This thesis is concerned with the feasibility and design of creating a low-cost prosthetic knee joint that uses a compliant member for stance-phase control. A mechanical locking mechanism was used in conjunction with a compliant control axis to achieve automatic stance-phase locking. The concept was designed with the aid of CAE software, and validated through the design and testing of a simplified prototype. A prosthetic knee joint was then designed incorporating the compliant member concept. After modelling, fabrication, and laboratory testing, a pilot study was conducted in a clinical setting that proved the prototype knee provided the stance-phase control for which it was designed. Simple gait analysis showed highly asymmetric gait that demonstrated the need for improved swing-phase control and damping, while qualitative feedback indicated the need to reduce the noise produced by the knee.