Validity of a computer postural analysis to estimate 3-dimensional rotations and translations of the head from three 2-dimensional digital images.

ABSTRACT

OBJECTIVE: The purpose of this study is to describe and evaluate the validity/accuracy of the computerized system PosturePrint for measuring head posture. METHODS: Computer analysis was compared with 125 measured positions of a mannequin head in 5 degrees of freedom. For each mannequin position, 3 digital photographs were obtained (left lateral, anteroposterior, and right lateral) and were processed through the PosturePrint computer system. For the head analysis, a headgear with 3 reflective markers was placed on a subject; and there were additional click-on markers at the ear tragus, upper lip, acromioclavicular joints, and episternal notch. Head postures were calculated as lateral translation (T(x)), lateral flexion (R(z)), axial rotation (R(y)), flexion-extension (R(x)), and anterior-posterior translation (T(z)). For an error analysis, PosturePrint algorithm calculations were compared with the true mannequin head positions. Furthermore, average head posture was determined in student volunteers (n = 40). RESULTS: Mean computational errors were R(x) = 1.3 degrees (SD 0.6 degrees) and T(z) = 1.1 mm (SD 0.5 mm) for sagittal displacements and R(y) = 1.1 degrees (SD 0.7 degrees), R(z) = 0.6 degrees (SD 0.4 degrees), and T(x) = 1.1 mm (SD 0.5 mm) for frontal view displacements. For the normal group, mean head displacements were 1.1 degrees or less for all rotations and 1 mm or less for lateral translations (T(x)); and forward head posture (T(z)) averaged 3 cm. CONCLUSION: From the mannequin positions, small mean errors indicate that the PosturePrint system is accurate. In the future, statistical research determining the correlation between head displacements, neck pain, function, and health status should be performed.