J. BIOMED. MATER. RES. SYMPOSIUM
NO. 6 , pp. 227-232 (1975)
Experiences with A1,0, Implantations in Humans to Bridge Resection Defects A. ENGELHARDT, Orthopadische Universitats Klinik, Frankfurt-Muin Germany, M. SALZER, Orthopadische Universitats Klinik, Vienna, Austria, A. ZEIBIG and H. LOCKE, Rosenthul Stemag, Technische Keramik A G , Lauj, Germany
Summary Various implants have been developed for the upper and lower extremities and the spine. In order to establish whether endoprostheses made of AI,O, will show the same good biocompatibility in humans as it has in experiments with animals, endoprostheses implantations were performed in 4 patients: 2 upper arms, 1 radius, I vertebra body. The implants were exposed to various loads. The hiomechanical conditions were considered in the construction. The results reveal that the knowledge of material properties and prior calculations make possible the development of satisfactory endoprostheses. X-ray examinations confirm these deductions. Good functionality was achieved in vivo with all implants. They were all mechanically anchored, no bone cement was used. Thus the biocompatibility of the material was not limited. A histological examination is made of one implant. The macroscopic examination showed a stable fit and no pathological reactions. X-rays revealed that the bone remained in good contact with the implant. The longest observation period was over 1 years. Present observations show that the use of A1,0, implants, without the use of additional materials (bone cement), results in a tight fit of the implants.
An endoprosthesis should restore the function of a defective part of the skeletal system. Loosenings of the implant and alterations of the physical and chemical properties must be avoided. The following report shows the effects of prior theoretical biomechanical considerations with regard t o the physical properties of A1,0, and some practical results and experiences with implantations in patients with malignant tumors. Four patients have been supplied with different types of implants. We replaced various parts of the skeleton which are exposed to different stresses. MATERIALS AND METHODS
In our opinion the biocompatibility of the aluminum oxide ceramic, as established in experiments with animals, is due to its chemical inertness and subsequent lack of electrochemical reactions, such as corrosion. 227
0 1975 by John Wiley & Sons, Inc.
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Thus, toxins inhibiting the regeneration of tissue do not develop. The elimination of such adverse reactions at the tissue-implant interface improves the prognosis of long-term implant behavior in human bodies. The careful shaping of the bone with specially developed instruments provides for exact implant fitting. The module technique allows selection of proper implant parts during the operation, thus guaranteeing an immediate load bearing stable fit, without the use of a filling material. In our cases the conditions for the osseous fixation were worse than usual due t o the cytostatic treatment of the carcinoma patients which has an adverse effect on the regeneration process of the bone matrix. Three alternative methods for anchoring an implant exist: 1) intramedullary fixation; 2) supracortical fixation; and 3) a combination of both methods. Based on our present results we found that bending strains in the connective area of implants for the upper extremity cannot be entirely eliminated, because of the following reasons. 1) It is not possible to make a perfect imitation of the natural shape of the shaft with its flexings. 2) The direction of the muscle force (M,) generated by the upper arm musculature, seen from the lateral view, crosses the axis of the femur under the angle yl; from the front view the angle Y~ is smaller. After a resection of muscles, or parts of muscles, the direction of the generated forces might change due to a change in the muscle initiating the action. Such individual changes in musculature and its activating potential must be considered in the designing of implants. Bending, tension, and pressure loads at the bone-implant interface must all be allowed for in the design and attachment of each implant. In order to obtain good adhesive forces in the upper part of the resection, an area twice the size of the cross section of the cone is employed for attachment. A small cone angle supports the adhesion. In addition a plastic deformation occurs at the time the cone is implanted. The effect is increased by thread-like grooves at the inner bone surface which can easily be impressed into the cone surface through plastic deformation. The skeletal elements are not round, but more or less of a triangle shape. Thus it is possible to achieve a three-point fixation at the distal end of the implant after previously tapering the crest. This method has the following advantages. 1) The continuous transition without interfering binding materials, from implant to bone eliminates areas of stress concentration. 2) Tongue-shaped areas of the periosteum can be saved. These can extend deeper into the resectioned end and thus maintain the blood supply and metabolism. The cone must be set up in such way that the ceramic surface at its terminal end will be in intimate contact with the resectioned end. This provides an additional area for the transmission of pressure. During the operation the cone sleeve is checked for tightness
of fit. Use of the module technique allows selection of a sleeve with another, more suitable, diameter.
RESULTS In our first implantation  we used, in addition, an intramedular screw. The screw threads and almost all other surface grooves in the contacting bone areas were rounded off, thus avoiding load concentrations, which, according to Wolff's Law, lead to necrotic reactions. Endostal and subperiostal areas with necrotic reactions due to interference with blood circulation did not appear, as some had predicted. After an implantation period of l'i, year there was no evidence of such reactions. The tumor operation necessitated either resection of parts of the deltoides, the adductors, the biceps, triceps, and brachialis or that they be contacted by myoplasty. Therefore the full range of movement in the shoulder joint was only achieved with the use of the other arm, although lesser movement could be performed actively. The elbow retained full functional capacity. X-rays show a stable fit of the implant. The outlines of the bone are sharp. Shadows appear in the threading area indicating an osseous structure. Our first implant is now available for extracorporeal investigation. The macroscopic examination disclosed that, without any irritation, the implant had been encased with a thin-layer of soft connective tissue at the implant-musculature interface. A small amount of serous liquid was found in the capsula. Where the muscles attached to the implant, scattered infiltrations of collagenous fibers were found in the connective tissue. No pathological reactions were observed at the implant-bone interface. The mechanical examination revealed a tight fit of the implant, as had been previously observed in experiments using corpses. The attachment was resistant to all loads. As histological examinations were to be run on the bone-implant interface, the implant was not separated from the bone. Extracorporeal x-ray pictures taken of the preparation after removal of the soft tissue show no evidence of necrotic reactions. Partly one could not detect a fissure at the junction between bone and ceramic implant. To a different degree all of the threads were filled with shadows which we assume resulted from osseous ingrowth. The implant remained in the original position where it was fitted. There was no evidence of an atrophy from disuse.
DISCUSSION The present results show: 1) It is possible to accomplish a permanent mechanical fixation of a ceramic implant without using additional
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auxiliary filling materials. 2) After an observation of more than 1 year no evidence of necrotic reactions was seen on x-ray pictures. 3 ) The mechanical load test shows a stable fit despite the poor starting conditions due to the carcinoma and the related postoperative treatment. 4) The function of the distal joint was fully maintained, while the function of the proximal joint was achieved with partially active and partially passive movements in its terminal part. Thus the implant was always exposed to acting forces during its daily use. The other two implants, the distal part of the radius and the proximal part of the humerus, were only fitted with a sleeve. Since we have improved the method of operation and have previously defined the fitting area for the sleeve, we had no problems with fixation. The radius was implanted on the patient’s request. H e is a painter and needs free movement of the wrist joint. Nine months after the implantation was performed, full function of the wrist was restored. Detrimental effects were not observed in the second humerus implantation. The range of movement in the shoulder was limited in its terminal part, however, due t o the partial resection of the shoulder musculature. With regard t o the present implants, it should be noted that stresses acting on the upper extremities are rather small. The replacement of a vertebra imposes other requirements. The resection of a vertebra body together with the intervertebral discs and ligaments necessitates a break in the continuity of the spine. Our patient had undergone two decompression operations in order t o stop the progression of a n existing partial transverse paralysis. I n a following operation we resected the body of the vertebra Th XI1 because of a tumor metastasis and replaced it with a ceramic implant. The insertion was performed in the following way. Below the aorta both halves of the ceramic vertebra body, which had loose contact with each other through a screw, were placed with a turning movement into final position. When the connecting screw was tightened, two pins were laterally pressed into the vertebra bodies of the vertebrae lying above and below. Because of the conical shape of the sleeve-like connecting pieces diverging towards the implant center they were closely fitted. A slight plastic deformation of these vertebra bodies took place through the tightening of the screw, thereby enlarging the fitting area. At the same time the gap between both halves of the ceramic vertebra body was closed. The comprehensive attachment, and the pressing in of the pins fixes the implant well in all directions. X-rays taken while the patient is in motion, show a fixation of the spine in the bridging section while the other sections maintain their mobility. N o movement could be seen in the connecting area between spine and implant.
The prerequisite for the application of such an implant is that the connecting vertebrae are fully intact. In a second operation on a different patient it was not possible to use a single ceramic implant because of bone instability due to metastases. Additional fixation with bone cement was necessary, as well as a metal plate protection. The use of segmented implants to mimic the spine's flexibility has proved to be unprofitable. The operation is excessively complicated. Safe connections with adhesive material or cement cannot be achieved during the operation. Because of respiration, parts of the implant are slightly displaced during the time of polymerization. This lessens the stability of the attachment. The first patient with a vertebra body replacement left the clinic after 3 weeks. During a routine investigation after 6 weeks he asked for permission to go swimming. H e worked again in his own profession. The observation period extended over 9 months. No negative reactions can be seen in the implantation area. His prognosis depends on the carcinoma. Our present experiences show that it is possible to obtain a tight fit of an implant with a mechanical anchorage, even in skeletal regions with unfavorable conditions and high stress. The prerequisite for establishing this type of fixation is to eliminate all movements at the implant-skeleton interface. Alternating loads have to be absorbed by elastic deformation of the connecting parts of the skeleton. In this connection, stress concentrations as defined by Wolff's Law must be avoided. The impairment of metabolism has to be kept at a minimum by the method of operation. Chemical and physical inertness favors the stabilization of the pH-value of the surrounding body electrolytes. Thus toxic reactions affecting the tissue growth in the osseous implant bed can be eliminated. CONCLUSIONS
In summary we can say that we gained experience with skeletal implants which were exposed to various loads. As a consequence of our presurgical consideration of the biomechanical requisites and avoidance of the development of toxins by the singular use of aluminum oxide, we obtained a good mechanical fixation of the endoprostheses with osseous ingrowth. These experiments are now the basis for the construction of implants for the lower extremity which are at present in different stages of development. Data received from experiments with animals do not give sufficient information. The combination of temporary therapeutic aid to cancer patients and the knowledge gained therefrom cannot be matched by other types of experiments or calculations because of the magnitude of unreliable parameters. This combination has many ad-
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vantages for the patients and the research team. The satisfying results which we gained from the small number of implants replacing different skeletal parts indicate how much the method of construction and choice of implant material can positively influence the conditions for the application of permanent implants. References [I]J . Wolff, Gesetz der Transformation der Knochen, Berlin, 1892.  R. Fick, Handbuch der Anatomie und Mechanik unter Beriicksichtigung der hewegenden Muskeln, 3. Teil, Spezielle Gelenk- und Muskelmech., Jena, 191 1 .  E. G. C. Clarke and J. Hickmann,J. Bone Joint Surg., 35B, (1953).  F. Pauwels, Gesammelte Ahhandlungen zur funktionellen Anatomie des Bewegungsapparutes, Springer-Verl, Berlin, 1965.  H. G. Lefort, C. C. Fain, and P. Hairston, Ceram. Soc. Bull., 47 (4), 370 (1968).  0. D. Petersen, J. S. Miles, C . Solomons, P. K. Predecki. and J . E. Stephan, paper presentcd at the Orthop. Res. Soc. Meeting, N.Y., Jan 17, 1969.  F. G. Evans. Arch. Putti Chir. Organi M o v . , 24, 1 (1969).  J . Charnley, J . BoneJoint Surg., 5 2 8 , 340 (1970).  J . Charnley, Acrylic Cement in Orthopaedic Surgery, Livingstone, London, 1970. [lo] S. F. Hulbert. F. A . Young, R. S . Matthews, J. J . Klawitter, 0. D. Talbert, F. H. Stelling, J . Biomed. Muter. Res.. 4 , 433 (1970). [II ] R. 1 . Hentrich, G. A. Graves, H. G . Stein, P. K. Bajpai, J . Biomed. Mat. Res., 5 , 25 (I97 I). [I21 F. W. Rhinelander, M. Rouweyha. J . C. Milner,J. Biomed. Mat. R e s . , 5 , 81 (1971). [I31 A . Engelhardt, 3rd. Int. Conf. on Med. Phys., incl. Med. Eng., Goeteborg, 1972. [ 141 A . Engelhardt, Stand der Entwicklung einer individuellen Lastermittlung mit der Methode der finiten Elemente als Grundlage fur orthop. Eingriffe am Skelett. Sicot 12, Tel Aviv, 1972. [I51 P. Predecki, B. A. Auslaender, J . E. Stephen, et al., J . Biomed. Mater. Res., 6, 401 (1 972). [I61 W. J . Selting, and S. N . Bhaskar,J. Dent. Res.. 52, 91 (1973). [I71 C . A. Homsy, Orthop. Clin. North. A m . , 4 , 295 (1973). [ 181 S. F. Hulbert, J . Biomed. Mater. Res. Symp. No. 5 , (1974). [I91 A. Engelhardt, “Development of non-metallic implants with consideration of Wolff‘s Law and human implantation experiences,” paper presented at 5th Annu. Biomater. Symp., Clemson University, Clemson, South Carolina, 1973.