What is the primary goal of facial paralysis reanimation surgery, and what are the key challenges in achieving it?

Facial paralysis reanimation surgery aims to restore facial movement, particularly the smile. Free functional muscle transfer (FFMT) is a key technique, where a muscle from another body part is transplanted to the face and re-innervated to enable voluntary movement. However, achieving a natural, spontaneous, and symmetrical smile remains a challenge.

What were the main findings of the study regarding the predictive power of pre-operative EMG in determining smile synchronicity after facial reanimation?

The study revealed that 94% of patients exhibiting pre-operative co-activation of the masseter muscle achieved synchronous smiles post-surgery. Conversely, none of the patients without pre-operative masseter muscle activation developed synchronous smiles. The pre-operative EMG displayed a sensitivity of 99.7% and a specificity of 88.5% in predicting smile synchronicity.

How is pre-operative EMG testing conducted, and what specific muscle activity are researchers looking for to predict smile synchronicity?

Pre-operative EMG testing involves assessing the activity of the masseter muscle while a patient attempts to smile before surgery. Researchers look for 'co-activation,' where the masseter muscle involuntarily contracts during smiling. This involuntary activation is predictive of outcomes using the masseteric nerve.

How can the results of pre-operative EMG testing influence and personalize the approach to facial paralysis treatment, particularly when considering the use of the masseteric nerve?

The study indicates that pre-operative EMG testing can help personalize facial paralysis treatment. Surgeons can use EMG results to assess the potential benefits and limitations of using the masseteric nerve for facial reanimation. For patients without pre-operative co-activation, surgeons might consider alternative strategies beyond relying solely on the masseteric nerve to achieve a synchronous smile, potentially combining techniques or exploring different donor nerves to optimize outcomes.

Illustration showing one side of face with a natural smile and electric pulses for muscle activity, other side shows muscle disfunction and no pulses

Smile Synchronicity: Can a Simple Test Predict Success After Facial Paralysis Surgery?

Q: What is a cross-face nerve graft (CFNG), and how does it compare to using the masseteric nerve as a donor nerve in facial reanimation surgery?

A cross-face nerve graft (CFNG) involves connecting a nerve from the healthy side of the face to the paralyzed side. While CFNG can yield good results, it often requires multiple stages and may not always provide the desired level of muscle contraction. The masseteric nerve, which controls chewing muscles, serves as an alternative, offering a single-stage approach with potentially stronger muscle activation.

Nico Varela in Health & Wellness November 2025 • 5 min read.

"New research suggests a pre-surgery EMG test could help predict natural-looking smiles after nerve reanimation, offering hope and personalized approaches for patients with facial paralysis."

Facial paralysis can significantly impact an individual's life, affecting not only their ability to express emotions but also their self-esteem and social interactions. Reanimation surgery, particularly free functional muscle transfer (FFMT), offers a promising solution for restoring facial movement and function. This procedure involves transplanting a muscle from another part of the body to the face, re-innervating it with a nerve to enable voluntary movement. However, the quest for a truly natural smile – one that is both spontaneous and symmetrical – remains a significant challenge in facial reanimation surgery.

One of the critical factors determining the success of smile reanimation is the choice of donor nerve. Traditionally, surgeons have used the cross-face nerve graft (CFNG), which involves connecting a nerve from the healthy side of the face to the paralyzed side. While CFNG can yield good results, it often requires multiple stages and may not always provide the desired level of muscle contraction, especially in older patients. The masseteric nerve, which controls the muscles used for chewing, has emerged as an alternative donor nerve, offering a single-stage approach with the potential for stronger muscle activation.

Despite its advantages, the masseteric nerve doesn't always guarantee a spontaneous smile. Approximately 59% of patients who undergo FFMT using the masseteric nerve develop a smile that appears natural and effortless. Researchers have been exploring the underlying mechanisms behind this phenomenon, seeking ways to predict which patients are most likely to achieve a synchronous and spontaneous smile after surgery. Recent studies suggest that pre-existing co-activation of the masseter muscle during smiling may play a crucial role. Now, a new study investigates whether pre-operative electromyography (EMG) can effectively predict smile synchronicity in patients undergoing facial reanimation using the masseter nerve.

Unlocking the Secret to a Natural Smile: How EMG Testing Can Help

Illustration showing one side of face with a natural smile and electric pulses for muscle activity, other side shows muscle disfunction and no pulses

The study, conducted by Yvonne Lenz, Jurij Kiefer, Franziska Dietrich, G. Björn Stark, and Steffen U. Eisenhardt at the University of Freiburg Medical Centre, explored whether involuntary activation of the masseteric nerve during smiling before surgery could predict the development of a synchronous smile after reanimation. The research team recruited 30 patients with long-standing facial paralysis who were scheduled for FFMT using the masseteric nerve as a donor nerve. Before surgery, each patient underwent EMG to assess the activity of their masseter muscle while smiling. Researchers looked for 'co-activation,' where the masseter muscle involuntarily contracts when the patient smiles.

The study meticulously tracked patients' progress, with a key focus on smile synchronicity – the simultaneous movement of both corners of the mouth during smiling. Six months after the initial signs of muscle contraction, researchers analyzed slow-motion video recordings of patients as they watched humorous content. This approach allowed for a detailed assessment of how naturally and synchronously their smiles developed. The results were remarkable:

Predictive Power: An impressive 94% of patients exhibiting pre-operative co-activation achieved synchronous smiles post-surgery.
Zero Synchronicity Without Co-activation: In stark contrast, none of the patients without pre-operative masseter muscle activation developed synchronous smiles.
High Accuracy: The pre-operative EMG displayed a sensitivity of 99.7% and a specificity of 88.5% in predicting smile synchronicity. Its positive predictive value was 92.5%, and negative predictive value, 99.6% (p < 0.001 for all).

These findings suggest that pre-operative EMG can serve as a valuable tool for predicting the likelihood of achieving a synchronous smile after facial reanimation with the masseteric nerve. Patients who exhibit co-activation of the masseter muscle during smiling are significantly more likely to develop a natural-looking smile after surgery. Conversely, the absence of co-activation strongly suggests that the patient may not achieve a spontaneous, synchronous smile with this particular surgical approach.

Personalizing Facial Paralysis Treatment: A New Era

The results of this study pave the way for a more personalized approach to facial paralysis treatment. By incorporating pre-operative EMG testing into the evaluation process, surgeons can better assess the potential benefits and limitations of using the masseteric nerve for facial reanimation. This information can help guide surgical decisions, manage patient expectations, and explore alternative strategies for those less likely to achieve a synchronous smile with the masseteric nerve alone. While further research is needed to refine and validate these findings, the study represents a significant step forward in the quest to restore natural, confident smiles for individuals affected by facial paralysis.