Surgery for failed total knee arthroplasty

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28806/1/0000640.pd

Sonic diagnosis of bone fracture healing--A preliminary study

The definition of bone fracture healing onset, progress and extent is a difficult clinical diagnosis. Available criteria of manual stability, X-ray appearance, symptomatic pain and passage of time are indeed valuable, but subjective in nature. This study explores the transmission and comparative measurement of stress wave disturbances across a fracture site as a technique of quantifying the union state. Results from laboratory animal experimentation and subsequent clinical usage indicate a potentially valuable method has been developed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21921/1/0000328.pd

Causes and prevention--(i) biomechanics

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26051/1/0000125.pd

The limitations of canine trabecular bone as a model for human: A biomechanical study

Distal canine femurs were sectioned into 8mm cubic specimens. Orthogonal compression tests were performed to preyield in two or three directions and to failure in a third. Apparent density and ash weight density were measured for a subset of specimens. The results were compared to the human distal femur results of Ciarelli et al. (Transactions of the 32nd Annual Meeting of the Orthopaedic Research Society, Vol. 11, p. 42, 1986). Quantitative similarities existed in the fraction of components comprising the trabecular tissue of the two species. Qualitative similarities were seen in the positional and anisotropic variation of the mechanical properties, and also in the form and strength of the relationships between the mean modulus and bone density, ultimate stress and density, and ultimate stress and modulus. However, significantly different regression equations resulted for the mean modulus-density, and ultimate stress-modulus relationships, indicating that for the same density, canine trabecular bone displays a lower modulus than human, and may achieve greater compressive strains before failure.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28130/1/0000581.pd

The mechanical properties of human tibial trabecular bone as a function of metaphyseal location

Experimental determination of the elastic modulus and ultimate strength of human tibial trabecular bone as a function of metaphyseal location is presented.A 1 cm cubic matrix with planes parallel to the subchondral plate was defined on five fresh frozen cadaver tibias. Approximately 400, 7 mm x 10 mm cylindrical bone plugs were cut from the locations defined by the matrix and tested in uniaxial compressive stress at a strain rate of 0.1%s-1. Results of the study indicate that the trabecular bone properties vary as much as two orders of magnitude from one location to another. As might be predicted from Wolff's law, and noted by previous investigators, concentrations of strength arise from the medial and lateral metaphyseal cortices toward the major medial and lateral contact regions.These results may be valuable for improved analytical modeling and optimal prosthetic design.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25447/1/0000897.pd

Trabecular bone remodeling: An experimental model

An experimental model, capable of inducing controlled stress fields to the distal femoral metaphyses of large dogs, is presented. This model utilized an implantable hydraulic device incorporating five loading cylinders and platens in direct contact with an exposed plane of trabecular bone. A microprocessor controls the loading characteristics, and finite element models were created to calculate the induced stress and strain fields. The trabecular remodeling response is measured using serial in vivo computed tomography, in vitro microcomputed tomography, and histologic analysis. The results of the experiment indicate that significant remodeling can be induced by the activated implant. An increase in trabecular orientation toward the loaded platens was observed, and a statistically significant decrease in connectivity was documented. The greatest effect was associated with a change in the loading rate. A fast rise time (70 ms) loading waveform induced significant bone ingrowth at the implant interface when compared to a slow rise time waveform (700 ms), and demonstrated high correlations with the calculated stress fields as remodeling approached an equilibrium state.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29555/1/0000643.pd

Analysis of cumulative strain in tendons and tendon sheaths

Twenty-five fresh frozen flexor digitorum profundus tendons stratified by sex were subjected to uniaxial step stress and cyclic loads in twelve intact human cadaver hands. By attaching specially designed clip strain gage transducers on tendons just proximal and distal to an undisrupted carpal tunnel, the interactions of the tendons, tendon sheath and retinacula were measured.The elastic and viscous response of the tendon composites to step stresses were found to fit fractional power functions of stress and time respectively. A significant and quantifiable decrease in strain from the proximal to the distal tendon segment was found to be a function of wrist deviation.The results indicate that an accumulation of strain does occur in tendinous tissues during physiologic loading.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26842/1/0000402.pd

Computed tomography and plain radiography in experimental fracture healing

We evaluated the relative contribution of plain radiographs and computed tomography to the assessment of fracture healing under experimental circumstances. In 15 sheep, we performed midshaft femoral osteotomies and internal fixation of the resultant segmental fractures. Radiographs were obtained preoperatively and immediately postoperatively. Animals were sacrificed at 3 weeks, 6 weeks, 12 weeks, 24 weeks, and 36 weeks after surgery, and the femoral specimens radiographed. After removal of the internal fixation devices, computed tomographic scans of the specimens were performed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46780/1/256_2004_Article_BF00355070.pd

Does Sex Trade with Violence among Genotypes in Drosophila melanogaster?

The evolutionary forces shaping the ability to win competitive interactions, such as aggressive encounters, are still poorly understood. Given a fitness advantage for competitive success, variance in aggressive and sexual display traits should be depleted, but a great deal of variation in these traits is consistently found. While life history tradeoffs have been commonly cited as a mechanism for the maintenance of variation, the variability of competing strategies of conspecifics may mean there is no single optimum strategy. We measured the genetically determined outcomes of aggressive interactions, and the resulting effects on mating success, in a panel of diverse inbred lines representing both natural variation and artificially selected genotypes. Males of one genotype which consistently lost territorial encounters with other genotypes were nonetheless successful against males that were artificially selected for supernormal aggression and dominated all other lines. Intransitive patterns of territorial success could maintain variation in aggressive strategies if there is a preference for territorial males. Territorial success was not always associated with male mating success however and females preferred ‘winners’ among some male genotypes, and ‘losers’ among other male genotypes. This suggests that studying behaviour from the perspective of population means may provide limited evolutionary and genetic insight. Overall patterns of competitive success among males and mating transactions between the sexes are consistent with mechanisms proposed for the maintenance of genetic variation due to nonlinear outcomes of competitive interactions