The present disclosure concerns implants to at least partially replace the nucleus of a spinal disc. In one embodiment, a prosthetic structure is provided which includes a bag operable to contain at least one internal implant within the bag. In another embodiment, a sinusoidal-shaped structure made of a flexible material is provided with various unique configurations to act as the internal implant and once released from a stretched or compressed configuration resumes nearly its original shape. In one embodiment, for delivery, a sinusoidal-shaped structure may be in a reduced amplitude state. In another embodiment, a sinusoidal-shaped structure is alternately woven from one end to the other with a second sinusoidal-shaped structure.