Abstract
BACKGROUND CONTEXT For interbody fusion implant material, autogenous bone graft is current gold standard, but it also carries several disadvantages. Tantalum and titanium are both ideal materials for interbody cages for their biocompatibility. New cage design utilizing three-dimensional (3D) printing technique, selective laser melting (SLM), to conjugate titanium powder into 3D-porous structure (porous titanium, PTi) may be an optimal choice for interbody fusion. PURPOSE To further investigate the cell properties and bone in-growth characteristics, the study aims to evaluate the PTi interbody device on the biocompatibility and the in-vivo bone ingrowth characteristics compared to nonporous titanium (NPTi), porous tantalum (PTa) interbody device. STUDY DESIGN/SETTING In vitro and in vivo study. PATIENT SAMPLE A total of six cages in six groups for in vitro study (total 36 cages). Twelve pigs for in vivo bone ingrowth study. Each pig had three cages implanted (total 36 cages). OUTCOME MEASURES Cell attachment and osteogenic markers were evaluated for in vitro study. Cage migration, subsidence, bone ingrowth were evaluated for in vivo study. METHODS For in vitro study, we made uniform PTi (20%, 40%, 60%, 80%), NPTi and PTa cages (n=6 in each group, total 36 cages) to investigate the cell attachment and osteogenic markers using MG63 cell line. SEM was used to observe the cell attachment on the implants. Osteogenic markers were evaluated with the mRNA expression and activity of alkaline phosphatase and mRNA expression of osteocalcin. In vivo study was performed using pig posterior instrumented anterior interbody fusion model comparing PTi (60%), NPTi, and PTa interbody device in twelve pigs.For evaluating the migration and subsidence of implants, plain radiographs were performed before and after surgery, and postoperative 1, 3, and 6 months. All implants (total 33 cages) were harvested the implants with neighboring vertebral bodies after sacrifice. The harvested implants were assessed by micro-CT, histologic section for their bone ingrowth and bone attachment. RESULTS The in vitro micrographics were showed that cells had similar attachment behavior on PTi, NPTi and PTa cages. More cellular migration into cage pores was noticedin 60% and 80% PTi cages. The osteogenic markersALP activity and mRNA expression were highest in 60% cages while the osteocalcin was highest in NPTi cages.In vivo study eleven pigs were completed the radiographic exams. One pig was expired early due to poor postoperative recovery after 1 month. All interbody cages had successful fusion without obvious migration or cage failure. However, 60% PTi cage had less subsidence compared to other cages. The micro-CT showed better pore bone-ingrowth percentage (18%, 8%, 0% in PTi, PTa, NPTi cages, respectively) and the bone histomorphometry demonstrated better new-bone mineralization and trabeculation in PTi cages. CONCLUSIONS In conclusion, our in vitro and in vivo results express that the innovative designed PTi device that manufacture by SLM, it is biocompatible and work well in lumbar interbody fusion surgery. The fusion character of PTi cages seems to be faster with less subsidence compared to PTa and NPTi cages.
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