Clinical Study Determinants of initial bone graft volume loss in posterolateral lumbar fusion Manish K. Aghi a , Brian P. Walcott b,⇑ , Brian V. Nahed b , Gregory L. Cvetanovich c , Kristopher T. Kahle b , Navid Redjal b , Jean-Valery Coumans b,  a Department of Neurosurgery, University of California, San Francisco, CA, USA b Department of Neurosurgery, Massachusetts General Hospital and Harvard Medical School, White Building, Room 502, 55 Fruit Street, Boston, MA 02114, USA c Harvard Medical School, Boston, MA, USA article info Article history: Received 26 January 2011 Accepted 6 February 2011 Keywords: Bone graft Lumbar spine Pseudarthrosis Smoking Spinal fusion abstract Bone graft volume decreases postoperatively without known etiology. We sought to determine the bone graft volume over time in 15 consecutive patients undergoing a single-level, instrumented, posterolateral lumbar fusion for degeneration causing mechanical pain or spondylolisthesis, and to identify factors asso- ciated with bone graft resorption. Following Institutional Review Board approval, a retrospective analysis was performed. Immediate and 3-month postoperative lumbar spine CT scans were imported into imag- ing software for volumetric analysis. We found that the 15 patients averaged approximately 11% graft volume loss at 3 months postoperatively. All patients exhibited volumetric graft loss on each side (range, 0.3–45%). A paired t-test revealed that immediate postoperative graft volume on a patient’s left or right did not reflect graft volume on that side 3 months postoperatively (p = 0.0008). Gender, age, history of prior operation, history of regular exercise, body mass index, level fused, operative time, initial graft vol- ume, and laterality did not influence percentage volumetric loss (p = 0.1–0.5). Interestingly, people who smoked cigarettes (range, 10–40 pack-years) exhibited 27% graft loss, compared to 7% in those who did not (Spearman p = 0.009 graft loss versus pack-years smoked). We concluded that bone graft exhibited resorption 3 months postoperatively on both sides of all patients in this series, and that smoking was sig- nificantly associated with increased bone graft resorption. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Lumbar inter-transverse fusion is used in the treatment of spondylolisthesis or degenerative spine disease associated with mechanical lumbar pain refractory to conservative measures. In patients undergoing lumbar fusion, the bone graft volume appears to diminish over time. 1 In some patients it resorbs significantly, resulting in pseudarthrosis. Despite a recent average of more than 350,000 spinal fusions being performed annually in the USA, 2,3 the factors leading to pseudarthrosis are incompletely understood. In particular, the expected amount of bone graft volume loss and the factors affecting bone graft volume remain uncertain. Thus, we aimed to quantify the degree of volume loss in healing lumbar inter-transverse fusions and to identify related factors. 2. Methods and materials 2.1. Study design This study is a retrospective analysis of surgeries performed by the senior author at a university affiliated teaching hospital. The main outcome measure was postoperative loss of bone graft vol- ume at 3 months. Fifteen consecutive patients who underwent a single level lum- bar decompression and instrumented fusion for treatment of degenerative disease or spondylolisthesis between February 2005 and May 2006 were included. Exclusion criteria included surgical site infection and interbody grafts. 2.2. Methods Institutional Review Board approval for this study Protocol 2009-P-002795/1 was granted with assurance #FWA00003136. All patients underwent a similar surgical procedure; a single-level laminectomy, foraminotomy, insertion of pedicle screws, and bone graft. In all patients, the bone graft consisted of autologous iliac crest bone, supplemented with 30 cm 3 of freeze-dried can- cellous allograft and 5 cm 3 of demineralized bone matrix (DBX putty, Musculoskeletal Transplant Foundation, Edison, NJ, USA). The mixture was inserted following a thorough decortication of the pars interarticularis, the facet joint, and the transverse pro- cesses with a cutting burr. All patients underwent CT scans immediately after surgery and again at 3 months postoperatively. All patients were maintained in a rigid external orthosis for 3 months. 0967-5868/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jocn.2011.02.017 ⇑ Corresponding author. Tel.: +1 617 726 2000; fax: +1 617 643 4113. E-mail address: Walcott.brian@mgh.harvard.edu (B.P. Walcott).   Senior author. Journal of Clinical Neuroscience 18 (2011) 1193–1196 Contents lists available at ScienceDirect Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn