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At least 955 records · Page 53Linked to original sources
PubMed2004

Sensitivity of finite helical axis parameters to temporally varying realistic motion utilizing an idealized knee model.

Various uses of the screw or helical axis have previously been reported in the literature in an attempt to quantify the complex displacements and coupled rotations of in vivo human knee kinematics. Multiple methods have been used by previous authors to calculate the axis parameters, and it has been theorized that the mathematical stability and accuracy of the finite helical axis (FHA) is highly dependent on experimental variability and rotation increment spacing between axis calculations. Previous research has not addressed the sensitivity of the FHA for true in vivo data collection, as required for gait laboratory analysis. This research presents a controlled series of experiments simulating continuous data collection as utilized in gait analysis to investigate the sensitivity of the three-dimensional finite screw axis parameters of rotation, displacement, orientation and location with regard to time step increment spacing, utilizing two different methods for spatial location. Six-degree-of-freedom motion parameters are measured for an idealized rigid body knee model that is constrained to a planar motion profile for the purposes of error analysis. The kinematic data are collected using a multicamera optoelectronic system combined with an error minimization algorithm known as the point cluster method. Rotation about the screw axis is seen to be repeatable, accurate and time step increment insensitive. Displacement along the axis is highly dependent on time step increment sizing, with smaller rotation angles between calculations producing more accuracy. Orientation of the axis in space is accurate with only a slight filtering effect noticed during motion reversal. Locating the screw axis by a projected point onto the screw axis from the mid-point of the finite displacement is found to be less sensitive to motion reversal than finding the intersection of the axis with a reference plane. A filtering effect of the spatial location parameters was noted for larger time step increments during periods of little or no rotation.

Algorithms↗
PubMed2006

Three dimensional stereolithography models of cancellous bone structures from muCT data: testing and validation of finite element results.

Stereolithography (STL) models of complex cancellous bone structures have been produced from three-dimensional micro-computed tomography data sets of human cancellous bone histological samples from four skeletal sites. The STL models have been mechanically tested and the derived stiffness compared with that predicted by finite element analysis. The results show a strong correlation (R2 = 0.941) between the predicted and calculated stiffnesses of the structures and show promise for the use of STL as an additional technique to complement the use of finite element models, for the assessment of the mechanical properties of complex cancellous bone structures.

Biomimetics↗
PubMed1995

Roentgen stereophotogrammetric analysis for assessing migration of total hip replacement femoral components.

A new Roentgen stereophotogrammetric analysis system, using a biplane technique, has been developed to determine the migration and rotation of total hip replacement (THR) femoral components in three dimensions. Stainless steel marker balls were injected into the femur during the operation. The patients stood within a calibration frame during the X-ray. The two exposures were taken consecutively allowing radio-opaque shutters to be moved in front of the films to prevent fogging. Studies with a model demonstrated that the system was capable of measuring the position of an implant to better than 0.11 mm (2 SD). In vivo measurements demonstrated that the migration rate of the different parts of the femoral component could be determined with an accuracy of 0.25 to 0.50 mm/year. By considering the accuracy determined in different ways, methods for improving the system have been identified. The migration and rotation rate of 58 Hinek cemented femoral components was studied for four years. Migration was three to five times greater (p < 0.001) during the first year than subsequently. The prosthesis head moved the most during the first year (0.94 mm). A better understanding of the cause of implant failure could be obtained by studying the early migration of different types of prosthesis and comparing this with their clinical results and design features.

Algorithms↗
PubMed1993

Alignment errors in bitewing radiographs using uncoupled positioning devices.

Errors in X-ray beam alignment account for many of the exposure errors in bitewing radiography. A new method for measuring these alignment errors is described. The alignment accuracy of two different models of inexpensive plastic positioning devices, used for bitewing radiography, were quantified and compared. The technique involves documenting the alignment of an 'ideal' reference radiograph and successive exposures. It permits calculation of X-ray beam-film alignment errors in all subsequent radiographs using the 'ideal' reference. Bitewing radiographs were taken on 61 patients and 19 of these were re-radiographed at 6-month intervals over a 2-year period, providing a total of 156 radiographs for the study. Horizontal and vertical angular deviations were measured and total alignment errors calculated for each radiograph. The average angular alignment error was less than 2 degrees total angular error (1.3-2.4 degrees, 95% confidence intervals). It is concluded that these devices can be used when X-ray beam-film alignment error below 2.5 degrees is acceptable.

Humans↗
PubMed1994

Biostereometric measurement of oral tumour growth. Description of the technique and case report.

Following radiotherapy, it may be difficult to determine clinically whether tumour regression, stabilization or growth has occurred. Traditional diagnostic imaging may not be possible due to the small size of the tumour and the proximity of metallic restorations. A case of squamous cell carcinoma of the mandibular alveolar process in which these problems arose is presented. A computer-assisted biostereometric technique was used to identify volumetric change of the tumour. Polyvinylsiloxane impressions were obtained to record the anatomy of the tumour site. From these, stone models were made at four and eight weeks following radiotherapy. Using optical mapping techniques, tumour growth was demonstrated which was not evident on follow-up examinations. The methodolgy of biostereometry is presented and its advantages and potential applications are discussed.

Carcinoma, Squamous Cell↗
PubMed1992

Nuclear morphometry and stereology in nasopharyngeal carcinoma.

The prognostic value of nuclear morphometry in nasopharyngeal carcinoma (NPC) was investigated in 28 patients. Seven morphometric nuclear variables were measured on 100 randomly selected tumor cells in nasopharyngeal biopsies from 18 patients with NPC confined to the nasopharynx. The same variables were measured in 6 patients with metastatic NPC, as well as in lymph node biopsies from 4 patients with metastatic NPC. Nuclear area, nuclear perimeter, long and short nuclear axes, nuclear form factor, nucleolar area, and the ratio of nucleolar area to nuclear area were all measured. Volume-weighted mean nuclear volume was also obtained. Tumor cells from patients with NPC confined to the nasopharynx had significantly larger mean nuclear areas, perimeters, and volume-weighted mean nuclear volumes but significantly smaller nucleolar to nuclear area ratios than tumor cells from patients with nodal metastases. Assessment of nuclear form factor and diameters did not differentiate the two groups.

Carcinoma↗
PubMed1981

The use of stereophotogrammetry to measure acetabular and femoral anteversion.

Stereoradiography with a base shift of the source of illumination was used to produce pairs of radiographs to be measured by stereophotogrammetric techniques. The direction of shift was parallel with the longitudinal axis of the body, so that each radiograph in the stereopair could be used for other clinical purposes. A base shift of 10 centimetres with a distance of 100 centimetres between the focus and the film gave acceptable value of stereoscopic parallax. The radiographs were measured using a Hilger and Watts medical stereometer. This method was checked with test specimens, namely an osteotomised pelvis in which one acetabulum could be rotated and an osteotomised femur in which the whole upper portion could be rotated against the shaft. Measurements made on the acetabulum and its radiographs showed a correlation coefficient of 0.9838 over the range 0 to 30 degrees of anteversion, with a mean error +2.54 degrees and a standard deviation of +/- 1.52 degrees (n = 21). For the femoral neck, over the range from 10 degrees of retroversion to 80 degrees of anteversion, the correlation coefficient was 0.9979, the mean error +2.46 and the standard deviation +/- 1.48 degrees (n = 30).

Acetabulum↗
PubMed1985

Moiré topography in scoliosis. Its accuracy in detecting the site and size of the curve.

Moiré topography was added to school scoliosis screening in Singapore in 1982. The results from 1342 topographs, assessed in isolation, were used to study the accuracy of the method in predicting the radiographic location and magnitude of scoliotic curves. Accuracy in identifying the site of the curve was 68% in the thoracic spine, 54% in the thoracolumbar spine, and 15% in the lumbar region. There were 12.7% false-positive results and 4.3% false negatives. Of patients with a deviation of one moiré fringe, 76.5% had a curve of 15 degrees or less; of those with a deviation of four moiré fringes, 69% had a curve greater than 26 degrees. The prediction of the Cobb angle was less accurate when there was a deviation of two or three fringes. It is suggested that moiré topography as a screening device should be reserved for use in the second tier of screening, since the forward-bending test is an effective and cheap method for the first tier of a mass school-screening programme.

Back↗
PubMed1986

Mechanical loosening of total hip prostheses. A radiographic and roentgen stereophotogrammetric study.

Twenty patients were examined by standard radiography and roentgen stereophotogrammetric analysis (RSA) during a two-year period after total hip arthroplasty. Eleven of the acetabular components migrated cranially and three femoral components migrated distally. This migration was most rapid during the first four months after operation. Our findings support the possibility that mechanical loosening is initiated by thermal injury during polymerisation of the cement; the less frequent migration of the metallic femoral component compared with the polyethylene acetabular component may be because the metal acts as a heat sink. Standard radiographs were inadequate for assessment of early mechanical loosening, whereas RSA could reveal migration within four months of the arthroplasty.

Follow-Up Studies↗
PubMed1988

Scoliosis surgery and its effect on back shape.

Thirty-four patients with adolescent idiopathic scoliosis were assessed by radiography and the integrated shape imaging system (ISIS) both before and after spinal surgery. Twenty-seven patients underwent Harrington instrumentation, after which lateral indices of curvature were significantly improved, but changes in the transverse plane were less pronounced. Sublaminar wiring was carried out in two patients whose thoracic lordosis was corrected by the surgery. Five patients whose severe deformity had persisted after previous spinal surgery underwent costoplasty, which resulted in a significant improvement in back shape measurements. We conclude that the cosmetic deformity of the back in scoliosis is only partially corrected by operations on the spine itself, whilst costoplasty addresses the problem directly, and improves the surface shape.

Adolescent↗
PubMed1988

Three-dimensional instability of the anterior cruciate deficient knee.

Using roentgen stereophotogrammetry we have recorded the three-dimensional movements of the knee during an anteroposterior laxity test in 36 patients with torn anterior cruciate ligaments and in three cadaver knees. At 30 degrees of knee flexion and before loads were applied the tibia occupied a more laterally rotated position if the anterior cruciate ligament had been injured. When the tibia was pulled anteriorly knees with cruciate deficiency rotated more laterally and were more abducted than normal knees. Posterior traction induced lateral rotation in the injured knee and medial rotation in the intact one. Precise knowledge of the three-dimensional instability of the anterior cruciate deficient knee may be important when the laxity is evaluated only in relation to one of the three cardinal axes.

Adult↗
PubMed1989

The axis of rotation of the ankle joint.

The axis of the talo-crural joint was analysed by roentgen stereophotogrammetry in eight healthy volunteers. Examinations were performed at 10 degrees increments of flexion and pronation/supination of the foot as well as medial and lateral rotation of the leg. Results indicate that the talo-crural joint axis changes continuously throughout the range of movement. In dorsiflexion it tended to be oblique downward and laterally. In rotation of the leg, the axis took varying inclinations between horizontal and vertical. All axes in each subject lay close to the midpoint of a line between the tips of the malleoli. Our study indicates that the talo-crural joint axis may alter considerably during the arc of motion and differ significantly between individuals. This prompts caution in the use of hinge axes in orthoses and prostheses for the ankle.

Adult↗
PubMed1990

Improvement in the deformity of the face in Paget's disease treated with diphosphonates.

We studied nine patients with Paget's disease affecting the skull or facial bones, who were subsequently treated with either dichloromethylene diphosphonate (clodronate) or ethylene-1-hydroxy-1,1-diphosphonate (etidronate). Long-term treatment induced a clinical and biochemical improvement in eight, and this was associated with a reduction in maxillary or skull volume as assessed by quantitative stereophotogrammetry. The one patient whose disease was resistant to treatment with diphosphonate, showed no change in maxillary shape. These studies suggest that the long-term control of disease activity attained with diphosphonates, results in the improvement of skeletal deformity.

Aged↗
PubMed1990

The effect of a stem on the tibial component of knee arthroplasty. A roentgen stereophotogrammetric study of uncemented tibial components in the Freeman-Samuelson knee arthroplasty.

We studied the effect of a metal tray with an intramedullary stem on the micromotion of the tibial component in total knee arthroplasty. Of 32 uncemented Freeman-Samuelson knee arthroplasties performed in London and Gothenburg, nine had a metal backing and stem added to the tibial component. Micromotion of the tibial components, expressed as migration and inducible displacement, was analysed using roentgen stereophotogrammetric analysis up to two years follow-up. The addition of a metal back and a 110 mm stem to the standard polyethylene component significantly reduced both migration over two years and inducible displacement.

Adult↗
PubMed1990

Primary migration of fully-threaded acetabular prostheses. A roentgen stereophotogrammetric analysis.

We investigated the fixation of fully-threaded cementless acetabular prostheses in 20 patients with osteoarthritis, measuring the migration of the cup using roentgen stereophotogrammetric analysis (RSA). All the cups migrated proximally, 13 moved laterally or medially, and nine moved anteriorly or posteriorly in the first two postoperative years, the average migration being 1.1 to 1.4 mm in either direction. Rotatory movements of up to 5.7 degrees were found in nine of the 13 hips where this analysis could be performed. Movements of cobalt-chrome (12) and titanium alloy (8) cups did not differ significantly. Seventeen of the 20 patients had some pain two years after the operation. The migration of the prostheses indicates that 'osseointegration' had not occurred. The combination of this with persistent pain suggests that the long-term results will be unfavourable.

Acetabulum↗
PubMed1990

Movement of the femoral head after Salter osteotomy for acetabular dysplasia.

A Salter innominate osteotomy is used to treat acetabular dysplasia, but reports of its effects on the position of the femoral head are few and conflicting. Lateral shift would increase the resultant forces acting on the joint and be detrimental. We studied 15 Salter innominate osteotomies and demonstrated that a correctly performed osteotomy does not significantly alter the distance from the centre of the femoral head to the midline of the body. Stereophotogrammetry was used in three patients to delineate the axis of rotation of the distal acetabular fragment and determine the locus of movement of the centre of the femoral head about it. Our results explain why the Salter osteotomy does not lateralise the femoral head.

Acetabulum↗