Your description is a little vague. Was the wrist in 45 degrees or the elbow in 45 degrees. I am thinking the wrist? I would not think that the position would be the factor involved here. More likely the patient moving the joing around to much post the surgery. A back slab isn't always that supportive and there are a number of things one needs to ensure are done to maintain the position. The 45 degress for the longer period would just have perhaps been overkill leading to some wrist stiffness which might have been lessened if the wrist was placed back in neutral following.

Overall my opinion would be that we couldn't advise on this one as there are so many factors that could be involved. The cast position in the second 2 weeks is perhaps least likely.