Coupling behavior of the cervical spine: A systematic review of the literature

Objective: The purpose of this study was to investigate evidence of consistency of reported directional coupling patterns among selected studies and to determine its use in manual medical treatment. Methods: The study was a systematic literature review of English-only journals using PubMed and CINAHL. The keywords included "cervical vertebrae," "biomechanics," "coupling," and "three-dimensional movement" and required coupling directional assessment of individual spine segments. Results: Four 2-dimensional and 8 3-dimensional studies met inclusion criteria. This study found 100% agreement in coupling direction (side flexion and rotation to the same side) in lower cervical vertebral segments (C2-3 and lower) and variation in coupling patterns in the upper cervical segments of occiput-Cl (during side flexion initiation) and C1-2. Dissimilarities may be explained by differences in measurement devices, movement initiation, in vivo vs in vitro specimens, and anatomical variations. Conclusions: These findings suggest that use of 3-dimensional analyzed cervical coupling patterns for the lower cervical vertebral during apposition and treatment application may show clinical use for manual clinicians. The use of directional coupling based on 2-dimensional cervical coupling patterns or upper cervical spine coupling that addresses C1-2 should be questioned.