Comparative bone growth behavior in granules of bioceramic materials of various sizes.

Various bioceramic materials were implanted into 6-mm-diameter holes made in the femoral condyles of mature Japanese white rabbits using different-sized granules to find an optimal material and granule diameter for use as a bone graft. Bioceramics include a bioinert ceramic (Alumina), surface-bioactive ceramics [hydroxyapatite (HAp) and Bioglass(R)], and resorbable bioactive ceramics [alphatricalcium phosphate (alpha-TCP), beta-TCP, tetracalcium phosphate (TeCP), Te. DCPD, Te. DCPA, and low-crystalline HAp]. Granule sizes were 100-300, 10, and 1-3 microm. Bone growth behavior varied with the kind of bioceramic and the size used. For surface-bioactive ceramics, 45S5 Bioglass(R) led to more rapid bone proliferation than synthetic HAp. In resorbable bioactive ceramics, the order of resorption was: low-crystalline HAp and OCP > TeCP, Te DCPD, Te DCPA > alpha-TCP, beta-TCP. In terms of biocompatibility, alpha-TCP was better than beta-TCP.

The effects of polyethylene cup thickness on wear of total hip prostheses.

The wear rate of the ultrahigh molecular weight polyethylene cups in combination with a 28 mm alumina femoral head was measured on the radiographs of patients without any complications, and on cups retrieved due to slight loosening of the prosthesis or due to late infection between bone and components. The wear rate on the radiographs did not include the initial wear, but the wear rate on the retrieved cups did include the initial wear. The wear rate on the retrieved cups was higher, by 50%, than that measured on the radiographs. In both cases, the thicker the polyethylene cups, the lower was the wear rate measured. The average wear rate of the 7 and 8 mm thick cups was about twice that of cups 10 and 11 mm thick. From these results, we conclude that polyethylene cups more than 11 mm thick should be used.

Hydroxyapatite in revision of total hip replacements with massive acetabular defects: 4- to 10-year clinical results.

Hydroxyapatite (HA) granules of 100 to 300 microm, 0.9 to 1.2 mm and 3.0 to 5.0 mm were mixed in a ratio of 10:45:45 and packed into massive bone deficiencies in revision operations for total hip arthroplasty. We did not use additional graft or cup support for deficiencies of the lateral and medial wall. The procedure was carried out in 40 hips between 1986 and 1992. The radiographic spaces seen at the interface between HA and bone immediately after surgery disappeared within three months. Some spaces appeared between HA granules near the bone in the lateral part of two joints, and three sockets migrated in patients with severe segmental and cavitary deficiencies. Direct bonding of HA to bone was observed radiologically without morphological changes, except in the three joints with migration. All patients could walk without pain but the three with definite loosening needed crutches.

Particulate bioglass compared with hydroxyapatite as a bone graft substitute.

Bioactive ceramics, notably hydroxyapatite, have been used clinically in various situations in which bone augmentation and restoration are required. Particulate material has been used either alone or in conjunction with freeze dried or autologous bone, with variable clinical success. In this study a bioactive glass, 45S5 Bioglass, has been compared with hydroxyapatite in an animal model to discover whether the 2 major disadvantages of hydroxyapatite may be overcome. These are the difficulty of placing and retaining the particulate in the defect and the length of time needed before full bony restoration is achieved. Bioglass is shown to be easy to manipulate and hemostatic and allows full restoration of bone in 2 weeks, rather than the 12 weeks needed for the particulate hydroxyapatite to produce a comparable response. The Bioglass particulate is used up in the process, and any problems that may be associated with the production of a composite of bone and biomaterial are avoided in the fully restored bone. In any procedure that requires bony augmentation, this rapid response to Bioglass is expected to provide a clinical advantage.

Alumina versus polyethylene in total knee arthroplasty.

The cementless alumina total knee prosthesis, which uses alumina in the portions coming in contact with the bone and a combination of alumina and ultra-high molecular-weight polyethylene (UHMWPE) in the sliding portions, is referred to as a total condylar. Alumina total knee arthroplasty was performed on 137 patients, including 103 rheumatoid arthritis (RA) and 34 osteoarthrosis (OA) patients, from January 1982 to February 1985. The follow-up period was seven years 11 months and four years ten months, respectively. At follow-up evaluation, 108 patients were available for clinical and roentgenographic examinations, amounting to a 79% follow-up rate. At follow-up examination, 67 joints (62%) were completely pain free and 28 joints (26%) caused slight pain on bearing weight. Walking ability was recovered moderately in RA and markedly in OA. In RA, 14 of 84 knees were cemented and one knee was treated with loosening. Of 72 cementless implantations, 55 sustained displacing distally and one sustained loosening in the tibia, whereas 31 sustained displacing proximally and six sustained loosening in the femur. In OA, 21 cementless knees had 17 displacings in the tibia, and ten displacings and two loosenings in the femur. Scanning electron microscopy (SEM) observation of the UHMWPE surface in tibial plates revealed smoothing and burnishing. Alumina is far superior to metal for the sliding part, although it is not always best for the portion in contact with the bone. To resolve these problems, for cementless fixation, anchoring portions of Ti alloy and alumina implants were covered with beads and coated with hydroxyapatite. For cement fixation, "the interface bioactive bone cement technique" interposing hydroxyapatite granules between bone and cement was performed.

[Total hip replacement and acetabular bone grafting to acetabular dysplasia].

We have described the problems of deficient acetabular and femoral bone stock in the Japanese total hip prosthesis patients. From the mechanical viewpoint, coverage of the ultra-high-molecular-weight-polyethylene (UHMWPE) socket with bone graft is a prerequisite for preventing socket loosening. Use of a larger diameter UHMWPE cup in combination with new grafting techniques is highly desirable for reasons of creep reduction and minimal wear. From 1984 on, we reported on about 300 cases of dysplasia, high dislocation, RA and osteonecrosis of the hip. Depending on the severity of the problems, various configurations of femoral-head and neck bone grafts and hydroxyapatite particles (100-300 microns in diameter) in combination with bone cement were used. Bone resorption was seen only in the non-weight bearing regions of the graft. With our interface bioactive bone cement and grafting techniques, some of the problems of radiolucent zones and socket wear common to such difficult cases are believed to have been overcome.

The effect of hydroxyapatite coating on bone growth into porous titanium alloy implants.

In rabbits and goats, test implants with a porous surface of two layers of Tl-6A;-4V beads were examined at intervals for bond strength with bone. Half of the implants were coated with hydroxyapatite by plasma spray. The bonding strength with bone in the coated specimens was about four times greater than that of the uncoated specimens at two weeks, and twice as strong at six weeks. Twelve weeks after implantation, the strengths were similar. The hydroxyapatite coating of the beads provided earlier and stronger fixation.