The Correlation Between Cage Subsidence, Bone Mineral Density, and Clinical Results in Posterior Lumbar Interbody Fusion

Study Design: A retrospective review of prospectively collected radiographic and clinical data. Objective: This study aims to investigate the relationship between cage subsidence and bone mineral density (BMD), and to reveal the clinical implications of cage subsidence. Summary of Background Data: Posterior lumbar interbody fusion (PLIF) has become one of the standard treatment modality for lumbar degenerative disease. However, cage subsidence might result in recurrent foraminal stenosis and deteriorate the clinical results. Furthermore, numbers of osteoporosis patients who underwent PLIF are increasing. Therefore, the information on the correlations between cage subsidence, BMD, and clinical results will be of great significance. Materials and Methods: A total 139 segments was included in this retrospective study. We examined functional rating index (Visual Analogue Scale for pain, Oswestry Disability Index, Short Form-36 score) preoperatively, and investigated their changes after postoperative 1 year. Correlation between cage subsidence and clinical scores was investigated. Plain anteroposterior and lateral radiograph were taken preoperatively and postoperatively and during follow-up. Preoperative BMD and subsidence measured by postoperative 1 year 3-dimensional computed tomography were achieved and their correlation was assessed. Results: All postoperative clinical scores improved significantly compared with preoperative ones (pain Visual Analogue Scale: 7.34-2.89, Oswestry Disability Index: 25.34-15.86, Short Form36: 26.45-16.46, all P< 0.001). BMD showed significant weak correlation with subsidence (r= - 0.285, P< 0.001). Severe osteoporotic segments (T score < - 3.0) had more risk to develop severe subsidence (> 3mm) compared with the segments in which T score were higher than - 3.0 (P= 0.012), and its odds ratio was 8.44. Subsidence had no significant correlation with all clinical scores. Conclusions: This study revealed that cage subsidence is relevant to BMD. However, it was demonstrated that subsidence is not related to the clinical deterioration. Therefore, PLIF procedure which is conducted carefully can be a good surgical option to treat lumbar degenerative disease for osteoporotic patients.