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PubMed2003

A removal torque of the laser-treated titanium implants in rabbit tibia.

The purpose of the present study is to evaluate the significance of different surface textures by comparison of the removal forces for laser-treated and machined titanium screw 8 weeks after the installation in rabbit tibia. A total of 14 screw shaped, commercially pure titanium implants with a length of 5 mm, a diameter of 3.75 mm were grouped as follows: Group A: seven implants left as-machined; Group B: seven implants treated with laser method (CSM implant, CSM company, Daegu, Korea) Topographic evaluation was performed with scanning electron microscope (Hitachi S-4200, Japan) to compare the surface structure of laser-treated and machined ones. Installation procedures were done according to Branemark protocol after pre-threading, machined implants were inserted in right tibia metaphysics and laser-treated surface implants were inserted in left ones. Eight weeks post surgically seven rabbits were sacrificed. The implant sites were exposed, and the bone and soft tissues that had formed on top of the implants were carefully removed. Subsequently, the force needed to unscrew the implants (n=14) was measured using a digital torque gauge (Mark-10 corporation, USA). Scanning electron micrographs of the laser-treated and machined control groups demonstrated created a deep and regular honey-comb pattern with small pore, while machined treatment created the typical microscopically grooved and relatively smooth surface characteristic. Eight weeks after implant placement, the average removal torque was 23.58+/-3.71 N cm for the machined implants, 62.57+/-10.44 N cm for the laser-treated implants. The torque measurements yielded statistically significant differences between the machined group and the laser-etched group (p=0.00055) (Wilcoxon's signed-rank test). The laser-treated group achieved higher removal torque values compared to the machined control group.

Animals↗
PubMedDate not supplied

[Migration analysis of cemented Müller polyethylene acetabular cups versus cement-free Zweymüller screw-attached acetabular cups].

OBJECTIVE: Is the cementless Zweymüller hip cup superior to the cemented Müller cup? METHOD: This article presents a radiographic analysis of 25 cemented Müller acetabular cups versus 22 cementless Zweymüller cups using the Einbildröntgenanalyse (EBRA), a software tool for radiographic measurement of acetabular cup migration. In addition, we determined the effects of the cup anteversion and inclination, the polyethylene wear, the lateral bone coverage of the acetabular cup, the position of the center of rotation, and individual factors on the incidence of cup migration. RESULTS: The incidence of cup migration was 64% in the cementless group and 48% in the cemented group after a mean follow-up of 6 years. The average migration rate was 0.33 mm/a for cementless Zweymüller cups and 0.38 mm/a for cemented Müller cups. Cup anteversion and inclination showed no effect on the incidence of cup migration. The combination metal-polyethylene (0.17 mm per year) demonstrated a significantly higher wear rate in comparison to the ceramic-polyethylene combination (0.11 mm per year). Incompletely lateral covered cups demonstrated a significantly higher incidence of cup migration. Cranial or medial deviations of the center of rotation up to 5 mm are tolerable, in contrast to caudal or lateral deviations that lead to a significantly higher incidence of cup migration. CONCLUSION: The superiority of the cementless Zweymüller cup was not observed. We recommend a complete lateral bone coverage of the hip cup. Cranial and medial deviations of the center of rotation up to 5 mm are tolerable. In the present study the polyethylene wear of the ceramic-polyethylene combination was significantly less as compared with the metal-polyethylene combination.

Acetabulum↗
PubMed1998

Capsular calcification associated with silicone breast implants: incidence, determinants, and characterization.

Capsular calcification was present clinically in 64 of 404 silicone gel breast implant capsules (15.8%) analyzed from 1981 to 1996. It presented as white-gray plaques on the inner surface of capsules in 62 of 64 capsules, and as massive heterotopic ossification in 2 capsules. Chi-squared analysis confirmed that calcification was related to the generation of the implant (i.e., year of manufacture; p < 0.001). All 28 first-generation implants (1963-1972, with Dacron patches) were clinically intact and all demonstrated extensive calcification. Their mean duration in situ was 17.6 years (range, 14-28 years). Thirty-four of the 348 second-generation implants (9.8%; 1973-1987) were associated with capsular calcification. Their mean duration in situ was 16.0 years (range, 13-22 years). Because all first-generation implants demonstrated calcification, they were compared with the second-generation implants that had been in place for the same duration (>14 years). Only 42% of these 81 second-generation implants demonstrated calcification, compared with 100% of the first-generation implants (p < 0.001). Thus, thicker first-generation implants with Dacron patches are more likely to calcify and the effect is not entirely due to their longevity. None of the 28 third-generation implants (1987-1991) demonstrated calcification. Their mean duration in situ was 4.2 years (range, 2-7 years). For second-generation implants, calcification was related to duration in situ (p < 0.001). None of the 294 implants in place for less than 11 years were associated with significant clinical calcification. The percentages of capsules with calcification were 13 to 14 years, 33%; 15 to 16 years, 45%; and 17 to 22 years, 57%. Calcification with second-generation implants was not associated with patches on the envelopes. Of the 34 second-generation implants with calcification, only two had patches (composed of silicone, not Dacron). Among second-generation implants, calcification was related to implant integrity. Of implants in place for more than 12 years, 52.5% of those implants that were ruptured showed calcification, but only 10.0% of intact implants demonstrated calcification (p < 0.001). Seventeen of the 64 calcified capsules were examined histologically. In all of these specimens, calcification existed in two forms: globular aggregates on the surface of the capsule (adjacent to the implant) and actual bone formation within the fibrous tissue of the capsule. All calcified capsules demonstrated both globular aggregates and true bone formation regardless of the implant generation, duration in situ, or integrity. Ultrastructural analysis was performed on four capsules from 2 women who had received first-generation Dow Corning gel implants 24 and 28 years previously, and on 2 capsules from one woman who had received Heyer-Schulte gel implants 21 years previously. These capsules were analyzed according to distribution, density, mineral nature, crystal phases, and elements within crystals by electron microscopy, energy-dispersive X-ray spectrometry, and electron diffraction. These analyses confirmed two types of calcification, each with hydroxyapatite crystals. In areas of heterotopic bone, crystals 40 x 10 nm were deposited in an orderly fashion on collagen fibers. In contrast, in areas of globular aggregates, spherulitic aggregates of much larger crystals were present, without any relationship to the collagen. Titanium was demonstrated in capsules of first-generation implants at areas of attachment of the Dacron patches. The calcification associated with saline implants revealed only one form of crystal: agglomerates, which were adherent to the elastomeric shell of the implants. A hypothesis is presented to explain the differences in calcification deposition properties between silicone gel-filled and saline-filled breast implants.

Adult↗
PubMedDate not supplied

Pseudointima in inflow and outflow conduits of a left ventricular assist system: possible role in clinical outcome.

Activation of blood coagulation and thromboemboli have been shown to present significant clinical risks in patients supported with an left ventricular assist system (LVAS). The interaction of pseudointima (PI) with blood in the conduits of the device could be involved in these clinical complications. Our aim was to study the morphology of the PI versus duration of circulatory support. Novacor N 100 PC LVASs were explanted from 10 men and 2 women after a mean of 209 days (range 23-560 days) of circulatory assistance. PI in the inflow and outflow conduits were investigated with immunohistochemical assays. In the inflow conduits, a loosely adherent PI had built up from collagen type I and III fibers growing into and between fibrin deposits. Disorganized collagenous matrix and longitudinally oriented collagen fibers included alpha-smooth muscle actin positive cells with random orientation. Macrophages were concentrated in the fibrin and were dispersed throughout the extracellular matrix. In the outflow conduits, a thin, adherent PI was composed of regular collagen type I and III layers. Collagen type I fibers had grown into the woven Dacron and alpha-smooth muscle actin positive cells were oriented in the axis of the blood flow. Macrophages were concentrated in the Dacron and reached the inner collagen layers. Venous blood flow in the inflow conduits allows the development of a non endothelialized irregular collagenous matrix intermingled with fibrin and invaded by macrophages. These persistent structural features progress with duration of circulatory assistance and reflect matrix degradation and remodeling. The potential to release thromboembolic fragments from the non stable, thrombogenic PI may be involved in the thromboembolic or neurologic complications sustained by 5 of 12 patients who were on circulatory support for as long as 200 days.

Actins↗
PubMedDate not supplied

Implantable left ventricular assist devices.

The first bridge to transplant with a left ventricular assist device (LVAD) was preformed over 20 years ago. Since that time, the devices have continued to evolve and now patients are being supported with devices as an alternative to transplantation. The primary indication of end-stage heart failure remains the same but increased knowledge about patient selection, the timing of implant, and patient management have contributed to improved outcomes with decreasing adverse events. Multiorgan failure, right ventricular failure, bleeding, infection, thromboembolism, and device malfunction continue to be the most serious threats to long-term survival in these patients. Despite that, patients who do well are now able to be discharged from the hospital and resume relatively normal lives with the devices. The article reviews 3 of the most widely used LVADs for bridge to transplant therapy: the Thoratec; HeartMate vented electric; and the Novacor Left Ventricular Assist System. Indications, mechanism of operation, clinical problems, and out-of-hospital preparation are outlined.

Cost-Benefit Analysis↗
PubMed2003

Migration of metal-on-metal versus ceramic-on-polyethylene hip prostheses.

In a prospective randomized study, 32 metal-on-metal prostheses and 29 ceramic-on-polyethylene prostheses of similar design were implanted in 59 patients. Radiolucency, cup migration, wear, and function were examined after a minimum of 2 years followup (followup rate, 87%). The purpose of the current study was to evaluate whether higher frictional torque of metal-on-metal will lead to a higher rate of early metal-on-metal cup loosening. A computer-assisted method was used for wear and migration measurements of the acetabular component. Metal-on-metal prostheses migrated in a craniocaudad direction significantly less than ceramic-on-polyethylene prostheses. The mean total migration for both types of prostheses exceeded 1.5 mm at 2 years. Clinically, no difference between the two prostheses regarding activity, pain, or range of motion was found at 2 years. As migration of metal-on-metal prostheses was not higher in comparison with ceramic-on-polyethylene prostheses, the expected higher frictional torque of metal-on-metal prostheses did not increase migration during short-term followup. The different debris produced by both bearings did not influence the short-term results of this study, but might cause different long-term results.

Aged↗
PubMed2005

Surgical approach influences periprosthetic femoral bone density.

Our hypothesis was that the bone mineral density of the proximal femur is altered significantly by surgical approach. The change in long-term periprosthetic bone mineral density in relation to the alteration of the musculature after the anterolateral (Group A) and transgluteal approaches (Group B) has been compared. There were 35 hips (30 patients) in Group A and 47 hips (37 patients) in Group B. No significant differences were seen between groups with respect to age, gender, diaphyseal bone mineral density distribution, or average stem size in a Wilcoxon-Mann-Whitney test. Measurement of bone mineral density in femoral Gruen zones revealed a significant bone loss in Group B compared with Group A in the multivariate analysis, which was confirmed by univariate post hoc tests in Zones I, II, VI, and VII (multiple significance according to Bonferroni-Holm's procedure). The functional outcome, however, showed no significant differences between the two groups postoperatively. A potential reason for the bone mineral density shift might have been a redistribution of the musculoskeletal loading across the hip after a transgluteal, compared with an anterolateral, surgical approach. A difference in the muscular damage caused by the two surgical approaches seems to have a significant influence on the long-term bone loss.

Adult↗
PubMed2004

The pros and cons of polyethylene sterilization with gamma irradiation.

This retrospective study evaluated the implant, patient and surgical factors associated with polyethylene wear for one type of porous-coated hemispheric total hip arthroplasty cup. Radiographic wear measurements among 567 Duraloc cups (512 patients) revealed that liners sterilized by gamma-irradiation wore 0.085 mm/year less than those that were sterilized by gas-plasma, a noncross-linking chemical surface treatment. The substantially decreased wear rate associated with gamma-irradiation was attributed to sterilization-induced polyethylene cross-linking. Shelf-aging adversely affected liners that were gamma irradiated in air. On average, highly crystalline Hylamer liners showed a 0.064 mm/year increase in wear rates for each year of shelf storage after terminal sterilization with gamma-irradiation in air. Among conventional Enduron liners, the effect of shelf aging after gamma-irradiation in air was more modest, increasing wear rates by 0.014 mm/year for each year of shelf storage. Because Hylamer's wear performance degraded at about five times the rate of Enduron's, the improved wear resistance associated with gamma-irradiation in air would be lost after 1.3 years of shelf aging for Hylamer compared with 6.1 years for Enduron. For every additional year of age at the time of surgery, the wear rate decreased by 0.003 mm/year. Increased body mass index, a preoperative diagnosis of inflammatory arthritis, and a ceramic femoral head also were associated with decreased wear rates.

Aged↗
PubMed2005

Latent period best predicts acetabular cup failure after total hip arthroplasties in radiated hips.

UNLABELLED: We retrospectively analyzed the prognostic factors related to the failure of acetabular components after total hip arthroplasties in radiated hips. Eighteen hips from 12 patients who had primary arthroplasties were followed up for a mean of 58 months (range, 20-139 months). The patients' age, total radiation dose, latent period, presence of infection, and the type of the acetabular component were examined as possible predictors of failure using the Cox proportional hazard regression. Multivariate analyses showed that a longer latent period was the most important risk factor for failure, increasing 1.72 times when the latent period was greater than 1 year, after adjusting for other predictors. The latent period might be helpful for clinicians in choosing a treatment method for patients. LEVEL OF EVIDENCE: Prognostic study, Level IV (case series). See the Guidelines for Authors for a complete description of levels of evidence.

Acetabulum↗
PubMed2006

Determination of minimum required halo pin force.

The motivation for this study is to provide design guidance for a new halo system that minimizes pin loosening. If halo pin loosening can be substantially decreased with a new halo system, then the current standard of care of overtightening halo pins will not be necessary. Accordingly, there is a need to determine the halo pin force that should be applied to ensure adequate fixation. A biomechanical test was performed using cadaver head constructs, a custom halo fixture, and a tensile testing machine in an attempt to determine the relationship between the force required to dislodge a halo ring and the initial halo pin force. Three cadaver head constructs were tested at initial pin forces of 120, 240, and 360 N. For each test, the halo was pulled from a cadaver head with a displacement rate of 2.5 mm/min until the halo ring disengaged from the head. The vertical force that caused disengagement of the halo from the head was determined from the resulting load-displacement curves. A linear regression of the data predicts disengagement forces of 80, 320, and 570 N, respectively, for initial pin forces of 120, 240, and 360 N. The 95% prediction interval of disengagement forces for initial pin forces of 120, 240, and 360 N were +/-130, 120, and 130 N, respectively. A previously published study reported the maximum vertical load on a halo orthosis during patient usage to be 186 N. The lower 95% prediction interval from this study indicates that an average initial pin force of 230 N is necessary to prevent halo pin disengagement from a 186-N vertical load.

Adult↗
PubMed2006

Prevalence of rupture in inamed silicone breast implants.

BACKGROUND: Silicone breast implants have been used for decades and are arguably the most studied implantable device. However, the vast body of scientific literature has been unable to establish a definitive rupture rate. Various studies have evaluated implant rupture, but the meaningfulness of these data was confounded by the inclusion of different generations of implants and multiple manufacturers' implants and the selection of subjects who were already suspected of having ruptured implants. The authors' study was designed to acquire long-term rupture data specific to Inamed's third-generation silicone breast implants using magnetic resonance imaging technology. METHODS: A total of 106 women with at least one Inamed silicone breast implant (styles 40, 110, and 120) were enrolled in this multicenter, cross-sectional study. The majority received implants for cosmetic augmentation (n = 77, 72.6 percent), with a smaller number having undergone breast reconstruction (n = 11, 10.4 percent) or revision of previous breast implant operations (n = 18, 17.0 percent). Most subjects were Caucasian (n = 99, 93.4 percent) with a median age at implantation of 34 years (range, 18 to 70 years). Enrolled subjects underwent a physical examination and magnetic resonance imaging screening at one of five sites to determine the prevalence of asymptomatic rupture. RESULTS: A total of 199 implants were evaluated, with a median implantation time of 10.9 years (range, 9.5 to 13.2 years). Overall, 183 implants (92.0 percent) showed no evidence of rupture, 12 (6.0 percent) showed evidence of rupture, and four (2.0 percent) were indeterminate. All indeterminate evaluations were considered ruptures, providing a worst-case rupture prevalence of 8.0 percent. CONCLUSION: The study results establish a rupture prevalence rate of 8.0 percent at 11 years for Inamed's silicone breast implants.

Adolescent↗
PubMed2006

Mechanical failure in intramedullary interlocking nails.

PURPOSE: To study clinical and mechanical factors that predispose to failure of interlocking nails. METHODS: Between October 1996 and December 2002, 286 femoral fractures, 211 tibial fractures, and 47 humeral fractures were repaired using variously designed interlocking nails. Fracture pattern, level and site, nail size and type, weight bearing after nailing, and union status were reviewed after a mean follow-up of 22 months. RESULTS: Nail failure occurred in 27 fracture repairs (17 femoral, 9 tibial, and one humeral; 13 from our institution and 14 referred from elsewhere). In 55% of failed repairs, the fracture was distal. A high rate of tibial nail failure was noted. CONCLUSION: Distal fractures and stress concentration at the distal screws predispose to interlocking nail failure and can be prevented by protected weight bearing combined with the use of longer and larger nails. Routine supplementary cancellous bone grafting is unnecessary during renailing surgery when adequate reaming and a larger nail are used.

Adolescent↗
PubMed2003

A different fixation of the femoral component in total knee arthroplasty may lead to preservation of femoral bone stock.

Good femoral bone stock is important for the stability of the femoral component in revision knee arthroplasty. However, the primary total knee replacement (TKR) may cause significant loss of bone stock in the distal anterior femur. Earlier stress-induced bone remodelling simulations have suggested that a completely debonded component may save bone stock in the distal anterior region. However, these simulations did not consider the fixation of a debonded implant and possible secondary effects of micromotions and osteolysis at the interface. The current study tries to combine the preservation of bone stock with adequate component fixation. Different bone remodelling simulations were performed around femoral knee components with different sizes of bonding area and different friction characteristics of the debonded area. The fixation of the femoral component with different bonding characteristics is quantified with calculated implant-bone interface stresses. The results show that a bonded femoral component with a debonded inner side of the anterior flange may significantly reduce bone resorption in the endangered distal anterior femur, without jeopardizing the fixation of the femoral implant. This effect may be obtained in vivo by using a femoral component with a highly polished inner side of the anterior flange.

Arthroplasty, Replacement, Knee↗
PubMed2006

Finite element analysis of the long-term fixation strength of cemented ceramic cups.

Clinical studies have shown that adequate fixation of ceramic cups using bone cement is difficult to achieve. As the cement-ceramic bond strength is low, a satisfactory fixation strength requires a cup design that allows mechanical interlocking, although such a design will probably promote cement cracking and therefore cup loosening in the long term. An investigation has been carried out to establish whether a cemented ceramic cup can be designed in such a way that both a satisfactory initial fixation strength is obtained and cement cracking is reduced to levels found around PE cups functioning well in vivo. By means of finite element analysis, the fatigue loading of three geometrically different cemented acetabular cups, with ceramic and PE material properties, has been simulated, and the severity of the crack patterns produced in the cement has been analysed. Furthermore, the fixation strength has been analysed by simulating a pull-out test prior to and after fatigue testing. All ceramic cups produced much larger amounts of cement damage during fatigue testing than any PE cup, caused by stress concentrations in the cement that were attributable to the high stiffness of the ceramic. Even a completely smooth ceramic cup produced more damage than a sharp-grooved PE cup. Owing to the excessive cement cracking, the fixation strength of the ceramic cups dropped after fatigue loading. It is concluded that cemented ceramic cups have an increased risk of long-term mechanical failure by comparison with PE cups, and that a ceramic cup design that combines sufficient fixation strength with low cement failure may be difficult to achieve.

Acetabulum↗
PubMed2005

Backside wear of polyethylene tibial inserts: mechanism and magnitude of material loss.

BACKGROUND: Wear of the underside of modular tibial inserts (backside wear) in total knee replacements has been reported by several authors. Although, for some implant designs, this phenomenon seems to contribute to osteolysis, the actual volume of material lost through wear of the backside surface has not been quantified. This study describes the results of computerized measurements of tibial inserts of one design known to be associated with a high prevalence of backside wear in situ. METHODS: A series of retrieved total knee components of one design were examined. The duration of implantation of the retrieved components ranged from thirty-six to 146 months. Laser surface profilometry and computer-aided design software were used to develop individual three-dimensional models of each worn, retrieved tibial insert to compare with scanned unused inserts. Volumetric subtraction of both models revealed the material lost because of backside wear. RESULTS: Worn and unworn areas on the backside surface were easily identified by stereomicroscopy and laser profilometry. The computer reconstructions showed that, in all retrievals, all unworn surfaces on the nonarticulating surface lay in one plane. The average volume (and standard deviation) of the material lost because of backside wear was 925 +/- 637 mm(3) (range, 197 to 2720 mm(3)). On the basis of the time in situ for each implant, the average volumetric wear rate was 138 +/- 95 mm(3)/yr. CONCLUSIONS: The predicted volume of material removed because of backside wear is substantial and may be sufficient to induce osteolysis. Our results suggest that peg-like protrusions are not generated by the extrusion of polyethylene into screw-holes within the base-plate but by abrasion of the underside of the bearing insert, leaving the protruding pegs as the only remnants of the original surface.

Aged↗
PubMed1999

Reconstruction plates to bridge mandibular defects: a clinical and experimental investigation in biomechanical aspects.

A retrospective study of 68 patients was carried out to assess the complications arising from the use of reconstruction plates in the maintainance of space and contour following mandibular segmental resection. Skin or mucosal perforation, plate fracture and loss of screw retention were the main complications. The most susceptible sites to screw loosening in the plates were situated nearest to and farthest from the resection margin on the proximal residual segments. Some of the possible causative biomechanical mechanisms of plate failure were studied using photoelastic models simulating the types of mandibular defect and plate fixation. Isochromatic fringe analysis was used to analyse stress lines in the bone surrounding screws. It was found that, during functional loading, moment and shear forces produced high concentrations of squeeze and press stress in this bone, causing bone resorption with consequent loss of screw retention.

Birefringence↗
PubMed2004

Geometric element analysis of fretting in a model of a modular femoral component of a hip implant.

The study utilized the geometric element analysis method to investigate the effect of three variables (head diameter, d; head material; and neck material) on the y-direction displacement, due to fretting (delta), in a model of the head-neck connection in a modular version of the femoral component of a hip implant, subjected to a resultant hip joint force only. It was found that while d and neck material exerted a strong effect on delta, the head material had practically no such effect. The implications of this finding for design and materials selection issues for this connection are discussed.

Computer Simulation↗