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Biomedical subjects

G Täger

Publications and source records attributed to G Täger.

8 recordsLinked to original sources
PubMed2006

Investigation on stick phenomena in metal-on-metal hip joints after resting periods.

Insufficient understanding of tribological behaviour in total joint arthroplasty is considered as one of the reasons for prosthesis failure. Contrary to the continuous motion input profiles of hip simulators, human locomotion contains motion interruptions. These occurring resting periods can cause stick phenomena in metal-on-metal hip joints. The aim of the present study was to investigate the tribological sensitivity of all-metal bearings to motion interruptions on in vitro test specimens and retrieved implants. Friction and wear with and without resting periods were quantified. Unlike the metal-on-polyethylene joints, the static friction of metal-on-metal joints increased up to micros = 0.3 with rest, while wear appeared to be unaffected. This effect is caused by the interlocking of firmly adhered carbon layers, which were generated from the protein-containing lubricant through tribochemical reactions. Since more than 80 per cent of the retrieved implants exhibited macroscopically visible carbon layers, the increase in friction presumably also occurs under physiological conditions, which is then transferred to the bone-implant interface. These recurrent tangential stress peaks should be considered for the design features of the cup-bone interface, in particular when larger-sized implant heads are used.

Biocompatible Materials↗
PubMed2005

Subsurface microstructure of metal-on-metal hip joints and its relationship to wear particle generation.

To control and minimize wear of metal-on-metal hip joints it is essential to understand the mechanisms of debris generation. In vivo, mainly nanosize globular and needle-shaped particles are found. These can neither stem from the action of abrasion nor from tribochemical reactions. In this study the acting wear mechanisms have been first identified on the surface by means of scanning electron microscopy (SEM). Afterwards, the microstructures of the subsurface regions of explants have been investigated using a transmission electron microscope (TEM). Observation of the subsurface gave additional insight about the microstructural changes of cobalt-base alloys subjected to wear. At some distance from the surface, a network of stacking faults and hexagonal epsilon-martensite was found strengthening the bulk material. This microstructure changed into a nanocrystalline type moving closer towards the surface. A comparison of in vivo debris size and grain size of the surface suggests that the globular wear particles result from torn off nanocrystals, while the needle shaped particles are generated by fractured epsilon-martensite. Identified cracks, propagating through the nanocrystalline layer, further support these findings. Thus, it is suggested that the dominating mechanism of particle generation for metal-on-metal joints is surface fatigue within a nanocrystalline surface layer.

Adolescent↗
PubMed2004

[The infected hip prosthesis].

Therapy of infected hip prosthesis should always be based on a structured treatment concept. When short-termed early infection is present or impending, with meticulous debridement of the soft tissue surroundings, the implant may be left in place. Chronic infection (>30 days) should lead to complete removal of implant and cement. A one-staged revision of the implant may be considered for patients without additional chronic disease, good vascularization of soft tissue and bones and bacteria susceptible to antibiotics. In most cases though two-staged revision is indicated. The interval between implant removal and re-implantation ranges between one and four months. Re-implantation should only be performed when laboratory parameters are normalized and the local wound site has turned to an unsuspicious condition. By insertion of a cement spacer during the interval period soft tissue shortening and local scar formation can be prevented. Parenteral antibiotics should be applied for four to six weeks. In patients with reduced general health state and extremely severe infection permanent resection of the hip or limp ablation may be indicated.

Arthroplasty, Replacement, Hip↗
PubMed2001

[Interdisciplinary quality management in the treatment of severely injured patients. Validation of a QM system for the diagnostic and therapeutic process in early clinical management].

A multidisciplinary quality management system (QMS) for the early treatment of severely injured patients was validated in a trauma center in Germany. In the presented prospective study a QMS developed at another trauma center was implemented at the department of trauma surgery of the University of Essen for the presented study. The essential elements of the QMS were the establishment of (1) an adequate protocol for documentation, (2) 20 criteria for the assessment of treatment quality, (3) regular statistical analysis of treatment quality and (4) a quality circle comprising all medical specialties for data discussion. From 5/98-9/99 a cohort of 447 patients with an average injury severity score (ISS) of 22 +/- 17 was treated in the emergency department. The impact of the QMS was assessed in 4 periods (1: 5/1998-8/1998; 2: 9-12/1998; 3: 1-4/1999; 4: 5-8/1999). The quality circle met 8 times. For the improvement of the process 16 long-term changes were introduced. In 60% (n = 12) of the 20 assessment criteria significant improvements were detected. In diagnostics there were significant reductions of the time needed for basic radiological and sonographic check-up (from 24 +/- 12 min in the first to 14 +/- 8 min in the last period) and of the duration until performance of a cranial computed tomography in severe traumatic brain injury (sTBI; from 45 +/- 22 to 28 +/- 8 min). The rate of delayed diagnoses remained low (4% in the first, 5% in the last period). Further positive changes were the time savings in transfusion (from 35 +/- 20 to 20 +/- 4 min) and emergency operations (from 67 +/- 20 to 48 +/- 4 min) in hemorrhagic shock as well as for craniotomies (77 +/- 41 to 54 +/- 19 min) in sTBI. Apart from the significant time reductions other improvements were found. Overall mortality was diminished from 17% in the first to 10% in the last observation period. In conclusion the study revealed that the quality of the early therapy of severely injured patients was significantly improved by implementation of a multidisciplinary quality management system especially with respect to treatment efficiency.

Adolescent↗
PubMed1997

[Changes in shape of the McKee-Farrar hip endoprosthesis].

The still unsolved problem of aseptic loosening in total hip arthroplasties with identification of polyethylene wear particles as one of its major causes, has led to reintroduction of metal-to-metal articulations, as indicated by a few good clinical long-term results with all-metal McKee-Farrar arthroplasties. In this paper, data on 145 patients from a population of more than 1400, all with implanted McKee-Farrars, who underwent revision surgery for aseptic loosening, are collected and analysed for dependence of duration to brands of the implants and position of the cups. The surface of each of 55 revised implants was measured using a 3-D device. The results showed no interdependence between time of loosening, brand inclination of the cup and deviation in shape of ball and cup. Additionally, the deviations in shape were slight.

Acetabulum↗
PubMed1994

[Bone defects as complication following total hip endoprosthesis implant].

The authors present a relatively short followup study of 129 patients who were treated with cementless revision for loosened previous arthroplasties. Elderly patients with a first revision and good bone stock condition were excluded as were septic failures. All patients were treated with cementless, hollow-designed implants. Following previous THA and, also repeated revisions--nearly all of them using a cemented technique--many of the patients developed mostly acetabular, but also femoral loss of bone stock of various quality. Many of these cases required extensive allogenic bone grafting; some of the cases with severe loss of bone stock in young patients necessitated two-stage surgery. Despite this high rate of allografts, no infection occurred. Five patients were revised again for loosening or for femoral fracture; two patients showed sinking of the femoral component and clinical deterioration. The possibilities and advantages of restoration of the implant bed in destructive, aseptic loosening with demanding bone graft and cementless techniques are encouraged by the early results of the patients remobilization and radiologically recognizable revitalization of bone stock. Long-term follow-up will be necessary to evaluate allograft incorporation exactly.

Acetabulum↗