(L-453) Pressure Offloading Associated With Custom Socket Inlays in Transtibial Prostheses

Introduction:: 57% of people with lower limb amputations are dissatisfied with the comfort of their prostheses [1]. In the case of lower limb amputations, the residual limb tissue is bearing far more weight than it was before the amputation. The pressure put on the soft tissue of the residual limb causes discomfort. In previous work, custom inlays were created, which fit inside the prosthesis and offload pressure, with the goal of helping to increase the comfort and satisfaction of the prosthesis user. In this project a benchtop prosthetic socket loading fixture was used to quantify the pressure distributions in a reproducible fashion. For this work, a lower leg amputation phantom was created and fitted into the prosthesis with the inlays. Static loads were applied, and socket interface pressures were measured.

Materials and Methods:: Inlays were created, which fit into the indentions made in the socket of a lower limb prosthesis. The blank inlay had a smooth, solid exterior surface, while the pressure-offloading meta-material inlay had a triangular pattern cut into the surface of one face of the inlay. The pattern was intended to change the properties of the material and offload pressure. The blank inlay was placed into the socket, then silicone was poured into the socket. As the silicone was being poured in, a PVC rod was placed into the socket to represent the bony anatomy of the residual limb. The silicone and PVC rod combined represented a residual limb. After the silicone set, the fake residual limb was taken out of the socket. Pressure sensors were placed over the surface of the blank inlays, then the fake residual limb was placed back into the socket. The socket with the fake residual limb was placed into the testing apparatus (Figure 1). 50 lbs of weights were placed on the platform of the testing apparatus, and a column that extended from the loading platform touched the top of the PVC pipe, thus transferring the load to the PVC pipe. Pressure mapping data was collected via the pressure sensors. The blank inlay was replaced with the meta-material inlay, and the procedure was repeated, with data being collected once again with the pressure sensors. The pressure data from the blank inlay and the meta-material inlay were compared.

Results, Conclusions, and Discussions:: Results and Discussion: The overall pressure read at the surface of the blank inlay was 5.6 kPa. The overall pressure read at the surface of the meta-material inlay was 3.2 kPa. These results support the initial hypothesis that the meta-material inlay design will offload pressure. As a result of this offloaded pressure, the patient should experience more comfort with their lower limb prosthesis. Moving forward, the PVC rod in the fake residual limb will be replaced with fake bone, so that the bony anatomy of the residual limb can be better represented. Additionally, different stance phases of gait, and different inlay architectures will be tested to better quantify socket pressure offloading performance.

Conclusion: In conclusion, the custom prosthetic inlays offloaded pressure within the prosthesis. Meta-material inlays such as these have the potential to improve the comfort and quality of life for people with amputations.


Acknowledgements (Optional): : Research support for this work was provided by Clemson University.

References (Optional): : [1] Baars, E. et al., Prosthesis satisfaction in lower limb amputees, 2018. [2] Brown, N. et al., Design of a single layer metamaterial for pressure offloading of transtibial amputees, 2021.