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Biomedical subjects

M Tanzer

Publications and source records attributed to M Tanzer.

At least 37 records · Page 2Linked to original sources
PubMed1999

Tissue response to porous tantalum acetabular cups: a canine model.

This study evaluated the osseous tissue response to a noncemented metal-backed acetabular component made of a new porous tantalum biomaterial. Eleven dogs with bilateral total hip arthroplasties (22 acetabular implants) were studied for a period of 6 months. Thin section histology, high-resolution radiography, and backscattered scanning electron microscopy revealed that all 22 implants had stable bone-implant interfaces. Regions of bone ingrowth were present in all histologic sections. The depth of bone ingrowth varied from 0.2 mm to the maximal limit of 2 mm. Analyzing contiguous regions of interest across the full bone-implant interface, the mean bone ingrowth for all sections was 16.8% +/- 5.7%. In the peripheral regions of the cup where bone-implant contact was most consistent, bone ingrowth averaged 25.1% +/- 10.1%. The data indicate that the porous tantalum material is effective for biologic fixation in the dog and may provide a suitable alternative to other porous materials used in acetabular cup design.

Acetabulum↗
PubMed1999

The osseous response to corundum blasted implant surfaces in a canine hip model.

The purpose of this study was to examine the radiographic and histologic response to corundum blasted implant surfaces of varying roughness in a canine total hip arthroplasty model. Three types of tapered femoral implants were made from titanium alloy and were identical in every respect except surface finish. The entire surface of the femoral implant had a 2.9-, 4.2-, or 6.7-micron average surface roughness (Ra) from blasting with 60-, 24-, or 16-grit corundum particles, respectively. Twenty-two stems in 11 dogs were evaluated at 6 months. Twenty-one of the stems showed osseointegration, whereas in one stem a fibrous interface developed. Abundant new periimplant bone formation occurred, particularly within the intramedullary canal where trabeculae spanned implant to endosteal cortex gaps as large as 5 mm. Bone apposition with the 60-, 24-, and 16-grit stems averaged 31.7%, 32%, and 27.9%, respectively; the differences were not statistically significant. However, the pattern of new bone formation was different in that the average length of each region of bone apposition for the 60- and 24-grit surfaces was 50% greater than that for the coarser 16-grit surface. The observations of this study indicate that because of their highly osteoconductive nature, corundum blasted surfaces represent an important and valuable technology for the design of noncemented implants.

Aluminum Oxide↗
PubMed1999

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↗
PubMed1999

In vitro measurement of the tracking pattern of the human patella.

This study sought to determine whether a general pattern describing the three-dimensional tracking characteristics of the human patella could be established, and if not, then to determine the extent and nature of interspecimen variations in the characteristics in a normal population. Using 32 fresh-frozen knees subjected to extensor moment magnitudes similar to those in "static-lifting" and "leg-raising against resistance" maneuvers, patellar displacements were measured in the knee extension range 120 to 0 deg. For static-lifting, a constant foot-floor reaction of 334 N was applied. For leg-raising, a constant net quadriceps tension of 668 N was used throughout the extension range. Measurements were taken with a calibrated six-degree-of-freedom electromechanical goniometer and a displacement coordinate system referenced to the geometry of individual specimens. The three patellar displacements in the plane of knee extension/flexion (extension rotation, and anterior and proximal translations) consistently demonstrated the same pattern in the entire knee extension range with an average coefficient of variation of 13 percent. For knee angles greater than 45 deg, the three other displacements (medial-lateral translation, and rotations about the anterior--posterior and proximal--distal axes) followed a general pattern. However, for knee angles less than 45 deg, these displacements differed considerably between specimens for each loading condition, both in terms of magnitude (average coefficient of variation: 70 percent), and direction.

Adult↗
PubMed1999

Characteristics of bone ingrowth and interface mechanics of a new porous tantalum biomaterial.

We have studied the characteristics of bone ingrowth of a new porous tantalum biomaterial in a simple transcortical canine model using cylindrical implants 5 x 10 mm in size. The material was 75% to 80% porous by volume and had a repeating arrangement of slender interconnecting struts which formed a regular array of dodecahedron-shaped pores. We performed histological studies on two types of material, one with a smaller pore size averaging 430 microm at 4, 16 and 52 weeks and the other with a larger pore size averaging 650 microm at 2, 3, 4, 16 and 52 weeks. Mechanical push-out tests at 4 and 16 weeks were used to assess the shear strength of the bone-implant interface on implants of the smaller pore size. The extent of filling of the pores of the tantalum material with new bone increased from 13% at two weeks to between 42% and 53% at four weeks. By 16 and 52 weeks the average extent of bone ingrowth ranged from 63% to 80%. The tissue response to the small and large pore sizes was similar, with regions of contact between bone and implant increasing with time and with evidence of Haversian remodelling within the pores at later periods. Mechanical tests at four weeks indicated a minimum shear fixation strength of 18.5 MPa, substantially higher than has been obtained with other porous materials with less volumetric porosity. This porous tantalum biomaterial has desirable characteristics for bone ingrowth; further studies are warranted to ascertain its potential for clinical reconstructive orthopaedics.

Animals↗
PubMed1999

Effect of flexibility of the femoral stem on bone-remodeling and fixation of the stem in a canine total hip arthroplasty model without cement.

The purpose of this study was to compare, with regard to fixation of the implant and femoral bone resorption, two fully porous-coated stems of different stiffnesses in a canine total hip arthroplasty model. A bilateral arthroplasty was carried out with insertion of a titanium-alloy stem (which had stiffness properties comparable with those of the canine femur) on one side and with insertion of a composite stem (which was three to fivefold more flexible than the canine femur) on the contralateral side. Eight femora were evaluated at six months and eight, at eighteen months after the operation, to determine the extent of bone ingrowth, periprosthetic cortical area, intracortical porosity, and bone-remodeling. Despite the markedly greater flexibility of the composite stems, no significant difference could be detected (with the numbers available), with regard to the overall degree of femoral stress-shielding, cortical area, or cortical porosity, between these stems and the stiffer, titanium-alloy stems at either time-period. However, the composite stems had less bone ingrowth and more formation of radiopaque lines than did the titanium-alloy stems. At eighteen months, the values for bone ingrowth were 9.7 +/- 5.38 percent (mean and standard deviation) for the composite stems compared with 28.1 +/- 5.31 percent for the titanium-alloy stems (p = 0.003). Furthermore, the histological sections from the femora containing a composite stem showed radiopaque lines indicative of fibrous ingrowth approximately threefold more often than did those from the femora containing a titanium-alloy stem (p = 0.02).

Alloys↗
PubMed1998

Evidence for altered synthesis of type II collagen in patients with osteoarthritis.

There is evidence to suggest that the synthesis of type II collagen is increased in osteoarthritis (OA). Using an immunoassay, we show that the content of the C-propeptide of type II procollagen (CPII), released extracellularly from the newly synthesized molecule, is directly related to the synthesis of this molecule in healthy and osteoarthritic articular cartilages. In OA cartilage, CPII content is often markedly elevated (mean 7.6-fold), particularly in the mid and deep zones, reaching 29.6% of the content in newborn. Synthesis is also directly related to total collagen II content in OA, suggesting its importance in maintaining collagen content and cartilage structure. The release of CPII from cartilage is correlated directly with cartilage content. However, the increase in CPII in OA cartilage is not reflected in serum, where a significant reduction is observed. Together these studies provide evidence for alterations in procollagen II synthesis in vivo in patients with OA.

Adult↗
PubMed1998

Role and results of the high hip center.

Anatomic placement of the acetabular component should be the surgeon's goal at the time of revision THA. However, Acetabular loosening with subsequent implant migration, progressive superior acetabular bone destruction or severe pelvic osteolysis, may prevent the surgeon from obtaining adequate host bone-implant contact needed for a successful reconstruction while maintaining a normal hip center. The high hip center offers a technique for reconstruction of an acetabulum with severe bony deficiency and where the majority of the remaining host bone is superior to the anatomic hip centre.

Acetabulum↗
PubMed1998

Femoral cement grading in total hip arthroplasty.

The current gold standard for primary total hip arthroplasty is a cemented femoral component combined with a porous-coated acetabular component. Barrack and colleagues described a femoral cement mantle grading system which is increasingly being used to evaluate surgical technique and to compare arthroplasty results. The immediate postoperative radiographs of 100 primary total hip arthroplasty cases from five community surgeons were assessed by three observers to evaluate the overall quality of cement technique, the interobserver variability in cement mantle grading, and specific characteristics of the grading system. All three observers agreed on the grading in only 73% of the x-rays (anteroposterior view, 69%; lateral view, 77%). Compared with reports in the literature from specialized hip arthroplasty centers, a very high proportion of the cases had grade C mantles. To gain a balanced perspective of the global effectiveness and longevity of cemented total hip arthroplasty it is important that follow-up studies be reported upon from representative cross sections of the orthopaedic community.

Acetabulum↗
PubMed1997

Kinematics of the MATCO hip simulator and issues related to wear testing of metal-metal implants.

Metal-metal hip implants have been used clinically in Europe to reduce the risk of wear particle induced osteolysis. Joint simulator devices could provide useful information for design improvement of the modern generation of metal-metal hip implants. Early wear results for metal-metal hip specimens were obtained using a MATCO hip simulator. A detailed kinematic analysis was developed for the MATCO simulator and applied to two of the wear experiments to predict the starting surface motion, contact zone and lubricant film thickness. It was shown that points on cup surfaces were not subjected to a reciprocating interaction with the head during wear at the beginning of testing but as wear proceeded, it was suggested that, in some cases, reciprocating interaction did occur on the cup surface. Comparison between simulator and in vivo kinematics suggested a more realistic representation for cup than for head wear. In the simulator, the Hertzian contact zone moved in a circular path over the cup surface and changed in size in correspondence with the applied load. Elastohydrodynamic lubrication was considered to be possible in the simulator, with estimated fluid film thickness as great as 0.1 micron. However, such thick films were not likely to have occurred at the start of the two wear tests which were examined in detail, although some mixed film lubrication might have accounted for the relatively low wear of one of the specimens. The inclusion of kinematic details, contact mechanics and elastohydrodynamic lubrication analysis in simulator testing protocols and in design of metal metal hip implants was recommended.

Elasticity↗
PubMed1996

Effect of noninvasive low intensity ultrasound on bone growth into porous-coated implants.

Noninvasive low intensity ultrasound has been shown to be an effective means of accelerating bone fracture healing in both animal and clinical studies. An in vivo canine study was designed to determine if noninvasive low intensity ultrasound could influence the rate and extent of bone growth into porous-coated implants. Twenty-two pairs of fully porous transcortical implants were inserted bilaterally into the femora of 12 dogs. In each dog, one femur served as a control and the other was subjected to daily ultrasound stimulation for 2, 3, or 4 weeks. Overall, the ultrasound-stimulated implants demonstrated an 18% increase in bone ingrowth compared with their contralateral controls (p = 0.02). Noninvasive low intensity ultrasound had its greatest effect in the first 2-3 weeks of stimulation. At 2 and 3 weeks, the ultrasound-stimulated implants showed 21 and 16% more ingrowth than their respective contralateral controls. Because noninvasive low intensity ultrasound had a positive effect on bone ingrowth in this experimental investigation, further research is suggested to assess the clinical potential for application to noncemented porous-coated total joint replacements.

Animals↗
PubMed1996

Engineering issues and wear performance of metal on metal hip implants.

A major concern in total hip arthroplasty is the generation of polyethylene wear particles at the articulating surfaces and resulting macrophage mediated periimplant osteolysis. There is renewed interest in metal on metal bearings as a solution to this problem in view of their potential for greatly improved wear performance. Using a commercially available hip simulator, the wear performance of metal on metal femoral head and acetabular cup combinations was evaluated and various parameters affecting metal on metal implant wear were identified. Nine implants custom manufactured from 2 medical grades of CoCrMo alloy (ASTM F1537-95 and F75-92) were tested within bovine serum as the lubricant to 3 million cycles (equivalent to approximately 3 years of service in vivo). The progressive wear of the components was determined by gravimetric methods at approximately every 300,000 cycles. The wear rates were characterized by an initial period of accelerated wear after which a lower steady state wear rate was observed for subsequent cycles. The presence of calcium phosphate films on the component surfaces, the microstructure of the lower carbon, wrought alloy, and increased effective radii (decreased diametral clearances) were identified as factors that may be favorable to improved wear performance. The extent of the effect on wear of each parameter, however, cannot be discerned at this point and necessitates a study in which parametric changes are more tightly controlled. The present study suggests that the use of metal on metal articulating surfaces may mitigate the problem of osteolysis by offering improved wear performance.

Hip Prosthesis↗
PubMed1995

The susceptibility of smooth implant surfaces to periimplant fibrosis and migration of polyethylene wear debris.

The purpose of this investigation was to establish whether the tissue response and migration of polyethylene debris differed at noncemented smooth and porous implant surfaces. This was accomplished through 3 separate but closely related studies: (1) a canine cylindrical implant model with smooth and porous surfaces exposed to polyethylene debris; (2) a canine total hip arthroplasty model analyzing the interface between bone and femoral implants with various porous-coating configurations; and (3) a histologic analysis of autopsy-retrieved, human, noncemented hip prostheses with noncircumferential porous coating. The cylindrical implant model involved the placement of split cylinders, 1/2 porous and 1/2 smooth, into the distal femur and proximal tibia of 4 dogs. Four control implants and 10 test implants (chronically exposed to simulated polyethylene debris with a mean size of 4.7 microns) were examined histologically as long as 30 weeks after surgery. The canine hip study involved the study of 54 noncemented hip prostheses at periods of 1, 6, and 24 months. The prostheses possessed 4 different porous surface configurations: 1 with circumferential porous coating, 2 with noncircumferential coating, and 1 without porous coating. The human retrieval analysis involved the study of 7 cadaveric femora (age, 6 months-5 years) implanted with a straight titanium-alloy prosthesis possessing proximal pads of titanium fiber metal on the anterior, posterior, and medial aspects. With all implants in all 3 studies, there was the common finding of bone ingrowth at the porous implant surface and a fibrous interface or periprosthetic cavity around the portion of the implant that was smooth surfaced. The periprosthetic cavity typically was encapsulated by a thin continuous shell of trabecular bone. In addition, polyethylene debris was found to have preferentially migrated along the smooth implant surfaces. In the longer-term canine and human hip retrievals, polyethylene particles in the micron size range were present within histiocytes, whereas larger particles as much as 100 microns were found within foreign-body giant cells. Of importance for the implants from all 3 studies, with the exception of some pronounced cavities on the lateral aspect of the human hip prostheses, the periimplant cavities around the smooth surfaces were not detectable radiographically. This study clearly established a fundamental principle of relative barriers to particulate debris migration. Smooth implant surfaces are more susceptible than porous surfaces to the development of a fibrous tissue filled periimplant cavity and the subsequent migration of polyethylene wear debris.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1995

Vesico-acetabular fistula.

To our knowledge we report the first case of an isolated prosthetic vesico-acetabular fistula in a woman 12 years after total hip arthroplasty. Etiology, presentation, diagnosis and management are discussed.

Acetabulum↗
PubMed1994

The value of contrast arthrography in assessing loosening of symptomatic uncemented total hip components.

Twenty-five patients with symptomatic uncemented total hip components were studied with contrast arthrography prior to surgical exploration. All but one had uncemented femoral stems and 16 had an uncemented acetabular component. As judged by the findings at surgery, on the femoral side the sensitivity, specificity, and accuracy of arthrography were 57%, 60%, and 58% respectively. There was a relatively high incidence of both false positives (17%) and false negatives (25%). On the acetabular side sensitivity, specificity, and accuracy were 29%, 89%, and 62.5%. False negatives were common (31%), while there was only one false positive. The results in this small series show that arthrography has distinct limitations in identifying the fixation status of uncemented total hip components.

Adult↗
PubMed1994

Concerns with modularity in total hip arthroplasty.

Modularity is being diversified in total hip prostheses to increase surgical latitude in optimizing implant fixation and adjusting hip biomechanics. However, several problems have been clearly identified with implant modularity. First generation metal-backed acetabular components have shown deficiencies in the locking mechanism, the congruency and extent of polyethylene liner support, and polyethylene thickness, all of which have been implicated in accelerated polyethylene wear and failure. Evidence of screw motion against the metal backing, release of particulate material, and focal osteolysis have also been observed. At the head/neck junction evidence of corrosion and fretting has been documented with both similar-metal and mixed-metal taper combinations. Femoral prostheses with other sites of modularity present additional concerns with regard to mechanical integrity and generation of particulate debris by fretting. The modular junctions of three hip prostheses, the S-ROM, Infinity, and RMHS, were subjected to wet environment high cycle mechanical testing in a worst-case loading scenario. Preliminary results at relatively low loads up to three times body weight indicated gross stability of the modular junctions with evidence of minor fretting damage. Analysis of water solutions surrounding the modular junctions after ten to 20 million loading cycles yielded counts of one to three micron sized particles totalling several hundred thousand to several million. It is unknown what quantity of particulate material is sufficient to cause macrophage-mediated osteolysis or whether the debris from modular junctions can cause third-body wear of the articulating surfaces. Modular hip prostheses should be examined under stringent test conditions in order to characterize their fretting behavior and establish their mechanical limitations.

Biomechanical Phenomena↗
PubMed1994

Preoperative assessment of skin colonization and antibiotic effectiveness in total knee arthroplasty.

A bacteriologic screening procedure was performed to preoperatively assess the skin flora of 152 total knee arthroplasty patients and to determine the appropriate prophylactic antibiotic and skin-cleansing technique. Staphylococcus epidermidis resistant to standard prophylactic antibiotics was present in 4.6% of patients, whereas 44% of the patients had Staphylococcus aureus, which is poorly eradicated by standard cleansing techniques. Preoperative assessment of skin colonization has demonstrated that standard preoperative antibiotics and skin-cleansing techniques will not completely eradicate all pathogenic skin bacteria in every case. Preoperative screening effectively identifies bacterial skin flora and allows for the modification of antibiotic selection and preoperative cleansing to eradicate resistant bacterial organisms and thereby decrease the risk of postoperative prosthetic infections.

Adult↗