Cement migration after THR. A comparison of charnley elite and exeter femoral stems using RSA.
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Studies using roentgen stereophotogrammetric analysis (RSA) have shown that the femoral components of cemented total hip replacements (THR) migrate distally relative to the bone, but it is not clear whether this occurs at the cement-implant or the cement-bone interface or within the cement mantle. Our aim was to determine where this migration occurred, since this has important implications for the way in which implants function and fail. Using RSA we compared for two years the migration of the tip of the stem with that of the cement restrictor for two different designs of THR, the Exeter and Charnley Elite. We have assumed that if the cement restrictor migrates, then at least part of the cement mantle also migrates. Our results have shown that the Exeter migrates distally three times faster than the Charnley Elite and at different interfaces. With the Exeter migration was at the cement-implant interface whereas with the Charnley Elite there was migration at both the cement-bone and the cement-implant interfaces. (+info)
Knee cartilage topography, thickness, and contact areas from MRI: in-vitro calibration and in-vivo measurements.
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OBJECTIVE: This study assessed the three-dimensional accuracy of magnetic resonance imaging (MRI) for measuring articular surface topographies and cartilage thicknesses of human cadaveric knee joints, by comparison with the calibrated stereophotogrammetric (SPG) method. METHODS: Six fresh frozen cadaveric knees and the knees of four volunteers were imaged with a three-dimensional spoiled gradient-recalled acquisition with fat suppression using a linear extremity coil in a 1.5 T superconducting magnet. The imaging voxel size was 0.47 x 0.47 x 1.0 mm. Both a manual and a semi-automated segmentation method were employed to extract topographic measurements from MRI. Following MRI, each of the six cadaveric knees was dissected and its articular surfaces quantified using stereophotogrammetry. The MRI surface measurements were compared numerically with the SPG measurements. RESULTS: For six cadaveric knees, the average accuracies of cartilage and subchondral bone surface measurements were found to be 0.22 mm and 0.14 mm respectively and the thickness measurements demonstrated an average accuracy of 0.31 mm. It was found that while most of the error may be attributed to random measurement error, the accuracy was somewhat affected by systematic errors. For each bone of the knee, accuracies were most favorable in the patella, followed by the femur and then the tibia. The more efficient semi-automated method provided equally good and sometimes better accuracies than manual segmentation. CONCLUSIONS: This study demonstrates that clinical MRI can provide accurate measurements of cartilage topography, thickness, contact areas and surface curvatures of the knee. (+info)
Mid-term migration of a cemented total hip replacement assessed by radiostereometric analysis.
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We have previously reported the short-term migration of cemented Hinek femoral components using radiostereometric analysis (RSA). We now report the mid-term migration. During the first 2 years after implantation the prosthesis subsided into varus and rotated internally. Between years 3 and 8 the prosthesis continued to rotate internally with the head moving posteriorly (0.07 mm/year, P=0.004). It also continued to fall into varus with the tip moving laterally (0.07 mm/year, P=0.04). The head (0.06 mm/year, P<0.0001), shoulder (0.04 mm/year, P=0.0001) and tip (0.04 mm/year, P=0.001) continued to migrate distally. There were two cases of failure due to aseptic loosening during the follow-up period. During the second year both of these had posterior head migration, which was abnormally rapid (>2 SD from the mean). We have demonstrated that a cemented implant has slow but significant levels of migration and rotation for at least 8 years after implantation. Our study confirms that implants with abnormally rapid posterior head migration during the second year are likely to fail. (+info)
A new photogrammetric method to measure fetal breathing movements.
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OBJECTIVE: In most recent studies, fetal respiratory movements have been measured with real-time and Doppler echography. We describe an alternative approach using photogrammetry that provides more objective measurements. METHODS: Respiratory movements were studied in 28 women with uncomplicated pregnancies of 30-38 weeks' gestation. Fetal echographic images were recorded on videotape and digitized to obtain coordinates of the reference point (midpoint on the anterior abdominal wall of the fetus between the xiphoid process and the insertion of the umbilical vessels) and generate graphic representations of fetal movements in the anterior abdomen. RESULTS: The mean duration of a complete respiratory cycle was 1.194 s, the mean distance representing the extent of movement was 2.92 mm, the mean inspiratory velocity was 5.52 mm/s and the mean expiratory velocity was 5.06 mm/s. CONCLUSIONS: Photogrammetric analysis of images obtained with real-time echography provided accurate measurements of fetal breathing movements. (+info)
Estimation of the migration of tibial components in total knee arthroplasty. A roentgen stereophotogrammetric analysis.
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Accurate quantitative measurements of micromovement immediately after operation would be a reliable indicator of the stability of an individual component. We have therefore developed a system for measuring micromovement of the tibial component using three non-contact displacement transducers attached to the tibial cortex during total knee arthroplasty (TKA). Using this system we measured the initial stability in 31 uncemented TKAs. All the tibial components were fixed by a stem and four screws. The initial stability was defined as the amount of displacement when a load of 20 kg was applied. The mean subsidence was 60.7 microm and the mean lift-off was 103.3 microm. We also studied the migration of the tibial component using roentgen stereophotogrammetric analysis (RSA) for up to two years after operation. Most migration occurred during the first six months, after which all prostheses remained stable. We defined migration as the maximum total point motion (MTPM) at two years after operation. The mean migration was 1.29 mm at two years. Our results show that there was a significant correlation between the initial stability and migration (p < 0.05) and emphasise the importance of the initial stability of the tibial component. (+info)
A method to evaluate the in vivo behaviour of lumbar spine implants.
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The aim of the study was to design a method for evaluating the stabilizing effect of different lumbar spine implants in vivo, and to apply this method to a comparison of plates versus rods in lumbar spine posterolateral fusion using transpedicular screw fixation. Fourteen patients, seven operated on with transpedicular plates and screws (VSP), and seven operated on with rods and screws (Diapason), matched according to number of levels fused, had tantalum markers inserted in the vertebrae at surgery, enabling roentgen stereophotogrammetric analysis (RSA). Mean patient age was 45 (range 33-56) years. In each group, two patients underwent fusion between L4 and L5, three between L5 and S1, and two from L4 to S1. In three patients, concomitant nerve root decompression was performed using a facet joint preserving technique. RSA was performed 4 weeks after surgery. This interval was chosen to allow enough time for soft tissue healing, but not fusion healing, to occur. RSA was performed in supine and standing position without any mobility provocation, in line with the postoperative regimen given. Movements between the outermost vertebrae of the fusion were calculated along the transverse, vertical and sagittal axes. The method of measurement along these three axes has previously been determined to be accurate to 0.3, 0.6 and 0.7 mm, respectively. One patient stabilized with rods and screws between L5 and S1 displayed a sagittal translation of 1.01 mm but no mobility along the transverse or vertical axes. In the remaining 13 patients, positional change from supine to standing did not provoke any intervertebral mobility above the RSA accuracy along any of the axes. With the limited provocation described, in line with the postoperative regimen for lumbar fusion patients, plates with transpedicular screws and rods with transpedicular screws both seem to give adequate intervertebral stability in posterolateral lumbar fusions. (+info)
Tibiofemoral movement 4: changes of axial tibial rotation caused by forced rotation at the weight-bearing knee studied by RSA.
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We studied the knees of 11 volunteers using RSA during a step-up exercise requiring extension while weight-bearing from 50 degrees to 0 degrees. The findings on weight-bearing flexion with and without external rotation of the tibia based on MRI were confirmed. (+info)
Three-dimensional kinematics of skeletal elements in avian prokinetic and rhynchokinetic skulls determined by Roentgen stereophotogrammetry.
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Several different types of cranial kinesis are present within modern birds, enabling them to move (part of) the upper bill relative to the braincase. This movement of the upper bill results from movement of the quadrate and the pterygoid-palatine complex (PPC). The taxon Palaeognathae is characterised by a very distinct PPC and a special type of cranial kinesis (central kinesis) that is very different from that found in the Neognathae. This has led some authors to hypothesise that there is a functional relationship between the morphology of the PPC and the type of cranial kinesis. This hypothesis is tested here by analysing the movement pattern of both the upper bill and the PPC in birds with three different types of cranial kinesis: prokinesis, distal rhynchokinesis and central rhynchokinesis. Movement patterns were determined using a Roentgen stereophotogrammetry method, which made it possible to detect very small displacements (0.5 mm) of bony elements in three dimensions, while the jaw muscles and ligaments remained intact. We found that in all types of kinesis investigated the movements of the quadrate, jugal bars and PPC are similar. Movement of the quadrate is transferred to the upper beak by the jugal bar and the PPC, which moves almost exclusively forwards and backwards, thereby elevating or depressing the upper bill. The differences between the types of kinesis lie only in the position of the point of rotation. These findings indicate that there is no correlation between the specific morphology of the PPC and the type of cranial kinesis. Several other factors, including the external forces applied during food acquisition, may influence the morphology of the PPC. Differences in PPC morphology therefore appear to be the result of different functional demands acting on the system simultaneously but with different strengths, depending on the species. (+info)