• Saeed Khayatzadeh, Olivia A Kalmanson, Dale Schuit, Robert M Havey, Leonard I Voronov, Alexander J Ghanayem, and Avinash G Patwardhan.
• Musculoskeletal Biomechanics Laboratory, Edward Hines Jr VA Hospital, Hines, Illinois.
• Phys Ther. 2017 Jul 1; 97 (7): 756-766.

BackgroundForward head posture (FHP) may be associated with neck pain and poor health-related quality of life. Literature describes only qualitative muscle length changes associated with FHP.ObjectiveThe purpose of this study was to quantify how muscle-tendon unit lengths are altered when human cadaveric specimens are placed in alignments representing different severities of FHP.DesignThis biomechanical study used 13 fresh-frozen cadaveric cervical spine specimens (Occiput-T1, 54±15 y).MethodsSpecimens' postural changes simulating increasing FHP severity while maintaining horizontal gaze were assessed. Specimen-specific anatomic models derived from computed tomography-based anatomic data were combined with postural data and specimen-specific anatomy of muscle attachment points to estimate the muscle length changes associated with FHP.ResultsForward head posture was associated with flexion of the mid-lower cervical spine and extension of the upper cervical (sub-occipital) spine. Muscles that insert on the cervical spine and function as flexors (termed "cervical flexors") as well as muscles that insert on the cranium and function as extensors ("occipital extensors") shortened in FHP when compared to neutral posture. In contrast, muscles that insert on the cervical spine and function as extensors ("cervical extensors") as well as muscles that insert on the cranium and function as flexors ("occipital flexors") lengthened. The greatest shortening was seen in the major and minor rectus capitis posterior muscles. These muscles cross the Occiput-C2 segments, which exhibited extension to maintain horizontal gaze. The greatest lengthening was seen in posterior muscles crossing the C4-C6 segments, which exhibited the most flexion.LimitationsThis cadaver study did not incorporate the biomechanical influence of active musculature.ConclusionsThis study offers a novel way to quantify postural alignment and muscle length changes associated with FHP. Model predictions are consistent with qualitative descriptions in the literature.© 2017 American Physical Therapy Association

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