Quantitative Analysis of Temporal Bone Density and Thickness for Robotic Ear Surgery

Background and Objective: Quantitative assessment of bone density and thickness in computed-tomography images offers great potential for preoperative planning procedures in robotic ear surgery.Methods: We retrospectively analyzed computed-tomography scans of subjects undergoing cochlear implantation (N = 39). In addition, scans of Thiel-fixated ex-vivo specimens were analyzed (N = 15). To estimate bone mineral density, quantitative computed-tomography data were obtained using a calibration phantom. The temporal bone thickness and cortical bone density were systematically assessed at retroauricular positions using an automated algorithm referenced by an anatomy-based coordinate system. Two indices are proposed to include information of bone density and thickness for the preoperative assessment of safe screw positions (Screw Implantation Safety Index, SISI) and mass distribution (Column Density Index, CODI). Linear mixed-effects models were used to assess the effects of age, gender, ear side and position on bone thickness, cortical bone density and the distribution of the indices.Results: Age, gender, and ear side only had negligible effects on temporal bone thickness and cortical bone density. The average radiodensity of cortical bone was 1,511 Hounsfield units, corresponding to a bone mineral density of 1,145 mg HA/cm3. Temporal bone thickness and cortical bone density depend on the distance from Henle's spine in posterior direction. Moreover, safe screw placement locations can be identified by computation of the SISI distribution. A local maximum in mass distribution was observed posteriorly to the supramastoid crest.Conclusions: We provide quantitative information about temporal bone density and thickness for applications in robotic and computer-assisted ear surgery. The proposed preoperative indices (SISI and CODI) can be applied to patient-specific cases to identify optimal regions with respect to bone density and thickness for safe screw placement and effective implant positioning.

Abstract P002: Associations Of Bone Fracture Outcomes With Body Compositions Measurements In A Fragility Fracture Clinic Population

Introduction: While preoperative bone health optimization is typical in the fragile population, objective assessment is limited. Among the aged, localized discordance in bone loss is prevalent and may not be assessed properly with traditional diagnostic measures. Etiology for bone loss discordance is unknown, but may be attributed to aging, disease state, habitus, or activity. This study investigated the association between body composition measures and common fragility fractures. Hypothesis: We hypothesized that each different fracture outcome would associate differently with measures of body composition. Methods: The Fragility Fracture Clinic at the University of Michigan provides comprehensive care to promote bone health, accelerate healing, and reduce fracture risk in those with and at-risk for fractures. Participants (N=344) included those who enrolled at the clinic between 2013 and 2020 and received an abdomen and/or pelvis computed tomography (CT) scan up to 120 days prior to initial enrollment date. Fracture categorizations included acute vs. non-acute, intensity (high vs. low energy), and location (thoracic vs. lumbar vertebral). Retrospective CT-scans were obtained from the University of Michigan Picture Archive and Communication System. Analytic Morphomics was used to obtain granular vertebral-indexed measurements of vertebral bone density, fascia, adipose tissue, muscle, vasculature, and interior body dimensions. Relevant measures include bone mineral density (BMD) [vertebral body trabecular bone density in Hounsfield Units (HU)], lower muscle group density in HU (DMG) (cross sectional area of DMG in HU range of 31-100), cortical bone density [anterior cortical half-maximum (in HU)], and fascial width (in mm). Measurements were divided by their standard deviation to ease interpretation of odds ratios. Multivariable logistic regression was used to evaluate the relationship between body measures and fracture type. Coefficients are reported as odds ratio (OR) and 95% confidence interval (CI). An alpha level of 0.05 determine statistical significance. Results: Associations were observed between acute fracture and BMD at L3 [OR 0.58, 95% CI 0.36-0.85]; high energy fracture and DMG at L3 [OR 2.08, 1.05-4.64]; low energy fracture and BMD at T8 [OR 0.39, 0.17-0.81]; thoracic vertebral fractures and BMD at T11 [OR 0.39, 0.17-0.81], cortical bone density at T11 [OR 0.64, 0.40-0.95], and fascial width at L4 [OR 0.67, 0.43-0.98]; lumbar vertebral fracture and BMD at L3 [OR 0.44, 95% CI 0.20-0.88]. Conclusion: Body composition measures uniquely associated with fracture outcomes. Lower vertebral trabecular bone density was associated with acute, high energy, thoracic vertebral, and lumbar vertebral fractures; lower lean muscle with high energy fractures; cortical bone density and facial (i.e. visceral cavity) width with thoracic vertebral fractures.

Effects of Intrabony Length and Cortical Bone Density on the Primary Stability of Orthodontic Miniscrews

Miniscrews have gained recent popularity as temporary anchorage devices in orthodontic treatments, where failure due to sinus perforations or damage to the neighboring roots have increased. Issues regarding miniscrews in insufficient interradicular space must also be resolved. This study aimed to evaluate the primary stability of miniscrews shorter than 6 mm and their feasibility in artificial bone with densities of 30, 40, and 50 pounds per cubic foot (pcf). The primary stability was evaluated by adjusting the intrabony miniscrew length, based on several physical properties: maximum insertion torque (MIT), maximum removal torque (MRT), removal angular momentum (RAM), horizontal resistance, and micromotion. The MIT and micromotion results demonstrated that the intrabony length of a miniscrew significantly affected its stability in low-density cortical bone, unlike cases with a higher cortical bone density (p < 0.05). The horizontal resistance, MRT, and RAM were affected by the intrabony length, regardless of the bone density (p < 0.05). Thus, the primary stability of miniscrews was affected by both the cortical bone density and intrabony length. The effect of the intrabony length was more significant in low-density cortical bone, where the implantation depth increased as more energy was required to remove the miniscrew. This facilitated higher resistance and a lower risk of falling out.

Association between forearm cortical bone properties and handgrip strength in women with distal radius fractures: A cross-sectional study

Objectives Mechanical and biochemical bone properties are influenced by muscles. However, the muscle-bone interaction has not been fully elucidated regarding the upper extremities. The objective of the present study was to evaluate the mechanical muscle-bone interaction at the forearm by evaluating the relationship between the properties of three-dimensional (3D) forearm cortical bone models derived from conventional computed tomography (CT) images and handgrip strength (HGS). Methods A total of 108 women (mean age, 75.2 ± 9.4 years; range, 62–101 years) with a distal radius fracture who took conventional CT scans for the assessment of the fracture were included in this study. Distal radius 3D models were reconstructed and the average cortical bone density (Cd) and thickness (Ct) of the region of interest (ROI), which might be affected by the forearm flexor muscles, were calculated using a 3D modeling software. Clinical parameters including HGS, lumbar and hip bone mineral densities (BMDs), and other demographic factors were also obtained. A multivariate linear regression analysis was performed to identify relevant factors associated with HGS. Results HGS was found to be independently associated with height and Cd, but no significant difference was found between HGS and Ct, age, weight, as well as lumber and hip BMDs. Conclusions Cortical bone density might be associated with HGS, which is generated by the forearm flexor muscles. Hence, the mechanical muscle-bone interaction in the upper extremities could be supported by the present study.

Primary Stability of Orthodontic Titanium Miniscrews due to Cortical Bone Density and Re-Insertion

The increasing demand for orthodontic treatment over recent years has led to a growing need for the retrieval and reuse of titanium-based miniscrews to reduce the cost of treatment, especially in patients with early treatment failure due to insufficient primary stability. This in vitro study aimed to evaluate differences in the primary stability between initially inserted and re-inserted miniscrews within different cortical bone densities. Artificial bone was used to simulate cortical bone of different densities, namely 20, 30, 40, and 50 pound per cubic foot (pcf), where primary stability was evaluated based on maximum insertion torque (MIT), maximum removal torque (MRT), horizontal resistance, and micromotion. Scanning electron microscopy was used to evaluate morphological changes in the retrieved miniscrews. The MIT, MRT, horizontal resistance, and micromotion was better in samples with higher cortical bone density, thereby indicating better primary stability (P < 0.05). Furthermore, a significant reduction of MIT, MRT, and horizontal resistance was observed during re-insertion compared with the initial insertion, especially in the higher density cortical bone groups. However, there was no significant change in micromotion. While higher cortical bone density led to better primary stability, it also caused more abrasion to the miniscrews, thereby decreasing the primary stability during re-insertion.