Early hemi-mandibular lengthening by distraction osteogenesis contributes to compensatory maxillary growth.

Mandibular distraction osteogenesis at an early age is the standard hemifacial microsomia treatment. Nevertheless, the recurrence rate remains high and the definition of early age is controversial. We explored the optimal timing for mandibular distraction, when the surrounding skeleton, such as maxilla, can grow compensatory, to reduce recurrence. Hemifacial microsomia patients were prospectively divided into Groups A (1-3 years old) and B (4-6 years old), according to maxillary and mandibular growth curves. Computed tomography scans were obtained before distractor implantation and after removal surgery. Maxillary volume increase percentage was the main outcome indicator; other indicators (maxillary symmetry and complications) were secondary outcomes. Fifty-eight patients were enrolled and all but one patient in Group A (failed distraction) completed the study. Two patients had facial nerve injury and another two had mouth-opening limitation, which was relieved after coracoid resection. The difference in percentage increase in maxillary volume between the affected and unaffected sides was 5.06 ± 2.73% and 3.18 ± 1.99% in Groups A and B, respectively, suggesting better compensatory growth in younger patients (P = 0.004). Maxillary symmetry was apparently elevated after mandibular distraction. Mandibular distraction osteogenesis was confirmed to be feasible and safe at age <4 years.