Findings: Plain radiographs of the lumbar spine demonstrate two intervertebral disc cages at the L-3/L-4 level. The disc cage on the patient's left has migrated inferiorly, having eroded into the superior end plate of the L-4 vertebral body. In addition, a ring of lucency surrounds this disc cage.

Diagnosis: Infection of intervertebral disc cages.

Discussion: The development of laparascopic placement of intervertebral disc cages allows spinal fusion with reduced hospitalization time, recovery time, patient discomfort, and expense. Hollow disc cages made of either titanium or a carbon fiber reinforced polymer are packed with autologous bone and inserted into a diseased interspace laparoscopically, utilizing a transperitoneal approach (3).

One of the possible complications, as with the placement of any type of hardware, is infection of the disc cages. Furthermore, infection can lead to nonunion, thus defeating the purpose of the procedure. This is demonstrated in this case by the region of a lucency surrounding the left disc cage. In addition, there have been case reports of carbon cages breaking if there is nonunion (2).

Reference:

1. Lund T, et al. Interbody Cage Stabilization in the Lumbar Spine:
   Biomechanical Evaluation of Cage Design, Posterior Instrumentation
   and Bone Density. J Bone Joint Surg BR. 1998, March; 80(2):351-359.

2. Tullberg T. Failure of a Carbon Fiber Implant. A Case Report.
   Spine. 1998, August 15; 23(16):1804-1806.

3. Zucherman JF, et al. Instrumented Laparascopic Spinal Fusion.
   Preliminary Results. Spine. 1995, September 15; 20(18):2029-2034.