Biomedical subjects

R D Bloebaum

Publications and source records attributed to R D Bloebaum.

At least 37 records · Page 2Linked to original sources

PubMed1997

Analysis of particles in acetabular components from patients with osteolysis.

Acetabular polyethylene components were quantitatively analyzed for the presence of third body particles from 38 consecutively retrieved components. Backscattered electron imaging and correlated energy dispersive x-ray analysis were used for the assessments. Retrievals were divided into 4 groups based on methods of fixation and metal alloy types: 8 hydroxyapatite coated, 6 cobalt chrome porous coated, 17 titanium porous coated, and 7 cemented implants were evaluated. The backscattered electron imaging data showed that the components from the hydroxyapatite coated implants had larger particles than did the components from the cemented group. The hydroxyapatite group had 51 +/- 52 particles per mm2. The cobalt chrome alloy group had 10 +/- 9 particles per mm2, and the titanium alloy group had 9 +/- 16 particles per mm2. The cemented group had 5 +/- 4 particles per mm2. The difference between the cement group and the hydroxyapatite group was statistically significant. The elemental analysis showed that 70% of the particles in the hydroxyapatite group had calcium and phosphorus elements. Third body particles likely contribute to particulate generation. The results suggest that the hydroxyapatite coated components have the potential for producing greater amounts of particulate debris. Continued analysis of retrieved components for the presence of the third body particles is required.

Acetabulum↗

PubMed1997

Lymphoreticular dissemination of metal particles after primary joint replacements.

Twenty-three patients with a history of primary joint replacement followed by lymph node dissection procedure were studied. These specimens included pelvic, gastric, paraaortic, inguinal, retroduodenal, and axillary node chains. The lymph node specimens were sectioned, processed for scanning electron microscopic study, and viewed with backscattered electron imaging to identify metal particles. On detection of a metal particle, energy dispersive x-ray microanalysis was conducted to determine its elemental composition. Seven of 23 patients had metal alloy particles within the lymph node specimens. Metal particles were identified in the pelvic and axillary node chains. In each case, the metal alloy identified corresponded with the implanted type of alloy. The shortest interval between joint implantation and dissemination of metal to a lymph node chain was 6 months. These data suggest the need for continued followup to determine long term effects, if any, of this distribution of metal particles through the lymphatic system.

Aged↗

PubMed1997

Postmortem analysis of bone growth into porous-coated acetabular components.

Microradiography, backscattered electron microscopy, and histological analysis were used to conduct a quantitative postmortem study of seven consecutively retrieved anatomical porous replacement acetabular components that had been inserted during total hip arthroplasties. Screws had been used for the initial fixation of six components. The microradiographic analysis of all seven components showed that an average (and standard deviation) of 84 +/- 9 per cent (range, 72 to 93 per cent) of the porous coating was in direct apposition to the periprosthetic bone. The backscattered electron images demonstrated that an average of 12 +/- 6 per cent (range, 4 to 21 per cent) of the space available in the porous coating was occupied by ingrown bone. The amount of bone ingrowth was not significantly different among the three zones delineated by DeLee and Charnley. Uniformity of bone growth into the porous coating suggests that the preferential loading that occurs in the superior region did not differentially affect the bone ingrowth. The present study showed that consistent bone growth into anatomical porous replacement acetabular components can be achieved.

Acetabulum↗

PubMed1997

Progression of human bone ingrowth into porous-coated implants. Rate of bone ingrowth in humans.

We report the measured progression of human cancellous bone ingrowth into load-bearing porous-coated titanium implants over 5 time periods (0, 3, 6, 9, and 12 months). There was a statistically significant progression of bone ingrowth into the implants over a 9-month period, but the 9- and 12-month data were not different. Investigators are advised to analyze time "0" implants in order to distinguish mechanical impaction of bone from the biological process of bone ingrowth.

Aged↗

PubMed1996

Evidence of structural and material adaptation to specific strain features in cortical bone.

BACKGROUND: Functionally induced strains provide epigenetic signaling for bone modeling and remodeling activities. Strain gauge documentation of the equine third metacarpal reveals a neutral axis passing through the craniolateral cortex, resulting in a narrow band of cortex loaded predominantly in tension, with the remainder of the cortex experiencing a wide range of compression strain magnitudes that are maximal in the caudomedial cortex. This predictable strain pattern provides a model for examining the hypothesis that strain mode, magnitude, and strain energy density are potential correlates of compact bone structural and material organization. METHODS: Structural and material variables were quantified in nine equine (standard breeds) third metacarpals for comparison with the in vivo strain milieu that was evaluated in thoroughbred horses. The variables quantified included secondary osteon population density (OPD), fractional area of secondary bone (FASB), fractional area of porous spaces, collagen fiber orientation, mineral content (% ash), and cortical thickness. Each bone was sectioned transversely at 50% of length, with subsequent quantification of eight radial sectors and three intracortical regions (periosteal, middle, endosteal). Linear regression analysis compared these variables to magnitudes of corresponding regional in vivo longitudinal strain, shear strain, and strain energy density values reported in the literature. RESULTS: The craniolateral ("tension") cortex of this bone is distinguished by its 30% lower FASB and with the lateral cortex exhibits 20% darker gray level (more longitudinal collagen) compared with the average of all other locations. Conversely, the remaining ("compression") cortices as a group have a high OPD, are more extensively remodeled, and contain more oblique-to-transverse collagen. The caudal cortices (caudomedial, caudal, caudolateral) are significantly thinner (P < 0.01) and have 4% lower mineral content (P < 0.05) than all other locations. Moderately strong correlations exist between collagen fiber orientation and normal strain (r = 0.752) and shear strain (r = 0.555). When normal and shear strains were transformed to their respective absolute values, thus eliminating the effects of strain mode (tension vs. compression), these correlation coefficients decreased markedly. CONCLUSIONS: Collagen fiber orientation is related to strain mode and may function to accentuate rather than attenuate bending. These differences may represent adaptations that function synergistically with bone geometry to promote a beneficial strain distribution and loading predictability during functional loading.

Adaptation, Physiological↗

PubMed1996

Inability of energy dispersive X-ray analysis to identify particulate polyethylene.

There are limitations to all techniques used to identify particulate polyethylene in histological specimens. The goal of our study was to determine if remnant metal elements used during the catalytic production of ultra high molecular weight polyethylene, could be used as markers for particulate polyethylene detection in histological specimens. It was hypothesized that these catalyst elements could be detected in polyethylene using energy dispersive X-ray elemental analysis. Six samples from five different companies were evaluated. These included virgin polymer powder, polyethylene bar stock, and artificial joint components. Five specimens from each of the six samples were analyzed with energy dispersive X-ray elemental analysis. After elemental analysis was completed, only 2 of 30 specimens were positive for the catalyst elements. In the remaining 28 specimens, catalyst elements were not detected. Our investigation demonstrates that energy dispersive X-ray elemental analysis is not currently a feasible method of particulate polyethylene detection. Additional techniques will need to be developed to accurately identify particulate polyethylene in histological specimens.

Beryllium↗

PubMed1996

Analysis of lymph nodes for polyethylene particles in patients who have had a primary joint replacement.

Polarized light microscopy has been used for more than forty years to identify polyethylene particles in histological specimens; however, few investigators have assessed the specificity of this technique. We examined specimens from dissected lymph nodes for the presence of strongly birefringent particles resembling polyethylene. Twenty-seven patients had dissection of lymph nodes after a total joint replacement (Group 1), and a control group of eighteen patients had dissection of lymph nodes before a total joint replacement (Group 2). Specimens from both groups of lymph nodes were examined under plain and polarized light. The presence of strongly birefringent particulate debris was graded from 0 to 4. Twenty-one (78 per cent) of the twenty-seven patients in Group 1 and eight of the eighteen patients in Group 2 had strongly birefringent particles in the lymph nodes. Our results demonstrate that, in the assessment of the systemic dissemination of polyethylene in the lymphoreticular system, polarized light microscopy has important limitations. More refined techniques employing polarized light and other methods of physical and chemical analysis may be necessary to identify polyethylene particles accurately within the lymphoreticular system and periprosthetic tissue.

Adult↗

PubMed1995

Distinguishing wear and creep in clinically retrieved polyethylene inserts.

There is an increasing awareness of the clinical problems associated with ultra-high-molecular-weight polyethylene (UHMWPE) wear and failure in orthopedics. To better understand the reasons for wear and failure, methods were developed using polarized light microscopic analysis and backscattered electron (BSE) imaging with correlated elemental analysis to distinguish the contributions of wear, creep, and third-body particulate. This study determined that microscopic metal particles (< 10 microns) previously not observed with the stereomicroscope could be easily observed with the BSE technique. BSE imaging identified embedded metal in 5/5 of the tibial and 2/4 of the acetabular inserts, which were thought to be free of metal debris after stereoscopic examination. Correlated elemental analysis showed that the microscopic particles could be traced to the elements known to be present in the porous coatings of the retrieved uncemented implants. Creep was distinguished from wear in the total hip and total knee inserts by using polarized light microscopic techniques. Continued development of polarized light microscopic techniques applied in this investigation should assist biomaterials experts in the future to better distinguish wear and creep in retrieved clinical inserts. The correlated BSE and elemental analysis will assist in determining the roll of microscopic third-body particular in wear and osteolysis in total joint replacement.

Adult↗

PubMed1995

Evidence of strain-mode-related cortical adaptation in the diaphysis of the horse radius.

The relative importance that certain strain features, including mode (e.g., tension vs. compression) and magnitude, have in affecting adaptive bone remodeling seen in normal skeletally mature bones remains controversial. The equine radius is used as a model because in vivo strain data show that the mid-to-proximal diaphysis receives a consistent history of predominantly cranial-caudal bending loads, in contrast to the distal diaphysis which receives relatively more torsional loading superimposed on cranial-caudal bending. Medial and lateral cortices serve as control regions because they correspond to a neutral axis of bending. Equine radii were sectioned transversely at 65% (proximal), 50%, and 35% (distal) of length and cortical bone from the cranial ("tension"), caudal ("compression"), medial, and lateral regions was examined to determine if one, of many, structural and material features could be distinguished as being consistently related to the distribution of the prevailing strain modes. Mineral content (percent ash) differences, though statistically significant (p < 0.01), vary less than 1% between regions of the cortex at all sections. Porosity is not significantly different between any of the regions (p = 0.13). In the 65% and 50% sections, secondary osteon population density (OPD, osteons per square millimeter) and fractional area of secondary bone (FASB) are each nearly two times as great in the caudal regions than in the other three regions (p < 0.01). The 35% section shows a pattern opposite of that in the other sections--there are more than two times as many osteons in the cranial cortex than in the caudal cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Three-dimensional surface analysis of young adult human articular cartilage.

The objective of this investigation was to determine whether the surface of young adult human articular cartilage was smooth as defined by industrial standards for metal surfaces. Human articular cartilage with attached subchondral bone from the midregion of the trochlear surface of the talus was obtained postmortem from 7 donors (aged 29 +/- 9 y). The specimens were processed using multiple fixation techniques prior to scanning electron microscopy and 3-dimensional stereoscopic analysis. Three-dimensional stereoscopic data showed that 92.78 +/- 16.90% of the articular surface was devoid of surface irregularities and was considered to be smooth. The remaining regions comprising 7.22 +/- 17.20% of the area demonstrated bumps measuring 7.70 +/- 4.58 microns in height. When the results of this study were compared with the international standards for surface preparations used by machinists for metal surfaces, they clearly showed that even when the regions with bumps were considered, the articular cartilage surface could be characterised as smooth.

Adolescent↗

PubMed1995

Consistency in calibrated backscattered electron images of calcified tissues and minerals analyzed in multiple imaging sessions.

Pure metal standards have been used to calibrate the operating envionment in quatitative backscattered electron (BSE) imaging of mineralized tissue, allowing comparisons to be made between various mineralization states of bone at the microscopic level. It has not previuously been documented that calibration procedures produce consistent, reliable results over multiple imaging sessions. In this study, BSE images were obtained from bones, pure metals, and a naturally occurring mineral in multiple imaging sessions over a six day period. The graylevel histogram profile (GHP) from each specimen was analyzed for changes in the shape and relative placement on the graylevel spectrum. Computer controlled calibration and a restrospective calibration method using pure aluminum and pure magnesium-aluminum-zinc demonstrated consistency between imaging sessions. Calibrated weighted mean graylevels (WMGLs) for biological meterials had an average standard deviation of 5.9 graylevels (2.4% variation) during the course of the study. WMGLs for inorganic materials had an average standard deviation of 0.9 graylevels (0.4% variation). A trend towards increased image brightness, due to specimen and/or embedding media degradation, was observed in the biological tissues. No increase in rightness was observed for the inorgtanic specimens. Kurtosis and skewness tests revealed a slight deviation from normality in all specimens, which remained consistent between multiple imaging sessions. These results demonstrate the BSE image analysis of bones and mineral can be calibrated with negligible precision error allowing comparisons between data within and between multiple imaging sessions.

Aluminum↗

PubMed1994

Analysis of a tension/compression skeletal system: possible strain-specific differences in the hierarchical organization of bone.

BACKGROUND: Examination of a simple skeletal cantilevered beam-like bone (artiodactyl calcaneus) suggests that regional differences in strain magnitude and mode (tension vs. compression) reflect regional adaptation in the structural/material organization of bone. The artiodactyl (e.g., sheep and deer) calcaneus has a predominant loading condition typified by the unambiguous presence of prevailing compressive and tensile strains on opposite cortices. Bone habitually loaded in bending may accommodate regional disparities in loading conditions through modifications of various aspects of its organization. These include overall bone build (gross size and shape), cross-sectional shape, cortical thickness, and mineral content. METHODS & RESULTS: Cross-sections taken along the calcaneal body exhibited cranial-caudal elongation with the compression (cranial) cortex thicker than the tension cortex (P < 0.01). Mineral content (ash fraction) was significantly greater in the compression cortex (P < 0.01), averaging 6.6% greater than in the tension cortex. Strong positive correlations were found between mineral content and section location in both the tension (r2 = 0.955) and compression (r2 = 0.812) cortices. These correlations may reflect functional adaptations to the linear increases in stress that are known to occur in the distal-to-proximal direction in simple, unidirectionally loaded cantilevered beams. According to engineering principles, the roughly triangular transverse cross-sectional geometries and thicker compression cortex are features consistent with a short cantilevered structure designed to resist unidirectional bending. CONCLUSIONS: Known differences in mechanical properties of bone in tension vs. compression suggest that these regional differences in cortical thickness and mineralization may be related to differences in strain mode. These structural/material dissimilarities, however, may be related to regional variations in strain magnitude, since bending and axially directed stresses in a simple cantilevered structure produce greater strain magnitudes in the compression domain. It is possible that the superimposed habitual strain magnitudes enhance strain-mode-specific adaptive responses. We hypothesize that these structural/material differences reflect the capacity of bone to process local information and produce a regionally heterogeneous organization that is appropriate for prevailing loading conditions.

Adaptation, Physiological↗

PubMed1994

Differences in osteonal micromorphology between tensile and compressive cortices of a bending skeletal system: indications of potential strain-specific differences in bone microstructure.

BACKGROUND: It has been hypothesized that bone has the capacity to accommodate regional differences in tension and compression strain mode and/or magnitude by altering its osteonal microstructure. We examined a simple cantilevered bone to determine whether regional differences in particular strain-related features are reflected in the microstructural organization of compact bone. METHODS & RESULTS: The artiodactyl (e.g., sheep and deer) calcaneus has a predominant loading condition which is typified by prevailing compressive and tensile strains on opposite cortices, and variations in strain magnitudes across each of these cortices. Microscopic examination showed osteon density and cortical porosity differences between tension (caudal) and compression (cranial) cortices, averaging 11.4% more osteons in the compression cortex (P < 0.01) and 80.2% greater porosity in the tension cortex (P < 0.01). There is 43.5% more interstitial bone in the compression cortex (P < 0.01). Osteons in the compression cortex also have smaller areas in contrast to the larger area per osteon in the tension cortex. Although no definite transcortical gradient in osteonal density or cortical porosity is found, fractional area of interstitial bone is larger and osteon population density is lowest in the endocortical regions of both tension and compression cortices. The endocortical regions also have greater porosity than their corresponding middle and pericortical regions (P < 0.01). CONCLUSIONS: These osteonal microstructure and cortical porosity differences may be adaptations related to regional differences in strain mode and/or strain magnitude. This may be related to the disparity in mechanical properties of compact bone in tension vs. compression. These differences may reflect a capacity of bone to process local and regional strain-related information.

Adaptation, Physiological↗

PubMed1994

Mineral apposition rates of human cancellous bone at the interface of porous coated implants.

Human cancellous bone ingrowth studies were conducted on 19 consenting bilateral total knee arthroplasty (TKA) patients. Titanium porous coated cylinders were implanted into the medial femoral condyle of the contralateral knee during the first of two TKAs. Retrieval was performed at the time of the second TKA (6-131 weeks later), and fluorochrome analysis was conducted. Mean mineral apposition rates (MAR) at the interface measured 1.0 micron/day, whereas 4 mm away, the peripheral bone had a mean MAR of 0.8 micron/day. This represented a 25% acceleration in the interface bone remodeling rate when compared with the periphery (P < .05). This study showed the bone advanced appositionally at the interface at a rate of approximately 1 micron/day. Analysis showed that when bone was over 50 microns from the porous coating, bone ingrowth did not occur. These results emphasize the need for surgical precision and careful postoperative management to achieve bone ingrowth.

Aged↗

PubMed1994

Analysis of the bone surface area in resected tibia. Implications in tibial component subsidence and fixation.

Anterior subsidence of the tibial component is still a clinical complication requiring revision in total knee replacement. Using the scanning electron microscope, a quantitative 3-dimensional stereoscopic and digitizing study was conducted on the cortical and cancellous bone surface area from 10 resected human cadaveric tibia. The data demonstrated that the cortical bone surface area covered an average of 6% of the total tibial surface area, cancellous bone 18%, and bone marrow space 76%. By conducting anatomic regional analysis, the data showed significantly higher (p < or = 0.05) bone quantities in the posteromedial and medial regions as compared with the anterior and anterolateral regions. These data help to explain why tibial component subsidence occurs anteriorly in total knee replacement. The data also suggest that if long-term component subsidence and loosening is to be limited, either biologic cement or bone cement would be required to increase the surface attachment between the tibial component and resected cancellous bone.

Adult↗

PubMed1994

Complications with hydroxyapatite particulate separation in total hip arthroplasty.

This study reports on the results of the implant and tissue analysis of clinically retrieved hydroxyapatite (HA)-coated implants. Five of the patients with fixed HA-coated stems had been clinically diagnosed with osteolysis. The semiquantitative histologic grading in these patients showed HA, polyethylene, and metal particles were all present (Grade 3+) in the osteolytic regions of the periprosthetic tissue. Additionally, inflammatory cells (Grade 3+) were present in these regions. Back-scattered electron (BSE) and correlated elemental analysis showed HA particulate was present in the polyethylene inserts. The HA could be distinguished from bone chips in the polyethylene based on morphology and anatomic number gray level differences. This study was limited in that no clinical results of particular HA-coated implant series were reported. Careful follow-up care in patients with coated devices is recommended.

Adult↗

PubMed1993

The meaning of graylevels in backscattered electron images of bone.

Backscattered electron (BSE) imaging is considered to be a useful technique for determining relative differences in bone tissue density. However, it is not clear how graylevel variations seen in BSE images of bone tissue, which are primarily dependent on the tissue's average atomic number, correlate to tissue density (g/cm3) and mineral content. Simulated bone tissues, ranging from 32-50% mineral by volume, were made by mixing synthetic hydroxyapatite with a simulated organic matrix. This technique allowed mineral content to be varied while mineral composition and crystallography remained constant. The densities of the simulated tissues were determined using Archimedes' principle. Average atomic numbers of the simulated tissues were interpolated from a regression of BSE graylevel against average atomic numbers of pure standard materials. A strong positive correlation was found to exist between mineral content and density (r2 = 0.978) as well as between mineral content and atomic number (r2 = 0.965). The average graylevel in the BSE image also exhibited a positive correlation to mineral content (r2 = 0.965) and density (r2 = 0.923). Graylevel variations in BSE images of simulated bone tissue were shown to be strongly correlated to density and mineral content, but only as a coincidence of their association with atomic number.

Biocompatible Materials↗

PubMed1993

Influence of mineral content and composition on graylevels in backscattered electron images of bone.

To determine the meaning of graylevels in backscattered electron (BSE) images of actual bone tissues, the influence of mineral content and mineral composition on BSE image graylevels was studied using chick bone tissue representing a broad age range. These tissues were analyzed for BSE image graylevels, Ca/P molar ratios, mineral composition mineral content (v/v), ash fraction (w/w), and density (g/cm3). Linear regression analyses showed that the weighted mean graylevels (WMGLs) in BSE images were positively correlated to ash fraction (r2 = 0.711), mineral content (r2 = 0.720), and density (r2 = 0.843). Although the Ca/P ratio increased from 1.65 in embryos to 1.80 in 2-year olds, the compositional changes corresponding to this Ca/P molar ratio were estimated to produce a relatively minor (< 4.0%) change in BSE image graylevel. These results demonstrate that graylevels in BSE images of actual bone tissue can be attributed to mineral content and density, but only as a coincidence of their association with atomic number.

Age Factors↗