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THAs were performed with conventional cementing on one side (1985 to 1986) and with modified cementing using HA granules on the other side (1986) of the same patients. Both hips were compared 19 to 20 years after surgery. In IBBC, there was no loosening, radiolucent line (RLL) < 1 mm was in one acetabulum and osteolysis was in one femur. In conventional cementing three hips were revised within 18 years in five acetabular loosenings. RLL > 2 mm and osteolysis were defined in every patients in both femur and acetabulaum.

We evaluated the differences of histological findings of the retrieved specimens from the different areas in the same hip with interposing HA granules and without interposing HA granules between the bone and bone cement interface. In the area existing HA, bone ingrowth into the spaces of HA granules was very dense and a thick bone layer with HA granules contacted around the bone cement. In the area not-existing HA, bone formation at the base was seen poorly and bone formation at the area adjacent to the bone cement was not seen.

A growing fatigue crack is known to be retarded on application of an overload cycle. The retardation may be characterized by the total number of cycles involved during retardation and the retarded crack length. The overload ratio plays an important role to influence the retardation behavior. The objective of the present investigation is to study the effect of different overload ratio on the retardation behavior. For ESET (eccentrically-loaded single edge crack tension) specimens, fatigue crack growth tests were conducted under cyclic constant-amplitude loading including a single tensile overloading with different overload ratios. The proposed crack retardation model predicted crack growth retardation due to a single tensile overloading. The predicted results were compared with the experimental ones to confirm the reliability of this model.