Subregional statistical shape modelling identifies lesser trochanter size as a possible risk factor for radiographic hip osteoarthritis, a cross-sectional analysis from the Osteoporotic Fractures in Men Study.

OBJECTIVE: Statistical shape modelling (SSM) of hip dual-energy X-ray absorptiometry (DXA) scans has identified relationships between hip shape and radiographic hip OA (rHOA). We aimed to further elucidate shape characteristics related to rHOA by focusing on subregions identified from whole-hip shape models. METHOD: SSM was applied to hip DXAs obtained in the Osteoporotic Fractures in Men Study. Whole-hip shape modes (HSMs) associated with rHOA were combined to form a composite at-risk-shape. Subsequently, subregional HSMs (cam-type and lesser trochanter modes) were built, and associations with rHOA were examined by logistic regression. Subregional HSMs were further characterised, by examining associations with 3D-HSMs derived from concurrent hip CT scans. RESULTS: 4,098 participants were identified with hip DXAs and radiographs. Composite shapes from whole-hip HSMs revealed that lesser trochanter size and cam-type femoral head are related to rHOA. From sub-regional models, lesser trochanter mode (LTM)1 [OR 0.74; 95%CI 0.63.0.87] and cam-type mode (CTM)3 [OR 1.27; 1.13.1.42] were associated with rHOA, associations being similar to those for whole hip HSMs. 515 MrOS participants had hip DXAs and 3D-HSMs derived from hip CT scans. LTM1 was associated with 3D-HSMs that also represented a larger lesser trochanter [3D-HSM7 (beta (ß)-0.23;-0.33,-0.14) and 3D-HSM9 (ß0.36; 0.27.0.45)], and CTM3 with 3D-HSMs describing cam morphology [3D-HSM3 (ß-0.16;-0.25,-0.07) and 3D-HSM6 (ß 0.19; 0.10.0.28)]. CONCLUSION: Subregional SSM of hip DXA scans suggested larger lesser trochanter and cam morphology underlie associations between overall hip shape and rHOA. 3D hip modelling suggests our subregional SSMs represent true anatomical variations in hip shape, warranting further investigation.

Reproductive status and sex show strong effects on knee OA in a baboon model.

OBJECTIVE: We aimed to characterize severity and occurrence of knee osteoarthritis (OA), and effects of age, sex, body mass, and reproductive status on population-level normal variation in this condition in the baboon, a natural model of human knee OA. METHODS: We visually inspected articular cartilage of distal right femora of 464 baboons (309 females, 155 males) and assigned an OA severity score (comparable to a modified Outerbridge score) from 1 = unaffected to 4 = advanced OA (eburnation). Presence/absence of osteophytes was recorded. We tested for significant effects of age, sex, body mass, and, in females, reproductive status (pre-, peri-, or post-menopausal) on OA. When appropriate, analyses were repeated on an age-matched subset (153 of each sex). RESULTS: Knee OA was more frequent and severe in older animals (P < 0.0001), but significant age variation was apparent in each severity grade. Sex differences within the younger and older age groups suggest that males develop knee OA earlier, but females progress more quickly to advanced disease. There is a strong relationship between reproductive status and OA severity grade in females (P = 0.0005) with more severe OA in peri- and post-menopausal female baboons, as in humans. CONCLUSIONS: Idiopathic knee OA is common in adult baboons. Occurrence and severity are influenced strongly by reproductive status in females, and by sex with regard to patterns of disease progression - providing an animal model to investigate sex-specific variation in OA susceptibility in which the environmental heterogeneity inherent in human populations is vastly reduced.

Heritability of lumbar trabecular bone mechanical properties in baboons.

Genetic effects on mechanical properties have been demonstrated in rodents, but not confirmed in primates. Our aim was to quantify the proportion of variation in vertebral trabecular bone mechanical properties that is due to the effects of genes. L3 vertebrae were collected from 110 females and 46 male baboons (6-32 years old) from a single extended pedigree. Cranio-caudally oriented trabecular bone cores were scanned with microCT then tested in monotonic compression to determine apparent ultimate stress, modulus, and toughness. Age and sex effects and heritability (h(2)) were assessed using maximum likelihood-based variance components methods. Additive effects of genes on residual trait variance were significant for ultimate stress (h(2)=0.58), toughness (h(2)=0.64), and BV/TV (h(2)=0.55). When BV/TV was accounted for, the residual variance in ultimate stress accounted for by the additive effects of genes was no longer significant. Toughness, however, showed evidence of a non-BV/TV-related genetic effect. Overall, maximum stress and modulus show strong genetic effects that are nearly entirely due to bone volume. Toughness shows strong genetic effects related to bone volume and shows additional genetic effects (accounting for 10% of the total trait variance) that are independent of bone volume. These results support continued use of bone volume as a focal trait to identify genes related to skeletal fragility, but also show that other focal traits related to toughness and variation in the organic component of bone matrix will enhance our ability to find additional genes that are particularly relevant to fatigue-related fractures.

Substitutes for human cadaveric bone in maxillofacial rigid fixation research.

OBJECTIVE: Various materials have been used as human bone substitutes in rigid fixation research. We hypothesize that these substitutes behave differently than human cadaveric bone in maxillofacial research. STUDY DESIGN: Screw insertion torque and pull-out strength of titanium maxillofacial self-tapping bone screws (1.0 mm and 2.4 mm outer diameter) were measured in cadaveric mandible and in the following materials: bovine rib, porcine rib, photoelastic epoxy, red oak, and 2 types of synthetic mandibles. Results were tested for statistically significant differences (unpaired t test, P <.05) in comparison with human bone. RESULTS: For 1.0-mm screws, statistically significant differences were found for the synthetic mandibles groups and oak groups for insertion torque and porcine rib for pull-out strength. For 2.4-mm screws, statistically significant differences were found for the porcine rib and oak groups for insertion torque and the bovine rib and epoxy groups for pull-out strength. CONCLUSION: The results suggest that human bone can be simulated in fixation studies with bone substitute materials.