Does bioresorbable cage material influence segment stability in spinal interbody fusion?

To reduce long term complications associated with nonresorbable interbody fusion cages, bioresorbable cages are being developed. We investigated the influence of bioresorbable cage material on segment stability, intervertebral disc height and fusion in vivo using radiostereometric analysis comparing 70/30 poly(L-lactide-co-D,L-lactide) (PLDLLA) cages with titanium cages. Twenty-eight goats were randomized to receive PLDLLA (n = 21) or a titanium control (n = 7) cage at L3-L4. Range of motion for flexion and extension and change in intervertebral disc height were measured before and after surgery and at followup (3, 6, and 12 months). Fusion was graded with a validated radiographic score. Although the PLDLLA cage could not provide the optimal environment for a successful high fusion rate, the range of motion of the PLDLLA segments gradually decreased in time and was similar to the titanium control group at 12 months. In addition the decrease of intervertebral disc height was similar for both PLDLLA (1.4 +/- 0.8 mm) and titanium (1.3 +/- 1.0 mm) specimens. Both results showed a bioresorbable cage does not lead to less decrease of motion or more loss of intervertebral disc height in time compared to titanium. This study therefore supports further development of a bioresorbable cage concept.