Biomedical subjects

J C Lotz

Publications and source records attributed to J C Lotz.

39 records · Page 3Linked to original sources

PubMed1989

Biomechanical properties of the proximal femur determined in vitro by single-energy quantitative computed tomography.

To assess the use of quantitative computed tomography as an in vivo predictor of fracture in the osteoporotic hip, we examined the in vitro relationship between single-energy quantitative computed tomography data, calibrated for scanner drift, and the mechanical properties of trabecular bone from the proximal femur. For 49 samples, the apparent density and ultimate strength were measured and their functional relationship to the computed tomography data determined. Apparent density demonstrated a moderate linear correlation to the computed tomography numbers (R2 = 0.60), and the ultimate strength was related through a power law (R2 = 0.83). In addition, for 8 intact femora, average computed tomographic data from the sub-capital region were moderately correlated to the ultimate fracture load applied under controlled in vitro conditions (R2 = 0.64). The average fracture energy for these femora was 43 J, a value more than an order of magnitude less than the energy available in a fall from standing height, suggesting that fall mechanics are a more important determinant of fracture risk than has been previously thought. The relationship between the energy absorbed to failure and the computed tomography data was best described by a power law (R2 = 0.90). Based on these results, it appears that quantitative computed tomography provides a potentially useful approach for the direct estimate of that component of fracture risk that can be attributed to a reduction in bone strength.

Aged↗

PubMedDate not supplied

The effect of static in vivo bending on the murine intervertebral disc.

BACKGROUND CONTEXT: Intervertebral disc cell function in vitro has been linked to features of the local environment that can be related to deformation of the extracellular matrix. Epidemiologic data suggest that certain regimens of spinal loading accelerate disc degeneration in vivo. Yet, the direct association between disc cell function, spinal loading and ultimately tissue degeneration is poorly characterized. PURPOSE: To examine the relationships between tensile and compressive matrix strains, cell activity and annular degradation. STUDY DESIGN/SETTING: An in vivo study of the biologic, morphologic and biomechanical consequences of static bending applied to the murine intervertebral disc. SUBJECT SAMPLE: Twenty-five skeletally mature Swiss Webster mice (12-week-old males) were used in this study. OUTCOME MEASURES: Bending neutral zone, bending stiffness, yield point in bending, number of apoptotic cells, annular matrix organization, cell shape, aggrecan gene expression, and collagen II gene expression. METHODS: Mouse tail discs were loaded for 1 week in vivo with an external device that applied bending stresses. Mid-sagittal sections of the discs were analyzed for cell death, collagen II and aggrecan gene expression, and tissue organization. Biomechanical testing was also performed to measure the bending stiffness and strength. RESULTS: Forceful disc bending induced increased cell death, decreased aggrecan gene expression and decreased tissue organization preferentially on the concave side. By contrast, collagen II gene expression was symmetrically reduced. Asymmetric loading did not alter bending mechanical behavior of the discs. CONCLUSIONS: In this model, annular cell death was related to excessive matrix compression (as opposed to tension). Collagen II gene expression was most negatively influenced by the static nature of the loading (immobilization), rather than the specific state of stress (tension or compression).

Analysis of Variance↗

PubMedDate not supplied

Mechanical properties of trabecular bone from the proximal femur: a quantitative CT study.

We have investigated the relationships between trabecular bone compressive strength and elastic modulus and the directly measured apparent density and noninvasively measured CT equivalent mineral density for 49 cylindrical specimens harvested from fresh human proximal femora. Compressive strength demonstrated a high positive correlation with both densities, being proportional to the apparent density raised to the 1.8 power (R2 = 0.93) and equivalent mineral density to the 1.5 power (R2 = 0.89). Similarly, the compressive modulus demonstrated a high correlation with both density measures, being proportional to the apparent density raised to the 1.4 power (R2 = 0.91) and CT equivalent mineral density to the 1.2 power (R2 = 0.90). Though variations in architecture and bone marrow fat were observed to influence trabecular properties, the data presented here demonstrate that apparent density, compressive strength, and elastic modulus can be determined accurately using single energy quantitative CT. We expect that the use of these noninvasive data will result in improved estimates of that component of hip fracture risk that is attributable to bone strength.

Biomechanical Phenomena↗