In vitro stabilizing effect of a transforaminal compared with two posterior lumbar interbody fusion cages

Study Design. An in vitro biomechanical flexibility test on different lumbar interbody fusion cages using mono-segmental lumbar spine specimens. Objective. To investigate the stabilizing effect of a transforaminal lumbar interbody fusion (TLIF) cage compared with two established posterior lumbar interbody fusion (PLIF) cages. Summary of Background Data. TLIF using interbody fusion cages is gaining more and more popularity in the treatment of degenerative disc disease. However, only little is known on its biomechanical behavior. Methods. Eighteen intact human lumbar spine segments were tested for flexibility in a specially designed spine tester. Pure moments were applied in the three main planes, and range of motion and neutral zone were determined. Then, TLIF using the sickle-shaped MOON cage (AMT AG), PLIF using the cubic Stryker cages (Stryker Orthopaedics), or PLIF using the threaded BAK cages (Zimmer Spinetech) was carried out and the specimens tested again. Results. The stability after implantation of the MOON TLIF cage did not significantly differ from that after implantation of the cubic Stryker PLIF cages (P > 0.05). In contrast, the threaded BAK PLIF cages had a significantly higher primary stability than both the MOON TLIF and the Stryker PLIF cages in lateral bending, flexion, and extension ( P < 0.05) but not in axial rotation (P > 0.05). Conclusions. In terms of its stabilizing effect, TLIF using the MOON cage can be recommended as an alternative to PLIF using the cubic Stryker cages. Compared with the threaded BAK PLIF cages, however, the MOON TLIF cage provides a lower primary stability in lateral bending, flexion, and extension.