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Although autologous bone grafting is widely considered as an ideal source for interbody fusion, it still carries a risk of nonunion. The influence of the intervertebral device should not be overlooked. Requirements for artificial spinal devices are to join the vertebrae together and recover the original function of the spine rapidly. Ordered mineralization of apatite crystals on collagen accelerates bone functionalization during the healing process. Particularly, the stable spinal function requires the ingrowth of an ordered collagen and apatite matrix which mimics the intact intervertebral microstructure. This collagen and apatite ordering is imperative for functional bone regeneration, which has not been achieved using classical autologous grafting.We developed an intervertebral body device to achieve high stability between the host bone and synthesized bone by controlling the ordered collagen and apatite microstructure.This was an in vivo animal study.Intervertebral spacers with a through-pore grooved surface structure, referred to as a honeycomb tree structure, were produced using metal 3D printing. These spacers were implanted into normal sheep at the L2-L3 or L4-L5 disc levels. As a control group, grafting autologous bone was embedded. The mechanical integrity of the spacer/bone interface was evaluated through push-out tests.The spacer with honeycomb tree structure induced anisotropic trabecular bone growth with textured collagen and apatite orientation in the through-pore and groove directions. The push-out load of the spacer was significantly higher than that of the conventional autologous graft spacer. Moreover, the load was significantly correlated with the anisotropic texture of the newly formed bone matrix.The developed intervertebral spacer guided the regenerated bone matrix orientation of collagen and apatite, resulting in greater strength at the spacer/host bone interface than that obtained using a conventional gold-standard autologous bone graft.Our results provide a foundation for designing future spacers for interbody fusion in human.

BACKGROUND CONTEXT As anchors for defining minimum clinical important difference (MCID) thresholds are determined by individual values, we sought to evaluate if MCID thresholds can be affected by cultural differences. PURPOSE The purpose of this study was to compare the MCID threshold and the proportion of adult spinal deformity (ASD) patients achieving SRS-22R MCID in North America (NA) versus Japan (Jp). STUDY DESIGN/SETTING Retrospective review of prospectively collected data. PATIENT SAMPLE Two hundred-eight cases [NA; 148 cases (male 16, female 132, average 59.8years old), Jp; 60 cases (male 4, female 56, average 65.5years old)] who followed for at least more than 2years after corrective fixation surgery for ASD patients with coronal Cobb angle of over 30° and over 40years old. OUTCOME MEASURES SRS22R MCID thresholds. METHODS There were 148 cases from NA (132 females, mean age=59.8 years) and 60 cases from Jp (56 females, mean age=65.5 years) with at least 2-year follow-up after corrective spine surgery for ASD. Except for self-image, published Jp MCID values are higher (function=0.90, pain=0.85 and self-image=1.05, subtotal=1.05) than the published NA MCID values (function=0.60, pain=0.40, self-image=1.23, subtotal=0.43). RESULTS There was statistically significant improvement in all domain scores at 2-year follow-up compared to baseline in both cohorts. Except for mental health (NA:0.32, Jp:0.72, p=.005), the mean improvement from baseline to 2 years was similar between the North American and Japanese cohorts. Except for self-image (NA:57%, Jp:58%, p=.877), the proportion of patients achieving MCID was higher in North America for function (NA:51%, Jp:30%, p=.006), pain (NA:80%, Jp:47%, p CONCLUSIONS Despite similar improvements in SRS22R domain scores from baseline to 2years postop, the proportion of patients reaching SRS22R MCID for function, pain and subtotal after ASD surgery are higher in a North American cohort compared to a Japanese cohort. This may imply that patients in North America and Japan may regard the value of these changes differently.

IntroductionRegression analysis of adult spinal deformity (ASD) databases in North America (NA) has yielded radiographic disability thresholds for sagittal vertical axis (SVA), pelvic tilt (PT), an...