OBJECTIVE: To determine the validity of the Biotonix PosturePrintTM Internet computer system (Montreal, Quebec, Canada) used to measure standing pelvic posture in 3-D.
METHODS: In a university biomechanics laboratory, photographs of a mannequin pelvis were obtained in different postures on a stand in front of a digital camera. For each pelvic posture, three photographs were obtained (left lateral, right lateral, and anterior to posterior). 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 pelvis was placed in 68 different single and combined postures (requiring 204 photographs) in five degrees of freedom: lateral translation, lateral flexion, axial rotation, flexion-extension, and anterior-posterior translation. The PosturePrintTM 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 PosturePrintTM computer system over the Internet. The PosturePrintTM 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 posture to the PosturePrintTM’s computed values. Mean and standard deviation of computational errors for sagittal displacements of the pelvis were: flexion-extension, 0.5º ± 0.8º; and anterior-posterior translation, 1.2 mm ± 0.6mm. For frontal view displacements, mean and standard deviation of computational errors were: axial rotation, 1.3º ± 0.8º; lateral flexion, 0.5º ± 0.3º; and lateral translation, 0.9 mm ± 0.5mm.
DISCUSSION: To those working within biomechanics and physical medicine settings, a practical notion is that static parameters determine dynamics (structure determines function). This is also true when applied to neutral posture pelvic alignment and its effects on subsequent gait motion. In fact, pelvic posture is considered an important component in gait, leg length inequality determination, dynamics in running, patient range of motion assessment and in static analysis of patient posture. The pelvis is also an integral part of abnormal gait evaluations for pregnancy, gait in stroke victims, gait in hip osteoarthritis, gait in pain subjects, trunk flexibility, impact biomechanics, and in biomechanics of hip surgery. Because pelvic posture is a clinically important parameter for patient health, an accurate means to assess pelvic posture is essential. An earlier study categorized pelvic postures as rotations and translations in 3-D, but no studies could be located providing these movements as rotations and translations in gait or in ROM studies. Although the validity and reliability of using radiographic procedures for assessing pelvic posture (i.e. pelvic obliquity) has been established, this method is costly, invasive, requires special expertise and does not afford itself as a clinically simple patient screening tool. Further, as ionizing radiation is thought to pose potential risk to patients, use of digital pictures used within the comprehensive PosturePrintTM system allows a rapid and ionizing radiation-free means of data extraction to assess and/or monitor patient disease or treatment progression.
CONCLUSIONS: The Biotonix PosturePrintTM system is accurate in measuring pelvic standing static postures in five degrees of freedom. Because this system allows for accurate pelvic postural measurement as rotations and translations, statistical research determining the correlation between pelvic postural displacements, back pain, function, and health status can be performed.
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