Postmenopausal Women Presenting for Spinal Fusion Surgery Have Abnormal Microarchitecture Despite Normal DXA

BACKGROUND CONTEXT More than 400,000 spinal fusion surgeries are performed annually in the US, with related health care costs exceeding $287 billion. As spinal fusion involves extensive instrumentation of the vertebrae, patients with skeletal abnormalities may be at increased risk for complications. However, preoperative identification of high-risk patients remains a challenge. Due to skeletal effects of aging and estrogen deficiency, postmenopausal (PM) women may be at particular risk. Dual energy x-ray absorptiometry (DXA) measurements of areal BMD are subject to artifact in patients with spinal pathology, and may be limited as screening tests. PURPOSE This prospective study investigated skeletal health in postmenopausal women having lumbar spine fusion and matched controls using DXA and high resolution peripheral QCT (HRpQCT) measurements of volumetric BMD (vBMD) and microarchitecture. We aimed to determine if HRpQCT would reveal additional abnormalities in vBMD and microarchitecture in fusion patients compared to DXA. STUDY DESIGN/SETTING Prospective, single center study. PATIENT SAMPLE A total of 60 patients were included in this study. PM women undergoing lumbar fusion were prospectively enrolled and compared to PM controls. OUTCOME MEASURES HRpQCT measurements of cortical and trabecular vBMD and microarchitecture, DXA, age and BMI. METHODS PM women undergoing lumbar fusion (n=20) were matched 1:2 by age with PM controls (n=40) who had no history of spine surgery or secondary osteoporosis. Subjects had assessments by standard DXA and high resolution peripheral QCT (HRpQCT) to measure cortical (Ct) and trabecular (Tb) vBMD and microarchitecture of the distal radius and tibia. RESULTS Mean age of subjects was 66+/-6 years, BMI (28+/-6 kg/m2) without any significant differences between groups. By DXA, T-scores in fusion patients were normal at the lumbar spine (mean 0.0) and osteopenic at the total hip (-1.2), femoral neck (-1.5) and 1/3 radius (-1.5). T- Scores did not differ significantly from controls at any site. In contrast, HRpQCT revealed low vBMD (total, Ct, Tb) in fusion patients compared to controls at both radius and tibia, with total vBMD 21-30% lower, Ct density ∼7% and Tb density ∼25% lower. Fusion patients had microarchitectural abnormalities, significantly fewer, thinner and more widely spaced trabeculae. Specifically, Tb number was 9% lower, Tb thickness 6% lower, and Tb separation 23% greater at the radius with similar differences at the tibia. CONCLUSIONS In summary, PM women presenting for spine fusion surgery had low volumetric BMD and abnormal trabecular microarchitecture, despite DXA values that were normal or slightly low. Our results suggest that additional techniques may be necessary for detection of bone quality deficits in patients presenting for spinal fusion. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.