Single Axis Pneumatic Modular Hip Joint for Hip Disarticulation Amputees

The single-axis pneumatic modular hip joint is a pivotal component in hip disarticulation prostheses, addressing the needs of a niche but highly challenged amputee population (2% of amputees) facing high energy expenditure (200% of normal ambulation) and prosthesis rejection rates. This study aimed to develop a lightweight, low-cost, pneumatic single-axis hip joint tailored for K2 and K3 activity levels in developing countries like India, prioritizing affordability, stance-phase stability, swing-phase control, and ease of use. The methodology involved design conceptualization, precise measurements (joint length: 225 mm, width: 90 mm), cost-effective material selection (locally sourced steel pneumatic cylinder, aluminum, and stainless steel), and meticulous fabrication for seamless integration with modular prosthetic components, including a molded socket, polycentric knee, and SACH foot. Motion analysis and clinical evaluations demonstrated a 30% reduction in stance-phase sway, 20–30% improvement in gait cadence variability, and 25% enhanced stride symmetry, enabling independent ambulation without axillary aids. The design, costing 80–90% less than commercial alternatives (e.g., Ottobock 7E5), leverages a $20–$30 pneumatic cylinder and withstands over 500,000 gait cycles. Despite its slightly massive construction (600 grams), potentially affecting long-term comfort, the joint offers a scalable, reliable solution for low-income settings. Future improvements could include lighter materials and customizable resistance to enhance performance, making this indigenous design a transformative step in improving mobility and quality of life for hip disarticulation amputees in resource-constrained environments.