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The True Incidence Of Marginal Mandibular Nerve Palsy Following Mandibular Distraction Osteogenesis
Justin Beiriger, BSE, Sarah Myers, BA, Madeleine Bruce, BA, Sayna Matinrazm, BA, Anjali Raghuram, MD, John Smetona, MD, Jesse Goldstein, MD.
University of Pittsburgh, Pittsburgh, PA, USA.

PURPOSE:
In children with Pierre Robin Sequence (PRS), mandibular distraction osteogenesis (MDO) is routinely performed to alleviate tongue-based airway obstruction. Though MDO avoids the need to perform a tracheostomy in these patients, the procedure involves risk of injury to the marginal mandibular nerve (MMN), which can cause significant deficits in facial expression, eating, and drinking. We hypothesize that the incidence of MMN palsy following MDO, previously reported at 1-15%, is an underestimate due to short follow-up times and small sample sizes. This study aims to investigate the true incidence of MMN palsy after MDO to better guide follow-up care and improve treatment of this nerve injury after distraction. METHODS:
A retrospective single center review of patients with PRS who underwent MDO at a tertiary pediatric hospital’s Cleft-Craniofacial Center between September 2007 and March 2021 was conducted. Patients who underwent MDO at less than one year of age and had postoperative clinical evaluations detailing MMN function were included. Assessment of MMN status was recorded at least one month postoperatively. A logistic regression analysis was performed to investigate predictors of MMN injury. RESULTS:
Of the 93 patients who underwent MDO, 57 patients (61.3%) met inclusion criteria. In this cohort, 56.1% were female, 42.1% were syndromic, and the average age at MDO was 1.51 ± 2.02 months (0.03-9.63 months). The average length of mandibular distraction was 17.5 ± 4.68 mm (10-30 mm), average duration of intubation was 6.58 ± 2.35 days (0-12 days), and average time until hardware removal was 110.8 ± 23.4 days (71-179 days). Seventeen patients (29.8%) presented with permanent MMN dysfunction on postoperative clinical evaluation. Four patients (7.0%) presented with bilateral weakness and 13 (22.8%) with unilateral weakness (8 right-sided, 5 left-sided). Two of the 21 patients (9.5%) presented with chin dimpling. Four patients (7.0%) presented with transient MMN weakness that resolved. The average length of follow-up postoperatively was 5.12 ± 2.87 years (0.26-10.6 years). With logistic regression analysis, there were no significant predictors of nerve injury when considering age at surgery (p=0.82), length of distraction (p=0.38), time until hardware removal (p=0.11), or duration of intubation (p=0.71). CONCLUSION:
In this 14-year review of patients with PRS who underwent MDO at our institution, 36.8% demonstrated evidence of MMN palsy. This incidence is much greater than previously indicated in the literature. Several patients experienced transient nerve injury that resolved spontaneously. The results of this study reveal that MMN palsy is a relatively common finding after MDO. Further research is necessary to examine the factors resulting in MMN injury and delineate efforts to mitigate this patient complication.


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