Improved Hodgkin-Huxley type model for neural action potentials.

The simple Goldman-Hodgkin-Katz model for resting-state membrane potentials has been generalized to provide a new nonlinear theoretical model for action potentials in perfused axons. Our minimalistic model appeals naturally to physically based electrodiffusion principles to describe electric-current densities inside sodium and potassium-ion channels whereas the 1952 Hodgkin-Huxley model describes such current densities in an ad hoc way. Although the two models share similar schemes for the kinetics of ion-channel gating, our relaxation times for channel gating are simpler, being independent of membrane potential. Like the theoretical model of Hodgkin and Huxley, based primarily on experimental data at [Formula: see text], our dynamical system behaves as a 4-dimensional resonator exhibiting subthreshold oscillations. Although our present analysis refers to experiments at [Formula: see text], re-parameterizations of this model should permit consideration of action potentials at alternative temperatures. The predicted speed of propagating action potentials in giant axons of squid at [Formula: see text] is in excellent agreement with the Hodgkin-Huxley experimental value at [Formula: see text]. In cases where our model predictions differ from those of the Hodgkin-Huxley model, new experiments will be required to determine which model is more accurate.

Evaluation of Protective Equipment Used Among Motorbike Riders.

INTRODUCTION: This study compared outcomes between patients injured at a motorbike track, which requires riders to follow safety equipment guidelines, and those involved in recreational riding where safety equipment usage is voluntary. METHODS: A retrospective review was conducted of all patients presenting with motorbike-related injuries at an American College of Surgeons verified level-I trauma center between January 1, 2009 and December 31, 2013. Data collected included demographics, injury details, safety equipment use, hospitalization details, and discharge disposition. Comparisons were made regarding protective equipment usage. RESULTS: Among the 115 patients admitted, more than half (54.8%, n = 63) were injured on a motorbike track, and 45.2% (n = 52) were injured in a recreational setting. The majority of patients were male (93.9%), Caucasian (97.4%), and between the ages of 18 to 54 (64.4%). Helmet usage was higher among track riders (95.2%, n = 60) than recreational riders (46.2%, n = 24, p < 0.0001). Comparisons of injury severity and outcomes between those who wore protective equipment and those who did not were not significant. CONCLUSION: Even though track riders wore protective equipment more than recreational riders, there was no difference between the groups regarding injury severity or hospital outcomes. These results suggested that motocross riders should not rely on protective equipment as the only measure of injury prevention.

Repeat head imaging in blunt pediatric trauma patients: Is it necessary?

BACKGROUND: Children with confirmed brain injury usually undergo follow-up computed tomography (CT) scan of the head within 24 hours of admission. To date, no evidence exists to validate the diagnostic or therapeutic value of these repeat CTs. The purpose of this study was to (1) evaluate progression of traumatic brain injuries, (2) determine if routine repeat imaging changes management, and (3) compare the efficacy of recognizing worsening hemorrhage with serial neurological examination versus repeat imaging. METHODS: A 5-year retrospective review was conducted of all patients aged under 18 years with blunt traumatic head injury (n = 95). Data included demographics, type and size of intracranial hemorrhage, exam findings, diagnostic and management changes, and hospital outcomes. RESULTS: Most patients (68.4%) had at least one repeat CT; of these, 67.7% (n = 44) showed no change or reduced hemorrhage. In only one patient did a repeat CT scan result in a surgical procedure; however, that CT scan was prompted by a change in neurological status. Among patients with more than two repeat head CTs, 42.9% led to a change in management, most frequently an additional CT scan. Presence of neurological symptoms was associated with having repeat CT scans (p = 0.025). Changes in Glasgow Coma Scale score were associated with increased hemorrhage (p = 0.012) but not repeat scans (p = 0.496). In the majority of cases, increased hemorrhage only resulted in an additional head CT and prolonged intensive care unit stay. Excluding patients who arrived with brain death, there was no difference in mortality between patients with and without repeat imaging. CONCLUSION: Findings from this study support a selective approach for repeating head CTs with emphasis on changes in neurological symptoms and Glasgow Coma Scale score. Prospective studies on timing and indications for repeat CT scans are needed to support development of clinical guidelines. LEVEL OF EVIDENCE: Therapeutic study, level III.

Pediatric trauma system models: do systems using adult trauma surgeons exclusively compare favorably with those using pediatric surgeons after initial resuscitation with an adult trauma surgeon?

BACKGROUND: A shortage of pediatric surgeons exists. The purpose of this study was to evaluate pediatric outcomes using pediatric surgeons vs adult trauma surgeons. METHODS: A review was conducted at 2 level II pediatric trauma centers. Center I provides 24-hour in-house trauma surgeons for resuscitations, with patient hand-off to a pediatric surgery service. Center II provides 24-hour in-house senior surgical resident coverage with an on-call trauma surgeon. Data on demographics, resource utilization, and outcomes were collected. RESULTS: Center I patients were more severely injured (injury severity score = 8.3 vs 6.2; Glasgow coma scale score = 13.7 vs 14.3). Center I patients were more often admitted to the intensive care unit (52.2% vs 33.5%) and more often mechanically ventilated (12.9% vs 7.7%), with longer hospital length of stay (2.8 vs 2.3 days). However, mortality was not different between Center I and II (3.1% vs 2.4%). By logistic regression analyses, the only variables predictive of mortality were injury severity score and Glasgow coma scale score. CONCLUSION: As it appears that trauma surgeons' outcomes compare favorably with those of pediatric surgeons, utilizing adult trauma surgeons may help alleviate shortages in pediatric surgeon coverage.

Evaluation of chest tube administration of tissue plasminogen activator to treat retained hemothorax.

BACKGROUND: When retained hemothorax occurs, video-assisted thoracoscopy or thoracotomy is performed, but recently, tissue plasminogen activator (tPA) has been used. This study evaluated intrapleural tPA use for retained traumatic hemothoraces. METHODS: A retrospective review was conducted of trauma patients treated with intrapleural tPA for retained hemothorax. Data included demographics, past medical and surgical histories, injury details, treatment details, and outcomes. RESULTS: Seven patients (median age = 47 years, male = 6, blunt trauma = 6) met study criteria. All patients received a chest tube. Six patients later received computed tomography-guided drains for tPA infusion. Number of tPA treatments per patient varied from 1 to 5. Median total tPA dosage was 24 mg. Median time from injury to chest tube placement was 11 days and from chest tube placement to first tPA treatment was 4 days. No patients required a video-assisted thoracoscopy; however, 1 patient required thoracotomy. There were no deaths or bleeding complications attributed to intrapleural tPA. CONCLUSION: Although future studies are needed to identify optimum treatment guidelines, intrapleural tPA appears to be a safe and efficacious treatment option.

Rehabilitation of lower limb traumatic amputees: the Sandy Gall Afghanistan Appeal's experience.

Physical rehabilitation after lower limb traumatic amputation due to acts of war has not yet been investigated. It has been shown that patients suffering non-war injuries rehabilitate well. This study shows that despite the difficult circumstances and limited resources available in an area of conflict, good rehabilitation of war victims is possible. However, economic rehabilitation is worse than that seen in non-war populations. Given that this type of injury is very common in war zones worldwide, this failure of economic rehabilitation may represent a major healthcare issue.

Early failure of titanium alloy femoral components: a quantitative radiological analysis of osteolytic and granulomatous change.

Shot blasted titanium alloy femoral components with a coarse finish were withdrawn from use in 1987 following reports of early component failure. We reviewed all coarse titanium femoral stems used in primary total hip arthroplasty in our institution between 1985 and 1987 and compared them to a similar stem made of vitallium which was also used over the same period. We found that, at an average of 5.2 years following implantation, over two-thirds of titanium components were associated with endosteal lysis. In many of the cases the early lytic changes were asymptomatic with significant bone loss occurring prior to presentation. We discuss our findings in relation to revision surgery. We advocate that all those with coarse stem titanium components should be positively reviewed to detect early lytic change before extensive bone destruction occurs.

The Guildford elbow.

A new unconstrained elbow replacement is described and the results of 44 primary and 5 revision operations assessed. A high incidence of pain relief (82%) and functional improvement (73%) was achieved. However 23% of primary replacements later underwent loosening as assessed radiologically and 12% have undergone revision for pain. Minor complications not affecting the final result occurred in 28%. The causes and significance of the complications are analysed.

Cubital bursitis.

We describe two cases of bursitis at the insertion of the biceps tendon. They presented as swellings in the cubital fossa with symptoms of median nerve irritation. The aetiology was probably mechanical trauma; both patients were cured by operation.

Osteomyelitis in a general hospital. A five-year study showing an increase in subacute osteomyelitis.

We have reviewed 60 patients with primary bone infections; 21 of these (35%) had subacute osteomyelitis, a figure which supports other recent observations that this variant of bone infection is becoming more widespread. In this group open culture and biopsy were necessary in order to exclude bony malignancy, and a raised erythrocyte sedimentation rate proved a useful diagnostic aid. All the patients with acute osteomyelitis or with vertebral infection responded to primary treatment, but five of those with subacute osteomyelitis had recurrences.

The Guildford elbow joint.

The Guildford Elbow Joint prosthesis uses a non-rigid hinge articulation combined with intra-medullary stems to replace the humero-ulnar joint. The metal-on-plastic articulating surfaces are designed to allow some subluxation and accessory movements while remaining self-centering and stable under load. The intra-medullary stems are shaped to provide a good fit in the curves shafts of the ulna and humerus and should provide good fixation without the removal of large amounts of bone. The prosthesis is fixed with acrylic cement. The design follows, where possible, the normal anatomy and function of the elbow. A correct operative technique is important, but the procedure shows no particular difficulties.