Opportunistic Osteoporosis Screening Reveals Low Bone Density in Patients With Screw Loosening After Lumbar Semi-Rigid Instrumentation: A Case-Control Study

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.

Automatic opportunistic osteoporosis screening in routine CT: improved prediction of patients with prevalent vertebral fractures compared to DXA

“…In contrast to these previous studies, we report on calibrated bone measures (aBMD, vBMD, or BMC) that were fully automatically extracted using fast and reliable CNNs. Using an earlier version of this automatic framework we were able to predict screw loosening after lumbar spinal instrumentation in patients with osteoporotic trabecular vBMD [40]. Given that integral vBMD performed almost as good as trabecular vBMD, it would be convenient to have diagnostic thresholds available for integral vBMD that define osteoporosis and low bone mass similar to those defined by the ACR for trabecular vBMD [24]-an idea that has been previously proposed [27].…”

Texture Analysis Using CT and Chemical Shift Encoding-Based Water-Fat MRI Can Improve Differentiation Between Patients With and Without Osteoporotic Vertebral Fractures

“…Although vertebral body segmentation as well as texture analysis are not part of the clinical routine, approaches are feasible without considerable computational efforts. In detail, CT image segmentation and vBMD extraction are already established, automated, computationally optimized, and their computational effort can therefore be considered negligible in comparison to the remaining tasks (when implementing a pipeline such as the herein used CNN-based framework for vertebral body labeling and segmentation with parameter extraction) (43)(44)(45). Details on the computational efficiency of the water-fat separation for generating PDFF and T2* maps have been reported previously for a similar workflow (49).…”

“…From PACS, images were transferred to our in-house developed, convolutional neural network (CNN)-based framework (https:// anduin.bonescreen.de) (Figures 1 and 2) (43)(44)(45). This tool identifies and labels each vertebra in an automated process, followed by creating corresponding segmentation masks for each vertebra as well as its subregions.…”

“…This tool identifies and labels each vertebra in an automated process, followed by creating corresponding segmentation masks for each vertebra as well as its subregions. Furthermore, it adjusts for the used scanner, scanning parameters, and contrast media (if administered during imaging) to asynchronously convert measured HU into vBMD (43)(44)(45).…”

MR-based proton density fat fraction (PDFF) of the vertebral bone marrow differentiates between patients with and without osteoporotic vertebral fractures

“…Even though, it is well known, that bone marrow edema (BME) in MR imaging may be helpful for differentiating between acute high-energy traumatic and chronic low-energy osteoporotic fractures [ 54 ], in this study, the presence of BME was not analyzed. However, while BME is mostly absent in later phase after osteoporotic vertebral fractures, it is regularly found in the acute phase of the osteoporotic fracture as well [ 55 ], even if the findings may be more subtle than in high-energy traumatic fractures. Further more detailed analyses regarding the difference of the edema in high-energy traumatic and low-energy osteoporotic fractures (acute and chronic) are needed in future studies.…”