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Titanium plates and screws have become widely used for the fixation of fractures and osteotomies. We began using them in 1992; however, several early hardware failure prompted a retrospective review of the occurrence of this complication. A 2-year time period was reviewed at two institutions with comparison of hardware failure rates using titanium and stainless steel implants. At one institution, 51 fractures or osteotomies of the long bones were fixed by the senior author using titanium implants between July 1992 and July 1994. One hundred one similar cases were treated over the same period by the same surgeon using stainless steel implants. The outcome is known for 48 of the cases performed with titanium and for 80 of the cases performed with stainless steel. There were five postoperative implant failures using titanium and one using stainless steel. Metallurgical analysis of one set of broken implants retrieved during a revision surgery showed no manufacturing defects. At the second institution, 21 titanium and 138 stainless steel platings were performed over 2 years. There were four titanium implant failures in four patients and one stainless steel implant failure. Our experience suggests that these implants should be used with care, particularly in high-demand settings such as nonunion or noncompliance, and that further research needs to be conducted to establish appropriate clinical indications for their usage.

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Electromyographic activity of dorsal neck muscles and neck torques was recorded to study vestibulocollic, cervicocollic, and combined reflexes in alert and decerebrate cats during rotations of the whole body, the body except for the head, and the head but not the rest of the body. Cats were rotated about many axes that lay in the frontal, sagittal, and horizontal planes using sinusoidal 0.25-Hz waveforms or sum-of-sinusoid wave-forms. Robust electromyographic responses were recorded from six muscles, with response directionality that in most cases did not show strong dependence on the reflex tested or on other factors including exact neck angle, stimulus amplitude from 5 degrees to 60 degrees, and intact versus decerebrate state. Based on the strength of responses to rotations about all the tested axes, neck muscles could be characterized by maximal activation direction vectors representing the axis and direction of rotation in three-dimensional space that was most excitatory during reflex responses. Responses to rotations about axes that lay in a coordinate plane were predicted by a cosine function of the angle between the axis under test and the maximally excitatory axis in the plane. All muscles were excited by the nose down phase of pitch rotation and by yaw and roll away from the side on which the muscle lay. Biventer cervicis was best activated by rotations with axes near nose-down pitch, and its axis of maximal activation also had small, approximately equal components of yaw and roll toward the contralateral side. Complexus was best excited by rotations with axes nearest roll, but with large components along all three axes. Occipitoscapularis was best excited by rotations about axes near pitch, but with a moderately large contralateral yaw component and a smaller but significant contralateral roll component. Splenius was best excited by rotations with a large component of contralateral yaw, considerable nose-down pitch, and a smaller component of contralateral roll. Rectus major was best excited by rotations near nose-down pitch, but with a substantial contralateral yaw component and smaller contralateral roll component. Obliquus inferior was best excited by rotations with a large component of contralateral yaw, but with considerable contralateral roll and nose-down pitch components. All muscles responded as though they received convergent input from all three semicircular canals. Vestibulocollic and combined reflex responses in alert cats and vestibulocollic, cervicocollic, and combined responses in decerebrate cats appeared to have the same directionality, as evidenced by insignificant shifts in maximal activation vectors.(ABSTRACT TRUNCATED AT 250 WORDS)

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The vestibulo-ocular and vestibulo-collic reflexes are well-studied sensorimotor systems with dynamic properties that have been successfully modeled. Recently proposed matrix and tensorial models attempt to describe the spatial organization of these reflexes in three dimensions. Here we describe experiments that test these models. We show that a matrix model of the vestibulo-ocular reflex provides a satisfactory description of its spatial properties. The vestibulo-collic reflex is more complex, but a tensorial model makes close predictions of neck muscle excitation by the vestibulo-collic reflex. In addition, our preliminary data show that the cervico-collic or neck stretch reflex produces essentially the same spatial pattern of neck muscle excitation as the vestibulo-collic reflex, a finding predicted by the tensorial model. We conclude by showing electromyographic and single neuron responses that can be modeled only by combining models of dynamics with models of spatial organization. We believe that the development of such models is the next major challenge in the application of quantitative methods to analysis of reflex behavior.

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