Long‐term Growth in Nontreated Hemifacial Microsomia Patients

One of the most controversial topics in the literature regards the progressive nature of the clinical asymmetry during growth of a patient affected by HFM. It has been suggested that the anomaly worsens during growth and the facial asymmetry of the child becomes more severe with time (Converse et al. 1973; Murray et al. 1984; Kearns et al. 2000). This is what occurs, for example, in a child with a unilateral ankylosis of the TMJ. The progressiveness of the asymmetry would dictate the need for surgery as early as possible. Other authors, on the contrary, suggested that the asymmetry in HFM is not progressive. Polley et al. (1997), following the growth from 6 months of age till the end of craniofacial growth of 26 HFM nonoperated patients on serial posteroanterior cephalometric X‐rays, collected by Pruzansky, have demonstrated that the affected side of the mandible continues to grow with a rate that maintains the vertical ratio between both sides. The same was concluded in a later longitudinal study on panoramic X‐rays, calculating the ratio between affected and nonaffected side, of untreated type I and II patients, from 5 years till the completion of growth (Meazzini et al. 2012). These findings mean that the facial proportion of the patient affected by HFM is maintained throughout the whole process of craniofacial growth (Figure 12.8.2). As noted by Mommaerts and Nagy (2002), much confusion exists between the rate of growth, meaning the yearly amount of growth, and the ratio between the affected and the nonaffected side. Authors who studied patients longitudinally and not cross‐sectionally, as Kearns et al. (2000), noted that the growth of the affected side maintains the same proportion, in the same patient, relative to the nonaffected side so that the degree of asymmetry and neuro‐muscular architecture remain constant during development (Rune et al. 1981; Polley et al. (1997); Meazzini et al. 2012; Ongkosuwito et al. 2013).

Is Maxillary Growth in Hemifacial Microsomia Inhibited by Mandibular Growth?

Another long‐believed “dogma” in HFM literature is that early surgery is also indicated to prevent maxillary and zygomatic deformities, which are believed to be secondary to a primary mandibular deformity (Kaban et al. 1998). Padwa et al. (1998) suggested to perform costochondral grafting (CCG) in early adolescence, to “unlock” maxillary growth. A way to evaluate the hypothesized influence of mandibular hypoplasia on maxillary growth is to look at studies conducted on patients affected by HFM subjected to unilateral mandibular surgical lengthening. In these patients, the “deforming” effect of the hypoplastic mandible on the maxillary complex has been “removed” by mandibular lengthening, consequently, “uninhibited” maxillary growth may be investigated. In a 5‐year follow‐up study on mandibular distraction osteogenesis (DO) in HFM, conducted on a very homogeneous sample in terms of age at the time of surgery (average age 5.6 ± 0.6 years) and in terms of the initial severity of the mandibular hypoplasia (type I and type II according to Pruzansky) patients were monitored with posteroanterior cephalometric X‐rays immediately before surgery, and every year till the longest follow‐up, 5.8 ± 0.4 years. After distraction, the asymmetry of the maxillary skeletal base (infra‐orbital plane and in the nasal floor) was unchanged. On the contrary, the dentoalveolar component of the maxilla (occlusal plane inclination) was reduced significantly, as the distraction had created a gradually increasing open bite on the affected side, which was closed by eruption guidance. These data suggested that, thanks to DO, a significant dentoalveolar remodeling of the maxilla is possible, as every orthodontist knows, but no true skeletal modification of the maxilla can be obtained. Additionally, there was a gradual return toward the original occlusal plane inclination in the subsequent 5 years (Meazzini et al. 2005). Another very suitable example of effect of the “removal” of the distorting influence of the mandible on the maxillary bone, was a study after CCG, which showed comparable results to the study after DO, reporting occlusal plane improvement but no nasal floor improvement, thus no skeletal base “catch‐up” growth (Padwa et al. 1997).

Therefore, it is reasonable to believe that the maxillary deformity in HFM is primary and associated to the embryological first branchial arch defect (maxilla and zygomatic arch are first branchial arch derivatives), and this is the reason why there is no spontaneous correction of the maxillary skeletal base when the mandibular interference is eliminated. Only the dentoalveolar component of the maxilla may be temporarily remodeled, both after DO and CCG. These data contradict the previous “conviction” that early surgery might actually prevent the “supposed” secondary adaptation of the maxilla, zygoma, and soft tissues to mandibular deformity (David 2018).

Can Functional Appliances Increase Postsurgical Stability After Distraction Osteogenesis?

In a very early study, on a small sample of patients subjected to DO, a recurrence of the mandibular morphology during the first year after distraction had already been reported (Meazzini et al. 1997). At the time, it was hoped that the association of functional jaw orthopedics might help reduce this recurrence of the phenotype. It was hypothesized that a pre‐DO and post‐DO orthopedic treatment, as suggested by Vargervik et al. (1986), might help maintain a better stability of the skeletal correction. The biological hypothesis was that muscles need a slower rate of elongation than bone, thus, early muscle stretching might improve stability (Simpson et al. 1995). In order to demonstrate whether the combined orthopedic‐distraction treatment had any real advantage, we compared two groups of patients, treated consecutively with two different protocols. One group (treated in a different hospital) had no orthopedic preparation before or after DO (only occlusal guidance post‐DO), while the second group had at least 1 year of orthopedic treatment, with an asymmetric functional appliance, prior to DO and 1 year post‐DO. The results of this study unfortunately eventually demonstrated that orthopedic treatment may initially slow down (Meazzini et al. 1999), but does not stop, the process of “return” to the original pattern of asymmetry and, again, the beneficial influence of orthopedic treatment expresses itself more at the dento‐alveolar level then at a skeletal level (Meazzini et al. 2008a).

Final Considerations on Distraction Osteogenesis in Hemifacial Microsomia

Although the term “return” is usually not as clinically clear as the term “relapse,” it was preferred, because what is truly happening in these patients, is not an actual relapse. Relapse refers to loss of the regenerate, whereas, in HFM, the return to the original pattern is related to a differential growth which is directly linked to the congenital pathological neuromuscular pattern of growth. Stability of the regenerate is usually measured during the first 6 months to 1 year after DO. The literature agrees that there is little loss of regenerate (relapse) after DO (Hollier et al. 1999). The controversy is more on long‐term effects. DO guarantees the achievement of good symmetry in the short‐term (Figure 12.8.3c). In the long‐term, mandibular morphology is remodeled through a process of re‐expression of the syndrome‐specific pattern of growth (Figure 12.8.3d). The contradiction in HFM was originated by the belief that the growth of the patients was of a progressive nature. The literature, thanks to long‐term longitudinal studies, seems now oriented toward the clinical indication that HFM patients, whether operated or not, present, at the end of growth, an asymmetry which has a very similar proportion to the initial disproportion (Hollier et al. 1999; Kusnoto et al. 1999; Huisinga‐Fischer et al. 2003; Meazzini et al. 2005, 2012; Nagy et al. 2009; Suh et al. 2013; Ascenço et al. 2014). It is important to realize that DO is just a tool, extremely efficient in its ability to modify the skeletal structure of young patients, but not their genetic code. This knowledge forces us to select patients with great care and to be honest and transparent with families regarding long‐term prognosis, making it very clear, that the hope that an early correction through DO will be a definitive procedure, is extremely unrealistic.