Cervical Spinal Muscle Length Changes Associated with Forward Head Posture

Forward head posture (FHO) is a common clinical entity that may result from multiple etiologies, and has been linked to neck pain, disability, and poor health related quality of life. The purpose of this study was to quantitatively assess the muscle tendon length changes associated with varying degrees of forward head posture. Thirteen human cadaveric cervical spines were used. The T1 vertebra was anchored to a translating base in a sophisticated apparatus that permitted translation of T1 on a relatively fixed occiput. The angular orientation of the occiput was constrained to maintain a horizontal gaze. A 5 kg mass was attached to the occiput to mimic head weight. The position of the T1 in the apparatus was changed to measure the varying severity of FHP, and segmental vertebral motions were measured by optoelectronic markers attached to each vertebra to document the postural compensation that occurred to maintain horizontal gaze. Computerized tomography (CT) scans were utilized to create a specimen-specific model for each cadaveric specimen based on the specific anatomy and kinematic response of each specimen measured. The response of each specific model was used to calculate the changes in muscle lengths, based on known muscle attachment data, for 10 cervical muscle groups at varying amounts of FHP. The amount of FHP was determined by measurement of the sagittal vertical alignment (SVA). An increase in FHP was associated with shortening of the rectus capitus Poster Sessionior major, rectus capitus Poster Sessionior minor, and the semispinalis capitus. Muscle lengthening in response to increased FHP was most pronounced in the cervical multifidus muscles. Maintenance of a horizontal gaze in the presence of FHP is associated with substantial shortening of the suboccipital muscle-tendon units along with lengthening of the deep mid and lower cervical multifidi. This experiment provides data that supports clinical assumptions regarding cervical spinal muscle shortening and lengthening in the presence of FHP. An implication is that strategies aimed at reducing the magnitude of FHP may potentially minimize symptoms associated with upper cervical muscle shortening and lower cervical muscle lengthening