This paper proposes a torsion spring-based joint mechanism, specifically designed to use as a part of a Lumbar Assistive Orthosis(LAsO) for patients with lumbar degenerative kyphosis. The purpose is to support the patient's posture during stance phase in gait while allowing unrestrained legs movement during swing phase. It is also intended to be used in daily life by the patients. Therefore, the design principle revolves around creating a light-weighted and compact device that can be simply used. The mechanism limits the user hip joint range of motion through the spring stiffness of the torsion spring. The stiffness of the joint can be adjusted by manipulating the spring pre-tension through the geneva mechanism that houses the torsion spring. From performance evaluation, the developed prototype device properties have shown potential for it's intended application.