Since 1984, we began to use Interface Bioactive Bone Cement (IBBC) technique by interposing osteoconductive and not resorbable crystalline HA granules of 0.3 to 0.6 mm in diameter between bone and bone cement at cementation during surgery. We expected super long term longevity of bone/bone cement bonding in IBBC technique.

Specimens were retrieved at the revision THA from the eight patients. They were operated for hip due to OA and RA. Revision THAs were done 4, 6, 8, 10, 13, 14, 18, 19 and 21 years after primary THA due to separation of polyethylene cup with metal-back from the bone cement, late infection and ceramic cup breakage. The specimens were obtained in bloc to keep the bone cement-HA granules-bone interfaces intact. Non-decalcified specimens were cut perpendicular to the interface and were stained by Toluidine blue. They were investigated by an optical microscopy.

Cancellous bone entered into the space of HA granules from the cancellous bone base and cortical bone entered into the space of HA granules from the cortical bone base. When several layers of HA granules were smeared densely on the bone, bone ingrowth into the spaces of HA granules was obvious and thick bone layer with HA granules directly contacted to the bone cement. When HA granules were smeared sparsely even if several layer of HA granules were smeared, bone ingrowth into the spaces of HA granules was not dense. Even if one layer of HA granules was smeared sparsely, bone formation was seen around the HA. Through out 4 to 21 years bone ingrowth into the spaces of HA granules was the same at the interface of bone/bone cement. However, at the area existing no HA granule, bone formation at the interface of bone/bone cement decreased after the onset of osteoporosis due to aging.

When HA granules were smeared in several layers and densely, thick bone layer with HA granules directly contacted to the bone cement even after 21 years after surgery and after onset of osteoporosis due to aging. As previously reported, the appearance rate of radiolucent line on the radiograph was extremely low even 21 years after surgery. Form these clinical results long term longevity over 30 to 40 years could be expected.