Search PubMed⌕ Search

Biomedical subjects

W H Harris

Publications and source records attributed to W H Harris.

At least 199 records · Page 11Linked to original sources
PubMed1991

Micromotion of cemented and uncemented femoral components.

We evaluated the initial stability of cemented and uncemented femoral components within the femoral canals of cadaver femurs during simulated single limb stance and stair climbing. Both types were very stable in simulated single limb stance (maximum micromotion of 42 microns for cemented and 30 microns for uncemented components). However, in simulated stair climbing, the cemented components were much more stable than the uncemented components (76 microns as against 280 microns). There was also greater variation in the stability of uncemented components in simulated stair climbing, with two of the seven components moving 200 microns or more. Future implant designs should aim to improve the initial stability of cementless femoral components under torsional loads; this should improve the chances of bony ingrowth.

Adult↗
PubMed1991

The initiation of failure in cemented femoral components of hip arthroplasties.

We studied 16 femora retrieved at post-mortem from symptomless patients who had a satisfactory cemented total hip arthroplasty from two weeks to 17 years earlier, with the aim of delineating the initial mechanisms involved in loosening. Only one specimen showed radiographic evidence of loosening; the other 15 were stable to mechanical testing at 17.0 Nm of torque. In all 16 specimens, the cement-bone interface was intact with little fibrous tissue formation. By contrast, separation at the cement-prosthesis interface and fractures in the cement mantle were frequent. The most common early feature was debonding of the cement from the metal, seen at the proximal and distal ends of the prosthesis. Specimens which had been in place for longer also showed circumferential fractures in the cement, near the cement-metal interface, and radial fractures extending from this interface into the cement and sometimes to the bony interface. The most extensive cement fractures appeared to have started at or near sharp corners in the metal, or where the cement mantle was thin or incomplete. Fractures were also related to voids in the cement. The time relationship in this series suggested that long-term failure of the fixation of cemented femoral components was primarily mechanical, starting with debonding at the interface between the cement and the prosthesis, and continuing as slowly developing fractures in the cement mantle.

Adult↗
PubMed1991

Autocrine production of insulin-like growth factor II using an inducible expression system results in reduced estrogen sensitivity of MCF-7 human breast cancer cells.

An inducible expression vector, utilizing the metal response elements from the human metallothionein IIA promoter and encoding human prepro-insulin-like growth factor II (IGF-II), was transfected into MCF-7 McG cells, an MCF-7 subline which exhibits an estrogen dependent phenotype in vitro and does not express detectable levels of IGF-II mRNA. Two stably transfected clones, designated MI5 and MI7, which expressed IGF-II mRNA in a Zn2+ regulated manner, were isolated. Clone MI5 did not secrete detectable levels of IGF-II activity, as determined by radioimmunoassay of conditioned medium, but clone MI7 secreted high levels of IGF-II activity in a Zn2+ inducible fashion. Clone MI5 and control clones transfected with the selection plasmid pSV2 neo and the control plasmid pSP65 continued to display an estrogen dependent phenotype in vitro. However, under both anchorage dependent and anchorage independent growth conditions, clone MI7 cells exhibited an estrogen responsive, rather than dependent, phenotype. Moreover, when grown in the presence of inducing concentrations of Zn2+, MI7 cells were either virtually (for anchorage dependent growth) or completely (anchorage independent growth) unresponsive to estradiol. Both the basal growth rate in the absence of metal ions and the Zn2+ induced increases in cell proliferation could be inhibited by the monoclonal antibody alpha-IR3, which blocks the binding site of the IGF-I receptor. The antiestrogens tamoxifen and 4-hydroxytamoxifen were found to enhance the growth stimulation resulting from Zn2+ induced IGF-II production in MI7 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Breast Neoplasms↗
PubMed1991

Elevated-rim acetabular components. Effect on range of motion and stability in total hip arthroplasty.

The effect of "elevated-rim" (ER) acetabular components on prosthetic range of motion (ROM) and stability was studied in a laboratory simulator using three contemporary total hip arthroplasty (THA) systems. Acetabular components were tested in positions simulating both normal alignment and excess abduction. The geometry of the implants differed between systems--two types were identified, and their effect on ROM in comparison with their corresponding plain liners were quantified. The ability of the liners to improve instability appeared to be dependent on the cause of instability, the orientation of the metal shell and ER liner, and the ER liner geometry. The routine use of ER liners in otherwise satisfactorily positioned acetabular components appeared to offer no demonstrable benefit and raised concern over theoretical disadvantages. The primary indication for these implants appeared to be in cases of instability due to acetabular malposition in which the metal shell is already well fixed by cement or bone ingrowth or cannot be readily changed.

Acetabulum↗
PubMed1991

Incidence of heterotopic ossification after total hip replacement: effect of the type of fixation of the femoral component.

The incidence and severity of heterotopic ossification after sixty-five consecutive primary uncemented total hip replacements were compared with those after seventy consecutive primary hybrid total hip replacements (consisting of an uncemented acetabular component and a cemented femoral component). All patients had had the arthroplasty because of osteoarthrosis. The sex distribution, prevalence of bilateral disease of the hip, and frequency of previous operations were similar in both groups. All of the operations were performed by one surgeon who used the same operative approach. Preoperative, immediate postoperative, and six-month follow-up radiographs were reviewed for all patients. For 90 per cent of the hips, radiographs that were made after a minimum follow-up of one year were also reviewed. In the group of patients who had an uncemented femoral component, there was a statistically significant increase in the frequency of heterotopic bone and in its severity. Either none or only class-I ectopic bone developed in 74 per cent of the hips in the hybrid group, compared with 40 per cent of the hips in the uncemented group (p less than 0.005). In contrast, class-III or IV heterotopic ossification was evident in 13 per cent of the hips in the uncemented group (p less than 0.005). None of the patients in the hybrid group needed reoperation for excision of ectopic bone, but four (6 per cent) of the patients in the uncemented group needed such a reoperation because of severe limitation of motion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Ingrowth of bone in failed fixation of porous-coated femoral components.

In five straight-stemmed, proximally porous-coated femoral components that were retrieved at revision arthroplasty from patients who had radiographic and clinical evidence of loosening, there was growth of bone into the porous coating. The components had been inserted during a primary arthroplasty in one woman and four men. The patients ranged in age from thirty-seven to sixty-seven years. Three patients were heavy, and all five were active. All patients had had an excellent early result from the initial arthroplasty; at the one-year follow-up, the mean Harris hip score had been 91 points. Pain in the hip developed in all of the patients, between one and three years after the index procedure. Initial radiographs had revealed excellent position and fixation of the prosthetic components, but the components then subsided between one and three and one-half years after the index procedure. All of the femoral components were found to be grossly loose at the revision operation. Nevertheless, all of the prosthetic components demonstrated growth of bone into 4 to 44 per cent (mean, 24 per cent) of the pore spaces available for ingrowth. Woven bone and fracture callus were found in the curettings from the proximal part of the femur. The findings in these five patients suggest that late failure of uncemented porous-surfaced femoral components can occur despite the presence of extensive ingrowth of bone. These failures may be the result of fatigue fractures of the trabeculae of the osseous ingrowth into the porous surfaces. Caution is warranted in the liberal use of these prosthetic components in heavy, active patients.

Adult↗
PubMed1991

Proximal placement of the acetabular component in total hip arthroplasty. A long-term follow-up study.

A retrospective review was undertaken of thirty-seven hips (thirty-four patients) that had had a complex cemented total hip arthroplasty. In these hips, circumstances had necessitated that the center of the hip be placed farther proximally, as measured from the interteardrop line, than the anatomical position that is normally used. The mean duration of clinical and roentgenographic follow-up was eleven years (range, seven to seventeen years), and the mean age of the patients was fifty-one years (range, sixteen to seventy-three years). Most of these hips had a major deficiency or defect of the acetabular bone stock, or both. Of the six acetabular components (16 per cent) that became loose and were followed for ten years, only one needed revision. Because this study was aimed specifically at assessment of the acetabular component, if the femoral component alone needed revision, the final clinical rating that was used was the one obtained after the femoral revision. Thirty-one hips (84 per cent) were rated as having a good or excellent result; they had an average Harris hip-rating score of 43 points preoperatively and 93 points postoperatively. Thirty-three of the thirty-seven acetabular components were not substantially displaced laterally as compared with the anatomical location that is normally used. Our findings suggest that, when circumstances dictate, proximal positioning of the acetabular component without lateral displacement can give an acceptable result in cemented total hip-replacement procedures.

Adolescent↗
PubMed1991

Intraoperative measurement of rotational stability of femoral components of total hip arthroplasty.

High out-of-plane forces acting on the hip joint can produce important rotational micromotion of the femoral component. This micromotion at the prosthesis interface may be detrimental to the stability of the implant. In cementless femoral implants this could prevent bone ingrowth, and in the cemented component this could cause generation of particulate debris, lysis, and loosening. The introduction of the torque wrench micrometer for assessment of intraoperative femoral component stability can quantify the initial stability of primary cementless femoral components and critically evaluate the stability (at either the initial or revision arthroplasty) of both cemented and cementless femoral components. It allows the surgeon to produce a known torque in the direction and magnitude of the out-of-plane forces that load the hip in vivo.

Arthrography↗
PubMed1990

The influence of support conditions in the loading fixture on failure mechanisms in the push-out test: a finite element study.

The usefulness of the push-out test as an indicator of interface strength was evaluated using finite element models of intact and partially failed cylindrical push-out specimens loaded against a rigid annular support. The irregular stress distributions that were found in intact specimens depended more on interface conditions at the loading fixture than on a 35% increase in interface area. The maximum stress at the interface was a tensile stress. Critical energy release rates for interface failure were calculated for flawed specimens in which flaw size was either 10 or 100 microns, and for boundary conditions at the loading fixture that were either fixed or slipping in the radial direction. The critical energy release rates depended heavily on the support boundary conditions. Thus, the results of parametric push-out tests can be reasonably compared only for specimens that are very similar in geometry and that are loaded in very carefully controlled fixtures.

Bone Cements↗
PubMed1990

Salvage total hip reconstruction in patients with major acetabular bone deficiency using structural femoral head allografts.

We evaluated 38 hip reconstructions in 36 patients at a mean follow-up of 5.9 years (range 4 to 9.1) after femoral head allografts had been used to augment severely deficient acetabular bone stock. The patients were all relatively young and had many previous operations. Their pre-operative Harris hip rating averaged 46 points (range 18 to 73). All the allografts united and there were no infections. However, 12 acetabular components (32%) became loose; six of these had needed revision using the healed allograft, and two hips had required resection arthroplasty. The 30 surviving hips had a mean Harris hip score of 82 points. Some radiographic evidence of graft resorption was seen in 23 hips, though this was mild in 17. The extent of cover provided by the allograft and the severity of graft resorption both correlated with acetabular loosening. Although structural allografts had allowed successful hip reconstructions in many of these patients with major bone loss, the failure rate had increased from zero at four years to 32% at six years; clearly they provide only a short-term solution.

Acetabulum↗
PubMed1990

Insertion of a prosthetic hip into a total hip allograft. Case report.

We describe a patient in whom a total hip replacement had failed and who subsequently fractured her proximal femur. The prosthetic hip and the surrounding bone were excised and replaced by a matched pair of allograft components. She obtained seven years of pain free hip function before the graft showed radiographic signs of failure; it was then replaced by a new prosthetic hip.

Arthritis, Rheumatoid↗
PubMed1990

The effect of improved cementing techniques on component loosening in total hip replacement. An 11-year radiographic review.

Improved cementing techniques have been shown to decrease the rate of aseptic loosening of femoral components of cemented total hip replacements at five to seven years. We now report our results in 105 hips in 93 patients at 10 to 12.7 years (mean 11.2). The improved techniques included use of a medullary plug, a cement gun, a doughy mix of Simplex P and a collared stem of chrome cobalt. Only three femoral components had definitely loosened, none were probably loose and 24 were graded as possibly loose. In contrast, the incidence of radiographic loosening on the acetabular side was 42%. Improved cementing techniques have produced a marked reduction in the rate of aseptic loosening of the femoral component, but the incidence of acetabular loosening is unchanged.

Adult↗
PubMed1990

Bone lysis in well-fixed cemented femoral components.

We have reviewed 25 cases of focal femoral osteolysis in radiographically stable, cemented femoral implants. In three hips retrieved at post-mortem from two patients, we have been able to make a detailed biomechanical and histological analysis. The interval between arthroplasty and the appearance of focal osteolysis on clinical radiographs ranged from 40 to 168 months, and in over 70% of the cases this did not appear until after five or more years. Few had significant pain and there was no relation to age, sex or original diagnosis. The most common site for osteolysis were Gruen zones 2 and 3 on the anteroposterior radiograph and zones 5 and 6 on the lateral radiograph. In 15 cases (60%), the area of osteolysis corresponded to either a defect in the cement mantle or an area of very thin cement. The rate of progression of these lesions was variable, but to date only one has progressed to gross loosening of the femoral component. The back-scatter scanning electron microscopic examination of serial sections and biomechanical testing of the post-mortem specimens demonstrated focal cement fracture around implants that were otherwise rigidly fixed. In eight cases from which tissue was available, histology showed a histiocytic reaction with evidence of particulate polymethylmethacrylate. We consider that this local fragmentation was the stimulus for local osteolysis in an otherwise stable cemented femoral component.

Biomechanical Phenomena↗
PubMed1990

Radiation-blocking shields to localize periarticular radiation precisely for prevention of heterotopic bone formation around uncemented total hip arthroplasties.

Sixteen patients (18 hips) were treated with localized radiation therapy limited to periarticular regions surrounding the femoral neck by shielding the prosthesis and the adjacent regions to prevent heterotopic bone formation around the uncemented prosthesis. All hips received 1500 rads. Eight of these hips were irradiated after excising severe heterotopic bone, five because they developed extensive heterotopic ossification in the opposite hip, and five others because they were considered to be at high risk for developing heterotopic ossification. Only two of the 18 hips developed a small amount of heterotopic bone after localized periarticular radiation. All wounds healed primarily. No progressive radiolucencies developed at the bone-prosthesis interface. There was only one trochanteric nonunion of six trochanteric osteotomies. Localized periarticular radiation therapy with precision shielding of the prosthetic components and adjacent skeletal structures is an effective means to prevent heterotopic bone formation around cementless total hip arthroplasties. It also has the advantage of not adversely affecting the healing of the trochanteric osteotomy.

Adult↗