Sensitivity of the Cervical Disc Loads, Translations, Intradiscal Pressure, and Muscle Activity Due to Segmental Mass, Disc Stiffness, and Muscle Strength in an Upright Neutral Posture

Quantifying the Importance of Active Muscle Repositioning a Finite Element Neck Model in Flexion Using Kinematic, Kinetic, and Tissue-Level Responses

PURPOSE

Non-neutral neck positions are important initial conditions in impact scenarios, associated with a higher incidence of injury. Repositioning in finite element (FE) neck models is often achieved by applying external boundary conditions (BCs) to the head while constraining the first thoracic vertebra (T1). However, in vivo, neck muscles contract to achieve a desired head and neck position generating initial loads and deformations in the tissues. In the present study, a new muscle-based repositioning method was compared to traditional applied BCs using a contemporary FE neck model for forward head flexion of 30°.

METHODS

For the BC method, an external moment (2.6 Nm) was applied to the head with T1 fixed, while for the muscle-based method, the flexors and extensors were co-contracted under gravity loading to achieve the target flexion.

RESULTS

The kinematic response from muscle contraction was within 10% of the in vivo experimental data, while the BC method differed by 18%. The intervertebral disc forces from muscle contraction were agreeable with the literature (167 N compression, 12 N shear), while the BC methodology underpredicted the disc forces owing to the lack of spine compression. Correspondingly, the strains in the annulus fibrosus increased by an average of 60% across all levels due to muscle contraction compared to BC method.

CONCLUSION

The muscle repositioning method enhanced the kinetic response and subsequently led to differences in tissue-level responses compared to the conventional BC method. The improved kinematics and kinetics quantify the importance of repositioning FE neck models using active muscles to achieve non-neutral neck positions.

Rotation-traction manipulation induced intradiskal pressure changes in cervical spine-an in vitro study

Objective: Evaluate the effect of rotation-traction manipulation on intradiskal pressure in human cervical spine specimen with different force and duration parameters, and compare the intradiskal pressure changes between rotation-traction manipulation and traction. Methods: Seven human cervical spine specimens were included in this study. The intradiskal pressure was measured by miniature pressure sensor implanting in the nucleus pulposus. rotation-traction manipulation and cervical spine traction were simulated using the MTS biomechanical machine. Varied thrust forces (50N, 150N, and 250N) and durations (0.05 s, 0.1 s, and 0.15 s) were applied during rotation-traction manipulation with Intradiscal pressure recorded in the neutral position, rotation-anteflexion position, preloading, and thrusting phases. Futuremore, we documented changes in intradiscal pressure during cervical spine traction with different loading forces (50N, 150N, and 250N). And a comparative analysis was performed to discern the impact on intradiscal pressure between manipulation and traction. Results: Manipulation application induced a significant reduction in intradiscal pressure during preloading and thrusting phases for each cervical intervertebral disc (p < 0.05). When adjusting thrust parameters, a discernible decrease in intradiscal pressure was observed with increasing thrust force, and the variations between different thrust forces were statistically significant (p < 0.05). Conversely, changes in duration did not yield a significant impact on intradiscal pressure (p > 0.05). Additionally, after traction with varying loading forces (50N, 150N, 250N), a noteworthy decrease in intradiscal pressure was observed (p < 0.05). And a comparative analysis revealed that rotation-traction manipulation more markedly reduced intradiscal pressure compared to traction alone (p < 0.05). Conclusion: Both rotation-traction manipulation and cervical spine traction can reduce intradiscal pressure, exhibiting a positive correlation with force. Notably, manipulation elicits more pronounced and immediate decompression effect, contributing a potential biomechanical rationale for its therapeutic efficacy.

Tension-activated nanofiber patches delivering an anti-inflammatory drug improve repair in a goat intervertebral disc herniation model

Conventional microdiscectomy treatment for intervertebral disc herniation alleviates pain but does not repair the annulus fibrosus, resulting in a high incidence of recurrent herniation and persistent dysfunction. The lack of repair and the acute inflammation that arise after injury can further compromise the disc and result in disc-wide degeneration in the long term. To address this clinical need, we developed tension-activated repair patches (TARPs) for annulus fibrosus repair and local delivery of the anti-inflammatory factor anakinra (a recombinant interleukin-1 receptor antagonist). TARPs transmit physiologic strain to mechanically activated microcapsules embedded within the patch, which release encapsulated bioactive molecules in direct response to spinal loading. Mechanically activated microcapsules carrying anakinra were loaded into TARPs, and the effects of TARP-mediated annular repair and anakinra delivery were evaluated in a goat model of annular injury in the cervical spine. TARPs integrated with native tissue and provided structural reinforcement at the injury site that prevented aberrant disc-wide remodeling resulting from detensioning of the annular fibrosus. The delivery of anakinra by TARP implantation increased matrix deposition and retention at the injury site and improved maintenance of disc extracellular matrix. Anakinra delivery additionally attenuated the inflammatory response associated with TARP implantation, decreasing osteolysis in adjacent vertebrae and preserving disc cellularity and matrix organization throughout the annulus fibrosus. These results demonstrate the therapeutic potential of TARPs for the treatment of intervertebral disc herniation.

Relationship between Intervertebral Disc Compression Force and Sagittal Spinopelvic Lower Limb Alignment in Elderly Women in Standing Position with Patient-Specific Whole Body Musculoskeletal Model

The intervertebral disc loading based on compensated standing posture in patients with adult spinal deformity remains unclear. We analyzed the relationship between sagittal alignment and disc compression force (Fm). In 14 elderly women, the alignment of the sagittal spinopelvic and lower extremities was measured. Fm was calculated using the Anybody Modeling System. Patients were divided into low sagittal vertical axis (SVA) and high SVA groups. Comparisons between the two groups were performed and the relationship between the Fm and each parameter was examined using Spearman's correlation coefficient (r). The mean lumbar Fm in the high SVA group was 67.6%; significantly higher than that in the low SVA group (p = 0.046). There was a negative correlation between cervical Fm with T1 slope (r = -0.589, p = 0.034) and lumbar Fm with lumbar lordosis (r = -0.566, p = 0.035). Lumbar Fm was positively correlated with center of gravity-SVA (r = 0.615, p = 0.029), T1 slope (r = 0.613, p = 0.026), and SVA (r = 0.612, p = 0.020). The results suggested sagittal malalignment increased the load on the thoracolumbar and lower lumbar discs and was associated with cervical disc loading.

Temporomandibular Joint Disk Displacements in Class II Malocclusion and Cervical Spine Alterations: Systematic Review and Report of a Hypodivergent Case with MRI Bone and Soft Tissue Changes

(1) Background: This study aimed to perform a literature review related to disk displacement (DD) in class II malocclusion or cervical vertebrae position alterations and to report a hypodivergent case with cervical pain and right anterolateral DD with reduction, left anterolateral DD with reduction, and left joint effusion. (2) Methods: A structured electronic search was conducted between March 2022 and April 2022, without time limits, following PRISMA guidelines, in the following databases: PubMed, Scopus, Embase and Cochrane; the terms “disc displacement”, “disk displacement”, “temporomandibular joint”, “class II malocclusion” and “cervical vertebrae” are searched. (3) Results: the following thirteen publications are included in this review: two prospective studies and eleven cross-sectional studies; for evaluating disk position, eight included publications used magnetic resonance imaging (MRI), whilst six studies used lateral cephalogram to determine craniofacial morphology and relationships between the cranial base, vertical skeletal pattern, maxilla and mandible. (4) Conclusions: although the literature still shows contradictory opinions, a relationship between temporomandibular disorders and cervical posture has been shown in the presented case as well as in the literature review.