High rate of fusion in sheep cervical spines following anterior interbody surgery with absorbable and nonabsorbable implant devices.

Abstract

Fourteen sheep were fused using anterior interbody implants at C2-C3 and C4-C5 and followed for 6 months. To evaluate the effect of absorbable and nonabsorbable implants on fusion rate, cage migration, and implant integrity. Despite the high clinical success rate with metallic plates and interbody grafting, complications such as dysphagia, imaging artifacts, and revision difficulties exist. Less permanent and lower profile implants could minimize these problems. Four treatments were studied: 1) carbon fiber-reinforced polymer (CFRP) cage alone, 2) CFRP cage with an absorbable tension band, 3) absorbable cage with an absorbable tension band, and 4) absorbable cage with a titanium plate. Fusion was assessed using radiographs, biomechanical testing, and micro-CT analysis. Treatments with the CFRP cage alone had the lowest fusion rate at 3 months (2/6) and 6 months (4/6). The CFRP cage with the absorbable strap treatments had 5/6 fusions at 6 months. The absorbable cage with absorbable strap also had 5/6 fusions, but two of the cages fractured. The absorbable cage with titanium plate had 5/6 fusions, but the one partial fusion was attributed to poor screw and plate placement. Using both absorbable and nonabsorbable implants, high fusion rates were achieved in the challenging sheep cervical spine model. However, the absorbable cages were not able to withstand the mechanical forces during the 6-month survival period.