Out of these 3 gaps, the middle one is impossible with a simple arc. It will require a spline to be able to satisfy the tangent constraints.
The other two, though, you can achieve with simple arcs instead of splines if you create a plane between the rungs of this "ladder" frame (3D Model > Plane > select two perpendicular lines to the path of the curve), then pick to create an arc CENTER POINT option, selecting a far away center then the two connection points in the curve. Apply tangent constraints and use the "ON FACE" constraint to make the arc match the plane we just created.
I also used a simple spline with one middle point only, and constrained the spline in the middle gap to the surface/ruler dictated by the skeleton bend (used a surface extrusion to constrain the spline's middle-point to that surface). See attached.