The applications of lifting threads in patients with facial nerve palsy – a systematic review

Introduction

Facial expression is one of the main components of interpersonal communication, crucial for conveying emotions and non-verbal signals. Loss of facial expression can lead to depression, decreased quality of life, and social isolation. Impairment of the function of the facial nerve and muscles it innervates can result in partial or complete facial paralysis [1]. It can have congenital causes, such as unilateral lower lip palsy, which is one of the cranial neuropathies in children; however, acquired causes are much more common. They include Bell palsy, primary and secondary tumors of the facial nerve, trauma, inflammatory processes (viral, bacterial), degenerative conditions, iatrogenic injuries, vascular compression of the facial nerve, ischemic damage to facial motor centers, and others [1, 2]. Typical symptoms of facial nerve palsy include weakness of the upper and lower parts of the face on the affected side, clinically manifested as drooping of the eyebrow, inability to close the eye due to widening of the palpebral fissure, flattening or loss of the nasolabial fold, and drooping of the corner of the mouth (fig. 1).
The examination of the patient includes observation of the symmetry of facial expressions and muscle tension when asked to close the eyes, raise the eyebrows, frown, grit the teeth, purse the lips and smile. The evaluation also includes a general physical and neurological examination, including the assessment of each branch with the House-Brackmann scale. Accurate diagnosis is essential for the correct assessment of the cause of paralysis and further treatment [2, 3]. When causal treatment is not possible or ineffective, in cases of persistent facial nerve paralysis, dynamic and static methods are used to correct resulting asymmetries. From a medical standpoint, it is important to restore the proper function of mouth closure and speech as well as the closing of the eyelids, which prevents corneal ulcers and permanent visual impairments [1, 3]. Dynamic methods include reconstruction of the damaged nerve and functional transfer of neuromuscular units. Static methods involve suspending soft tissue structures of the paralyzed face to improve symmetry without providing active movement [1].
Lifting threads have been used as an alternative to surgical facelifts and as a method for less invasive facial rejuvenation [4]. Most threads are made of absorbable materials that degrade over time, such as polycaprolactone (PCL), poly-L-lactic acid (PLLA), and polydioxanone (PDO) [5]. Non-absorbable threads, such as those made of polypropylene, can last up to 4 years after the procedure [4]. In addition to the mechanical lifting effect of tissues, threads are supposed to stimulate local production of collagen and elastin by fibroblasts, which may contribute to longer lasting effect of the procedure [5].
The procedure involves the subcutaneous insertion of threads beneath the area of desired lifting. The threads lift the soft tissues upwards, and if necessary, the ends of the threads are additionally pulled to enhance the lifting effect. The vector of lifting threads should always be in the upper-lateral direction. Depending on the individual characteristics of the patient, modification of the quantity of threads needed and their placement may be necessary. The procedure is easy and quick to perform, associated with minimal tissue damage, slight swelling, and bruising. The result is immediately visible after a short postoperative period and does not entail significant postoperative limitations [4, 6]. The most commonly described complications are swelling and bruising after the procedure. Additionally, pain, superficial disfigurement of tissues (dimples or hollowing), paresthesia, petechiae, and infectious complications may occur. Physicians performing the procedure may encounter thread breakage, migration, or thread extrusion above the skin surface. Patients may also complain of lack or unsatisfactory cosmetic results. However, these complications are rare, and the procedure itself is considered safe and relatively effective [4–6].

Objective

This review aims to identify the applications, effectiveness, and safety of lifting threads in correcting facial asymmetry in patients with facial nerve paralysis.

Methods

In April 2024, databases including PubMed, Embase, Web of Science, and Scopus were searched using the keywords ”thread lift; lifting thread; facial paralysis”. The aim was to identify articles describing the use of lifting threads in patients with facial nerve paralysis consistent with the clinical question framework based on PICO (table 1). The exclusion criterion was publication in other language than English. There were no time restrictions on the publication dates of research papers. The first selection of articles was based on the compatibility of titles and abstracts with the review topic. Articles exclusively related to alternative methods of correcting facial asymmetry in patients with facial nerve paralysis were excluded, as well as publications where asymmetry in patients resulted from other conditions such as neuromuscular dystrophies. Articles meeting the inclusion criteria were evaluated for data on the applications of lifting threads in patients with facial nerve paralysis, their effectiveness in this regard, and any associated complications. This review follows the PRISMA guidelines [7].

Results

Systematic review

In the preliminary search, 34 articles were identified. Nineteen of them were duplicates. The remaining 15 articles were assessed for the compatibility of titles and abstracts with the review topic, resulting in the exclusion of 6 publications. Two additional articles were disqualified as they were not in English. Seven articles were found in their originally published versions. One publication was rejected due to insufficient data details, preventing further analysis of the work. Additionally, two articles were found using internet search engines and by reviewing reference lists in previously included publications. Finally, 8 articles were evaluated for content and the results and conclusions were summarized [8–15] (fig. 2).

Qualitative assessment of the publications found

The articles found included: two non-randomized prospective studies without a control group [8, 9], two retrospective studies without a control group [11, 14], three case series [10, 12, 13], and 1 case report [15]. According to recognized standards [16], the class of evidence of these publications can be assessed as III [8, 9, 11, 14], IV [10, 12, 13], or V [15], indicating a moderately high or high risk of systematic error. Conclusions regarding the effectiveness and safety of the applied method were consistent among all authors. For these reasons, the strength of evidence in this systematic review can be considered moderate.

Data synthesis

The collected data originated from 144 patients aged 21-84 years, including 69 women and 75 men. The causes of facial nerve paralysis in the described patients can be divided into iatrogenic (28), traumatic (18), neoplastic (7), viral (Ramsay Hunt syndrome – 8), and other (cholesteatoma – 1, tuberculosis – 1, malignant otitis externa – 1). In 44 patients, the cause of paralysis was determined to be idiopathic, and for 36 patients, information about the primary cause was not provided. The percentage distribution of the etiology of facial nerve paralysis in patients with known causes of paralysis is presented in figure 3.
The studies described in the review used various types of lifting threads. These included absorbable PDO threads [8, 9, 11, 13] as well as PLLA threads [12] and non-absorbable polypropylene threads [10, 12, 14]. In 1 case, the type of threads used was not specified [15]. The procedures were performed on patients with diversified symptoms resulting from facial nerve paralysis and varying degrees of severity. The corrected symptoms included brow ptosis [8, 10], drooping of the upper eyelid [8, 9], drooping corner of the mouth [8–10], reduced volume of the midface, and facial skin laxity [8–10, 15]. Threads were also used to restore the proper shape of the nasolabial fold.
Endpoints assessed were non-uniform. They included patient satisfaction assessment [9, 10, 12, 14, 15], evaluation of improvement in motor function of facial muscles (chewing, speech, eye closure) [11–13], objective assessment scales such as the Sunnybrook Facial Grading Scale [8, 9], Facial Grading System [8], or Arianna Disease Scale [11], and assessment of static and/or dynamic symmetry based on comparison of pre- and postoperative photographs [9, 12, 13, 15].
In 75% of the studies identified, additional treatment methods were used in combination with thread lifting. These included the use of botulinum toxin to weaken the muscles on the opposite side of the face, thereby restoring symmetry of their action or treating previously occurring synkinesis [8, 9, 15]. Other interventions were hyaluronic acid-based fillers used to correct facial volume deficits [13, 15], simultaneous partial surgical facelift and/or eyebrow lift [10], correction of eyelid ptosis with a gold implant [11], and physiotherapy [11]. Procedures using lifting threads were described as effective by all authors. Facial symmetry in patients improved [8, 9, 12, 15], as did their active facial expression [8, 9], chewing and speech abilities [11–13], and eyelid closure ability [11, 13]. Most patients experienced improvement compared to their preoperative condition and positively assessed their appearance [10–14]. A statistically significant improvement (p < 0.05) was demonstrated in the Sunnybrook Facial Grading Scale [8, 9]. Incorporating physiotherapy and rehabilitation exercises before surgical intervention increased the chances of treatment success [11]. Results did not deteriorate during the 1-year observation period [8–10, 14]. The outcome of the procedure is visualized in figure 4.
Complications were only described by two authors and included dissatisfaction with appearance [9], partial thread extrusion, and 1 case of herpes labialis occurring after the procedure [14]. Some individual patients reported discomfort or anxiety during the procedure [8]. No allergic or infectious complications were recorded.
A detailed summary of the articles included in the review is provided in table 2.

Discussion

Facial nerve paralysis can occur in patients of all ages. Despite the availability of surgical methods for correcting facial nerve paralysis such as reconstruction of the damaged nerve or functional transfer of neuromuscular units, they cannot be applied in every case. Particularly in older patients, the balance between benefits and risks of more invasive procedures is considered due to the frequency of comorbidities. High-specialty surgical treatment is often associated with the inherent risks of the operation and often involves long waiting times for surgery or high costs of the procedure. Introducing alternative treatment methods, characterized by greater accessibility and safety, could be beneficial for patients [9]. The indications for facial paralysis treatment are both medical and aesthetic. Among the more pressing medical reasons for the procedure is eyelid drooping, which can cause disturbances in the tear film and drying of the ocular surface, leading to corneal ulcers and consequently permanent visual acuity impairment. In addition to the physical exposure to external factors caused by weakened eyelids, there is a decrease in tear production by the lacrimal gland, which is also innervated by the facial nerve. Patients not undergoing specialized treatment should remember to use moisturizing drops and ointments to avoid long-term complications. [3]. Seemingly less important aesthetic factors also need to be considered as they can lead to depression and social isolation of the patients. It has been demonstrated that psychosocial disturbances resulting from facial nerve paralysis symptoms only weakly correlate with their severity (0.36, 95% CI: 0.24–0.46). Other factors contributing to the severity of disorders include older age, female gender, and a history of anxiety or depressive disorders [3]. Unilateral facial paralysis in middle-aged individuals worsens gradually due to concurrent aging process, leading to herniation of the infraorbital fat pad and softening of the skin and muscles. Facial paralysis causes progressive softness of the soft tissues and loss of subcutaneous volume leading to an overall less desirable appearance [8]. All of that could be maintained with an appropriately planned treatment.
Patients considered for the procedure using lifting threads must undergo appropriate assessment. But for the examination, patients should be thoroughly informed about their alternative treatment option – in this case – about the surgical approach, its possibilities and sequels. In addition to symptoms resulting from facial nerve paralysis itself, factors such as facial structure, presence of comorbidities, and patient expectations regarding the achievable outcome are considered. Despite the relatively straightforward execution of the procedure, a key element is a thorough understanding of the facial anatomy. The symptoms of the facial nerve paralysis and those resulting from the natural aging process must be considered in the assessment, planning, and treatment of the patient to achieve the best results. Both patients with advanced facial lipoatrophy and those with excess fat tissue in the facial area may be less satisfied with the outcome of the procedure. Furthermore, patients expecting an immediate effect comparable to surgical facelifts should be qualified with great caution [4]. The use of botulinum toxin as an additional therapy in conjunction with lifting threads in patients with facial nerve paralysis has several justifications. One of them is the treatment of synkinesis, which refers to the involuntary contraction or twitching of facial muscles during conscious movements of other facial muscles [3]. The application of botulinum toxin to the muscles undergoing involuntary contractions restores natural facial expression. Additionally, in patients with facial nerve paralysis, there is often hypertrophy of muscles on the unaffected side due to the weakened antagonism of muscles rendered inactive by paralysis. Botulinum toxin enables the reduction of hypertrophy and restores symmetry. Furthermore, after the application of botulinum toxin on the unaffected side of the paralysis, an increase in facial strength on the paralyzed side could be observed. This “strength redistribution” may result from central cortex reorganization, similar to what has been observed in the treatment of hemifacial spasms [9].
An undeniable drawback of using solely lifting threads is their ability to shift tissues only in a specific plane without a true volumetric effect [4]. On the other hand, the use of hyaluronic acid-based fillers alone, without tissue lifting, may result in swelling with an unnatural contour, and the center of facial gravity will be visually shifted downwards, which is the opposite effect from the one desired by patients [6]. The application of fillers after a previously performed lifting procedure allows for the restoration of lost volume and complements the final aesthetic outcome of the procedure. Currently, the use of threads possessing collagen-stimulating properties at the treated site, combines both aspects of treatment. However, there is a gap in scientific research regarding reliable data on this topic [5].
Complications described in the literature regarding the use of lifting threads include swelling and bruising after the procedure, folds in the skin, pain, paresthesia, and infectious complications. There may be breakage of the threads, migration, or piercing above the skin surface. Although the studies included in this review only described complications in the form of partial extrusion of the threads through the skin, herpes labialis, and dissatisfaction with appearance, it is always important to consider other possible complications. Patients with facial nerve paralysis are a particular group when it comes to the durability of the effect of using lifting threads. Due to reduced muscle activity in the paralysis area, the risk of thread rupture due to muscle movement decreases, extending the effectiveness of the procedure [9]. However, contemporary literature lacks direct evidence or either shortened or prolonged effect of thread lifting in facial reanimation cohort.
Currently, the use of combined techniques is proposed to maximize the effectiveness of the procedure [5]. Each case should be considered individually due to the significant variability in facial anatomy and muscle strength, diverse etiologies of facial paralysis, and varied medical comorbidities. It is not possible to establish a single treatment scheme covering the placement of threads, their type, quantity, frequency of procedure repetition, and additional methods necessary to achieve the desired effect [9]. Data on the effectiveness of physiotherapy are conflicting between sources, and based on currently available data, the validity of such therapy cannot be definitively confirmed or denied [1, 3, 11].
This review gathers and summarizes all available reports regarding the use of thread lifting in patients with facial nerve paralysis. The data included here may serve as valuable guidance for specialists seeking alternative therapies for patients with persistent facial nerve paralysis, as well as for physicians using threads for aesthetic purposes to expand services for reconstructive patients. However, this work has certain limitations. Presented and analysed studies lack class I or II evidence, therefore they should be interpreted adequately with the risk of bias. Furthermore, the small total number of patients (144) in the collected studies, varying etiology and time from nerve injury to the procedure, different therapy-assisting methods, various types of implemented threads and non-uniform endpoints and outcome assessment, hampers a definitive synthesis of the data. Additionally, the age of participants is inconsistent among the collected studies, ranging from 21 to 84, without division into age groups, which could provide unreliable results. The dataset is rather of indicative value. Yet, it points out that such procedures may be effective in some populations of patients with facial palsy. However, since 75% of the cases have had other aesthetic procedures done, it may be hypothesized that threads are rather a component of a complex non-surgical treatment algorithm along with fillers and botulinum toxin.
Also, it is worth noting that the literature findings on the use of thread lifting mainly come from Caucasian patients. It would be advisable to research differences in their use and effectiveness in patients with skin of color, as well as in different ethnic and racial groups [5].

Conclusions

The conclusions drawn from this study are as follows: indications for the use of thread lifting in patients with facial nerve paralysis include correcting ptosis of the eyebrows and eyelids, flattening of the nasolabial fold, drooping corners of the mouth, and sagging facial skin. Correction procedures for asymmetry with lifting threads in patients with facial nerve paralysis are characterized by a relatively high level of safety, making them suitable for medically compromised patients who do not qualify for invasive surgical procedures. In the treatment of symptoms of complete facial nerve paralysis, it is worth considering the use of combined non-surgical techniques. High-quality, comparative studies on a larger cohort are demanded to properly assess the long-term effectiveness and safety of threads in facial palsy. There are no available data on the use of threads in either temporary or definitive treatment of nerve palsy in adolescents and children.

Acknowledgments

We want to thank Aleksandra Sołtysiak for creating illustrations for figures 1 and 4.

Funding

No external funding.

Ethical approval

Not applicable.

Conflict of interest

The authors declare no conflict of interest.

References