Are hyperhydration and endplate-anulus integrity potential key drivers of cervical disc herniation? – An ex vivo study
Brain and Spine, vol. 6, pp. 106337
Abstract
Introduction: Pathomechanisms underlying cervical intervertebral disc (IVD) herniation remain poorly understood, including the role of structural tissue damage to herniation susceptibility.While complex loading promotes herniation in lumbar IVDs [1], its relevance to the cervical spine is unclear.Astronauts show a 21-fold higher risk of cervical IVD herniation, potentially linked to microgravity-induced IVD hyperhydration [2].Building on these considerations, the aim of this study was to assess whether swelling-induced changes in intradiscal pressure (IDP), range of motion (ROM), and neutral zone (NZ), in combination with endplate-anulus compromise, influence susceptibility to cervical IVD herniation under complex loading.Materials and Methods: Six fresh-frozen human cervical motion segments (1x C3-C4, 3x C5-C6, 2x C6-C7; 17-42 years; 2 female / 4 male) were hydrated in distilled water (to obtain hyperhydration) for 14h, while IDP was monitored using fibreoptic pressure transducers.A paramedial posterior defect at the cranial endplate-anulus transition was created under radiographic control.Specimens were then subjected to 3000 cycles of complex loading at 1 Hz in a dynamic disc-loading simulator [3], consisting of 100 N axial compression combined with flexion/extension (FE), lateral bending (LB), and axial rotation (AR) within physiological ROM [4].Flexibility was evaluated before and after hydration and after complex loading using pure moments of 2.5 Nm in a spine tester.Friedman test with Bonferroni correction was performed in SPSS29.Results: Hyperhydration increased median intrinsic IDP by +243% (p<0.05) and reduced median NZ (FE: -46%, LB: -56%; p<0.05).Complex loading induced herniation in one of six IVDs, characterized by posterior, paramedial extrusion of nucleus pulposus material into the spinal canal at the cranial endplate defect site (Fig. 1).After complex loading, both median ROM (FE: +36%, LB: +56%, AR: +31%) and median NZ (FE: +148%, LB: +216%, AR: +138%) increased significantly compared to the hyperhydrated condition (p < 0.05).Conclusion: Hyperhydration increases IDP and reduces NZ, indicating elevated stiffness and mechanical stress within IVD tissues.As IDP reflects the load acting on the IVD, this hydration-related pressure increase together with complex loading may therefore promote cervical IVD herniation.Conversely, a compromise at the endplate-anulus interface did not consistently induce herniation, suggesting that this structural disruption alone is unlikely to be a decisive factor.Overall, the results show that hyperhydration increases IDP and IVD stiffness, making the cervical IVD more susceptible to herniation during high-risk movements.
Authors 12
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Affiliation as printed
Institute of Orthopaedic Research and Biomechanics, Ulm University Medical Centre, Ulm, Germany
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Affiliation as printed
Institute of Orthopaedic Research and Biomechanics, Ulm University Medical Centre, Ulm, Germany
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Affiliation as printed
Institute of Orthopaedic Research and Biomechanics, Ulm University Medical Centre, Ulm, Germany
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Affiliation as printed
Department of Nursing, Midwifery and Therapeutic Sciences, Division of Physiotherapy, University of Health Sciences, Bochum, Germany
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Charité - Universitätsmedizin Berlin
Affiliation as printed
Center for Muscle and Bone Research, Charité – University Medicine Berlin, Berlin, Germany
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German Sport University Cologne · FH Aachen
Affiliation as printed
Department of Medical Engineering and Technomathematics, Aachen University of Applied Sciences, Aachen, Germany
Institute of Movement and Neuroscience, Center for Health and Integrative Physiology in Space, German Sport University, Cologne, Germany
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Sahlgrenska University Hospital
Affiliation as printed
Department of Orthopaedics, Sahlgrenska University Hospital, Gothenburg, Sweden
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Affiliation as printed
Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), University of Birmingham, Birmingham, United Kingdom
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Affiliation as printed
Johnson Space Center, Houston, United States of America
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Affiliation as printed
Finnish Defence Force, Aeromedical Centre, Helsinki, Finland
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Sahlgrenska University Hospital
Affiliation as printed
Department of Orthopaedics, Sahlgrenska University Hospital, Gothenburg, Sweden
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Affiliation as printed
Institute of Orthopaedic Research and Biomechanics, Ulm University Medical Centre, Ulm, Germany
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