Safety parameter considerations of anodal transcranial Direct Current Stimulation in rats.

A commonly referenced transcranial Direct Current Stimulation (tDCS) safety threshold derives from tDCS lesion studies in the rat and relies on electrode current density (and related electrode charge density) to support clinical guidelines. Concerns about the role of polarity (e.g. anodal tDCS), sub-lesion threshold injury (e.g. neuroinflammatory processes), and role of electrode montage across rodent and human studies support further investigation into animal models of tDCS safety. Thirty-two anesthetized rats received anodal tDCS between 0 and 5mA for 60min through one of three epicranial electrode montages. Tissue damage was evaluated using hemotoxylin and eosin (H&E) staining, Iba-1 immunohistochemistry, and computational brain current density modeling. Brain lesion occurred after anodal tDCS at and above 0.5mA using a 25.0mm2 electrode (electrode current density: 20.0A/m2). Lesion initially occurred using smaller 10.6mm2 or 5.3mm2 electrodes at 0.25mA (23.5A/m2) and 0.5mA (94.2A/m2), respectively. Histological damage was correlated with computational brain current density predictions. Changes in microglial phenotype occurred in higher stimulation groups. Lesions were observed using anodal tDCS at an electrode current density of 20.0A/m2, which is below the previously reported safety threshold of 142.9A/m2 using cathodal tDCS. The lesion area is not simply predicted by electrode current density (and so not by charge density as duration was fixed); rather computational modeling suggests average brain current density as a better predictor for anodal tDCS. Nonetheless, under the assumption that rodent epicranial stimulation is a hypersensitive model, an electrode current density of 20.0A/m2 represents a conservative threshold for clinical tDCS, which typically uses an electrode current density of 2A/m2 when electrodes are placed on the skin (resulting in a lower brain current density).

Animal models of transcranial direct current stimulation: Methods and mechanisms.

The objective of this review is to summarize the contribution of animal research using direct current stimulation (DCS) to our understanding of the physiological effects of transcranial direct current stimulation (tDCS). We comprehensively address experimental methodology in animal studies, broadly classified as: (1) transcranial stimulation; (2) direct cortical stimulation in vivo and (3) in vitro models. In each case advantages and disadvantages for translational research are discussed including dose translation and the overarching "quasi-uniform" assumption, which underpins translational relevance in all animal models of tDCS. Terminology such as anode, cathode, inward current, outward current, current density, electric field, and uniform are defined. Though we put key animal experiments spanning decades in perspective, our goal is not simply an exhaustive cataloging of relevant animal studies, but rather to put them in context of ongoing efforts to improve tDCS. Cellular targets, including excitatory neuronal somas, dendrites, axons, interneurons, glial cells, and endothelial cells are considered. We emphasize neurons are always depolarized and hyperpolarized such that effects of DCS on neuronal excitability can only be evaluated within subcellular regions of the neuron. Findings from animal studies on the effects of DCS on plasticity (LTP/LTD) and network oscillations are reviewed extensively. Any endogenous phenomena dependent on membrane potential changes are, in theory, susceptible to modulation by DCS. The relevance of morphological changes (galvanotropy) to tDCS is also considered, as we suggest microscopic migration of axon terminals or dendritic spines may be relevant during tDCS. A majority of clinical studies using tDCS employ a simplistic dose strategy where excitability is singularly increased or decreased under the anode and cathode, respectively. We discuss how this strategy, itself based on classic animal studies, cannot account for the complexity of normal and pathological brain function, and how recent studies have already indicated more sophisticated approaches are necessary. One tDCS theory regarding "functional targeting" suggests the specificity of tDCS effects are possible by modulating ongoing function (plasticity). Use of animal models of disease are summarized including pain, movement disorders, stroke, and epilepsy.

Mid-term results of third-generation alumina-on-alumina ceramic bearings in cementless total hip arthroplasty: a ten-year minimum follow-up.

BACKGROUND: Alumina ceramic-on-ceramic bearings have gained popularity in hip arthroplasty because of their properties of low wear and chemical inertness. In a previous study, we reported the excellent clinical results in a series of cementless ceramic-on-ceramic primary total hip arthroplasties at a minimum of five years of follow-up. The purpose of the present study was to determine the results in the same patient cohort at a minimum of ten years of follow-up. METHODS: A series of 301 consecutive primary cementless total hip arthroplasties was assessed clinically and radiographically. Clinical information was available for 244 hips in 227 surviving patients at a minimum of ten years of follow-up, and radiographic information was available for 184 hips in 172 patients. RESULTS: Twenty-six (9.2%) of the patients had died of an unrelated cause and eight (2.7%) had undergone revision arthroplasty by the time of the latest follow-up. The average Harris hip score was 94 points, with 95% (232) of the patients having an excellent or good result and <4% (nine) having moderate residual pain. All radiographic assessments showed evidence of stable osseous ingrowth. Nine revisions had been performed, including four femoral component revisions due to periprosthetic fracture, one femoral revision due to aseptic loosening, one femoral revision secondary to a femoral shortening osteotomy for nerve palsy, two acetabular cup revisions due to psoas tendinitis, and a repeat revision in one of the patients with psoas tendinitis due to acetabular osteolysis. The overall survival rate of the implants was 98% (95% confidence interval, 94.2% to 99.6%) at ten years with revision for any reason as the end point. CONCLUSIONS: The patients in our series had a good implant survival rate, good function, a low implant wear rate as reported in the previous study, and no further radiographic evidence of failure at ten years after cementless primary total hip arthroplasty with alumina ceramic-on-ceramic bearings.

Medial tibial plateau fracture complicating unicompartmental knee arthroplasty.

We describe a new cause of a medial tibial plateau fracture complicating the early postoperative rehabilitation following unicompartmental knee arthroplasty. The patient was successfully treated by open reduction and internal fixation by buttress plating the fracture and retaining the prosthesis. The treatment option used proved to be successful, although careful patient selection for unicompartmental knee arthroplasty should be recommended to decrease the risk of this complication.