4. Discussion
headaches, muscle contraction, brow ptosis, headache, muscle fatigue
RECURRENCE, MINOR, TENSION-TYPE HEADACHE, CONTRACTION, RECRUITMENT, REGRESSION
In this study, we demonstrate a decrease in eyebrow height and in headache complaints after an upper blepharoplasty, regardless of whether only skin or skin with an additional strip of orbicularis oculi muscle is resected.After an upper blepharoplasty, the frontalis muscles do not need to lift the eyebrows anymore to compensate for excessive eyelid skin. Subsequently, the frontalis muscles can relax and, as a result, the eyebrows tend to move down postoperatively. An anatomical and physiological relationship between the eyebrows, eyelid opening, and frontalis activation is suggested. When raising the eyebrows, the eyelid opening increases [Multiple studies have assessed the occurrence of brow ptosis after an upper blepharoplasty and, in general, the eyebrows tend to move down postoperatively [Whether lowering the eyebrows has a negative effect on the aesthetic results is unclear. When the eyebrows move down postoperatively, the tarsal platform show may be less visible with time and may lead to a recurrence of excess upper eyelid skin. Whether this results in a softening of the forehead wrinkles is not clear. Another important factor is the shape and inclination of the eyebrows, since this affects eyebrow aesthetics [In theory, preoperatively, continuous eyebrow elevation during the day may lead to problems such as tension-type headache. We found a low positive correlation [Although the relationship between muscle activation and tension-type headache is controversial [We also found a significant decrease in group A’s RMS sEMG during maximal contraction 12 months after the upper blepharoplasty. This is an indication that the frontalis muscle requires less motor recruitment to elevate the eyebrow to the same height during maximal contraction compared to baseline. This is in line with the expectation of less local muscle fatigue (electrical activity) of the frontalis muscle postoperatively, but we do not know why we did not observe this in the skin/muscle group. One explanation could be that the delicate balance between the frontalis muscle and its antagonist orbicularis oculi muscle differs between the skin-only blepharoplasty and when the orbicularis oculi muscle is resected.In general, during isometric contraction, muscle fatigue is accompanied by a decrease in motor unit firing rate. The EMG power density shifts to lower frequencies and, consequently, the median frequency decreases. As the muscle fatigues, additional fibres have to be recruited in order to generate the same force. This results in an increase in EMG amplitude and an increase in RMS values [Our study did not assess the levator palpebrae superioris muscle, whose primary function is to elevate the upper eyelid. Excess eyelid skin might lead to muscle fatigue and so the frontalis muscle is recruited to elevate the eyelid–eyebrow unit as a whole. However, we could not acquire an sEMG of this muscle due to practical difficulties. The surface EMG electrodes would interfere with normal eyelid opening and we would have had to resort to invasive techniques such as needle or wire electrode EMGs. In addition, due to the position of the muscle, it is difficult to acquire an EMG measurement. Kim et al. [The non-normalised frontalis muscle RMS values showed that the electrical activity of the frontalis muscle was significantly lower in group A compared to group B two months postoperatively. This indicates that the skin-only participants’ muscles required less motor recruitment to elevate the eyebrow to the same height during maximal contraction (raising the eyebrows maximally) compared to the skin/muscle group. Although group A demonstrated lower electrical activity of the frontalis muscle, this did not lead to differences in patient-reported headaches between the groups.Regarding the 12-month follow-up of orbicularis oculi muscle RMS results, the group B value was lower compared to group A. Therefore, it seems that the skin/muscle group needed less motor recruitment to achieve the same amount of muscle contraction compared to the skin-only group. This implies that a skin-only blepharoplasty possibly induces minor difficulties in contraction of the orbicularis oculi. However, it is important to mention that the differences between the groups regarding sEMG do not seem to be clinically relevant. When the regression coefficients were subjected to back-transformation with the log transformed raw values, an adjusted difference of −1.7 mV (RMS) in the of the frontalis muscle between groups was found, and 1.9 mV (RMS) in the orbicularis oculi muscle between groups. These differences are smaller than the intra-individual day-t-day variability (13% during maximal contraction) in healthy subjects [A limitation of our study is that our patients only showed mild headache symptoms preoperatively, so we could not assess the effect of an upper blepharoplasty on moderate to severe headaches. In addition, the HIT-6 questionnaire was designed to provide a global measure and does not differentiate between various types and causes of headache. Another thought for future studies entails the eyebrow height measurements. Although our eyebrow measurements showed excellent repeatability, some improvements in eyebrow height measurements are possible. For example, the upper limit of the eyebrows could be used as a cut-off point, since this area is usually not subjected to eyebrow epilation. Future studies should standardise and make eyebrow height measurements uniform since a variety of methods have been used so far.