Biomedical subjects

G Willmann

Publications and source records attributed to G Willmann.

At least 19 recordsLinked to original sources

PubMed2003

[Ceramic couplings in orthopedic surgery].

Ceramic materials have been used as a coupling in total hip arthroplasty since the 1970s to solve the problem of polyethylene particle disease. Several problems with the material and the design have been identified and solved. Using inlays and ceramic heads of the latest generation offers the possibility of reducing the wear rate to as low as 0.001 mm per year. The problem of ceramic fractures is rare. Recently due to the manufacturing process some zirconia ceramic heads have been problematic. New developments with other ceramics are discussed.

Aluminum Oxide↗

PubMed2003

Immuno-allergological properties of aluminium oxide (Al2O3) ceramics and nickel sulfate in humans.

For more than 30 years aluminium oxide (Al(2)O(3)) ceramics have been used for implants in maxillofacial and orthopaedic surgery. Up to now, there are no reports and also no investigations on hypersensitivity reactions. In order to evaluate the aspects of immuno-allergological reactivity to aluminium oxide ceramics, skin testing and in vitro lymphocyte activation studies were performed. The patch test reactivity to a standard series of contact allergens and to an aluminium oxide (Al(2)O(3)) disk was examined in a consecutive series of 250 patients frequenting a University Dermatology Clinic. Furthermore, peripheral blood mononuclear cells (PBMC) of 15 nickel-allergic and 15 non-allergic individuals were cultured with medium alone, with the pan T-cell mitogen phytohemagglutinine (PHA) or with nickel sulfate (NiSO(4)). By additional presence/absence of Al(2)O(3) disk its influence on the cytokine secretion pattern and proliferative response was investigated. The results show that in contrast to a high frequency of delayed-type hypersensitivity to standard contact allergens, no allergic skin reactions to Al(2)O(3) ceramics occured. The IL-4 and IFN-gamma production in vitro remained almost unchanged by the presence of Al(2)O(3) disk as well as the proliferative response of PBMC of non-allergic individuals. Cellular reactivity of nickel allergic and non-allergic donors was partly enhanced upon contact to Al(2)O(3) disks.

Allergens↗

PubMed2001

Mismatched wear couple zirconium oxide and aluminum oxide in total hip arthroplasty.

A patient complained about a squeaking noise in his total hip arthroplasty. Clinical evaluation revealed good function, and there were no signs of loosening on the radiograph. Physiotherapy did not alter this phenomenon, and ultimately a revision was performed 42 months after the first surgery. The analysis of the retrievals revealed that a zirconium oxide ceramic head had been paired with a monolithic alumina ceramic cup. The cup showed large deviations from an ideal sphere but minor wear signs. The head exhibited heavy local damage in the articulation zone. This damage might have been caused by the observed unsatisfactory fit between cup and ball, resulting in high stress concentrations and increased wear of the zirconium head. The characteristics of the zirconium and aluminum ceramics pairing might have worsened the process. The combination of implants used in this retrieved wear couple was never approved. To prevent such problems, components of different manufacturers should never be mixed and matched unless explicitly stated.

Aluminum Oxide↗

PubMed2001

Morphologic characteristics of periprosthetic tissues from hip prostheses with ceramic-ceramic couples: a comparative histologic investigation of 18 revision and 30 autopsy cases.

Pseudocapsules and interface membranes from 18 revision cases having hip prostheses with ceramic-ceramic couples and 30 autopsy specimens (6 with ceramic-ceramic couples, 7 with ceramic-polyethylene combinations and 17 with metal-polyethylene combinations) were histomorphologically analyzed, including a semiquantitative grading of the wear particles and histologic changes. Unlike the revision cases, which usually showed ceramic wear particles in the adjacent tissues, only half of the autopsy cases revealed ceramic wear. As compared to the ceramic-polyethylene and metal-polyethylene couples, the alumina on alumina combinations showed a thinner synovial layer with reduced villous transformation and smaller infiltrates of macrophages and necroses, which can be explained by the absence of polyethylene wear. Metal-polyethylene couplings produced more than twice as many polyethylene wear particles with correspondingly more marked foreign body reaction than the ceramic-polyethylene couplings.

Adult↗

PubMed2001

Initial stability of modular acetabular components. Comparative in-vitro study with polyethylene and ceramic liners.

Modular acetabular components with alumina ceramic liners are currently used in total hip arthroplasty, but concerns have emerged regarding their high stiffness, which could cause impairment of stability, stress-shielding phenomena, and loosening. The purpose of the present biomechanical investigation was to compare the in-vitro initial stability of a modular press-fit acetabular component using a polyethylene liner and using an alumina liner. The initial stability was investigated by measuring the micromotion between the implant and the acetabulum during the application of physiological load (2.39 kN). The micromotion of the acetabular component was investigated in 10 acetabuli using a polyethylene liner and in 10 acetabuli using an alumina liner. Micromotion was assessed at the level of the Os ilium, Os pubis, and Os ischium using 3 electromagnetic transducers. The transducers have a sensitivity of 1 micron and a range of measurement of 500 microns. All implants have been fixed on human pelves made of polyurethane. Measurement of implant micromotion showed stable conditions at the level of the three main sectors of the acetabulum during all tests. No statistically significant differences of results were observed between the group of specimens with polyethylene liner and the group of specimens with alumina liner. The mean micromotion values of the uncemented cups were similar to the mean micromotion values of 10 cemented cups investigated to achieve comparative data of stability. In conclusion, the modular acetabular components inserted using an alumina liner showed a satisfactory initial stability in-vitro. The results do not contrast with those achieved using the same cup inserted with a polyethylene liner.

Acetabulum↗

PubMed2001

Long-term results after operative treatment of femoral neck fractures with ceramic head prostheses.

From 1985-1990, a total of 277 elderly patients underwent hemiarthroplasty using a ceramic head prosthesis. Average patient age was 81.7 years. Of these, 77 patients were available for follow-up examination in 1993. A standardized score was calculated assessing activity, gait, and hip pain; the average score was 58 out of 78 possible points. Three patients had hip pain, and in 4 patients, radiographic examination revealed protrusio acetabuli. Two of 4 patients underwent revision surgery for replacement of the cup, leaving the stem in situ. Because of the small number of prosthetic-related complications, hemiarthroplasty using a ceramic head prosthesis is the recommended surgical treatment for femoral neck fractures in elderly patients. In the rare patient with protrusio acetabuli, revision surgery can be performed to replace the cup, leaving the stem in situ.

Acetabulum↗

PubMed2001

[Investigation of explanted hip and acetabulum hip prostheses].

Retrieved ceramic femoral heads and acetabular cups were investigated. On the basis of the case studies, the reasons for revision are discussed. Wear patterns and wear rates were found to differ from those observed in hip simulating testing. Monolithic ceramic cups showed a high wear rate. Owing to their limited range of motion, ceramic "mushroom heads" are associated with impingement that leads to a high risk of cup loosening, high wear rates and in vivo fractures. The combination of ceramic "mushroom heads" and cups is not recommended. An evaluation of complications shows that some can be explained by patient behaviour--e.g. Japanese sitting position, horse riding. Designers need to develop new concepts offering a larger range of motion, for example, with head diameters of 32 and 36 mm that reduce the risk of impingement, subluxation and dislocation, while increasing the range of motion. The potential of ceramic/ceramic coupling has been known since the 70s, and ceramic concepts for total hip replacement are currently experiencing a renaissance, although further developments are still possible.

Acetabulum↗

PubMed2000

Ceramic femoral head retrieval data.

In the 1970s it was first realized that the properties of alumina ceramics could be exploited to provide better implants for orthopaedic applications. Applications depend on the fact that ceramics provided wear characteristics suitable for bearing surfaces in total hip replacement. Resultant orthopaedic use had more than 20 years' clinical success. To date more than 2.5 million alumina femoral heads have been implanted. Published reports of fracture rates of the alumina heads range between 0% for ceramics manufactured after 1990 and 13.4% for ceramics manufactured before 1990. These high fracture rates were caused by materials manufactured by companies that are not on the market today. These old aluminas had a low density, had a very coarse microstructure, and were not in compliance with specifications that are valid today. Materials scientists have substantially improved the mechanical strength of alumina. There are three generations of medical grade aluminas. The latest generation is an alumina that is hot isostatic pressed, laser marked, and proof tested. This material has been on the market since 1994. The fracture rates of the most commonly used ceramics have been analyzed by various groups, and are based on .5 million femoral heads to 1.5 million femoral heads. The fracture rate of ceramic Biolox femoral heads are 0.026 % for first generation alumina, 0.014% for second generation alumina, and 0.004% for femoral heads manufactured after 1994. Analyzing the clinical experience of more than 20 years, it can be concluded that all the improvements have produced reliable ceramic femoral heads.

Aluminum Oxide↗

PubMed2000

[Ceramic acetabulum for hip endoprostheses. 8: Revisions].

For total hip replacement, ceramic femoral heads and acetabular liners are being used with success. However, reports of revision surgery necessitated by fractures or marked wear of ceramic components are still being published. The revision rate due to fracture is less than 0.01%, and much lower than for other complications. Nevertheless, improvement of safety remains a topic of discussion. This article reviews the results of investigations of explanted ceramic heads and liners, and discusses the problems caused by ceramic wear and chipping. Recommendations for revision surgery in such cases are given.

Acetabulum↗

PubMed1999

[Ceramic acetabular cups for hip endoprostheses. 7: How do position of the center of rotation and the CCD angle of the shaft modify range of motion and impingement?].

The range of motion (ROM) of total hip prostheses is influenced by a number of parameters. An insufficient ROM may cause impingement, which may result in subluxation, dislocation or material failure of the prostheses. In a three-dimensional CAD simulation, the position of the centre of rotation and the CCD angle of the stem were investigated. Displacement of the centre of rotation of the femoral head may be due to wear (PE cups) or to the design of the prosthesis (ceramic cups). Stems of widely differing design have been developed and implanted. The results of the present study demonstrate that the ROM is clearly reduced by increasing penetration of the femoral head. At an inclination angle of 45 degrees, a depth of penetration of 2 mm restricts flexion by about 15 degrees, and a depth of penetration of 3 mm by about 30 degrees. At smaller angles of inclination the ROM is reduced and flexion and abduction are associated with an increased risk of impingement. With steeper acetabular cup inclinations, the risk of impingement decreases, but dislocation, the risk of rim fractures (ceramic cups), and wear and penetration rates (PE cups) increase. The CCD angle of the stem should be oriented to the anatomical situation. At high CCD angles (> 135 degrees), flexion is clearly limited, in particular when there is penetration of the femoral head. For modern total hip arthroplasty, prosthetic systems characterised by precise positioning of components, minimum wear, slightly recessed inserts, and appropriate CCD angles should be used.

Arthroplasty, Replacement, Hip↗

PubMed1998

Tribological investigations of the wear couple alumina-CFRP for total hip replacement.

Wear debris is the main reason for aseptic loosening in total hip. Most troublesome is the wear of polyethylene cups. Ceramic femoral heads were introduced about 20 years ago. The combination ceramic-on-polyethylene reduces the wear rate and the loosening rate. But cups of polyethylene are still the weakest link in a hip prosthesis. Carbon fibre reinforced plastic (CFRP) was proposed as an alternative for polyethylene. Various test were performed to study the combination metal-on-CFRP, zirconia-on-CFRP, and alumina-on-CFRP. The simulator tests showed that the wear rate of alumina-on-CFRP is in the order of 1-3 microm per year. Based on investigation of retrieved implants the wear rate is 6.3 microm per year. Based on these results the combination alumina femoral heads (Biolox-forte) and CFRP cups (Caproman) could be approved for total hip replacement.

Aluminum Oxide↗

PubMed1998

[Ceramic cups for hip endoprostheses. 5: Consideration of designs].

Using the combination ceramic on ceramic for hip prostheses, the wear rate can be reduced to less than 1 micron per million cycles. More than 20 years of experience are now available for various concepts involving alumina ceramics in THR. In the early days, monolithic ceramic cups were employed. However, since alumina ceramic has an unsatisfactory potential for bone integration, soft tissue forms at the interface, with the result that the sockets migrate and penetrate. To improve bony integration, monoblock cups surfaced with ceramic beads were introduced. For the past 10 years, there has been a trend towards the use of modular acetabular components comprising a metal shell and a liner made of Biolox forte ceramic. Two concepts for the fixation of the ceramic liners are employed: locking of the ceramic in the metal shell (CeraLock) and the sandwich concept with a polyethylene layer interposed between liner and shell. The basic design and important aspects such as diameter, range of motion, and the possibility for revision, clinical experience, and trends are discussed.

Ceramics↗

PubMed1998

[Polyethylene in total endoprosthetics--a dead end for permanent implants?].

Faced with a growing number of younger patients in need of total joint arthroplasty, orthopaedic surgeons are demanding long-term implants for total joint replacement. An assessment of the long-term mechanical behaviour is vivo of all biomaterials in common use in prostheses is in progress. In the present paper, we discuss the long-term reliability of polyethylene (UHMWPE) in joint replacement in terms of tribology and the different biomechanical situation in various human joints. Long-term failure mechanisms for polyethylene in total hip arthoplasty (THA) differ from those seen in total knee arthroplasty (TKA) although the same materials are used. It is thus questionable whether improvements in wear rates of polyethylene in THA would be helpful in TKA.

Biomechanical Phenomena↗

PubMed1998

[Ceramic cups for hip endoprostheses. 4: Never mix and match].

Femoral ball heads for total hip replacement are made of various materials, e.g. cobalt chrome alloy, coated metal, or various ceramics. Standard sockets are made of polyethylene, alumina ceramics, or CFRP. Due to tribological reasons some of the combinations of head and socket that seem possible are prohibited. The approved and prohibited combinations are reviewed and reasons for not approving are discussed.

Acetabulum↗

PubMed1998

Ceramics for total hip replacement--what a surgeon should know.

Numerous clinical results reported in the literature prove that ceramic femoral heads reduce wear, osteolysis, and revision rates in total hip replacements (THRs). Femoral heads and cups made out of alumina ceramics were introduced about 25 years ago, and femoral heads made out of zirconia were introduced about 10 years ago. Today, the wear couples of alumina-on-polyethylene or zirconia-on-polyethylene have become the standard in THR. The wear couple offering the lowest wear rate is alumina-on-alumina. This article discusses the state of the art and lists advantages as well as problems with the various materials used for prostheses in THR.

Aluminum Oxide↗

PubMed1997

Wear characteristics of ceramic-on-ceramic for hip endoprostheses.

Femoral ball heads of aluminium oxide or zirconium oxide ceramics are used for total hip replacement. This application is based on their attractive tribological properties. Standard and state-of-the-art are femoral ball heads made of alumina (Al2O3) articulating against acetabular cups of polyethylene (PE-UHMW) and zirconia (Y-TZP) heads articulating against polyethylene cups. A very attractive wear couple is ceramic-on-ceramic. Some of the various ceramic combinations have been tested using the ring-on-disc method according to ISO 6474. The combination alumina/alumina was found to produce extremely low wear; catastrophic wear was found for the combinations alumina/Y-TZP and Y-TZP/Y-TZP.

Aluminum Oxide↗

PubMed1997

[Standardization of zirconia ceramics for hip endoprostheses].

Bioceramics are used in a wide range of different clinical applications, the most important being femoral heads in total hip replacement. Because of their very attractive mechanical properties, zirconia ceramics (ZrO2) have recently been used as implant material. At the present time, two medical-grade types of zirconia are available: Mg-PSZ and Y-TZP. For the Y-TZP, an international standard (ISO) was issued. The standard is discussed, and the properties that are of importance in the field of orthopaedics are identified.

Biomechanical Phenomena↗

PubMed1997

[Load bearing capacity of CFK hip prosthesis with ceramic femoral heads].

Wear of the articulating surfaces of mating components of total hip endoprostheses is the most important technical factor limiting the functional lifetime of the prosthesis. Biolox ceramic femoral heads have been used successfully throughout the world for more than 20 years. In vitro tests and clinical results show that the artificial modular hip joint system employing a Caproman stem and a ball made of Biolox or Biolox -forte is resistant to mechanical failure. The threshold values for burst load and cyclic load prescribed by the FDA are achieved or bettered. Clinical results support those of the in vitro tests. The femoral head made of Biolox or Biolox -forte used in combination with cups and stems made of Caproman thus complies with the required standards.

Biomechanical Phenomena↗