Biomedical subjects

H T Aro

Publications and source records attributed to H T Aro.

58 records · Page 4Linked to original sources

PubMed1990

The effects of physiologic dynamic compression on bone healing under external fixation.

The effects of early physiologic dynamic compression on fracture healing were studied in the dog. Transverse midtibial osteotomies were performed bilaterally and stabilized with a relatively rigid external fixation system in a neutralization mode (800 microns) to prevent compression of the osteotomy ends during weight bearing. On the 15th day, one osteotomy in each animal was subjected to dynamic compression through weight bearing by release of the fixator-telescoping mechanism (axial dynamization), while the other side remained unchanged as the control. Analysis of sequential roentgenograms showed that the callus distribution was more symmetric on the dynamic compression side. The two sides showed no significant differences in quantitative technetium-99 bone scans or in osteotomy-site blood flow. There were no statistical differences in new bone formation, bone porosity, or maximum torque between sides. The fixation had maintained the initially created osteotomy gap on the control side and tended to unite through a gap-healing mechanism. The dynamic compression side showed reduction in gap size and union by more of a contact-healing mechanism. There were no statistical differences in the rate of pin loosening, but its distribution according to pin location was significantly different between the two sides.

Animals↗

PubMed1989

The effect of rigidity on fracture healing in external fixation.

Knowledge of the basic biomechanics of external fixation is necessary to obtain the full benefits of the technique for bone fracture treatment. The rigidity of external fixation, including pin-bone interface stresses, is discussed and bone healing and remodeling under different fixation stiffnesses and fracture gap conditions are described. The rigidity of fixation ultimately depends on the biomechanical characteristics of the fracture, the accuracy of reduction, and the amount of physiologic loading. Comparative experiments using a canine tibial fracture model have suggested that fixation rigidity is important in early bone healing and in the prevention of pin loosening. Bone union can be achieved under external fixation through different pathways, ranging from callus-free gap healing under a rigid neutralization configuration to direct-contact healing with periosteal new bone formation under axially dynamized stable fixation. Cortical reconstruction by secondary osteons seems to be important for the ultimate strength of the bone union.

Animals↗

PubMed1989

Prediction of properties of fracture callus by measurement of mineral density using micro-bone densitometry.

UNLABELLED: An experiment was designed to determine whether the material properties of fracture callus can be predicted by the measurement of mineral density. Rat tibiae that had a closed fracture were used to obtain uniform specimens of fracture callus at sequential stages of healing. An in vitro indentation test was done and tissue was biopsied, using a trephine, to determine the hardness and calcium content of a standardized area of callus tissue. The hardness of the callus was correlated with the mineral density of the local tissue, which initially had been measured non-invasively with single-photon-based micro-bone densitometry. The progress of differentiation and remodeling of callus was determined by comparative planimetric and microradiographic analyses of tissue. Determinations of density showed a linear correlation with concentrations of a hydroxyapatite equivalent solution (r = 0.997, p less than 0.001), with the ash weight of control specimens of cortical-trabecular bone (r = 0.998, p less than 0.001), and with the calcium content (micrograms per cubic millimeter) of the fracture callus (r = 0.854, p less than 0.001). The hardness of the callus had a non-linear relationship (r = 0.959, p less than 0.005) with the mineral density per volume of tissue, as measured by micro-bone densitometry. CLINICAL RELEVANCE: The appearance of fracture callus on conventional radiographs is an important clinical finding in the assessment of fracture-healing. It is, however, an unreliable predictor of the strength of the union of the fracture. Three-dimensional imaging and quantification of bone mineral provide additional data about the quality and geometry of fracture callus. Our study showed that mineral content per unit of volume is a good index of hardness of the fracture callus. Thus, quantitative imaging may be useful clinically for monitoring fracture-healing.

Animals↗

PubMed1989

Mechanical performance of pin clamps in external fixators.

Insufficient holding strength on a pin within a clamp may result in the diminution of the overall fixation rigidity as well as pin movement at the pin-bone interface. In this study the holding strength of pin fixation clamps in two representative external fixators (Hoffmann and Orthofix) was evaluated by determination of the torque resistance of pins within a clamp. In the standard Hoffman clamp, the pin-clamping effect was satisfactory in the symmetric two-, three-, and four-pin configurations, whereas the standard Orthofix clamp provided higher holding strength in the symmetric two- and three-pin configurations. All other pin configurations in both clamps resulted in a high variation of pin torsional resistance, and sometimes one of the pins registered low or had no resistance to torsion. The results indicated that the holding power of the clamps was adequate only if certain guidelines were followed at the time of external fixator application. An instrumented torque wrench may be helpful to assess the pin-fastening strength within the clamp. This wrench should also be used to introduce appropriate and uniform tightening torques to the pin clamp screws. However, these results do not apply to those fixators in which each pin will be tightened individually.

Fracture Fixation↗