The materials and combinations of materials presently used for joint replacements are not completely satisfactory. Therefore, special types of ceramics have been studied for the application of endoprostheses of the heavy load bearing joints. High purity aluminium oxide ceramics have shown the most promising results. In a comparison between the material properties required for joint endoprostheses and the properties of dense, high purity A120 3 ceramics particular emphasis is placed on the problems of mechanical strength of total hip endoprostheses capable of being implanted without the use of any cement as well as on the problem of friction in artifical hip joint.

SummaryTwo types of dense A1,0, ceramics (99.6% purity, 96% purity) were tested in the following fields of interest. I ) Wear resistibility using a pin and disk method under distilled water and human synovial fluid. Both types showed minimal initial corpuscular wear.2) Biocompatibility of ceramic wear particles in mice and rats after injection by different ways. The crystal material is permanently deposited in macrophages, after transport via lymphpatic and blood vessels also in the RES without chronic inflammatory and progressive fibrotic response.3) Under moderate stress conditions ceramic plates are fixed firmly by new bone formation within 2-3 months according to tetracycline label studies of bone growth in rats. 4) A new ceramic total hip prosthesis with two different socket designs for cement free fixation in bone is proposed and used in sheep experiments. The results of a 4 month experiment is presented showing firm fixation of tbe prosthesis under full stress conditions.

The authors present the results of 20 corrective procedures for juvenile cyphosis using Harrington compressive rods and Hibbs spondylodesis. 16 procedures date back more than one year (average 3 years, 4 months). 10 cases of pure dorsal cyphosis. The pre-operative Cobb-angles for cyphosis averaged 52 degrees, postoperatively an average of 24 degrees was measured. This reflects a 57 p.c. average immediate correction (41 p.c. for pure dorsal cyphosis, 71 p.c. for dorso-lumbar cyphosis) following surgery nearly all cases showed a significant loss of correction (average 43 p.c., dorsal 37 p.c., dorso-lumbar 49 p.c.). Three main reasons for this loss of correction are discussed and documented in detail. 1. Mal-centered and too short a length of spondylodesis; 2. insufficient corrective growth of wedge shaped vertebral bodies post surgery and 3. frequent lumbar decompensation into total round back deformity of the pure thoracic spondylodesis. The following changes in procedure to solve the problem of loss of correction are proposed. 1. Combined posterior and anterior fusions and 2. upper lumbar dorsal fusion together with extended thoracic spondylodesis. The changing indication is discussed. The main but not fatal complication was postoperative wound infection (15 p.c.).

The favorable combination of properties of dense, pure Al2O3-ceramics as a material for endoprostheses of the high load bearing joints have been confirmed in more than 4 years of experimental work with different types of animals. During this period Al2O3-ceramic parts for total hip replacement have already been developed and tested as well as the special instrumentation and the technique of the surgical procedure concerned. Based on these experiences a new total hip endoprostheses together with its complete technique for the operation is presented with which an improved alternative for replacements of Weber-Huggler-prostheses is offered and the application of total hip replacements can be extended to patients below 60 years of age.

Total replacement of the knee joint often remains unsatisfactory because of severe femoro-patellar osteoarthritis.Twenty-four Walldius knee prostheses were inserted in 21 cases. Since March 1971 we have used a combination of this type of hinge prosthesis with a high-density polyethylene retropatellar facet prosthesis developed by our group in cooperation with the Badische Anilin-& Soda Fabrik AG (BASF).Fourteen knees of this combined type have been implanted and resulted in considerably less complaints than the original Walldius knee. The postoperative range of motion with an average of 66" does not differ in both groups. 1953 [6] reported on acrylic knee joints. In 1958 Walldius [7] changed-289