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PubMed2004

Changes in the contact area during the bedding-in wear of different sizes of metal on metal hip prostheses.

In metal on metal hip prostheses, the contact mechanics can influence the lubrication and wear rate. In particular, during the bedding-in wear, the contact area gradually increases to an optimal value, and the wear rate reduces as the contact stress reduces and the lubrication conditions improve. Geometrical designs that reduce the volume of bedding-in wear as the optimal contact area develops are preferable. The objective of this study was to analyse the wear volume as a function of contact area during the bedding-in period, with the aim of identifying geometrical design configurations that give lower bedding-in wear. As the radial clearance was reduced, the bedding-in wear volume to reach an optimal contact area also reduced. For a fixed radial clearance, increasing the head diameter also reduced the bedding-in wear volume.

Computer Simulation↗
PubMed1989

Cause of intraocular lens removal.

To determine the rates of and reasons for removal of intraocular lenses (IOLs) during the first 6 years of implant surgery at Halifax Infirmary Hospital, we reviewed the medical records of all patients who underwent primary cataract extraction with IOL implantation and subsequent removal of the IOL between 1980 and 1985. Among 2482 patients 21 cases of secondary explanation (0.8%) were identified. Of the 21 IOLs 20 were anterior chamber lenses and 1 was a posterior chamber lens. The most frequent causes of IOL removal were suspected bacterial endophthalmitis, excessive lens movement due to poor fit and traumatic dislocation of the lens.

Cataract Extraction↗
PubMed1988

Cementless revisions of failed aseptic cemented and cementless total hip arthroplasties. 284 cases.

Over the past 13 years, 284 revisions of aseptic total hip arthroplasty failures have been performed with cementless implants. There were 213 cases involving cemented implant failures and 71 involving cementless ones. Considered as salvage procedures, these revisions provided a satisfactory result in about 70% of the reviewed patients after five years. A biologic fixation by bony ingrowth can be expected under certain conditions from decorticated living bone, a tight mechanical fitting, and a retentive corrugated surface of the implant. A prosthetic reimplantation, safely done without cement, appears more economical for the bone stock and prevents the long-term complications related with cement. Bone grafts are often required but cannot ensure the incoming osteogenic fixation of the implant. Long-term results and complications mandate harmless extractability of the revisional implant, a forged stem, an easy exchange of the plastic liner (in a two-part acetabular component), and an updated low-friction system (high-density polyethylene wear being a potential long-term problem).

Asepsis↗
PubMed1984

Bioprosthetic heart valve failure: pathology and pathogenesis.

Bioprosthetic heart valves are widely used because of their low risk of thromboembolic complications. The major limitation to the long-term success of these prostheses is caused by degenerative processes leading to late primary valve failure, including calcification. Research into these processes has suggested potential approaches for inhibiting calcification and other degradative phenomena.

Aortic Valve↗
PubMed1993

The response to particulate debris.

The most common cause of failure of total hip and other arthroplasties is aseptic loosening of the prosthesis. Substantial evidence suggests that the adverse tissue response to prosthesis wear particles is an important contributor to bone loss around implants. The results may be an increased risk of loosening and severe bone loss, which makes revision surgery more difficult. Studies in humans have demonstrated that the appearances of the periprosthetic tissues are related to the type, number, and size of wear particles. The appearance and tissue response around any given prosthesis is related to the balance among the rate of production of wear particles, the ability of the tissues to deal with the particles, and the rate of clearance of the particles from the joint. Prosthesis wear particles may be produced by wear at the articulating surface, particularly if there is three-body wear, by abrasion due to movement at the prosthesis-bone interface of uncemented prostheses, by abrasion at the prosthesis-cement and cement-bone interfaces of cemented prostheses, or at any articulation of the components of modular prostheses. Future in vivo and in vitro studies of the effects of wear particles should focus on quantitative measurement of the effects of particles and on the use of particles of comparable size and in concentrations similar to those found in the tissues surrounding failed prostheses.

Animals↗
PubMed1996

Total hip arthroplasty complicated by tuberculous infection.

The case of a 66-year-old woman with tuberculous infection complicating a total hip arthroplasty that had been performed 4 years previously for degenerative arthritis is reported. The patient had no prior history of exposure to tuberculosis and no evidence of skeletal or nonskeletal tuberculous infection. The need for a high index of suspicion when dealing with unexpected arthroplasty failure is emphasized. Tuberculous cultures are recommended in these cases prior to revision surgery.

Aged↗
PubMed1995

Osteonecrosis of the hip in sickle cell hemoglobinopathy.

Osteonecrosis secondary to sickle cell anemia and its genetic variants has many presentations depending on the age of onset and the extent of femoral head involvement. Total hip arthroplasty provides the greatest opportunity for clinical improvement of all treatment options, though early and late complication rates are high. Technical difficulties of total hip arthroplasty are related to marrow hyperplasia and the presence of sclerotic intramedullary bone. Surgical complications related to sickle cell hemoglobinopathy include vaso-occlusive crises, congestive heart failure, major transfusion reactions, intraoperative femoral fracture, femoral perforation, late aseptic loosening of acetabular and femoral components, and sepsis.

Adolescent↗
PubMed1994

Implant failure and the immuno-incompetent fibro-inflammatory zone.

Biomaterial implants are surrounded by an immuno-incompetent, fibro-inflammatory, integration-deficient zone within which stimulation of cellular immune responses results in superoxide radical and cytokine-mediated tissue damage with increased susceptibility to infection or aseptic loosening. Three important questions that pertain to surgical implants are (1) What are the mechanisms that cause abnormal inflammatory responses in the absence of infection and result in interface cellular disorganization and device failure? (2) What causes host defenses to be compromised to the extent that normal flora organisms like Staphylococcus epidermidis, with little or no virulence potential, can cause life-threatening infections at the implant-host interface? (3) What is the nature of surface regions of biomaterials that facilitate bacterial adherence? Pathogenic strains of S. epidermidis and Staphylococcus aureus have an affinity for biomaterial surfaces and are capable of initiating infection. Binding may be nonspecific and glue-like rather than a receptor-ligand event as for S. aureus and matrix proteins. This study indicates bacterial binding to sites of higher vanadium concentration at grain boundaries and mixed phases in titanium alloys. Repeated macrophage priming by biomaterial particulates results in the production of reactive oxygen intermediates, macrophage exhaustion, and adjacent tissue damage. A cytokine cascade is also initiated. A self-perpetuating enlarging immuno-incompetent fibro-inflammatory zone develops about implants, which features tissue cell damage, increased susceptibility to infection, and results in septic or aseptic failure of the implant. These effects are clearly exemplified by fibrosis about breast implants and osteolysis at the interface of total joint replacements.

Bacterial Adhesion↗
PubMed1993

Failure of the porous-coated anatomic prosthesis in total knee arthroplasty due to severe polyethylene wear.

Four hundred and eighty-seven total knee arthroplasties were performed by a single surgeon with use of a porous-coated anatomic prosthesis between 1982 and 1989. There were thirty-two clinical failures (7 per cent) due to severe wear of the surfaces of the tibial and patellar polyethylene components. Thirty patients had a revision. The average time to failure of the implant was four and one-half years. The initial clinical symptoms of failure by wear consisted of a painless effusion with a decreased range of motion. Subsequent pain was considered as the criterion for failure necessitating operative intervention. Increased weight and decreased age of the patient and a thinner tibial component were significant predictors of an increased risk of failure (p < 0.01). Examination of retrieved tibial components revealed extensive delamination caused by fracture of the polyethylene at a depth of about one millimeter below the surface. Cracks that had propagated in from the medial and lateral peripheries of the tibial component toward the center of the condyles were also a common finding. It appears that the design of the implant as well as clinical factors (the age and weight of the patient) contributed to the mechanical failure of the polyethylene of these implants.

Aged↗
PubMed1998

Experience with low-dose aspirin as thromboprophylaxis for the Tissuemed porcine aortic bioprosthesis: a survey of five years' experience.

BACKGROUND AND AIMS OF THE STUDY: In patients in sinus rhythm following aortic valve replacement (AVR) with bioprosthetic valves, aspirin prophylaxis generally keeps bleeding complications to a minimum without increasing the risks of thromboembolic events. To study the efficacy of aspirin prophylaxis in patients receiving the recently introduced Tissuemed porcine bioprosthetic implant in the aortic position we reviewed our database of 145 patients who underwent AVR between 1991 and 1996. METHODS: Mean patient age was 73.5 years (range: 56 to 94 years); 85 were males and 60 females. Preoperatively, 70% of the patients were in NYHA functional class III or IV. Concomitant procedures were performed in 26% of patients. Following AVR, low-dose aspirin prophylaxis (75 mg/day) was commenced in all patients in sinus rhythm. The bioprosthesis was evaluated using standard Society of Thoracic Surgery guidelines. RESULTS: Follow up was 100% complete (total cumulative follow up 253.7 patient-years (pt-yr)). There were three minor thromboembolic episodes, all occurring at least one year after surgery; there were no major thromboembolic complications and bleeding events. Valve-related complication rates (expressed as %/pt-yr and number of events) were thromboembolism 0.7%/yr (three episodes), hemorrhage 0.4%/yr (one) and bacterial endocarditis 0.4%/yr (one). The reoperation rate was 0.4%/yr (one). At five years, actuarial freedom from thromboembolism was 95 +/- 3.6% (SE); hemorrhage 99.2 +/- 0.75%; endocarditis 98.4 +/- 1.5); non-structural valve failure 100%; structural valve dysfunction 100% and reoperation 98.4 +/- 1.5%. The 30-day mortality rate in this elderly population, influenced by clinical status (NYHA class III and IV; p = 0.005), was 9.6% (95% CI, 4.8 to 14.4), with no early valve-related deaths. Patient survival at five years was 78.5 +/- 3.7%. At follow up, 94.8% of the patients were in NYHA functional class I or II. CONCLUSIONS: Early clinical evaluation showed that, following AVR, bleeding complications were minimal with no increase in thromboembolic events in the first three months and on long-term follow up, when low-dose aspirin prophylaxis was started in patients in sinus rhythm. There was overall improvement in patient symptoms while valve-related complications were minimal with no episode of structural deterioration or non-structural failure.

Aged↗
PubMed1993

Microbiology of the dental implant.

Longitudinal studies have shown that successful implants are colonized by a predominantly Gram-positive, facultative flora, which is established shortly after implantation. Repeated microbiological sampling in patients with clinically stable implants showed no significant shifts in the composition of this flora over five years. In patients with bone loss and pocket formation around implants, however, a significantly different flora was found: Gram-negative anaerobic bacteria, particularly fusobacteria, spirochetes, and black-pigmenting organisms such as Prevotella intermedia were often present in high proportions. Antimicrobial treatment with agents specifically active against anaerobes could halt progression of peri-implant infections in such cases. Although there may be non-microbial primary causes for implant failure, these studies show that Gram-negative anaerobes may play a rôle in peri-implant infections, and that their elimination leads to improvement of the clinical condition.

Animals↗
PubMed1994

Modular uncemented prosthetic reconstruction after resection of tumours of the distal femur.

We report the use of the uncemented Kotz modular femur and tibia reconstruction system after 95 distal femoral resections performed from 1983 to 1989. The average follow-up was 51 months; 62 patients had at least 36 months' follow-up and 36 at least 60 months. Complications required reoperation in 55%. The postoperative infection rate was 5% for primary cases, 6% for revision cases, and 43% for revision of previously infected cases. The polyethylene bushes failed in 42% of cases at an average of 64 months postoperatively. Stem breakage occurred in 6% and was associated with the use of narrow stems and extensive quadriceps excision. The radiological results were excellent or good in most cases and were related to the initial screw fixation, but not to age, chemotherapy, length of resection or size of stem. The clinical results were excellent or good in 75%, failure usually being associated with a complication, especially infection.

Adolescent↗
PubMed1998

Late complications of nasal augmentation using silicone implants.

Alloplastic nasal augmentation with silicone elastomer (Silastic) is popular in areas of Asia. Although the silicones are bio-inert, they have been implicated in a number of adverse reactions after implantation. We report our experience of three patients who presented with late complications after nasal augmentation using Silastic implants. The mechanisms of implant failure are proposed. It is advised that this material should only be used on an individual basis in carefully selected cases.

Adult↗
PubMedDate not supplied

Clinical evaluation of mandibular overdentures supported by multiple-bar fabrication: a follow-up study of two implant systems.

A retrospective follow-up study was undertaken to assess the clinical condition, complications, and prosthodontic aftercare of two different implant systems over a long period. Thirty-six patients treated with a total of 135 ITI type F endosseous implants, and 37 patients treated with the transmandibular implants and a total of 146 transmandibular posts, were studied during a mean follow-up period of 70 months and 44 months, respectively. The choice of implant type was mainly influenced by a change in financial support by the National Health Insurance Company in The Netherlands in 1987. Cumulative success rates were calculated using the Kaplan-Meier product limit method. In the analysis, the risk for failure of the implants was adjusted for differences in mandibular bone height. There were no differences between the two treatment groups with regard to age, gender, period of edentulousness, and mandibular bone height. During the follow-up period, plaque, bleeding, and hyperplasia scores demonstrated no significant differences between the two groups. The ITI type F group showed significantly more recession, and the transmandibular implant group demonstrated significantly increased Periotest values. After adjusting for differences in bone height, patients treated with ITI type F implants had a lower risk of failure (relative risk, 0.55; 95% confidence interval 0.32 to 0.95). However, neither of the implant systems fulfilled Albrektsson's criteria of success.

Alveolar Bone Loss↗
PubMed1990

Patterns of failure in the original Besser bipolar prosthesis.

Fourteen original Besser endoprostheses inserted in young patients with osteonecrosis of the femoral head were reviewed. Two cups dislocated early and 1 other required replacement due to acetabular degeneration. Component disassembly occurred in 4 hips, which had exhibited persistently vertical cups. Their stems revealed notching medially and the cups showed gross erosion and failure. The remaining 5 hips were mobile and pain free, but in 3 of these the cups exhibited a persistently vertical orientation and, as such, are predisposed to failure. Only one article reporting early good results using this prosthesis has been published. The failure rate of 50% in this series is disappointing.

Adult↗
PubMedDate not supplied

Options for treatment of persistent aneurysm perfusion after endovascular repair.

Persistent aneurysm perfusion represents failure of endovascular repair. The leak may occur around either end of the prosthesis or through a collateral route. Most cases can be treated by endovascular means. Stents can be rotated, the prosthesis can be lengthened at either end, and collateral pathways can be occluded, all without recourse to open repair. This report describes the management of persistent aneurysm perfusion in five patients from a total experience of 32 cases of endovascular aneurysm repair.

Aneurysm↗