Rheumatoid Arthritis Affecting the Upper Cervical Spine: Biomechanical Assessment of the Stabilizing Ligaments.

Diameters of anterior and posterior atlantodental intervals (AADI and PADI) are diagnostically conclusive regarding ongoing neurological disorders in rheumatoid arthritis. MRI and X-ray are mostly used for patients' follow-up. This investigation aimed at analyzing these intervals during motion of cervical spine, when transverse and alar ligaments are damaged. AADI and PADI of 10 native, human cervical spines were measured using lateral fluoroscopy, while the spines were assessed in neutral position first, in maximal inclination second, and in maximal extension at last. First, specimens were evaluated under intact conditions, followed by analysis after transverse and alar ligaments were destroyed. Damage of the transverse ligament leads to an increase of the AADI's diameter about 0.65 mm in flexion and damage of alar ligaments results in significant enhancement of 3.59 mm at mean. In extension, the AADI rises 0.60 mm after the transverse ligament was cut and 0.90 mm when the alar ligaments are damaged. After all ligaments are destroyed, AADI assessed in extension closely resembles AADI at neutral position. Ligamentous damage showed an average significant decrease of the PADI of 1.37 mm in the first step and of 3.57 mm in the second step in flexion, while it is reduced about 1.61 mm and 0.41 mm in the extended and similarly in the neutrally positioned spine. Alar and transverse ligaments are both of obvious importance in order to prevent AAS and movement-related spinal cord compression. Functional imaging is necessary at follow-up in order to identify patients having an advanced risk of neurological disorders.

[Influence of Osseous and Ligamentous Injuries on the Stability of the Atlantoaxial Complex]. / Einfluss osteoligamentärer Verletzungen auf die Stabilität des atlantoaxialen Komplexes.

Background The odontoid process and the transverse ligament are the most important structures stabilising the atlantoaxial complex. It has not been fully elucidated how injuries of these structures contribute towards instability and a potential narrowing of the spinal canal. Therefore, our investigation aimed to perform a biomechanical analysis of spinal width and dislocation of the odontoid process depending on injuries of the aforementioned structures. Methods In 10 fresh human cadaveric specimens, physiologic flexion and extension were simulated under fluoroscopy in intact specimens and after application of an odontoid process fracture and transverse ligament rupture in a crossover design. The width of the spinal canal and the dislocation of fragments were measured. Results In the intact condition, values of 19.8/19.5/19.8 mm (neutral/flexion/extension) were observed regarding spinal width. After an isolated fracture, values were 18.5/18.9/17.9 mm. With additional ligamentous injury, values changed to 20.3/19.4/22.6 mm. In the second group, values after initial ligament injury were 18.6/16.2/17.3 mm and 16.6/14.1/18.7 mm after fracture. Dislocation of fragments after an isolated fracture averaged 2.2/2.5/2.5 mm; an additional ligamentous injury led to 2.6/2.2/2.2 mm. In the second group, where a ligamentous injury preceded the fracture, a dislocation of 1.5/1.9/3.5 mm was detected after the fracture. Conclusion Neurological disorders have been observed starting at a spinal canal constriction of 2.0 mm. Our results demonstrate that a relevant constriction of the spinal canal may be due to isolated or combined injuries of the bone and the transverse ligament. Furthermore, our results show the importance of posttraumatic immobilisation of the spine with a view to the role of the transverse ligament for stabilisation of the atlantoaxial complex.