Dominique G. Poitout (ed.)Biomechanics and Biomaterials in Orthopedics10.1007/978-1-84882-664-9_13

13. Clinical Application of Glass Ceramics

Takao Yamamuro^{1, 2}

(1)

Kyoto University, Sakyo-ku, Kyoto 606-0805, Japan

(2)

Research Institute for Production Development, Shimogamo, Sakyo-ku, Kyoto, Japan

Takao Yamamuro

Email: mmozume-takaoyama@sweet.odn.ne.jp

Keywords

Glass ceramicsSynthetic hydroxyapatite as bone substituteBone substituteBiomaterials in orthopedicsSpacers for spineWollastonite-containing glass-ceramic for orthopedics

It is now widely known that bioactive ceramics such as Bioglass®, Ceravital®, synthetic hydroxyapatite (HA), apatite- and wollastonite-containing glass-ceramic (AW-GC) and ß-tricalcium phosphate (ß-TCP) have a character of osteoconduction and a capability of forming a direct bond to the living bone tissue [1, 2]. In other words, they are incorporated into the living bone tissue in accordance with the pattern of bonding osteogenesis. In their clinical use, however, the mechanical property and the grade of bioactivity required to each material differ depending on the case, i.e., size, shape and location of the bone defect, and the purpose of application. For example, when they are to be used for replacing a vertebral body, a high mechanical strength rather than a high bioactivity is required, if both are not available at the same time. On the contrary, when they are to be used as a coating material over the surface of joint prosthesis, a high bioactivity rather than a high mechanical strength is required. Generally in orthopaedic application of bioactive ceramics to substitute for a large bone defect, a high mechanical strength is always required. For this reason, Bioglass® and Ceravital® which have much lower mechanical strength than that of the human cortical bone have not been used in the field of orthopaedic surgery, although their bioactivity is higher than others. As ß-TCP is a biodegradable ceramic, its mechanical property after implantation can not be compared with those of others. The author’s personal experience of their clinical use is, therefore, mostly limited to HA and AW-GC that were used in forms of either granular, porous or dense bone substitute in combination with autogenous bone, and also in forms of coating material for joint prosthesis or bioactive cement.

Why Glass Ceramic

At Kyoto University Hospital, in 1981, probably for the first time in the world as far as known from literatures and meetings, a large amount of synthetic HA granules was implanted into the human bone for a purpose to replace a large giant cell tumor which developed in the right ilium of a 27 year old female. At operation, the tumor was resected through a window made in the lateral wall of the ilium. The bone defect remained in the pelvic bone after the resection was too large to be completely filled in with autogenous bone chips, but bone allograft was not yet available in 1981. Then, a large amount of granular and porous HA was prepared mixed with fibrin glue and autogenous bone chips, and the mixture was compactly filled into the bone defect. The clear line, which was demonstrated on the postoperative radiograph between the implanted mass and the pelvic bone, persisted for about 8 months after surgery suggesting that the implant had not yet united with the pelvic bone. At 10 months after surgery, a biopsy of the implanted mass was performed and it was confirmed histologically that the implanted HA granules have directly united with the newly formed bone in places. The radiograph taken 1 year postoperatively showed no clear line between the implanted mass and the pelvic bone. Then, the patient was allowed to bear the full body weight on the affected side. Thus, in this case, it took nearly 1 year after implantation to obtain complete gap filling and bone bonding with HA granule. The patient has been doing well up to now for 25 years after surgery with neither recurrence of the tumor nor limitation of movements of the hip joint of the affected side.

What we learned from this case a quarter of century ago were; firstly, that synthetic HA really bonded to the living bone tissue, but it took nearly 1 year after implantation for gap filling and bone bonding, indicating that HA has a relatively low osteoconductivity; and secondly, HA granule is mechanically too weak to be used under the situation where body weight should be loaded. Nevertheless, synthetic HA has widely been used thereafter in cases of bone tumors and hip revisions. In our surgical practice, however, often there is a need for a more bioactive and mechanically stronger bone substitute than synthetic HA, so that patients will be able to start the weight bearing much earlier after surgery.

At Kyoto University, the research group led by Yamamuro and Kokubo had attempted to synthesize such a biomaterial as that which has a stronger bioactivity and a higher mechanical strength than synthetic HA, and finally reached the synthesis of a new glass-ceramic in 1982 which was named apatite- and wollastonite-containing glass-ceramic (AW-GC) [3]. It was found that dense AW-GC has a bending strength and compressive strength both significantly higher than those of the human cortical bone, while the bending strength of dense HA is considerably lower than that of the human cortical bone. As for their bioactivity, when they were soaked in the simulated body fluid at body temperature, apatite formation was usually observed within 7 days over AW-GC, while it took 28 days for HA.

Application of AW-GC to the Spine

Vertebral Body Prosthesis

In February 1982, a vertebral body prosthesis made of AW-GC was first prepared for the purpose to replace the lumbar vertebra of a sheep [4, 5]. The prosthesis was implanted into the spinal column of a sheep to replace the 3rd and 4th vertebral bodies. A contact microradiograph of the specimen harvested 6 months after implantation demonstrated that the prosthesis had already bonded to the bone trabeculae all the way around. Thus, animal experiments performed on a number of sheep suggested that the vertebral body prosthesis made of AW-GC would be clinically better applicable, due to its stronger osteoconductivity as well as higher mechanical strength, than those made of HA. For these reasons, vertebral body prostheses made of AW-GC with different sizes were prepared for clinical application.

A 50 year old female who developed a breast cancer metastasis in the 10th thoracic vertebra with early sign of paraplegia. As the patient had multiple metastases in the bilateral ilia, it was difficult to harvest the autogenous bone graft. Therefore, in December 1982, the tumor in the spine was simply replaced with a vertebral body prosthesis made of AW-GC, and the body weight bearing was started 1 month after surgery. In spite of multiple metastases developed 5 years later in other organs, the patient survived 14 years after the first operation without paraplegia by the support of chemotherapy.

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