Development of the trabecular structure within the ulnar medial coronoid process of young dogs. (57/321)

This study describes the timing of development of the trabecular structure of the ulnar medial coronoid process (MCP) in the dog. The right MCPs of nine healthy golden retrievers, aged 4 to 24 weeks, without signs of secondary joint disease were dissected and scanned with microcomputed tomography (micro-CT) at a voxel size of 34 microm to determine histomorphometric parameters. Bone volume fraction and mean trabecular separation show a reciprocal pattern in time, reflecting an initial high bone density (and low trabecular separation), and then a sharp drop in density at 8-10 weeks, followed by a gradual increase to high values at 24 weeks. With a similar bone volume fraction as in young bone, the older bone shows thicker trabeculae and a more plate-like structure. This is reflected in the much smaller number of trabeculae and the lower surface/volume ratio at higher age. An anisotropic structure of the trabeculae with an orientation in the direction of the proximodistal axis of the ulna is already present at 6 weeks after birth. This primary alignment was perpendicular to the humeroulnar articular surface, matching the direction of the compressive forces applied to the MCP by the humeral trochlea. The secondary alignment appeared at 13 weeks after birth and was directed along the craniocaudal axis of the MCP, toward the attachment of the anular ligament. In comparison with data from long bones and vertebrae, the findings of a high bone volume fraction and a well-defined trabecular alignment at a very early age are remarkable. The high bone volume fraction is possibly a remnant of the fetal trabecular structure, as dogs are relatively immature at birth compared to other animals. Soon after the start of steady locomotion, the trabecular structure changes into a more mature-like structure. The early trabecular alignment is possibly a reflection of the early load-bearing function of the MCP in the elbow joint.  (+info)

Protection from ethanol-induced limb malformations by the superoxide dismutase/catalase mimetic, EUK-134. (58/321)

Based on previous in vitro studies that have illustrated prevention of ethanol-induced cell death by antioxidants, using an in vivo model, we have tested the anti-teratogenic potential of a potent synthetic superoxide dismutase plus catalase mimetic, EUK-134. The developing limb of C57BL/6J mice, which is sensitive to ethanol-induced reduction defects, served as the model system. On their ninth day of pregnancy, C57BL/6J mice were administered ethanol (two intraperitoneal doses of 2.9 g/kg given 4 h apart) alone or in combination with EUK-134 (two doses of 10 mg/kg). Pregnant control mice were similarly treated with either vehicle or EUK-134, alone. Within 15 h of the initial ethanol exposure, excessive apoptotic cell death was observed in the apical ectodermal ridge (AER) of the newly forming forelimb buds. Forelimb defects, including postaxial ectrodactyly, metacarpal, and ulnar deficiencies, occurred in 67.3% of the ethanol-exposed fetuses that were examined at 18 days of gestation. The right forelimbs were preferentially affected. No limb malformations were observed in control fetuses. Cell death in the AER of embryos concurrently exposed to ethanol and EUK-134 was notably reduced compared with that in embryos from ethanol-treated dams. Additionally, the antioxidant treatment reduced the incidence of forelimb malformations to 35.9%. This work illustrates that antioxidants can significantly improve the adverse developmental outcome that results from ethanol exposure in utero, diminishing the incidence and severity of major malformations that result from exposure to this important human teratogen.  (+info)

Adaptations to free-fall impact are different in the shafts and bone ends of rat forelimbs. (59/321)

Impact exercise can have beneficial effects on the growing skeleton. To understand what changes it promotes in the shafts and ends of weight-bearing bones, we measured the effects of impact from repetitive free falls in growing rats. Fischer 344 female rats, 6.5 wk old, were assigned to one of three groups (n = 10 each). Controls were not dropped, whereas those subjected to impact were dropped from 30 or 60 cm. Rats in both free-fall groups were dropped 10 times per day for 8 wk. Leg bones were mechanically tested, and their cross-sectional area (CSA), cross-sectional moments of inertia, and volumetric bone mineral density (BMD) were measured by peripheral quantitative computed tomography. In the shafts of the forelimbs, but not the hindlimbs, free-fall impact resulted in greater ultimate breaking force, minimum and maximum second moments of area, and CSA but not BMD. In the bone ends of the forelimb and tibial bones, trabecular BMD increased but CSA did not. Landing from 30 and 60 cm produced peak impact forces of 12.0 and 16.7 times the standing forefoot weight for each front leg and of 4.5 and 7.7 times the standing hind foot weight for each hind foot. Overall, free-fall impact affected the forelimbs by increasing trabecular bone density in the bone ends and improving the strength at the shaft as a result of geometric improvements. These results indicate that adaptation to impact may occur by different mechanisms in bone end and shaft regions.  (+info)

The adaptive response of bone to mechanical loading in female transgenic mice is deficient in the absence of oestrogen receptor-alpha and -beta. (60/321)

Postmenopausal osteoporosis represents a failure of the response by which bone cells adapt bone mass and architecture to be sufficiently strong to withstand loading without fracture. To address why this failure should be associated with oestrogen withdrawal, we investigated the ulna's adaptive response to mechanical loading in adult female mice lacking oestrogen receptor-alpha (ERalpha(-/-)), those lacking oestrogen receptor-beta (ERbeta(-/-)) and their wild-type littermates. In wild-type mice, short periods of physiologic cyclic compressive loading of the ulna in vivo over a 2-week period stimulates new bone formation. In ERalpha(-/-) and ERbeta(-/-) mice this osteogenic response was respectively threefold and twofold less (P<0.05). In vitro, primary cultures of osteoblast-like cells derived from these mice were subjected to a single short period of mechanical strain. Twenty-four hours after strain the number of wild-type cells was 61+/-25% higher than in unstrained controls (P<0.05), whereas in ERalpha(-/-) cells there was no strain-related increase in cell number. However, the strain-related response of ERalpha(-/-) cells could be partially rescued by transfection with functional human ERalpha (P<0.05). ERbeta(-/-) cells showed a 125+/-40% increase in cell number following strain. This was significantly greater than in wild types (P<0.05).These data support previous findings that functional ERalpha is required for the full osteogenic response to mechanical loading and particularly the stage of this response, which involves an increase in osteoblast number. ERbeta appears to depress the ERalpha-mediated strain-related increase in osteoblast number in vitro, but in female transgenic mice in vivo the constitutive absence of either ERalpha or ERbeta appears to diminish the osteogenic response to loading.  (+info)

Does the degree of laminarity correlate with site-specific differences in collagen fibre orientation in primary bone? An evaluation in the turkey ulna diaphysis. (61/321)

de Margerie hypothesized that preferred orientations of primary vascular canals in avian primary cortical bone mediate important mechanical adaptations. Specifically, bones that receive habitual compression, tension or bending stresses typically have cortices with a low laminarity index (LI) (i.e. relatively lower cross-sectional areas of circularly (C) orientated primary vascular canals, and relatively higher areas of canals with radial (R), oblique (O) or longitudinal (L) orientations. By contrast, bones subject to habitual torsion have a high LI (i.e. relatively higher C-orientated canal area) [LI, based on percentage vascular canal area, = C/(C + R + O + L)]. Regional variations in predominant collagen fibre orientation (CFO) may be the adaptive characteristic mediated by LI. Using turkey ulnae, we tested the hypothesis that site-specific variations in predominant CFO and LI are strongly correlated. Mid-diaphyseal cross-sections (100 +/- 5 micro m) from subadult and adult bones were evaluated for CFO and LI using circularly polarized light images of cortical octants. Results showing significant differences between mean LI of subadult (40.0% +/- 10.7%) and adult (50.9% +/- 10.4%) (P < 0.01) bones suggest that adult bones experience more prevalent/predominant torsion. Alternatively, this relationship may reflect differences in growth rates. High positive correlations between LI and predominant CFO (subadults: r = 0.735; adults: r = 0.866; P < 0.001) suggest that primary bone can exhibit potentially adaptive material variations that are independent of secondary osteon formation.  (+info)

Ulnohumeral arthroplasty. (62/321)

Seven patients underwent 9 ulnohumeral arthroplasties for degenerative arthritis of the elbow. At mean follow-up of 26 months, 5 elbows were pain free; two continued to cause mild pain and one to cause moderate pain. Extension improved from 22 degrees+/-8 degrees preoperatively to 12 degrees+/-9 degrees postoperatively (p=0.02); the average correction was 10 degrees+/-10 degrees. Flexion improved from 122 degrees+/-8 degrees to 133 degrees +/- 8 degrees (p=0.02); the average correction was 11 degrees+/-11 degrees. One patient had a late supracondylar humerus fracture which healed well with open reduction and internal fixation. Overall, we believe that ulnohumeral arthroplasty is relatively safe and easy to perform. Our patients did have modest improvements in range of motion, but complete relief of pain occurred in only about two thirds of the patients.  (+info)

Bone formation induced by a novel form of mechanical loading on joint tissue. (63/321)

Because of insufficient mechanical loading, exposure to weightlessness in space flight reduces bone mass. In order to maintain bone mass in a weightless condition, we investigated a novel form of mechanical loading--joint loading. Since some part of gravity-induced loading to our skeletal system is absorbed by viscoelastic deformation of joint tissues, we hypothesized that deformation of joint tissues would generate fluid flow in bone and stimulate bone formation in diaphyseal cortical bone. In order to test the hypothesis, we applied directly oscillatory loading to an elbow joint of mice and conducted bone histomorphometry on the diaphysis of ulnae. Using murine femurs ex vivo, streaming potentials were measured to evaluate a fluid flow induced by joint loading. Bone histomorphometry revealed that compared to no loading control, elbow loading increased mineralizing surface, mineral apposition rate, and bone formation rate 3.2-fold, 3.0-fold, and 7.9-fold, respectively. We demonstrated that joint loading generated a streaming potential in a medullar cavity of femurs. The results support a novel mechanism, in which joint loading stimulates effectively bone formation possibly by generating fluid flow, and suggest that a supportive attachment to joints, driven passively or actively, would be useful to maintain bone mass of astronauts during an exposure to weightlessness.  (+info)

Overuse injuries of the olecranon in young gymnasts. (64/321)

We report overuse injuries in 14 elbows of ten elite young gymnasts. In 12 elbows of eight patients aged 11 to 15 years there was a spectrum of radiological abnormalities including widening of the olecranon physis and fragmentation of the epiphysis. The radiographs were compared with those of normal elbows matched for age and sex. The radiograph appearances were very similar to those of the Osgood-Schlatter lesion of the tibial tuberosity. Two older boys, aged 18 and 19, had stress fractures through the olecranon growth plate. Conservative management was successful in all except one case of stress fracture which required internal fixation.  (+info)