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At least 469 records · Page 26Linked to original sources
PubMed2004

Lengthening of double-looped tendon graft constructs in three regions after cyclic loading: a study using Roentgen stereophotogrammetric analysis.

Lengthening of a double-looped tendon graft construct used to reconstruct the anterior cruciate ligament (ACL) can result in an increase in anterior knee laxity and affect the stability of the reconstructed knee. Three possible regions where lengthening of the construct can occur are (1) the region of the tibial fixation, (2) the region of the femoral fixation, and (3) the region of the graft between the fixations. One objective of this study was to demonstrate the feasibility of using Roentgen stereophotogrammetric analysis (RSA) to determine the lengthening in each region of a double-looped graft construct subjected to cyclic loading. A second objective was to determine which region(s) contributes most to an increase in length of this graft construct. Radio-opaque markers were attached to ten grafts to measure the lengthening in each of the three regions. Each graft was passed through a tibial tunnel in a bovine tibia, looped around a rigid cross-pin, and fixed to the tibia with a Washerloc fixation device. The grafts were cyclically loaded for 225,000 cycles from 20 to 170 N. Prior to and at intervals during the cyclic loading, simultaneous radiographs were taken of the tibia and graft. RSA was used to determine the 3-dimensional coordinates of the markers from which the lengthening in each region was computed at each interval. The regions of the tibial and femoral fixations were the largest contributors to the increase in length of the graft, with maximum average values of 0.91 and 0.76 mm respectively after 225,000 cycles. The region between the fixations contributed least to lengthening of the graft, with a maximum average value of 0.23 mm. More than 90% of the lengthening in each region occurred before 100,000 cycles of loading. RSA proved to be a useful method for measuring lengthening in all three regions of the graft construct. Lengthening of the graft construct in both regions of fixation is sufficiently large that the combined contributions may cause a recurrence of instability in some knees.

Animals↗
PubMed2005

Accuracy and precision of radiostereometric analysis in the measurement of three-dimensional micromotion in a fracture model of the distal radius.

The purpose of the current study was to verify the feasibility of radiostereometric analysis (RSA) in monitoring three-dimensional fracture micromotion in fractures of the distal radius. The experimental set-up consisted of a simulated model of an extra-articular Colles' fracture, including metallic beads inserted into the bone on either side of the fracture site. The model was rigidly fixed to high precision micrometer stages allowing controlled translation in three axes and rotation about the longitudinal and transverse axes. The whole construct was placed inside a RSA calibration cage with two perpendicular radiographic film cassettes. Accuracy was calculated as the 95% prediction intervals from the regression analyses between the micromotion measured by RSA and actual displacements measured by micrometers. Precision was determined as the standard deviation of five repeated measurements of a 200 microm displacement or a 0.5 degrees rotation along a specific axis. Translations from 25 microm to 5mm were measured with an accuracy of +/-6 microm and translations of 200 microm were measured with a precision of 2-6 microm. Rotations ranging from 1/6 degrees to 2 degrees were measured with an accuracy of +/-0.073 degrees and rotations of 1/2 degrees were measured with a precision of 0.025 degrees -0.096 degrees . The number of markers and their configuration had greater impact on the accuracy and precision of rotation than on those of translation. Aside from the unknown rate of clinical marker loosening, the current results favor the use of at least four markers in each bone fragment in distal radius fractures. These results suggest a strong rationale for the use of RSA as an objective tool for comparing different treatment modalities and novel bone graft substitutes aimed at stabilization of fractures of the distal radius.

Humans↗
PubMed2005

A new tibial coordinate system improves the precision of anterior-posterior knee laxity measurements: a cadaveric study using Roentgen stereophotogrammetric analysis.

Roentgen stereophotogrammetric analysis (RSA) can be used to measure changes in anterior-posterior (A-P) knee laxity after anterior cruciate ligament (ACL) reconstruction. Previous measurements of A-P knee laxity using RSA have employed a tibial coordinate system with the origin placed midway between the tips of the tibial-eminences. However, the precision in measuring A-P knee laxity might be improved if the origin was placed on the flexion-extension axis of rotation of the knee. The purpose of this study was to determine whether a center-of-rotation tibial coordinate system with the origin placed midway between the centers of the posterior femoral condyles, which closely approximates the flexion-extension center-of-rotation of the knee, improves the precision in measuring A-P knee laxity compared to the tibial-eminence-based coordinate system. A-P knee laxity was measured using each coordinate system six times in three human cadaveric knees implanted with 0.8-mm diameter tantalum markers. For each laxity measurement, the knee was placed in a custom loading apparatus and biplanar radiographs were obtained while the knee resisted a 44 N posterior shear force and 136 N anterior shear force. A-P knee laxity was determined from the change in position of the tibia, with respect to the femur, resulting from the posterior and anterior shear forces. The precision for each coordinate system was calculated as the pooled standard deviation of A-P knee laxity measurements. The precision of the center-of-rotation coordinate system was 0.33 mm, which was about a factor of 2 better than the 0.62 mm precision of the tibial-eminence coordinate system (p=0.006). The 0.33 mm precision with the center-of-rotation coordinate system suggests that an observed change of either 0.56 mm (i.e. 1.7 standard deviations) or greater in A-P knee laxity over time is a real change and not due to measurement error when the new tibial coordinate system is used and other factors contributing to variability are controlled as was done in this study. Accordingly, clinicians and researchers should consider the use of this alternate tibial coordinate system when making serial measurements of A-P knee laxity using RSA because the improved precision allows for the observation of smaller differences.

Adult↗
PubMed2005

Differences in stability and bone remodeling between a customized uncemented hydroxyapatite coated and a standard cemented femoral stem A randomized study with use of radiostereometry and bone densitometry.

The custom made Unique stem is designed to fit closely to the metaphyseal region of the femur in order to obtain maximum mechanical stability and optimal load transfer. Thirty-seven patients (38 hips) with non-inflammatory arthritis were randomized to the uncemented custom made Unique stem or the Elite Plus stem inserted with cement. The patients have been followed clinically as well as with radiostereometry (RSA) and Dual-energy X-ray Absorptiometry (DXA) for 2 years. After 2 years the RSA result showed minimal translation and rotation for the Unique stem while the Elite Plus rotated slightly (mean 1.05 degrees) into retroversion. Compared to previous studies the Elite Plus was as stable as the Charnley prosthesis. The DXA results showed a significantly higher proximal and total (10% for the Unique versus 5% for Elite) bone loss for the Unique stem compared to the Elite Plus. Thus the optimal proximal press-fit of the custom made stem did secure a stable fixation, but did not decrease the proximal bone loss.

Absorptiometry, Photon↗
PubMed2004

Volumetric density of elastic and reticular fibers in transition zone of controls and patients with benign prostatic hyperplasia.

OBJECTIVES: To analyze the volumetric density (Vv) of elastic and reticular fibers in the transition zone of controls and patients with benign prostatic hyperplasia (BPH). METHODS: Prostatic tissue samples were obtained from 25 patients (age range 63 to 79 years, mean 68) with clinical symptoms of bladder outlet obstruction who had undergone open prostatectomy. The control group was composed of 25 transition zone samples from prostates obtained during autopsy of adults aged younger than 30 years (killed in accidents). The Vv of the elastic and reticular fibers was determined in 25 random fields per prostate, using the point-count method with an M-42 grid test system. The data were analyzed using the Kolmogorov-Smirnov, Shapiro-Wilk W, and Mann-Whitney U tests. The Vv of these components was determined by stereologic methods. RESULTS: The Vv in the control and BPH groups was 12.47% +/- 3.6% and 16.55% +/- 9.11% in the elastic system fibers (difference not statistically significant) and 22.75% +/- 1.66% and 29.33% +/- 1.08% in the reticular fibers (difference statistically significant), respectively. CONCLUSIONS: Reticular fibers showed a statistically significant increase in the BPH samples, and this finding suggests that stromal network fibers play a significant role in BPH.

Adolescent↗
PubMed2005

The shape of the anterior and posterior surface of the aging human cornea.

PURPOSE: To determine the shape and astigmatism of the posterior corneal surface in a healthy population with age, using Scheimpflug photography corrected for distortion due to the geometry of the Scheimpflug imaging system and the refraction of the anterior corneal surface. METHODS: Scheimpflug imaging was used to measure in six meridians the cornea of the right eye of 114 subjects, ranging in age from 18 to 65 years. RESULTS: The average radius of the anterior corneal surface was 7.79+/-0.27 (SD) mm and the average radius of the posterior corneal surface was 6.53+/-0.25 (SD) mm. Both surfaces were found to be flatter horizontally than vertically. The cylindrical component of the posterior surface of 0.33 mm is twice that of the anterior surface (0.16 mm). The asphericity of both the anterior and the posterior surface was independent of the radius of curvature at the vertex, refractive error and gender. In contrast with that of the anterior corneal surface, the asphericity of the posterior corneal surface varied significantly between meridians. With age, the asphericity of both the anterior and the posterior corneal surface changes significantly, which results in a slight peripheral thinning of the cornea. CONCLUSION: On average, the astigmatism of the posterior corneal surface (-0.305 D) compensates the astigmatism of the anterior corneal surface (0.99 D) with 31%. The results show that the effective refractive index is 1.329, which is lower than values commonly used. There is no correlation between the asphericity of the anterior and the posterior corneal surface. As a result, the shape of the anterior corneal surface provides no definitive basis for knowing the asphericity of the posterior surface.

Adolescent↗
PubMed2006

In vitro dimensions and curvatures of human lenses.

The purpose of this study was to determine dimensions and curvatures of excised human lenses using the technique of shadowphotogrammetry. A modified optical comparator and digital camera were used to photograph magnified sagittal and coronal lens profiles. Equatorial diameter, anterior and posterior sagittal thickness, anterior and posterior curvatures, and shape factors were obtained from these images. The data were used to calculate lens volumes, which were compared with the lens weights. Measurements were made on 37 human lenses ranging in age from 20 to 99 years. These showed that lens dimensions and the anterior radius of curvature increase linearly throughout adult life while posterior curvature remains constant. The relative shape (or aspect ratio) of the posterior lens is unchanged through adult life since both equatorial diameter and posterior thickness increase at the same rate. The ratio of anterior thickness to posterior thickness is constant at 0.70. It is suggested that in vivo forces alter the apparent location of the lens equator, that the in vitro lens shape corresponds to the maximally accommodated shape in vivo and that the shapes of the accommodated and unaccommodated lens progressively converge toward each other due to lens growth with age, with a convergence point located near the age of total loss of accommodation (55-60 years). Together, these observations provide additional support for the Helmholtz theory of accommodation.

Accommodation, Ocular↗
PubMed1987

Optic disk cupping and pallor measurements of patients with a disk hemorrhage.

We evaluated whether the rate of occurrence of glaucomatous disk damage in eyes with an optic disk hemorrhage differed from the rate of occurrence in control eyes. We compared 24 patients with a disk hemorrhage to 24 control patients, who had been matched for diagnosis, disk appearance, and visual fields. Cup volume and cup-to-disk area ratio of the optic disk were measured using the stereophotogrammetric technique, and area of pallor was measured using computerized image analysis. We found that diabetes increased the probability that a patient would have a disk hemorrhage, and that a hemorrhage was associated with progression of glaucomatous disk changes in half of the cases during the mean 3.1-year follow-up period. However, the mean rate of glaucomatous disk damage in patients with a hemorrhage was not different from matched control patients. A disk hemorrhage is a sign of later disk damage, but it does not alter the rate of glaucomatous disk progression.

Eye Hemorrhage↗
PubMed1990

Contact B-scan echography in the assessment of optic nerve cupping.

We determined the reliability of high-resolution contact B-scan echography for estimating the optic cup size in 56 eyes of 28 patients with glaucoma or ocular hypertension. Two trained observers independently evaluated horizontal and vertical cup/disk ratios in stereophotographs, and two skilled echographers independently estimated optic cup size in photoechograms in a masked fashion. The reliability of echographic interpretation varied (kappa 0.29 to 0.71), but it always exceeded that expected by chance alone, even for cups of 0.3 disk diameter or less. Subtly saucer-shaped cups (three of 50 eyes) and deep cups with intact neuroretinal rims (two of 50 eyes) were misinterpreted echographically. High-resolution contact B-scan echography may provide a useful and reliable estimate of the optic cup size in eyes with opaque media.

Fundus Oculi↗
PubMed1983

Three-dimensional x-ray stereometry from paired coplanar images: a progress report.

More than fifty years ago, Broadbent reported the development of a three-dimensional cephalometric method which complexed information from pairs of x-ray images oriented in two planes at right angles to each other. Empirical problems have prevented the routine clinical use of this "biplanar" method, notwithstanding its obvious conceptual brilliance. The present article reports on recent work toward the development of an alternative method of three-dimensional cephalometry in which the two images of each x-ray pair are positioned in the same plane rather than being at right angles to each other. It is believed that this "coplanar" method avoids many of the technical problems that have limited the use of the Broadbent method.

Cephalometry↗
PubMed1983

The geometry of three-dimensional measurement from paired coplanar x-ray images.

This article outlines the geometric principles which underlie the process of making craniofacial measurements in three dimensions by combining information from pairs of coplanar x-ray images. The main focus is upon the rationale of the method rather than upon the computational details. We stress particularly the importance of having available accurate measurements as to the relative positions of the x-ray tubes and the film plane. The use of control arrays of radiopaque "points" whose projected images upon the film plane allow the retrospective calculation of the spatial relationship between the x-ray tubes and the film plane is explained. Finally, the question of correcting for movement of the subject between two films of an image pair is considered briefly.

Cephalometry↗
PubMed1979

The development of a method of assessing swelling following third molar surgery.

A method of measuring post-operative facial swelling following third molar surgery should satisfy the following criteria. Firstly, the accuracy should be assessed, secondly the measurement should be in volume units, and thirdly the method should be both practical and ethical in the clinical situation and not limited by static apparatus. No published method satisfies all of these criteria. In an attempt to develop a satisfactory method, direct physical measurements using a face bow, ultrasound and portable stereophotogrammetry were investigated. None of these three methods was limited by static apparatus. Portable stereophotogrammetry could not be used because of variations in posing for which a correction could not be applied. Repeated measurements on non-operated subjects showed that the face bow was more accurate than the ultrasound method at a single measurement site. Therefore, the face bow method was developed to give volume measurements in cubic centrimetres by using nine measurement sites at the intersections of a square grid located over the swelling. The mean difference between two readings taken on separate occasions on non-operated subjects was -0.94 cc (s.d. +/- 1.90). The mean swelling measured at twenty third molar operation sites was 23.19 cc. It is concluded that this face bow method satisfies the criteria laid down.

Edema↗
PubMedDate not supplied

Use of dynamic and colored stereogram to measure stereopsis in strabismic patients.

The effectiveness of movement or color has not been well studied in assessing stereopsis in patients with strabismus. We developed a new stereotest equipped with both a monochromatic dynamic random dot stereogram (DRDS) and a static-colored stereogram (SCS) and examined the stereopsis of patients with strabismus. Three-dimensional (3D) images were displayed on a liquid crystal display equipped with a parallax barrier system, allowing 3D images to be seen independently by each eye without glasses. A DRDS with maximum disparity of 3200 seconds of arc was displayed having front-rear movement. An SCS displaying cartoon characters with disparities of 400 seconds of arc was also tested and compared with the Titmus stereotest. A total of 52 strabismic patients were tested. The DRDS showed a significantly higher (P = 0.02) detection rate of stereopsis (39/52, 75%) as compared with the Titmus fly test (28/52, 54%). The SCS did not show any difference in the stereopsis detection rate (24/521, 46%) when compared with the Titmus animal test (20/52, 38%). Thus, the DRDS was useful in detecting stereopsis in patients without stereopsis on the conventional Titmus fly test, while the SCS did not show any difference when compared with the Titmus animal test. The DRDS may examine a different aspect of stereopsis from the static stereopsis measured by the Titmus stereotest or SCS.

Adolescent↗
PubMed2000

A single camera roentgen stereophotogrammetry method for static displacement analysis.

A new method to quantify motion or deformation of bony structures has been developed, since quantification is often difficult due to overlaying tissue, and the currently used roentgen stereophotogrammetry method requires significant investment. In our method, a single stationary roentgen source is used, as opposed to the usual two, which, in combination with a fixed radiogram cassette holder, forms a camera with constant interior orientation. By rotating the experimental object, it is possible to achieve a sufficient angle between the various viewing directions, enabling photogrammetric calculations. The photogrammetric procedure was performed on digitised radiograms and involved template matching to increase accuracy. Co-ordinates of spherical markers in the head of a bird (Rhea americana), were calculated with an accuracy of 0.12mm. When these co-ordinates were used in a deformation analysis, relocations of about 0.5mm could be accurately determined.

Animals↗
PubMed2000

A continuous pure moment loading apparatus for biomechanical testing of multi-segment spine specimens.

An apparatus is described that enables the application of continuous pure moment loads to multi-segment spine specimens. This loading apparatus allows continuous cycling of the spine between specified flexion and extension (or right and left lateral bending) maximum load endpoints. Using a six-degree-of-freedom load cell and three-dimensional optoelectronic stereophotogrammetry, characteristic displacement versus load hysteresis curves can be generated and analyzed for different spinal constructs of interest. Unlike quasi-static loading, the use of continuous loading permits the analysis of the spine's behaviour within the neutral zone. This information is of particular clinical significance given that the instability of a spinal segment is related to its flexibility within the neutral zone. Representative curves for the porcine lumbar spine in flexion-extension and lateral bending are presented to illustrate the capabilities of this system.

Animals↗
PubMed2000

Digital automated RSA compared to manually operated RSA.

The accuracy of digital Roentgen stereophotogrammetric analysis (RSA) was compared to the accuracy of a manually operated RSA system. For this purpose, we used radiographs of a phantom and radiographs of patients. The radiographs of the patients consisted of double examinations of 12 patients that had a tibial osteotomy and of double examinations of 12 patients that received a total hip prosthesis. First, the radiographs were measured manually with an accurate measurement table. Subsequently, the images were digitized by a film scanner at 150 DPI and 300 DPI resolutions and analyzed with the RSA-CMS software. In the phantom experiment, the manually operated system produced significantly better results than the digital system, although the maximum difference between the median values of the manually operated system and the digital system was as low as 0.013mm for translations and 0.033 degrees for rotations. In the radiographs of the patients, the manually operated system and the digital system produced equally accurate results: no significant differences in translations and rotations were found. We conclude that digital RSA is an accurate, fast, and user friendly alternative for manually operated RSA. Currently, digital RSA systems are being used in a growing number of clinical RSA-studies.

Arthroplasty, Replacement, Hip↗
PubMed2001

Model-based Roentgen stereophotogrammetry of orthopaedic implants.

Attaching tantalum markers to prostheses for Roentgen stereophotogrammetry (RSA) may be difficult and is sometimes even impossible. In this study, a model-based RSA method that avoids the attachment of markers to prostheses is presented and validated. This model-based RSA method uses a triangulated surface model of the implant. A projected contour of this model is calculated and this calculated model contour is matched onto the detected contour of the actual implant in the RSA radiograph. The difference between the two contours is minimized by variation of the position and orientation of the model. When a minimal difference between the contours is found, an optimal position and orientation of the model has been obtained. The method was validated by means of a phantom experiment. Three prosthesis components were used in this experiment: the femoral and tibial component of an Interax total knee prosthesis (Stryker Howmedica Osteonics Corp., Rutherfort, USA) and the femoral component of a Profix total knee prosthesis (Smith & Nephew, Memphis, USA). For the prosthesis components used in this study, the accuracy of the model-based method is lower than the accuracy of traditional RSA. For the Interax femoral and tibial components, significant dimensional tolerances were found that were probably caused by the casting process and manual polishing of the components surfaces. The largest standard deviation for any translation was 0.19mm and for any rotation it was 0.52 degrees. For the Profix femoral component that had no large dimensional tolerances, the largest standard deviation for any translation was 0.22mm and for any rotation it was 0.22 degrees. From this study we may conclude that the accuracy of the current model-based RSA method is sensitive to dimensional tolerances of the implant. Research is now being conducted to make model-based RSA less sensitive to dimensional tolerances and thereby improving its accuracy.

Biomechanical Phenomena↗