Mechanical evaluation of external fixators used in limb lengthening

Four external fixator systems (five configurations) used for limb lengthening were tested to determine the fixator stiffness and the fracture gap rigidity. There was a statistical difference between fixators in all modes of loading with respect to stiffness, shear, and axial motion. The fixators were graded to determine their relative stiffness, shear rigidity, and axial rigidity. The EBI Orthofix proved to be the most rigid fixator relative to the configurations tested with minimal shear or axial motion at the fracture site. The Ilizarov tibial configuration was the least rigid, demonstrating more shear and axial motion at the fracture gap. The Ilizarov femoral system combined excellent stability and shear resistance with preservation of axial dynamization. Fixators with a high stiffness provide less motion at the fracture site, which may cause stress shielding of the osteotomy. Fixators that provide more motion at the fracture gap are less stable. These data may be useful in determining which fixator may be ideal for a particular clinical situation.

A biomechanical analysis of the Ilizarov external fixator

Five configurations of the Ilizarov fixator were analyzed in vitro. The overall stiffness, shear stiffness, and axial motion of the fracture site were determined. The data were compared with the results of eight conventional one-half frame fixators previously tested in the same manner. The Ilizarov fixator allowed significantly more axial motion at the fracture site during axial compression than the other fixators tested. The overall stiffness and shear rigidity of the Ilizarov external fixator were similar to those of the one-half pin fixators in bending and torsion. The stability of the Ilizarov fixator was a function of bone position within the fixator rings and fixation wire tension. The use of olive stop wires increased the shear resistance of the Ilizarov system.

Total knee arthroplasty kinematics. An in vivo evaluation of four different designs

Thirty-four patients who had 42 total knee arthroplasties during the past 5 years were examined. Four types of total knee arthroplasties (Tricon-M, PCA, Variable Axis, and Anametric) were evaluated, using a computerized knee evaluation system. The patients and 10 controls with normal knees were tested for anteroposterior stability with the Lachman test, medial/lateral stability at 20 degrees, varus/valgus stability at 20 degrees, internal/external rotation at 80 degrees and 20 degrees of flexion, and internal/lateral rotation (screw home) over the active range of motion. At 30 degrees of flexion, the Variable Axis prosthesis was 54% more constrained than the normal knee to anterior/posterior shear. The Anametric and the Variable Axis were more lax under varus/valgus stress than the normal knee by 85% and 71%, respectively. There were no statistical differences for any of the other tests.

Comparative study of fracture gap motion in external fixation

Different external fixators demonstrated different motion patterns at the fracture site in AP bending. This indicates that fracture gap motion patterns cannot be predicted from a single value of overall frame stiffness. This type of information may be useful in examining existing theories of fracture healing in response to different types of fracture gap motion.

T-cell-dependent polyclonal activation by soluble mycobacterial extracts of B cells in peripheral blood mononuclear cell populations from leprosy patients and normal donors

Soluble extracts of ultrasonically disrupted mycobacteria (including Mycobacterium leprae) cause strong T-cell-dependent, Cyclosporin A-sensitive, polyclonal B-cell activation, in human peripheral blood mononuclear cell preparations. It is not enhanced by cortisol. Cells from cases of lepromatous leprosy show no polyclonal B-cell activation in the presence of extracts of M. leprae, although they respond normally to other mycobacterial species. The polyclonal B-cell activation response to the M. leprae extract, of a small group of normal leprosy contacts, was reduced relative to that of non-contacts.

Effects of degree of obesity, age of onset, and weight loss on responsiveness to sensory and external stimuli

Four experiments tested responsiveness to external and sensory stimuli in female human subjects who differed in degree of overweight and in age of onset of their obesity. The effects of weight loss upon external responsiveness were assessed by testing subjects before and after weight reduction in order to determine the role of energy deficit and deprivation in mediating heightened responsiveness to external cues. There was no significant positive correlation between degree of overweight and degree of external responsiveness. In general, the age of onset of the obesity was also not a relevant factor in the degree of externality. Weight loss did not change responses to visual and cognitive cue salience manipulations in measures of feeding, emotionality, time perception, and short-term recall, whereas responsiveness to variations in palatability increased following weight reduction. While external cue responsiveness does not appear to result from adiposity per se or from deprivation, responsiveness to taste stimuli may reflect these parameters. The role of external and sensory cues in the development and maintenance of obesity is discussed.