Abstract
ObjectiveDecreased bone mineral density (BMD) impairs screw purchase in trabecular bone and can cause screw loosening following spinal instrumentation. Existing computed tomography (CT) scans could be used for opportunistic osteoporosis screening for decreased BMD. Purpose of this case-control study was to investigate the association of opportunistically assessed BMD with the outcome after spinal surgery with semi-rigid instrumentation for lumbar degenerative instability.MethodsWe reviewed consecutive patients that had primary surgery with semi-rigid instrumentation in our hospital. Patients that showed screw loosening in follow-up imaging qualified as cases. Patients that did not show screw loosening or—if no follow-up imaging was available (n = 8)—reported benefit from surgery ≥ 6 months after primary surgery qualified as controls. Matching criteria were sex, age, and surgical construct. Opportunistic BMD screening was performed at L1 to L4 in perioperative CT scans by automatic spine segmentation and using asynchronous calibration. Processing steps of this deep learning-driven approach can be reproduced using the freely available online-tool Anduin (https://anduin.bonescreen.de). Area under the curve (AUC) was calculated for BMD as a predictor of screw loosening.ResultsForty-six elderly patients (69.9 ± 9.1 years)—23 cases and 23 controls—were included. The majority of surgeries involved three spinal motion segments (n = 34). Twenty patients had low bone mass and 13 had osteoporotic BMD. Cases had significantly lower mean BMD (86.5 ± 29.5 mg/cm³) compared to controls (118.2 ± 32.9 mg/cm³, p = 0.001), i.e. patients with screw loosening showed reduced BMD. Screw loosening was best predicted by a BMD < 81.8 mg/cm³ (sensitivity = 91.3%, specificity = 56.5%, AUC = 0.769, p = 0.002).ConclusionPrevalence of osteoporosis or low bone mass (BMD ≤ 120 mg/cm³) was relatively high in this group of elderly patients undergoing spinal surgery. Screw loosening was associated with BMD close to the threshold for osteoporosis (< 80 mg/cm³). Opportunistic BMD screening is feasible using the presented approach and can guide the surgeon to take measures to prevent screw loosening and to increase favorable outcomes.
Highlights
Osteoporosis is the most common metabolic bone disease [1]
We present a new screening approach for decreased bone mineral density (BMD) that involves automatic spine segmentation by a fully convolutional neural network and requires little user interaction [27, 28]. In this case-control study we investigate the association of opportunistically assessed BMD with screw loosening in patients undergoing spinal surgery with semi-rigid instrumentation in the treatment of lumbar degenerative instability
We conducted a case-control study to investigate whether opportunistically assessed BMD is associated with the risk of screw loosening after spinal surgery with semi-rigid instrumentation for indications of lumbar degeneration
Summary
Predisposing the individual to an increased risk of fracture osteoporosis is characterized by compromised bone strength due to decreased bone mineral density (BMD) [2]. A higher incidence of indications for spinal surgery overlaps with a higher prevalence of osteoporosis [3, 4]. The intended motion in the upper most instrumented segment puts additional forces on the screw-bone interface, which is likely to cause increased rates of screw loosening. Screw loosing is caused by multiple factors that can be categorized into mechanical load and screw-bone purchase. The former is influenced by sagittal balance and body mass index (BMI), the latter by bone quality and BMD
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call