Biomedical subjects

M A Wikenheiser

Publications and source records attributed to M A Wikenheiser.

9 recordsLinked to original sources

PubMed1997

Gait abnormalities following resection of talocalcaneal coalition.

Eleven patients (fourteen feet) had resection of a coalition of the middle facet of the talocalcaneal joint because of symptoms that had been present for a mean of four years (range, 0.5 to nine years). The mean age at the time of the resection was seventeen years (range, thirteen to thirty-two years). Nine patients were male and two were female. Five feet had resection of the bone bridge with interposition of fat or tendon, and nine had resection without any interposed material. The mean duration of follow-up was six years (range, two to thirteen years). The clinical result was excellent for five feet, good for four, fair for three, and poor for two. Inversion was 8 +/- 4.5 degrees (mean and standard deviation) on the involved side and 17 +/- 6.2 degrees on the uninvolved side (p = 0.002). Three feet later had evidence of osteoarthrosis of the subtalar joint. Gait analysis demonstrated decreased motion of the hindfoot and the ankle, compared with that in normal subjects and with that in the contralateral (uninvolved) foot, in the sagittal and coronal planes during walking on a level surface. Motion was also reduced, particularly in the sagittal and coronal planes, during walking on a side slope. Ground-reaction forces (F8 and F9), temporal force factors (T2, T3, and T7), and the percentage of the gait cycle that consisted of the stance phase on the side-sloping walkway were different from those in normal subjects or in the uninvolved foot. These data indicate that, although most of our patients who had resection of a talocalcaneal coalition had a successful clinical result, most had a residual functional deficit.

Adolescent↗

PubMed1995

Thermal response and torque resistance of five cortical half-pins under simulated insertion technique.

A model was developed that can quantitate heat generation during placement of half-pins in cortical bone. Five half-pins were tested to assess differences in insertion torque, heat generation, and micro-damage at the pin-bone interface. Thin thermocouple probes were placed 0.5 mm from the track of the pin and within the pin to measure its temperature during insertion. Scanning electron microscopy was used to view the pin-bone interface to assess the microdamage during placement. The design of the tip of the pin influenced insertion torque and heat generation. Higher heat generation was measured when a thermocouple was placed within the pin itself and less was measured when thermocouple probes were placed within bone samples 0.5 mm from the impending pin track. Furthermore, insertion torque and thermal responses were related, but there were no significant differences in microdamage to bone when different pins and drilling/tapping techniques were used. Due to the significant heat generation at the pin-bone interface, proper cooling with saline irrigation should be applied during pin insertion regardless of the design of the pin. The microdamage observed at the surface of the pin track may have significant implications with regard to loosening of pins, but such effects must be studied with in vivo models.

Animals↗

PubMed1994

Pull-out strength of screws from polymethylmethacrylate cement.

We aimed to determine the optimal method of inserting a screw into polymethylmethacrylate (PMMA) cement to enhance fixation. We performed six groups of ten axial pull-out tests with two sizes of screw (3.5 and 4.5 mm AO cortical) and three methods of insertion. Screws were placed into 'fluid' PMMA, into 'solid' PMMA by drilling and tapping, or into 'curing' PMMA with quarter-revolution turns every 30 seconds until the PMMA had hardened. After full hardening, we measured the maximum load to failure for each screw-PMMA construct. We found no significant difference in the pull-out strengths between screw sizes or between screws placed in fluid or solid PMMA. Screws placed in curing PMMA were significantly weaker: the relative strengths of solid, fluid and curing groups were 100%, 97% and 71%, respectively. We recommend the use of either solid or fluid insertion according to the circumstances and the preference of the surgeon.

Biomechanical Phenomena↗

PubMed1991

Quantitative CT for the evaluation of bone healing.

Quantitative computed tomography (QCT) was used to quantitate the structural strength and local material properties of healing tibial osteotomies in 32 dogs. Dogs were divided into four equal groups, euthanatized at either 2, 4, 8, or 12 weeks and imaged with QCT. Invasive techniques were used to determine (1) the torsional properties of the bone; (2) the local stiffness properties and calcium content within the bone; and (3) histologically determined new bone formation and porosity. QCT was strongly associated with the maximum torque (R2 = 0.44) and torsional stiffness (R2 = 0.69) of the healing bone. QCT had strong correlations with the local stiffness (R2 = 0.64), calcium content (R2 = 0.61), new bone (R2 = 0.84), and porosity (R2 = 0.84) of healing tissues.

Animals↗

PubMed1991

The determination of bone fracture properties by dual-energy X-ray absorptiometry and single-photon absorptiometry: a comparative study.

Dual-energy X-ray absorptiometry (DEXA) and single-photon absorptiometry (SPA) were used to quantitate the structural strength and local material properties of healing tibial osteotomies in 32 dogs. Dogs were divided into four equal groups, euthanatized at either 2, 4, 8, or 12 weeks, and imaged with DEXA and SPA. Invasive techniques were used to determine (1) the torsional properties of the bone, (2) the local stiffness properties and calcium content within the bone, and (3) new bone formation and porosity by histology. There were no differences between SPA and DEXA in their associations with the torsional properties of bone. SPA and DEXA had strong correlations with the ultimate torque (R2 = 0.76, 0.51) and the torsional stiffness (R2 = 0.68, 0.53) of bone. SPA and DEXA of periosteal callus, endosteal callus, and cortical bone had similar associations with indentation stiffness, calcium content, new bone formation, and porosity. SPA of gap tissue had significantly stronger associations with these four parameters than DEXA (P less than 0.05). Correlation coefficients (R2) with these local material properties ranged as high as 0.82 for SPA with new bone formation in the gap tissue and 0.73 for DEXA with indentation stiffness of periosteal callus.

Absorptiometry, Photon↗

PubMed1991

Multiplanar quantitative computed tomography for bone mineral analysis in dogs.

The purpose of this study was to determine the precision and accuracy of quantitative computed tomography bone mineral analysis in dogs in coronally reconstructed images. Nonhomogeneous tissues, such as bones with fractures or deformities, may be better analyzed if multiplanar reconstruction of the transaxial data could be performed without degradation of information. Our analysis demonstrated that coronal reconstruction of quantitative-computed tomography data was precise (1.2 to 4.7%) and accurate (1.3 to 7.5%) in vitro. The technique displays high-quality images, which can be analyzed at any location within the volume scanned. Quantitative computed tomography of canine osteotomy healing in vivo accurately determined bone mineral density of selected regions of interest. Bone mineral density correlated highly with calcium content of the tissue (R2 = 0.76, P less than 0.0001).

Animals↗

PubMed1991

Formation of bone in tibial defects in a canine model. Histomorphometric and biomechanical studies.

The histomorphometric, material, and structural properties of the reparative tissue and bone that formed in a two-millimeter tibial defect in dogs were determined at two, four, eight, and twelve weeks after the operation. At two weeks, the tibial defect was filled mainly with undifferentiated connective tissue. After two weeks, the relative proportion of undifferentiated connective tissue decreased and the amount of bone progressively increased throughout the twelve weeks. New bone formed primarily by intramembranous ossification, with a small degree of endochondral ossification. At twelve weeks, bone occupied 62 per cent of the defect. The calcium content of the reparative tissue increased between four and eight weeks and then, at twelve weeks, reached a plateau of 77 per cent that of normal cortical bone. Anisotropy of the new bone that formed in the defect increased from 13.8 per cent to 26 per cent, and the mean width of the trabecular bone increased 27 per cent between the eighth and twelfth weeks. Maximum torque and torsional stiffness increased between two and eight weeks and then, by twelve weeks, the values leveled off at 44 and 29 per cent of the values for intact bone. Indentation stiffness increased between the fourth and twelfth weeks; at twelve weeks, it was 22 per cent of the stiffness of normal cortical bone. Indentation stiffness increased 283 per cent between eight and twelve weeks, despite insignificant changes in calcium content, amount of new bone, non-osseous space, water content, or volume of trabecular bone during this time. This change in indentation stiffness did correlate with increases in anisotropy of the new bone between eight and twelve weeks.

Animals↗

PubMed1990

A study of fracture callus material properties: relationship to the torsional strength of bone.

This study was designed to quantitate the local material properties of fracture callus during gap healing and to relate these local properties to the torsional strength of bone in a canine model under external fixation. Bilateral tibial transverse osteotomies were performed in 32 dogs and stabilized using unilateral external skeletal fixators with a 2-mm gap. Dogs were divided into four equal groups and euthanized at either 2, 4, 8, or 12 weeks. The torsional properties of one bone of each pair were determined. In both bones of each pair, the indentation stiffness, calcium content, and histomorphometric properties of six sites of periosteal callus, six sites of endosteal callus, four sites of cortical bone, and two sites of gap tissue were determined. Each of the four types of tissue had a specific structural or material property change during the study period. The indentation stiffness of periosteal callus increased up to 8 weeks and then plateaued. Endosteal callus stiffness peaked at 8 weeks and then decreased by 12 weeks. Gap tissue stiffness increased linearly over time. Cortical bone stiffness decreased over time. Indentation stiffness was significantly associated with the calcium content of periosteal callus (R2 = 0.50, p less than 0.0001) and gap tissue (R2 = 0.66, p less than 0.0001). The local stiffnesses of gap tissue and periosteal callus were significantly associated with the maximum torque (gap, R2 = 0.50, p less than 0.0001; periosteal, R2 = 0.34, p less than 0.05) and the torsional stiffness (gap, R2 = 0.44, p less than 0.0001; periosteal, R2 = 0.65, p less than 0.0001) of the bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Quantification of bone healing. Comparison of QCT, SPA, MRI, and DEXA in dog osteotomies.

Four noninvasive imaging modalities were used to quantitatively evaluate and compare tibial osteotomy healing in dogs. Quantitative computed tomography (QCT), magnetic resonance imaging (MRI), single-photon absorptiometry (SPA), and dual-energy x-ray absorptiometry (DEXA) were the four techniques examined. Bilateral tibial osteotomies were performed in 32 dogs divided into four groups. The osteotomies were stabilized with a 2-mm gap using unilateral external skeletal fixation. Dogs were anesthetized, imaged with the four noninvasive techniques, and killed at 2-12 weeks. Invasive techniques were used to determine: 1) the torsional properties of the bone; and 2) the local stiffness properties and calcium content within the bone. The techniques which had the strongest associations with the torsional properties of the osteotomies were QCT, SPA and DEXA. Generally, QCT and SPA had marginally stronger correlations than DEXA; but, overall, there were no differences between the techniques. MRI had the poorest associations with the torsional properties of the osteotomies. Generally, QCT had the strongest correlations with local material properties, such as indentation stiffness and calcium content. SPA had the second strongest correlations with calcium content and had the third strongest correlations with indentation stiffness behind DEXA. DEXA had the third strongest correlations for calcium content. With the exception of some of the correlations with indentation stiffness, MRI had the poorest associations with the local parameters studied.

Absorptiometry, Photon↗