Fabrication and evaluation of a multi-axis prosthetic foot with a flexible ankle joint simulating the natural biomechanical motion of the human foot

Abstract Background Multi-axis prosthetic feet are designed to replicate the natural anatomical motion of the human foot and enhance functional gait performance. Objective This study aimed to design, fabricate, and clinically evaluate a locally manufactured multi-axis ankle–foot prosthesis that anatomically replicates the four principal motions—plantarflexion, dorsiflexion, inversion, and eversion—and to compare its performance with reference values of the human foot. This work represents the first locally developed multi-axis ankle–foot prosthesis in Iraq, designed as a purely mechanical system without electronic components, combining CNC machining and carbon-fiber 3D printing to achieve anatomically realistic motion and cost-effective production. Methods The prosthetic foot was modeled in SolidWorks to reproduce the kinematics of the ankle–foot complex and fabricated using a combination of CNC machining and 3D printing. Tensile and bending tests were conducted on Al-7075-T651 and PA6-CF according to ASTM standards to confirm their structural suitability, while compression tests were performed on NBR and PU to determine elastic modulus and deformation behavior for soft-tissue mimicry. Clinical evaluation included gait trials with a force plate and G-Walk sensor system, capturing ground reaction forces (GRFs), spatiotemporal parameters, and ankle range of motion (ROM). Results The prosthesis achieved ROM values closely matching human anatomy: ∼15.5° dorsiflexion, ∼30° plantarflexion, and ∼±10.5° inversion/eversion. GRF components and spatiotemporal gait parameters were within normal reference ranges. Compression tests confirmed elastic behavior comparable to biological soft tissues, enabling shock absorption and improving walking comfort. G-Walk data demonstrated smooth phase transitions and good dynamic stability. Conclusion The proposed multi-axis foot provides anatomically realistic motion and physiologically acceptable gait performance. The combination of structural material integrity and compliant elements ensures natural joint behavior, making this locally fabricated design a promising solution for clinical application and future multi-patient trials.