Biomechanical and clinical evaluations of a porous tantalum implant for the treatment of early-stage osteonecrosis.
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Adult↗
Biomedical subjects
D D Robertson
Publications and source records attributed to D D Robertson.
Precision and accuracy of computed tomography foot measurements.
OBJECTIVE: To test the accuracy and precision of computed tomography (CT) imaging for describing the 3-dimensional structure of the foot in patients with diabetes mellitus and peripheral neuropathy. DESIGN: Experimental, test-retest. SETTING: Clinical CT scanner at a local hospital. SPECIMENS: Two tissue-equivalent phantoms and 6 cadaver feet. MAIN OUTCOME MEASURES: Measurements taken from CT data of phantoms and cadaver feet were compared with physical (caliper) measurements. The feasibility of creating a computer-aided design/rapid prototyping 3-dimensional model from CT data was assessed by using 1 cadaver foot. RESULTS: No bias was found for phantom or cadaver CT measurements compared with caliper measurements. The mean difference between repeat scans of cadaver feet (1 observer) was 0.1 +/- 0.8 mm and between observers, 0.4 +/- 0.8 mm. Comparing caliper measurements of the rapid prototype model and actual foot measurements revealed an error of 0.3 +/- 0.4 mm. CONCLUSION: CT-based 3-dimensional imaging produced accurate and precise foot measurements, enabling description of internal and external structures. This capability will be coupled with plantar pressure measurements to improve our understanding and treatment of foot ulcers in people with diabetes.
Cadaver↗
X-ray CT metal artifact reduction using wavelets: an application for imaging total hip prostheses.
Traditional computed tomography (CT) reconstructions of total joint prostheses are limited by metal artifacts from corrupted projection data. Published metal artifact reduction methods are based on the assumption that severe attenuation of X-rays by prostheses renders corresponding portions of projection data unavailable, hence the "missing" data are either avoided (in iterative reconstruction) or interpolated (in filtered backprojection with data completion; typically, with filling data "gaps" via linear functions). In this paper, we propose a wavelet-based multiresolution analysis method for metal artifact reduction, in which information is extracted from corrupted projection data. The wavelet method improves image quality by a successive interpolation in the wavelet domain. Theoretical analysis and experimental results demonstrate that the metal artifacts due to both photon starving and beam hardening can be effectively suppressed using our method. As compared to the filtered backprojection after linear interpolation, the wavelet-based reconstruction is significantly more accurate for depiction of anatomical structures, especially in the immediate neighborhood of the prostheses. This superior imaging precision is highly advantageous in geometric modeling for fitting hip prostheses.
Artifacts↗
Three-dimensional analysis of the proximal part of the humerus: relevance to arthroplasty.
BACKGROUND: Recreation of normal anatomical relationships may be important to optimize the outcome of proximal humeral arthroplasty. With use of computerized tomographic data and three-dimensional computer modeling, we concurrently studied both extramedullary and intramedullary humeral morphology, including canal shape, and related these findings to the design of proximal humeral prostheses. METHODS: Sixty cadaveric humeri (thirty pairs: fifteen from male donors and fifteen from female donors) were studied. Three-dimensional computer models were built from canal and periosteal contours extracted from computerized tomographic data and multiple measured anatomical parameters, including humeral canal axis, humeral head center, and hinge point offset; greater tuberosity and bicipital groove offset; humeral head center, radius, thickness, retroversion, and inclination; and size and torsion of sections of the canal. RESULTS: On the average, the humeral head center was offset both medially (seven millimeters) and posteriorly (two millimeters) from the humeral axis. The humeral head hinge point did not line up with the axis but instead was laterally offset by an average of seven millimeters. The average humeral head thickness was nineteen millimeters. The humeral head thickness and length were proportionately linked. There was marked variability in all of these parameters. Humeral head inclination averaged 41 degrees but was less variable than previously described, with 95 percent of our sample within the range of 35 to 46 degrees. The proximal section of the humeral canal was retroverted, and the retroversion was found to be similar to that of the humeral head on statistical analysis. Version of the middle and distal sections of the canal, however, was dissimilar to that of the proximal section of the canal. Proximal humeral retroversion was found to be extremely variable and averaged 19 degrees. The accuracy, reliability, and repeatability of the computer-based-model measurements were found to be excellent. CONCLUSIONS: Measurements of external proximal humeral morphology made with three-dimensional computer models of cadaveric specimens derived from the Midwestern United States agreed, in general, with those described for different populations evaluated with different measuring techniques. Proximal humeral morphology was extremely variable as highlighted by the large ranges of measurements seen for all variables. Examination of the intramedullary morphology showed that there is an internal version, with measurements dependent on the canal distance distal to the anatomical neck. CLINICAL RELEVANCE: Because of the marked variabilities seen in proximal humeral morphology, newer prosthetic designs are now allowing surgeons to control multiple prosthetic variables. An understanding of the normal values for proximal humeral morphology can serve as an important guideline for component selection, especially when the normal anatomy is distorted. Additionally, variations in intramedullary version may have important consequences for future designs of press-fit proximal humeral replacement.
Arthroplasty, Replacement↗
Reduced bone stress as predicted by composite beam theory correlates with cortical bone loss following cemented total hip arthroplasty.
Clinical and experimental evidence suggest that periprosthetic bone loss following total hip arthroplasty is caused in part by stress-shielding. Changes in bone stress in the proximal femur following implantation can be estimated with use of composite beam theory. We hypothesized that the degree of stress-shielding predicted by beam theory correlates with the magnitude of bone loss following cemented total hip arthroplasty. We analyzed cross sections from the proximal femur of 13 patients who had undergone unilateral cemented total hip arthroplasty. A matching implant was inserted contralaterally, and the cross-sectional properties of the implant and bone and the bone density were determined. Bone loss was calculated on the basis of differences between contralateral (control) and ipsilateral (remodeled) sections and correlated to several beam-theory parameters calculated from the control sections: implant rigidity, bone rigidity, ratio of implant to bone rigidity, and predicted decrease in bone stress. All parameters except implant rigidity were significantly correlated with bone loss (p < 0.05). Parameters that included implant and bone properties were more strongly correlated with bone loss than were those based on bone properties alone. The predicted decrease in bone stress explained 50-60% of the variance in bone loss. The data also indicated that patients were not likely to lose substantial amounts of bone unless the reduction in bone stress exceeded a threshold value. Although limited by a small and heterogeneous sample, these results indicate that beam-theory predictions correlate with the degree of femoral resorption and should be investigated further as a means to identify patients at high risk for bone loss.
Arthroplasty, Replacement, Hip↗
Use of computed tomography and plantar pressure measurement for management of neuropathic ulcers in patients with diabetes.
BACKGROUND AND PURPOSE: Total contact casting is effective at healing neuropathic ulcers, but patients have a high rate (30%-57%) of ulcer recurrence when they resume walking without the cast. The purposes of this case report are to describe how data from plantar pressure measurement and spiral x-ray computed tomography (SXCT) were used to help manage a patient with recurrent plantar ulcers and to discuss potential future benefits of this technology. CASE DESCRIPTION: The patient was a 62-year-old man with type 1 diabetes mellitus (DM) of 34 years' duration, peripheral neuropathy, and a recurrent plantar ulcer. Although total contact casting or relieving weight bearing with crutches apparently allowed the ulcer to heal, the ulcer recurred 3 times in an 18-month period. Spiral x-ray computed tomography and simultaneous pressure measurement were conducted to better understand the mechanism of his ulceration. OUTCOMES: The patient had a severe bony deformity that coincided with the location of highest plantar pressures (886 kPa). The results of the SXCT and pressure measurement convinced the patient to wear his prescribed footwear always, even when getting up in the middle of the night. The ulcer healed in 6 weeks, and the patient resumed his work, which required standing and walking for 8 to 10 hours a day. DISCUSSION: Following intervention, the patient's recurrent ulcer healed and remained healed for several months. Future benefits of these methods may include the ability to define how structural changes of the foot relate to increased plantar pressures and to help design and fabricate optimal orthoses.
Casts, Surgical↗
Subjective visual vertical in patients with benign paroxysmal positional vertigo.
The ocular tilt reaction leads to an alteration in the subjective visual vertical (SVV). Nonsurgical peripheral vestibular dysfunction only rarely leads to changes in the SVV. To our knowledge, no studies have examined the effects on the SVV in patients with benign positional paroxysmal vertigo (BPPV) post Hallpike and Semont maneuvers. Sixteen patients with posterior canal BPPV were assessed in the vestibular clinic in Winnipeg, Manitoba. These patients had assessment of their SVV at baseline, post Hallpike and Semont maneuvers, and at follow-up 2 weeks later. These patients were also compared to a control group (n = 9). Ten of 16 patients showed a statistically significant change in SVV post Hallpike maneuver. An even larger number of patients, 14 of 16, showed a significant difference when compared to the control group post Hallpike. These findings suggest that the inferior vestibular nerve may to some degree influence the ocular tilt reaction.
Adult↗
Observer variation in the detection of acetabular bone deficiencies.
To determine observer variation in the detection of acetabular bone deficiencies, 42 pairs of frontal (AP) and lateral hip radiographs and CT studies for total hip arthroplasty patients obtained within an average of 4 weeks of each other were reviewed separately by five radiologists and one orthopedic surgeon. Interobserver variations were calculated for each individual reading the films using kappa values. The individual film readings were then compared with a consensus reading of the CT data. When separate observers were analyzed, agreement on plain film readings was slight to fair (av. kappa = 0.1440 +/- 0.1047). The individual observers were not able to give readings which were very consistent with the CT consensus reading, resulting in a low sensitivity (65%) and specificity (74%) for acetabular defect classification with plain radiographs. The identification of acetabular bone defects from the AP and lateral views of the hip is highly subjective and variable from observer to observer.
Acetabulum↗
Femoral deformity in adults with developmental hip dysplasia.
Quantitative computed tomography and 3 dimensional modeling were used to portray the deformity of the proximal femur in 24 Japanese adults with low subluxations to high dislocations secondary to developmental dysplasia of the hip. Periosteal and canal bony contours were extracted, 3 dimensional models generated, and morphologic parameters were calculated for each femur. Three dimensional illustrations of the average deformity and variability were created. Morphologic parameters were not found to be statistically correlated with the degree of the disease. Interestingly, the major axis of the canal contours of the proximal femur was found to be aligned with the plane of the femoral neck (anteversion), regardless of the degree of anteversion. Thus, the amount of version correctable in an uncemented prosthesis is limited, and at times may require a special prosthesis, overreaming, undersizing and cementing, or an osteotomy. Additionally, the proximal medial curvature of the dysplastic femurs was straighter than that of normal femurs. This necessitated a corresponding reduction in the proximal medial curvature of a conventional uncemented prosthesis to match the medial curvature of the individual femur and the average developmentally dysplastic femur. This objective description of the developmentally dysplastic femur corroborates clinical observations, highlights some unrecognized findings, provides a rationale for planning reconstructions, and aids in the design of prostheses for adult patients with this deformity.
Adult↗
Ocular torsion monitoring in chemical labyrinthectomy.
OBJECTIVE: To study the usefulness of ocular torsion analysis as an adjunct to examining central vestibular compensation. DESIGN: Prospective evaluation. SETTING: The Vestibular Disorders Clinic, University of Manitoba Health Sciences Centre. METHODS: Seven patients with intractable Meniere's disease underwent elective transtympanic gentamycin labyrinthectomy. Serial examination of patient progress was performed using fundus photography, subjective visual vertical estimations, electronystagmography, and audiometry. RESULTS: Ocular torsion analysis reveals unexpected initial and early contraversive torsion behaviour in some patients, which may represent an early irritative phenomenon stemming from either the gentamicin or the Meniere's disease itself. CONCLUSION: Despite the sensitivity of the ocular torsion measures, there appears to be no useful predictive correlation between ocular torsion and audiometric functioning that might predict impending hearing loss. Nevertheless, ocular torsion analysis reveals subtle changes in vestibular system functioning and may provide useful adjunctive information in the assessment of vestibular ototoxicity.
Adult↗
Decision matrix analysis for tonic ocular torsional abnormalities with posturography abnormalities.
Tonic ocular torsions can arise from a variety of central or peripheral, vestibular, and nonvestibular lesions. However, the role of tonic ocular torsions in neurotology has been limited to surgical patients after unilateral vestibular deafferentation. By using 12 patients with a spectrum of well-defined unilateral peripheral vestibular lesions confirmed by electronystagmography (ENG), we identified a link between ipsiversive tonic ocular torsion compensation and vestibulospinal compensation, as measured by computerized dynamic posturography. In the context of ENG findings and posturography, the differential diagnosis of ocular torsions may be localized to the otoliths by using a decision matrix. Specifically, conditions of absent vision and sway-referenced support on computerized dynamic posturography associated with concurrent static ocular torsional abnormalities may suggest an otolith disorder. Furthermore, static ocular torsion assessment provides another important window on central vestibular compensation.
Adult↗
Dizziness Handicap Inventory correlates of computerized dynamic posturography.
To assess the handicapping effect of dizziness related to posture and balance, the Dizziness Handicap Inventory (DHI) and Computerized Dynamic Posturography (CDP) were used to assess 101 consecutive patients referred for neurotologic evaluation of dizziness. Most patients, regardless of diagnosis, related some level of preexisting handicap, most often in the DHI Physical subscale. Generally, females and patients with bilateral lesions scored higher in all DHI subscales. No clinically useful correlations emerged between DHI and CDP testing, although DHI scores were marginally higher for patients failing CDP conditions. Functional balance ability could not be correlated with patient handicap, but a literature review suggests that the desynchrony between dizziness signs and symptoms may be related to underlying patient anxiety and differences in coping strategies.
Adaptation, Psychological↗
Vestibular evoked myogenic potentials.
A pilot study was undertaken in our Vestibular Disorders Clinic to re-evaluate the clinical benefits of vestibular evoked myogenic potentials (VEMP). In seven normal subjects and 20 documented unilateral peripheral vestibular disorder patients, electromyograms were recorded from surface electrodes over the sternomastoid muscles and averaged in response to 0.1-millisecond clicks played through headphones. Control patients demonstrated EMG positive-negative potentials (p14-n21) of equivalent latencies and amplitudes both ipsilateral and contralateral to the stimuli. In patients with documented unilateral peripheral vestibular disorders, the p14-n21 potentials were preserved in the presence of sensorineural hearing loss and absent in those patients with partial or total vestibular loss. A high directional correlation is noted between the p14-n21 potential and gold-standard caloric testing. We suspect the origin of the response may be in the saccule and suggest that VEMP testing may be useful in assessing intact vestibulocollic pathways in humans.
Adult↗
Distal loss of femoral bone following total knee arthroplasty. Measurement with visual and computer-processing of roentgenograms and dual-energy x-ray absorptiometry.
The changes in bone-mineral content in the distal aspect of a cadaveric femur that had been prepared for insertion of the femoral component of a total condylar knee prosthesis were evaluated with visual inspection and computer-processing of roentgenograms and with dual-energy x-ray absorptiometry. Seventeen small slices of bone, each three millimeters wide, were removed so that, finally, 89 per cent of the bone was lost from the distal femoral metaphysis. Standardized lateral roentgenograms of the specimen were made with use of a reference step-wedge of hydroxyapatite, and dual-energy x-ray absorptiometry studies were performed with the x-ray beam tangential to the interface. The roentgenograms were digitized and the bone mineral was measured with use of computer analysis. Dual-energy x-ray absorptiometry was performed with and without the femoral prosthesis in place, in order to determine the effect of the metallic prosthesis on the accuracy of the measurement. A bone loss of 25 per cent or more was identified visually by all five of the readers 100 per cent of the time; losses of 20 to 24 per cent, 15 to 19 per cent, 10 to 14 per cent, and 3 to 9 per cent were correctly identified 92, 75, 66, and 59 per cent of the time, respectively. The measurements of bone-mineral content that were obtained from the digitized roentgenograms were linearly correlated with the actual bone-mineral content (the ash content) (r = 0.97, p < 0.001) and were three times more accurate than the visual readings. The determinations of bone-mineral content with dual-energy x-ray absorptiometry correlated highly with the ash content (r = 1.00, p < 0.001) and were seven times more accurate than the visual readings. There was only a 4 per cent difference between the measurements with dual-energy x-ray absorptiometry made with the prosthesis in place and those made without it in place (p < 0.01). Dual-energy x-ray absorptiometry was the most accurate of the three methods and could detect the smallest experimentally created loss; computer-processing and visual-processing of roentgenograms detected losses of 8 per cent or more and 25 per cent or more, respectively. Dual-energy x-ray absorptiometry and computer-processing of the roentgenograms quantified the bone loss, while visual-processing could detect only the presence or absence of bone loss.(ABSTRACT TRUNCATED AT 400 WORDS)
Absorptiometry, Photon↗
Unilateral vestibular deafferentation: a model of adaptation.
After acute loss of peripheral vestibular function, a centrally adaptive process takes place. Clinical measurements of vestibular adaptation are useful, both diagnostically and as a means of following patients after acute vestibular deficits. Ocular torsion is one measurement that can be used to follow these acutely disabled patients. The measurement is made from fundus photographs and is technically easy to perform and interpret. We present a pilot study from our Vestibular Disorders Clinic using fundus photography to measure the optic nerve head-foveal angle in six patients undergoing unilateral vestibular neurectomy, with subsequent analysis resulting in a speculative mathematical model of vestibular compensation in the roll plane. While the identification or selection of patients with significant ocular torsions from the vestibular population remains ill-defined, fundus photography remains an easy and useful method of following compensation in postoperative patients.
Adaptation, Physiological↗
Effect of image display on the quality of multiplanar reconstruction of computed tomography data.
RATIONALE AND OBJECTIVES: The objective of this study is to determine whether the use of edge-enhancement post-processing filters was useful in the computed tomographic (CT) multiplanar evaluation of skeletal trauma. METHODS: The group consisted of a series of 10 cases of skeletal trauma (3 cases of acetabular fractures, 3 cases of tibial plateau fractures, and 4 cases of ankle fractures). All patients had a CT scan using a scan protocol of 4-mm collimation and 3-mm interscan interval. All transaxial images were reconstructed with both a standard algorithm and with an edge-enhancement filter. The images from each group were then reconstructed into coronal and sagittal planes. Three individuals independently reviewed each case and compared image pairs to determine whether images using an edge-enhancement filter were of better or worse quality than standard images. RESULTS: The reviewers found the images with edge-enhancement to be equal to or superior to images reconstructed with a standard algorithm, regardless of the image plane chosen. This bias was especially true in cases of hip and ankle trauma. CONCLUSIONS: When CT supplemented by multiplanar imaging is used in patients with skeletal trauma, image data reconstruction should be done with an edge-enhancement filter to optimize image detail.
Acetabulum↗
Comparison of helical and serial CT with regard to three-dimensional imaging of musculoskeletal anatomy.
To test the hypothesis that helical computed tomographic (CT) scans provide three-dimensional images as good as or better than those provided by serial CT, two objects were used to study the effects of helical CT: an angled cylindrical bone phantom and a human cadaveric femur specimen with a simulated fracture 1 mm wide. Both objects were immersed in a water bath, and a series of helical and serial CT scans were obtained with various parameters. Volumetric rendering was applied to the resultant data sets to create three-dimensional images, which three radiologists reviewed in a blinded manner to rate their fidelity, accuracy, and diagnostic usefulness. As expected, the images obtained with thin collimation and small intersection spacing or slow table movement were considered superior. Helical and serial CT data acquired with similar parameters were similar in quality, but helical CT is approximately five times faster than serial CT; hence, it is possible to use thinner collimation and obtain more sectional data with helical CT.
Femur↗
Three-dimensional imaging.
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Bone and Bones↗