Nerve transfers for facial palsy: grading of volitional control after using the hypoglossal and masseter nerves

Nerve transfers are utilized to restore function in cases of facial palsy when the proximal nerve stump is not available for reconstruction. The process of regaining partial or complete voluntary control of the reinnervated muscles is mediated by changes in the central nervous system, known as brain plasticity. This involves the disconnection of the original donor nerve-related neural programs and their reconnection to the programs of the acceptor nerve. In this study, the authors aimed to evaluate the degree of voluntary control achieved after 2 nerve transfer procedures for facial palsy.

A series of patients with complete unilateral facial palsy (cranial nerve [CN] VII) who underwent nerve transfer surgery using the hypoglossal (CNXII) or the masseter (CNV) as donors were analyzed. A modified 4-point plasticity grading scale (PGS) was used to determine the level of donor nerve disconnection from its original brain program and reconnection to the central program of the facial muscles, with grade 1 defined as a complete lack of plasticity and grade 4 as full independent control. Patient variables, including sex, age, time from trauma to surgery, duration of follow-up, and PGS outcomes, were recorded and statistically analyzed.

A total of 91 patients were included in the study: 67 patients (74%) underwent CNXII-CNVII nerve transfer, while 24 (26%) received CNV-CNVII nerve transfer. The mean ± SD PGS scores of the CNXII-CNVII and CNV-CNVII transfer groups were 1.64 ± 0.6 and 1.63 ± 0.6, respectively. Within the CNXII-CNVII subgroup, age at time of surgery (p < 0.001) and time from trauma to surgery (p = 0.008) were identified as negative predictors for PGS outcomes, whereas quality of rehabilitation emerged as a positive predictive factor (p = 0.005). No associations were observed between sex, follow-up duration, and brain plasticity.

After nerve transfer for facial palsy, brain plasticity is often insufficient to achieve full independence of movements generated by the donor motor program.