Wu, Chin-Hsien, et al. “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”. Acta Orthopaedica, vol. 79, no. 1, Jan. 2008, pp. 67-73, doi:10.1080/17453670710014789.