OBJECTIVES: To evaluate the validity of the new Biotonix PosturePrint computer analysis that claims to determine rotations and translations of the head in 3-dimensions.
BACKGROUND: Methods for measurement of head posture include the linear excursion measurement device, body photographs, the CROM device, and simple plumb line methods. Problematically, these methods are not able to measure postural rotations and translations in six degrees of freedom.
MATERIAL AND METHODS: In a university biomechanics laboratory, photographs of a mannequin head were obtained in different postures on a stand in front of a digital camera. For each mannequin posture, three photographs were obtained (left lateral, right lateral, and AP). The mannequin was positioned 2 feet from a calibrated wall grid, while the camera was at 33 inches in height and at 11 feet from and perpendicular to the wall grid. The mannequin head was placed in 125 different single and combined postures (requiring 375 photographs) in five degrees of freedom: lateral translation, lateral flexion, axial rotation, flexion-extension, and anterior-posterior translation. The PosturePrint™ system requires 14 reflective markers to be placed on the subject (mannequin) during photography and 15 additional “click-on” markers via computer mouse before a set of three photographs is analyzed by the PosturePrint computer system over the Internet. The PosturePrint™ algorithm returns an analysis of the head, rib cage, and pelvis in 3-D as rotations (degrees) and translations (millimeters).
RESULTS: Average absolute value errors were obtained by comparing the exact inputted head postures to the PosturePrint™’s computed values. Mean and standard deviation of computational errors for sagittal displacements were flexion-extension = 1.3º ± 0.6º, anterior-posterior translation = 1.1 mm ± 0.5mm, and for frontal view displacements were axial rotation = 1.1º ± 0.7º, lateral flexion = 0.6º ± 0.4º, and lateral translation = 1.1 mm ± 0.5mm.
DISCUSSION: In previous postural studies, very few of the 12 movements of the head have been measured. Predominantly, forward and backward translations and flexion/extension of the head are measured as part of a postural analysis. Importantly, axial rotation is a degree of freedom of the head that is commonly measured for its range of motion and spinal coupling (vertebral displacement) pattern. To our knowledge, previous reports have presented neither a method to extract a value of axial rotation nor a value of other rotations and translations of a subject’s head from photographs. Currently, upright posture evaluation is recommended as part of a comprehensive but focused spine-related physical examination of the cervical spine. Despite this, static postural displacements of the head on photographs has not been measured accurately in the anterior to posterior view as a displacement within the range of motion. Our study provides a method of objective measurement of the rotational and translational degrees of freedom for the human head; therefore, improvement or worsening of a patient’s condition can be reliably documented. The PosturePrint™ system is accurate in measuring head postures in five degrees of freedom. Because this system allows for accurate postural measurement as rotations and translations, statistical research determining the correlation between head postural displacements, neck pain, function, and health status can be performed. Furthermore, documentation as to the incidence/prevalence and magnitude of human head postural displacements can be obtained in both normal and pain populations.
ACKNOWLEDGMENTS: For funding support: Université du Québec à Trois-Rivières, and CBP Nonprofit, Inc.
DATA COLLECTION: Claude Brouillette, electronic technician
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