Stability After Anterior Lumbar Fusion with Interbody Cages: A Radiostereometric Evaluation

Background: Interbody cage stabilization as a stand-alone procedure in lumbar spine fusion is questioned due to inconsistent mechanical effects registered in human cadaveric studies. Even segmental mobility exceeding the normal range of motion is described after cage implantation. For the anterior interbody cage fusion, this potential, undesired destabilization is explained by the resection of the anterior longitudinal ligament included in the surgical procedure. Patients and Methods: Four patients with degenerative disc disease and long-standing lumbar pain had an anterior lumbar fusion using threaded interbody cages. Five segments with defined preoperative mobility measured by radiostereometry (RSA) were treated. The postoperative mobility effects after cage stabilization were assessed by repeat RSA 1, 6 and 12 months after surgery and related to the preoperative findings. Results: Before surgery, the lumbar segments aimed for fusion were all mobile with a significant sagittal mobility, range 1.3 to 3.1 mm. One month after cage implantation, the intervertebral mobility was reduced in all segments and fully abolished in three. Persisting but minor sagittal translations were seen in two segments. One of these turned fully stable at the one-year follow-up. Interpretation: According to our study, the anterior interbody cage fusion has the biomechanical potential to provide immediate segmental stabilization. The technique can be used as a stand-alone procedure without supplementary instrumentation. The adequate mechanical properties justify extended clinical studies on outcome and complications to evaluate the anterior interbody cage stabilization as instrument in lumbar fusion.