Vertebral body fracture after anterolateral instrumentation and interbody fusion in two osteoporotic patients.

BACKGROUND CONTEXT The XLP plate is an anterolateral instrumentation system developed as a part of the eXtreme Lateral Interbody Fusion (XLIF) system for lateral transpsoas interbody fusion, an alternative to anterior interbody fusion. PURPOSE To report two cases of atraumatic coronal plane vertebral body fractures in the early postoperative period after interbody fusion using XLIF cages, lateral plating using the XLP plate, and unilateral posterior pedicle screw instrumentation. STUDY DESIGN Case report. METHODS/SUMMARIES: Both patients were septuagenarian women with normal body mass indices and osteoporosis. The patients underwent L4-L5 XLIF with anterolateral instrumentation followed by posterior decompression and fusion using unilateral pedicle screws. In the early postoperative period (<or=6 weeks), the patients developed acute onset of severe low back pain without history of trauma. Imaging demonstrated coronal plane vertebral body fracture through the screw hole of the XLP plate in the superior vertebral body in one case and the inferior vertebral body in the other. One patient required kyphoplasty at the L4 level for pain relief. The other was treated conservatively. The nondisplaced fractures went on to union with pain resolution and successful fusion in both patients. RESULTS Coronal plane fractures occurred in 2 of 13 patients treated by the senior author using XLIF, the XLP plate, and unilateral pedicle screw instrumentation. Osteoporosis was likely a contributing factor in both patients. One potential mechanism for this unusual fracture pattern is subsidence of the cage with resultant cut-through of the fixed-angle screws through the osteoporotic vertebral body. Alternately, the fracture could have resulted from the stress riser created by the screw hole traversing an area of relative stress concentration directly adjacent to the cage. CONCLUSION Coronal plane vertebral fracture may occur in osteoporotic patients treated with XLIF and XLP lateral instrumentation. Unilateral pedicle screw instrumentation does not prevent this complication.