Tunturi, T., P. Niemelä, J. Laurinkari, H. Páytiälä, and P. Rokkanen. 1979. “Cost-Benefit Analysis of Posterior Fusion of the Lumbosacral Spine”. Acta Orthopaedica 50 (4):427-32. https://doi.org/10.3109/17453677908989786.