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Ultrasonically driven tools have been employed extensively in revision hip surgery during the last 2 years at the Nuffield Orthopaedic Centre. In combination with hand revision instruments, the removal of cement, in particular the removal of the distal cement plug, has been made safer. One significant complication that has occurred with this device is reported and advice on its prevention offered.
Medium- and long-term results from cemented total hip arthroplasty (THA) in patients with rheumatoid arthritis (RA) show a higher incidence of infection and aseptic loosening when compared to other diagnoses. Early results using uncemented prostheses are variable. Hydroxyapatite (HA) coatings are thought to improve early osseointegration in uncemented THA. In a prospective, international, multicenter clinical study, 32 RA patients who received 33 uncemented HA-coated prostheses were followed up for a minimum of 5 years. Medium-term clinical results are excellent. No infection or aseptic loosening has been recorded. Excellent osseointegration was observed radiographically. Bone remodeling was consistent with mainly proximal to midstem stress transfer. We conclude that uncemented, proximally HA-coated prostheses are a promising alternative to cemented prostheses for RA patients.
Consecutive series of 90 hips that had had a primary cementless arthroplasty with use of straight collarless stems between January 1988 and September 1992 were reviewed. Twenty-eight hips with Omnifit Normalized Stems (Fit-N) and 45 hips with Omniflex Normalized Stems (Flex-N) without porous coatings were compared clinically and radiographically with 17 hips with Omnifit Microstructured Stems (Fit-M) with porous coating. The average follow-up periods for the 3 stems were 97 months, 73 months, and 93 months. Revision was performed or awaited in 9 cases (32.1%) in the Fit-N group, 18 cases (40.0%) in the Flex-N group, and 1 case (5.8%) in the Fit-M group. The average annual subsidence was 0.62 mm/y, 0.73 mm/y, and 0.17 mm/y. Osteolysis of more than 3 mm occurred in 28.6%, 37.8%, and 23.5%. Fit-N stems and Flex-N stems without porous coatings are not appropriate for cementless total hip arthroplasty.
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Cross-linked polyethylenes are being introduced widely in acetabular cups in hip prostheses as a strategy to reduce the incidence of wear debris-induced osteolysis. It will be many years before substantial clinical data can be collected on the wear of these new materials. Silane cross-linked polyethylene (XLPE) was introduced into clinical practice in a limited series of acetabular cups in 1986 articulating against 22.225-mm alumina ceramic femoral heads and showed reduced wear rates compared with conventionally sterilized (gamma irradiation in air) ultra-high molecular weight polyethylene (UHMWPE). We compared the wear of XLPE manufactured in 1986 with the wear of UHMWPE manufactured in 1986 in nonirradiated and irradiated forms. In the nonirradiated forms, the wear of XLPE was 3 times less than UHWMPE when articulating against smooth counterfaces. The nonirradiated materials did not show signs of oxidation. In the irradiated forms, only UHMWPE showed high levels of oxidation, and this caused a substantial increase in wear. Antioxidants added to XLPE during processing gave resistance to oxidative degradation. When sliding against scratched counterfaces, the wear of UHMWPE increased by a factor of 2 to 3 times. Against the same scratched counterfaces, the wear of XLPE increased dramatically by 30 to 200 times. This difference may be attributed to the reduction in toughness of XLPE. Clinically, XLPE has been articulated against damage-resistant ceramic heads, and this probably has been an important factor in contributing to reduced wear. New cross-linked polyethylenes differ considerably from XLPE. This study indicates that it is prudent to examine the wear of new polyethylenes under a range of conditions that may occur in vivo.
The purpose of this study was to indirectly quantify the effect of patient and component factors on polyethylene wear in patients with bilateral hip arthroplasties. Assuming that both hips experience similar levels of activity, the confounding influence of activity on wear can be removed by comparing wear rates within subjects. We studied temporal wear patterns in 21 patients with bilateral hip arthroplasty with a mean follow-up of 102 months. Each patient had matching acetabular cup and femoral head components implanted in both hips. Regression analyses were used to assess the variation in wear rates between the first and second implanted hips. The r(2) value demonstrated that matched components and patient factors accounted for 61% of the variance in wear rates. The remaining 39% of the variance, which is unaccounted for, indicates that factors other than those related to the components and patient also play a role.
AIM: The purpose of this study was to examine the FDG-PET in respect of its diagnostic valency with regard to septic/aseptic loosening of lower limb prostheses. METHOD: 28 patients with 41 lower limb prostheses were examined by means of FDG-PET to evaluate septic/aseptic loosening of their hip prostheses. Therefore, a differentiated FDG-PET result interpretation subdivided into five categories was developed. The final diagnosis was based on operative findings with following culture and histological outcome. RESULTS: The worked-out categories showed a high agreement to the intraoperative macroscopic and histological results (n = 23 correctly positive, n = 1 false positive, n = 1 correctly negative and n = 3 false negative). CONCLUSION: With a subtly differentiated interpretation (categories I - V) of the qualitative glucose metabolism safe statements can be made regarding septic/aseptic endoprostheses loosening. This was impressively confirmed by the agreement of the FDG results with the histological results.
AIM: The aim of this study was an analysis of the long-term behaviour and implant migration of the Parhofer-Mönch-screw cup seen in patients between 1982 and 1991. METHOD: 92 cups (m : f = 53 : 39, mean age 53 +/- 7 years) were included mainly prospectively. After 118 +/- 45 months all patients were examined clinically and radiologically. Digital migration analysis was performed using the single-film X-ray analysis (Einbildröntgenanalyse, EBRA). RESULTS: 5 patients had died. 32 cups were revised, in 7 patients a loosening of the cup was suspected. The 10-year-survival was 71.4 %. In 53 of 81 analysed cups a migration of more than 1 mm was shown, 28 cups did not migrate. In comparison to these stable implants the survival of migrated cups was significantly inferior. CONCLUSION: The 10-year-survival and the high rate of implant migration document the poor results of the PM cup. In spite of an extraordinary primary stability, the failure of secondary osseointegration represents the main cause of loosening in this type of cup.
QUESTION: Is it possible to reduce the rate of thrombembolic events during total hip arthroplasty (THA) by the intraoperative use of a mechanical device for thrombembolic prophylaxis (A-V Impulse System). METHOD: The efficacy of additional mechanical thrombembolic prophylaxis was investigated in a prospective randomised trial on 104 patients who underwent cementless THA. All patients received low dose heparin. In 52 patients the additional application of the A-V Impulse System was introduced intraoperatively for the next 24 h. A perfusion scintigram of the lung was performed before and 7 days after the operation in both groups to detect embolic patterns. RESULTS: Perfusion deficits typical for thromboembolic events were detected postoperatively in 8 patients (15.4 %) of the controls and 5 patients (9.6 %) of the A-V Impulse System group. CONCLUSIONS: With the perfusion lung scan we saw postoperatively a total of 13 patients (12.5 %, n=104) with an asymptomatic microthromboembolism of the lungs. Hence it is necessary to increase the protection against thromboembolism. Although statistically not significant (p=0.374), there is a tendency that the additional use of the mechanical thrombotic prophylaxis can reduce thromboembolic events in THA. The impact of the intraoperative introduction of the A-V Impulse System is not really clear. However, for a higher velocity of blood flow during the operation it makes sense to start the procedure intraoperatively.
We report a patient with a malfunctioning Lillehei-Kaster aortic valve which presented only as loss of the normal valve click, 7 months after temporary interruption of anticoagulation at the time of abdominal surgery. Loss of a normal prosthetic valve click may be the only sign of prosthetic valve malfunction, and it is a surgical emergency. Patients with prosthetic heart valves, who undergo non-cardiac surgery, should not receive vitamin K1, and anticoagulation should be restarted promptly after surgery with intravenous heparin as well as warfarin.
A case of fatal thrombotic obstruction of aortic, mitral and tricuspid Björk-Shiley prostheses in the same patient is described. This case suggests that when triple valve replacement is required the use of 3 mechanical valves should be avoided.
PURPOSE: The hydrolytic degradation of the implant-cement interface has to be seen as the main reason for aseptic loosening of cemented total hip replacements. Therefore, a new method of conditioning the metallic surface was developed in order to achieve a hydrolytic-resistant bound stability between the implant and bone cement. Preliminary experimental data on test bodies are presented here. METHOD: The metallic surface of 6 pairs of cylindrical test bodies each (CoCr-alloy, circular testing surface with O 6 mm) were conditioned by the method of silicoating/silanisation to gain a covalent coupling with the applied bone cement. In order to examine the initial stability and the hydrolytic resistance of the metal-cement compound, these pairs of surface-conditioned test bodies (SCT) as well as a reference series of surface-unconditioned test bodies (SUT) were immersed for 0, 30, 90, 150 days (d) in moisture environment (physiological saline solution, 37 degrees C) after coupling with bone cement. The adhesive strength of the test bodies-(bone cement-compounds) were determined by tensile tests on an universal testing machine (Typ Z030, Zwick, Ulm) with gimbal suspension. RESULTS: At time 0 d (that was without immersion of the test bodies) the mean maximum tensile bond strength of the SCT-cement-compounds was 39.5 MPa (SD +/- 4.7 MPa) and that of the SUT-cement-compounds 37.1 MPa (SD +/- 7.3 MPa) (p = 0.575). After immersion the tensile bond strength of the SUT-cement-compounds significantly decreased to an average of 13.5 MPa (SD +/- 2.7 MPa) (30 d), 10 MPa (SD +/- 1.7 MPa) (90 d) and 12.3 MPa (SD +/- 1.4 MPa) (150 d) (p < 0.01). In contrast, the SCT-cement-compounds showed a nearly unchanged high mechanical stability with tensile bond strength values of 37.0 MPa (SD +/- 4.9 MPa) after 30 d, 36.1 MPa (SD +/- 5.0 MPa) after 90 d und 30.2 MPa (SD +/- 4.7 MPa) after 150 d (p > 0.01). CONCLUSIONS: With reservation as to further in vitro and in vivo investigations the increased hydrolytic stability of the metal-cement-bound of surface-conditioned CoCr-alloy test bodies promises an improvement of the long-term stability of cement total joint replacements.
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Primary tissue failure of bioprosthetic heart valves refers primarily to calcification of the leaflets of the bioprosthesis. A 75 year old patient underwent reoperation 15 years after mitral valve replacement with a Carpentier-Edwards porcine bioprosthesis. The extracted bioprosthetic valve was found to have one prolapsed leaflet and a small amount of calcification on all three leaflets without tear or perforation. The two commissures suspending the prolapsed leaflet were detached, causing mitral valve regurgitation.
The question whether thin cement mantles around cemented femoral components led to an increased frequency of cracks in the cement was asked. Microscopically, multiple cross sections of eight femurs retrieved at autopsy from clinically successful total hip replacements after prolonged in vivo service containing well fixed Harris Design 2 cemented femoral components were studied. None of the components were loose by radiographic criteria. All were fixed solidly when loaded in vitro in simulated stair climbing and gait, as assessed by high resolution micromotion sensors. The specimens were sectioned transversely at 5-mm increments. The cross sections were examined under a dissecting microscope at x 100. A thin mantle arbitrarily was defined as a mantle of less than 1 mm in thickness. The analysis of the contact radiographs showed that the routine anteroposterior and lateral radiographs underestimated the prevalence of thin cement mantles and mantle defects. Although overall on all the cross sections 9% of the aggregated cement mantles was classified as having thin cement, 92 of the 101 cement cracks occurred in areas of the mantles that were less than 1 mm thick.
A multicenter retrieval analysis of 231 modular hip implants was done to investigate the effects of material combination, metallurgic condition, flexural rigidity, head and neck moment arm, neck length, and implantation time on corrosion and fretting of modular taper surfaces. Scores for corrosion and fretting were assigned to medial, lateral, anterior, and posterior quadrants of the necks, and proximal and distal regions of the heads. Neck and head corrosion and fretting scores were found to be significantly higher for mixed alloy versus similar alloy couples. Moderate to severe corrosion was observed in 28% of the heads of similar alloy couples and 42% of the heads of mixed alloy couples. Differences in corrosion scores were observed between components made from the same base alloy, but of different metallurgic conditions. Corrosion and fretting scores tended to be higher for heads than necks. Implantation time and flexural rigidity of the neck were predictors of head and neck corrosion and head fretting. The results of this study suggest that in vivo corrosion of modular hip taper interfaces is attributable to a mechanically-assisted crevice corrosion process. Larger diameter necks will increase neck stiffness and may reduce fretting and subsequent corrosion of the taper interface regardless of the alloy used. Increasing neck diameter must be balanced, however, with the resulting loss of range of motion and joint stability.
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Fifty-five retrieved tibial inserts with four different locking mechanisms were evaluated for evidence for polyethylene wear between the inferior surface of the tibial insert and metal tray. This type of wear will be referred to as backside wear. Backside wear was assessed by evaluating manufacturer's stamped markings on the inferior polyethylene surface. Because these markings are embossed into the polyethylene surface, they were used as indicators of backside wear. Decreases in the depths of markings indicated that backside wear was clearly evident, regardless of design, in 24 (44%) of the inserts. In eight of these 24 inserts, the manufacturer's stamped markings were removed completely. The amount of polyethylene wear was as a high as 591 mg from the inferior surface. This corresponds to a polyethylene wear rate from the backside of the tibial insert of greater than 100 mg per year, which is two to four times higher than wear rates associated with total hip replacements. The current work provides direct evidence of backside wear in all four tibial insert designs. Backside wear of tibial inserts can be a significant contributor to polyethylene wear in total knee arthroplasty. Close attention should be given to the fixation of tibial inserts to metal trays by manufacturers and surgeons.