Catheter fracture-an underrecognized and serious condition in haemodialysis.
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Aged↗
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Assessment of chronic tricuspid regurgitation by colour Doppler echocardiography: a comparison with angiography in the catheterization room.
Colour Doppler echocardiographic (CDE) assessment of tricuspid regurgitation (TR) has been limited by the lack of an accepted model against which it can be compared. Angiography is said to be inadequate because catheter placement across the tricuspid valve could induce artifactual TR. Thirty-five consecutive patients with left-sided valvulopathy and recent heart failure were studied. Angiography was validated by CDE, which demonstrated that catheter placement across the tricuspid valve did not increase the size of the regurgitant jet in the first 30 cases. All the patients were studied with CDE immediately before performing the angiography in order to compare the findings of both techniques. From all the CDE parameters measured among the angiographic groups, the jet area overlapped the least (P = 0.024). The diameters of the right cardiac chambers were larger in angiographically severe cases (P = < 0.003 to 0.041), and a scale of severity that combined jet area and right atrium area showed an excellent correlation with angiography (r = 0.924; P < 0.001). Furthermore, maximal instant systolic gradients between the right cavities, estimated by catheterization, were lower in severe cases (P = 0.038). Assessment of these gradients by continuous Doppler can enhance recognition of severe TR. The analysis of jet area, right atrium area and regurgitant gradient by CDE can provide excellent assessment of TR.
Adult↗
Mechanical failures of the pneumatic Utah-100 and Jarvik total artificial hearts. A comparative study.
Jarvik-5 and Jarvik-7 total artificial hearts (TAHs) and Utah-100 TAHs were fabricated and implanted in calves and sheep. In the Jarvik series, 30.7% had mechanical failures (16.1% catastrophic). In the Utah-100 TAH series, 11.1% had mechanical failures (3.7% catastrophic). Failures were classified as: 1) diaphragm failures; 2) valve-holding ring failures; 3) air-leak failures; and 4) prosthetic valve failures. Marked reduction in mechanical failure for the Utah-100 TAH is attributed to progressive component redesign, material selection, and more stringent quality control criteria.
Animals↗
Loosening rates and bone lysis with rough finished and polished stems.
In the senior author's 27-year experience in cementing femoral components, stems with smooth and rough surfaces were implanted. Prospective data have been kept on all patients allowing extensive long term followup. The polished Charnley stem was implanted in 168 hips from 1971 to 1975. To date, only four (2.4%) stems have required revision for aseptic loosening and four others for fracture. None showed significant bone lysis. The experience with the T-28 and TR-28 allows comparison of stems of similar geometry, but with different surface finishes. From 1972 to 1977, 209 polished T-28 stems were inserted and to date 18 (14 for fracture and four for loosening, 1.9%) have required revision. None had associated bone lysis. From 1977 to 1982, 227 second generation TR-28 matte surface finish stems (Ra 30) were implanted. Five required revision, three (2.2%) with major bone lysis. Radiographic review revealed minimal lysis in four (1.9%) polished T-28 stems and in 11 (4.9%) TR-28 stems, three of which showed major bone destruction. From 1980 to 1993, 1061 Iowa stems were implanted. In 1986 proximal precoat was added, which required additional roughening of the surface. In 1995 a 1.5% early loosening rate was reported with significant bone lysis, complicating revision. By 1998 34 (3.2%) stems have required revision, all associated with significant bone loss. Revision of one of 12 original Iowa (Ra 30) and 12 of 22 (Ra 80) grit blasted stems was needed before 5 years postoperatively. These early failures prompted the author to return to a polished stem with a geometry almost identical to the Charnley stem.
Adult↗
The Otto Aufranc Award. Wear and lubrication of metal-on-metal hip implants.
The implication of polyethylene wear particles as the dominant cause of periprosthetic osteolysis has created a resurgence of interest in metal-on-metal implants for total hip arthroplasty because of their potential for improved wear performance. Twenty-two cobalt chromium molybdenum metal-on-metal implants were custom-manufactured and tested in a hip simulator. Accelerated wear occurred within the first million cycles followed by a marked decrease in wear rate to low steady-state values. The volumetric wear at 3 million cycles was very small, ranging from 0.15 to 2.56 mm3 for all implants tested. Larger head-cup clearance and increased surface roughness were associated with increased wear. Independent effects on wear of material processing (wrought, cast) and carbon content were not identified. Implant wear decreased with increasing lambda ratio, a parameter used to relate lubricant film thickness to surface roughness, suggesting some degree of fluid film lubrication during testing. This study provided important insight into the design and engineering parameters that affect the wear behavior of metal-on-metal hip implants and indicated that high quality manufacturing can reproducibly lead to very low wear.
Analysis of Variance↗
Analysis of long-term cemented total hip arthroplasty retrievals.
A detailed biomechanical, histologic, and histomorphometric analysis of autopsy specimens from patients who previously had cemented total hip arthroplasty has helped to elucidate the skeletal response to cemented components. Bone cement has the capacity to provide long-term implant stability. The biologic response to polyethylene wear debris has a more critical effect on destabilization of cemented sockets compared with the femoral side. In contrast, mechanical events tended to predominate the early mode of destabilization of cemented femoral components with debonding at the metal-cement interface and fracture in the cement. Fractures predominate in cement mantles less than 1 mm thick and are associated with mantle defects, debonded interfaces, and sharp corners of the implants. Correlation of the histologic findings at the cement-bone interface with radiolucencies seen on clinical radiographs show that on the acetabular side radiolucencies represent a soft tissue membrane that is the biologic response to polyethylene debris. In contrast, on the femoral side, most radiolucencies were as a result of skeletal remodeling. Femoral adaptive bone remodeling is a diffuse process that occurs over the entire fixation surface. The most profound disuse osteoporosis occurred proximally in the proximal medial quadrant; however, when one takes into account all four quadrants, anterior, posterior, medial, and lateral, the most severe osteoporosis occurred at the midpoint of the stem.
Arthroplasty, Replacement, Hip↗
A bioresorbable molding mesh for impaction grafting revision hip surgery.
Impacted morselized allografts are used to treat bone loss in revision surgery. This technique depends on adequate mechanical support of the graft. Metal support devices function well, but there are disadvantages associated with the use of steel meshes. In this cadaveric, surgical simulation model we investigated the surgical and mechanical suitability of a bioresorbable molding mesh for use in impaction grafting revision surgery. Surgical feasibility was assessed, and mechanical deformation of the mesh during the surgical procedure and postoperative cyclic loading of the specimens were measured with strain gauges. All meshes were surgically usable. The exterior surface deformation of the meshes during the surgical procedure and postoperative mechanical loading did not exceed 4500 microm/m, although the meshes were not damaged in a four-point bending test in which deformations higher than 19,000 microm/m were reached. Therefore, results of this study suggest that this type of bioresorbable mesh seems to have sufficient initial mechanical properties to warrant additional preclinical in vivo study.
Arthroplasty, Replacement, Hip↗
Concerns about ceramics in THA.
Currently available ceramic materials are superior to those used originally in total hip arthroplasty, which should translate into a much lower complication rate than what has been reported previously. In spite of this, a number of concerns remain. The ceramic-on-ceramic articulation is not immune to wear and surface damage. Conditions associated with ceramic wear include vertical cup position, femoral neck impingement, and femoral head separation. A unique pattern of stripe wear has been described as something that results from microseparation during gait. Catastrophic failure, although rare, continues to be a concern, and not all fractures can be predicted by proof testing. Revisions needed because of ceramic fractures can be extensive, and the results of the revision procedures can be compromised by the presence of highly abrasive particulate debris that is retained. Other concerns include the generation of debris from modular interfaces, neck damage and debris generation from impingement of some designs, inability to use a ceramic head a second time on a metal trunnion, and the dramatic loss of head and liner options intraoperatively. Although ceramics show great promise as a lower wear articulation, manufacturing and design modifications and improvements will continue in an attempt to address the substantial concerns that persist.
Ceramics↗
Correction of error in two-dimensional wear measurements of cemented hip arthroplasties.
The irregularity of individual wear patterns of total hip prostheses seen during patient followup may result partially from differences in radiographic projection of the components between radiographs. A method to adjust for this source of error would increase the value of individual wear curves. We developed and tested a method to correct for this source of error. The influence of patient position on validity of wear measurements was investigated with controlled manipulation of a cadaveric pelvis. Without correction, the error exceeded 0.2 mm if differences in cup projection were as small as 5 degrees. When using the described correction method, cup positioning differences could be greater than 20 degrees before introducing an error exceeding 0.2 mm. For followup of patients in clinical practice, we recommend using the correction method to enhance accuracy of the results.
Arthroplasty, Replacement, Hip↗
Applications of digital image correlation to biological tissues.
Optical methods are becoming commonplace in investigations of the physical and mechanical behavior of biological tissues. Digital image correlation (DIC) is a versatile optical method that shows tremendous promise for applications involving biological tissues and biomaterials. We present the fundamentals of DIC with an emphasis on the application to biological materials. An approach for surface preparation is described that facilitates its application to hydrated substrates. Three examples are presented that highlight the use of DIC for biomedical research. The first example describes the use of DIC to study the mechanical behavior of arterial tissues up to 40% elongation. The second example describes an evaluation of the mechanical properties of bovine hoof horn in the dehydrated and fully hydrated states. Uniaxial tension experiments are performed to determine the elastic modulus (E) and Poisson's ratio (nu) of both the arterial and dermal tissues. Spatial variations in the mechanical properties are evident from the full-field characterization of both tissues. Finally, an application of DIC to study the evolution of loosening in cemented total hip replacements is described. The noncontact analysis enables measurement of the relative displacement between the bone/bone cement and bone cement/prosthesis interfaces. Based on the elementary optical arrangement, the simple surface preparation, and the ability to acquire displacement/strain measurements over a large range of deformation, DIC should serve as a valuable tool for biomedical research. Further developments will enable the use of DIC for in vivo applications.
Algorithms↗
Fluorescence spectroscopic analysis of surface and subsurface residual stress fields in alumina hip joints.
We aim to establish a confocal spectroscopic technique able to study the features of fluorescence spectra arising from native Cr3+ impurity in polycrystalline alumina (Al2O3) as a biomaterial and to use their emission lines as microscopic probes for the characterization of residual stress fields stored in artificial hip prostheses during their implantation in vivo. As an application of the technique, we report for the first time concerning the evolution of microscopic (residual) stress fields stored on the surface and in the subsurface of N=7 retrieved Al2O3 hip joints after exposure in the human body from a few months to 19 yr. The micrometric diameter of the laser beam waist impinging on the joint surface (typically about 1 microm in lateral resolution) enables us to estimate the patterns and magnitude of residual stress with high spatial resolution, at least comparable with the grain size of the material. In addition, a selected confocal configuration for the optical probe enables minimization of the probe size along the in-depth direction. According to a statistical collection of data on the microscopic level for retrieved femoral heads in toto, a residual stress field arising from loading history in vivo during the lifetime of the Al2O3 femoral head can be revealed. Finally, an interpretation is given of microscopic wear mechanisms in Al2O3 artificial hip joints consistent with the observed evolution of surface residual stress fields on elapsed time in vivo.
Aluminum Oxide↗
Direct percutaneous left ventricular puncture.
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Aged↗
A case of 24 years longevity of an Ionescu-Shiley bioprosthesis in the mitral position.
Valve dysfunction, attributed to primary tissue failure several years after implantation of Ionescu-Shiley bioprostheses, has led to re-operation in most cases. We report a rare case of this bioprosthesis showing stenosis and regurgitation after implantation in the mitral position 24 years previously. No cusp tears, but severe calcification and well-grown neointima over the Dacron cloth of the inner surface were observed. This may explain how the valve functioned for such a long period of time. We replaced it with a Carpentier-Edwards pericardial bioprosthesis.
Aged↗
Synovial reaction associated with disruption of polypropylene braid-augmented intraarticular anterior cruciate ligament reconstruction. A case report.
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Adult↗
The influence of stem insertion rate on the porosity of the cement mantle of hip joint replacements.
This study investigates the effect of stem insertion rate on the porosity of the cement mantle. An experimental protocol was developed to simulate the surgical technique of cementing a prosthetic stem into the medullary canal of the femur. Cement mantle specimens were produced for three different stem insertion rates. The presence of porosity in the cement mantle was investigated. Additionally, the mechanical strength of the bone cement was assessed. Increasing the stem insertion rate did not have a significant effect on the porosity distribution within the bulk cement mantle. However, for all stem insertion rates investigated, the porosity concentration increased significantly moving from the cement/pseudofemur interface through to the stem/cement interface. In all cases, the presence of porosity significantly decreased the mechanical behaviour of the bone cement. High porosity concentration at the stem/cement interface seems to be attributed also to the rheology of the cement during implant insertion. Nevertheless, the surgeon cannot influence the formation of porosity by changing the stem insertion rate.
Arthroplasty, Replacement, Hip↗
Reciprocal walking orthosis with composite material body brace: initial development.
Reciprocal walking orthoses are routinely used by thoracic lesion patients for ambulation using crutches. A primary reason for their prescription is to provide therapeutic benefit and improved independence. To achieve this, maximum efficiency of walking and acceptance of the device is necessary to promote long-term compliance. Lateral rigidity in the orthosis influences walking efficiency, but the structural properties of conventional techniques for producing a sufficiently rigid body brace makes them unattractive. Currently patients and clinicians are forced to choose between greater efficiency or cosmesis of the orthosis. Composite materials have the potential to permit the required rigidity in a structure that is less obtrusive. However, their material properties could lead to unsafe forms of failure unless suitable manufacturing methods are devised. It is therefore inappropriate to supply prototypes to patients for field evaluation until laboratory investigation of innovative production methods has ensured that the orthosis is safe. A production technique has been devised that is ostensibly suitable. Prototype body braces have been tested and have been shown to have improved structural properties and safe failure modes. A test programme implemented on a complete concept orthosis has confirmed that improved lateral rigidity can be achieved with a less obtrusive body brace, and that it will behave safely for long enough to permit field evaluation.
Braces↗
A novel test method for evaluation of the abrasive wear behaviour of total hip stems at the interface between implant surface and bone cement.
After total hip replacement, some cemented titanium stems show above-average early loosening rates. Increased release of wear particles and resulting reaction of the peri-prosthetic tissue were considered responsible. The objective was to develop a test method for analysing the abrasive wear behaviour of cemented stems and for generating wear particles at the interface with the bone cement. By means of the novel test device, cemented hip stems with different designs, surface topographies and material compositions using various bone cements could be investigated. Before testing, the cemented stems were disconnected from the cement mantle to simulate the situation of stem loosening (debonding). Subsequently, constant radial contact pressures were applied on to the stem surface by a force-controlled hydraulic cylinder. Oscillating micromotions of the stem (+/- 250 microm; 3 x 10(6)cycles; 5 Hz) were carried out at the cement interface initiating the wear process. The usability of the method was demonstrated by testing geometrically identical Ti-6A1-7Nb and Co-28Cr-6Mo hip stems (n= 12) with definite rough and smooth surfaces, combined with commercially available bone cement containing zirconium oxide particles. Under identical frictional conditions with the rough shot-blasted stems, clearly more wear particles were generated than with the smooth stems, whereas the material composition of the hip stems had less impact on the wear behaviour.
Biocompatible Materials↗
Is the wear factor in total joint replacements dependent on the nominal contact stress in ultra-high molecular weight polyethylene contacts?
The exact dependence of wear factor on contact stress, load and apparent contact area is much disputed in the literature. This study attempts to solve this dispute. Pin-on-plate studies of ultra high molecular weight polyethylene against stainless steel were conducted under different combinations of load (33-250 N), nominal stress (0.56-12.73 MPa) and face diameter, as well as two tests where both stress and load were kept constant, while the diameter was changed. For these tests the centre of the pin face was bored out to create four different average pin diameters with similar face areas. Diameter and load were found to have no significant effect on the wear factor, while the wear factor decreased with increasing contact stress according to the relation K = 2 x 10(-6) sigma(-0.84).
Compressive Strength↗