Biomedical subjects

N A Waanders

Publications and source records attributed to N A Waanders.

8 recordsLinked to original sources

PubMed1999

Reduced gap strains induce changes in bone regeneration during distraction.

A bilateral New Zealand white rabbit model of distraction osteogenesis (DO) was used to investigate the relationship between strain environment and bone regeneration during limb lengthening. In seven (n = 7) rabbits, a stiffener was applied to the fixator on one side to reduce strains within the gap tissue after lengthening was completed. Animals were euthanized six days later and their distraction zones were harvested and analyzed for changes in new bone volume and architecture. Nonlinear finite element analyses (FEA) were performed to predict changes in the gap strain environment. FEA results predicted a nearly uniform sevenfold decrease in average strain measures within the distraction zone. No change in total average new bone volume and significant decreases in both bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) were observed in tibiae in which gap strains were reduced experimentally, compared to contralateral controls. These results suggest that fixator stiffening influenced the architecture but not the amount of newly formed bone. This animal model of distraction might be used to study the mechanisms by which strain fields affect events in bone repair and regeneration, such as cell proliferation, precursor tissue differentiation, and altered growth factor and nutrient delivery to tissues.

Animals↗

PubMed1998

Evaluation of the mechanical environment during distraction osteogenesis.

Physical forces have been hypothesized to direct the process of bone regeneration during distraction osteogenesis. However, despite significant clinical experience, relatively little is known about how the mechanics of distraction influence bone formation. This study investigated net fixator forces and strains in the distraction callus during bilateral lengthening of tibiae in New Zealand White rabbits. Distractions yielded a classic viscoelastic response with a sharp increase in fixator force, followed immediately by significant relaxation. Tension acting on mesenchymal gap tissue caused by distraction was estimated to reach more than 30 N by the time full lengthening was achieved. Average maximum cyclic strains within the distraction zone during ambulation were estimated to be 14% to 15% and supported by the results of fluoroscopic imaging. Paradigms for fracture healing have hypothesized that such strains are incompatible with new bone formation. The documented clinical success of distraction osteogenesis at stimulating large volumes of new bone suggests that other mechanisms that warrant additional investigation may be at work during distraction.

Animals↗

PubMed1998

Bone regeneration and fracture healing. Experience with distraction osteogenesis model.

The relation between physical forces and the processes of bone regeneration and healing remains incompletely understood. Gaps in understanding of these processes stem in part from models that produce inadequate amounts of new bone for study. Bone created through the use of distraction osteogenesis provides an attractive substrate for the study of mechanical forces and their effects on bone formation because this technique produces large volumes of new bone in a controlled fashion. The optimal mechanical environment in which bone formation occurs clinically has not been fully determined. In laboratory studies, however, the mechanical environment can be manipulated, and resultant changes in bone formation can be measured. To investigate how changes in strain environment influence patterns of bone formation, a bilateral New Zealand White rabbit model of bilateral distraction osteogensis was implemented. When a stiffener was applied to the external distractor, computation analyses predicted a sevenfold to eightfold decrease in all strain measures. These reductions in gap strains appeared to induce significant decreases in bone volume fraction and mean trabecular thickness. When osteotomies were created at a 30 degrees angle to the bony axis to generate more shear within the gap tissue, changes in the distribution of gap strains and resultant new bone architecture were observed. Specific correlations between changes in tissue level strains and the pattern of bone regeneration were seen in both experiments. These results provide direct in vivo evidence that pluripotential gap tissues are sensitive to their physical surroundings. Mechanisms responsible for this sensitivity might include vascularity, stem cell supply, and scaffolding architecture. The process of bone formation in distraction osteogenesis appears to be related to bone formation processes associated with more common conditions. The distraction osteogenesis model described suggests a mechanism for bone formation that seems applicable to other more common processes associated with bone formation, including fracture healing and impaired fracture healing.

Adult↗

PubMed1994

The use of ultrasound mean acoustic attenuation to quantify bone formation during distraction osteogenesis performed by the Ilizarov method. Preliminary results in five dogs.

RATIONALE AND OBJECTIVES: Management of distraction during Ilizarov limb lengthening remains primarily clinical and empirical. Estimates of tissue acoustic attenuation were evaluated for their ability to quantify bone formation within the distraction gap. METHODS: Five dogs had tibias lengthened by the method of Ilizarov. Mean acoustic attenuation measurements at multiple positions across the distraction gap were compared with corresponding x-ray computed tomography attenuation measurements. RESULTS: Computed tomography and ultrasound attenuation displayed similar quantitative behavior across the gap. Linear correlation between them ranged from R2 = .878 to R2 = .131. Fibrous interzone width estimates based on computed tomography and ultrasound attenuation measurements were correlated, based on our preliminary data with R2 = .519. These estimates are independent of the width of distraction. CONCLUSIONS: Ultrasound parallels computed tomography as a measure of bone formation within the distraction gap. Future studies are needed to improve acoustic attenuation data acquisition techniques and to evaluate their potential as a tool for optimizing early distraction rates in patients at risk for rate-related complications.

Acoustics↗

PubMed1992

The theoretical application of inclined hinges with the Ilizarov external fixator for simultaneous angulation and rotation correction.

The mathematical concepts of single-cut osteotomies for simultaneous correction of angulation and rotation have been adapted and simplified for gradual distraction-osteogenic correction with the Ilizarov external fixator. Validation studies were performed analytically, using a solid modeling analysis, and experimentally with an Ilizarov external fixator mounted on a wood dowel. The resultant equations have been simplified and are easy to use. Starting from the hinge which would correct the angulation, the axis must be reoriented in the horizontal plane by half the rotation deformity (R/2) and given an inclination slope equal to the rotation divided by the angulation (R/A).

Biomechanical Phenomena↗

PubMed1991

Calculating rate and duration of distraction for deformity correction with the Ilizarov technique.

Longitudinal bone lengthening with distraction histogenesis is typically carried out at a rate of 1 mm per day. Angular corrections require an adjustment of the rate of distraction according to the geometry of the external fixator relative to the bone or soft tissue being lengthened. Modeling the deformity correction construct using simple geometric principles allows calculation of both the rate of correction and the expected duration of distraction.

Bone Lengthening↗

PubMed1990

Cobb angle versus spinous process angle in adolescent idiopathic scoliosis. The relationship of the anterior and posterior deformities.

The standard clinical measurement for adolescent idiopathic scoliosis is the Cobb angle, measured from the end-plates of the end vertebral bodies in a standing radiograph. This measurement of anterior column structures describes the anterior spinal deformity. The posterior spinal deformity can be described by the "spinous process angle," measured from a curve joining the tips of the spinous processes. A computer model, and a radiographic study of Cobb angle, spinous process angle and vertebral rotation show that adolescent idiopathic scoliosis results in larger angulations of the anterior elements than posterior elements. This helps to explain some of the inherent limitations of posterior instrumentation, including Cotrel-Dubousset instrumentation, and of noninvasive posterior surface measurement systems.

Adolescent↗

PubMedDate not supplied

Clinical estimation of ilizarov fixator axial stiffness based on wire and half pin contributions.

A key parameter in the mechanical environment created in distraction osteogenesis is the axial stiffness of the external fixator. Mechanical testing of the frames with wire and half pins has been used to estimate the stiffness contributions of wires based on the span length and of half pins based on the offset length. A summation of the wire and half pin contributions appears to represent a suitable estimate for the axial stiffness of frames composed of a mixture of wires and half pins. Using this estimate, clinicians can make informed decisions regarding frame construction, and it may be possible to investigate the rate of bone formation relative to axial frame stiffness in the clinical setting.

Biomechanical Phenomena↗