Suitability of bioresorbable cages for anterior cervical fusion

Object. The authors conducted a pilot study to determine whether a bioresorbable intervertebral fusion device composed of 85/15 polylactide-polyglycolide (PLA-PGA) copolymer packed with bone autograft is a suitable alternative to promote arthrodesis after anterior cervical diseectomy (ACD) in a caprine model. Methods. The caprine cervical spine model has been used to evaluate interbody healing and fusion after application of bone grafts and instrumentation. Whether a bioresorbable device is suitable for facilitating intervertebral bone union has not been determined. Twelve goats underwent two-level ACD and fusion; eight received bioresorbable cages packed with autologous bone, and four received autologous bone alone. Goats were maintained without an orthosis and after 12 weeks underwent physical, radiographic, and histological evaluation. Cages had structurally degraded, and two had become extruded. Stable intervertebral union developed in three (19%) of 16 cage-implanted interspaces, and one (14%) of seven bone autograft-implanted interspaces; each was judged manually to be rigid (Grade 2), radiographically to be bridged by new osseous densities (Grade 2), and histologically to have marked new bone formation (Grade 3). A primarily fibrous union, however, stabilized the cage-implanted interspaces, and eight (50%) had developed a 4 to 6-mm foreign body granuloma. These interposed soft tissues were not present in the stable autologous bone-implanted interspace, which had successfully become fused. Conclusions. Interbody cages composed of 85/15 PLA-PGA copolymer contributed to a stable fibrous union, degraded, and produced granuloma after 12 weeks. Additional evaluations are necessary to determine whether other copolymer mixtures, or other bioresorbable materials, can contribute to an arthodesis without deleterious consequences.