Outdoor dynamic subject-specific evaluation of internal stresses in the residual limb: hydraulic energy-stored prosthetic foot compared to conventional energy-stored prosthetic feet

The prosthetic foot plays an important role in propelling, breaking, balancing and supporting body loads while the amputee ambulates on different grounds. It is therefore important to quantify the effect of the prosthetic foot mechanism on biomechanical parameters, in order to prevent pressure ulcers and deep tissue injury. Our aim was to monitor the internal stresses in the residuum of transtibial amputation (TTA) prosthetic-users ambulating on different terrains, which the amputees encounter during their daily activities, i.e. paved floor, grass, ascending and descending stairs and slope. We specifically aimed to compare between the internal stresses in the TTA residuum of amputees ambulating with a novel hydraulic prosthetic foot compared to conventional energy storage and return (ESR) prosthetic feet. Monitoring of internal stresses was accomplished using a portable subject-specific real-time internal stress monitor. We found significant decrease (p<0.01) in peak internal stresses and in the loading rate of the amputated limb, while walking with the hydraulic foot, compared to walking with ESR feet. The loading rate calculated while ambulating with the hydraulic foot was at least three times lower than the loading rate calculated while ambulating with the ESR foot. Although the average decrease in internal stresses was ≈ 2-fold larger when replacing single-toe ESR feet with the hydraulic foot than when replacing split-toed ESR feet with the hydraulic foot, the differences were statistically insignificant. Our findings suggest that using a hydraulic prosthetic foot may protect the distal tibial end of the TTA residuum from high stresses, therefore preventing pressure-related injury and pain.     

Intracranial compliance is time-dependent

Compliance is considered a fundamental characteristic of the intracranial system, is measured by the volume pressure test (VPT), and is considered to be related to the cerebrospinal fluid (CSF) pulse pressure (delta Pcsf). This study was carried out to determine the time-dependent relationship of intracranial compliance and the relationship between intracranial pulse pressure and compliance. In nine dogs divided into two groups, the rate of injection of a test volume and the physical compliance of the intracranial system was altered by opening or closing the skull without altering the base line intracranial pressure. The VPT was carried out by three methods: slow infusion--infusion of 0.3 ml at 1.5 to 0.2 ml/second, fast infusion--infusion of 0.2 ml in 0.5 second, and bolus injection--injection of 0.05 ml as rapidly as possible. With the skull closed, there were linear relationships between diastolic CSF pressure (Pcsf-d) and delta Pcsf; Pcsf-d and slow infusion, fast infusion, or bolus injection; and Pcsf-d and CSF respiratory wave amplitude. With the skull open, the linear relationship was retained only for Pcsf-d vs. delta Pcsf and Pcsf-d vs. bolus injection. Furthermore, delta Pcsf amplitude at any level of Pcsf-d was the same whether the skull was open or closed. It is concluded that intracranial compliance can be divided into two components based on the time constant of the injected volume: physical compliance, which has a short time constant and is related to delta Pcsf, and physiological compliance, which has a longer time constant and is related to the VPT.     

Cochlear implants as a contraindication to magnetic resonance imaging

Magnetic resonance imaging poses little risk to the majority of patients undergoing scanning. However, cochlear implantation should pose a contraindication to this imaging process. This conclusion is based on several findings of in vitro testing of three cochlear implants: the 3M/House and 3M/Vienna designs and the Nucleus device. Specifically, tremendous torques are generated by each of these devices when they are introduced into the coil of a magnetic resonance imager; in addition, the 3M products not only were noted to induce an electrical current, but also were significantly magnetized and rendered afunctional. The clinical implications are discussed.     

Effects of methylphenidate discontinuation on cerebral blood flow in prepubescent boys with attention deficit hyperactivity disorder.

Methylphenidate (MPH) is an effective symptomatic treatment of attention deficit hyperactivity disorder (ADHD), but the mechanisms of its therapeutic action have not been fully elucidated. To address this issue, we assessed the effects of discontinuation of chronic MPH treatment on regional cerebral blood flow (rCBF) in ADHD patients. METHODS: Twenty-two prepubescent boys with ADHD (age range, 8.2-11.5 y) and 7 healthy volunteers were studied with SPECT on and off MPH. Their rCBF data were automatically normalized to whole-brain counts and coregistered with standard anatomic space. rCBF changes were evaluated with statistical parametric mapping based on voxel-by-voxel ANOVA. RESULTS: When the subjects were not taking MPH, rCBF was higher in the motor, premotor, and the anterior cingulate cortices (Brodmann's areas 4, 6, and 32). CONCLUSION: Brief discontinuation of MPH treatment is associated with increased motor and anterior cingulate cortical activity. Our findings suggest that MPH treatment modulates motor and anterior cingulate cortical activity directly or indirectly. Alternatively, our findings may be related to MPH withdrawal. These data provide novel information on the potential mechanisms of the therapeutic action of MPH. Furthermore, they are clinically relevant to the commonly occurring brief interruptions in MPH treatment.