PP1409 - Does Forward Head Posture Affect the cVEMP Response?

Abstract:
Forward Head Posture (FHP) is a common postural deviation characterized by the forward positioning of the head relative to the shoulders, placing increased strain on the cervical spine and sternocleidomastoid (SCM) muscle. This altered posture may impact SCM activation patterns and, in turn, cervical control mechanisms. Cervical Vestibular-Evoked Myogenic Potentials (cVEMPs) assess vestibular function by recording SCM contraction in response to auditory stimuli. Given FHP's potential effects on SCM recruitment, cVEMP responses may be altered, affecting amplitude and latency. This study investigates how FHP influences cVEMP outcomes by comparing responses between normal head posture and FHP participants.

Summary:
Background
Forward Head Posture (FHP) is a common postural deviation where the head protrudes anteriorly relative to the shoulders, significantly straining cervical ligaments and neck musculature, especially the sternocleidomastoid (SCM) muscle. Although not primarily a stabilizer, SCM overactivity in FHP can disrupt the balance between neck flexors and extensors. Over time, SCM adaptations for head support may alter activation patterns, impacting muscle strength and cervical control mechanisms (Shaghayeghfard et al., 2015). Cervical Vestibular-Evoked Myogenic Potentials (cVEMPs) serve as a clinical test for assessing vestibular system integrity, specifically evaluating the function of the otolithic organs through SCM contraction responses to auditory stimuli. This test leverages the vestibulo-collic reflex (VCR), which links vestibular inputs with neck muscle responses. Given that cVEMP generation requires consistent SCM contraction, FHP-related changes in SCM activation patterns may influence cVEMP parameters, including response amplitude and latency. Prior studies have shown that SCM activation methods such as head rotation or flexion affect cVEMP amplitude (Ashford et al., 2016), implying that postural deviations like FHP may similarly impact vestibular test outcomes similarly. Despite this potential influence, no study has examined how FHP impacts cVEMP responses. This study aims to investigate whether FHP affects cVEMP response metrics.

Methods
The study includes 40 participants divided into two groups: those with normal head posture (NHP) and those with FHP, based on a craniovertebral angle (CVA) assessment by a licensed physiotherapist. The CVA was measured using a digital imaging technique, forming an angle (°) between a horizontal line through the C7 vertebra and a line from C7 to the tragus. Participants with a CVA < 48° were categorized as having FHP, while those with a CVA ≥ 50° were classified as having normal head posture (NHP). All participants were free from neurological disorders, vestibular pathologies, chronic noise exposure, and conductive hearing loss. For cVEMP recordings, a two-channel montage was employed, with non-inverting electrodes on the right and left SCM, an inverting electrode on the upper sternum, and a ground electrode on the mid-forehead. Participants maintained a steady SCM contraction by turning their heads contralaterally, with verbal feedback provided to ensure consistent effort. Acoustic cVEMP responses were recorded using a 500 Hz tone burst at 95 dBnHL. cVEMP metrics, including P1 and N1 latencies, P1-N1 peak-to-peak amplitude, and interaural asymmetry ratio (IAR), were compared between the NHP and FHP groups.

Results
Ongoing analyses indicate a potential relationship between FHP and reduced cVEMP amplitudes, with preliminary data suggesting that increased FHP angle correlates with decreased response amplitudes. While these findings are tentative, they provide initial support for the hypothesis that FHP-related changes in SCM activation patterns could impact cVEMP response amplitude. Further data collection and analysis are ongoing to substantiate these observations.

Brief Summary of Clinical Takeaways:
Preliminary findings cautiously indicate that FHP may affect cVEMP amplitudes, suggesting that postural deviations could affect vestibular diagnostic accuracy. Further research is needed to investigate the influence of FHP on other vestibular assessments and gait and postural control to deepen our understanding of posture's role in vestibular function and diagnostic interpretation.