A non-invasive technique for measurement of cervical vertebral angle: report of a preliminary study.

Non-invasive methods have traditionally been used to assess spine positioning and range of motion. Recently, the use of prediction models derived from external stick markers and videographic analysis has been shown to be effective at predicting lumbosacral and segmental lumbar vertebral angles. The objective of this study was to develop a similar non-invasive method to predict cervical vertebral inclination in forward head flexion. Fourteen subjects with no history of trauma or inflammatory or arthritic disorders (mean age: 25+/-1 years) participated in this study on a voluntary basis. Radiographic and videographic measurements of four external markers (C0, C2, C6, C7) were taken for each subject at three different static head positions (neutral, and 30 degrees and 60 degrees of flexion). The data obtained from nine subjects with normal cervical configuration (lordosis) were used to develop statistical models predicting the radiographic segmental angles (dependent variables) from external markers (independent variables). A multiple regression model was developed for each vertebra (C1 to C6). These regression models predict the inclination of each cervical vertebra at three different neck angles with positional data derived from the four external skin markers. Adjusted R2 values of 0.97, 0.93, 0.93, 0.96, 0.95 and 0.89 were obtained for C1, C2, C3, C4, C5 and C6, respectively. The prediction models developed in this study can explain a large part of the variance for the relative contribution of each vertebral segment to global neck flexion and provide a greater accuracy then using external stick markers only. These models were not able to adequately predict the vertebral angular positioning of subjects presenting a cervical alordosis or kyphosis.