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Biomedical subjects

M Jasty

Publications and source records attributed to M Jasty.

At least 37 records · Page 2Linked to original sources
PubMed1996

Differences in stiffness of the interface between a cementless porous implant and cancellous bone in vivo in dogs due to varying amounts of implant motion.

To determine the mechanical properties of the interface between the tissue ingrowth into porous coatings and the implant, porous-coated cylindrical implants were inserted into the distal femur in 20 mature dogs and oscillated in vivo 8 hours per day for 6 weeks at fixed amounts of micromotion (0, 20, 40 and 150 microns). Applied torques and resulting displacements were recorded. The torsional resistance per unit angular displacement (TR/AD), reflecting the stiffness of the bone-porous coating interface, was 0.88 +/- 0.25 N-M/deg immediately after implantation in the 20-micron displacement group. It increased with time after surgery, reaching a maximum of 1.25 +/- 0.60 N-M/deg at 6 weeks. The TR/AD was lower initially (0.77 +/- 0.43 N-M/deg) in the 40-micron group and gradually decreased with time after surgery, reaching a maximum of 0.54 +/- 0.13 N-M/deg at 6 weeks. The TR/AD was even lower (0.24 +/- 0.10 N-M/deg) in the 150-micron group initially and remained the same (0.16 +/- 0.09 N-M/deg) with time after surgery. Histologic evaluation showed bone ingrowth in continuity with the surrounding bone in the 20-micron group consistent with the high stiffness values at sacrifice. In contrast, a mixture of fibrocallus and bone were found at the bone-porous coating interface in the 40-micron group, consistent with the intermediate stiffness values. In contrast, despite the fact that bone was found in the depth of the porous coating in the dogs in the 150-micron group, the low stiffness values were a reflection of fibrous tissue formation at the interface in that group, because of the large motion disrupting bony ingrowth at the bone-porous coating interface. By monitoring the torsional resistance per unit of angular displacement dynamically in vivo, it was possible to evaluate the mechanical properties of the bone-porous coating interface as tissue ingrowth proceeded. Twenty microns of oscillating displacement was compatible with stable bone ingrowth with high interface stiffness, whereas 40 and 150 microns of motion was not.

Animals↗
PubMed1996

Loci of movement of selected points on the femoral head during normal gait. Three-dimensional computer simulation.

Wear of ultrahigh-molecular-weight polyethylene and the subsequent lytic response to the particulate wear debris are the dominant problems in total joint arthroplasty surgery. Wear testing apparatus can play a vital role in the in vitro evaluation of the many factors involved in wear, such as head size, surface roughness, materials for the head, and new materials for the socket. Wear of ultrahigh-molecular-weight polyethylene may be influenced by the wear path. For the related polymer, high-density polyethylene, the wear path is critical to wear magnitude. What is the actual path taken by a single point (or by multiple representative points) on the femoral head of a total hip arthroplasty as it passes through the gait cycle? The goal of this computer simulation study was to trace the paths of specific points on the femoral head as they moved against the polyethylene cup during a single cycle of normal gait to illustrate the motions occurring at the intraarticular surface of the hip joint. This study also yielded unusual data on the "distance traversed" by these points during a single gait cycle. It was found that there was not one path, but rather there were many, and the paths varied widely in both shape and length depending on the location on the femoral head. Moreover, the differences in excursion and direction at different sites during the loaded phase were great. In addition, distances traveled by different points on the femoral head of any given size varied by a factor greater than 2. Most of the points traced quasielliptical paths. This automatically means that the paths of neighboring points cross each other, creating multidirectional shear forces on the acetabular cup surface which may be important in the localization and extent of wear. The plots of traces of the points derived from this study can serve as benchmarks for the ability of hip simulators to reproduce the actual distances and paths of travel of individual points on the femoral head.

Computer Simulation↗
PubMed1996

The importance of multidirectional motion on the wear of polyethylene.

The development of a new hip simulator for the study of bearing materials used in total hip replacements has led to several findings which add important new information to the understanding of wear process of ultra-high molecular weight polyethylene, the most commonly used bearing material today for total joint replacements. Using this hip simulator which is capable of applying the physiological motion pathways occurring during gait to total hip components which are held in the correct anatomical position under the complex loading conditions of the hip in gait, the authors have shown that physiological motion pathways produce very different wear rates and morphology of the wear surface than unidirectional reciprocating pathways. Scanning electron microscopy studies show striking differences in the morphology of the wear surfaces of the polyethylene depending upon the relative motions of the components. Wear rates, surface morphology and particle debris generation consistent with clinical and retrieved studies are achieved when physiological conditions are simulated.

Hip Joint↗
PubMed1996

The Otto Aufranc Award. Skeletal response to well fixed femoral components inserted with and without cement.

Previous studies evaluating femoral remodeling after total hip arthroplasty have used clinical radiographs and dual energy xray absorptiometry. Limitation of these techniques make it impossible to quantify the magnitude of bone loss in terms of cortical thinning and cortical bone area and bone mineral density changes. Femoral cortical bone remodeling after cemented and cementless replacement was quantified and possible determinants of bone remodeling in terms of clinical and radiographic variables were evaluated. Forty-eight anatomic specimen femora from 24 patients with unilateral cemented and cementless hip replacements were analyzed. Cortical thickness, cortical bone area, and bone mineral density was assessed in 4 quadrants at 5 discrete levels. The maximum cortical bone loss by level was at the middle section for the cemented femurs and at the midproximal and middle sections for the cementless femurs. However, if one examines individual quadrants, the proximal medial cortex still represents the specific region of maximal bone loss for both types of implant fixation. The posterior cortex had substantially more bone loss, even in the diaphyseal levels, than had been previously appreciated. A strong correlation was noted between the bone mineral density of the control femur and the percentage decrease of bone mineral density in the remodeled femur. Based on this data, it seems that the less dense the bone is before hip replacement surgery, the greater the extent of bone loss after total hip arthroplasty regardless of the fixation type.

Adult↗
PubMed1996

Management of limb length inequality during total hip replacement.

Significant limb length inequality is not an uncommon problem after total hip replacement. Preoperative measurement of limb length inequality, preoperative planning with radiographic templates, and intraoperative correction with measurements of limb lengths before and after the insertion of the trial components using special calipers can reduce the incidence and magnitude of this problem. A review of 85 consecutive patients who had primary total hip arthroplasty in which these techniques were used by a single surgeon, showed that 43 had limb inequality preoperatively ranging from 0.5 to 7.25 cm, but only 14 (16%) had limb length inequality after surgery. Eleven limbs (13%) had been lengthened 0.5 to 1 cm compared with the contralateral limb. Of the 42 patients with equal limb lengths preoperatively, 3 had a lengthened limb postoperatively compared with their contralateral limb. Four patients were using lifts on the same side because the limb was too short, and 2 were using lifts on the other side because the limb was too long. None of the other patients complained about limb length inequality. The techniques described above are helpful in minimizing limb length inequality during total hip replacements.

Hip Prosthesis↗
PubMed1995

Influence of intraoperative femoral fractures and cerclage wiring on bone ingrowth into canine porous-coated femoral components.

Intraoperative femoral fractures occur more frequently with cementless than with cemented components. In this study, the influence of controlled femoral fractures fixed with cerclage wires on rotational stability and bone ingrowth into porous-coated canine femoral components was evaluated. These data were compared with results of previous studies on unrecognized femoral fractures (not stabilized) and on the intact canine femur. Micromotion analysis revealed a significant increase in rotational instability in fractures not stabilized with cerclage wires (P < .05) compared with the intact femur. Experimentally created femoral fractures had a significantly deleterious effect on bone ingrowth even after cerclage wiring. This appears to be caused by a lack of bone ingrowth deep to the fracture and an increase in femoral component micromotion. In clinical practice, femoral fractures occurring during cementless total hip arthroplasty are a serious problem, and use of a cemented prosthesis is recommended if rotational stability of the stem cannot be ensured.

Animals↗
PubMed1995

Tissue response to particulate polymethylmethacrylate in mice with various immune deficiencies.

We examined the tissue response to subcutaneous injections of particulate polymethylmethacrylate powder in fully immunocompetent C3Hf/Sed mice as well as three strains of mice with different levels of lymphocyte dysfunction. Five weeks after the injection, we found clearly demarcated granulomas. Histological and immunohistochemical studies showed that these granulomas were similar among all strains, with either paucity or absence of lymphoid cells. In situ hybridization with use of complementary RNA probes indicated that macrophages were synthesizing interleukin-1 beta messenger RNA (mRNA), a marker of macrophage activation, and a cytokine implicated in pathological bone resorption. We concluded that, in mice, there is a lymphocyte-independent pathway of macrophage activation in response to particulate polymethylmethacrylate. This suggests that the foreign-body response to particulate orthopaedic biomaterials is macrophage-initiated and maintained and that lymphocytes are not essential to this response, although they may modulate it.

Analysis of Variance↗
PubMed1995

The use of a high-hip center in revision total hip arthroplasty.

In certain cases, primary and revision total hip arthroplasty is complicated by insufficient bone stock and distorted acetabular anatomy such that the craniocaudal dimension of the acetabular recess is greater than the anteroposterior dimension. Acetabular reconstruction in such cases can be carried out by placing the acetabular component more proximally than normal (high-hip center). Recent biomechanical and clinical data suggest that placement of the acetabular component at a higher than normal hip center does not adversely effect the longevity of the component fixation. Proximal placement of the hip center also facilitates the contact between the host bone and the porous coating when uncemented porous coated components are used, and minimizes the need for structural bone grafts. However, femoral components with longer neck lengths and removal of impinging bone are needed when the acetabular components are placed more proximally in order to restore the limb lengths and minimize the chances for dislocation.

Acetabulum↗
PubMed1995

Local and distant products from modularity.

In this study, the local and distant distribution of solid and soluble products of corrosion from the head and neck junction of modular femoral total hip prosthetic components were characterized. Particulate corrosion products from retrieved implants and surrounding tissues were analyzed. Serum transport and urinary excretion of metal was measured in correlation with the degree of corrosion at the head and neck junction. Particles of metal oxides, metal chlorides, and chromium phosphate corrosion products were identified on implants of 10 designs from 6 manufacturers. The most abundant solid corrosion product on the implant and within the periprosthetic tissues (size range, < 1-200 micrometers) was an amorphous chromium orthophosphate hydrate-rich material. Serum cobalt and urine chromium concentrations were elevated significantly in patients with implants that had moderate to severe corrosion in comparison with those with no to mild corrosion. Solid corrosion products from modular femoral stems may accelerate articular wear via a 3-body mechanism. Phagocytosable particles of these corrosion products may stimulate macrophage-mediated periprosthetic bone loss. Systemic dissemination of metallic corrosion products raises the issue of systemic toxicity; however, no overt evidence of metal toxicity was observed in this study.

Adult↗
PubMed1995

Total hip replacement for developmental dysplasia of the hip.

Total hip arthroplasty relieves pain and improves function for many patients with endstage arthritis secondary to developmental dysplasia of the hip. Acetabular dysplasia, however, presents a special problem for total hip reconstruction in these patients. Structural bone grafting with femoral head autografting to the dysplastic acetabulum and cementing acetabular components into the graft provides satisfactory short-term results, but longer-term followup data show high acetabular component failure rates. At a mean followup period of 7 years, 20% of components were loose, and at a mean followup period of 12 years, 46% were loose. Noncemented porous-coated hemispherical acetabular components have considerably expanded the success of total hip replacement without the need for structural bone grafting in such patients. At a mean followup period of almost 7 years, none of the acetabular components were reported to be loose in 1 series. For most patients, the acetabular dysplasia can be managed by techniques such as reaming deeper, using small-diameter porous-coated acetabular components, using screws to provide rigid initial stability for the components, increasing the height of the prosthetic hip center, and covering small portions of the components with bone graft chips if necessary.

Hip Dislocation↗
PubMed1994

Polyethylene wear debris and tissue reactions in knee as compared to hip replacement prostheses.

Differences in bearing surface conformity and wear mechanisms suggest that the polyethylene (PE) wear debris generated by total knee replacement (TKR) prostheses should be different than that in total hip replacement prostheses (THR). To address this issue, PE wear debris and the cellular response in periprosthetic tissues from 19 failed TKRs was compared to that from 24 failed THRs using polarized light microscopy and a semiquantitative grading system. The foreign-body inflammatory reaction in the THR case was characterized by plump macrophages with a diffuse cytoplasmic birefringence when examined under polarized light, indicating the presence of multiple submicron particles of PE. The majority of PE particles were less than 1 mum in size and only a small fraction of the total were greater than 10 mum. The foreign-body inflammatory reaction in the TKR cases was characterized by giant cells with fewer macrophages. In the TKR specimens, the size range of PE particles was broader than in the hips. PE particles between 2 and 20 mum were frequent in TKR specimens; particles less than 1 mum in length were less common than in the THR specimens. Diffuse cytoplasmic birefringence was not a characteristic of the TKR cases. These histologic differences were so consistently distinct that the source of the specimen (i.e., from a THR or TKR) could be blindly determined by light microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)

Foreign-Body Reaction↗
PubMed1994

Fit of the uncemented femoral component and the use of cement influence the strain transfer the femoral cortex.

To determine whether the strain patterns produced in the femoral cortex after uncemented femoral arthroplasty are influenced by the fit of the component and whether these patterns are different from those of cemented components, cortical surface strains of cadaveric femurs subjected to loads simulating single-limb stance were measured before and after the insertion of uncemented, collared, straight-stemmed femoral components. The effects of press fit, loose fit, and precise fit of the components were evaluated and were contrasted to the strain patterns occurring after insertion of cemented femoral components. Strains varied markedly, depending on the fit of the stem of the uncemented femoral component within the isthmus. Nearly normal patterns of femoral strain were produced when the femoral stem was fit precisely at the isthmus, and the proximal femoral strains were similar to those of the intact state. In contrast, press fit and loose fit at the isthmus altered the strain patterns. The proximal medial axial strains were significantly reduced with press fit, to a mean of 39% of normal (p < 0.05), and increased with loose fit, to a mean of 141% of normal (p < 0.05). The prostheses fixed with cement showed a mean reduction in proximal medial axial strains to 33% of normal, which was comparable with press fit uncemented components even though the collar was well seated. Thus, our findings indicated that, in the immediate postoperative period, femoral strain patterns can be influenced by the fit of an uncemented component within the isthmus and by the use of cement.

Aged↗
PubMed1994

Etiology of osteolysis around porous-coated cementless total hip arthroplasties.

The prosthetic components and tissues retrieved from 12 hips with osteolysis in association with well-fixed cementless porous-coated total hip prostheses (5 Porous Coated Anatomic, 6 Harris-Galante Porous, and 1 Omniflex) were examined using a variety specific techniques including electron microscopy, standard histology, immunohistochemistry, and particle identification. The patients were young and active. Extensive osteolysis developed in all 12 femurs and 3 acetabula between 36 and 84 months after arthroplasty (mean, 63 months). All of the polyethylene liners were noted to be worn substantially (mean volumetric wear, 1140 +/- 810 mm3). The wear was unrelated to the head diameter in this small number of cases. In all 12 cases, the articulating surfaces were wear polished and contained numerous fine multidirectional scratches, suggesting 3-body abrasive wear mechanisms in addition to adhesive wear liberating very small (micron to submicron) wear particles. In 4 cases, surface delamination and flaking of polyethylene were also found, suggesting fatigue wear liberating larger wear particles. Nine of 10 cobalt alloy heads showed numerous fine scratches with sharp edges presumably from 3-body abrasive wear. Corrosion and fretting at the femoral head-neck junction in 5 cases, burnishing of the femoral stem against bone in 4 cases, and metal staining of tissues opposite the porous coatings in 7 cases provided evidence for the liberation of fine metal particles from outside the articulation. Histologic and immunohistochemical studies of tissue in the regions of osteolysis in all cases showed numerous focal aggregates of KP1 antibody positive activated macrophages containing large amounts of submicron intracellular particles of polyethylene (presumably related to the 3-body abrasive wear polishing) and giant cells within a fibrous stroma. In 5 cases, some of the macrophages also contained submicron metal particles but smaller in numbers. T lymphocytes, plasma cells, and mast cells that might indicate hypersensitivity were found in 4 of the 12 cases (33%), and none of the cases had B lymphocytes. These data suggest that abrasive wear at the articulation leads to the liberation of abundant fine particulate wear debris of polyethylene into the tissues around cementless prostheses. Small amounts of particulate metal debris are also liberated from corrosion and fretting of the metal components and can contribute to accelerated 3-body abrasive wear at the articulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1994

Osteolysis around uncemented acetabular components of cobalt-chrome surface replacement hip arthroplasty.

Ten cases of major osteolysis were identified in patients with hemispherical cobalt chrome acetabular components of cementless resurfacing total hip prostheses at follow-up examinations ranging from two to five years. All components were porous coated with cobalt chrome spheres and were stabilized initially with screws. Five patients were women and five were men, with ages ranging from 20 to 59 years. The radiolucent cystic lesions with peripheral rims of reactive bone formation appeared one to five years after the operation. They measured from 1.5 to 6 cm in the largest diameter and were most often found adjacent to the screws used to secure the acetabular components to the skeleton. On the radiographs, none of the components appeared to be loose. Three patients had revision surgery. In two of the three cases, the implants were found to be firmly fixed. There was no clinical or bacteriologic evidence of infection. The polyethylene articulating surface showed signs of wear in all three cases and in one of the three it dislocated from the metal shell. Granulation tissue was found in the regions of osteolysis, and the diseased tissue contained numerous macrophages and giant cells. Lymphocytes and plasma cells were rare. Numerous small particles of phagocytosed polyethylene and metal in the cells were noted in two cases, whereas only polyethylene was found in the third.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetabulum↗
PubMed1994

Surface damage to cobalt-chrome femoral head prostheses.

Fifty-four cobalt-chrome alloy femoral heads were retrieved at revision surgery or at post-mortem; 23 came from uncemented, eight from hybrid and 23 from cemented hip arthroplasties. The uncemented and hybrid implants had porous coating, metal backing and modular femoral heads; with one exception none of the cemented implants had any of these. Twenty-five of the 31 heads from uncemented and hybrid arthroplasties, and 11 of the 23 heads from cemented arthroplasties showed surface damage involving more than 25% of the surface. Scanning electron microscopy revealed multidirectional fine scratches 1 micron to 10 microns in depth and width which appeared to have been made by fine, hard particles. There was a higher rate of such damage in the uncemented and hybrid arthroplasties than in the cemented implants, suggesting that the abrasive particles were mainly released from the metal, rather than from the cement or polyethylene components of the implants.

Adult↗
PubMed1993

Histologic identification of polyethylene wear debris using Oil Red O stain.

Ultra high molecular weight polyethylene (UHMWPE) wear particles are frequently implicated in causing failure of total joint arthroplasties by eliciting a foreign body reaction. The majority of these particles are subcellular and many are submicron in size. Identification of these small particles of UHMWPE by conventional histologic techniques is difficult. We have therefore investigated the utility of Oil Red O (ORO) stain to identify UHMWPE on histologic sections. A wide variety of specimens was studied including an experimental rabbit model with subcutaneous implantation of polyethylene particles as well as specimens from clinical cases with joint arthroplasties. The sensitivity and specificity of ORO stain was compared to conventional polarized light microscopy for the identification of particulate UHMWPE debris. The ORO stain was found to be as sensitive in identifying particulate UHMWPE debris as polarized light microscopy. However, ORO stain was less specific: two specimens did not contain any UHMWPE also stained with ORO. Careful examination of standard hematoxylin and eosin stained sections with polarized light was therefore more specific for the identification of particulate UHMWPE. As a single test, the ORO stain does not appear to offer any clear advantage specifically for the identification of UHMWPE.

Animals↗