A bioceramic endoprosthesis for the replacement of the proximal humerus.

In patients with malignant tumors in the region of the shoulder, radical resection can avoid amputation in most instances. To improve the function of the arm, endoprosthetic replacement of the defect is desirable. A three-component endoprosthesis made of a bioceramic material (aluminium oxide) was designed, implanted without bone cement. Fast anchorage to bone is achieved by using a conical sleeve, fixed upon the previously conically reamed humerus shaft. A stable primary fit is always feasible. Subsequent bone in growth into grooves inside the conical sleeve provides a permanent anchorage of the endoprosthesis. The authors experiences are based on implantations of 38 endoprostheses. The original diseases were primary malignant bone tumors in 19 patients, one case of "solitary" plasmocytoma and metastases into the proximal humerus in 16 patients. In two women, resection was made because of posttraumatic subcapital humeral pseudarthrosis. The follow-up study includes only those 27 cases operated on at least one year ago. 12 of the 14 patients with primary tumors have been surviving for 12-55 months (range 27.4) without signs of metastases or recurrent disease. Seven patients with metastases died of their original diseases after 7.7 months on the average. Owing to extensive resection of the shoulder musculature the mobility in the shoulder joint is considerably reduced. All the patients have good movement of the elbow joint and free function of the hand.

Extracortical attachment of bioceramic endoprostheses to long bones without bone cement.

Dense, highly pure A12O3 ceramic not only shows excellent wear resistance and tissue biocompatibility, but also has sufficient mechanical strength for loaded endoprostheses. The necessary diameter size of the material to sustain adequate shear stresses can be achieved, if the endoprosthesis is attached extracortically to the conically truncated long bone according to the principle of the conical sleeve. Extracortical attachment of the endoprosthesis causes minor nutritive damage since long bones derive their vascular supply mainly from the medullary cavity. In this way a primary stable and loadable connection is established, which is a prerequisite for permanent anchorage of the implant through new bone formation. After experiments in 12 dogs bioceramic endoprostheses were implanted in a total of 40 human patients using this technique of extracortical attachment (12 hip joints, 24 proximal humeri, 4 special constructions). Thirty-six of these implants were stable after observation periods ranging from one to 49 months. A stable anchorage of the prostheses to the pre-existing bone through new bone formation could be demonstrated histologically. The above preliminary results show that bioceramic endoprostheses can be "incorporated" in the skeleton and possibly also withstand the functional stresses.

Further experimental and clinical experience with aluminum oxide endoprostheses.

This paper describes the design principles of a new endoprosthesis made of dense aluminum oxide (A12O3) and implanted without bone cement. Mechanical tests and animal experiments have proved the sufficient mechanical strength of the bone-prosthesis connection as well as the biocompatibility of the material. So far, 12 tumor patients selected according to strict indication criteria have been operated on. Both the clinical-radiologic and the first histological findings available are encouraging. Special reference is made to the first fully ceramic total hip joint endoprostheses implanted in a human without bone cement.