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Aluminum Oxide↗
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Tricuspid bioprosthesis replacement with cryopreserved mitral homograft.
We report the case of replacement of a dysfunctional tricuspid Hancock bioprosthesis by a cryopreserved mitral homograft. Tricuspid bioprosthesis was approached on a beating heart. The mitral homograft was orientated so as the anatomic anterior leaflets corresponding and a semi rigid prosthetic ring was inserted. At 1 year follow-up, the patient's clinical condition and echocardiographic results were satisfactory.
Adult↗
Recanalization of thrombosed dialysis access with use of a rotating mini-pigtail catheter: follow-up study.
PURPOSE: To evaluate the feasibility, efficacy, and safety of mechanical thrombectomy of occluded dialysis access with use of a rotating mini-pigtail catheter. MATERIALS AND METHODS: Thrombus was fragmented by mechanical action of the rotating pigtail tip (5-mm diameter), while the guide wire exited a sidehole at the pigtail curvature and served as a fixed rotation axis. Twenty-six procedures were performed in 22 patients (12 men, 10 women; mean age, 55.5 years). Native fistulas were treated in 15 instances, polytetrafluoroethylene (PTFE) grafts were treated in 11 instances. Average occlusion time was 20 hours +/- 13 (range, 5-46 hours), average occlusion length was 25.6 cm +/- 10.1 (range, 6-45 cm). Thrombus fragmentation was followed by balloon angioplasty of underlying stenoses. RESULTS: In all 26 procedures, the dialysis access was successfully declotted with subsequent dialysis using the access (clinical success rate, 100%). Handling of the mini-pigtail catheter was simple and rapid, regardless of whether a graft or a native fistula was treated. Average duration of the intervention was 118 minutes +/- 30. Mean primary patency was 165 days +/- 167. Primary patency rate was 82% at 30 days, 65% at 3 months, and 47% at 6 months. There was no evidence of complications due to the thrombus fragmentation procedure. CONCLUSION: The results suggest that declotting of occluded dialysis grafts and fistulas with the mini-pigtail catheter is as effective and safe as other more established percutaneous therapies. It may serve as an easy-to-handle, low-budget alternative to current thrombectomy devices.
Adult↗
[Femoral periprosthetic bone remodelling to the proximal femur after implantation of custom made anatomic and standard straight stem hip prostheses].
AIM: As a result of stress shielding bone resorption occurs around straight femoral stems following total hip replacement (THR). The question arises whether this pattern of periprosthetic bone loss is altered with use of custom made anatomic femoral stems. METHOD: DEXA method was used to examine proximal femora of two groups of patients after cementless THR. Data of 16 patients with a standard straight femoral stem and 15 patients with a custom made anatomic stem were acquired at 1 week and 2, 4, 6, 9, 12 and 24 months postoperatively. Periprosthetic bone density was recorded in regions of interest (ROI). RESULTS: Similar pattern of periprosthetic bone changes were seen in femora with straight and anatomic hip stems at 24 months postoperatively. Femoral bone loss, up to 36 % in the calcar ROI, was seen with straight and anatomic stems. CONCLUSION: Custom designed anatomic femoral hip stems were unable to prevent periprosthetic bone resorption. However it is concluded, that implantation of custom made stems in grossly distorted femoral anatomy induces transmission of forces similar to standard femoral stems implanted in normal medullary anatomy.
Absorptiometry, Photon↗
[Radiological appearance of the cementless ALLOCLASSIC SL-stem implanted in very old patients with primary hip osteoarthritis].
AIM: The radiological appearance of the cementless ALLOCLASSIC SL-stem, implanted in patients with primary osteoarthritis of the hip and aged at least 80 years at time of surgery, was investigated. METHOD: 66 hips in 58 patients were analysed. 17 patients (19 hips) died in the interim, 5 patients (5 hips) were not available for follow-up because of health reasons (4) or lack of co-operation (1). 1 stem had to be explanted after a periprosthetic fracture of the femur. Finally, 41 total hip arthroplasties in 35 patients could be analysed after an average of 67.9 months (39.2-93.4). RESULTS: Bone atrophy - especially in the proximal Gruen zones - was frequently found. In contrast, radiolucent lines and osteolyses were rare occurrences. The Harris Hip score was preoperatively on average 33.0 points, at time of follow-up 81.7 points. The survival rate (endpoint aseptic loosening) was 100 % after a mean follow-up of 5.7 years. CONCLUSION: Also in very old patients the implantation of a cementless stem is possible and provides very good results.
Aged↗
[Residual stability of different interbody fusion techniques after pedicle screw loosening].
INTRODUCTION: In spinal surgery, postoperative failure of pedicle screw instrumentation due to loosening of the implant at the bone-screw interface is a clinically relevant problem. While there are numerous biomechanical studies dealing with stability after internal fixation, little is known about the remaining segmental stability after pedicle screw loosening. We hypothesize that, in cases of implant loosening, the remaining stability is dependent on whether the segment received an isolated pedicle screw instrumentation or a 360 degrees instrumentation. METHODS: Motion analysis was performed under static, damage-free, sagittal strain (preload 100 N) on intact (controls) and posterior monosegmental L5/6 destabilized lumbar spines of sheep. Spine preparations underwent a flectional torque. Changes of spinal profile were radiographically documented, digitalized and then evaluated. Primary insertion of the conical pedicle screws was performed with a torque of 1.4 Nm. Pedicle screw loosening was simulated by turning the inserted screw back either 180 degrees or 540 degrees . Specimens instrumented with screws of differing diameters (5.5 mm and 6.7 mm) as well as non-instrumented pedicles were also compared. RESULTS: Independent of the type of instrumentation, we found that a loosening of pedicle screws increased remaining segmental motion. In maximal flexion (20 degrees ) and loosening of pedicle screws by 540 degrees, we found a statistically significant increase of remaining segmental motion with sole pedicle instrumentation (- 3.1 degrees ) in contrast to 360 degrees instrumentation (- 1.6 degrees ). For extension, a significant discrepancy between the two stabilization methods could not be shown. In cases where screws were firmly inserted, there was no advantage of using pedicle screws with an increased diameter of 6.7 mm. Independent of the type of fixation method, 5.5 mm screws that were inserted in widened pedicles showed a marked decrease of primary segmental stability. CONCLUSION: This study suggests that, concerning the remaining stability, 360 degrees instrumentation is superior in cases where pedicle screw loosening has occurred. The screw diameter plays an only subordinate role in primary segmental stability when the pedicle screws are inserted firmly.
Animals↗
Experience with an adjustable pulmonary artery banding device in two cases: initial success--midterm failure.
Retraining of the left ventricle in congenitally corrected TGA or after Senning or Mustard operation is necessary when right-ventricular failure is developing and an arterial switch operation is indicated. As these hearts have little tolerance of marginal overbanding, a long-term adjustable pulmonary artery banding device would lower stress and risk of training. Although the inserted device (Osypka) allowed convenient intraoperative pressure ratio adjustment, mid-term adjustment failed due to dysfunction of the system.
Cardiac Surgical Procedures↗
Early cardiac valve replacement in infective endocarditis: a 10-year experience.
Thirty one patients underwent early valve replacement for infective endocarditis during a 10-year period (between September 1973 and December 1983). Intractable heart failure, persistent infection and systemic emboli were the indications for urgent surgical intervention. Native valve endocarditis had been present in 22 patients (71%) and surgery was performed 14-105 (mean 51) days after the onset of symptoms. Nine patients (29%) had prosthetic valve endocarditis and surgery was performed within 6 to 51 (mean 28) days. The aortic valve was replaced in 22 patients (71%), the mitral valve in 5 patients (16%) and both valves in 4 patients (13%). Four patients (12.9%) died during hospitalization. There were no late deaths or reinfection in this series. The remaining 27 patients were discharged and after a mean follow-up period of 36 months, 25 patients were in NYHA functional class I or II. Only 9 patients (29%) underwent cardiac catheterization prior to surgery and the other patients were operated upon on the basis of echocardiographic data alone. The post-operative results with a survival rate of 87%, justify an aggressive surgical approach in order to prevent serious complications and cardiovascular deterioration. It appears that surgical decision-making can be made on the basis of echocardiography. The risk of cardiac catheterization can be avoided with the newer generation of echocardiographic equipment which allows a detailed and complete analysis of cardiac abnormalities and function.
Adolescent↗
Mechanical effects of stem cement interface characteristics in total hip replacement.
Stem cement debonding is 1 of the most common forms of fixation failure and is thought to be a prelude to gross loosening of a total hip reconstruction. However, the immediate consequences of debonding remains a matter of controversy. The dynamic effects of stem cement debonding in total hip reconstruction were analyzed using 3-dimensional finite element techniques. Stem cement interface conditions were assumed as completely bonded or unbonded, with or without friction. The dynamic effects were accounted for, as presented by the stance and swing phases of the gait cycle. It was found that both cyclic micromotions at the stem cement interface and stresses in the cement mantle were effectively reduced by friction. The friction cases produced failure probabilities of the cement mantle that were relatively close to the one generated by the bonded stem. The probability of mechanical failure of the cement bone interface decreased after debonding and decreased more with reduced stem cement friction. These results show that, although a firm and lasting bond between stem and cement may be desirable for preventing cement failure, the mechanical effects of a debonded stem are less detrimental than were assumed earlier. For straight tapered stem shapes subjected to the loading conditions described, a polished stem may be desirable for the cement bone interface mechanics.
Bone Cements↗
Migration, stem shape, and surface finish in cemented total hip arthroplasty.
In many recent publications it was suggested that the amount of early subsidence of a femoral stem in total hip arthroplasty is indicative for later revision. In this article it is argued that stems can be designed according to alternative objectives, resulting in different shapes and surface roughness, each producing its own characteristic postoperative subsidence pattern. It was investigated whether these inherent subsidence patterns can be estimated in preclinical testing. For that purpose two stems, both without a collar, relying on cement fixation only, were compared regarding their stress transfer, migration, and induced micromotion behavior. Finite element analysis, cyclic bench testing of substitute bone reconstructions, and clinical radiostereophotogrammetric analysis were applied. The stems investigated were the Exeter, which is assumed to be a force closed fixation design, relying on subsidence under load as a method of maintaining stability, and the SHP, as a shape closed fixation design, meant to be contained by the cement mantle. Both designs were true to their design concepts in the analyses, in the sense that migrations and micromotions of the Exeter stems far exceeded those of the SHP stems. It was found that preclinical studies such as finite element analysis or bench tests give reasonable indications of in vivo postoperative behavior. It is concluded that early clinical migration values should be considered relative to stem shape and surface finish, when prediction of later revision probability is the issue.
Aged↗
The counterface, surface smoothness, tolerances, and coatings in total joint prostheses.
Proper counterface material combinations, surface finish, and tolerances of contact surfaces are important issues in minimizing friction, wear, and corrosion of total joint prostheses. In the current study, the potential of novel amorphous diamond coatings to solve some present problems in total joint prostheses was studied by using tribological tests with a hip joint simulator and pin-on-disk testers. Based on the tests, the wear of amorphous diamond is negligible compared with conventional hip joint materials (10,000 to 1,000,000 times lower). The coefficient of friction of diamond-coated artificial hip joint was 0.03 to 0.06 when tested in saline solution with loads from 200 to 1000 kg for as many as two million cycles. The friction remained stable throughout the tests. Methylmethacrylate (bone cement) is a typical source of third body wear particles in cemented total hip replacements. The wear tests showed that bone cement (containing hard ceramic particles of barium sulfate or zirconia) severely scratched cobalt chromium molybdenum alloy samples. These scratches enhance the wear of softer counterpart materials, such as polyethylene or bone cement, whereas diamond-coated surfaces remained undamaged. High quality amorphous diamond coatings offer superior stability (minimal wear debris release in surrounding tissues) and good biomechanical performance.
Acetabulum↗
A modified VSP screw: two-year experience.
A new pedicle screw was designed to address the insertion limitations of the existing VSP and TIMX screws. In the standard VSP insertion technique, the T-handle wrench has an enlarged foot, which contacts the superior facet and interferes with countersinking the fixed nut. The hex of the machine screw may strip in hard bone. The hexagonal design of the fixed nut may make explantation difficult. The evolution of the VSP into the TIMX addresses some of these issues. However, the screw design still has problems. The tapered spacer extends beyond the diameter of the fixed nut and must be applied after the screw is inserted. The flattening of the machine thread requires rotational alignment of the screws before the plate can be inserted. The design does not allow for easy placement of the acorn nut. The modified VSP screw preserves the superior facet, allows for countersinking, permits application of the spacer prior to insertion, and facilitates application of the acorn nut. Rotational alignment of the screw is not required to accommodate the plate. The surgeon can save time and effort inserting and explanting the modified VSP screw.
Bone Screws↗
Polyethylene sterilization and production affects wear in total hip arthroplasties.
Production and package sterilization techniques for the polyethylene used in acetabular components for total hip arthroplasties are known to affect wear. We considered three combinations of techniques: sterilization by radiation in inert gas with isostatically molded polyethylene, in inert gas and ram-extruded polyethylene, and in air with extruded polyethylene. The intent of this study was to confirm that molded polyethylene and polyethylene radiated in inert environments reduce wear rates in vivo, to determine the combination of methods with the least wear, and to determine how much variance in wear is attributable to these methods. We reviewed 150 consecutive total hip arthroplasties done in 133 patients using 28-mm cobalt-chrome femoral heads and polyethylene-lined, titanium, ring-locked acetabular components. The least wear occurred in gamma inert-molded polyethylene components. The mean volumetric wear rates were 52.12 mm3/year for gamma inert-molded, 62.32 mm3/year for gamma inert-extruded, and 66.09 mm3/year for gamma air-extruded polyethylene components. Relative risk assessment found gamma air-extruded and gamma inert-extruded polyethylene components to wear 16% and 11% more than gamma inert-molded polyethylene components, respectively. Gender, body mass index, and age accounted for the greatest amount of the explained variance in volumetric wear (57.5%, 21.6%, and 14.4, respectively), followed by angle of wear (3.4%), and sterilization and production technique (3.2%).
Acetabulum↗
Observation of cavitation in a mechanical heart valve in a total artificial heart.
Recently, cavitation on the surface of mechanical heart valves has been studied as a cause of fractures occurring in implanted mechanical heart valves. The cause of cavitation in mechanical heart valves was investigated using the 25 mm Medtronic Hall valve and the 23 mm Omnicarbon valve. Closing of these valves in the mitral position was simulated in an electrohydraulic totally artificial heart. Tests were conducted under physiologic pressures at heart rates from 60 to 100 beats per minute with cardiac outputs from 4.8 to 7.7 L/min. The disk closing motion was measured by a laser displacement sensor. A high-speed video camera was used to observe the cavitation bubbles in the mechanical heart valves. The maximum closing velocity of the Omnicarbon valve was faster than that of the Medtronic Hall valve. In both valves, the closing velocity of the leaflet, used as the cavitation threshold, was approximately 1.3-1.5 m/s. In the case of the Medtronic Hall valve, cavitation bubbles were generated by the squeeze flow and by the effects of the venturi and the water hammer. With the Omnicarbon valve, the cavitation bubbles were generated by the squeeze flow and the water hammer. The mechanism leading to the development of cavitation bubbles depended on the valve closing velocity and the valve stop geometry. Most of the cavitation bubbles were observed around the valve stop and were generated by the squeeze flow.
Biomechanical Phenomena↗
Recanalization of obstructed cerebrospinal fluid ventricular catheters using ultrasonic cavitation.
OBJECTIVE: Fifty percent of implanted cerebrospinal fluid (CSF) shunts fail within 2 years, primarily because of obstruction of the proximal catheter. Percutaneous techniques to reduce the morbidity of shunt revision are being developed. The authors describe the development of a device that uses ultrasonic cavitation to unblock ventricular catheters. METHODS: In collaboration with Cybersonics, Inc. (Erie, PA), we designed, built, and tested a system that produces low-frequency ultrasound (20-28 kHz). Extensional ultrasonic waves are transmitted along a tapered wire (final diameter, approximately 0.8 mm) to the tip, where cavitation is produced in a highly localized region. An in vitro model of sheep choroid plexus occluding typical ventricular catheters was developed. The device was safety tested in vivo in rat and pig brains by introducing the device into shunt catheters inserted during simulated shunt surgery. A clinical safety trial using the device to attempt to remove blocked and adherent ventricular catheters has commenced. RESULTS: In the sheep choroid plexus model, at least 90% of the occluded holes were unblocked in a few minutes, restoring normal flow. There was no adverse effect of the device within shunt catheters inserted into live animal brains. Four patients have undergone treatment with the device at open CSF shunt surgery without adverse effect, and the device seems effective at unblocking and freeing the occluded catheters. CONCLUSION: Ultrasonic cavitation produced at the end of a fine wire that is introduced percutaneously into a CSF shunt promises to be a useful technique for minimally invasive proximal ventricular CSF shunt catheter revision.
Animals↗
Fatigue testing of a proximal femoral hip component.
The Gothenburg Osseointegrated Titanium (GOT) implant is a novel total hip replacement including a metaphyseal loading proximal femoral component fixed in the retained femoral neck. Endurance testing was performed under conditions analogous to ISO 7206-4: 1989. The cement-free implant is not fixed distally within the intramedullary canal, so distal embedding (as specified in the standard) would have been unrealistic. Instead glass-fibre-reinforced epoxy (GFRE) bushings were used to model reduced bone support mid-length at the medial cortex and distally at the lateral cortex. Such support simulated proximal bone loss, realistically reproducing the effect of osteolysis or fixation failure. Under such conditions the component survived unbroken for 10 million cycles at 3.0 kN peak load.
Compressive Strength↗