Evaluation of metabolic bone disease as a risk factor for lumbar fusion

Abstract

Purpose of study: To evaluate the effect of metabolic bone disease on the success rate of lumbar fusion.Methods used: Over a 4-year period (1992–1996), iliac crest specimens were procured at the time of lumbar spine fusion surgery from 197 patients undergoing L4 to S1 fusion procedures. Patients were followed up for a minimum of 4 years with regular clinical and radiographic evaluations. The specimens were analyzed with histomorphometric techniques looking at multiple parameters, including trabecular bone volume, mineralized trabecular bone volume, osteoid volume, osteoid surface, osteoid thickness, trabecular thickness, eroded surface, trabecular number, and trabecular separation. Clinical parameters were collected prospectively and entered into a database using Excel spreadsheet software. Radiographic categories included not fused, questionably fused and definitely fused.of findings: There were 197 patients included in the study, of which 92 were female and 105 male. There were 183 white, 6 Hispanic, 7 black and 1 Asian patients. One hundred eighty-nine of the 197 patients (96%) underwent laminectomy +/− discectomy procedure in addition to the fusion from L4 to S1. Of the 197 patients, 114 had TSRH instrumentation, 36 had Long Beach instrumentation, 18 had CD instrumentation, 4 had Zielke instrumentation and 25 were done without instrumentation. All patients were primary fusions, and all patients' fusions were carried out with autogenous iliac crest bone graft. Sixty-six of the patients (34%) were nonsmokers with another 28 being smokers who were able to quit after surgery. Of the 172 patients that had instrumented fusions, definite fusion occurred in 151 (88%), with 5 (3%) being questionably fused and 16 (9.3%) being considered nonfused. Fusion criteria was determined by anteroposterior left and right bending films along with flexion extension lateral views and oblique views. Of the 25 patients treated without instrumentation, 18 went on to definite fusion (72%), with 2 being considered questionably fused (8%) and 5 being considered nonfused (20%). In review of the histomophometric data, the trabecular bone volume percent did not correlate with fusion success and, in fact, there was a trend to suggest that patients with greater osteoid volume and osteoid surfaces, indicating metabolic turnover such as seen in osteoporotic states, actually lent to better fusion success rates. Patients with more quiescent bone states with higher bone density and volume and less osteoid tended to have lower fusion rates. There was also a correlation with higher trabecular density and bone volume in patients in the middle decades of life, such as the fourth and fifth decades. Patients in the older decades were found to have less trabecular volume on average and greater trabecular separation distances.Relationship between findings and existing knowledge: There has been very little published in regard to the effect of metabolic bone disease in osteoporosis on lumbar fusion. Throughout the literature, however, it is often alluded to as a “risk factor” for lumbar fusion. This paper attempts to study this matter in a scientific manner and provides some data that is more objective in regard to this issue.Overall significance of findings: This paper is the first known attempt to scientifically evaluate the effect of metabolic bone disease and osteoporosis on lumbar fusion. It provides a basic science approach to this matter, with histomorphometeric analysis of iliac crest specimens from patients who had undergone posterolateral lumbar fusion.Disclosures: No disclosures.Conflict of interest: No conflicts.