Study Design. Retrospective radiographic review.
Objective. To determine the incidence of osteolysis, graft subsidence, and cage migration after recombinant human bone morphogenetic protein-2 (rhBMP-2) use with transforaminal lumbar interbody fusion (TLIF).
Summary of Background Data. Osteolysis after TLIF is a recently described phenomenon associated with rhBMP-2 use. Although this is typically a self-limiting condition, complications such as graft subsidence and cage migration have been described. The incidence of this is not well defined and most studies use plain radiographs for diagnosis rather than more advanced imaging. This study serves to quantify the risk of osteolysis and its associated graft complications with routine use of computed tomography.
Methods. A total of 58 patients who underwent primary TLIF from a single surgeon between 2004 and 2007 underwent routine postoperative computed tomographic scan. Seventy-seven levels of fusion were evaluated for osteolysis. All patients received the same dose of rhBMP-2 of 5 mg per level. Imaging was performed immediately postoperative and again at an average of 4.3 months postoperative (range = 2.4–9.0 months). These images were evaluated for the presence of osteolysis, graft subsidence, and cage migration. These changes were then graded according to their severity.
Results. Osteolysis was found in 16 of the 58 (27.6%) patients and 19 of the 77 (24.7%) levels treated. No significant difference was found between single and two-level fusions. The degree of osteolysis ranged from 3 to 20 mm with an average of 12.5 mm. The osteolysis was characterized as severe (>1 cm) in 12 of the 19 levels. Of the patients with osteolysis, 31.6% demonstrated graft subsidence all of which occurred with severe osteolytic defects. Migration of the intervertebral cage was found in 8.8% of patients.
Conclusion. rhBMP-2 use with TLIF is associated with a significant risk of postoperative osteolysis. Patients who demonstrated postoperative osteolysis were associated with significant risk of subsidence or migration of the intervertebral cage. The clinical implications of these changes are not currently known.