Increased Stretching of Mechanoreceptors in Superior Tarsal Muscle Reflexively Contracts Upper Trapezius Muscle as well as Levator Palpebrae Superioris and Occipitofrontalis Muscles as Eye-Eyelid-Eyebrow-Head Coordinated Movements: A Case Series.

To maintain a vertical visual field, fast-twitch fibers in the levator palpebrae superioris muscle (LPSM) stretch mechanoreceptors in the superior tarsal muscle (STM), which contracts the slow-twitch fibers in both the LPSM and the occipitofrontalis muscle (OFM). Exceeding the upgaze limit without head movement increases reflex contraction of the OFM to raise the eyebrows and pull the scalp backward while also causing involuntary contraction of the upper trapezius muscle (UTM) to extend the head backward, resulting in tension-type headaches (TTH) and neck pain. Due to aponeurosis disinsertion from the tarsus, we hypothesized that increased mechanoreceptor stretching in the STM reflexively contracts both the OFM and UTM. We report a case series of five patients whose aponeurosis disinsertion caused tonic eyebrow-raising, TTH, and neck pain. In the first case, asymmetrical disinsertion with dominance on the left side led to a more pronounced contraction of the OFM and UTM, resulting in TTH and neck pain on that side. After surgery to reduce mechanoreceptor stretching, symptoms resolved. The second and third cases, which involved symmetrical disinsertion, showed that unilateral eyebrow lifting using tape to alleviate mechanoreceptor stretching reduced ipsilateral UTM contraction in length and hardness. The fourth case, also with symmetrical disinsertion, experienced symptom relief post-surgery. In the fifth case, the eyebrows were maximally raised due to severe aponeurosis disinsertion, and the head was extended backward and protruded. Bilateral aponeurosis reinsertion lowered the eyebrows and reduced the extension/protrusion of the head, relieving TTH and neck pain. These cases suggest that increased mechanoreceptor stretching in the STM reflexively contracts the slow-twitch fibers of the OFM and UTM, contributing to TTH and neck pain as part of coordinated eye, eyebrow, and head movements.