A clinical, radiological and computational analysis of the thrust plate prosthesis in young patients.

BACKGROUND AND PURPOSE: A thrust plate prosthesis can be used as an alternative to a conventional stem prosthesis, preserving the diaphyseal bone stock. Recent findings however predict a higher rate of aseptic loosening than with intramedullary devices. The purpose of our investigation was to compare the clinical outcome and radiological findings with a finite element analysis of bone remodeling. The hypothesis was that aseptic loosening after thrust plate prosthesis of the hip is inherent to the design. METHODS: From 1997 to 2001, 58 thrust plates were implanted in 52 patients. Average age at the time of surgery was 40.9 years. Ninety four percent returned for follow up at an average of 26 months. A finite element model of the thrust plate within the femur was developed and stress shielding as well as bone remodeling were analyzed. RESULTS: A total of 4 patients required revision surgery (6.9%). Data from the finite element analysis revealed an inherent failure mechanism to the implant, facilitating stress shielding and loosening. INTERPRETATION: Lacking the ideal total hip prosthesis in young patients, the thrust plate can still be regarded as a feasible implant. However, surgeons and patients should be aware of possible mechanical problems regarding the design of the thrust plate. There is evidence that thrust plate prostheses are prone to early aseptic loosening. Clinical and radiological observations are in agreement with the results from the numerical simulations. Stress concentrations computed at the leash are interpreted as an explanation for leash pain. The authors regard computational methods as an aid to improve existing prosthesis design and future developments.

Notebook input devices put to the age test: the usability of trackpoint and touchpad for middle-aged adults.

In two experiments, the usability of input devices integrated into computer notebooks was under study. The most common input devices, touchpad (experiment 1) and trackpoint (experiment 2) were examined. So far, the evaluation of mobile input devices has been restricted to younger users. However, due to ongoing demographic change, the main target group of mobile devices will be older users. Therefore, the present study focused on ageing effects. A total of 14 middle-aged (40-65 years) and 20 younger (20-32 years) users were compared regarding speed and accuracy of cursor control in a point-click and a point-drag-drop task. Moreover, the effects of training were addressed by examining the performance increase over time. In total, 640 trials per task and input device were executed. The results show that ageing is a central factor to be considered in input device design. Middle-aged users were significantly slower than younger users when executing the different tasks. Over time, a significant training effect was observed for both devices and both age groups, although the benefit of training was greater for the middle-aged group. Generally, the touchpad performance was higher than the trackpoint performance in both age groups, but the age-related performance decrements were less distinct when using the touchpad.

Effects of display resolution on visual performance.

The role of display resolution in visual information processing was investigated in 2 experiments. Experiment 1 examined the effects of 2 CRT conditions (resolutions of 60 and 120 dots per inch [dpi]) and a paper control condition (255 dpi) on proofreading speed and accuracy. The results showed that reading performance was significantly better in the paper condition than in the 2 CRT conditions. Experiment 2 examined the effects of 3 different CRT resolutions (62, 69, and 89 dpi) on eye movement parameters (fixation duration and number of fixations) in a visual search task. Further, search reaction times (RTs) and observers' ratings of visual fatigue were analyzed. RTs and fixation durations were significantly increased in the low-resolution condition (62 dpi) as compared with the high-resolution condition (89 dpi). The significant interaction between display resolution and time both for search RTs and fixation durations was taken as evidence for stronger fatigue in the low-resolution conditions. Additionally, the extent of visual fatigue correlates both with search RTs and eye movement parameters. This finding gives rise to the assumption that observers' responsiveness to effects of display resolution in terms of visual fatigue differs markedly. Actual or potential applications of this research include recommendations for the use of high-resolution displays (90 dpi and greater) to optimize visual performance, to make prolonged on-screen viewing more comfortable, and to avoid visual fatigue.

[Motion aftereffect in analysis of the visual system]. / Der Bewegungsnacheffekt als Analyseinstrument des visuellen Systems.

In several experiments the motion after-effect as elicited by spirals and gratings ("waterfall displays") is used to analyze the processing of information within the visual system. The duration and judged strength of after-effects are determined with respect to different fixation conditions (monocular and binocular fixation conditions as well as centric and eccentric fixation). The results show, that motion after-effects in spirals and waterfall displays are generated and processed in different ways within the visual system. The results are discussed on the basis of a metric of the visual system by means of the motion after-effect.