C.-H. Wu, Y.-H. Kao, S.-C. Yang, T.-S. Fu, P.-L. Lai, and W.-J. Chen, “Supplementary pedicle screw fixation in spinal fusion for degenerative spondylolisthesis in patients aged 65 and over: Outcome after a minimum of 2 years follow-up in 82 patients”, ActaO, vol. 79, no. 1, pp. 67–73, Jan. 2008.