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PubMed1999

Histologic evaluation of a natural permanent percutaneous structure and clinical percutaneous devices.

The longevity of percutaneous devices (PD) is often hampered by exit-site infection. The babyrussa tusk, the only permanent natural percutaneous structure, was histologically studied and the implant-tissue interface of 11 continuous ambulatory peritoneal dialysis (CAPD) catheters that had been implanted in humans was evaluated histologically. Attachment of the epidermis to the tusk surface was observed. All the CAPD catheters showed varying degrees of epidermal downgrowth. These results demonstrate that the epidermis is capable of adhering closely to a percutaneous structure. Regarding the CAPD catheters, no steady state at the epidermis-implant interface was achieved, so the risk of infection still remains.

Adult↗
PubMed1996

High failure rate of soft-interface stem coating for fixation of femoral endoprostheses.

Twenty-five total hip arthroplasties were performed in 25 patients using a femoral stem with a soft-interface coating of Proplast (Vitek, Houston, TX). Follow-up periods for 24 of the hips ranged from 82 to 104 months (median, 96 months). Fourteen (58%) of the hips were judged to be failures, and nine of the failures were revised. The prostheses were thought to have failed because the coating was not strong enough to withstand normal weight-bearing loads. This inner-substance failure of the coating was seen in all revision operations. During these revisions, parts of the coating remained in the shaft as well as on the prosthesis stem. The combination of clinically manifest midthigh pain and radiologic scalloping and/or the pedestal sign seem to justify a strong suspicion of looseness of this type of cementless femoral endoprosthesis.

Adult↗
PubMed2004

Cardiac replacement with a total artificial heart as a bridge to transplantation.

BACKGROUND: The CardioWest Total Artificial Heart orthotopically replaces both native cardiac ventricles and all cardiac valves, thus eliminating problems commonly seen in the bridge to transplantation with left ventricular and biventricular assist devices, such as right heart failure, valvular regurgitation, cardiac arrhythmias, ventricular clots, intraventricular communications, and low blood flows. METHODS: We conducted a nonrandomized, prospective study in five centers with the use of historical controls. The purpose was to assess the safety and efficacy of the CardioWest Total Artificial Heart in transplant-eligible patients at risk for imminent death from irreversible biventricular cardiac failure. The primary end points included the rates of survival to heart transplantation and of survival after transplantation. RESULTS: Eighty-one patients received the artificial-heart device. The rate of survival to transplantation was 79 percent (95 percent confidence interval, 68 to 87 percent). Of the 35 control patients who met the same entry criteria but did not receive the artificial heart, 46 percent survived to transplantation (P<0.001). Overall, the one-year survival rate among the patients who received the artificial heart was 70 percent, as compared with 31 percent among the controls (P<0.001). One-year and five-year survival rates after transplantation among patients who had received a total artificial heart as a bridge to transplantation were 86 and 64 percent. CONCLUSIONS: Implantation of the total artificial heart improved the rate of survival to cardiac transplantation and survival after transplantation. This device prevents death in critically ill patients who have irreversible biventricular failure and are candidates for cardiac transplantation.

Critical Illness↗
PubMed2001

Alarming wear of the first-generation polyethylene liner of the cementless porous-coated Biomet Universal cup: 107 hips followed for mean 6 years.

Wear of the socket liner and resulting osteolysis are the major causes of failure in cementless hip arthroplasties. We report alarming wear of the first-generation polyethylene liner of the cementless porous-coated Biomet Universal cup. Radiographs of 107 primary hip arthroplasties were analyzed retrospectively. The mean follow-up time was 74 (47-91) months. The linear wear of the polyethylene liners was assessed using a modification of the Livermore method. The median linear wear was 1.0 (0-6.2) and the median linear wear rate was 0.17 mm/year. There was a statistically significant difference between the 28 mm and 32 mm femoral head groups both in the volumetric wear and in the volumetric wear rate. The median linear wear was 0.28 mm/year and 0.14 mm/year for the 32 mm and 28 mm heads, respectively. So far, 14 revisions have been performed or have been scheduled because of excessive wear of the polyethylene liner. In regression analysis, the factors related to the wear rate were the 32 mm size of the femoral head and screw fixation of acetabular shell. We found that the cases with calcar rounding were associated with significantly greater wear. Possible reasons for increased wear of the Hexloc liner may be the cylindrical design, thin polyethylene, and poor quality of the polyethylene. Regular clinical and radiographic follow-ups are recommended especially for hips with 32 mm femoral heads or with screw fixation. If progressive wear of the liner is observed, revision must be considered.

Adult↗
PubMed1996

Titanium plate fixation: a review of implant failures.

Titanium plates and screws have become widely used for the fixation of fractures and osteotomies. We began using them in 1992; however, several early hardware failure prompted a retrospective review of the occurrence of this complication. A 2-year time period was reviewed at two institutions with comparison of hardware failure rates using titanium and stainless steel implants. At one institution, 51 fractures or osteotomies of the long bones were fixed by the senior author using titanium implants between July 1992 and July 1994. One hundred one similar cases were treated over the same period by the same surgeon using stainless steel implants. The outcome is known for 48 of the cases performed with titanium and for 80 of the cases performed with stainless steel. There were five postoperative implant failures using titanium and one using stainless steel. Metallurgical analysis of one set of broken implants retrieved during a revision surgery showed no manufacturing defects. At the second institution, 21 titanium and 138 stainless steel platings were performed over 2 years. There were four titanium implant failures in four patients and one stainless steel implant failure. Our experience suggests that these implants should be used with care, particularly in high-demand settings such as nonunion or noncompliance, and that further research needs to be conducted to establish appropriate clinical indications for their usage.

Adolescent↗
PubMed2005

PIV measurements of flow in a centrifugal blood pump: steady flow.

Magnetically suspended left ventricular assist devices have only one moving part, the impeller. The impeller has absolutely no contact with any of the fixed parts, thus greatly reducing the regions of stagnant or high shear stress that surround a mechanical or fluid bearing. Measurements of the mean flow patterns as well as viscous and turbulent stresses were made in a shaft-driven prototype of a magnetically suspended centrifugal blood pump at several constant flow rates (3-9 L/min) using particle image velocimetry (PIV). The chosen range of flow rates is representative of the range over which the pump may operate while implanted. Measurements on a three-dimensional measurement grid within several regions of the pump, including the inlet, blade passage, exit volute, and diffuser are reported. The measurements are used to identify regions of potential blood damage due to high shear stress and/or stagnation of the blood, both of which have been associated with blood damage within artificial heart valves and diaphragm-type pumps. Levels of turbulence intensity and Reynolds stresses that are comparable to those in artificial heart valves are reported. At the design flow rate (6 L/min), the flow is generally well behaved (no recirculation or stagnant flow) and stress levels are below levels that would be expected to contribute to hemolysis or thrombosis. The flow at both high (9 L/min) and low (3 L/min) flow rates introduces anomalies into the flow, such as recirculation, stagnation, and high stress regions. Levels of viscous and Reynolds shear stresses everywhere within the pump are below reported threshold values for damage to red cells over the entire range of flow rates investigated; however, at both high and low flow rate conditions, the flow field may promote activation of the clotting cascade due to regions of elevated shear stress adjacent to separated or stagnant flow.

Algorithms↗
PubMed2005

PIV measurements of flow in a centrifugal blood pump: time-varying flow.

Measurements of the time-varying flow in a centrifugal blood pump operating as a left ventricular assist device (LVAD) are presented. This includes changes in both the pump flow rate as a function of the left ventricle contraction and the interaction of the rotating impeller and fixed exit volute. When operating with a pulsing ventricle, the flow rate through the LVAD varies from 0-11 L/min during each cycle of the heartbeat. Phase-averaged measurements of mean velocity and some turbulence statistics within several regions of the pump, including the inlet, blade passage, exit volute, and diffuser, are reported at 20 phases of the cardiac cycle. The transient flow fields are compared to the constant flow rate condition that was reported previously in order to investigate the transient effects within the pump. It is shown that the quasi-steady assumption is a fair treatment of the time varying flow field in all regions of this representative pump, which greatly simplifies the comprehension and modeling of this flow field. The measurements are further interpreted to identify the effects that the transient nature of the flow field will have on blood damage. Although regions of recirculation and stagnant flow exist at some phases of the cardiac cycle, there is no location where flow is stagnant during the entire heartbeat.

Algorithms↗
PubMed2004

Prediction of scratch resistance of cobalt chromium alloy bearing surface, articulating against ultra-high molecular weight polyethylene, due to third-body wear particles.

The entrapment of abrasive particles within the articulation between a cobalt chromium alloy (CoCrMo) femoral component and an ultra-high molecular weight polyethylene (UHMWPE) cup of artificial hip joints or tibial inserts of artificial knee joints usually scratches the metallic bearing surface and consequently increases the surface roughness. This has been recognized as one of the main causes of excessive polyethylene wear, leading to osteolysis and loosening of the prosthetic components. The purpose of this study was to use the finite element method to investigate the resistance of the cobalt chromium alloy bearing surface to plastic deformation, as a first approximation to causing scratches, due to various entrapped debris such as bone, CoCrMo and ZrO2 (contained in radiopaque polymethyl methacrylate cement). A simple axisymmetric micro contact mechanics model was developed, where a spherical third-body wear particle was indented between the two bearing surfaces, modelled as two solid cylinders of a given diameter, under the contact pressure determined from macro-models representing either hip or knee implants. The deformation of both the wear particle and the bearing surfaces was modelled and was treated as elastic-plastic. The indented peak-to-valley height on the CoCrMo bearing surface from the finite element model was found to be in good agreement with that reported in a previous study when the third-body wear particle was assumed to be rigid. Under the physiological contact pressure experienced in both hip and knee implants, ZrO2 wear particles were found to be fully embedded within the UHMWPE bearing surface, and the maximum von Mises stresses within the CoCrMo bearing surface reached the corresponding yield strength. Consequently, the CoCrMo bearing surface was deformed plastically and the corresponding peak-to-valley height (surface roughness) was found to increase with both the hardness and the size of the wear particle. Even in the case of CoCrMo wear particles, with similar mechanical properties to those of the CoCrMo bearing surface, a significant plastic deformation of the bearing surface was also noted; this highlighted the importance of considering the deformation of the wear particles. These findings support the hypotheses made by clinical studies on the contribution of entrapped debris to increased surface roughness of CoCrMo femoral bearing surfaces.

Compressive Strength↗
PubMed2003

Revision total hip arthroplasty performed after fracture of a ceramic femoral head. A multicenter survivorship study.

BACKGROUND: The alumina ceramic femoral head was introduced for total hip arthroplasty approximately thirty years ago. One of its main drawbacks was the risk of implant fracture. The aim of this study was to examine the results of revision total hip replacement performed specifically to treat a fracture of a ceramic femoral head and to identify technical factors that affected the outcomes. METHODS: One hundred and five surgical revisions to treat a fracture of a ceramic femoral head, performed at thirty-five institutions, were studied. The patients were examined clinically by the operating surgeon at the time of the last follow-up. The surgeon provided the latest follow-up radiographs, which were compared with the immediate postoperative radiographs. The success of the revisions was assessed with Kaplan-Meier survivorship analysis, with the need for repeat revision as the end point. We evaluated the complication rate and radiographic changes indicative of implant loosening. The average duration of follow-up between the index revision and the last clinical and radiographic review was 3.5 years (range, six months to twenty years). RESULTS: Following the revisions, radiographic evidence of cup loosening was seen in twenty-two hips (21%) and radiographic evidence of femoral loosening was seen in twenty-two (21%). One or several repeat revisions were necessary in thirty-three patients (31%) because of infection (four patients), implant loosening (twenty), osteolysis (eight), or fracture of the revision femoral head component (one). The survival rate at five years was 63% (95% confidence interval, 51% to 75%). The survival rate was significantly worse when the cup had not been changed, when the new femoral head was made of stainless steel, when a total synovectomy had not been done, and when the patient was less than fifty years old. CONCLUSIONS: Fracture of a ceramic femoral head component is a rare but potentially serious event. A suitable surgical approach, including total synovectomy, cup exchange, and insertion of a cobalt-chromium or new ceramic femoral ball minimizes the chance of early loosening of the implants and the need for one or more repeat revisions. LEVEL OF EVIDENCE: Therapeutic study, Level IV (case series [no, or historical, control group]).

Adult↗
PubMed2002

Effect of an accelerated aging protocol on viscoelastic properties of UHMWPE.

The values of two viscoelastic properties (storage modulus and loss angle) of four sets of ultra-high-molecular-weight polyethylene specimens were obtained. Two sets comprised specimens that had been sterilized (using gamma radiation in air or ethylene oxide gas) while the other two sets comprised specimens that were sterilized and then exposed to an accelerated aging protocol that, in the literature, has been proposed as simulating 5 years of real-time shelf aging. An analysis of the present results from the four specimen sets and those obtained, in a previous study by the present author, on specimens machined from real-time shelf aged tibial inserts suggests that the claim made for the accelerated aging protocol may be conservative.

Biocompatible Materials↗
PubMed2005

Minimally invasive hip resurfacing.

Metal-on-metal hip resurfacing is an emerging surgical alternative for younger patients who are expected to outlive a conventional total hip replacement implant. Minimally invasive hip resurfacing uses a smaller surgical incision and new techniques to expose the hip joint. Possible advantages include less damage to soft tissue, muscle and bone; smaller scars; less blood loss; and shorter hospital stays and rehabilitation. Possible disadvantages include damage to soft tissue, femur fracture, neurovascular damage, implant malposition and a longer operating time. The lack of published or unpublished trials or case reports makes it impossible to draw conclusions about the relative effectiveness of minimally invasive procedures for hip resurfacing. Developments in computer navigation systems and fluoroscopic imaging may permit more widespread use of minimally invasive hip resurfacing in the future.

Acetabulum↗
PubMed2006

[Dislocations hip arthroplasty].

The authors present analysis of dislocation following hip arthroplasty based on their own clinical material of 1985-2005 year. It contain 2712 cases of total hip arthroplasty, 2171 (80.1%) cases were cemented including 64 (2.4%) cases of revised arthroplasty, 541 (19.9%) cases were cement-free stabilized including 7 (0.2%) cases of revised arthroplasty. Obtained outcomes of analysis permit to make assertion that dislocation following hip arthroplasty occurred during first three month after surgery, more frequently in case of revised arthroplasty and following fractures of femoral neck. Requirement of success is appropriate steady of implant and right done supervision of rehabilitation with learned necessary motoric behaviors.

Arthroplasty, Replacement, Hip↗
PubMed1986

The prosthetic replacement of the cruciate ligament.

In the design of a ligament replacement, the elastic behavior of the ligament as well as the failure strength of the natural ligament should be reproduced. The implantation sites and alignment are very important in order to reduce the mechanical loads on the prosthesis.

Humans↗
PubMed1998

Hydroxyapatite in total hip arthroplasty. Clinical results and critical issues.

Surgeons who perform arthroplasties have posed some critical questions about hydroxyapatite. Does hydroxyapatite coating enhance bone ingrowth or ongrowth? Will hydroxyapatite lead to increased polyethylene wear or an increased incidence of osteolysis? Will the hydroxyapatite coating disappear, and if so, what will be left to maintain implant fixation? A multicenter study of 316 hips (282 patients) with a proximally hydroxyapatite coated stem and either a hydroxyapatite or porous coated cup were followed up 8.1 years (range, 5.6-9.9 years). The average patient age was 50 years (range, 16-81 years), and 61% of the patients were male. One (0.3%) stem, three (2.7%) porous coated cups, and 25 (11.9%) hydroxyapatite coated cups were revised for aseptic loosening. Disappointing results on the acetabular side indicate that substrate design is critical. There were no cases of intramedullary femoral osteolysis, and the incidence of acetabular and proximal femoral osteolysis- and polyethylene wear was no greater than that seen with other cementless or cemented components. Based on these clinical results and a critical review of the literature, it is concluded that hydroxyapatite coated hip components do enhance ingrowth or ongrowth with no increased incidence of osteolysis for as many as 10 years. Concern about the disappearance of the hydroxyapatite coating with time seems moot in light of the above clinical findings.

Adolescent↗