Reduction of total knee replacement wear with vitamin E blended highly cross-linked ultra-high molecular weight polyethylene.

Ultra-high molecular weight polyethylene (UHMWPE) is a common bearing component in total knee replacement (TKR) implants, and its susceptibility to wear continues to be the long-term limiting factor in the life of these implants. This study hypothesized that in TKR systems, a highly cross-linked (HXL) UHMWPE blended with vitamin E will result in reduced wear as compared to a direct compression-moulded (DCM) UHMWPE. A wear simulation study was conducted using an asymmetric lateral pivoting '3D Knee' design to compare the two inserts. The highly cross-linked UHMWPE was aged prior to the testing and force-controlled wear testing was carried out for 5 million cycles using a load-controlled ISO-14243 standard at a frequency of 1 Hz on both groups. Gravimetric measurements of DCM UHMWPE (4.4 +/- 3.0 mg/million cycles) and HXL UHMWPE with vitamin E (1.9 +/- 1.9 mg/million cycles) showed significant statistical differences (p < 0.01) between the wear rates. Wear modes and surface roughness for both groups revealed no significant dissimilarities.

Modeling of peptide adsorption interactions with a poly(lactic acid) surface.

The biocompatibility of implanted materials and devices is governed by the conformation, orientation, and composition of the layer of proteins that adsorb to the surface of the material immediately upon implantation, so an understanding of this adsorbed protein layer is essential to the rigorous and methodical design of implant materials. In this study, novel molecular dynamics techniques were employed in order to determine the change in free energy for the adsorption of a solvated nine-residue peptide (GGGG-K-GGGG) to a crystalline polylactide surface in an effort to elucidate the fundamental mechanisms that govern protein adsorption. This system, like many others, involves two distinct types of sampling problems: a spatial sampling problem, which arises due to entropic effects creating barriers in the free energy profile, and a conformational sampling problem, which occurs due to barriers in the potential energy landscape. In a two-step process that addresses each sampling problem in turn, the technique of biased replica exchange molecular dynamics was refined and applied in order to overcome these sampling problems and, using the information available at the atomic level of detail afforded by molecular simulation, both quantify and characterize the interactions between the peptide and a relevant biomaterial surface. The results from these simulations predict a fairly strong adsorption response with an adsorption free energy of -2.5 +/- 0.6 kcal/mol (mean +/- 95% confidence interval), with adsorption primarily due to hydrophobic interactions between the nonpolar groups of the peptide and the PLA surface. As part of a larger and ongoing effort involving both simulation and experimental investigations, this work contributes to the goal of transforming the engineering of biomaterials from one dominated by trial-and-error to one which is guided by an atomic-level understanding of the interactions that occur at the tissue-biomaterial interface.

New methods for the evaluation and treatment of craniofacial dysostosis-associated cerebellar tonsillar herniation.

Herniation of the cerebellar tonsils may occur in children with craniofacial dysostosis (e.g., Apert, Carpenter, Crouzon, Jackson-Weiss, Pfeiffer, and Saethre-Chotzen syndromes), occasionally, with serious sequelae. Cerebellar tonsillar herniation is probably acquired in children affected with craniofacial dysostosis, raising the question, How should we be screening for this anomaly? This retrospective clinical study was undertaken to review the authors' series of what they believe to be a new surgical treatment for craniofacial dysostosis-associated cerebellar tonsillar herniation and to report their experience with a new screening technique. In an attempt to find a low-cost alternative to the use of routine magnetic resonance imaging for identifying cerebellar tonsillar herniation, the authors instituted sagittal reformatting of three-dimensional computed tomographic scans through the foramen magnum. Scans are considered positive if soft tissue is noted to extend below the foramen magnum, and all positive scans are further evaluated by magnetic resonance imaging with flow studies of the cerebrospinal fluid. These sagittally reformatted scans add no additional cost, and they seem to be highly sensitive in screening for cerebellar tonsillar herniation. Over a 13-month period, five children (one with Apert syndrome; four with Crouzon syndrome) with craniofacial dysostosis-associated cerebellar tonsillar herniation underwent isolated anterior cranial vault remodeling to treat observed brachycephaly (standard neurosurgical posterior decompression was not performed). All patients (mean age, 6 years; range, 2 to 14 years) were without the symptoms typically associated with cerebellar tonsillar herniation. Only those patients who had preoperative and postoperative magnetic resonance imaging scans were included in this review. All patients showed some improvement by the authors' magnetic imaging criteria after anterior cranial vault remodeling. Despite these findings, the authors recommend that until the anterior approach can be further studied, symptomatic children should undergo standard posterior neurosurgical decompression. The authors speculate that the presence of cerebellar tonsillar herniation may be a relative indication for decompressing the cranial vault in the craniofacial dysostoses. In addition, they propose that the descriptive anatomic term "cerebellar tonsillar herniation" be substituted for the misnomer "Chiari malformation" in these children.

The slit ventricle syndrome.

This article reviews the collection of entities that still are described as slit ventricle syndrome, discusses the various diagnoses, and reviews the investigation and treatment of children with small ventricles after ventricular shunting.

Deep venous thrombosis with suspected pulmonary embolism: detection with combined CT venography and pulmonary angiography.

PURPOSE: To determine the frequency and location of deep venous thrombosis at computed tomographic (CT) venography after CT pulmonary angiography in a large series of patients clinically suspected of having pulmonary embolism and to compare the accuracy of CT venography with lower-extremity venous sonography. MATERIALS AND METHODS: Venous phase images were acquired from the diaphragm to the upper calves after completion of CT pulmonary angiography in 650 patients (373 women, 277 men; age range, 18-99 years; mean age, 63 years) to determine the presence and location of deep venous thrombosis. Results of CT venography were compared with those of bilateral lower-extremity venous sonography in 308 patients. RESULTS: A total of 116 patients had pulmonary embolism and/or deep venous thrombosis, including 27 patients with pulmonary embolism alone, 31 patients with deep venous thrombosis alone, and 58 patients with both. Among 89 patients with deep venous thrombosis, thrombosis was bilateral in 26, involved the abdominal or pelvic veins in 11, and was isolated to the abdominal or pelvic veins in four. In patients in whom sonographic correlation was available, CT venography had a sensitivity of 97% and a specificity of 100% for femoropopliteal deep venous thrombosis. CONCLUSION: Combined CT venography and pulmonary angiography can accurately depict the femoropopliteal deep veins, permitting concurrent testing for venous thrombosis and pulmonary embolism. CT venography also defines pelvic or abdominal thrombus, which was seen in 17% of patients with deep venous thrombosis.

Surgical technique for the insertion of grids and strips for invasive monitoring in children with intractable epilepsy.

Despite improved imaging, and electrical and magnetic external mapping, there are a large number of children with intractable epilepsy in whom a focus cannot be defined by non-invasive techniques. Invasive monitoring with depth electrodes, electrode grids and/or strips is required in up to 50% of children with a suspected focal seizure disorder. In children with suspected temporal lobe epilepsy the invasive techniques are required to identify which temporal lobe is the primary focus, to separate temporal from frontal foci, and to define the extent of involvement of the lateral temporal cortex. In children and infants with non-temporal epilepsy, invasive monitoring is required to define the epileptogenic zone and to map areas of cortical specialization. The current techniques used for surgical implantation are described here. In a correctly selected population invasive monitoring will define the epileptogenic focus or foci in 90% of children; 80% will have surgically treatable epilepsy. Infection rates are less than 1% for subdural strips and 6% for grids. In 88 cases no incidence of meningitis occurred.

Imaging after head trauma: why, when and which.

CT scanning is the current first imaging technique to be used after head injury, in those settings where a CT scan is available. The first scan is usually done without contrast enhancement. The value of CT is the demonstration of scalp, bone, extra-axial hematomas and parenchymal injury. It is rapid and easily done in the presence of the multiple monitors that many trauma patients have in place. It can be used to demonstrate the bony anatomy of the spine and is good for evaluation of abdominal and chest trauma also. MRI is more sensitive for all posttraumatic lesions other than skull fracture and subarachnoid hemorrhage, and can demonstrate parenchymal spinal cord injury. The cons are a longer scanning time, interference of the imaging by certain ICP monitors and problems with the positions of the monitoring equipment and ventilators outside the MRI magnetic field. MRI will be used increasingly to study early head injury because of its ability to measure cerebral blood flow, cerebral blood volume and the location and extent of cerebral edema. If the CT does not demonstrate pathology adequate to account for the clinical state, MRI is warranted. Follow up is best done with MRI as it is more sensitive to parenchymal change than is CT.

Surgical treatment of focal epilepsy in children: results in 37 patients.

This report concerns 37 children and teenagers operated upon for intractable seizures between 1990 and 1994. Follow-up is at least 3 years. Fourteen children underwent pure temporal lobe resections; 71% are seizure free, and 93% have a better than 90% decrease in seizure frequency. The presence of a lesion on magnetic resonance imaging, the side of the lesion, or the presence of abnormal pathology had no influence on the result of resection. 28% of the children who had extratemporal resections are seizure free, and 83% have a greater than 90% decrease in seizure frequency. There was a trend to better results in those with a lesion on magnetic resonance imaging. In the small group with temporal plus extratemporal foci, the results were poor with only 60% showing a greater than 90% reduction in seizure frequency.

Consensus: craniofacial synostoses. Apert and Crouzon syndromes.

A critical analysis of functional and morphological aspects of Apert and Crouzon syndromes is presented, with reference to the papers presented in this session of the Consensus Conference on Craniosynostoses. Targets and limits of surgical correction are also discussed.

Ventriculoperitoneal shunts for hydrocephalus: a focus group discussion on the selection of shunt systems in pediatrics. A report of the Pediatric Neurosurgery Research Group meeting, December 1992.

As part of the Continuing Quality Improvement Study, phase I, 12 pediatric neurosurgeons participated in a discussion group to respond to the various issues related to selection of ventriculoperitoneal shunt systems in their practice. It was estimated that between then all the 12 participants performed approximately 1200 shunt procedures per year in the USA. The data were analyzed by grid and fish-bone charts as part of the data collection. All 12 participants indicated that they preferred a reservoir in the shunt system, 8 of them indicating that they preferred this for a manual test of the system. Three indicated that they did not routinely manipulate the system for testing. One participant stated that he placed a reservoir within the shunt system primarily to prevent migration of the ventricular catheter. Nine neurosurgeons indicated that they employed cranial valves in their shunt systems, and three indicated that they employed slit-end peritoneal catheters only. In reference to Delta valves, nine participants indicated that they employed them on occasions. In reference to pressure in the valve system, one participant employed high-pressure valves at all times, five employed only medium-pressure systems, and the remaining six always employed low-pressure valves. All 12 neurosurgeons stated that the incidence of symptomatic slit ventricle in their practices was between 1% and 5%, in their mind irrespective of the system used. It was concluded that any form of ventriculoperitoneal shunt, with or without valves, with slit-end valves or cranial valves seemed to work equally well in the hands of a dedicated pediatric neurological surgeon.(ABSTRACT TRUNCATED AT 250 WORDS)

Transfacial approaches to the cranial base.

This article classifies and describes the anterior transfacial approaches to the cranial base as determined by the anatomic location of the lesions. With the use of craniofacial techniques, many of these lesions now may be resected without any significant functional or anesthetic morbidity.

Observations on the use of rigid fixation for craniofacial deformities in infants and young children.

With the introduction of smaller plating systems, many surgeons have adopted their use for craniofacial procedures in infants and small children. We have encountered some previously undescribed problems associated with the use of plates and screws in infants and children. These problems can be classified into three general areas: 1) Plate displacement. This occurs after placement of the metal plates on the outside of the infant calvaria. With subsequent growth, these plates and screws may be found along the inner cortex of the skull with screw points embedded through dura. 2) Plate and screw isolation. In certain locations in young children, plates placed on the outer cortex of bone may later be found to be more prominent, isolated on a peninsula of bone. 3) Plate placement. We have also encountered plates that have been placed along the inner cortex of the skull during a previous operative procedure. This makes subsequent surgery extremely difficult and may increase the risk for secondary surgery. We propose that a previously described model for growth, involving areas of bony resorption and deposition, may be responsible for the observed plate displacement.

Dissociation between delayed alternation and memory after pediatric head injury: relationship to MRI findings.

This study investigated the usefulness of a delayed alternation task in characterizing the cognitive sequelae of closed head injury in children and adolescents. Verbal learning and memory (California Verbal Learning Test) were also studied for comparison. Sixty-two closed head injury patients (mean age, 9.6 years), who were studied after an average postinjury interval of 20 months, were divided according to both their lowest postresuscitation Glasgow Coma Scale score (3 to 8 versus 9 to 15) and age range (5 to 7 years versus 8 to 16 years) at the time of testing. Magnetic resonance imaging was performed to evaluate the relationship of focal brain lesions to cognitive and memory performance. Fifty-six neurologically normal children (mean age, 9.9 years) were tested on the same measures. The results disclosed no relationship between delayed alternation performance and severity of injury. In contrast, verbal memory was impaired in the severely-injured patients, relative to both controls and less severely-injured patients. Frontal lobe (but not extrafrontal) lesion size incremented the Glasgow Coma Scale score in predicting verbal memory, but there was no relationship between focal brain lesions and delayed alternation performance. In contrast to the tendency for more efficient delayed alternation performance in the 5- to 7-year-old subjects than in the 8- to 16-year-old subjects, verbal memory significantly improved with age in the closed head injury and control groups. Notwithstanding our essentially negative findings for delayed alternation, it is possible that this task may be useful for assessing frontal lobe injury in younger children or infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain tumors in children under 2 years: treatment, survival and long-term prognosis.

Survival for children with brain tumors less than 2 years of age at diagnosis is dismal, and the quality of life of long-term survivors poor. Between 1975 and 1987, 78 (13%) of 579 patients with brain tumors treated at Children's Hospital of Philadelphia were under 2 years of age. Tumor site was posterior fossa in 31 (40%) and supratentorial in 47 (60%). Nine of 37 patients (24%) with malignant tumors, and 30 of 41 (73%) patients with benign tumors are alive with a mean follow-up of 116 months. Long-term survival after treatment with chemotherapy alone occurred in 10 patients, including 3 with malignant tumors. In 5 additional patients, chemotherapy delayed the need for irradiation a mean of 30 months. Of the 29 patients who relapsed after initial therapy, 12 are alive without progressive disease (2 patients with malignant tumors and 10 with benign tumors) a mean of 80 months after relapse, 2 children are alive with progressive disease, and 14 died a median of 48 months (range 9-115 months) after relapse. Twenty-one of the 39 survivors have minimal or no neurological or intellectual dysfunction. Surviving patients treated with surgery and chemotherapy have better intellectual function than patients treated with surgery and radiation (with or without chemotherapy) in that 8 of 10 children treated with surgery and chemotherapy have normal or above normal intelligence compared with 5 of 12 children receiving irradiation before their second birthday.