Biomedical subjects

T C Sun

Publications and source records attributed to T C Sun.

5 recordsLinked to original sources

PubMed1995

High frequency components of bone strain in dogs measured during various activities.

Rubin et al. [J. Biomechanics 23, 43-54 (1990)] proposed that high frequency bone strains in the 15-30 Hz range might have significant influence on the morphological adaptation of bone tissue. We sought to further their findings by determining the magnitude of high frequency strains during various activities. We measured strains in the forelimbs of dogs during walking, standing and with their limbs unweighted. As negative controls, we measured strains while the dogs were tranquilized and after sacrifice. Strains in the 15-30 Hz range were not significantly greater than controls for any activity except walking, in which they were less than 4% as large as in the 0-15 Hz range. The high frequency strains observed during walking seemed to occur prior to footfall, suggesting that they were not the result of foot strike. The biological significance of high frequency bone strains has yet to be determined, but may be less than originally proposed because of the relatively small magnitude of these strains.

Adaptation, Physiological↗

PubMed1994

The effects of muscle fatigue on bone strain.

There is anecdotal evidence that bone strains may increase to the point that bone becomes susceptible to rapid failure when muscles become fatigued. To determine whether neuromuscular response could be a factor in accelerating bone failure, we tested the hypothesis that muscle fatigue causes a significant increase in peak principal and shear strains in bone. Ten adult foxhounds were subjected to rigorous exercise that caused muscular fatigue while myoelectrical activity of the quadriceps and hamstrings and strain on the distal tibia were monitored simultaneously. Ground reaction forces on the dog hindlimbs were measured before and after strain gauges had been applied to the tibia. The data show a significant shift to lower median myoelectrical frequencies in the quadriceps, indicating muscular fatigue, following the 20 min exercise period. In conjunction with this shift, peak principal and shear strains increased on both compressive and tensile cortices of the tibia and shear strain on the tensile cortex increased significantly (P = 0.02). The largest changes were along the anterior and anterolateral surfaces of the tibia, where peak principal strain increased by an average of 26-35% following muscular fatigue. The cross-sectional strain distribution was calculated at the gauge site at peak strain at the beginning of the exercise period and at peak strain after 20 min of exercise. These data show a change in strain distribution when muscle becomes fatigued. Strains on the posterior cortex of the bone showed the greatest change. Correlation analysis demonstrated a significant inverse association between median myoelectrical frequency and bone strain after 20 min of exercise (Spearman r2 = 1.00; P = 0.05). These data show that muscle fatigue may be associated with increased bone strain.

Animals↗

PubMed1993

Histomorphometric assessment of the mechanisms for rapid ingrowth of bone to HA/TCP coated implants.

The purpose of this work is to use dynamic histomorphometry to evaluate the basic biological mechanisms by which hydroxyapatite/tricalcium phosphate (HA/TCP) implant coatings accelerate bone formation rates. Twenty-five rabbits had an HA/TCP coated cylindrical titanium fiber metal mesh implant surgically placed in the subchondral bone of the proximal tibia and a noncoated implant placed in the contralateral tibia. Twenty-two of these animals had HA/TCP coated cylindrical solid titanium implants placed in the distal femur and an uncoated implant placed in the contralateral femur. The animals were double labeled with vital stains, and sacrificed at 3, 6, 16, or 26 weeks after surgery. Histomorphometric analyses were done of the bone implant interfaces. Both static and dynamic histomorphometric parameters indicate that HA/TCP coatings stimulate faster bone ingrowth to coated fiber metal implants through the early production of woven bone and by subsequent rapid lamellar bone formation rates. Coated fiber metal implants demonstrated significantly more bone ingrowth than noncoated implants through 16 weeks postimplantation, but not by 26 weeks. In solid implants, the differences between coated and noncoated implants are less pronounced and not statistically significant, although there is a trend toward increased bone apposition to the surface of the implants over the first 16 weeks following implantation. The clinical significance of these results is that coated implants may allow earlier return to normal weightbearing.

Alloys↗

PubMed1992

Do different fluorochrome labels give equivalent histomorphometric information?

Substances that bind calcium are given to determine where and how fast bone is forming. Several vital dyes are used (tetracycline, calcein, alizarin, xylenol), but it is not known whether the histomorphometric results they provide are equivalent. This work tests whether different fluorochrome labels give the same results when they are quantitatively measured. Twelve-week-old rats (n = 58) were divided into six groups and given double labels IP of calcein, tetracycline HCl, alizarin complexone, or xylenol using a 1-7-1 scheme. Two other groups received either calcein followed by tetracycline, or tetracycline followed by calcein. Our results show that (a) tetracycline hydrochloride leads to a significant underestimation of mineralizing surface when given as the second label, probably because of its weak fluorescence; (b) there were no differences among any of the non-tetracycline labels for any of the histomorphometric measurements; (c) there was no evidence of osteoblast suppression with any label; and (d) there was no evidence that tetracycline caused increased osteoblast resting periods.

Animals↗

PubMed1985

Chondrosarcoma in Maffucci's syndrome.

Nine patients with Maffucci's syndrome were seen at our institution; chondrosarcoma developed in five. On the basis of the cases of these patients and those reported in the English literature since 1973, we determined that the incidence of chondrosarcoma in patients with Maffucci's syndrome is 17.8 per cent.

Adolescent↗