Lumbar sagittal alignment after fusion with a threaded interbody cage.

STUDY
DESIGN: Records of 111 patients randomly selected from a population who received an interbody fusion cage during a clinical Investigation Device Exemption trial (BAK/L) yielded 126 operative levels and were retrospectively assessed.
OBJECTIVES: This study examined lumbar spine sagittal alignment and clinical outcomes before and 2 years after fusion surgery. SUMMARY OF BACKGROUND DATA: Lumbar lordosis is important in spinal sagittal alignment and balance, especially the L4-S1 area. Perceived consensus is that anatomically correct lumbar lordosis is desired and that a loss of lumbar lordosis may lead to spine pathology. There is little information on lumbar lordosis after interbody fusion.
METHODS: A random sample of 111 patients who received a cylindrical cage implant (total pool of 947 patients) yielded 126 operative lumbar segments. There were 52 posterior approaches and 59 anterior approaches, and all cages were placed in the L4-L5 or L5-S1 levels. Preoperative and 2-year follow-up lateral radiographs were measured for segmental lordosis. Cage position was measured relative to the posterior longitudinal ligament. Segmental lordotic change was correlated to clinical outcome at the 2-year follow-up.
RESULTS: Preoperative lordosis was different as a function of surgical approach. There was a significant 2-year decrease in lordosis with the posterior approach group; however, all intervertebral angles were within typical ranges. Clinical outcomes were significantly improved 2 years postsurgery. There was no correlation between changes in lordosis and clinical outcomes.
CONCLUSIONS: Interbody lumbar fusion with a threaded cylindrical cage does not appear to have any clinically relevant effects on segmental lordosis, which is maintained within anatomically normal levels. Clinical outcome measures show significant postsurgery improvement, and changes in lordotic angles are not predictive of clinical outcome.