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Biomedical subjects

W H Harris

Publications and source records attributed to W H Harris.

At least 289 records · Page 16Linked to original sources
PubMed1983

Tensile fatigue failure of acrylic bone cement.

Tensile fatigue tests of acrylic bone cement were conducted under strain control in a wet environment at 37 degrees C. A constant strain rate of 0.02s-1 was used, resulting in physiologic loading frequencies. Comparison of the tensile fatigue data with the results of previous tension-compression fatigue tests indicates that fatigue failure is governed primarily by the maximum cyclic tensile strain. The compressive portion of the loading cycle has little effect on the number of cycles to failure. A new empirically derived equation is introduced to describe the influence of mean strain and strain amplitude on fatigue endurance. The results emphasize the critical role tensile strains may play in cement failure and loosening of total joint replacements.

Bone Cements↗
PubMed1983

Plasma and erythrocyte volumes of newborn rabbits delivered after 30 days of gestation.

The plasma and erythrocyte volumes of 18 rabbit fetuses delivered by caesarean section on day 30 of gestation were measured by a double labelling radioisotope technique after separation from the placenta. These late gestation fetuses were viable. A negative correlation was found between the bodyweight of the neonate and its blood volume expressed as a percentage of bodyweight. The equation of the linear regression line was Y = 92.3 - 3.9X. The haematocrit was 0.494 +/- 0.029 l/l.

Animals↗
PubMed1983

Periacetabular stress distributions after joint replacement with subchondral bone retention.

Two-dimensional finite element stress analyses were conducted of the acetabular region after total joint replacement. The effect of subchondral bone retention was evaluated for both conventional and metal-backed acetabular components. Stresses in the bone, cement and acetabular cup were significantly reduced when subchondral bone was retained for both component types. The results indicate that the most favorable stress conditions are created when a metal-backed acetabular component is implanted with subchondral bone retention.

Acetabulum↗
PubMed1983

The synovial-like membrane at the bone-cement interface in loose total hip replacements and its proposed role in bone lysis.

UNLABELLED: The membrane present at the bone-cement interface was retrieved from twenty patients with a loose, non-septic failed total hip replacement at a site clearly remote from the pseudocapsule that reformed postoperatively. The orientation of the membrane was carefully marked to identify the surface in contact with cement. The membrane was studied histologically, histochemically, by cell culture, by organ culture, and by assessment of its ability to synthesize prostaglandin E2 and collagenase. This membrane, rather than being a nondescript so-called fibrous membrane, has the histological and histochemical characteristics of a synovial-like lining. The synovial-like cells are adjacent to the cement layer. Deep to them macrophages predominate. Inflammatory cells are absent. Cell cultures of this membrane contain stellate cells similar to those found in cell cultures of normal and rheumatoid synovial tissue. This membrane has the capacity to produce large amounts of prostaglandin E2 and collagenase. CLINICAL RELEVANCE: This transformation of tissue at the bone-cement interface in patients with a non-septic, loose total hip component to a synovial-like tissue with the capacity to generate prostaglandin E2 and collagenase may explain the progressive lysis of bone that is seen in some patients with loose cemented total joint implants. Loosening of the component may be a stimulus to the synthetic activity of this tissue, which leads to further resorption of bone. Understanding and the possibility of pharmacological control of this membrane may contribute to improved duration of total joint implants.

Bone Resorption↗
PubMed1983

Complex total hip replacement for dysplastic or hypoplastic hips using miniature or microminiature components.

We analyzed the preoperative and perioperative data on sixty-nine consecutive complex total hip replacements performed in fifty-seven patients using miniature or microminiature custom-made femoral components. The patients' average age was 45.7 years. The preoperative diagnosis was congenital dysplasia or dislocation of the hip in 72 per cent of the hips. Acetabular bone grafts were required in thirty-seven of the sixty-nine hips. Operative complications occurred in thirteen (19 per cent) and postoperative dislocation occurred in eleven (16 per cent) of the sixty-nine hips. Fifty-five hips in forty-seven patients were followed for a minimum of two years, the average follow-up being 4.8 years and the longest, 9.8 years. All acetabular grafts united. Loosening of one or both prosthetic components occurred in ten (18 per cent) of the fifty-five hips (twelve of the 110 components became loose). There were no instances of a stem bending or fracturing, despite the small size of the femoral components. Eight hips (14.5 per cent) had undergone revision, six for painful loose components and two for recurrent dislocation. For the forty-seven hips that were not revised, the average Harris hip score rose from 43 points preoperatively to 80 points postoperatively.

Adolescent↗
PubMed1983

The femoral cement compactor. An improvement in cementing technique in total hip replacement.

Aseptic loosening is the most common cause of femoral component failure in total hip arthroplasty. Even with new cementing techniques, bone-cement pressurization is low in the most proximal area of the femoral canal. To correct this problem, we devised the femoral cement compactor. This device increased the pressurization of bone cement in the proximal area of the femur by 71 per cent and increased the duration of the pressurization fourfold as compared with the results achieved by finger-packing methods. Pressurization of the cement was also increased in the middle and distal areas of the proximal portion of the femoral canal. These findings suggest that using the femoral cement compactor may contribute to improved cement fixation of the femoral component during total hip replacement.

Bone Cements↗
PubMed1983

Advantages of metal-backed acetabular components for a total hip replacement: a clinical assessment with a minimum 5-year follow-up.

A group of 53 hips in which metal-backed acetabular components had been inserted with the use of bone cement were reviewed roentgenographically at an average of 6.5 years following insertion, with a minimum follow-up of 5 years. Of this group, two were excluded for special reasons. Among the remaining hips, with an average age of 41 years at the time of insertion, the incidence of acetabular component loosening was 6%. In fact, the only acetabular component loosening occurred in three patients whose surgery was done at the age of 25 years or younger. No patient over the age of 25 years demonstrated a loose acetabular component. By selecting the subset of patients age 45 years and under, we could make a comparison with a similar group of patients reported by Dorr and Takai, in whom acetabular components had been inserted without metal backing. The group with the metal-backed acetabular components had a statistically significant reduction in acetabular component loosening. These clinical data, taken in conjunction with the finite-element studies reported in Chapters 11 and 12, make a very strong case for the use of the metal-backed acetabular component. Our clinical practice, and our recommendation, is to use a metal-backed acetabular component in every cemented total hip replacement, if possible.

Acetabulum↗
PubMed1983

The effects of cesarean section anesthesia on heat loss and heat production in the newborn rabbit.

The newborn of some smaller animals rely upon heat produced by nonshivering thermogenesis in the brown fat to prevent a fall in body temperature after birth. Because of their pharmacological properties, some drugs may affect nonshivering thermogenesis. Therefore, in this study, the ability of newborn rabbits delivered under Innovar-Vet, ketamine hydrochloride, methoxyflurane and epidural anesthesia to maintain the rectal, subcutaneous interscapular and lumbar temperature was investigated at an ambient temperature of 35 degrees C or 22 degrees C and the results compared with control newborns delivered without anesthesia. When the newborns were exposed to 35 degrees C, the anesthetics studied had no effect on the ability of the newborn to maintain the rectal temperature and the subcutaneous temperature over the interscapular fat pad was similar to the lumbar subcutaneous temperature thereby indicating that nonshivering thermogenesis was not activated. However, at an ambient temperature of 22 degrees C Innovar-Vet or methoxyflurane reduced the temperature difference between interscapular and lumbar temperatures to 1.6 degrees C compared to 2.5 degrees C in controls and the difference between core temperature and ambient temperature to 3.5 degrees C greater compared to 7.5 degrees C in controls. Ketamine hydrochloride or lidocaine hydrochloride plus meperidine has less effect because these compounds lack adrenergic blocking properties. These data suggest that newborns delivered under anesthetics or tranquillizers that have adrenergic blocking properties require a warm (35 degrees C) environment to prevent a fall in core temperature.

Anesthesia, Obstetrical↗
PubMed1983

Bony ingrowth fixation of the acetabular component in canine hip joint arthroplasty.

Five mature dogs were studied five to eight months after insertion of a newly designed acetabular component that eliminates the use of bone cement in total hip arthroplasty (THA). The component was hemispheric, with a layer of porous metal on its outside surface. It initially was fixed to the innominate bone by screws passed through projections from the edge of the metal substrate. When the dogs were killed five or eight months after implantation, all components were fixed rigidly to the bone. Bony ingrowth covered an average of 53% of the porous surface of the implant, penetrating three layers of balls.

Acetabulum↗
PubMed1982

Strain-controlled fatigue of acrylic bone cement.

Monotonic tensile tests and tension-compression fatigue tests were conducted of wet acrylic bone cement specimens at 37 degrees C. All testing was conducted in strain control at a strain rate of 0.02/s. Weibull analysis of the tensile tests indicated that monotonic fracture was governed more strongly by strain than stress. The number of cycles to fatigue failure was also more strongly controlled by strain amplitude than stress amplitude. Specimen porosity distribution played a major role in determining the tensile and fatigue strengths. The degree of data scatter suggests that Weibull analysis of fatigue data may be useful in developing design criteria for the surgical use of bone cement.

Acrylic Resins↗
PubMed1982

Stress distributions in the acetabular region--I. Before and after total joint replacement.

Two-dimensional finite element analyses of the acetabular region before and after hip replacement were conducted. The distribution of pressure at the acetabular surface for the single limb stance phase of gait was transformed to nodal loads to stimulate in vivo loading conditions. A nonhomogeneous distribution of bone elastic properties was incorporated in the models. The results demonstrated that the principal stresses in the normal acetabulum were aligned with the principal orientations of the trabeculae. Total joint replacement increased the von Mises' equivalent stresses in the cancellous bone immediately superior to the acetabular cup, and increased stresses in the medial wall of the ilium. Biaxial, tension-compression stresses were created in the layer of bone cement and introduced in the medial wall of the ilium. Tensile stresses in the bone cement were greatest at the superior roof and at the inferior margin of the cup. Tensile stresses in the cup were more pronounced at the margins, particularly near the inferior lip. The cup tended to close in such a manner as to grip the head of the femoral component as it was pressed between the medial and lateral walls of the ilium.

Acetabulum↗
PubMed1982

Stress distributions in the acetabular region--II. Effects of cement thickness and metal backing of the total hip acetabular component.

A two-dimensional finite element study was undertaken to establish the stresses in the acetabular region after total joint replacement. The influence of cement thickness and the effect of metal backing on the polyethylene cup were explored. Increasing cement thickness (from 1 to 3 to 5 mm) caused a decrease in the von Mises' equivalent stresses in the cement and surrounding cancellous bone. A more dramatic reduction in these stresses was found when a 2 mm thick cobalt-chromium alloy backing was added to the cup. The results indicate that increasing the stiffness of the composite implant by either method is helpful but that the metal backing causes a more efficient transfer of the stresses to the walls of the ilium. The finding strongly suggests that the use of a metal-backed acetabular component will help to delay or prevent cup loosening and migration in total hip replacement patients.

Acetabulum↗
PubMed1982

Accuracy enhancement of in-vivo bone strain measurements and analysis.

A numerical technique is presented to evaluate and correct the zero-strain reference points determined experimentally for certain in-vivo strain rosette applications on long bones. The method is used to determine whether significant transverse stresses are present at the gage site during in-vivo activities. If transverse stresses are shown to be negligible, the experimentally determined zeroes can be appropriately adjusted to provide an increased accuracy of the strain measurements. In addition, the transverse Poisson's ratio is calculated and can be incorporated in subsequent in-vivo stress calculations.

Animals↗
PubMed1982

High and low-dose aspirin prophylaxis against venous thromboembolic disease in total hip replacement.

Aspirin has been demonstrated to be an effective prophylactic agent against postoperative venous thromboembolic disease, but the optimum dosage is unknown. We compared the efficacy of daily doses of 3.6 grams of aspirin (high dose) with that of 1.2 grams (low dose) in 182 patients. All patients were more than forty years old and all underwent a total hip replacement. This randomized, prospective, double-blind study was done using only objective dta for diagnosis. Twenty-three (44 per cent) of fifty-two women who were treated with the low dose had thrombi, compared with eighteen (34 per cent) of fifty-three women who were given the high dose. Thrombi developed in thirteen (32 per cent) and in eighteen (49 per cent) of thirty-seven men who were given the high dose. There were no statistically significant differences among the four groups, nor was there a significant difference among the subgroups that were determined according to prior history of venous thromboembolic disease. Therefore, the higher dose of aspirin was neither more nor less effective than the lower dose. Our data continue to support the use of 1.2 grams in men.

Adult↗
PubMed1982

A cement fixation system for total hip arthroplasty.

To combat the most common and most serious cause of mechanical failure of total hip arthroplastics, namely loosening, a method of improving the insertion of methacrylate is presented, called the cement fixation system. Using the cement gun with the keying hole seal, the methacrylate is pressure injected into the keying holes in the acetabulum. The acetabular cement compactor pressurizes the rest of the cement used in the acetabulum. The medullary canal of the femur is occluded by a bolus of methacrylate delivered to the desired depth by the medullary plug syringe. Thus, the cement is delivered from the plug proximally via the cement gun and femoral cement syringe. Finger packing is not used. The entire femoral cement mass is then pressurized using the femoral cement compactor. This cement fixation system produces higher extrusion pressure, better penetration of the cement, better fixation to the bone and reduces voids, defects, and discontinuities in the methacrylate mantle.

Bone Cements↗
PubMed1982

Socket fixation using a metal-backed acetabular component for total hip replacement. A minimum five-year follow-up.

We did a follow-up study on fifty-three total hip-replacement procedures in forty-seven patients in whom a metal-backed acetabular component was used. The minimum follow-up was five years (average, six and one-half years). These relatively young patients ranged in age from seventeen to seventy-six years old (average, forty-one years old). Excluding one septic hip and one traumatic dislocation of the acetabular component, three sockets became loose in the remaining fifty-one hips. The results in thirty-four patients who were forty-five years old or younger were compared with those in a group of patients of similar age, reported by Dorr and Takei, in whom sockets without metal backing were used. Thirteen of the forty-three non-metal-backed sockets in their patients became loose or had a continuous radiolucent line at least two centimeters thick around the entire circumference of the cement on an anteroposterior radiograph, which they referred to as impending failure. In comparison, the three loose acetabular components in our thirty-four patients comprised a statistically significant reduction (p less than 0.05). No acetabular components in our series showed evidence of impending failure. We and others have reported finite-element analyses showing that a metal backing on the acetabular component reduces peak stresses in the bone, cement, and polyethylene. These analytical data are now supported by the clinical data reported here; that is, the metal backing of the acetabular component enhanced the duration of cement fixation.

Acetabulum↗
PubMed1982

Femoral component loosening using contemporary techniques of femoral cement fixation.

A radiographic study was done of 171 total hip replacements that had been followed for an average of 3.3 years (range, two to five years). The study was performed to assess the incidence of loosening of the femoral component in older adult patients (average age, sixty years) in whom the medullary canal had been plugged with methylmethacrylate (using the medullary plug syringe to introduce the plug) prior to introducing the cement (Simplex P) with a cement-gun. Most of the femoral components that were used were of the CAD or HD-2 design, and all were made of chromium-cobalt alloy. Three categories of loosening were defined: definite (requiring radiographic evidence of migration of the component or the cement), probable (requiring evidence of complete 100 per cent radiolucent zone around the cement mantle on one or more radiographs), and possible (requiring evidence of a radiolucent zone that occupied more than 50 but less than 100 per cent of the cement-bone interface on one or more radiographs). One hip required revision for a loose femoral component and another patient had asymptomatic subsidence of the femoral component. Thus, the total incidence of definitely loose femoral components was 1.1 per cent. No hip was classified as having probable loosening; seven hips (4 per cent) were rated as having possible loosening. Compared with the results of four other published reports of patients of similar age with similar follow-up, and using the same radiographic criterion for loosening, the current series demonstrated a statistically significant reduction in the incidence of definitely loose femoral components.

Adult↗