Biomaterials: taming the beast.
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Animals↗
Biomedical subjects
M Spector
Publications and source records attributed to M Spector.
Role of loads and prosthesis material properties on the mechanics of the proximal femur after total hip arthroplasty.
The objective of this study was to establish the role of loads and prosthesis material properties on the mechanics of the proximal femur after total hip arthroplasty. We developed a three-dimensional finite element model of an intact human femur and the same femur with a conventional collared straight-stem femoral component. Using published data, we defined two sets of loading conditions: one that represented three phases of gait, and one that represented four different extreme loads. The four extreme loads were based on the peak joint contact forces that occur during stair ascent and isometric contraction of various muscle groups. The model was analyzed with three different material properties for the prosthesis, including cobalt-chromium alloy, titanium alloy, and a carbon fiber-reinforced polymer (CFRP) laminate. We assumed that the implant was stable, with rigid bonding, collar contact, and no cement. To address femoral component loosening, we examined the shear stresses at the implant-bone interface; to address adaptive bone remodeling, we examined the principal stresses in the supporting cortical bone relative to those in the intact femur. Our analyses of the various loading conditions demonstrated large out-of-plane bending movements and torsional moments, especially for the load representing stair ascent. Based on stepwise multiple regressions, the maximum shear stresses at the implant-bone interface in the distal region were dependent on the total applied axial force and torsion; the maximum shear stresses in the proximal region were dependent on the axial component of the joint contact force alone. Reduction in the prosthesis stiffness, by substitution of the CFRP material properties, resulted in lower interface shear stresses at the distal end of the stem and higher interface shear stresses at the more proximal sections, consistent with the findings of others. We fit equations, based on composite beam theory, to the maximum implant-bone interface shear stresses and the cortical bone principal stresses as a function of the axial modulus of the prosthesis. These equations can be used to estimate the maximum stresses at the interface and in the cortical bone that would be predicted by similar models, for the same prosthesis constructed of alternative materials, relative to the stresses in the intact femur. The nonlinear nature of these relationships was such that the cortical bone stresses changed more rapidly, as a function of the prosthesis modulus, for lower values of elastic modulus, especially in the more proximal sections.
Biomechanical Phenomena↗
Synovium-like tissue from loose joint replacement prosthesis: comparison of human material with a canine model.
The formation of synovium-like tissue is a biological response to a loose joint replacement prosthesis. Histological examination of this tissue has shown a synovial lining with a predominance of fibroblasts and macrophages, some multinucleated giant cells, and dispersed particles from the implant. Previous studies have reported elevated interleukin 1 (IL-1), prostaglandin E2 (PGE2), and collagenase in this tissue. We developed a canine model for the loose cemented femoral stem. Tissue harvested from the canine model was compared with human tissue retrieved at revision arthroplasty. Histology showed synovium, similar to that observed around loose human prostheses, adjacent to the canine cement sheath. Cells were isolated from this tissue and incubated in culture medium with or without naproxen for 3 days. Aliquots of the conditioned media were tested in the thymocyte proliferation assay to determine IL-1-like activity. IL-1 beta levels in human cell-conditioned media were analyzed by enzyme-linked immunosorbent assay, and PGE2 levels were measured by radioimmunoassay (RIA) using a PGE2 RIA kit (New England Nuclear). Human tissue contained levels of IL-1 beta in the range of 150 to 7,040 pg/mL and PGE2 levels of 82 to 952 ng/mL. The canine specimens contained IL-1-like activity and significant amounts of PGE2 (76 to 1,720 ng/mL). Naproxen decreased PGE2 levels in vitro. This animal model provides the means to investigate the in vivo and in vitro activity of the synovial cells around loose total joint prostheses.
Adult↗
Biomaterial failure.
One conclusion that might be drawn from a review of the role of biomaterial failure in total hip arthroplasty is that the fracture, wear, and corrosion of materials often serve as the primary causes of failure of hip replacements. It is not yet possible, however, to conclude the prevalence or time course of these failures. We need to gain more knowledge about the properties of orthopedic biomaterials and the loading to which they are subjected during function. Judicious design and implementation of prostheses can serve to extend the serviceable life of an arthroplasty even with ongoing fracture, wear, and corrosion of biomaterials.
Biocompatible Materials↗
The biologic effects of implant materials.
The interaction between implant materials and the surrounding biological environment continues to be an area of intense research and clinical interest. This article presents the information presented in a symposium, held during the 36th Annual Meeting of the Orthopaedic Research Society, in which several important issues concerning the biologic effects of implant materials were discussed. These issues included the mechanisms by which implant materials are released to the surrounding tissues and the ways in which these tissues respond to implant materials. The problem of bone loss around cementless implants was discussed as a specific example of a biologic effect resulting in both bone remodelling and endosteal erosion.
Biocompatible Materials↗
Advances in implant-bone interface.
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Animals↗
Biochemical and histological evaluation of the synovial-like tissue around failed (loose) total joint replacement prostheses in human subjects and a canine model.
The tissue around loose total joint replacement prostheses displays a synovial-like lining comprised of cells that produce IL-1 and PGE2, mediators of inflammation that stimulate bone resorption. Particles of titanium alloy, as well as cobalt-chromium alloy and polyethylene, were found to aggravate the histiocytic response and production of IL-1 and PGE2. Tissue with similar histological and biochemical features was produced in a canine model of the aseptic loose cemented femoral stem.
Animals↗
Bone loss in the distal anterior femur after total knee arthroplasty.
Bone loss in the distal anterior femur in asymptomatic total knee arthroplasty (TKA) patients has been noted roentgenographically and during revision surgery. A retrospective roentgenographic review of 147 TKA cases was carried out to document bone loss. The influence that the mode of fixation (porous coated and cemented) and the implant design have on bone loss was examined. The time of onset and the progression of bone loss were studied. Bone loss occurred in the distal anterior femur in the majority of cases reviewed (68%). The prevalence of bone loss was independent of the mode of fixation and the implant design. By qualitative observation, roentgenographically detectable bone loss occurred within the first postoperative year and did not progress further. Previously three-dimensional finite element analysis demonstrated that the replacement of the bearing surface of the femur with a stiff metallic implant reduces the stress in the distal anterior femur by at least one order of magnitude. It is therefore speculated that the observed bone loss results from stress shielding. The apparent lack of progression may reflect the development of a new remodeling equilibrium under the altered stress conditions. The bone loss in the distal anterior femur described has not been implicated as a source of failure. However, since the bone strength in the femoral region is compromised as it becomes osteopenic, bone failure may occur with longer periods of cyclic loading. Furthermore, as a result of bone loss, revision arthroplasty may be more difficult.
Aged↗
Tissue changes around loose prostheses. A canine model to investigate the effects of an antiinflammatory agent.
The aseptically loosened prosthesis provided a means for investigating the in vivo and in vitro activity of the cells associated with the loosening process in seven dogs. The cells were isolated and maintained in culture for sufficient periods of time so that their biologic activity could be studied as well as the effect of different agents added to the cells in vivo or in vitro. The biologic response as determined by interleukin-1 and prostaglandin E2 activity paralleled the roentgenographic appearance of loosening and the technetium images and observations made at the time of revision surgery. The correlation between clinical, roentgenographic, histologic, and biochemical loosening indicates that the canine model is suitable for investigating the mechanisms of prosthetic failure. A canine model permits the study of possible nonsurgical therapeutic interventions with the ultimate hope of stopping or slowing the loosening process.
Animals↗
Hematocrit changes after uncomplicated percutaneous transluminal coronary angioplasty.
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Angioplasty, Balloon, Coronary↗
Disrupted coronary artery caused by angioplasty: supportive and surgical considerations.
Of 2,859 patients having percutaneous transluminal coronary angioplasty, 201 (7%) underwent emergency coronary artery bypass grafting. Two categories of patients were reviewed. Group 1 consisted of 126 patients of 2,304 who had immediate coronary artery bypass grafting after failed elective percutaneous transluminal coronary angioplasty. Ninety-eight of these patients had angiographic evidence of occlusion of a coronary artery, and 28 had angiographic evidence of coronary artery dissection. Epicardial hemorrhage was observed at operation in 20% (25 patients). Three deaths (2.4%) occurred in group 1, and an average of 3.3 grafts was performed per patient. Group 2 comprised 75 of 555 patients who had unsuccessful attempted percutaneous transluminal coronary angioplasty during an evolving myocardial infarction and required immediate coronary artery bypass grafting. Angiography revealed coronary artery occlusion in 61 patients with dissection in 14. All group 2 patients had evidence of myocardial injury by electrocardiographic and enzymatic (myocardial-specific isoenzyme of creatine kinase) criteria. Three deaths (4%) occurred in this group, and there was an average of 3.4 grafts per patient. Percutaneous transluminal coronary angioplasty is routinely performed without surgical consultation, although an operating room and team are usually available. Supportive techniques include the intraaortic balloon pump and percutaneous cardiopulmonary bypass. In those patients with coronary artery dissection, care must be taken to reestablish the true lumen of the coronary artery. Hemopericardium should be surgically explored and broken guidewires or other foreign bodies or debris removed. From 1979 through 1986, the number of patients requiring emergency coronary artery bypass grafting after percutaneous transluminal coronary angioplasty steadily declined to less than 5%.
Angioplasty, Balloon↗
Use of a double-lumen pressure monitoring catheter to facilitate pulmonary artery banding.
Pulmonary artery banding is facilitated by simultaneously measuring the pressure above and below the band. This can be accomplished with a commercially available double-lumen central venous pressure monitoring catheter. This catheter is inserted through the outflow tract of the right ventricle and positioned so that the band will be between the two lumens. Gradual tightening of the band can be accomplished while monitoring the pressures proximal and distal to the band.
Catheterization, Central Venous↗
Effect of knee component alignment on tibial load distribution with clinical correlation.
To determine ideal alignment and component placement of total knee prostheses, Kinematic (K) and total condylar (TC) devices were physiologically loaded and interface forces were measured. Laboratory observations were correlated with clinical (roentgenographic) findings. Asymmetric loading of the tibial component has been proposed as causing loosening and radiolucent lines. Misalignment of components is one factor that affects load sharing by bone under the medial and lateral regions of the tibial plateau. Tibial components of K and TC prostheses were inserted without cement into the cut surfaces of artificial tibiae. The mating femoral condylar components were mounted. The tibial and femoral components were individually positioned at 0 degrees (horizontal) and at certain angles of varus and valgus. Pressure-sensitive film was placed between the tibial component and the artificial tibia. A vertical load of 1500 N was used. The experiment was replicated twice. The percentages of the load on the medial and lateral regions of the tibial plateau were calculated from quantitative image analysis of the pressure patterns on the film. Roentgenograms from 532 K and 21 TC patients were examined to determine the orientations of the condylar and tibial components and the presence of radiolucent lines around the tibial component. An even distribution (ideal alignment) of load on the medial and lateral regions of the K tibial component occurred at 9 degrees of valgus tilt of the femoral component and 2 degrees of varus tilt of the tibial component and for the TC at 7 degrees valgus and 0 degrees varus. Misalignment by 5 degrees yielded a 7% change in the load distribution under the K plateau and a 40% change for the TC prosthesis; a 10 degrees misalignment produced changes of 34% and 62% for the K and TC, respectively. Small variations in clinical knee alignment produced the same percentage of radiolucent lines for each alignment group. The location of radiolucent lines was distributed among the medial, lateral, and both tibial plateaus regardless of knee alignment, although there were more medial reactions overall. The smallest incidence (8%) of radiolucent lines occurred with the K prosthesis at 7 degrees of knee valgus, the femoral component placed at 9 degrees valgus, and the tibial component at 2 degrees varus. This correlated with the ideal bench-test findings for the K device.
Humans↗
Internal mammary artery versus saphenous vein graft to the left anterior descending coronary artery: prospective randomized study with 10-year follow-up.
In 1975, 80 patients undergoing revascularization were prospectively randomized to receive either a greater saphenous vein (SV) graft (41 patients, Group 1) or a left internal mammary artery (LIMA) graft (39 patients, Group 2) to the left anterior descending coronary artery (LAD). All patients were completely revascularized. The average number of grafts per patient in both groups was 3.2. Patients were followed 10 years; follow-up was 97.5% complete. Group 1 and Group 2 were compared in regard to mortality, treadmill response, myocardial infarction, reoperation, percutaneous transluminal coronary angioplasty, and return to work. Mortality in Group 1 was 17.9% versus 7.7% in Group 2 (p less than 0.05). Treadmill studies were positive in 17 Group 1 patients and 7 Group 2 patients (p less than 0.05). Myocardial infarctions occurred in 8 patients in Group 1 versus 3 in Group 2. The number of reoperations was 2 in Group 1 versus 1 in Group 2. Percutaneous transluminal coronary angioplasty was performed in 3 patients in Group 1 and 2 in Group 2. Repeat studies revealed 76.3% patency of the SV graft to the LAD (Group 1) and 94.6% patency of the LIMA graft to the LAD (Group 2). Cardiac-related mortality in Group 1 was 12.8% at 10 years (5 patients) versus 7.7% in Group 2 (3 patients). Based on this study, the IMA is a superior conduit for bypass to the LAD.
Adult↗
Porous polymers for biological fixation.
Porous polymers are recommended as coatings for femoral stems on the basis of their low modulus, which allows uniform distribution of stress to surrounding bone and the fabrication of more flexible stems by reducing the metallic cross section. Application of the porous polymer coating to the metallic substrate reduces metal ion release; the polymer coating does not affect the mechanical properties of the device. Porous polytetrafluoroethylene-carbon fiber composite, (PCFC), porous polyethylene, and porous polysulfone are undergoing investigation for this application. However, the low strength of the PCFC makes its use for this application questionable. Recently reported unfavorable clinical results (i.e., a high incidence of pain) have led to the discontinuation of one trial of porous polyethylene. Clinical investigation of porous polysulfone-coated titanium alloy devices are in progress. Animal studies have shown bone ingrowth into porous polyethylene and porous polysulfone implants in cortical and cancellous bone and in canine femoral stems coated with these materials. Pull-out testing of porous polysulfone implants revealed that the strength of the porous material was higher than the strength of surrounding bone. Less cortical bone loss was found around porous polysulfone-coated canine stems than was reported for fully coated porous metallic prostheses, presumably because of the lower stiffness.
Animals↗
Strategies for improving fixation of femoral components in total hip arthroplasty.
As strategies are considered for improving fixation of femoral components in total hip arthroplasty (THA), one is challenged to exceed the standard set by contemporary cement procedures. However, despite the improved ten- to 15-year clinical results anticipated with current cementing techniques, the limited fatigue strength of polymethylmethacrylate warrants continued investigation of alternative systems, particularly for younger patients and in revision arthroplasty. Design considerations for femoral stems for cementless THA include (1) initial mechanical stability afforded by the stem shape, (2) strength and stiffness of the stem, and (3) surface features relating to biocompatibility and attachment to bone. In one approach a fit-and-fill algorithm has been implemented to design stems that maximize contact between prosthesis and cortex in priority areas to achieve stability. Titanium is recommended for the fabrication of such stems because of its corrosion resistance, its biocompatibility, and its modulus, which is lower than that of cobalt-chromium alloy. Long-term fixation of these implants will be dependent upon the maintenance of normal strain patterns in the host bone. Achievement of this goal will require additional strategies that combine optimal fit and optimal material properties of the prosthesis.
Biocompatible Materials↗
Porous-coated femoral components in a canine model for revision arthroplasty.
UNLABELLED: Six dogs had a total hip arthroplasty during which the femoral component was coated with methacrylate and inserted in the femoral canal, after the canal had been reamed to a larger diameter than that of the femoral stem (including the coating). Thus, the implant was loose and motion was present between it and the femur in each animal. Five dogs had a revision to a prosthesis with a porous polysulfone-coated stem. This prosthesis was not cemented in place. One dog was killed before the revision for the purpose of histological examination. Although bone was present in the porous surface of all five stems at the revision, the amount was scant in three. CLINICAL RELEVANCE: A model is described for the study of cemented hip-replacement prostheses that have failed. Although variable amounts of ingrowth of bone were observed after the revision to the porous-coated prostheses without bone cement, further study is needed to determine whether adequate ingrowth of bone occurs in this model.
Animals↗
Historical review of porous-coated implants.
The implementation of cementless joint replacement prostheses is proving to be a significant advance in orthopedic surgery. The porous-coated implant, stabilized by the biologic fixation resulting from bone ingrowth, is one of several types of cementless devices. A historical review of porous materials reveals that the concepts underlying biologic fixation date back decades. It was the initial concerns about the long-term performance of bone cement that, in the early 1970s, stimulated several groups more actively to pursue the development of porous systems. As a result of their efforts, there are currently many different porous coatings and prosthetic designs undergoing clinical investigation, with generally encouraging results. However, it is becoming clear that the importance of porous-coated prosthetic devices is not that they will serve to replace cemented prostheses entirely, but rather that they offer viable alternatives for the treatment of certain populations of patients. An understanding of the evolution of porous-coated implants can help to identify gaps in our knowledge and areas that require additional study, to direct future design modifications of implants, and to foster effective implementation of the prostheses.
Alloys↗