Intervertebral spinal fusion implants for interbody fusion of the anterior column of the spine are described. The implants have a substantially bi-convex or a substantially offset bi-convex shape. The implants are placed through a transforaminal or posterior approach at an oblique insertion angle. The implants have an outermost point on the superior convex surface and an outermost point on the inferior convex surface and four edges of differing heights. The outermost superior and inferior points of the implants are connected with the four edges with convex surfaces of different curvatures. The curvatures of the convex surfaces of the implants are designed to match the curvatures of concave vertebral surfaces when the implants are inserted at an oblique insertion angle.