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Equipment Failure Analysis↗
PubMed2003

Analysis of contact mechanics in McKee-farrar metal-on-metal hip implants.

Contact mechanics analysis for a typical McKee-Farrar metal-on-metal hip implant was carried out in this study. The finite element method was used to predict the contact area and the contact pressure distribution at the bearing surfaces. The study investigated the effects of the cement and underlying bone, the geometrical parameters such as the radial clearance between the acetabular cup and the femoral head, and the acetabular cup thickness, as well as other geometrical features on the acetabular cup such as lip and studs. For all the cases considered, the predicted contact pressure distribution was found to be significantly different from that based upon the classical Hertz contact theory, with the maximum value being away from the centre of the contact region. The lip on the cup was found to have a negligible effect on the predicted contact pressure distribution. The presence of the studs on the outside of the cup caused a significant increase in the local contact pressure distribution, and a slight decrease in the contact region. Reasonably good agreement of the predicted contact pressure distribution was found between a three-dimensional anatomical model and a simple two-dimensional axisymmetric model. The interfacial boundary condition between the acetabular cup and the underlying cement, modelled as perfectly fixed or perfectly unbonded, had a negligible effect on the predicted contact parameters. For a given radial clearance of 0.079 mm, the decrease in the thickness of the acetabular cup from 4.5 to 1.5 mm resulted in an increase in the contact half angle from 15 degrees to 26 degrees, and a decrease in the maximum contact pressure from 55 to 20 MPa. For a given acetabular cup thickness of 1.5 mm, a decrease in the radial clearance from 0.158 to 0.0395 mm led to an increase in the contact half-angle from 20 degrees to 30 degrees, and a decrease in the maximum contact pressure from 30 to 10 MPa. For zero clearance, although the contact pressure was significantly reduced over most of the contact area, the whole acetabular cup came into contact with the femoral head, leading to stress concentration at the edge of the cup. Design optimization of the geometrical parameters, in terms of the acetabular cup thickness and the radial clearance, is important, not only to minimize the contact stress at the bearing surfaces, but also to avoid equatorial and edge contact.

Acetabulum↗
PubMed2006

Biomechanical, morphological, and histological analysis of early failures in hip resurfacing arthroplasty.

The present revival of hip resurfacing arthroplasty may be related to an increase in early failures owing to the challenging technique of the procedure. Fifty-five retrieved implants were analysed with respect to wear, cement mantle and cement penetration, fracture and head morphology, as well as standard histology. Femoral neck fractures occurred in median after 102 days. The time to failure was shorter for older women. Major deviations from the suggested cement mantle thickness and cement penetration were found. Indications for high trauma during implantation leading to early failure due to weakening of the femoral neck were also observed. Some failures had signs of pseudarthrosis beneath the implant. Four different fracture patterns with different mean survival times were identified. Observed wear was minor with the exception of that due to alignment mistakes (rim loading). The cups were not damaged by the failures. Histological results indicate that avascular necrosis is not necessarily connected with this kind of endoprosthetic surgery. Most of the failures analysed can probably be attributed to the 'learning curve' effect, which is an unsatisfactory situation.

Aged↗
PubMed2004

[Are angle-fixed implants with elastic properties advantageous for the internal fixation of proximal humerus fractures?].

There is a recent interest for the use of angle-fixed plates in the management of proximal humerus fractures. Rigid implants might be associated with an increased risk of cutting-out. In order to analyse the potential beneficial effects of the implant elasticity on fracture fixation, the biomechanical properties of a rigid and an elastic angle-fixed plating system were assessed in an experimental study. An unstable fracture of the surgical neck was created in 8 pairs of human humeri. Specimens were subjected to axial loading and torque. Stiffness, subsidence and load to failure were assessed. The implant with elastic properties was characterized by a lower torsional stiffness and a higher subsidence during axial loading and torque. This implant failed at lower loads than the rigid implant did. Elastic implant properties of angle-fixed plates have shown not to be advantageous for the management of fractures of the proximal humerus.

Bone Plates↗
PubMed1991

Survivorship analysis of total knee arthroplasty. Cumulative rates of survival of 9200 total knee arthroplasties.

From 1971 through 1987, 9200 total knee arthroplasties were performed at the Mayo Clinic. Actuarial analysis was used to estimate cumulative rates of survival. Use of a proportional-hazard, general linear model led to the identification of four independent variables that were associated with a significantly lower risk of failure: primary total knee arthroplasty, a diagnosis of rheumatoid arthritis, an age of sixty years or more, and use of a condylar prosthesis with a metal-backed tibial component. When all four of these favorable variables were present (without regard for radiographic changes and non-disabling symptoms), the probability of an implant being in situ was 97 per cent at both five and ten years.

Aged↗
PubMed1986

Capsular contracture: a prospective study of the effect of local antibacterial agents.

In a prospective, random, double-blind, and concurrently controlled clinical study of 124 patients having augmentation mammaplasty, using multiple independent subjective judges as well as objective compressibility measurements, the use of a variety of local antibacterials in or around inflatable retromammary prosthetic implants reduced the early postoperative onset of class III to IV capsular contracture by sevenfold (85 percent) and the final incidence by more than half (50 percent) (p less than 0.01). We believe this study provides the most unequivocal evidence to date that the cause of capsular contracture in retromammary augmentation is periprosthetic bacterial contamination. Irrigation with a 5 percent povidone-iodine (50 percent Betadine) solution was as effective as other techniques and is currently our procedure of choice.

Administration, Topical↗
PubMedDate not supplied

Clinical evaluation of the HeartPak. A new pneumatic portable driver for use with the HeartMate Implantable Pneumatic Left Ventricular Assist System.

The HeartPak Portable Pneumatic Driver was designed for use with the HeartMate Implantable Pneumatic Left Ventricular Assist Device (IP-LVAS) (Thermo Cardiosystems, Inc., Woburn, MA). The HeartPak measures 48 x 23 x 15 cm, weighs 9.3 kg with batteries, and can be carried by a handle, by a shoulder strap, or on a trolley. Four 12 V batteries provide power for as long as 8 hr. To test the HeartPak in the hospital environment, seven men were studied who were bridge-to-transplant patients (mean age, 59.8 +/- 8.87 years) undergoing HeartMate IP-LVAS therapy. They were supported by the HeartPak for 429 days with a cycle count of 57,826,560. To normalize the mean pump flow rate, we used the body surface area to obtain a pump flow index in each case. The mean flow rate was 2.65 +/- 0.57 L/min/m2 for the HeartPak vs. 2.64 +/- 0.45 L/min/m2 for the HeartMate 1000, the conventional driver previously used in these patients. The only potentially serious problem with the HeartPak was console failure in one case. The patient took appropriate backup measures, and the HeartPak was replaced. In no case did the device cause any adverse effects or interruption of LVAS support. Compared with HeartMate 1000, the HeartPak was more convenient, easier to operate, and allowed better patient mobility.

Adult↗
PubMed1997

[Reoperations on prosthetic heart valves: an analysis of 64 cases].

During the period of Fabruary 1988 to May 1996, 64 reoperations were performed for prosthetic valve malfunction. Degeneration of bioprosthesis occurred in 46 patients, failure of mechanical prosthesis in 9, and periprosthetic leakage without evidence of infection in 9. In accordance with the status of cardiac function, 9 patients with acute dysfunction of mechanical prosthesis received emergency operations, and the remaining 55 patients with bioprosthetic valve failure or periprosthetic leakage received selective operation. There were 8 early deaths with a overall hsopital mortality rate of 12.5%. Three of the deaths occurred among the 55 selective procedures for a mortality of 5.3% and 3 of the deaths occurred among the 9 emergence procedures for mortality of 33.3%. The 56 long-term survivors were followed up from 3 months to 7 years (mean 2.1 years). There were 3 late deaths (5.3%). Forty-eight patients have been living more than 1 year. Their cardiac function after reoperation was class I (42 patients), class II (5), and class III (1). The timing of reoperation and surgical technique were discussed.

Adult↗
PubMed2003

Long-term outcome after aortic endovascular repair: the Buenos Aires experience.

Long-term (5 years) outcome of 30 patients whose aneurysm was excluded using the Parodi endograft (PE) was assessed. Thirty patients with a mean follow-up of 59 months were the basis of the analysis. Additionally, 100 consecutive patients treated with the Vanguard Endograft (VE) were followed up for 28 months (range, 7 to 56 months). Results were analyzed and both groups compared. There were no late failures related to the loss of the integrity of the device in the PE group. Aorto aortic systems showed distal neck dilatation in high proportion of patients (80%). Aorto-uni-iliac endograft was successful in 80% of the patients. Only one late type I endoleak developed in a patient in whom the proximal stent was placed far from the renal arteries and in contact with thrombus. Also, persistent type II endoleaks were the cause of failure. No neck dilatation was noted. In the VE group, most of the failures were device related.

Aged↗
PubMed1992

Prosthodontic claims in the Swedish Patient Insurance Scheme.

The Swedish Patient Insurance Scheme includes a guarantee insurance for prosthetic treatment. Retreatments of failures, up to 2 years after cementation of fixed prosthodontics and 1 year after delivery of removable prosthodontics, are covered by the guarantee insurance scheme. Almost all private practitioners were included in this scheme at the time of the study in 1989. During a specific period all claims were studied at the time of reporting, when annexed radiographs and so forth could be analyzed. One hundred and thirty-six claims were recorded with regard to treatment injury, reasons for remake, latency times from cementation or delivery to diagnosis, and details about the teeth or constructions involved in the claim. The dentist's opinion of the cause of the failure was also recorded. The reports covered treatment injuries, most of them root perforations during preparation for a post. The guarantee claims for single crowns concerned porcelain fractures, loss of retention, and root fractures as the most frequent failures. For fixed partial dentures the failures were recorded as loss of retention, porcelain fractures, tooth or root fractures, and metal framework fractures in that order. The dentist gave information about his/her opinion of the reason for the failure in only 38.5% of the claims. There were, however, no clear findings about the reasons for the failures.

Crowns↗