In a randomised study, 28 patients with a mean age of 62.2 years (32 to 81) with osteoarthritis or avascular necrosis of the hip received either a ceramic-on-ceramic or a metal-on-metal total hip replacement. Apart from the liners the acetabular and femoral components were made of Ti-Al-Nb alloy. The serum aluminium and cobalt levels were measured before, and at one year after surgery. The 15 patients in the ceramic-on-ceramic group had a median pre-operative aluminium level of 1.3 microg/l (0.25 to 8.4) and a cobalt level below the detection limit. At one year the aluminium level was 1.1 microg/l (0.25 to 2.3) and the cobalt level was 0.4 microg/l (0.15 to 0.7). The 13 patients in the metal-on-metal group had a median pre-operative aluminium level of 1.9 microg/l (0.25 to 4.4) and a cobalt level below the detection limit. At one year the median aluminium level was 0.9 microg/l (0.25 to 3.9) whereas the cobalt level was 1.4 microg/l (0.5 to 10.5). This increase in the cobalt level at one year was significant (p < 0.001). Our findings indicate that ceramic-on-ceramic bearings do not cause elevated levels of serum aluminium in the first post-operative year.
For the realization of efficient production processes, an understanding of the appropriate application of metal working fluids (MWF) is necessary. In addition to knowledge about the process-related aspect of chip transport and the macroscopic cooling effect, the characteristics and properties of the lubrication film thickness and the cooling conditions in the area of the secondary shear zone on the chip surface, i.e. in the direct vicinity of the material separation, represent a fundamental scientific issue within production technology. In particular, these areas generate a high proportion of heat during machining, so that the local friction phenomena have a significant influence on the resulting edge zone of the produced component and the thermomechanical load on the tool. Currently, there are no numerical models and methods for mapping and predicting the lubrication film thickness that can be used in the sense of a targeted design of the cooling lubricant supply. The aim is to transfer the methods from the field of tribology of machine elements, which have already led to significant knowledge gains in this discipline, to machining and couple them to approaches already established in machining. To this end, experiments on tribometers have been performed as a first step. For example, an oscillating pin-on-plate tribometer was used. In this setup, a steel plate is doing oscillating motion against a fixed ball (diameter of 6 mm) under a defined load. The frictional force is recorded during the test. A MWF in a heated tank is used for the lubricant. Additional investigations on the film thickness were performed on an optical EHL (elasto-hydrodynamic lubrication) tribometer. In this setup, a ball rolls on a glass-disc and the resulting film thickness is measured by interferometry.For comparison, the influence of the MWF on the chip formation process in metal cutting was investigated on a special test rig (machine tool). This test rig allows high speed imaging and force measurements of an orthogonal cutting process while using MWFs. The first results show a reduced contact length between chip and tool as well as lower process forces for processes with MWFs compared to dry cutting processes. In future investigations, this test rig will be applied for the identification of the local friction coefficient between chip and tool. The data gained from the cutting test are compared with the output of the tribological test rigs.
PURPOSE OF THE STUDYFrom an initial group of 206 hips in 190 patients we carried out a retrospective clinical and radiological control of 74 hips in 72 patients covering a period of 20 years. MATERIAL AND METHODIndications in 74 operated hips evidenced 48 x (64,9 %) primary and 26 x (35,1 %) secondary coxarthrosis. The average age at the time of operation was 53 years (37 years -68 years). All 72 patients with 74 hips received cement-free selfcutting Alloclassic screw cups of pure Titanium together with a cement-free square Alloclassic stem consisting of Titan-Aluminium-Niob alloy according to Zweymüller.Regarding the technique of operation we used the approach after Watson-Jones in the supine position. As prophylaxis against thrombosis 40 % of the patients received derivates of heparine and 60 % had anticoagulant therapy with cumarine.Prophylaxis against heterotopic ossifications were not carried out at this juncture in our department. RESULTSAfter an average post-operational examination lapse of 20 years we were able to examine 72 patients (37,9 %) with 74 hips (35,9 %) clinically and radiologically.Further classification of the 72 patients records 47 females and 25 males. The average age at the time of operation was 53 years and at the time of post-operational check-up to 74 years. For the clinical post-operational check-up (n = 74) we used the Harris Hip Score.Further evaluation shows 12 x (16,2 %) excellent results, 26 x (35,1 %) good and 29 x (39,2 %) fair results. In 7 patients (9,5 %) we had to observe poor results because of multimorbidity, although also in these cases stability of TEP had been achieved.The radiological post-operational check-up of the 74 stable hips (35,9 %) shows an average excentric position of the head of 1,4 mm (0 mm up until 4 mm) compared with 1 mm after 10 years.Over an average of about 20 years we carried out an exchange of the inlay and the head because of excentric position of the head, which correlates to a rate of reoperation of 6,8 %. DISCUSIONIn 2000 and 2001 we published our 10 year results with cement-free Alloclassic screw cup and cement-free stem in 133 hips in 123 patients and compared our findings with those of other authors. After 10 years we saw only 3 % complications with cups and an overall re-operation rate of 6,7 %. The 20-year-results show in all cases stable components of both cups and stems. 5 patients (6,8 %) had to undergo re-operation with an exchange of inlay and head, whereby the components of the prosthesis themselves turned out to be stable.An average polyethylene abrasion of 1 mm after 10 years compares with a value of abrasion of 1,4 mm after 20 years. The 6,8 % rate of re-operation after 20 years indicates the excellent results of the use of cement-free Alloclassic total endoprosthesis system of the hip according to Zweymüller. CONCLUSIONSThe biocompatible qualities of modern prosthesis material lead to a quicker and optimal bony incorporation of the prosthesis components. The excellent 20-year-results show a broad indicative spectrum, component st...
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