Polyethylene wear in unicondylar knee prostheses. 106 retrieved Marmor, PCA, and St Georg tibial components compared.

106 unicondylar knee replacement tibial components were retrieved and analyzed for the amount and type of polyethylene wear. Three different designs were retrieved which had essentially the same femorotibial conformity. Each design showed a characteristic failure pattern. The polyethylene of PCA tibial components showed serious delamination after only short durations, as a result of heat pressing. St Georg sledge prostheses showed some delamination after 4 years' duration due to sub-surface cracks which were initiated by fusion defects in the polyethylene; metal backing of the components did not affect delamination of this prosthesis. The Marmor designs showed the least wear, with shiny depressions and surface pitting; no delamination was observed in the Marmor prosthesis. Molecular weight determination by gel permeation chromatography and analysis of crystallinity using Fourier transformation infra-red spectroscopy demonstrated that St George polyethylene had higher molecular weight and crystallinity than Marmor polyethylene. In some of the components investigated, crystallinity and molecular weight of the polyethylene were reduced under the wear track when compared with the unworn polyethylene. Since fusion defects may cause delamination of polyethylene we urge manufacturers to reduce the number of such defects.

[Sled prosthesis, rotating knee and hinge prosthesis: St. Georg model and ENDO-model. Differential therapy in primary knee joint arthroplasty]. / Schlittenprothese, Rotationsknie und Scharnierprothese Modell St. Georg und ENDO-Modell. Differentialtherapie in der primären Kniegelenkalloarthroplastik.

During the last 20 years the surgeons at the ENDO Klinik in Hamburg have implanted more than 7,000 cemented primary knee prostheses of their own design, formerly the St. Georg models and now the ENDO models. The sled prosthesis, rotating knee and hinge prosthesis are each stabilized to a different degree. The indication depends on the type of deformity, the disease. affecting the knee and the type of patient. As a result of our experience with the three systems they are now implanted in the ratio of 30:60:10, and we are convinced that in order to treat all problems encountered in diseased knees it is essential to have different prostheses with various degrees of stabilization.

The saddle prosthesis for salvage of the destroyed acetabulum.

We report the 12 to 74 month results of our mark I saddle prosthesis after its use as a salvage device for gross loss of pelvic bone stock in 76 patients with failed hip arthroplasties. The implant transmits load between iliac bone and bare polish chrome-cobalt. Our clinical and radiological results indicate that a useful and stable articulation can be achieved in most cases, provided that continued deep infection can be avoided. The appearance of radiological sclerosis at the bearing site in successful cases seems to indicate that significant late migration will not occur. Based on our experience with the mark I prosthesis we have designed and developed a mark II model which has freedom of axial rotation of the saddle. Our early results in 40 cases show a significant improvement over the results which could have been predicted for the mark I device.

[Alloarthroplastic treatment of congenital hip dysplasia]. / Alloarthroplastische Therapie der kongenitalen Hüftgelenkdysplasie.

The implantation of a total prosthesis to treat the anatomical changes following dysplasia of the hip requires a special operative technique and the availability of implants that can be individually adapted to the joint at operation. This paper deals with special prosthesis systems, particularly in combination with autologous acetabular bone grafting. Long-term acetabulur results show rates of loosening comparable to those observed after the treatment of primary osteoarthrosis.

[Pelvic bone defects in alloarthroplasty]. / Beckenknochendefekte in der Alloarthroplastik.

Loss of acetabular bone renders secure fixation of an artificial cup difficult. Loss of pelvic bone mainly results from repeated revision of failed THR, tumor resection within the acetabular region and trauma. The main criteria for the method of treatment to be applied are the biomechanical condition of acetabular defects, the bacteriological situation, and the patient himself. In aseptic cases we regard bony reconstruction with homografts as the method of choice. From 1982 to 1986 about 1000 bony reconstructions were performed using more or less extensive facilities for support, i.e. screws, baskets, plates. In septic cases defects are closed using antibiotic-loaded acrylic cement in combination with screws. In the extreme case of bone destruction we recommend the saddle prosthesis as an alternative measure. This type of prosthesis was used in 76 cases from 1979 to 1984. Other methods of treatment, such as resection arthroplasty, arthrodesis, and partial pelvic replacement may be considered.

[Modular system for the total replacement of the femur--Endo-model]. / Modulares System für den Femurtotalersatz--Endo-Modell.

Total femur replacement may offer a useful solution in cases of severe trauma or neoplasia and in revision arthroplasty after failed total joint replacement when gross losses of bone have resulted in an unloadable femur and all other methods of treatment would fail to provide the patient with a stable leg. Until recently, total femur components were custom-made, but now we have a comprehensive modular total femur implant available reducing problems of preoperative preparation and simplifying the manufacture of custom-made designs. The new device can be shaped and adapted to the conditions encountered at the time of operation. The "push-through" type of prosthesis can be mounted step by step and converted into a total femur replacement with either a conventional head or a saddle at the proximal end and a total axial rotating knee prosthesis at the distal end. Elongation of the entire system is feasible.

[Intracondylar knee joint prosthesis with rotation capacity- Endo model]. / Intracondyläre Kneigelenksendoprothese mit Rotationsmöglichkeit--Endo-Modell.

The St. Georg total knee prosthesis has been modified to incorporate axial rotation of the tibial component. The kinematics approximate more those of the normal knee and the stress imposed at the bone-cement interface are attenuated, thus reducing the risk of mechanical failure. The construction and laboratory testing are described.

[Experimental study of the optimization of the hip endoprosthesis]. / Experimentelle Untersuchungen zur Optimierung der Hüftendoprothese.

Clinical and laboratory investigations have resulted in a new design for the shaft prosthesis of the "St. Georg" model total hip prosthesis, the purpose of which was to minmize the risk of biomechanical complications. The original method of attachment and the same material for the limb were retained for our investigations. It was possible to test the bending strength, the length, and the geometry of the shaft as well as how structure of the bearing surface of the collar influences the force flow within the compound system. The distrubances produced in physiological force flow produced on insertion were also investigated. The results obtained enabled us to design a new shaft prosthesis.

[Injury to pelvic vessels in total hip replacement surgery]. / Verletzung von Beckengefässen bei totalem Hüftgelenksersatz.

Massive bleeding of the pelvic vessels during an alloarthroplastic operation on the hip joint should be suspected in cases of abnormal anatomic conditions. Therefore, the operative procedure should be meticulously planned including extensive X-ray investigations such as angiography and computer-tomography. Surgical preparation and procedures in case of vascular complications are described. Hints on operative techniques are given to prevent vascular complications during and after surgical intervention of the hip joint.

[Possibilities of using ultrasonic tools in changing endoprostheses]. / Möglichkeiten der Anwendung von Ultraschallwerkzeug bei Endoprosthesenwechsel.

In joint replacement surgery an exchange of endoprostheses is technically most difficult, time consuming, and extremely unpleasant for the patient. Removal of the implant without damaging the bone entails many problems. Experience has shown that, in addition to the normal operative technique, the ultrasonic method may be very helpful. Ultrasonic implements that melt thermoplastic implants facilitate the removal of those implants (e.g., polymethylmethacrylate, polyethylene), protect the tissue, and save time. This method is not an alternative to the normal operative technique, but an additional help.