Unexpected Bone Formation after Stand-Alone Anterior Cervical Discectomy and Fusion Using Polyetheretherketone Cage with i-Factor

Several recent studies have revealed that anterior cervical discectomy and fusion (ACDF) with i-factor, a bone substitute material, is safe and effective, with a superior fusion rate. Clinical studies with i-factor have thus far been shown favorable results, despite theoretical concerns; moreover, no adverse events related to i-factor after ACDF have been reported. Herein, we discuss two cases that presented unexpected bone formation after ACDF using polyetheretherketone (PEEK) cage with i-factor. A 60-year-old male patient underwent stand-alone ACDF surgery at the C4–5–6–7 level. The appropriate PEEK cage was selected, filled with an i-factor 2.5 mL divided into 1/3 that was intermixed with autologous bone chips, The patient developed mild dysphagia 1 month after surgery. A simple cervical spine radiograph showed unexpected bone formation in the anterior portion of the vertebral body at C6 and C7 levels. A 67-year-old male patient underwent stand-alone ACDF surgery at the C3–4 level. The appropriate PEEK cage was selected, filled with 1 mL of i-factor 1 mL that was intermixed with autologous bone chips. The patient developed mild dysphagia 3 months after surgery. Computed tomography (CT) scan revealed the presence of a bridging bone at the graft level, but showed unexpected bone formation in the anterior portion of the vertebral body. The unexpected bone formation causing dysphagia that we observed may be due to the high potent bone-inductive capacity of i-factor, but instead because there are no guidelines on proper dosage and usage. Further biomechanical studies are required to determine the optimal dose and usage instruction of i-factor.