Numerical comparison of composite spring designs for an orthopaedic shoe based on experimental gait analysis
Topic(s) : Industrial applications
Co-authors :
John FINDER (GERMANY), Hendrik MÖLLERS , Carsten SCHMIDT , Sebastian HEIMBSAbstract :
The rise in diabetic patients undergoing less invasive surgery has resulted in an increase in minor foot amputations, such as the loss of toes. This loss leads to a reduction in leverage and force at the ankle joint. These patients require orthopaedic assistance with roll-off and push-off. Conventional prosthetics are primarily focused on aesthetics, while standard orthopaedic shoes lack support for push-off and energy recovery. Therefore, a novel spring element is proposed for the sole.
This paper presents a numerical simulation-based comparison of two orthopaedic shoes with composite spring elements. The designs are evaluated based on their roll-off and energy storage capabilities.
The first spring element has a double cantilever design and is fixed in the centre to the filler and insole. Each side can move independently and is curved to adjust the contact points at full loading (fig. 1).
The design of the second spring element follows a question mark shape with a fixture at the front and heel. This allows movement under the centre and bale and is supported with a heel block(fig. 2).
To avoid complications in the simulation of the combination of soft tissue and high stiffness composite, we use a more direct simulation approach. We obtain the pressure data under the foot of two subjects in a gait analysis and apply it to the insole in the finite element model. This approach also allows for a simple consideration of the patient's physiological behaviour.
We apply the pressure of a normal gait and that of an affected patient to both designs. The time discretisation follows the four medical gait phases during ground contact.
Design 1 exhibits a high deflection at the heel and a small deflection at the tip in both cases. In contrast, design 2 shows a similar deflection at the tip as design 1, but no deflection at the heel due to the heel blockand even shows a lift-off at the end of the gait. The heel and tip deformation in design 1 occur independently, suggesting no interaction between the heel and bale spring side and providing no additional benefit.
Furthermore, there is a significant difference in the strain energy of the two designs. Design 1 maintains a nearly constant strain energy, while design 2 shows a peak that is around $50~\%$ higher at the end, indicating greater support for push-off forces.
Although the simulation does not integrate the full roll-off trajectory, design 2's deflection suggests a roll-off behaviour. This is in line with additional experimental testing and the patients' subjective experiences. Design 2 has been selected for further, more extensive numerical studies. The simplified direct approach provides sufficient information on deformation and strain energy to predict the performance of the composite spring element and evaluate various designs.
This paper presents a numerical simulation-based comparison of two orthopaedic shoes with composite spring elements. The designs are evaluated based on their roll-off and energy storage capabilities.
The first spring element has a double cantilever design and is fixed in the centre to the filler and insole. Each side can move independently and is curved to adjust the contact points at full loading (fig. 1).
The design of the second spring element follows a question mark shape with a fixture at the front and heel. This allows movement under the centre and bale and is supported with a heel block(fig. 2).
To avoid complications in the simulation of the combination of soft tissue and high stiffness composite, we use a more direct simulation approach. We obtain the pressure data under the foot of two subjects in a gait analysis and apply it to the insole in the finite element model. This approach also allows for a simple consideration of the patient's physiological behaviour.
We apply the pressure of a normal gait and that of an affected patient to both designs. The time discretisation follows the four medical gait phases during ground contact.
Design 1 exhibits a high deflection at the heel and a small deflection at the tip in both cases. In contrast, design 2 shows a similar deflection at the tip as design 1, but no deflection at the heel due to the heel blockand even shows a lift-off at the end of the gait. The heel and tip deformation in design 1 occur independently, suggesting no interaction between the heel and bale spring side and providing no additional benefit.
Furthermore, there is a significant difference in the strain energy of the two designs. Design 1 maintains a nearly constant strain energy, while design 2 shows a peak that is around $50~\%$ higher at the end, indicating greater support for push-off forces.
Although the simulation does not integrate the full roll-off trajectory, design 2's deflection suggests a roll-off behaviour. This is in line with additional experimental testing and the patients' subjective experiences. Design 2 has been selected for further, more extensive numerical studies. The simplified direct approach provides sufficient information on deformation and strain energy to predict the performance of the composite spring element and evaluate various designs.