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Biomedical subjects

W H Harris

Publications and source records attributed to W H Harris.

At least 163 records · Page 9Linked to original sources
PubMed1993

Femoral component offset. Its effect on strain in bone-cement.

The magnitude of the offset of the femoral prosthesis strongly influences the mechanics of the hip following a total hip arthroplasty. An increased offset increases the moment arm of the abductor muscles. This reduces the abductor force required for normal gait and, consequently, reduces the resultant force across the hip joint. These factors are advantageous. However, increased offset also increases the bending moment on the implant, which could adversely increase the strain in the medial cement mantle. To evaluate the relative advantages and disadvantages of these conflicting results of increasing the offset of the femoral component the authors measured in vitro in cadaver femora the effect of differing offsets of the femoral component on strain in the cement mantle. After testing the intact femora, the authors cemented femoral prostheses in place and quantified the abductor force, resultant force, and strain in the cement mantle under loading conditions simulating single limb stance at different femoral offset levels. The reduction in both abductor and resultant force was substantial with increased femoral component offset, but the strain in the cement of the proximal medial portion of the cement mantle was not significantly increased.

Bone Cements↗
PubMed1993

Developments in diagnosis of the painful total hip replacement.

There has been significant improvement in the interpretation of diagnostic tests for the evaluation of the cemented and uncemented symptomatic total hip replacement. Lucent lines around cemented implants have often been found to represent remodeling rather than loosening. Lysis without looseness has been described as a cause of hip pain in both cemented and uncemented hip replacements. Therefore, there are a number of recent developments in diagnosis that must be considered when evaluating the symptomatic cemented or cementless total hip replacement. Some of these developments are reviewed in this paper. Other developments and contemporary algorithms for treatment incorporating these recent data will be presented in next month's issue.

Arthrography↗
PubMed1992

The effect of a thin coating of polymethylmethacrylate on the torsional fatigue strength of the cement-metal interface.

Recent studies have established that a mechanism of initiation of failure of fixation of cemented femoral components is debonding of the cement-metal interface. Other studies have shown that the torsional forces induced by stair climbing and rising from a chair are very high. Thus, the interface between the femoral prosthesis and the bone cement in total hip arthroplasty (THA) is required to transmit high torsional loads from the metal to the cement in a cyclic shear mode many times per year. These torsional loads likely contribute to the debonding. This study evaluated the efficacy of a thin layer of polymethylmethacrylate (PMMA) precoating in increasing the torsional fatigue strength of the cement-metal interface. Fatigue studies were performed on 15 specimens. Each specimen was tested with and without PMMA precoating. The PMMA precoat significantly and substantially increased the torsional fatigue strength of the cement-metal interface. Thus, PMMA precoating is likely to be a clinical advantage in maintaining the long-term integrity of the cement-prosthesis interface.

Bone Cements↗
PubMed1992

The effect of the addition of methylene blue on the fatigue strength of Simplex P bone-cement.

To aid in cement removal during revision arthroplasty, it has been proposed to add methylene blue to bone cement to provide contrast between the cement and bone. However, it is essential that the fatigue strength of the cement not be reduced by the addition of the methylene blue. The effect of adding 1 mL of an aqueous 1% solution of methylene blue to one pack of Simplex P prepared in the standard fashion (uncentrifuged) was studied. We also measured the fatigue properties of centrifuged Simplex P with three different methylene blue preparations. We studied adding 1 mL of an aqueous 1% solution of methylene blue, 0.5 g of methylene blue powder, and 0.1 mL of a 10% solution of methylene blue per pack of Simplex P bone cement. Adding 1 mL of a 1% methylene blue solution to 40 g of Simplex P without centrifuging the cement after mixing produced a cement with a mean fatigue life comparable to the uncentrifuged Simplex P without the methylene blue. However, the fatigue data scatter was higher for the uncentrifuged methylene blue preparation. The optimum methylene blue impregnated cement preparation was produced by adding 1 mL of a 1% methylene blue solution to 40 g of Simplex P powder, mixing with chilled monomer, and centrifuging for 60 s. Sterile 1 mL vials of 1% methylene blue solution are available in the operating room.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone Cements↗
PubMed1992

A fractographic investigation of PMMA bone cement focusing on the relationship between porosity reduction and increased fatigue life.

Fracture surfaces of both monotonic and fatigue loaded bone cement samples were examined to investigate the fractographic characteristics of PMMA. Classic cleavage step river patterns were observed on all monotonically loaded samples, running downstream in the direction of crack propagation. All fatigue cracks initiated at internal pores and the direction of crack propagation of many cracks was discernible. Porosity, pore size, and pore size distribution were found to affect the crack initiation and fatigue behavior of bone cement. Statistical analysis revealed a strong negative correlation between two-dimensional porosity present on the fracture surfaces and the cycles to failure. The fractographic observations of these fatigue samples elucidate one reason why porosity reduction by centrifugation or vacuum mixing increases the fatigue life of PMMA bone cement.

Biocompatible Materials↗
PubMed1992

A finite element study of the initiation of failure of fixation in cemented femoral total hip components.

In order to study initial mechanisms of failure in cemented femoral total hip components, an anatomically accurate three-dimensional linear finite element model was constructed and verified against experimental strain measurements in the cement mantle. Good agreement was found between predicted and measured strains. The likelihood of failure initiation due to cement-prosthesis debonding and crack initiation at voids was studied for loading conditions simulating both one-legged stance and stair climbing. The "out of plane" forces involved in stair climbing appear to be the greatest threat to the fixation of total hip replacements. In stair climbing, cement-prosthesis debonding and pore crack initiation were probable in the proximal anteromedial region of the cement mantle, and near the distal tip of the implant. The proximal stresses in stair climbing were higher than the distal stresses in either stair climbing or one-legged stance.

Bone Cements↗
PubMed1992

Bone ingrowth into a low-modulus composite plastic porous-coated canine femoral component.

Bone ingrowth into low-modulus canine femoral components made of composite plastics and porous coated with titanium fiber mesh was evaluated and compared to that found in femoral components of the same design made of titanium alloy and porous coated with titanium fiber mesh. Both types of components demonstrated extensive bone ingrowth into the porous coatings at 6 weeks and there were no differences in the histologic appearance of the tissue ingrowth in the two groups. The amount of bone that grew into the porous surface, the areal density of bone within the available pore space, and the extent of the prosthesis periphery with bone ingrowth were not significantly varied in the two different components. The results of this study show that adequate fixation of low-modulus composite femoral components porous coated with titanium fiber mesh by bone ingrowth can occur and that further investigation of these materials for femoral components may be warranted.

Animals↗
PubMed1992

Influence of prophylaxis on proximal venous thrombus formation after total hip arthroplasty.

Deep vein thrombosis (DVT) is the most frequent complication after total hip arthroplasty, and proximal DVT is more likely to produce clinical pulmonary emboli than distal DVT. The authors have assessed the incidence and anatomic location of phlebographically proven fresh DVT following total hip arthroplasty in 855 patients over 39 years of age. Eight different regimens (2 warfarin, 3 aspirin, 1 dextran, 1 external pneumatic compression, and 1 dextran combined with external pneumatic compression) were evaluated and compared with an historical placebo control group from the same institution. No significant difference (P < .05) existed in proximal DVT incidence between the placebo group and any of the three aspirin groups, the dextran group, the external pneumatic compression group, or the dextran combined with external pneumatic compression group. In contrast, warfarin, given both in traditional and low-dose regimens, provided a significant reduction in proximal DVT compared with the placebo group (P < .001; statistical power, 0.84 and 0.99, respectively). The low-dose regimen had 10 times fewer bleeding complications than the traditional regimen. All prophylaxis regimens should be evaluated for both proximal and distal DVT formation, as well as for overall incidence. Low-dose warfarin offers the best protection against proximal thrombi of the agents studied, and it is also safer than traditional dosages of warfarin.

Adult↗
PubMed1992

The histology of the radiolucent line.

The radiographic and histological features of radiolucent areas at the cement-bone interface were correlated in 15 specimens retrieved at post-mortem from patients who had undergone cemented total hip arthroplasty, two weeks to 15 years prior to death. All but one of the components were securely fixed, as demonstrated by direct measurements of micromotion. Extensive radiolucencies were present in all but one case. In 11 of the 14 specimens with radiolucencies, histological examination showed that the radiolucent areas represented regions of osteoporosis and bone remodelling. The remodelling changes were characterised by osteoporosis, cancellisation and thinning of the endosteal cortex, and osteopenia of the trabecular bone. In two specimens the appearance of radiolucency was found to be due to fibrous tissue at the cement-bone interface and in one specimen there was a mixed picture of osteolysis and fibrosis. The study demonstrates that radiolucent lines can occur with well-fixed components and that they may commonly represent osteoporosis rather than the presence of a fibrous membrane at the cement-bone interface.

Adult↗
PubMed1992

Improved cementing techniques and femoral component loosening in young patients with hip arthroplasty. A 12-year radiographic review.

To assess the effect of improved methods of femoral cementing on the loosening rates in young patients, we reviewed 50 'second-generation' cemented hip arthroplasties in 44 patients aged 50 years or less. The femoral stems were all collared and rectangular in cross-section with rounded corners. The cement was delivered by a gun into a medullary canal occluded distally with a cement plug. A clinical and radiographic review was undertaken at an average of 12 years (10 to 14.8) and no patient was lost to follow-up. No femoral component was revised for aseptic loosening, and only one stem was definitely loose by radiographic criteria. By contrast, 11 patients had undergone revision for symptomatic aseptic loosening of the acetabular component and 11 more had radiographic signs of acetabular loosening.

Acetabulum↗
PubMed1992

Thigh pain despite bone ingrowth into uncemented femoral stems.

Six porous-coated, uncemented femoral components were revised at a mean of 34.5 months for persistent thigh pain. At operation the stems were rigidly stable, difficult to extract, and showed good bony ingrowth. The four men and two women, with an average age of 59 years, all had thigh pain starting within the first year, progressive over time and unresponsive to conservative measures. These cases show that rigid fixation with good bony ingrowth does not guarantee the clinical success of a porous-coated uncemented femoral stem.

Adult↗
PubMed1992

The Harris-Galante porous-coated acetabular component with screw fixation. Radiographic analysis of eighty-three primary hip replacements at a minimum of five years.

The results of eighty-three consecutive primary total hip arthroplasties in which a Harris-Galante porous-coated acetabular component had been used were reviewed after a minimum of five years. In all patients, the stated diameter of the acetabular component (the diameter printed on the packaging for the implant) used was equal to the stated diameter of the reamer (the diameter printed on the reamer) that had been used last in the preparation of the acetabulum. As there was little or no press-fit stability, stability was obtained initially with multiple transfixing screws. No component was revised because of loosening, and none were radiographically loose at an average of sixty-eight months and a maximum of seven years after the operation. There was no evidence of disruption of the titanium porous mesh, and no screw had bent or broken. Two sockets, however, had been revised because of failure of the liner-locking mechanism as well as disassociation of the polyethylene liner from the titanium-alloy shell. Lysis of bone occurred in only one patient, around one screw. Areas of non-contact (gaps) between the porous mesh at the periphery of the acetabular component and the bone were seen on the immediate postoperative radiographs of nearly half of the patients. New areas of radiolucency, which had not been seen immediately postoperatively, were identified at two years in forty-nine hips. These radiolucent lines were never wider than one millimeter and were most frequently located in zone 3 and, less frequently, in zone 1. At the time of the most recent follow-up evaluation, a progressive radiolucent line was identified around twenty-two components and a discontinuous radiolucent line was present in all three zones around eleven components. No continuous radiolucent line was identified at the mesh-bone interface of any component. These results are superior to our results with cemented acetabular components after a similar period of follow-up. A longer period of follow-up is needed before the importance of these thin radiolucent lines can be determined, but experience with cemented acetabular components indicates that progressive or extensive radiolucent lines, or both, may represent resorption of bone at the porous mesh-bone interface and this can lead to loosening of the component. Our data suggest that the technique used for implantation may be important not only for the initial fixation and ingrowth of bone, but also for the long-term durability of the fixation of a porous-coated acetabular component.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetabulum↗
PubMed1992

Acrylic fragmentation in total hip replacements and its biological consequences.

Loosening of total joint prostheses is in part related to the fragmentation of the acrylic cement mantle surrounding the prosthesis and the biologic consequences to the particulate acrylic. Fractographic studies of femoral cement mantles retrieved at revision surgery and autopsy showed frequent fractures in varying stages of development in the cement and wear at the fracture surfaces. Defects in the cement mantle, thin mantles, sharp corners on the prosthesis, separation at the cement mantle interface, and pores in the cement were frequently associated with cement fractures. The progressive fractures and wear led to the liberation of particulate acrylic debris into the surrounding tissues. The tissues at the bone-cement interface removed at revision surgery showed that a macrophage, giant-cell foreign-body granulomatous reaction occurs in response to the particulate, but not bulk cement. This tissue can produce a variety of chemical mediators of inflammation and bone resorption, and can resorb bone in organ cultures. A granulomatous tissue reaction with a very similar appearance can be produced in experimental animals using particulate-form polymethylmethacrylate (PMMA), but not the bulk form of PMMA. The tissue reaction is not mediated by the classic cell or humeral immune mechanisms. Subcutaneous injection of particulate PMMA powder into fully immunocompetent C3Hf/SED mice as well as three strains of mice with progressive immunologic deficiencies (nude/nude, SCID, and triple deficient Nu-bg-XID/SED mice) led to a foreign-body reaction in all strains at five weeks as shown by histologic and immunohistochemical examination despite the differences in immune deficiency. This, along with the scarcity of lymphocytes in the human tissues, suggests that the biologic reactions to fragmented cement can be produced and sustained by nonimmune phagocytosis and activation by macrophages and giant cells without significant contribution by the immune system.

Aged↗
PubMed1992

Quantification of implant micromotion, strain shielding, and bone resorption with porous-coated anatomic medullary locking femoral prostheses.

Fourteen femora containing porous-coated anatomic medullary locking (AML) femoral prostheses were retrieved from 12 patients at autopsy. Clinical roentgenograms in 13 femora showed bone remodeling changes, indicating that the implants were fixed by osseointegration. Under simulated physiologic loading, micromotion between the implant and the bone was measured using electrical displacement transducers connected to the implant and to the adjacent cortex. The micromotion between the implants at the areas of porous coating and the adjacent cortex in the one case of failed bone ingrowth measured 150 microns. Maximum relative motion between the cortex and the implant in the areas of porous coating for the 13 cases showing signs of bone ingrowth was 40 microns, and this was completely elastic relative displacement. With all implants, the micromotion between the cortex and the stem was always greatest over the uncoated portion of the stem. Four of the implants were proximally porous coated. With these, the micromotion was greater over the uncoated areas than with more extensively coated stems and was always greatest at the uncoated tip of the prosthesis. The amount of micromotion was directly related to the extent of porous coating on the implant. Maximum tip motion for the proximally coated implants was 210 micra, whereas for the fully porous-coated implants, it was 40 microns. In nine of the autopsies, the contralateral normal femur was obtained in addition to the femur containing the AML (the in vivo remodeled femur). These were used for comparative studies of strain shielding and femoral remodeling. Cortical strains were measured in the in vivo remodeled femora and were compared with measurements made in the contralateral normal femora before and following implantation of a stem identical to that present on the clinically treated side. The data showed major strain reductions in all the postmortem implanted normal femora. Comparison of the strain data from the postmortem implanted normal femora with those from the in vivo remodeled femora clearly indicated that extensive bone remodeling did not result in restoration of cortical strain levels anywhere near normal. Strain shielding continued to exist in all of the remodeled specimens, even up to 7.5 years after surgery. This strain shielding was associated with bone remodeling changes that resulted in regional reductions in bone mineral content that ranged from 7% to 78%. These observations are unique, important, and valuable in defining the in vivo function and clinical behavior of this type of porous-coated femoral component.

Aged↗
PubMed1992

Is it advantageous to strengthen the cement-metal interface and use a collar for cemented femoral components of total hip replacements?

The mechanism of initiation of loosening of cemented femoral components is now known. It is debonding at the cement-metal interface. Current data strongly support the concept that a collar and improvement of the cement-metal interface are valuable. Precoating and having a roughened surface proximally and distally on the stem contribute to extended longevity of the cement-metal interface. Using contemporary instrumentation, collar-calcar contact can be achieved regularly and, once achieved, is well maintained for years.

Arthroplasty↗
PubMed1992

Bead loosening from a porous-coated acetabular component. A follow-up note.

Beaded porous-coated implants are commonly used in total joint arthroplasty. In this study, the authors extended the follow-up period for the Davey and Harris study of bead loosening in beaded cementless acetabular components. When 56 primary total hip arthroplasties were first reviewed, at an average of 2.5 years after surgery, the incidence of bead loosening was 8.9%. Reevaluation at a mean of 4.5 years after surgery revealed that the incidence of loosening had increased to 19.6%. Bead loosening was associated with acetabular migration in one component and a broken screw in a second. In the absence of loose beads, there were no broken fixation screws or socket migration. Radiolucencies at the bone-implant interface were seen in association with loose beads in only one case. Although long-term implications of bead loosening are not clear, bead migration may increase the possibility of macrophage response to metallic debris.

Acetabulum↗