Sagittal plane segmental motion of the cervical spine. A new precision measurement protocol and normal motion data of healthy adults.

OBJECTIVE (1) Precise documentation of sagittal plane segmental rotational and posteroanterior translational motion of segments C0/C1-C6/C7 of the human cervical spine from lateral radiographic views. (2) Compilation of a database describing normal motion. (3) Comparison of individual motion patterns with the normal database. DESIGN Descriptive study based on computer-aided measurements from lateral radiographic views taken in flexion and extension. BACKGROUND Previous studies concentrated on segmental rotational motion of the cervical spine. Normal data for translational motion were not available. Description of cervical spine motion patterns thus remained incomplete. METHODS Based on computer-aided measurements from lateral radiographic views taken in flexion and extension, a new protocol determines rotational and translational motion for all segments (C0/C1-C6/C7) imaged on the radiographic views. Measured results are corrected for radiographic magnification and variation in stature; they are virtually uninfluenced by radiographic distortion and patient alignment errors. A database describing normal motion was compiled from 137 sets of lateral views of healthy adults taken in active flexion and extension. A specimen study as well as inter- and intra-observer studies quantify measurement errors. RESULTS The error study demonstrated the error (SD) of a rotational motion measurement to amount to slightly less than 2 degrees. The error (SD) of a translational motion measurement amounts to less than 5% of vertebral depth; for a vertebra of 15 mm depth this corresponds to 0.7 mm. A normal database for rotational and translational motion was compiled. There was a linear relation between rotational and translational motion. This finding agrees qualitatively with results from previous studies; quantitative comparisons are not possible due to divergent definitions for translational motion. The relation between rotation and translation can be employed in individual cases to predict translational motion, in dependence on the rotation actually performed. A comparison of the rotational motion with the normal database and the difference between predicted and actual translational motion allow segmental hypo-, normal or hypermobility to be quantified. CONCLUSIONS The new protocol measures segmental motion with high precision and corrects for radiographic distortion, variation in stature and alignment errors of patients. Thus, archive studies using existing radiographs are feasible. RELEVANCE Flexion-extension radiographs of the cervical spine are performed to explore potential damage to the bony or ligamentous structure resulting in abnormal, segmental motion patterns. Determining rotational motion gives only an incomplete picture. The new protocol allows for precise quantification of translational motion and classification of segments as hypo- or hypermobile by comparison with normal motion data.