Do design variations in the artificial disc influence cervical spine biomechanics? A finite element investigation

Various ball and socket-type designs of cervical artificial discs are in use or under investigation. Many artificial disc designs claim to restore the normal kinematics of the cervical spine. What differentiates one type of design from another design is currently not well understood. In this study, authors examined various clinically relevant parameters using a finite element model of C3–C7 cervical spine to study the effects of variations of ball and socket disc designs. Four variations of ball and socket-type artificial disc were placed at the C5–C6 level in an experimentally validated finite element model. Biomechanical effects of the shape (oval vs. spherical ball) and location (inferior vs. superior ball) were studied in detail. Range of motion, facet loading, implant stresses and capsule ligament strains were computed to investigate the influence of disc designs on resulting biomechanics. Motions at the implant level tended to increase following disc replacement. No major kinematic differences were observed among the disc designs tested. However, implant stresses were substantially higher in the spherical designs when compared to the oval designs. For both spherical and oval designs, the facet loads were lower for the designs with an inferior ball component. The capsule ligament strains were lower for the oval design with an inferior ball component. Overall, the oval design with an inferior ball component, produced motion, facet loads, implant stresses and capsule ligament strains closest to the intact spine, which may be key to long-term implant survival

Effect of surgical experience and spine subspecialty on the reliability of the {AO} Spine Upper Cervical Injury Classification System

OBJECTIVE The objective of this paper was to determine the interobserver reliability and intraobserver reproducibility of the AO Spine Upper Cervical Injury Classification System based on surgeon experience (< 5 years, 5–10 years, 10–20 years, and > 20 years) and surgical subspecialty (orthopedic spine surgery, neurosurgery, and "other" surgery). METHODS A total of 11,601 assessments of upper cervical spine injuries were evaluated based on the AO Spine Upper Cervical Injury Classification System. Reliability and reproducibility scores were obtained twice, with a 3-week time interval. Descriptive statistics were utilized to examine the percentage of accurately classified injuries, and Pearson’s chi-square or Fisher’s exact test was used to screen for potentially relevant differences between study participants. Kappa coefficients (κ) determined the interobserver reliability and intraobserver reproducibility. RESULTS The intraobserver reproducibility was substantial for surgeon experience level (< 5 years: 0.74 vs 5–10 years: 0.69 vs 10–20 years: 0.69 vs > 20 years: 0.70) and surgical subspecialty (orthopedic spine: 0.71 vs neurosurgery: 0.69 vs other: 0.68). Furthermore, the interobserver reliability was substantial for all surgical experience groups on assessment 1 (< 5 years: 0.67 vs 5–10 years: 0.62 vs 10–20 years: 0.61 vs > 20 years: 0.62), and only surgeons with > 20 years of experience did not have substantial reliability on assessment 2 (< 5 years: 0.62 vs 5–10 years: 0.61 vs 10–20 years: 0.61 vs > 20 years: 0.59). Orthopedic spine surgeons and neurosurgeons had substantial intraobserver reproducibility on both assessment 1 (0.64 vs 0.63) and assessment 2 (0.62 vs 0.63), while other surgeons had moderate reliability on assessment 1 (0.43) and fair reliability on assessment 2 (0.36). CONCLUSIONS The international reliability and reproducibility scores for the AO Spine Upper Cervical Injury Classification System demonstrated substantial intraobserver reproducibility and interobserver reliability regardless of surgical experience and spine subspecialty. These results support the global application of this classification system

Spondyloarthropathies That Mimic Ankylosing Spondylitis: A Narrative Review

Ankylosing spondylitis is the most common type of seronegative inflammatory spondyloarthropathy often presenting with low back or neck pain, stiffness, kyphosis and fractures that are initially missed on presentation; however, there are other spondyloarthropathies that may present similarly making it a challenge to establish the correct diagnosis. Here, we will highlight the similarities and unique features of the epidemiology, pathophysiology, presentation, radiographic findings, and management of seronegative inflammatory and metabolic spondyloarthropathies as they affect the axial skeleton and mimic ankylosing spondylitis. Seronegative inflammatory spondyloarthropathies such as psoriatic arthritis, reactive arthritis, noninflammatory spondyloarthropathies such as diffuse idiopathic skeletal hyperostosis, and ochronotic arthritis resulting from alkaptonuria can affect the axial skeleton and present with symptoms similar those of ankylosing spondylitis. These similarities can create a challenge for providers as they attempt to identify a patient’s condition. However, there are characteristic radiographic findings and laboratory tests that may help in the differential diagnosis. Axial presentations of seronegative inflammatory, non-inflammatory, and metabolic spondyloarthropathies occur more often than previously thought. Identification of their associated symptoms and radiographic findings are imperative to effectively diagnose and properly manage patients with these diseases