Synkinesis scores from the Sunnybrook Facial Grading System averaged 0.7 (0–1) in all patients at the latest follow-up and was not affected by timing of transfer, location of transfer, or presence of intratemporal nerve grafting.
Objectively measured oral commissural excursions at the earliest date of documented return of motion was similar to that measured at the latest follow-up (9.8 mm; range, 6.4–12.6 mm). Patients who underwent nerve transfer before 6 months’ denervation achieved postoperative oral commissural excursion of 11.1 mm, versus 6.5 mm in patients who underwent nerve transfer after 6 months (P = 0.003). Oral commissural excursion recovery was otherwise not affected by age, location of transfer, or presence of CFNG.
When feasible, immediate intratemporal facial nerve grafting performed during tumor extirpation may partially restore facial tone, especially in the periorbital, oral, and buccinator regions, yet dynamic restoration is suboptimal especially in the brow, midface and perioral regions.16 Attempts at reinnervation solely with CFNG procedures theoretically achieve spontaneous motion, but reliably achieving symmetrical excursion is variable, particularly in the older patient.6 , 18–20
Nerve transfers utilizing nonfacial donor nerves can be performed with or without CFNG as a single-stage operation.7 , 21 , 22 The masseter nerve has become a popular donor nerve due to its consistent anatomy, high axonal count, and potential synergy with the facial nerve during smiling.1–6 Furthermore, masseteric nerve transfers result in better oral commissural excursion than hypoglossal nerve transfers, and comparable oral commissural excursion to the contralateral, normal side.4 , 8 , 9 , 14 Similarly, free functional muscle flaps innervated by the masseteric nerve also results in improved excursion over a CFNG.23 , 24
Previous data suggest that performing intratemporal or CFNG procedures before prolonged denervation times can improve reanimation outcomes.20 , 25 However, it remains unclear what role the duration of palsy in masseter-to-facial nerve transfers plays in ultimate outcomes. A study evaluating outcomes after selective fifth-to-seventh cranial nerve transfer to zygomatic and buccal facial nerve branches found no difference in improvement in smile function between different denervation durations.5 However, that study did not employ objective measurements to quantify results, did not note the degree of preoperative paralysis, nor comment on the continuity of facial nerve.
In our series, 7 patients had complete preoperative facial nerve palsy before fifth-to-seventh cranial nerve transfer resulting from intratemporal facial nerve resection. We utilized a combination of objective measures for postoperative analysis to characterize whether the timing of nerve transfers had an effect on outcomes.
Symmetry of Voluntary Movement
The Sunnybrook Facial Grading System was used to calculate scores for symmetry of voluntary movement and synkinesis. Synkinesis was not affected by the truncal or more proximal coaptation for the nerve transfer.
Symmetry of voluntary movement scores specifically for open-mouth smile and objective oral commissure excursion were significantly better in those patients undergoing nerve transfer with less than 6 months of paralysis. These results were not skewed by the postoperative results of patient 5 (Table 1). Although he was 11 years old and received an immediate nerve transfer, his postoperative smile excursion at 1-year of 10.36 mm was the second lowest of the early transfer cohort. Patient 3 (Table 1) was 53 year old with 61 days of denervation had a 1-year smile excursion of 11.18 mm, by comparison. Moreover, the 2 patients with greater than 6 months of denervation time were only 26 and 36 years old. Therefore, we believe the poor excursion results in these patients can be attributed to denervation time and not age. And although excursion is also affected by donor nerve axon load,24 , 26 motor endplate degeneration or fibrosis is likely important, thus this finding supports the concept that ultimate mimetic muscle recovery after nerve transfer can be time-dependent.6 , 20 , 25
Although we attempted to decrease the potential confounding variables by not including partial palsy patients, there is heterogeneity in the cohort with regard to intratemporal nerve grafting and the presence of a CFNG. However, what makes this small cohort analysis valuable is the time periods in which our measurements were made with respect to the both of these procedures. Four of 7 patients underwent intratemporal nerve grafting. Of those with intratemporal nerve grafts, 2 had the nerve grafting procedure over a year prior but still had prenerve transfer House-Brackmann Score of 6 with no movement and the highest scores on the Sunnybrook System for asymmetry.
The other 2 had intratemporal grafting 2 months before the nerve transfer, yet excursion or dynamic motion first occurred in these patients only 4 months postoperatively. These nerve grafts average 6–8 cm long from the proximal nerve stump with another 4–5 cm of nerve regeneration then required to even the most proximal branches innervating the mimetic musculature.Thus, the total distance required for nerve regeneration in these 2 patients is similar to the lengths of our typical CFNG grafts, which often take up to 9–12 months for nerve growth to the contralateral face.6 , 12 , 13 , 20
Therefore, to see significant contribution from these grafts on animation, which was first seen at 6 months after the intratemporal nerve grafts were done in these 2 patients, would be unlikely. Previous data on cable grafting have shown average first documented motion beyond 6 months even with including data from more distal and extracranial nerve coaptations.27.
Moreover, our previous work has shown that even with 50 months of follow-up after intratemporal nerve grafting, the primary benefit was for tone or resting symmetry and there was minimal to no effect on dynamic motion.16
The motion we saw at 4 months postnerve transfer was 9.8 mm, which was unchanged at follow-up at a year. If continued nerve regeneration from the CFNG or the intratemporal nerve graft contributed to excursion, then it would have increasingly improved excursion distances over time to and at the 1-year follow-up. This is when these grafts would be expected to start having more contributions due to the required regeneration distances from the motor endplates.10
Given that intratemporal nerve grafting has little effect on dynamic motion16 coupled with the time with which we saw motion after the nerve transfer, it is possible that the contribution in improving excursion and symmetry with the open mouth Sunnybrook scores is from the early CNV-to-CNVII transfer before 6 months of denervation. This finding, novel in masseter-to-facial nerve transfers, could further support the concept that earlier reinnervation improves outcomes.20 , 25 Given the small sample size of this study, however, larger studies are required before the common teaching that the reconstructive surgeon has up 18 months to provide new neural input to mimetic motor endplates can be adequately challenged.10–14
Resting symmetry scores by the Sunnybrook Facial Grading system were significantly worse in patients who underwent nerve transfer after paralysis of greater than 6 months. Interestingly, these scores did not improve after nerve transfer in our study. This is possibly because the CNV to CNVII transfer does not adequately provide resting tone, as the masseter muscle is not chronically contracting at baseline. However, this cannot be definitely concluded due to the fact that our follow-up time of 1 year may not have been sufficient to see sufficient changes in resting symmetry on the Sunnybrook System, particularly in the cases where a concomitant CFNG was performed.10 , 25 , 27.
The paralyzed side MP distances when compared with the normal side significantly improved in the nonselective truncal transfers only. This finding might be explained by the reinnervation of a higher number of branches, axons, and therefore neuromuscular units in the more proximal truncal transfers versus selective branches.28.
We additionally found that philtral correction was improved by 21% at 135 days after nerve transfer and improved by another 10% at a 1-year follow up. Thus, it is possible the intratemporal-nerve grafting and CFNG started contributing at this later follow-up time. Given that intratemporal nerve grafting indeed has an effect on resting tone, we cannot definitively conclude that the nerve transfer alone changed resting symmetry.16
The limitations of this study include the small sample size and retrospective nature of the study, which has inherent limitations. We attempted to improve the cohort by limiting it to only include patients with complete facial palsy resulting from transection of the facial nerve to minimize the confounding effect of partial palsy. Additionally, there was heterogeneity in terms of the presence of a CFNG and intratemporal nerve grafts.
Although this is a small cohort, our finding regarding improvement in modiolus excursion and open mouth smile scores for symmetry of voluntary motion after nerve transfers performed before 6 months of denervation was statistically significant. If one considers the careful timing when our postoperative measurements were performed, as described above, the heterogeneity in nerve grafting is additionally mitigated. Despite this, admittedly the study is imperfect and we understand this is not the ultimate solution to improving outcomes with nerve transfers. Our aim is that some of these data can shed light on where we should be heading, and with time and increasing knowledge of the entire community interested in this field, we will make progress.
A close analysis of the postoperative outcomes suggests that performing masseter-to-facial nerve transfers before 6 months of facial palsy duration may potentially improve smile excursion and open mouth smile symmetry. Because of the small sample size and heterogeneity in this cohort, we hope these early findings encourage further research regarding the importance of denervation time with fifth-to-seventh nerve transfers.
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