[Improvement of osseointegration of bio-inert ceramics by modification of the surface--results of an animal experiment]. / Verbesserung der knöchernen Integration bioinerter Keramiken durch Modifikation der Oberfläche--Ergebnisse eines Tierversuchs.

The aim of this experimental study was to screen different surface structures of alumina and zirconia ceramic implants for their osteointegration properties. Alumina and zirconia ceramic test implants having different surface structures (smooth, macro-structured, corundum-blasted, porous) were implanted in the femora of mini-pigs, and left in situ for 12 weeks. After removal, the implants were evaluated macroradiographically and histologically. The smooth and macro-structured ceramic surfaces showed virtually no bony ingrowth, neither in the cortical nor the cancellous bone areas. In contrast, a rough surface finish or a porous surface structure allowed extensive bony ingrowth. The osteointegration rates varied between 20.5% and 41.7% (cancellous bone), and between 26.0% and 52.8% (cortical bone). With regard to the development of ceramic implants for clinical use, for example in the field of total hip replacement, these data provide a basis for further, more comprehensive studies.

[Joint biomechanics and design of modern knee prostheses--time for revised thinking!]. / Gelenkmechanik und das Design moderner Knieprothesen--Zeit zum Umdenken!

AIM AND METHOD: This review article summarises new knowledge about knee kinematics and induces a new discussion about the design of total knee arthroplasty (TKA) components. RESULTS: According to these new observations, knee flexion is not linked to femoral rollback but to a rotational movement between tibia and femur. The axis of this rotation is situated in the medial compartment of the knee when an intact anterior craciate ligament is present and not centrally through the tibial spines. In case of ACL insufficiency, such as that following TKA, the center of rotation shifts into the lateral compartment. Furthermore, the form of the posterior femoral condyle is not elliptical but round. CONCLUSION: Rotational movements between femoral component and tibial baseplate with the polyethylene-inlay have to be possible. One needs an asymmetric surface of the polyethylene-inlay, because different movements occur in the medial compartment than in the lateral compartment. The option to construct the posterior femoral condyle with a single radius allows a high congruency with the articulating inlay. The surgeon should let the new findings influence his choice of a TKA system. A closer analysis of modern prosthetic designs with either fixed or mobile bearings reveals that a few systems have already incorporated some of the new kinematic aspects of the knee.

[Simulator for migration processes and wear in the artificial hip acetabulum for radiologic measurement]. / Simulator für Wanderungsvorgänge und Abrieb bei künstlichen Hüftpfannen zur radiologischen Vermessung.

For assessing migration of cups, standard X-rays or stereo radiological images (SRI) are available. In addition, software is also available for measurements. The accuracies of the various systems are established statistically, in part combined with phantoms, and compared. To date, no known phantom is available for the simulation of acetabular cup migration with account being taken of the position of the pelvis in the X-ray beam. Such an appliance covering 8 different parameters has now been developed, the cup can be moved horizontally, vertically and in the loading direction. Angular accuracy is +/- 0.5 degree, and wear of a magnitude of 0.25 mm can be simulated. Two degree elevation of the pelvis, left or right, can be simulated. The position of the pelvis around the horizontal axis permits continuous variation. This appliance can simulate migratory movements of the acetabular cup within a pelvis, and wear within the cup. In addition, the spatial position of the pelvis can be varied. The X-ray images can be used to investigate the accuracy of evaluation strategies.

[Osseontegration of trial implants of carbon fiber reinforced plastics]. / Knöchernes Einwachsverhalten von Probekörpern aus kohlefaserverstärktem Kunststoff.

PROBLEM: To what extent are carbon fibre-reinforced plastics (CFRP) suitable as an osseous integration surface for implants? METHOD: CFRP test implants having a plexus-structured, rhombus-structured, and plexus-structured, hydroxyapatite surface were implanted in the femura of mini-plgs. Exposure time lasted 12 weeks. The implants were subjected to a macroradiological, a histological-histomorphometrical, and a fluorescence-microscopical evaluation. RESULTS: One half of the uncoated, plexus-structured implants were not osteointegrated, the other half displayed an osteointegration rate of 11.8% in the spongy area and 29.8% in the cortex layer. The HA-coated test implants showed an osteointegration of 29.5% in the spongiosa and 56.8% in the cortex layer. The rhombus-structured test implants had an osteointegration of 29.2% (spongiosa) and 46.2% (cortex layer). CONCLUSION: Compared to the osteointegration of metallic, especially titanium surfaces the CFRP surfaces tested by us fared worse, especially the uncoated, plexus-structured surfaces. For this reason we view very critically the use of carbon-fibre reinforced plastics together with the surfaces tested by us as osteointegrating surfaces.

[Patellar resurfacing in total knee arthroplasty, current state of the controversy]. / Der Patellarückflächenersatz in der Knietotalendoprothetik, aktueller Stand der Kontroverse.

This article reviews the current controversy of resurfacing the patella in total knee arthroplasty. Up-to-date knowledge of experimental and biomechanical studies as well as the different types of implants and specifics of the patella preparation are described in detail. The author furthermore discusses the relevant clinical studies dealing with patellar resurfacing and tries to guide the reader in evaluating the results. Finally is summarized why the indication for resurfacing the patella is so controversial and how a differentiated indication for resurfacing the patella could be specified.

[Effect of component positioning on patellar problems in total knee replacement]. / Einfluss der Komponentenpositionierung auf Patella-Probleme beim totalen Kniegelenksersatz.

The alignment and size of the components of a knee-prosthesis is most important for a successful and durable total knee arthroplasty. The effect of positioning the components on the patellafemoral joint is described in detail.

[Patellar resurfacing. Results of a prospective randomized study]. / Der Patellarückflächenersatz. Ergebnisse einer prospektiv randomisierten Studie.

The mid-term results of this prospective randomized study illustrate why it is difficult to define a clear position concerning the issue of patellar resurfacing in total knee arthroplasty. In both groups of 20 patients typical complications for the respective procedures have occurred. One patient from group A with patellar resurfacing had to be revised for loosening of the patellar implant. In group B without resurfacing 3 patellae subluxated, 2 having been revised. Furthermore 4 patients complained about mild to moderate anterior knee pain. The Knee and Function Scores of the patients without revision were not significantly different except for the parameter pain (Knee Score Gr. A:84.8, Gr. B:77.8; pain Gr. A:46.9, Gr. B:41.9; Function Score Gr. A:78.5, Gr. B:71.9; climbing stairs Gr. A:38.5, Gr. B:33.8). The radiological measurements found the patellae with resurfacing significantly less tilted with 3.8 degrees than the patellae without resurfacing with 6.4 degrees. With the correct implantation technique patellar resurfacing guarantees a good clinical result within the first 5 years. Leaving the patella unresurfaced was associated with a higher rate of anterior knee pain and revision in our study.

[Reproducibility of radiologic markers of osteoarthritis. Evaluating a score for radiologic classification of degenerative changes in osteoarthritis of the knee joint]. / Reproduzierbarkeit von radiologischen Arthrosemerkmalen. Evaluierung eines Scores zur radiologischen Klassifikation von degenerativen Veränderungen bei Gonarthrose.

INTRODUCTION: The radiological assessment of osteoarthritis of the knee joint in longitudinal studies is usually performed with established classifications. It is disadvantageous that these features are always combined to describe a certain stage of the disease, even though they can develop independently. METHODS: A german score based on a publication by Scott et al. (1993) was designed. At first 100 X-ray series of knees were evaluated using the Jäger & Wirth, the Kellgren & Lawrence classification and the point score. Six observers then evaluated 200 anonymised radiographs of knee joints twice within 3 months. RESULTS: The most reliable criteria for the inter-observer reliancy were medial osteophytes, medial joint-line narrowing, patella osteophytes and chondrocalcinosis. At least 4 out of 6 observers had a high match in these criteria. The reproducability of most of the individual radiographic features was good, with a higher level of orthopaedic training resulting in a higher consistency of the score. DISCUSSION: A certain level of orthopaedic training is necessary for consistent results. The main focus of the score will be less the daily routine assessment of radiographs of the knee joint, but more the scientific assessment of radiographic progression of osteoarthritis in longitudinal studies.

[Review of the results of the ARO multicenter study]. / Uberblick und Ergebnisse der ARO-Multicenterstudie.

The ARO multicenter study intended to show clinical and radiological differences with regard to different systems of fixation and designs of the prothesis in total hip replacement in patients with hip dysplasia, osteoarthritis and rheumatoid arthritis. In 1987 and 1988 5255 total hip prothesis were implanted by the 24 hospitals which took part in the study. 3133 prothesis (95.6%) were clinically and radiologically examined. The follow-up period averaged 6.9 years. The results of the Aro multicenter-study showed that despite difficult preoperative conditions especially in cases of rheumatoid arthritis the satisfaction rate improved remarkably. During the operation less complications arose in comparison to patients with hip dysplasia and osteoarthritis. Regarding the rate of infection after operation there were no differences between the 3 groups. Only the rate of post-operative luxation concerning rheumatoid patients turned out to be twice the number of the others. In our opinion this is due to the fact that these rheumatics were operated by posterior approach. Patients with rheumatoid arthritis were satisfied most with their surgeries. Results of rheumatic patients according to Harris hip score were slightly worse than the results of the two other groups. This was due to systemic involvement and bad preoperative function of the hip. As a result of the study there were no differences in using cemented or cementless techniques for rheumatic hip replacement. The decision for the method of fixation should depend on the patient's ability to relief the prothesis after operation. The study has shown that cementless implantation can also be used for young rheumatics provided that a suitable design of prothesis will be selected.

[Radiologic results of the ARO multicenter study]. / Die Radiologischen Ergebnisse der ARO-Multicenterstudie.

We present the radiological results of 2286 total hip replacements (THR) from the multicenter study. Concerning the acetabular component the analysis showed that socket migration and radiolucent lines were much more dependent on the specific design of the socket than on the primary diagnosis. A similar results was found for the femoral stems: rheumatoid arthritis did not cause a higher percentage of stem subsidence, radiolucent lines or bone remodeling. Within a mid-term follow-up period the reduced bone quality in rheumatoid arthritis is not associated to premature failure of a cemented or cementless prosthesis. THR failure seems to be more dependent on specific construction features of the individual socket and stem.

[Implant failure after total hip replacement. Comparison of patients with primary coxarthrosis, rheumatoid arthritis and dysplastic coxarthrosis]. / Implantatversager nach Hüft-TEP-Implantation. Vergleich bei Patienten mit primärer Koxarthrose, rheumatischer Arthritis und Dysplasiekoxarthrose.

The analysis of THR-failures showed that the acetabular component still is the main problem of total hip replacement. The acetabular cup fails more often than the stem. In the midterm analysis the failure rate is a little bit higher in cementless than in cement fixed cups. The known effect that the failure rate of cups fixed with cement increases exponentially 8 to 10 years after implantation, could of course not be seen in this study. The success of the cementless fixation was negatively influenced by the diagnosis rheumatoid arthritis, age over 70 and the fixation manner: the failure rate of threaded cups was higher than the one of press-fit cups although the Zweymüller-cup as well as the Link type V-cup showed good results. The midterm results of the stem were very good for the cementless as for the cemented technique. Some implants showed compared to others significantly worse results. The further implantation should be thought of, what partially has already happened. The results of cementless stem fixation in patients with rheumatoid arthritis, osteoarthrosis and dysplastic osteoarthritis is comparable, so that cementless fixation should be thought of in case of adequate conditions (ability of partial weight bearing for some weeks, age under 60).

Advantages of patellar resurfacing in total knee arthroplasty. Two-year results of a prospective randomized study.

Complications of patellar resurfacing in total knee arthroplasty have rekindled the interest of many surgeons in patellar retention. In a prospective study 20 randomly selected patients of 40 underwent patellar resurfacing in combination with their total knee arthroplasty. The other 20 patients were left with an unresurfaced patella. Within 24 months of follow-up, the advantages of patellar resurfacing could be seen according to the Knee Society Score. Especially in advanced osteoarthritis of the knee joint, the patients achieved better scores in climbing stairs and in function. The superior functional results are arguments for patellar resurfacing, at least in knees with advanced osteoarthritis.

[Gliding polyethylene-PMMA combination as "wear model"]. / Die Gleitpaarung Polyethylen-PMMA als "Abriebmodell".

The situation, described in this casuistry, shows the fatal consequences of the huge amount of wear particles from the PE-PMMA-components of a total hip prosthesis. The prosthesis had been implanted in Russia. It was made of a PE-ball fixed to a titanium stem and a socket, which had been molded intraoperatively in situ. The combination of PMMA and PE in the bearing surface caused an extreme osteolysis in the proximal femur and the acetabulum and the loosening of the cup and the stem within only a few months.

[Effect of integrated distance studs on cement thickness of implanted PE-acetabulum cups--experimental in vitro studies for improved cementing technique]. / Der Einfluss von integrierten Abstandhaltern auf die Dicke des Zementmantels bei implantierten PE-Hüftpfannen--Experimentelle In-vitro-Untersuchungen zur Verbesserung der Zementiertechnik.

Variations in cement thickness between PE cups and acetabular bone are biomechanically unfavourable, and may contribute to prosthetic loosening. Integrated distance studs should in the first instance, prevent local thinning of the cement. In an experimental study we compared the thickness of the cement mantel of implanted PE cups without such studs. In the case of cups with studs, significantly fewer areas of thin cement (0-1 mm) were found in comparison with cups with no studs. "Bald" areas of cement (0-0.2 mm) were virtually prevented by the studs. We are of the opinion that PE cups with integrated studs on the surface ensure a uniform cement thickness around the cup, as well as decreasing the risk of "bald" areas in the cement, thus reducing loosening.