Suitability of bioresorbable cages for anterior cervical fusion

Abstract

<jats:p content-type="fine-print"><jats:italic>Object.</jats:italic> 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 discectomy (ACD) in a caprine model.</jats:p> <jats:p content-type="fine-print"><jats:italic>Methods.</jats:italic> 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.</jats:p> <jats:p content-type="fine-print">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.</jats:p> <jats:p content-type="fine-print"><jats:italic>Conclusions.</jats:italic> 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.</jats:p>

Bioabsorbable Interbody Cages in a Sheep Cervical Spine Fusion Model

“…The limited biomechanical properties of the tricortical iliac crest bone graft resulted in a compression and sometimes fragmentation of the graft, followed by extensive osteoclastic activity and finally, graft resorption. In contrast, the bone grafts packed inside the cages have a biomechanically protected, and as a result, biologically improved, environment for fusion, 31 leading to a higher interbody fusion mass, especially in the PCC-cage group. This effect, which should have also been available in the PLDLLA-cage group, was alleviated by the severe foreign body reactions associated with this implant.…”

“…Cages should retain interbody distraction and should be resistant against subsidence into the adjacent vertebrae in order to guarantee bony fusion in a desired quality. 31 However, currently subsidence of cages has only been investigated in some experimental animal in vivo studies. Using sheep animal models, Sandhu 32 and Kandziora 7 showed that metallic cages were able to preserve interbody distraction more effectively than an autologous iliac crest bone graft.…”

“…The initial biomechanical in vivo stability of the cage-plus-graft composite is almost exclusively a result of the biomechanical properties of the cage. 7,31 The interbody fusion mass arising from the incorporated bone graft contributes to biomechanical stability only secondarily. 8 With the biomechanical in vitro results of both bioabsorbable cages in mind, 13 the significantly higher biomechanical stability of the PCCcage group compared with the PLDLLA-cage group in this study might be an effect of the cage design and the biomechanical in vitro properties of these implants.…”

Competitiveness of chitosan-based implants

“…As spinal interbody implants need to maintain mechanical integrity for a period of at least six months [73], this has serious implications for the clinical application of absorbable polymer-based implants in load bearing situations. Moreover, some authors declare that the disintegration of absorbable polymerbased implants into particles with a very slow hydrolytic degradation rate, as recommended for spinal fusion applications, can induce and maintain a clinically detectable swelling, with the occurrence of foreign body reactions, allowing skepticism regarding the value of these bioabsorbable implants [74,75]. An ideal scenario for interbody fusion is a cage device that has a modulus of elasticity that is the same as or close to that of vertebral bone, that will be absorbed after interbody fusion, maintaining the strength under continuous and alternate loading throughout the period of time required for full spinal bony fusion (a minimum of 6 months) and that will be replaced by cancellous bone, not leaving foreign body material in the spinal segment, but only a bony fusion between the vertebrae [76,77].…”

Biodegradierbarer Cage

“…Cahill et al [10] untersuchten einen biodegradierbaren intervertebralen 85/15-Polylaktid-Polyglykolid(PLA-PGA)-Kopolymer-Cage in einem zervikalen Ziegenmodell. In einem Nachuntersuchungszeitraum von 12 Wochen konnten sie im Vergleich zur Kontrollgruppe keine stabile Fusion beobachten.…”