Introduction: A biodegradable interbody cage for lumbar spine fusion would be able to solve several problems associated with the use of metallic cages. In a biomechanical in vitro study using human lumbar spines three different biodegradable poly(L-lactide-co-D,L-lacitide)(PLDLLA) cages were compared to metallic cages of the same design.
Material and method: 40 human cadaver lumbar specimens (L3-S1) were tested in flexion, extension, rotation, and bending with a non-destructive flexibility method using a nonconstrained testing apparatus. Seven different groups were examined: (1) control group (intact) (n = 40); (2) unstable group (after discectomy L4/5) (n = 40), (3) autologous iliac crest bone graft (n = 8), (4) BAK-Cage (n = 8), (5) BIO-Cage 1 (PLDLLA) (n = 8), (6) BIO-Cage 2 (PLD-LLA/hydroxylapatite-buffer) (n = 8) and (7) BIO-Cage 3 (PLDLLA/hydroxylapatite particles of different size) (n = 8). Additionally, destructive compression tests of all implants were performed.
Results: In comparison to the intact motion segment all cages showed significantly lower range of motion (ROM) in all test modes (P < 0.01). There was no significant difference in stiffness values and ROM between BIO-Cages and metallic cages. Axial compression stiffness and failure load were significantly highest for metallic BAK-cages (P < 0.05). No significant difference for failure load was observed between BIO-cage 1 and the intact motion segment. However, in comparison to the intact motion segment failure load was significantly lower for BIO-cage 2 and 3 (P < 0.05).
Conclusion: The results of this study are encouraging, because the biodegradable cages were able to limit lumbar spine motion similar to the metallic cages. Especially, the biodegradable PLDLLA cage consisting of pure polymer (BIO-Cage 1) showed adequate initial compression strength. However, further in vivo animal experiments are essential prior to the clinical application of biodegradable lumbar interbody fusion cages.