Retrognathia is a term used to describe an unusual position of the mandible. Retro implies that there is deficient growth and ‘gnathia’ means about the jaws (particularly mandible). To the specialists above, describing a patient as retrognathic has specifically means the patient is deficient in the AP plane of growth. That is, when viewed from the side, the mandible is posterior to and behind where it should be. There is often a vertical component in growth deficiency and sometimes a transverse issue, but they are less critical in thinking about retrognathia unless one is planning a surgical correction. To summarize, when you describe a patient as retrognathic, it implies the mandible is deficient in growth, particularly in the AP plane.
Causes of Retrognathia
The mandible develops in the same area as the first pharyngeal arch and is associated with Meckel’s cartilage, though Meckel’s cartilage does not become the mandible. The mandible begins as a condensation of mesenchymal tissue lateral to Meckel’s cartilage and proceeds through development via intramembranous bone formation. At six weeks in utero, it starts to ossify. The condyle of the mandible, which articulates with the skull as part of the temporomandibular joint, develops as independent secondary cartilage, at approximately ten weeks, and undergoes endochondral ossification.
Simply put, the mandible grows down and forward, or anteriorly and inferiorly. It does this through a combination of processes. These include concurrent resorption of bone from the anterior surface of the ramus with apposition of bone along the posterior surface of the mandible. This process, in conjunction with growth at the condyle, creates the anterior and inferior vector of growth.[rx]
In growth and development, there are standard charts commonly used by health care professionals detailing the spectrum of height, weight, age, and growth. It is worth considering there can be significant variation between individuals and that there are both chronologic and biological ages (considering menarche/puberty). In general, facial height is the last dimension to finish growth and in females will be complete around ages 17-18, and in males in the early twenties. In a retrognathic patient or patients who have hypoplastic mandibles, this growth can be done much earlier.
Why does this matter? The timing of this growth and development is crucial when considering skeletal surgery to address retrognathia and is carefully ascertained for each patient.
Diagnosis of Retrognathia
On physical exam, a good place to start is with an intraoral examination. Dr. Edward Angle, widely known as the father of orthodontics, created a classification system for the occlusion of teeth and how they relate to each other. It is based on the relationship between certain parts of the first molars and canines. Suffice to say for those who do not specialize in teeth; Class 1 occlusion means there is an appropriate relationship between the maxillary teeth and mandibular teeth. Class 2 means that the mandibular teeth are posterior as in patients with retrognathia. Finally, Class 3 indicates that the mandibular teeth are anterior to where they should be (think of a bulldog with the lower jaw sticking out).
A Class 2 occlusion can often be associated with retrognathia. However, one must keep in mind that the teeth can hide this as our bodies will often dentally compensate for skeletal discrepancies (more in-depth discussion on this point is the purview of dental specialists)[rx].
Often just looking at the patient extraorally can help you determine if they are retrognathic. When viewed from the lateral, you will notice an exaggerated convex facial profile. On grown adults, as part of a standard airway examination, examining the thyromental distance can be a predictor of a difficult airway. This implies retrognathia if the patient has a mandible that has not developed, the thyromental distance will be less than the standard three finger’s breadth, or approximately 7mm.[rx][rx][rx]
Radiology plays a significant role in determining retrognathia. The standard lateral cephalometric radiograph and associated analysis are part of the determination. There are hundreds of different interpretations and, suffice to say, that there are many points and combinations of angles that measure the relationship between the cranial vault and the facial skeleton to determine growth and are used in treatment planning for orthodontics and orthognathic surgery.[rx][rx][rx][rx]
The most common diagnosis in the practice of orthodontics and oral and maxillofacial surgery associated with retrognathia is mandibular AP hypoplasia, a common diagnosis that supports a surgical correction of their deficiency, most commonly through a bilateral sagittal split osteotomy of the mandible.[rx]
Depending on the patient age and especially with infants and children, an astute practitioner must keep in mind some associated syndromes and conditions that are often associated with a hypoplastic mandible. This includes Pierre-Robin Sequence, Hemifacial Microsomia, DiGeorge Syndrome, Nager Syndrome, Treacher Collins, Goldenhar Syndrome, and Mobius Syndrome. (These specific entities are discussed in more detail under Treatment and Management).
Prior surgery to the head and neck or history of trauma can also produce retrognathia. For example, this practitioner recently had a male in his twenties with a history of a fall off his bicycle in the second grade. This caused trauma to one of his condyles and a unilateral aplasia in that location, resulting in a crooked face and retrognathic appearance, warranting surgical correction. Because of the condylar portion of the growth of the mandible, temporomandibular trauma can restrict growth. Any blow to the chin or lower face, if severe enough, can cause this type of growth pattern and result in retrognathia and is worth asking about during a history.
Evaluation
Physical exam, as described above, is the best way to analyze patients for retrognathia. A common adjunctive radiological review is the lateral cephalometric x-ray. This is typically traced and measured with a full cranio-cephalometic analysis that is beyond the scope of this article. There are a series of measurements that look at the position of the mandible to skull base to diagnosis mandibular hypoplasia (for example, the Sella-Nasion-B point angle (SNB) is generally 80 degrees in a Caucasian population, so an SNB angle of 72 degrees is indicative of retrognathia).[rx]
Treatment of Retrognathia
The treatment and management will depend on what your concerns are and what a patient or their parents desire. Most commonly retrognathia will be identified in children between the ages of four to ten years old and if the child has a dental home, will likely be referred to an orthodontist for evaluation ideally around the ages of seven to eight. Generally, this is a benign condition without any other effects. (In this practitioners’ experience, one could walk a busy street and identify an individual every minute who has retrognathia to some degree.) This will allow the orthodontist to begin tracking the patient with serial cephalometric radiographs and potentially intervene early with non-surgical therapy like headgear or newer intra-oral techniques that have a similar effect in repositioning the mandible. If the child does not have a dental home or has not seen an orthodontist, a referral is recommended.[rx][rx]
If one is concerned about airway management on a patient with retrognathia, this should be a strong indicator of a potentially difficult airway. Underdeveloped structures, anatomic distortion, potential malpositioning of the epiglottis, and tighter constriction of the muscles and surrounding structures all need to be considered. One is much more likely to have a Cormack and Lehane Grade III or IV view, and that needs to be planned for.[rx][rx][rx]
If the infant or child presents with retrognathia, or even if they are older and have associated findings that lead you to suspect a syndrome or myriad of issues, consider the following conditions:
Pierre-Robin Sequence
The classic triad of micrognathia (colloquially synonymous with retrognathia), glossoptosis, and cleft palate. Airway obstruction is likely, though the disease can present with a range from mild to severe. The patient will need a referral to a cleft and craniofacial team for evaluation and treatment.[rx][rx]
Hemifacial Microsomia
Part of the spectrum of Oculo-Auriculo-Vertebral (OAV) Syndromes, this is another entity with variable penetrance. It arises due to pathologic dysregulation of the first and second pharyngeal arches and can be unilateral or bilateral. It results in hypoplastic growth of not only the mandible and lower face but can affect the midface, temporomandibular joint, orbits, ears, and soft tissue. A common classification system used is the Kaban Classification (Types I, IIa, IIb, and III), which help guide surgical correction. If discovered as an infant, the patient will need a referral to a cleft and craniofacial team for evaluation and treatment. In this author’s experience, a surprisingly high number of adults have a mild expression which needs to be taken into close account during facial and orthognathic surgical planning.[rx][rx][rx]
Goldenhar Syndrome
Part of the spectrum of Oculo-Auriculo-Vertebral (OAV) Syndromes, the etiology behind Goldenhar Syndrome is unclear, with multiple chromosomes potentially affected and only theories offered as to a cause. This entity combines features of Hemifacial Microsomia with further facial clefting, colobomas of the eyes, vertebral anomalies, and other findings. The patient will need a referral to a cleft and craniofacial team for evaluation and treatment as well as ophthalmology.[rx][rx][rx]
Treacher Collins Syndrome
This syndrome is an autosomal dominant condition of a mutation of the TCOF1 gene with variable expression. Patients will have a unique facial appearance with extreme retrognathia leading to a very convex facial profile when viewed from the side, antimongoloid slanting eyes (that is the lateral corners of the eyes are turned down), colobomas, significant facial hypoplasia of the midface of the hard and soft tissues, and auricular deformities. Once born, these infants will need immediate and intense multidisciplinary therapy.[rx][ex][rx][rx]
Nager Syndrome
Similar to Treacher Collins. However, the cause is unknown. Similar therapies.[rx]
Mobius Syndrome
A very rare entity with etiology unclear, this presents with a characteristic “masklike face” as a component is paralysis of some or all of cranial nerves III, IV, V, VI, VII, IX, X, and XII. Retrognathia, ocular deformities, and other skeletal and limb abnormalities. The patient will need a referral to a cleft and craniofacial team for evaluation and treatment, as well as any other specialties warranted.[rx][rx][rx]