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At least 847 records · Page 47Linked to original sources
PubMed1992

Estrogen and progesterone withdrawal increases cerebral vasoreactivity to serotonin in rabbit basilar artery.

An in vitro animal model which examines the effects of sex hormone variations during the menstrual cycle on basilar artery reactivity is presented. Three groups of rabbits were utilized: a chronically depleted control group which received no further hormonal treatment after bilateral surgical oophorectomy (O), simulating menopause, and two groups of intact females, one of which was treated to mimic the estrogen and progesterone surge during the luteal phase (H) and the third group which was acutely estrogen and progesterone depleted after the luteal surges to simulate the immediate premenstrual state (W). We show that both acute and chronic estrogen and progesterone withdrawal significantly increase serotonin sensitivity (ED50) in basilar artery rings. There was no difference between groups for maximum contraction (Tmax) to serotonin, nor optimal resting tension. Furthermore, there was no difference in vasoreactivity and contractility to norepinephrine between groups. In order to distinguish between the effects of chronic and acute treatment we examined acute estrogen and progesterone superfusion in basilar artery rings from intact non-treated female rabbits. Acute superfusion of pre-contracted and non-pre-contracted artery segments resulted in significant dilatation only when supraphysiologic concentrations of estrogen and progesterone were used. We conclude that both acute and chronic female sex hormone withdrawal selectively increases cerebral vasoreactivity to serotonin.

Animals↗
PubMed1987

Acute abdomen in ruptured interstitial pregnancy following unilateral salpingectomy.

Interstitial pregnancy is an infrequent type of ectopic pregnancy. Two cases of acute abdomen due to ruptured interstitial pregnancy following salpingectomy, a rare event, are presented. Both patients were young women who had had a previous salpingo-oophorectomy due to ovarian cyst. The presenting symptoms were in the first case abdominal pain followed by hemorrhagic shock, and in the second a right iliac fossa syndrome simulating acute appendicitis. Surgical intervention consisted of wedge resection of the uterine segment involved. A review of the literature and practical considerations are presented.

Abdomen, Acute↗
PubMed2006

Stepwise reduction of functional spinal structures increase vertebral translation and intradiscal pressure.

To date, there are only a few studies that provide data to efficiently calibrate finite element models for the spine due to its complexity. In a recent study, we quantified the range of motion rotation and the lordosis angle. This paper provides complementary results regarding two more parameters, intradiscal pressure and vertebral translation. All parameters were obtained as a function of stepwise anatomical reduction, loading direction and magnitude. Eight lumbar spinal segments (L4-5) with a median age of 52 years (38-59 years) and no signs of disc degeneration were used for the in vitro testing. A miniaturized pressure probe was implanted into the nucleus. An ultrasound-based motion-tracking system was employed to record spatial movements of several landmarks on the specimens. The center of L4, the anterior, posterior, left and right point of the lower endplate of L4 were digitized as landmarks and its translation was determined. Specimens were loaded with pure moments (1-10Nm) in the three principal anatomical planes at a loading rate of 1.0 degrees /s. Anatomy was stepwise reduced by cutting different ligaments, facet capsules and joints and removing nucleus. Translation analysis showed that the L4 center point had its largest displacement in sagittal direction and almost none vertically. Removal of the supra- and interspinous, flaval ligaments showed a slight increase and further removal of structures, a higher increase of translation. Axial rotation also was accompanied with L4 to elevate when torsion was applied. This effect was found to be larger with progressing defects. Nucleotomy exhibited the most unstable situation for specimens. Results of the intradiscal pressure indicated a large increase after removing the facet capsules and joints. Furthermore, it was found that intradiscal pressure correlated well with data of range of motion for rotation. Predicting and simulating clinical defects, surgical intervention or treatment methods requires a well performed calibration based on in vitro data, whereas it is important to adapt all including structures with as many known parameters as possible. Results provided by these studies may be used as a database for researchers aiming to calibrate or validate finite element models of L4-5 segments.

Adult↗
PubMedDate not supplied

Biomechanics of posterior dynamic stabilizing device (DIAM) after facetectomy and discectomy.

BACKGROUND CONTEXT: Lumbar fusion has been associated with inconsistent clinical outcomes and significant complications. Posterior dynamic devices have been developed to stabilize painful diseased lumbar motion segments while avoiding fusion. The Device for Intervertebral Assisted Motion (DIAM) is a silicone interspinous process "bumper" that is being clinically implanted for varied indications. PURPOSE: We analyzed the effects of the DIAM device on the biomechanical response of the lumbar spine in flexion-extension, lateral bending, and axial rotation after partial facetectomy and discectomy; the clinical situations in which its use might be considered. STUDY DESIGN/SETTING: A biomechanical study was performed using whole lumbar spine specimens (L1-sacrum). Surgical interventions were simulated at the L4-L5 level, and motions were measured at the operated and adjacent segments. PATIENT SAMPLE: Six fresh human lumbar spine specimens were used. METHODS: The lumbar spines were subjected to moments in flexion-extension (+/-6 Nm), lateral bending (+/-5 Nm), and axial rotation (+/-4 Nm). The specimens were tested under the following conditions: 1) intact; 2) after unilateral hemifacetectomy at L4-L5; 3) #2 and discectomy; and 4) #3 with DIAM. The angular motion values at the operated and adjacent segments were analyzed using analysis of variance and multiple comparisons with Bonferroni correction. RESULTS: Unilateral hemifacetectomy did not increase angular motion. Subsequent discectomy increased L4-L5 angular motion (degrees) from 9.2+/-1.6 to 11.7+/-2.0 in flexion-extension (p=.01), from 6.7+/-1.1 to 8.5+/-1.5 in lateral bending (p=.01), and from 2.6+/-0.7 to 3.8+/-0.8 in axial rotation (p=.00). Insertion of the DIAM device after discectomy restored the angular motion to below the level of the intact segment in flexion-extension (6.7+/-0.7 vs. 9.2+/-1.6, p=.02). In lateral bending, DIAM reduced the increased motion induced by discectomy (7.8+/-1.0 vs. 8.5+/-1.5, p<.05), but not to the intact level (7.8+/-1.0 vs. 6.7+/-1.1, p=.05). DIAM insertion did not reduce the increased axial rotation induced by discectomy, and the axial rotation remained larger than the intact value (4.1+/-0.6 vs. 2.6+/-0.7, p=.00). CONCLUSIONS: The DIAM device is effective in stabilizing the unstable segment, reducing the increased segmental flexion-extension and lateral bending motions observed after discectomy. In flexion-extension the DIAM restored postdiscectomy motion to below the intact values (p<.05). Interestingly, the DIAM device did not reduce the increased axial rotation motion observed after discectomy. These biomechanical effects must be considered when evaluating the clinical applications of the DIAM.

Aged↗
PubMed1997

In vitro patellofemoral joint force determined by a non-invasive technique.

OBJECTIVE: To develop a method of measuring the magnitude, direction and point of application of the patellofemoral force (PFF), directly and non-invasively in three dimensions. DESIGN AND METHODS: The compressive PFF is replaced exactly with a tensile force applied to the front of the patella. The magnitude, direction and point of application of the tensile force are then measured. The technique was applied to six normal knees mounted in a 6 degree of freedom rig with quadriceps tendon tension force (QTF) applied to balance a flexing load and to simulate weight bearing. RESULTS: The PFF was greater than in previous more invasive in vitro studies but the results correlated well with recent theoretical analyses. At 20 degrees knee flexion the force was 75% of QTF. It increased to 100% of QTF at 60 degrees knee flexion and remained at this level at higher angles of flexion. The lateral vector of the PFF was small compared to the sagittal plane vector and became negligible beyond 60 degrees of knee flexion. The point of application of the PFF to the patella moved proximally and medially with knee flexion. CONCLUSIONS: A new and reliable method of measuring PFF non-invasively and in three dimensions has been developed. RELEVANCE: A new technique is described for measuring the PFF in vitro. The non-invasive nature of the technique makes it useful for studying the effect on the PFF of simulated pathological conditions, surgical procedures and different types of knee replacement.

Journal Article↗
PubMedDate not supplied

Biomechanics of the wrist.

This article summarizes six years of studies with an experimental model, which uses a static positioning frame, pressure-sensitive film, and a microcomputer-based videodigitizing system, to characterize the biomechanics of the human cadaver wrist by measuring the contact areas and pressures in a variety of normal, simulated traumatic, and surgically treated conditions. The results of these studies have provided clinically relevant information about the normal anatomy and functional mechanics of the wrist, as well as guidelines for the treatment for a number of different fractures and ligament injuries. The results of studies of radial carpal instabilities and fractures have demonstrated an increased load in the areas where degenerative arthritis is seen in these clinical conditions, and have furnished a means by which the biomechanical efficacy of certain surgical treatments can be measured.

Biomechanical Phenomena↗
PubMedDate not supplied

[Basic equipment for arthroscopic knee surgery].

Five hundred arthroscopic operations were carried out with a 10-part hand-operated instrument set since January 1984. The most frequent operation was meniscectomy (84%), followed by removal of free bodies (18%) and division of plicae (7%). In four cases, there were instrument-dependent complications. By simulation of the surgical work on the joint in a suitable model, undesired, automatic movements of various instruments could be demonstrated. They depended on the respective principle of construction. The reliable grasping of meniscus tissue and free bodies was often a critical phase of the operation. Traction experiments on meniscus preparations showed that the arthroscopic forceps offered are frequently not equivalent to conventional surgical clamps. Instrument breaks were reconstructed in bending experiments. With some materials, a few bending cycles were sufficient in order to bring about the break. The experience obtained in our operations as well as in the laboratory experiments mentioned are described. Criteria for selection and use of hand-operated instruments for arthroscopic knee surgery are enunciated.

Arthroscopes↗
PubMed2003

Planning, simulation and assistance with intraoperative MRI.

This paper introduces some of the authors' recent attempts to enhance image-guided treatment in intraoperative magnetic resonance imaging (MRI). These include the deformable registration of preoperative images obtained by 1.5 Tesla MRI to the intraoperative images, and a needle-holding robotic system that is MR-compatible and optimized to work with intraoperative MRI. The role of deformable registration is to enhance intraoperative planning and simulation, and the robotic system is to systematically link the result of such planning and simulation to active surgical assistance. The former was retrospectively examined in prostate cancer biopsy cases and statistically suggested that deformable registration significantly improved the quality of registration. The latter, which is planned to be applied to prostate brachytherapy, was found to have good MR compatibility and its maneuvering had no adverse effect on the imaging and vice versa .

Journal Article↗
PubMed2001

New equipment and techniques for airway management in trauma.

A patent, unobstructed airway is fundamental in the care of the trauma patient, and is most often obtained by placing a cuffed tube in the trachea. The presence of shock, respiratory distress, a full stomach, maxillofacial trauma, neck hematoma, laryngeal disruption, cervical spine instability, and head injury all combine to increase tracheal intubation difficulty in the trauma patient. Complications resulting from intubation difficulties include brain injury, aspiration, trauma to the airway, and death. The use of devices such as the gum-elastic bougie, McCoy laryngoscope, flexible and rigid fiberscopes, intubating laryngeal mask, light wand, and techniques such as rapid-sequence intubation, manual in-line axial stabilization, retrograde intubation, and cricothyroidotomy, enhance the ability to obtain a definitive airway safely. The management of the failed airway includes calling for assistance, optimal two-person bag-mask ventilation, and the use of the laryngeal mask airway, Combitube, or surgical airway. The simulation of airway management using realistic simulator tools (e.g. full-scale simulators, virtual reality airway simulators) is a promising modality for teaching physicians and advanced life support personnel emergency airway management skills.

Journal Article↗
PubMedDate not supplied

Metrizamide optic nerve sheath opacification.

The safety of metrizamide in the optic nerve sheath has not been studied to our knowledge. We studied histologic changes produced by metrizamide in the optic nerve of cats with surgically created lesions simulating orbital tumors and trauma. Displacement, compression, and disruption of the optic nerve sheath were detectable by radiographing the opacified sheath. Arachnoiditis of the optic nerve sheath is unlikely from a single exposure to metrizamide in a concentration less than 300mg I/ml.

Animals↗
PubMedDate not supplied

Three-dimensional characteristics of cartilaginous and bony components of dysplastic hips in children: three-dimensional computed tomography quantitative analysis.

A cartilage-viewing technique was developed to overcome the shortcoming of not seeing the cartilaginous components, believed to play more important role than the osseous components in children's hips, with computed tomography. This technique was applied to 25 dysplastic hips in children younger than 10 years to evaluate their global and local deficiencies. The findings helped us to understand more about their individual problems. To quantify the three-dimensional (3-D) parameters of acetabular anatomy and femoral head coverage, a measuring technique was developed based on digitization of the 3-D coordinates and fitting of every component of the hip. The improved images and the quantified parameters were expected to aid the planning, formulation, and even simulation of individualized surgical treatment for children with developmental dysplasia of the hip.

Acetabulum↗
PubMed1996

A proposed technique for intraoperative measurement of cervical spine stiffness.

OBJECTIVE: Classically cervical biomechanical data have been obtained using cadaver models. Few methods exist for in vivo measurement of cervical biomechanics. A technique for intraoperative measurement of cervical motion segment stiffness (load-axial displacement) has been developed, enabling load/displacement data to be obtained during surgery at the spinal levels operated on and at adjacent cervical levels. METHODS: The instrument used for measuring motion segment stiffness was a vertebral retractor equipped with displacement and strain transducers and designed to be placed over the shafts of Caspar distraction screws. Stiffness was measured under simulated anterior cervical surgical conditions. RESULTS: A preliminary study deciphering axial cervical spine load/displacement data on 12 cadavers was performed with this instrument. Using a distraction load of 88.8640 N, axial displacements of 2.110 +/- 0.258 mm (mean +/- standard error of the mean) at C3-C4, 2.367 +/- 0.304 mm at C4-C5, and 2.207 +/- 0.238 mm at C5-C6 were found. When data were evaluated for age, there was a significant decrease in stiffness with advancing age in two of the three spinal segments tested (P < 0.05 for C3-C4, P < 0.04 for C4-C5, P < 0.12 for C5-C6), which correlated with previous studies. CONCLUSION: These results suggest that this technique may be useful in assessing intraoperative motion-segment stability.

Adult↗
PubMed1991

Total perineal reconstruction after major obstetrical injuries with extensive tissue loss: a report of 2 cases.

Major perineal injuries following obstetrical complications represent difficult problems of reconstruction. We describe 2 such patients with perineal injuries simulating infantile cloacas. Surgical repair using an abdominoperineal pullthrough procedure in 1 patient, and a Bricker loop type of repair in another resulted in successful restoration of function in both. The operative details and basis for the reconstruction are described.

Adult↗
PubMed2002

[See-through head-mounted display augmented reality for maxillofacial surgery].

In this paper we present the medical augmented reality system INPRES for Intraoperative Presentation of surgical planning and simulation results. The system is based on a see-through head-mounted display for data visualization and overlay. Key challenges are tracking of the display and the patient, registration of virtual data with the real world and calibration of the display device. Further tasks are detection of occlusions, intuitive man-machine-cooperation and evaluation of the complete setup. The system configuration and the methods are shown, first results are given and future work is outlined.

Calibration↗
PubMed2006

Two-part surgical neck fractures of the proximal part of the humerus. A biomechanical evaluation of two fixation techniques.

BACKGROUND: Successful internal fixation of fractures of the surgical neck of the humerus can be difficult to achieve because of osteopenia of the proximal aspect of the humerus. The purpose of this study was to compare the biomechanical stability of a proximal humeral intramedullary nail and a locking plate for the treatment of a comminuted two-part fracture of the surgical neck in a human cadaver model. METHODS: Twenty-four cadaveric humeri were instrumented with use of either a titanium proximal humeral nail (PHN) or a 3.5-mm locking compression plate for the proximal part of the humerus (LCP-PH). The specimens were matched by bone mineral density and were separated into four experimental groups with six humeri in each: PHN bending, LCP-PH bending, PHN torsion, or LCP-PH torsion. Comminuted fractures of the surgical neck were simulated by excising a 10-mm wedge of bone. Bending specimens were cyclically loaded from 0 to 7.5 Nm of varus bending moment at the fracture site. Torsion specimens were cyclically loaded to +/-2 Nm of axial torque. The mean and maximum displacement in bending, mean and maximum angular rotation in torsion, and stiffness of the bone-implant constructs were compared. RESULTS: In bending, the LCP-PH group demonstrated significantly less mean displacement of the distal fragment than did the PHN group over 5000 cycles (p = 0.002). In torsion, the LCP-PH group demonstrated significantly less mean angular rotation than did the PHN group over 5000 cycles (p = 0.04). A significant number of specimens in the PHN group failed prior to reaching 5000 cycles (p = 0.04). The LCP-PH implant created a significantly stiffer bone-implant construct than did the PHN implant (p = 0.007). CONCLUSIONS: The LCP proximal humeral plate demonstrated superior biomechanical characteristics compared with the proximal humeral nail when tested cyclically in both cantilevered varus bending and torsion. The rate of early failure of the proximal humeral nail could reflect the high moment transmitted to the locking proximal screw-bone interface in this implant. CLINICAL RELEVANCE: The high failure rate in torsion of the proximal humeral nail-bone construct is concerning, and, with relatively osteoporotic bone and early motion, the results could be poor.

Adult↗
PubMed1997

Computed tomography data based rapid prototyping model of the temporal bone before cochlear implant surgery.

Rapid prototyping (RP) technique allows automatic fabrication of 3D model parts. This method was applied to make a temporal bone model before cochlear implant surgery. A helical CT scan is used to acquire high resolution data from the middle and the inner ear of the patient. From the scanning data bone structures and soft tissues can be separated because their different grayscale pixel values. By using a guided image processing tool the desired parts of the anatomy can be extracted and 3D data created. The segmented data are processed to the form suitable for creating a high accuracy RP model. The RP model is made in the stereolithography (SLA) process by means of a computer guided HeCd laser beam inducing polymerisation of acrylic solution as it passes layer by layer over the surface of the polymer solution. In this prototype model the anatomy of the temporal bone can be clearly visualised, including, e.g., mastoid cells, tympanic cavity, bony canal of facial nerve, and round and oval windows. The inner ear spaces including vestibule, semicircular canals and cochlear turn are also shaped. The transparent acrylic material allows bonelike mechanical handling. The RP model can be dissected and used in individual surgical planning and simulation prior to cochlear implantation.

Cochlear Implants↗
PubMed2006

Real-time tracking of vertebral body movement with implantable reference microsensors.

OBJECTIVE: In the spine, navigation techniques serve mainly to control and accurately target insertion of implants. The main source of error is that the spine is not a rigid organ, but rather a chain of semiflexible movement segments. Any intraoperative manipulation of the patient alters the geometry and volumetry as compared to the 3D volume model created from the image data. Thus, the objective of the study was to implement the theoretical principle of microsensor referencing in a model experiment and to clarify which anatomical structures are suitable for intermittent implantation of positional sensors, as illustrated with cervical vertebral bodies. MATERIALS AND METHODS: Laboratory tests were conducted using 70 models of human cervical vertebral bodies. The first experiment investigated whether arbitrary movements of vertebral bodies can be tracked with the positional information from the implanted microsensors. The accuracy of this movement monitoring was determined quantitatively on the basis of positional error measurement. In the second experiment, different ventral and dorsal surgical operations were simulated on five models of the cervical spine. Quantifiable measurement values such as the spatial extension of the intervertebral space and the relative positions of the planes of the upper plates were determined. RESULTS: With respect to the differing anatomy of the individual vertebral bodies of the cervical spine, the sensors could be placed securely with a 5x2 mm drill. The registration error (RE) was determined as a root mean square error. The mean value was 0.9425 mm (range: 0.57-1.2 mm; median: 0.9400 mm; SD: 0.1903 mm). The precision of the movement monitoring of the vertebral body was investigated along its three main axes. The error tolerance between post-interventional 3D reconstruction and direct measurement on the model did not exceed 1.3 mm in the distance measurements or 2.5 degrees in the angular measurements. The tomograms on the system monitor could be updated in close to real time on the basis of the positional information from the reference sensor. CONCLUSIONS: Motion sensors implanted into the vertebral bodies communicated any change in position to the navigation system in close to real time, thus enabling the preoperative image data set to be updated. The experiments described could ultimately show that continuous real-time visualization of individual vertebral body movements along the movement axes (flexion-extension, tilting and rotation) is possible with high accuracy using implantable microsensors. A future application of such microsensors might be the integration of robot systems into spinal microsurgery.

Cervical Vertebrae↗
PubMed1998

Patellar stabilization: a quantitative evaluation of the vastus medialis obliquus muscle.

Twenty-one cadaveric knees were dissected to analyze the functional anatomy of the vastus medialis complex (VMC), which is composed of the vastus medialis obliquus (VMO) and the vastus medialis longus (VML) muscles. The physiologic cross-sectional area of the VMO for 20 of the knees was 29% of the total physiologic cross-sectional area for the VMC. These values differed in one knee with a dysplastic VMO. The quantitative description of the VMO provided by this study will facilitate future efforts to accurately model the physiologic function of the VMO in cadaveric investigations on patellofemoral mechanics. The effect of simulated pathologies and surgical reconstructions then may be determined with more certainty to improve patient management.

Adult↗