower limb amputees was 1.6 million in the USA and is projected to reach 3.6 in 2050. Among causes for amputations, dysvascular diseases, trauma and diabetes are the main one and dysvascular conditions are increasing because of an ageing population [1]. The manufacturing of lower limb prosthesis is currently mainly artisanal while the use of computer assistance is still limited. As a consequence, the quality of the prosthesis will greatly depend on the prosthetist know-how. However, this is not the only factor influencing prosthesis quality, and the type of the prosthesis, its design, or the materials for both liner and socket should also be taken into account. Although prosthesis quality assessment is subjective, quantitative measurements such as pressures or temperatures in the liner and patient feedback through questionnaires can be assessed. Mechanical interactions between a stump and the prosthesis were accurately predicted using finite element method (FEM) [2,3]. Existing models mainly aim to develop a realistic model with no or limited validation. Complete optimization of the prosthesis using numerical analysis has, to the best of our knowledge, not been fully performed. Thus, the main objective of this project is to define a new FEM method to fully optimize prosthesis shape in order to improve the subject's comfort. The definition of this method will first need a validation of the FEM by comparing experiments and simulations results together with measuring the method reproducibility.