RESUMO
STUDY DESIGN: In vitro human cadaveric biomechanical study. OBJECTIVES: To investigate the roles of transverse atlantal ligament (TAL) and longitudinal ligament (LL) of the upper cervical spine (UCS) in maintaining atlantoaxial stability. SETTING: China. METHODS: Six intact UCS specimens were harvested and embedded in polymethylmethacrylate. Three-dimensional movements including flexion, extension, right and left lateral bending, and axial rotation, as well as the C1-C2 displacement in flexion (atlantodental interval, ADI), were tested on specimens with the following state sequentially: (1) intact (intact group), (2) TAL transected (TAL group) and (3) TAL and LL disrupted (TAL+LL group) using an electromechanical testing machine. RESULTS: Compared with intact group, the flexion/extension motion range and ADI were significantly higher in TAL group when the loading was 10 N or >100 N. However, no significant differences were detected between the two groups within a range of physiological loading (10-100 N). Similarly, significant differences in right-left lateral bending and axial rotation between TAL and intact groups occurred only when the loading was 150 N. However, when both of the TAL and LL were resected, the atlantoaxial joint showed obvious instability compared with TAL or intact group, which were further demonstrated in the analyses of the three-dimensional movements (significant differences at any loading). CONCLUSION: Within physiological loading range, the LLs have sufficient capacities to maintain the stability of atlantoaxial joint even if there are TAL injuries in atlas fractures.