Hydroxyapatite (HA) is a bioactive material with a high affinity for bone. Ti-6Al-4V is lightweight and less biotoxic. Using these materials, a cementless hip prosthesis has been clinically used, consisting mainly of a Ti femoral stem coated with plasma-sprayed biocompatible HA. However, this type of stem entails several disadvantages: HA is likely to decompose at the coating; long term HA coating layer bonding to Ti is unstable and optimal HA thickness is unfeasible. In many actual cases, debonding of HA coating layer from the Ti surface was found upon removal of stems.

To resolve these concerns, we started developing a new hip prosthesis using composite materials comprised of Ti-6Al-4V and HA containing bioinactive and highly stable glass in 1985. The cementless hip prosthesis, named HAPG-Profile, unites the bioactive stem surface with the surrounding bone via adhesive glass. In basic experiments, the glass-coated HAPG-Profile has been demonstrated to possess much higher bonding stability than the plasma-sprayed HA, with bone affinity and safety not compromised. On the basis of these results, we manufactured the HAPG-Profile jointly with DePuy International, UK, and initiated a clinical trial in January 1997 in the teaching Hospital, Nagoya University School of Medicine, and Tokyo Kosei Nenkin Hospital. A total of 63 patients were followed up for more than two year and evaluated according to the Japanese Orthopedic Association Score and Harris Hip Score (HHS) clinically, functionally and radiographically. The results of the two-year follow-up study indicated success of early fixation associated with favorable outcomes.