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The human cerebellum has been implicated in the control of a wide variety of motor control parameters, such as force amplitude, movement extent, and movement velocity. These parameters often covary in both movement and isometric force production tasks, so it is difficult to resolve whether specific regions of the cerebellum relate to specific parameters. In order to address this issue, the current study used two experiments and SUIT normalization to determine whether BOLD activation in the cerebellum scales with the amplitude or rate of change of isometric force production or both. In the first experiment, subjects produced isometric pinch-grip force over a range of force amplitudes without any constraints on the rate of force development. In the second experiment, subjects varied the rate of force production, but the target force amplitude remained constant. The data demonstrate that BOLD activation in separate sub-areas of cerebellar regions lobule VI and Crus I/II scales with both force amplitude and force rate. In addition, BOLD activation in cerebellar lobule V and vermis VI was specific to force amplitude, whereas BOLD activation in lobule VIIb was specific to force rate. Overall, cerebellar activity related to force amplitude was located superior and medial, whereas activity related to force rate was inferior and lateral. These findings suggest that specific circuitry in the cerebellum may be dedicated to specific motor control parameters such as force amplitude and force rate.

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BACKGROUND: In the midbrain of patients with Parkinson disease (PD), there is a selective loss of dopaminergic neurons in the ventrolateral and caudal substantia nigra (SN). In a mouse model of PD, investigators have administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and found that measures derived using diffusion tensor imaging (DTI) were correlated with the number of dopamine neurons lost following intoxication. METHODS: Twenty-eight subjects (14 with early stage, untreated PD and 14 age- and gender-matched controls) were studied with a high-resolution DTI protocol at 3 Tesla using an eight-channel phase array coil and parallel imaging to study specific segments of degeneration in the SN. Regions of interest were drawn in the rostral, middle, and caudal SN by two blinded and independent raters. RESULTS: Fractional anisotropy (FA) was reduced in the SN of subjects with PD compared with controls (p < 0.001). Post hoc analysis identified that reduced FA for patients with PD was greater in the caudal compared with the rostral region of interest (p < 0.00001). A receiver operator characteristic analysis in the caudal SN revealed that sensitivity and specificity were 100% for distinguishing patients with PD from healthy subjects. Findings were consistent across both raters. CONCLUSIONS: These findings provide evidence that high resolution diffusion tensor imaging in the substantia nigra distinguishes early stage, de novo patients with Parkinson disease (PD) from healthy individuals on a patient by patient basis and has the potential to serve as a noninvasive early biomarker for PD.

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BACKGROUND: A fundamental feature underlying many movement disorders is increased variability in the motor response. Despite abnormalities of grip force control in people with dystonia, it is not clear whether dystonia is also associated with increased variability in force output and whether force variability in dystonia is affected by the presence or absence of visual feedback. OBJECTIVE: To examine force variability in 16 patients with writer's cramp and 16 matched controls. METHODS: The variability of force output at the wrist under conditions of both vision and no vision was examined. The underlying frequency structure of the force signal was also compared across groups. Participants produced isometric wrist flexion to targets at 25% and 50% of their maximum voluntary contraction strength under conditions of both vision and no vision. RESULTS: Similar levels of force variability were observed in patients with dystonia and controls at the lower force levels, but patients with dystonia were less variable in their force output than controls at the higher force level. This reduction in variability in people with dystonia at 50% maximum voluntary contraction was not affected by vision. Although a similar dominant frequency in force output was observed in people with dystonia and controls, a reduced variability in the group with dystonia at the higher force level was due to reduced power in the 0-4-Hz frequency bin. CONCLUSIONS: The first evidence of a movement disorder with reduced variability is provided. The findings are compatible with a model of dystonia, which includes reduced cortical activation in response to sensory input from the periphery and reduced flexibility in motor output.

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We undertook this study to determine the types and frequency of injuries sustained in the sport of luge. Before this study, no data were available in the medical literature on luge injuries. We performed a retrospective analysis between the years 1985 and 1992 using data obtained from the athlete injury and illness report forms at the US Training Center Sports Medicine Clinic in Lake Placid, New York. During the 7 years examined, 1043 athletes took 57,244 track runs and sustained 407 injuries. The risk of sustaining an injury was 0.39 per person per year, and the risk of an injury causing the loss of more than 1 day of practice was 0.04 per person per year. Contusions were the major injury (51%), followed by strains (27%). Strains of the neck muscles and contusions of extremities, especially the hands, were characteristic injuries sustained by athletes. The most serious injuries were concussions (2%) and fractures (3%). Crashes were responsible for 64% of injuries. Luge appears to be a relatively safe sport with injury rates comparable with recreational alpine skiing.

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The purpose of this study was to evaluate the effects of various laser wavelengths on human meniscal tissue in vitro and to compare them with the effects of electrosurgical devices. The carbon dioxide (CO2) laser produced the best cutting and ablating effects among the infrared lasers, although the contact neodymium:yttrium-aluminum-garnet (Nd:YAG) and holmium:YAG (Ho:YAG)lasers were nearly as satisfactory, offering the additional advantage of fiberoptic capability and the ability to be used in saline. The free-beam Nd:YAG laser and coagulation mode electrosurgical device produced unacceptably severe thermal changes. The excimer laser at 308 nm produced the best tissue effect and caused no detectable adjacent thermal change in the tissue.

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This article reports the investigation of the XeCl excimer laser as a cutting-ablating tool for human fibrocartilage and hyaline cartilage. Quantitative measurements were made of tissue ablation rates as a function of fluence in meniscal fibrocartilage and articular hyaline cartilage. A force of 1.47 Newtons was applied to an 800-microns fiber with the laser delivering a range of fluences (40-190 mJ/mm2) firing at a frequency of 5 Hz. To assess the effect of repetition rate on depth per pulse, a set of measurements was made at a constant fluence of 60 mJ/mm2, with the repetition rate varying from 10 to 40 Hz. Histologic and morphometric analysis of preserved specimens was performed using light microscopy. The results of these studies revealed that the ablation rate was directly proportional to fluence over the range tested. Fibrocartilage was ablated at a rate 2.56 times faster than hyaline cartilage. Repetition rate had no effect on the penetration per pulse. Adjacent tissue damage was noted to be minimal (10-70 microns). The excimer laser achieved ablation rates adequate for arthroscopic applications.

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Discectomy with lasers is a technically easy procedure and permits a surgeon to place a predictably sized and configured defect in a predetermined position in the intervertebral disc. In a small series of patients, the procedure appears effective in controlling symptoms in a high percentage of patients. The efficacy of the procedure and wider acceptance will depend on the results of multicenter clinical trials.

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