Strength and strength retention in vitro, of absorbable, self-reinforced polyglycolide (PGA) rods for fracture fixation.

The initial shear strength and changes in flexural strength of self-reinforced, absorbable polyglycolide (PGA) composite rods, submerged in distilled water (at 37 degrees C) for a period of 6 wk, were investigated. The recently developed self-reinforced absorbable material consists of an absorbable polymeric matrix reinforced with fibres of the same polymer. The initial shear strength of self-reinforced cylindrical PGA rods with a diameter of 3.2 mm was 250 MPa and the initial flexural strength of the rods was 370 MPa. During the first week of immersion the level of flexural strength decreased very little i.e. to 320 MPa. The loss of flexural strength increased after 1 wk immersion. However, after 3 wk it was 90 MPa. After 5 wk the flexural strength decreased to the level of strength of cancellous bone i.e. 10-20 MPa. The gamma-irradiation of the PGA rods (total dosage 2.5 Mrad) decreased the initial bending strength to 300 MPa but the hydrolytic behaviour of the rods was not changed. The in vitro strength and the strength retention of self-reinforced PGA rods are clearly better than the corresponding values for self-reinforced glycolide/lactide copolymer rods which we developed recently. Self-reinforced PGA rods are now used routinely in Helsinki University Central Hospital in the treatment of certain types of cancellous bone fracture.