ABSTRACT Background Biomechanical cadaver studies consistently find that cervical arthrodesis leads to increased motion adjacent to the arthrodesis. However, in vivo evidence indicates adjacent segment end range motion does not reliably increase at 1 year after one‐level or two‐level cervical arthrodesis. Because changes beyond 1 year remain unknown, this study assessed the effects of one‐ and two‐level cervical arthrodesis on adjacent segment motion 3 years after arthrodesis. Methods Sixty‐two patients were tested preoperatively (PRE), 1 year postoperatively (1YR‐POST), and 3 years postoperatively (3YR‐POST) along with 22 asymptomatic controls, who were tested once. A validated CT model‐based tracking technique was used to measure three‐dimensional (3D) vertebral motion from biplane radiographs acquired during dynamic flexion‐extension and axial rotation of the cervical spine. Adjacent segment intervertebral end range of motion (ROM) and midrange ROM (i.e. , head within 20° of neutral) were compared between one‐level and two‐level arthrodesis patients and controls after accounting for head ROM. Results End range adjacent segment motion tended to increase over time after arthrodesis; however, significant increases were found only after two‐level arthrodesis. In contrast, midrange adjacent segment motion increased significantly after one‐ and two‐level arthrodesis and was greater than in corresponding motion segments in controls. Conclusions Midrange adjacent segment motion may be better than end range motion for detecting early mechanical changes after cervical arthrodesis that could contribute to adjacent segment degeneration. In vivo changes in adjacent segment motion are inconsistent across patients up to 3 years after anterior cervical arthrodesis.
ABSTRACT Background Subaxial cervical facet dislocation (CFD) is a severe neck injury associated with head‐first impact (HFI). However, CFD has not been reliably reproduced in experimental or numerical studies, limiting understanding of its underlying mechanics. This study quantified the influence of preimpact head‐forward posture on lower‐neck sagittal‐plane loading associated with CFD during HFI. Methods A detailed finite element head–neck model was enhanced and evaluated against literature data, then used to investigate HFI response at a 2 m/s vertical drop impact velocity. A reposturing procedure achieved graded head‐forward eccentricity from 0 to 50 mm in 5 mm increments, reflecting postures observed during anticipatory neck bracing. A matched cadaveric HFI experiment was subsequently performed with 30 mm eccentricity. Results Simulations demonstrated that eccentricities of 15 mm or more produced an S‐shaped neck deformation during impact, as observed in prior experiments that produced CFD, accompanied by marked increases in anterior intervertebral shear and flexion bending at C7/T1. The matched cadaveric experiment produced bilateral C7/T1 dislocation, consistent with the predicted loading and deformation trends. However, complete CFD was not reproduced computationally because current intervertebral soft‐tissue failure formulations did not capture the observed failure progression. Conclusions Preimpact head‐forward eccentricity can substantially increase lower‐neck loading and susceptibility to CFD under the inverted‐drop conditions studied.
ABSTRACT Background The Neurocore‐SENSED framework, derived from a three‐round modified Delphi process involving 77 international spine surgeons, provides a structured reference standard for reporting in endoscopic spine surgery (ESS) for disc disease. The ability of large language models (LLMs) to reproduce graded levels of expert agreement within a reporting framework has not been examined in ESS. Objective To evaluate the extent to which three contemporary LLMs align with the Neurocore‐SENSED consensus and whether they discriminate between items of differing consensus level. Methods In January 2026, each of the 166 framework items with published item‐level endorsement data was submitted once to GPT‐5.2, Gemini 3 Pro, and Claude Sonnet 4.6, in independent sessions with web retrieval disabled. Models selected one of five ordered response options directly. Alignment was assessed by Spearman correlation with panel endorsement and by four measures of categorical agreement, each with bootstrap 95% confidence intervals. Separate protocols examined response stability, response format, and prior exposure to the consensus. Results All three models correlated significantly with panel endorsement. Gemini 3 Pro aligned most closely (rs = 0.709, 95% CI 0.627–0.776), exceeding Claude Sonnet 4.6 (rs = 0.622; p = 0.009) and GPT‐5.2 (rs = 0.565; p < 0.001), which did not differ. Categorical agreement was limited and equivalent across models, with observed agreement of 0.506–0.518 and overlapping confidence intervals for all marginal‐robust statistics. Between 81.3% and 95.8% of responses fell in the top two categories, and discordance was almost entirely unidirectional: 31 items were endorsed by every model but by fewer than half the panel, against one item in the opposite direction. Weighted kappa was not interpretable in this setting. Conclusion Current LLMs reproduce the broad rank ordering of expert endorsement in ESS reporting but cannot reliably distinguish endorsed from contested propositions, principally because of a positive response bias.
ABSTRACT The intervertebral disc is a prime example of tissue adaptation to metabolic and mechanical extremes. As the largest avascular organ in the human body, the disc and the central nucleus pulposus (NP) endure constant compressive loading while sustaining a hypoxic, relatively acidic, and hyperosmotic microenvironment that would be inhospitable to most cell types. Over the past two decades, work from my laboratory has revealed extraordinary details of this type of adaptation, that hypoxia‐inducible factors (HIFs), particularly HIF‐1α, serve as master regulators of NP cell survival, metabolism, and matrix homeostasis. This review chronicles the scientific and personal journey that began with a single unexpected observation: the normoxic stabilization of HIF‐1α in NP cells. That finding grew into a substantial understanding of oxygen‐independent HIF regulation and biology in the disc. Through sustained collaborations with Irving Shapiro and other colleagues and a succession of talented trainees, we demonstrated that HIF‐1α is indispensable for disc development and homeostasis. In contrast, HIF‐2α plays a distinct, largely opposing role, promoting matrix catabolism and fibrosis. Our work has revealed the molecular architecture underlying the disc's adaptation to avascularity, encompassing HIF‐dependent regulation of glycolytic enzymes, glucose transporters, carbonic anhydrases CA9 and CA12, monocarboxylate transporter 4 (MCT4), and BNIP3‐mediated mitophagy, and has opened promising therapeutic avenues for disc regeneration. Recently, we discovered that NP‐derived lactate exported via MCT4 is actively imported primarily by vertebral endplate cells, and, to a lesser extent, by annulus fibrosus cells via MCT1, where it serves dual roles as a TCA metabolite and an epigenetic regulator through lactylation. This review celebrates the intellectual journey, the collaborative spirit that sustained it, and the honor of the Alexander von Humboldt Research Award, while providing a synthesis of HIF biology in the intervertebral disc spanning the discovery of oxygen by Priestley 1774 to the 2019 Nobel Prize and beyond.
ABSTRACT Background Adolescent idiopathic scoliosis (AIS) is the most common three‐dimensional spinal deformity, predominantly affecting females aged 10–16 years. Although no single etiological factor has been definitively identified, alterations in bone quality and biomechanical properties have been proposed as contributing factors to AIS development. Methods We developed a surgical protocol to obtain trabecular bone biopsies from the apex vertebra during anterior corrective surgery for AIS. Multimodal analysis was performed on samples from eight AIS participants (14.8 ± 1.5 years), including microstructural assessment via micro‐computed tomography (micro‐CT), bone mineral density distribution (BMDD) via quantitative backscattered electron imaging (qBEI), and mechanical characterization via nanoindentation. Correlations with major curve angle, apical wedge angle, and Risser grade were investigated. Results Mean trabecular bone volume fraction (BV/TV) was 0.146 ± 0.029, comparable to values reported in healthy populations. Mean trabecular thickness (Tb.Th) was 0.146 ± 0.011 mm, suggesting slightly thicker trabeculae than typically reported in healthy young cohorts. BMDD analysis revealed CaPeak values of 23.34 ± 1.02 wt% Ca, and greater CaWidth values (4.26 ± 0.33 wt% Ca) compared to healthy adolescent and adult reference data. CaPeak was significantly negatively correlated with apical wedge angle, indicating lower mineralization with increasing vertebral wedging. Nanoindentation showed a negative association between reduced modulus (13.37 ± 2.5 GPa) and apical wedge angle, with hardness values of 0.412 ± 0.079 GPa. Conclusions These findings provide novel insights into vertebral trabecular bone alterations in AIS and their association with deformity severity. To our knowledge, this is the first study to integrate micro‐CT, qBEI, and nanoindentation analyses in AIS vertebral biopsies, revealing structural, compositional, and mechanical differences that may contribute to the pathogenesis and progression of AIS.
