Shear-load carrying capacity of cancellous bone after implantation of self-reinforced polyglycolic acid and poly- -lactic acid pins: experimental study on rats

Both distal femora of 40 rats were implanted with a self-reinforced polyglycolic acid (SR-PGA) pin in the right femur and with a self-reinforced poly- -lactic acid (SR-PLLA) pin in the left femur. The intact femora of 20 rats served as controls. The follow-up times were 1, 3, 6, 12, 24, 36, 48, and 52 weeks. After killing all operated and control femora were examined macroscopically and radiographically. The shear-load carrying capacities of all the femurs were investigated, and the SR-PGA and SR-PLLA fixed specimens were compared with each other and with the control specimens. The shear-load carrying capacities reached their highest values at 36 weeks in the SR-PGA and SR-PLLA fixed and control specimens. Thereafter they gradually decreased. At 52 weeks both the SR-PGA fixed specimens and the control specimens had statistically significantly (p<0.001) higher values than the SR-PLLA fixed specimens, when the influence of the pins had ceased. Otherwise, the shear-load capacities showed higher values in the SR-PLLA fixed specimens, as the pins carried the load. During the whole follow-up period the mean shear-load carrying capacity of the SR-PGA fixed specimens was 171.2 N and that of the SR-PLLA fixed specimens 180.9 N, the corresponding value of the control specimens was 148.2 N.