Biomedical subjects

K N Bachus

Publications and source records attributed to K N Bachus.

At least 19 recordsLinked to original sources

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↗

PubMed1999

A biomechanical analysis of internal fixation of complex tibial plateau fractures.

OBJECTIVE: To compare the mechanical stability of fixation of an unstable bicondylar tibial plateau fracture with several different fixation techniques in a cadaveric model. DESIGN: Randomized laboratory investigation using a simulated bicondylar tibial plateau fracture with metaphyseal-diaphyseal dissociation. SETTING: Complex tibial plateau fractures were instrumented and tested under ramp and cyclic loading conditions on a servohydraulic materials testing machine. INTERVENTION: Each tibia was instrumented sequentially with a lateral buttress plate, a lateral and a medial buttress plate, and a lateral buttress and an anteromedial antiglide plate for ramp load testing. For cyclic testing, one of the three constructs was used on each specimen. MAIN OUTCOME MEASUREMENTS: Vertical subsidence of the medial tibial plateau was measured in both ramp and cyclic loading in order to evaluate the three internal fixation techniques. RESULTS: No significant difference was measurable between the dual buttress construct and the lateral buttress/anteromedial antiglide construct. However, the lateral buttress plate alone provided significantly less stability. CONCLUSIONS: A lateral buttress plate with an anteromedial antiglide plate may provide equally effective fixation as compared with the dual buttress plating technique in complex tibial plateau fractures. This less invasive technique may also be associated with fewer complications due to the lack of soft tissue stripping that is required for its application.

Aged↗

PubMed1999

Loading conditions and cortical bone construction of an artiodactyl calcaneus.

Customary nonuniform distributions of physiological bone strains are thought to evoke heterogeneous material adaptation in diaphyseal cortices of some limb bones. Recent studies of artiodactyl calcanei have suggested that the regional prevalence of specific mechanical strain features such as mode and magnitude correlate with specific variations in cortical bone ultrastructure, microstructure and mineralization. These data are also consistent with predictions of current algorithms of mechanically induced bone adaptation. However, detailed characterization of the customary functional strain environment of these bones is needed to understand better the mechanisms of these adaptations. An in vitro loading method and rosette strain gauges were used to record principal strains, maximum shear strains and principal strain angles at multiple locations on ten calcanei of adult male mule deer (Odocoileus hemionus hemionus). Each hind limb was fixed in an apparatus to mimic the mid-support phase of the gait and loaded via the Achilles tendon over a broad range of functional loads (0 to 2943 N). Strains were recorded on the craniolateral, craniomedial, caudal, medial and lateral cortices at mid-diaphysis. Loading variations included the progressive elimination of the ligament and tendon along the caudal calcaneus. The results showed that the cranial cortex experiences longitudinal compressive strains that are nearly equal to the principal minimum strains and that the caudal cortex receives longitudinal tensile strains that are nearly equal to the principal maximum strains. With a 981 N load, the mean principal compressive strain on the cranial cortex was -636+/-344 micro(&egr;) (mean +/- s.d., N=9) and the mean principal tensile strain on the caudal cortex was 1112+/-68 micro;(&egr;)x (N=9). In contrast to the cranial and caudal cortices, principal strains in the medial and lateral cortices displayed relatively large deviations from the longitudinal axis (medial, 24 degrees cranial; lateral, 27 degrees caudal). Although shear strains predominated at all gauge sites, variations in maximum shear strains showed no apparent regional pattern or consistent regional predominance. The plantar ligament and tendon of the superficial digital flexor muscle were shown to have important load-sharing functions. These results demonstrate that the functionally loaded artiodactyl calcaneus generally behaves like a cantilevered beam with longitudinal compression and tension strains predominating in opposing cranial and caudal cortices, respectively. Differences in osteon remodeling rates, osteon morphology and mineral content reported previously between the cranial and caudal cortices correlate, in part, with the magnitudes of the principal compressive and tensile strains, respectively. However, material differences that distinguish the medial and lateral cortices from the cranial and caudal cortices could not be primarily attributed to locally increased shear strains as previously suggested. Variations in osteon and/or collagen fiber orientation may correlate more strongly with principal strain direction.

Animals↗

PubMed1998

Dissolution of particulate hydroxyapatite in a macrophage organelle model.

It is controversial as to whether debris from hydroxyapatite (HA)-coated implants jeopardizes the long-term success of total joint replacements. It has been hypothesized that liberated HA particles are engulfed by macrophages and through normal cellular digestion prevent osteolysis and third-body wear. HA particulates, however, have been observed at the interface and on polyethylene articulating surfaces. There is limited data demonstrating the ability of HA to dissolve at the acidity levels associated with macrophage organelle digestion. The objective of this study was to determine if particulate HA could dissolve at the pH levels found in macrophage organelles. Characterized HA particles were placed into buffered solutions corresponding to phagosomal organelle pH levels: cytoplasmic (pH 7), phagosomal (pH 6), and lysosomal (pH 5). Flasks were under continuous agitation in a shaker chamber at 37 degrees C. Calcium and phosphate ions were measured beyond the maximum life span of an activated macrophage. The data showed that calcium ions rose within the first 24 h and then remained constant throughout the experiment for all pH groups. Phosphate ion concentration showed a similar pattern at the lysosomal pH but remained undetected at the other organelle pH levels. The saturation point was highest at the lysosomal pH level and lowest at the cytoplasmic pH level. The results of this experiment leave the potential for HA particles to dissolve following macrophage digestion. However, caution must be exercised when interpreting the macrophage organelle digestion hypothesis; the size of the HA particle, the length of time required to completely dissolve the particle, and potential cellular toxicity all are factors that have yet to be determined before this hypothesis can be validated.

Calcium↗

PubMed1998

Technique for identification of submicron metal particulate from implants in histological specimens.

Metal implants are being used with increasing frequency for the treatment of many diseases in the field of orthopedics, cardiology, cardiovascular surgery, and otolaryngology. Unfortunately, metals can be a source of submicron particles, which may have adverse effects on tissues. This article describes a technique that uses backscattered electron imaging and energy dispersive X-ray microanalysis, which have the capacity to perform both quantitative and qualitative analysis. The particles can be characterized by size, shape, amount, and composition. Although this technique can be used near the implant interface, it is particularly helpful in tissues a great distance from the implant site with a low concentration of metal debris. In addition, the sensitivity and specificity of this technique can be adjusted to the investigator's needs.

Electron Probe Microanalysis↗

PubMed1998

Porous-coated metal-backed patellar components in total knee replacement. A postmortem retrieval analysis.

The use of porous-coated metal-backed patellar components to achieve consistent fixation by bone ingrowth and to provide relief of pain warrants serious scrutiny. We conducted a quantitative postmortem investigation of eleven consecutively retrieved components with use of high-resolution contact radiographs, electron microscopy, and histological analysis. The implants had been in situ for a mean (and standard deviation) of 45+/-36 months (range, one to eighty-four months). Analysis of the high-resolution contact radiographs revealed that a mean of 86+/-12 per cent (range, 61 to 100 per cent) of the porous coating was in contact with the host bone. Backscattered electron imaging showed that the mean volume fraction of bone ingrowth was 13+/-9 per cent (range, 0 to 30 per cent). No significant difference was detected, with the numbers available, between the volume fraction of the bone ingrowth measured in the porous coating and that of the host cancellous bone in the patellae.

Aged↗

PubMed1998

Biomechanical evaluation of lateral patellar dislocations.

This investigation was undertaken to identify the structures torn within the medial retinaculum and localize the injury site anatomically following acute lateral dislocation of the patella in a cadaver model. The patellae of 10 fresh-frozen cadavers were translated laterally 135% of the patella width on a universal testing instrument. Magnetic resonance imaging (MRI) was performed on all specimens prior to testing and immediately following testing. Anatomical dissection also was performed on the medial retinaculum following testing. Dissection revealed avulsion fractures from the inferomedial border of the patella in 8 of the 10 knees. The medial patellofemoral ligament was injured in 8 of the 10 knees; the location of the injury varied. Tears of the medial patellofemoral ligament from the femur in 6, a midsubstance tear in 1, and stretch in 1 knee were noted. In a knee with a femoral-sided tear, an avulsion fracture of the medial patellofemoral ligament was identified. None of the cadaver knees demonstrated tears of the lateral retinaculum or medial patellotibial ligaments on dissection. Review of the MRIs revealed a medial retinaculum tear in 6 of the 10 knees. Two tears from the femur, 3 from the patella, and 1 tear from both the patella and femur were noted. An avulsion fracture was noted from the inferomedial patellar border in 3 of the 10 knees. No pathology was noted on 4 of the MRIs. When anatomically correlated, the 3 patellar retinacular tears and 3 avulsion fractures noted on MRI represented a tear of the medial patellomeniscal ligament from the patella. The femoral-sided tear represented a tear of the medial patellofemoral ligament from the femur. An appreciation of the spectrum of injury to the medial retinaculum may aid in the diagnosis of an acute dislocation of the patella and help establish the anatomical structures damaged. The pathology demonstrated in this study may explain the diversity of injury seen clinically. Whereas an avulsion fracture from the patella may represent the medial patellomeniscal ligament, a femoral-sided retinacular tear may represent the medial patellofemoral ligament. This may lead to future refinements of surgical options and anatomic restoration of the damaged structure.

Biomechanical Phenomena↗

PubMed1997

Crack-growth properties of various elastomers with potential application in small joint prostheses.

Silastic small joint spacers for the metacarpophalangeal joint fail catastrophically at a reported rate ranging from 2 to 26%. Although the exact cause of this problem is not known, it is speculated that failure is due to the propagation of flaws generated in the material surface. In addition to wear secondary to bony impingement, these flaws can be introduced through manufacturing, surgical handling, and in vivo frictional wear. In an effort to identify an elastomeric material that will function similarly to Silastic as a self-hinging joint spacer but provide an increased functional life, we have investigated and compared the crack-growth properties of two polyurethanes, ChronoFlex and Medicaflex, and a thermoplastic elastomer, Santoprene, with those of Silastic. The materials were evaluated after sterilization by either ethylene oxide or gamma irradiation in an ASTM standard flexing machine under conditions of high humidity and body temperature both before and after artificially aging. In each case, the materials investigated presented significantly lower crack-growth rates than Silastic (p < 0.001).

Biocompatible Materials↗

PubMed1997

Postmortem analysis of consecutively retrieved asymmetric porous-coated tibial components.

The objective of this investigation was to conduct a postmortem analysis of 8 porous-coated asymmetric tibial components to measure the extent of radiolucencies and bone ingrowth. With the use of radiographic, electron microscope, and histologic analysis techniques, a quantitative postmortem study of 8 consecutively retrieved porous-coated tibial components was conducted. Time in situ averaged 47+/-36 months. The components were secured with 4 pegs and 2 screws. Autograft bone chips were applied to the resected tibia during implantation. Contact radiographs of an average of 8 3-mm sections from each implant revealed that 73%+/-17% of the porous coating had no apparent radiolucencies present between the host bone and porous coating for the series. Backscattered electron imaging showed that the bone ingrowth averaged 6%+/-2%. Histologic analysis was unable to demonstrate any adverse cellular response. The analysis suggested that this asymmetric implant design is stable and biocompatible and has potential for long-term clinical durability.

Aged↗

PubMed1997

Reproducibility of techniques using Archimedes' principle in measuring cancellous bone volume.

Researchers have been interested in developing techniques to accurately and reproducibly measure the volume fraction of cancellous bone. Historically bone researchers have used Archimedes' principle with water to measure the volume fraction of cancellous bone. Preliminary results in our lab suggested that the calibrated water technique did not provide reproducible results. Because of this difficulty, it was decided to compare the conventional water method to a water with surfactant and a helium method using a micropycnometer. The water/surfactant and the helium methods were attempts to improve the fluid penetration into the small voids present in the cancellous bone structure. In order to compare the reproducibility of the new methods with the conventional water method, 16 cancellous bone specimens were obtained from femoral condyles of human and greyhound dog femora. The volume fraction measurements on each specimen were repeated three times with all three techniques. The results showed that the helium displacement method was more than an order of magnitudes more reproducible than the two other water methods (p < 0.05). Statistical analysis also showed that the conventional water method produced the lowest reproducibility (p < 0.05). The data from this study indicate that the helium displacement technique is a very useful, rapid and reproducible tool for quantitatively characterizing anisotropic porous tissue structures such as cancellous bone.

Animals↗

PubMed1997

Determining mineral content variations in bone using backscattered electron imaging.

The mechanical properties of bones are greatly influenced by the ratio of organic constituents to mineral. Determination of bone mineral content on a macroscopic scale is straightforward, but microscopic variations, which can yield new insights into remodelling activities, mechanical strength, and integrity, are profoundly more difficult to measure. Measurement of microscopic mineral content variations in bone material has traditionally been performed using microradiography. Backscattered electron (BSE) imaging is a technique with significantly better resolution than microradiography with demonstrated consistency, and it does not suffer from projection-effect errors. We report results demonstrating the applicability of quantitative BSE imaging as a tool for measuring microscopic mineral content variations in bones representing a broad range of mineralization. Bones from ten species were analyzed with Fourier-transformed infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectrometry, ash measurements, and BSE imaging. BSE image intensity (graylevel) had a very strong positive correlation to mineral (ash) content. Compositional and crystallographic variations among bones had negligible influence on backscattered electron graylevels. The present study confirms the use of BSE imaging as a tool to measure the microscopic mineral variability in a broad range of mineralized tissues.

Animals↗

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

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

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↗

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↗

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↗