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At least 685 records · Page 38Linked to original sources
PubMed1993

In vivo kinematics of the cervical spine. Part I: Development of a roentgen stereophotogrammetric technique using metallic markers and assessment of its accuracy.

A technique for simultaneous roentgen stereophotogrammetry (RS) was developed, and its accuracy was assessed. In vitro models fabricated from dried cadaveric C4 and C5 vertebrae were used to simulate the motion behavior of the cervical spine. Metallic markers made of Vitallium beads (diameter < 0.3 mm) were implanted into the posterior and anterior surfaces of each vertebra at surgically accessible locations to simulate the bead placement for both posterior and anterior surgical approaches to the cervical spine. A series of roentgen stereo pairs were obtained to systematically assess the accuracy (validity) of displacement measurements in anteroposterior (AP) translation, axial rotation, and flexion/extension. In addition, the effects of soft tissue density on the accuracy of the system were investigated by obtaining a series of roentgen stereo pairs with the experimental model immersed in a water bath. The coordinates of the metallic markers on the radiographs were then digitized by two raters who were not informed of the actual motion (i.e., blind study). The results indicated a high accuracy throughout the study. Overall root mean square errors were 0.07 mm for AP translation, 0.08 degrees for axial rotation, and 0.14 degrees for flexion/extension. The corresponding accuracy estimates (R2 values by linear regression analysis) were very high (0.992, 0.998, and 0.995) when the measurement results were compared with the actual displacements. The water bath did not affect measurement accuracy, indicating that soft tissue density should have little effect on the accuracy of the technique for in vivo applications. This system appears to be an accurate and reliable method for assessment of simulated in vivo cervical spine motion, regardless of the rater. The technique has been further used in in vivo assessment of cervical spine kinematics in one patient to confirm the efficacy of the developed technique.

Atlanto-Axial Joint↗
PubMed1997

Biomechanics of the hip joint and the effects of fracture of the acetabulum.

The biomechanical analysis of the normal and arthritic hip joint have been the subject of numerous publications in orthopaedics. Biomechanical investigations focusing on the effect of fractures of the acetabulum on the alteration of hip joint mechanics have been a recent development. This paper outlines currently available methodologies for simulating load across the hip, and as measuring articular contact and contact stresses. Results of investigations of posterior wall fractures and transverse fractures of the acetabulum are presented. Directions for future research in the area of mechanical investigations of acetabular fractures are discussed.

Acetabulum↗
PubMed1998

Migration, stem shape, and surface finish in cemented total hip arthroplasty.

In many recent publications it was suggested that the amount of early subsidence of a femoral stem in total hip arthroplasty is indicative for later revision. In this article it is argued that stems can be designed according to alternative objectives, resulting in different shapes and surface roughness, each producing its own characteristic postoperative subsidence pattern. It was investigated whether these inherent subsidence patterns can be estimated in preclinical testing. For that purpose two stems, both without a collar, relying on cement fixation only, were compared regarding their stress transfer, migration, and induced micromotion behavior. Finite element analysis, cyclic bench testing of substitute bone reconstructions, and clinical radiostereophotogrammetric analysis were applied. The stems investigated were the Exeter, which is assumed to be a force closed fixation design, relying on subsidence under load as a method of maintaining stability, and the SHP, as a shape closed fixation design, meant to be contained by the cement mantle. Both designs were true to their design concepts in the analyses, in the sense that migrations and micromotions of the Exeter stems far exceeded those of the SHP stems. It was found that preclinical studies such as finite element analysis or bench tests give reasonable indications of in vivo postoperative behavior. It is concluded that early clinical migration values should be considered relative to stem shape and surface finish, when prediction of later revision probability is the issue.

Aged↗
PubMed1999

Comparative micromotion of fully and proximally cemented femoral stems.

This investigation studied the differences of in vitro micromotion between two stem designs. The two stem types investigated were a proximally cemented stem with distal press fit and a fully cemented stem. After initial micromotion testing to 2250 N in simulated single leg stance and stair climb, six of each stem type were loaded dynamically for 1 million cycles at 950 N at 1 Hz. Micromotion studies were repeated. The two stem types had similar micromotion. For the single leg stance, fully cemented implant motion averaged (+/- 95% confidence) 18 +/- 8 microns toggle, 41 +/- 5 microns axial, and 59 +/- 22 microns rotation. Proximally cemented implant motion averaged 20 +/- 6 microns toggle, 42 +/- 6 microns axial, and 31 +/- 15 microns rotation. For the simulated stair climb, fully cemented implant motion averaged 24 +/- 10 microns toggle, 45 +/- 8 microns axial, and 92 +/- 32 microns rotation. Proximally cemented implant motion averaged 19 +/- 10 microns toggle, 42 +/- 9 microns axial, and 87 +/- 53 microns rotation. For both loading conditions, there were no significant differences measurable between the two systems. After dynamic testing of the fully cemented implants, there were no significant changes in the micromotion of either the toggle or the rotation, but an average of 18 microns increase of axial motion was measured in the fully cemented stem. For the proximally cemented implants, there were no significant changes after dynamic testing. This differences was not considered clinically significant because roentgen stereophotogrammetric analysis studies have shown that more than 4 mm of migration is required before clinical symptoms manifest. The protocol developed in this study may help provide a screening process to determine the stability of femoral stem designs before these devices are used clinically.

Adult↗
PubMed2000

The role of femoral stem extension in total knee arthroplasty.

Although stemmed femoral components often are used in revision total knee arthroplasty, no quantitative comparison of the relative stability of a femoral component with and without a stem has been performed previously. A radiostereophotogrammetric analysis was performed to determine the influence of stem extension on mechanical stability in a laboratory experiment. In addition, the contribution of impacted morselized bone graft used for reconstruction of bone defects to stability was determined. Ten fresh frozen distal femoral specimens, of which the bone mineral density was measured, were prepared to fit a cemented femoral component with an uncemented stem. A cyclic axial load of 750 N was applied to the medial part of the femoral component. The loading test was repeated after creation of a standard, unicondylar, uncontained medial bone defect, after reconstruction of the defect with impacted morselized bone graft, after disconnecting the stem from the component, and after removal of the morselized bone graft. A significant difference was found in rotation and translation of the femoral component with the stem and after its functional removal. The femoral component rotated significantly into varus and internal rotation, and the tip of the stem translated significantly laterally after disconnection of the stem. A linear correlation between bone mineral density in the femoral neck and the radiostereophotogrammetric motion data was absent, but a bone mineral density threshold level of 0.55 g/cm2 was present, below which stability decreased considerably. Morselized bone graft provided only a minor contribution to stability compared with a stem.

Arthroplasty, Replacement, Knee↗
PubMed2001

Results of hip revision using the Exeter stem, impacted allograft bone, and cement.

The Exeter stem and impacted, morselized allograft bone and cement were used in the revisions of 18 consecutive femoral components (17 patients). The primary arthroplasty had been done because of osteoarthritis. All of the femoral components were revised for the first time because of aseptic loosening. The migration pattern of the Exeter stem after revision was studied using roentgen stereophotogrammetric analysis. At 2 years after surgery, all 18 femoral stems had migrated in the distal direction (average, 2.5 mm). In addition, seven of the stems had migrated in the medial direction (average, 1.3 mm), and two stems had migrated in the lateral direction (0.5 mm and 1 mm, respectively). Sixteen of the femoral stems also had migrated in the posterior direction (average, 2.9 mm), but none migrated in the anterior direction. The migration rate decreased gradually with time during the followup. Six femoral stems continued to migrate between 1.5 and 2 years after surgery. In patients with major femoral bone deficiency at the time of hip revision, the use of impacted morselized allograft bone and cement yielded an initial fixation similar to that obtained in conventionally cemented revisions. Pain had improved in all patients at the 2-year followup.

Aged↗
PubMed2002

Biomechanical evaluation of the elbow using roentgen stereophotogrammetric analysis.

The medial collateral ligament complex is the primary constraint of the elbow to valgus forces and is composed of the anterior bundle, the posterior bundle, and a transverse part. Total and partial ruptures have been described. Clinical and radiologic examinations of medial or valgus instability of the elbow are difficult. The effect of different stages of medial collateral ligament ruptures on ulnohumeral movement in cadavers was determined to rationalize the use of physical and radiologic examinations in different stages of valgus instability in vivo. Using roentgen stereophotogrammetric analysis, motion is determined between the humerus and ulna under valgus load and between the humerus and radius during maximal pronation of the forearm after various dimensions of medial collateral ligament lesions. The increase in distance between the humerus and ulna under a 15 N valgus load varied from 2.7 mm to 9.8 mm. The increase in distance between the humerus and proximal radius with the forearm in pronation in an intact specimen and after transsection of the anterior medial collateral ligament and posterior medial collateral ligament in the anterior direction was 9.7 mm. These results suggest that detection of partial ruptures with clinical and radiologic examinations is difficult. Anterior movement of the radial head can be used as an additional parameter of valgus instability.

Aged↗
PubMedDate not supplied

Kinematic analysis of spinal fusions.

Two cases with clinical suspicion of incompletely healed anterior fusion between L5 and S1 were examined by means of a roentgen stereophotogrammetric method. In both cases a pseudarthrosis was found. The method makes it possible to disclose rotations and translations between veretebrae with an accuracy of about 0.2degree and 30-120 mum, respectively.

Biomechanical Phenomena↗
PubMed1991

Use of biostereometric analysis as a screen for breast cancer.

Biostereometric analysis, a photographic surface imaging technology that is noninvasive, was tested for its effectiveness in selecting breast pathology in a sample of 1000 female subjects, including 80 with cancers, 635 normals, and 285 with benign breast conditions. These individuals were recruited from the population of women undergoing routine mammographic examination. The project was designed specifically to determine whether biostereometric analysis could identify the individuals in the sample with malignant breast disease in the hope of providing information to aid in future development of a breast cancer screening protocol. The overall sensitivity of the method for cancers of all sizes was 76%. Biostereometric analysis was 85% sensitive for selection of cancers in the subjects over 50 years of age, and identified 80% (4 of 5) of the subjects with clinically confirmed breast cancers less than 1 cm in size. The method was 69% specific, but identified benign breast disease in only 51% of cases.

Adult↗
PubMed1995

Subsidence of tibial components in knee arthroplasty. A comparison between conventional radiography and roentgen stereophotogrammetry.

RATIONALE AND OBJECTIVES: To assess the ability of conventional radiography to identify subsidence of tibial components. METHODS: Forty-three cases of knee arthroplasty were followed for 4 years using roentgen stereophotogrammetric analysis as the gold standard. RESULTS: Roentgen stereophotogrammetric analysis showed subsidence in all uncemented prostheses, whereas two thirds of the cemented prostheses subsided. Medially, the sensitivity of conventional radiography was low, 25%, whereas the specificity was 83%. For the other regions, the sensitivity was almost 100%, although the specificity was as low as 66% frontally and dorsally. CONCLUSIONS: Medially, where most prostheses were inserted with a slight overhang, conventional radiography identified subsidence correctly. Laterally, frontally, and dorsally, however, conventional radiography overestimated the subsidence by a factor of 2 to 3. This error was caused by bony protrusions arising in the cranial direction from the uncovered bone surfaces, thus changing the points of reference. This problem arose more commonly in uncemented cases, whereas cement seemed to seal the bone.

Biomechanical Phenomena↗
PubMedDate not supplied

Visualization modes for CT colonography using cylindrical and planar map projections.

PURPOSE: The purpose of this study was to demonstrate the limitations to the effectiveness of CT colonography, colloquially called virtual colonoscopy (VC), for detecting polyps in the colon and to describe a new technique, map projection CT colonography using Mercator projection and stereographic projection, that overcomes these limitations. METHOD: In one experiment, data sets from nine patients undergoing CT colonography were analyzed to determine the percentage of the mucosal surface visible in various visualization modes as a function of field of view (FOV). In another experiment, 40 digitally synthesized polyps of various sizes (10, 7, 5, and 3.5 mm) were randomly inserted into four copies of one patient data set. Both Mercator and stereographic projections were used to visualize the surface of the colon of each data set. The sensitivity and positive predictive value (PPV) were calculated and compared with the results of an earlier study of visualization modes using the same CT colonography data. RESULTS: The percentage of mucosal surface visualized by VC increases with greater FOV but only approaches that of map projection VC (98.8%) at a distorting, very high FOV. For both readers and polyp sizes of > or =7 mm, sensitivity for Mercator projection (87.5%) and stereographic projection (82.5%) was significantly greater (p < 0.05) than for viewing axial slices (62.5%), and Mercator projection was significantly more sensitive than VC (67.5%). Mercator and stereographic projection had PPVs of 75.4 and 78.9%, respectively. CONCLUSION: The sensitivity of conventional CT colonography is limited by the percentage of the mucosal surface seen. Map projection CT colonography overcomes this problem and provides a more sensitive method with a high PPV for detecting polyps than other methods currently being investigated.

Adult↗
PubMed2000

A computerized method for mathematical description of three-dimensional root canal axis.

Knowledge of the three-dimensional (3D) morphology of root canals is important for successful endodontic treatment. The objective of the present study was to determine the 3D root canal axis mathematically. Two views (mesiodistal and buccolingual) of digitized images were taken from extracted natural human teeth. Geometric reconstruction to standardize projection geometry was conducted on images. Because 90-degree turn-around image pairs are Monge images of a given root canal, these Monge images were positioned using photogrammetric methods. Each well-ordered axis pair of a given root canal was put into a common coordinate system resulting in 3D polynomial function of the actual root canal. On the basis of the results gained using 10 samples evaluated with the Friedman statistical test, this description seems to be reproducible. The 3D representation of the root canal may help the clinicians in choosing the optimal instruments and shaping techniques. The root canal axis that is described by the 3D function forms a basis for determination of curvature values and torsion values in each of the axis points. Evaluating these values may also yield a new type of classification.

Algorithms↗
PubMed1992

Factors influencing postoperative movement in displaced femoral neck fractures: evaluation by conventional radiography and stereoradiography.

Postoperative movement in 46 displaced femoral neck fractures was studied using roentgen stereophotogrammetric analysis (RSA). Thirty-four fractures became stable, all within 1 year. Measurements on pre- and postreduction radiographs and scintimetry were performed to evaluate factors of importance in healing, redisplacement, and nonunion. Thirty-three fractures were treated with two hook-pins with (7 cases) or without (26 cases) a plate, and 13 were treated with two cancellous screws. Presence of intermediate fracture fragments and fixation with two screws implied increased movement of the femoral head center during the postoperative period. Remaining ad latus displacement on the anteroposterior or lateral view after reduction of more than 1 mm and low scintimetric uptake implied increased risk of redisplacement or pseudarthrosis. Increased displacement of the femoral head center during the first postoperative month was recorded in fractures that did not heal. The magnitude of the femoral head rotations did not differ between the implants, but smaller screw axis rotations were noted in fractures that subsequently healed. In most hips fixated with screws, the instant center of femoral head rotation went through the femoral head or neck, whereas hook-pin fixation more commonly was associated with screw axis position within or close to the trochanteric region, suggesting a more durable fixation in the femoral head of this device.

Aged↗
PubMed1982

Effect of orthoptic procedures on stereoscopic acuities.

Ten stereophotogrammetry students and three graduate photogrammetrists were given 7 weeks of nonspecific orthoptic exercises. The visual systems of these 13 experimental subjects were matched to those of 13 control subjects chosen from the students and staff of the Ferris State College of Optometry. Stereoscopic acuities were determined before and after the training period on both groups using a Wild Stereoplotter, a Howard-Dolman apparatus, and the Keystone Multi-Stereo Test. Stereoscopic acuities as determined on the stereoplotter and the Howard-Dolman apparatus were improved at better than a 0.05 significance level as computed on the Wilcoxon signed rank test and Student's t-test for the difference between two dependent means.

Adult↗
PubMed1988

Effect of vision therapy on stereophotogrammetric profiling--a controlled clinical trial.

A single, masked controlled clinical trial showed that vision therapy improved both the accuracy and repeatability of stereophotogrammetric performance on the profiling task with experienced, visually normal observers. The average fixation disparity measured under working conditions decreased and stereoscopic acuity as measured with a Howard-Dolman apparatus increased. The data suggest that vision therapy is most helpful for those profiling situations in which disparity stimuli are plentiful and stereopsis is the dominant depth cue.

Clinical Trials as Topic↗
PubMed1989

An instrument for in vivo tear film interferometry.

An instrument has been designed and constructed that facilitates the measurement of in vivo tear film topology, thickness, and wetting, using the principles of thin film interferometry. The use of this tear film interferometer (TFI) allows objective evaluation of the breakup characteristics of the tear film on contact lens surfaces and provides a means for examining the dynamic changes in thickness, thickness distribution, and wetting properties during sequential interblink periods. The effects of contact lens material, wetting solutions, and cleaning regimens can be compared objectively. The instrument is easy to use, no additives to the natural tear fluid are required.

Contact Lenses↗