Contributions of the Musculus Uvulae to Velopharyngeal Closure Quantified With a 3-Dimensional Multimuscle Computational Model

Abstract

The convexity of the dorsal surface of the velum is critical for normal velopharyngeal (VP) function and is largely attributed to the levator veli palatini (LVP) and musculus uvulae (MU). Studies have correlated a concave or flat nasal velar surface to symptoms of VP dysfunction including hypernasality and nasal air emission. In the context of surgical repair of cleft palates, the MU has been given relatively little attention in the literature compared with the larger LVP. A greater understanding of the mechanics of the MU will provide insight into understanding the influence of a dysmorphic MU, as seen in cleft palate, as it relates to VP function. The purpose of this study was to quantify the contributions of the MU to VP closure in a computational model. We created a novel 3D finite element model of the VP mechanism from MRI data collected from an individual with healthy non-cleft VP anatomy. The model components included the velum, posterior pharyngeal wall (PPW), LVP, and MU. Simulations were based on the muscle and soft tissue mechanical properties from the literature. We found that, similar to previous hypotheses, the MU acts as i) a space-occupying structure and ii) a velar extensor. As a space-occupying structure, the MU helps to nearly triple the midline VP contact length. As a velar extensor, the MU acting alone without the LVP decreases the VP distance 62%. Furthermore, activation of the MU decreases the LVP activation required for closure almost three-fold, from 20% (without MU) to 8% (with MU). Our study suggests that any possible salvaging and anatomical reconstruction of viable MU tissue in a cleft patient may improve VP closure due to its mechanical function. In the absence or dysfunction of MU tissue, implantation of autologous or engineered tissues at the velar midline, as a possible substitute for the MU, may produce a geometric convexity more favorable to VP closure. In the future, more complex models will provide further insight into optimal surgical reconstruction of the VP musculature in normal and cleft palate populations.

Morphology of the Musculus Uvulae In Vivo Using MRI and 3D Modeling Among Adults With Normal Anatomy and Preliminary Comparisons to Cleft Palate Anatomy

“…The observations from the present study agree with prior studies suggesting that the musculus uvulae are preserved to some degree in those with repaired cleft palate (F#x00E1;ra and Dvor#x00E1;k, 1970;Calnan, 1954). Inouye et al (2016) recently evaluated the contribution of the musculus uvulae to velopharyngeal closure using a computational model that simulates multiple scenarios of muscle abnormalities. The authors observed that with a 100% activation level of the musculus uvulae with low levels of levator veli palatini activation, the musculus uvulae had the capacity to preserve normal velopharyngeal closure.…”

“…Inouye et al (2016) recently evaluated the contribution of the musculus uvulae to velopharyngeal closure using a computational model that simulates multiple scenarios of muscle abnormalities. The authors observed that with a 100% activation level of the musculus uvulae with low levels of levator veli palatini activation, the musculus uvulae had the capacity to preserve normal velopharyngeal closure.…”

“…Contraction of the musculus uvulae produces the dorsal convexity of the velum, adds stiffness to the velum, and extends the velum toward the posterior pharyngeal wall (Kuehn et al, 1988). Recent computational modeling of the musculus uvulae demonstrated that an absent or dysmorphic musculus uvulae resulted in an inability of the velopharyngeal mechanism to establish appropriate closure force (Inouye et al, 2016).…”

“…To date, studies of the musculus uvulae have included histology, dissection, electromyography, and computational modeling based on hypothetical prediction-based scenarios (Azzam and Kuehn, 1977; Langdon and Klueber, 1978; Boorman and Sommerlad, 1985; Huang et al, 1997; Kuehn and Moon, 2005; Landes et al, 2012; Inouye et al, 2016). Because of the relative inaccessibility of the velopharyngeal system during dissection and the ex vivo process involved in histology, these methods provide a limited understanding of muscle tissue morphology.…”

Biomechanics of the soft-palate in sleep apnea patients with polycystic ovarian syndrome

“…Truly passive mechanical properties of airway tissue would have to be estimated using mechanical testing, although some studies have also proposed to obtain the same using MRE with respiratory gating (Cheng et al, 2011). Activation of the levator veli palitini and musculus uvulae has been studied previously using CSM (Inouye et al, 2016) and the same would have to be considered in a future study to model flow-induced palate movement during wakefulness. Modeling the same would necessitate MR images with higher image contrast between individual tissue structures (Perry et al, 2014).…”