Significance of the Marginal Mandibular Branch in Relation to Facial Palsy Reconstruction: Assessment of Microanatomy and Macroanatomy Including Axonal Load in 96 Facial Halves

The masseteric nerve for facial reanimation: Macroscopic and histomorphometric characteristics in 106 human cadavers and comparison of axonal ratio with recipient nerves

Peripheral facial palsy causes severe impairments. Sufficient axonal load is critical for adequate functional outcomes in reanimation procedures. The aim of our study was to attain a better understanding of the anatomy of the masseteric nerve as a donor, in order to optimize neurotization procedures. Biopsies were obtained from 106 hemifaces of fresh frozen human cadavers. Histological cross-sections were fixed, stained with PPD, and digitized. Histomorphometry and a validated software-based axon quantification were conducted. Of the 154 evaluated branches, 74 specimens were of the main trunk (MT), 40 of the anterior branch (AB), and 38 of the descending branch (DB), while two halves of one cadaver featured an additional branch. The MT showed a diameter of 1.4 ± 0.41 mm (n = 74) with 2213 ± 957 axons (n = 55). The AB diameter was 0.9 ± 0.33 mm (n = 40) with 725 ± 714 axons (n = 30). The DB diameter was 1.15 ± 0.34 mm (n = 380) with 1562 ± 926 axons (n = 30). The DB demonstrated a high axonal capacity - valuable for nerve transfers or muscle transplants. Our findings should facilitate a balanced selection of axonal load, and are potentially helpful in achieving more predictable results while preserving masseter muscle function.

Selective ansa cervicalis nerve transfer to the marginal mandibular nerve for lower lip reanimation: An anatomical study in cadavers and a case report

BACKGROUND

Donor nerve options for lower lip reanimation are limited in patients undergoing oncological resection of the facial nerve. The ansa cervicalis nerve (ACN) is an advantageously situated donor with great potential but has not been examined in detail. In the current study, the anatomical technical feasibility of selective ACN to marginal mandibular nerve (MMN) transfer for restoration of lower lip tone and symmetry was explored. A clinical case is presented.

METHODS

Dissections were conducted in 21 hemifaces in non-embalmed human cadavers. The maximal harvestable length of ACN was measured and transfer to MMN was simulated. A 28-year-old male underwent ACN-MMN transfer after parotidectomy (carcinoma) and was evaluated 12 months post-operatively (modified Terzis' Lower Lip Grading Scale [25 observers] and photogrammetry).

RESULTS

The harvestable length of ACN was 100 ± 12 mm. A clinically significant anatomical variant ("short ansa") was present in 33% of cases (length: 37 ± 12 mm). Tensionless coaptation was possible in all cases only when using a modification of the surgical technique in "short ansa" cases (using an infrahyoid muscle nerve branch as an extension). The post-operative course of the clinical case was uneventful without complications, with improvement in tone, symmetry, and function at the lower lip at 12-month post-operative follow-up.

CONCLUSIONS

Selective ACN-MMN nerve transfer is anatomically feasible in facial paralysis following oncological ablative procedures. It allows direct nerve coaptation without significant donor site morbidity. The clinical case showed good outcomes 12 months post-operatively. A strategy when encountering the "short ansa" anatomical variant in clinical cases is proposed.

A Ready-to-Use Grading Tool for Facial Palsy Examiners—Automated Grading System in Facial Palsy Patients Made Easy

Background: The grading process in facial palsy (FP) patients is crucial for time- and cost-effective therapy decision-making. The House-Brackmann scale (HBS) represents the most commonly used classification system in FP diagnostics. This study investigated the benefits of linking machine learning (ML) techniques with the HBS. Methods: Image datasets of 51 patients seen at the Department of Plastic, Hand, and Reconstructive Surgery at the University Hospital Regensburg, Germany, between June 2020 and May 2021, were used to build the neural network. A total of nine facial poses per patient were used to automatically determine the HBS. Results: The algorithm had an accuracy of 98%. The algorithm processed the real patient image series (i.e., nine images per patient) in 112 ms. For optimized accuracy, we found 30 training runs to be the most effective training length. Conclusion: We have developed an easy-to-use, time- and cost-efficient algorithm that provides highly accurate automated grading of FP patient images. In combination with our application, the algorithm may facilitate the FP surgeon’s clinical workflow.

Towards a Reliable and Rapid Automated Grading System in Facial Palsy Patients: Facial Palsy Surgery Meets Computer Science

Background: Reliable, time- and cost-effective, and clinician-friendly diagnostic tools are cornerstones in facial palsy (FP) patient management. Different automated FP grading systems have been developed but revealed persisting downsides such as insufficient accuracy and cost-intensive hardware. We aimed to overcome these barriers and programmed an automated grading system for FP patients utilizing the House and Brackmann scale (HBS). Methods: Image datasets of 86 patients seen at the Department of Plastic, Hand, and Reconstructive Surgery at the University Hospital Regensburg, Germany, between June 2017 and May 2021, were used to train the neural network and evaluate its accuracy. Nine facial poses per patient were analyzed by the algorithm. Results: The algorithm showed an accuracy of 100%. Oversampling did not result in altered outcomes, while the direct form displayed superior accuracy levels when compared to the modular classification form (n = 86; 100% vs. 99%). The Early Fusion technique was linked to improved accuracy outcomes in comparison to the Late Fusion and sequential method (n = 86; 100% vs. 96% vs. 97%). Conclusions: Our automated FP grading system combines high-level accuracy with cost- and time-effectiveness. Our algorithm may accelerate the grading process in FP patients and facilitate the FP surgeon’s workflow.

Using High-Resolution Ultrasound to Assess Post-Facial Paralysis Synkinesis—Machine Settings and Technical Aspects for Facial Surgeons

Background: Synkinesis of the facial musculature is a detrimental sequalae in post-paralytic facial palsy (PPFP) patients. Detailed knowledge on the technical requirements and device properties in a high-resolution ultrasound (HRUS) examination is mandatory for a reliable facial muscle assessment in PPFP patients. We therefore aimed to outline the key steps in a HRUS examination and extract an optimized workflow schema. Methods: From December 2020 to April 2021, 20 patients with unilateral synkinesis underwent HRUS. All HRUS examinations were performed by the first author using US devices with linear multifrequency transducers of 4–18 MHz, including a LOGIQ E9 and a LOGIQ S7 XDclear (GE Healthcare; Milwaukee, WI, USA), as well as Philips Affinity 50G (Philips Health Systems; Eindhoven, the Netherlands). Results: Higher-frequency and multifrequency linear probes ≥15 MHz provided superior imaging qualities. The selection of the preset program Small Parts, Breast or Thyroid was linked with a more detailed contrast of the imaging morphology of facial tissue layers. Frequency (Frq) = 15 MHz, Gain (Gn) = 25–35 db, Depth (D) = 1–1.5 cm, and Focus (F) = 0.5 cm enhanced the image quality and assessability. Conclusions: An optimized HRUS examination protocol for quantitative and qualitative facial muscle assessments was proposed.

Microanatomy of the Frontal Branch of the Facial Nerve: The Role of Nerve Caliber and Axonal Capacity

BACKGROUND

A commonly seen issue in facial palsy patients is brow ptosis caused by paralysis of the frontalis muscle powered by the frontal branch of the facial nerve. Predominantly, static methods are used for correction. Functional restoration concepts include the transfer of the deep temporal branch of the trigeminal nerve and cross-facial nerve grafts. Both techniques can neurotize the original mimic muscles in early cases or power muscle transplants in late cases. Because axonal capacity is particularly important in cross-facial nerve graft procedures, the authors investigated the microanatomical features of the frontal branch to provide the basis for its potential use and to ease intraoperative donor nerve selection.

METHODS

Nerve biopsy specimens from 106 fresh-frozen cadaver facial halves were obtained. Histologic processing and digitalization were followed by nerve morphometric analysis and semiautomated axon quantification.

RESULTS

The frontal branch showed a median of three fascicles (n = 100; range, one to nine fascicles). A mean axonal capacity of 1191 ± 668 axons (range, 186 to 3539 axons; n = 88) and an average cross-sectional diameter of 1.01 ± 0.26 mm (range, 0.43 to 1.74 mm; n = 67) were noted. In the linear regression model, diameter and axonal capacity demonstrated a positive relation (n = 57; r2 = 0.32; p < 0.001). Based on that equation, a nerve measuring 1 mm is expected to carry 1339 axons.

CONCLUSION

The authors' analysis on the microanatomy of the frontal branch could promote clinical use of cross-facial nerve graft procedures in frontalis muscle neurotization and free muscle transplantations.

A favorable donor site in microsurgery: Nerve and vein graft harvest from the dorsum of the foot

BACKGROUND AND OBJECTIVES

In complex hand traumas nerves and vessels are often destructed without the possibility for primary repair. For bridging defects of nerves, veins and arteries grafts are necessary. Commonly nerve and vein grafts from adjacent donor sites as the wrist, forearm or cubital region are harvested.

METHODS

This study is a retrospective cohort study. Between 2017 and 2019, 10 patients with complex hand injuries were treated. There were 8 males and 2 females, with an average age of 39 years (range 8-63 years). In all cases grafts were used of the dorsum of the foot for reconstructing of the severed digital nerves and arteries. All donor sites could be closed primarily.

RESULTS

In 100% of cases nerves and veins of the dorsum of the foot showed a good size match as well as adequate length for a sufficient repair. The overall Hand Injury Severity Score (HISS) was determined with a median of 86 (range 57 to 286). In the area of the donor site no relevant complications were seen.

CONCLUSIONS

In complex hand injuries the dorsum of the foot is a favorable donor site for nerve and vein graft harvest.

A supportive donor nerve for long-term facial paralysis: Anatomical analysis of the posterior auricular nerve and micro-anatomical comparison with zygomatic nerve

BACKGROUND

The posterior auricular nerve (PAN) is an inspiring candidate for the additional axonal source in long-term facial paralysis to improve the functional results of the cross-facial nerve (FN) graft technique. However, no studies have analyzed the PAN's axonal load and its microscopic anatomy to assess its utilization in facial reanimation. The present study aims to examine the anatomical and microscopic features of the PAN to analyze its feasibility as a donor nerve.

METHODS

The bilateral facial side of 14 fresh frozen adult human cadavers was examined for the study. The PAN's anatomical course was recorded, and nerve specimens from the PAN and zygomatic nerve (ZN) were obtained to compare their microscopic anatomy and axon counts using a light microscope and transmission electron microscope.

RESULTS

The PAN's average branching distance and its course length were 5.8 ± 2.69 mm and 59.2 ± 5.85, respectively. The mean number of myelinated axons was 600.28 ± 69.97 in the PAN and 728.85 ± 166.31 in the ZN. This difference between the two nerves was statistically significant (p = 0.002). However, considering the gender variable, the mean axon counts of PAN and ZN were statistically similar for face sides and their average. Furthermore, the ultrastructural anatomy of both nerves was similar in electron microscopic evaluation.

CONCLUSIONS

The present study confirms that the PAN is a proper candidate to be a supportive donor nerve due to its isolated site, consistent anatomical course, convenient ultrastructural anatomy as well as axonal load.

Rapid and Precise Semi-Automatic Axon Quantification in Human Peripheral Nerves

We developed a time-efficient semi-automated axon quantification method using freeware in human cranial nerve sections stained with paraphenylenediamine (PPD). It was used to analyze a total of 1238 facial and masseteric nerve biopsies. The technique was validated by comparing manual and semi-automated quantification of 129 (10.4%) randomly selected biopsies. The software-based method demonstrated a sensitivity of 94% and a specificity of 87%. Semi-automatic axon counting was significantly faster (p < 0.001) than manual counting. It took 1 hour and 47 minutes for all 129 biopsies (averaging 50 sec per biopsy, 0.04 seconds per axon). The counting process is automatic and does not need to be supervised. Manual counting took 21 hours and 6 minutes in total (average 9 minutes and 49 seconds per biopsy, 0.52 seconds per axon). Our method showed a linear correlation to the manual counts (R = 0.944 Spearman rho). Attempts have been made by several research groups to automate axonal load quantification. These methods often require specific hard- and software and are therefore only accessible to a few specialized laboratories. Our semi-automated axon quantification is precise, reliable and time-sparing using publicly available software and should be useful for an effective axon quantification in various human peripheral nerves.