Preclinical evaluation of a 3D-printed porous stand-alone interbody cage for cervical fusion in a sheep model

Abstract Objective This study aimed to assess the bone ingrowth and in vivo safety of a novel designed 3D-printed porous stand-alone cage (PSAC) for Cervical Fusion in a Sheep Model. Methods PASC was designed and fabricated by 3D-printing technology. We implanted the PSAC at the C2/C3 level and control cages at the C3/C4 level in 18 sheep. After 4, 12, and 24 weeks, X-ray was used to assess DSH, Micro-CT to evaluate bone volume fraction (BV/TV), biomechanical testing to determine bone-implant interface strength, and toluidine blue staining to assess bone ingrowth depth and new bone formation. Sheep health, blood markers, vital organ pathology and local tissue reaction (HE staining) were monitored to evaluate its safety. Results (1) X-ray results showed that both cages maintained stable DSH. (2) Micro-CT revealed greater bone volume within the porous structure of the PSAC group compared to the control group (BV1/TV1(%): 50.37 ± 4.79 vs. 43.98 ± 6.27, p = 0.076). (3) In terms of bone ingrowth, toluidine blue staining showed that new bone formation in the PSAC group was higher to the control at 4 and 12 weeks (1.64 ± 0.85 mm² vs. 2.86 ± 1.81 mm², p = 0.35) and was not inferior at 24 weeks. The bone ingrowth depth was consistent between the PSAC and control groups (24 weeks: 1116.28 ± 152.28 μm vs. 1161.36 ± 368.45 μm, p = 0.85). (4) The bone-implant interface strength of the PSAC was not inferior to the control group (24 weeks: maximum failure load 309.65 ± 47.13 vs. 302.93 ± 43.33 N, p = 0.88; failure displacement 2.20 ± 0.30 mm vs. 2.05 ± 0.40 mm, p = 0.70). (5) Safety: Blood tests and HE staining showed no significant toxic or inflammatory pathological changes. All animals remained in good health, with no infections or deaths. Conclusion Our findings suggest that the intervertebral PSAC are safe and effective for cervical fixation, showing no adverse effects on the cervical spine or animal bodies, and demonstrating equivalent fixation and healing capabilities compared to control devices.