Smartphone-assisted guide for the placement of ventricular catheters.

OBJECTIVE: Freehand placement of ventricular catheters (VC) is reported to be inaccurate in 10-40 %. Endoscopy, ultrasound, or neuronavigation are used in selected cases with significant technical and time-consuming efforts. We suggest a smartphone-assisted guiding tool for the placement of VC. METHODS: Measurements of relevant parameters in 3D-MRI datasets in a patient cohort with narrow ventricles for a frontal precoronal VC placement were performed. In this context, a guiding tool was developed to apply the respective measures for VC placement. The guiding tool was tested in a phantom followed by CT imaging to quantify placement precision. A smartphone application was designed to assist the relevant measurements. The guide was applied in 35 patients for VC placement. RESULTS: MRI measurements revealed the rectangular approach in the sagittal plane and the individual angle towards the tangent in the coronal section as relevant parameter for a frontal approach. The latter angle ranged from medial (91.96° ± 2.75°) to lateral margins (99.56° ± 4.14°) of the ventricle, which was similar in laterally shifted (±5 mm) entry points. The subsequently developed guiding tool revealed precision measurements in an agarose model with 1.1° ± 0.7° angle deviation. Using the smartphone-assisted guide in patients with narrow ventricles (frontal occipital horn ratio, 0.38 ± 0.05), a primary puncture of the ventricles was possible in all cases. No VC failure was observed during follow-up (9.1 ± 5.3 months). CONCLUSIONS: VC placement in narrow ventricles requires accurate placement with simple means in an every-case routine. The suggested smartphone-assisted guide meets these criteria. Further data are planned to be collected in a prospective randomized study.

The enigma of underdrainage in shunting with hydrostatic valves and possible solutions.

OBJECTIVE: Hydrostatic devices have considerable advantages compared to "conventional" differential-pressure-valves concerning overdrainage, but are thought to imply a tendency to underdrain or to clog. The aim of this study was to evaluate the ability of the hydrostatic gravitational Dual-Switch-Valve (DSV) to minimize overdrainage-related complications without increasing the danger of underdrainage. RESULTS: In a series of 202 adult patients with different etiologies treated with a ventriculo-peritoneal shunt including the hydrostatic Dual-Switch-valve (DSV), 21 cases were suspected of suffering from underdrainage. Using a new algorithm we were able to differentiate obstruction in 6 patients from functional underdrainage in 15 cases, thus we saw an indication to reimplant a DSV with a lower opening pressure in the latter. CONCLUSION: The reasons for functional underdrainage were multifold in our series, especially the intraperitoneal pressure is still a "black box". Despite the ability of the DSV to avoid clogging and to minimize overdrainage by its high-pressure-chamber, it remains difficult to determine the optimal opening pressure of the low-pressure-chamber of the DSV for ideal clinical improvement. Therefore a new hydrostatic gravitational "programmable" valve (proGAV), entitled on avoiding the disadvantages of other adjustable devices, has been developed and implanted in 16 patients with promising results.

Dual-switch valve: clinical performance of a new hydrocephalus valve.

The Dual-Switch valve (DSV) is the first construction on the market which changes between two different valve-chambers in parallel depending on the posture of the patient. In the lying position the valve acts like a conventional differential pressure valve, in the vertical position the high-pressure chamber only opens, when the pressure exceeds the hydrostatic pressure difference between the formanen of Monro and the peritoneal cavity. The new device has been implanted in 32 adult patients with hydrocephalus of different etiology. The clinical results are excellent to good accompanied by a remarkable slight reduction of the ventricular size. Apart from one case with a nonsymptomatic transient hygroma, we saw no valve related complications like overdrainage, underdrainage or dysfunction. Contrary to conventional differential-pressure valves, adjustable devices and other hydrostatic constructions like the Anti-Siphon-device (ASD) or Deltavalve, the DSV reliably controls the IVP independently of the posture of the patient, the CSF viscosity or the subcutaneous pressure. In contrast to the Orbis-Sigma-valve (OSV) or the Diamond-valve, the DSV does not control the flow but the physiological IVP avoiding the increased risk of mechanical failure. The results of this study give strong evidence that the shunt-therapy of adult hydrocephalic patients can be significantly improved by the DSV.

Pitfalls in shunting of hydrocephalus--clinical reality and improvement by the hydrostatic dual-switch valve.

The hydrostatic dual-switch valve (DSV) was implanted in 56 patients suffering from hydrocephalus of different causes. Evaluation of the clinical status 3 and 6 months after the operation revealed excellent and good neurological recoveries in the vast majority of cases. Only 7 patients demonstrated an unsatisfactory result according to the grading of Stein and Langfitt. The CT follow-up, evaluated by the reduction of the Evans index, was characterized by only minimal or even no reduction of the ventricular size in more than half of the patients. Only 2 patients of our series developed overdrainage-related problems. 5 cases are presented to illucidate the danger of overdrainage resulting from the implantation of conventional differential-pressure valves, and the possible solution of this problem by hydrostatic devices like the DSV. Our series gives strong evidence, that reestablishing physiological pressure-ranges after shunting is paralleled by a good clinical outcome independent of the ventricular size after shunting.

The importance of the dual-switch valve for the treatment of adult normotensive or hypertensive hydrocephalus.

Since the beginning of 1995 the new hydrostatic dual-switch valve (DSV) was implanted in 35 adult patients with hydrocephalus of different etiology. 26 patients suffered from normotensive hydrocephalus (10 idiopathic and 16 symptomatic), and 9 patients from hypertensive hydrocephalus of various origin. The first 21 cases of this cohort were compared in a randomized study with a comparable group of 21 hydrocephalic patients who received a conventional differential-pressure (DP-) valve. The clinical status and CT were assessed prior to shunting, 14 days and 3 and 6 months after the operation. The reduction of ventricular size was evaluated by the measurement of the Evans Index. The CT follow-up in the DSV group was characterized by an only minimal (14) or only slight (16) reduction of ventricular size in the vast majority of cases. A comparison of 21 patients with a DSV and the patients with DP valves, evaluated by measuring the reduction of the Evans Index, revealed a distinctly higher percentage of significant regressions in the DP valve collective, without doubt due to chronic overdrainage. The overall clinical result of our 35 patients with a DSV was excellent and good in 31 patients, but the outcome seems to be more dependent on the preshunt damage of the brain than on hydrocephalic aspects. A neglegible incidence of subdural effusions in the DSV group compared to 11 cases in the DP valve collective reflects the ability of the DSV to prevent overdrainage. The capability of the DSV to maintain the IVP within physiological limits after shunting, especially in the upright position, is documented by a comparison with possible unphysiological IVP variations in other valve constructions, which depend on the level of implantation, subcutaneous pressure or CSF flow through the valve.

The dual-switch valve. A new hydrostatic valve for the treatment of hydrocephalus.

The currently available hydrocephalus valves are still far from perfect. Whereas the design principles of differential pressure valves and adjustable devices involve the danger of overdrainage, hydrostatic valves have a tendency to clog. The new dual-switch valve (DSV) avoids overdrainage-related problems such as subdural hygromas/hematomas or slit-like ventricles with the high risk of proximal catheter obstruction by means of two parallel chambers in a titanium casing: one for the the horizontal and the other for the vertical position. The control chamber for the horizontal position is closed by a gravity-activated tantalum ball as soon as the patient moves into an upright position. Now the drainage of CSF is directed into the appropriate controller for the erect position. Thus, the hydrostatic differential pressure between ventricles and peritoneal cavity is counterbalanced and the intraventricular pressure (IVP) remains within physiological values independently of the CSF flow and the position of the patient. To avoid the problem of clogging, the newly designed valve introduces large-area diaphragms to create extensive acting forces. The forces generated in this way are able to overcome sticking forces set up as a result of high protein content or cellular debris. By this mechanism the IVP is maintained in physiological ranges regardless of the CSF composition. The new valve has been investigated with a computer controlled test apparatus especially designed to simulate different positions of the body. The in vitro test results according to ASTM standards document a superior performance in comparison with other valves. When the new device was interposed in external drainage systems precision of its function was confirmed even in the presence of elevated protein content and high CSF flow. Simulation of the upright position of the patient allowed documentation of the valve's reliability in maintaining the IVP within physiological ranges. A clinical trial with implantation of the new dual-switch valve was started at the beginning of 1995; so far follow up has been short. Clinical and computer tomographic monitoring has provided evidence of the valve's capacity to avoid the problems of overdrainage and early clogging.

A new valve for the treatment of hydrocephalus.

Presently available hydrocephalus valves still are not perfect. There are two major drawbacks: They have a tendency to clog and do not take into account the posture of the patient. The latter results in an intracranial pressure which is either too high or too low. To avoid these problems a new valve was designed which is described in this article. It introduces a pressure control: The force on the actual valve seat is augmented and balanced by a powerful spring. The large forces generated this way are able to overcome sticking forces due to fibrin or cellular debris. The valve functions well even with viscous and sticky cerebrospinal fluid (CSF). This mechanism maintains the pressure almost independent of the composition of the CSF. A valve insensitive to the posture of the patient can create an overdrainage, causing related problems such as subdural hygromas, slit ventricle syndrome, and consecutive proximal catheter obstruction. This is avoided by the valve presented here. It has two different pressure controllers: one designed for the supine position and another designed for the upright position of the patient. When the patient stands up or sits up, the pressure controller for the horizontal position is shut off by a gravity-activated sphere, and the drainage of CSF is directed into the appropriate controller for the upright position. In this way, the change of the hydrostatic differential pressure between the ventricles and the peritoneal cavity is taken into account and the intracranial pressure remains within physiological values. Laboratory investigations have shown that the new valve performs as designed.

[Anchoring problems in cemented total hip endoprosthesis--a review of the literature]. / Verankerungsprobleme bei der zementierten Hüfttotalendoprothese--Eine Literaturstudie.

The question as to what constitutes the most suitable material for the cemented total hip endoprosthesis has not yet been decided. Owing to the different modules of elasticity of titanium and CoCr alloy, the characteristics of force transmission into the proximal femur vary. Titanium alloys load the proximal femur earlier and more markedly, and therefore counteract possible bone degeneration; whereas the CoCr alloys are associated with less stressing of the bone cement in the critical region of the calcar femorale. This paper is a review of the various analytical, experimental and clinical publications on the subject. Besides the question of material, the problems of bone cement and its application are also discussed.