Understanding the effects of suspension systems on lower-limb prosthesis rotation

Background: Limb rotation within prosthetic sockets significantly affects the comfort, gait, and stability of lower-limb amputees. Despite advancements in suspension systems, empirical evidence validating their rotational control remains limited. This study aims to systematically compare the rotational resistance of 3 prosthetic suspension systems—Pin-Lock, Suction, and Hook-and-Loop (HOLO)—under controlled conditions, addressing a critical gap in prosthetic design research. Methods: We evaluate the rotational resistance of 3 different prosthetic suspension systems—Pin-Lock, Suction, and HOLO—under varying axial loads (0/40/80 kg) and both (medial and lateral) rotational directions. Using a custom-designed mock limb and identical 3D-printed sockets, each suspension system was evaluated using a materials testing machine. The angular displacement of the limb inside each socket was measured under a constant torque ramp of 1 Nm/s, up to a maximum torque of 8.5 Nm. Results: The HOLO system (9.67° at 80 kg) showed significantly less rotation than the Pin-Lock (13.34° at 80 kg, p < 0.01) and Suction (14.42° at 80 kg, p < 0.01) systems. The medial rotation was 10.5% and 26.9% less than lateral rotation for Pin-Lock and HOLO systems, respectively, and 25.5% greater for Suction (all p < 0.01). Increasing axial loads reduced rotation for the Pin-Lock system only. Conclusions: This is the first study to measure the effectiveness of different prosthetic suspension systems using a representative mock limb. The results show that there are significant differences between the systems, highlighting the need to consider a user's activity level and rotational demands in prosthetic provision.