A new kind of Cage made of poly-DL-lactic acid was designed and an in-vitro study was conducted to evaluate the biomechanical effect of PDLLA Cage on a goat cervical spine model. 27 goat cervical spines were divided into four groups randomly: intact group, PDLLA Cage group, titanium Cage group, and autologous tricortical iliac crest bone group. Different implants were implanted after complete discectomy (C3-4) was performed, then they were tested in flexion, extension, axial rotation, and lateral bending with a nondestructive stiffness method using a nonconstrained testing apparatus, and three-dimensional displacement was measured. The range of motion (ROM) and the mean stiffness values were calculated and compared between groups. The result showed that the ROM values between PDLLA Cage group and the titanium Cage group were not significantly different in extensional and rotational movement (P0.05), but they were lower than that of rest groups (P0.05). In flexional loading mode, the ROM values showed statistically significant difference between the four groups (P0.05). And in lateral bending loading mode, no significant difference was found between PDLLA Cage group and iliac crest bone group (P0.05), but significant difference was found among the other groups (P0.05). The stiffness of cervical spine was raised after Cage was implanted. In flexional and rotational loading mode, significant difference in stiffness was found between PDLLA Cage group and control group or iliac crest bone group (P0.05). So PDLLA Cage can provide enough primary stability for cervical intervertebral fusion.
