Intraoral Vertical Ramus Osteotomy of the Mandible

Deepak G. Krishnan

Haithem M. Elhadi Babiker

DEFINITION

The vertical ramus osteotomy of the mandible performed intraorally is a popular and simple technique used to achieve mandibular setback in patients with prognathism or asymmetry.
A variation of this technique was described first by Limberg in 1925.¹ Many others have attempted to modify his approach and found that it can be performed intraorally and can be used to reduce the horizontally excessive mandibular ramus.
A version of the vertical ramus osteotomy performed through a neck incision was popularized by Caldwell and Letterman in the 1950s.²
In 1968, Winstanley performed the first intraoral vertical ramus osteotomy (IVRO).³ It was the work of Hall and McKenna⁴ in the 1970s that simplified, refined, and thus popularized the procedure.

ANATOMY

The mandible is the horseshoe-shaped bone that forms the structural foundation of the lower third of the face. It is the only movable bone of the skull, articulating with the temporal bones at the temporomandibular joints.
It consists of a horizontal curved body and two broad and oblong rami projecting upward. The alveolar processes of the mandible house and support the mandibular teeth.
The inferior alveolar nerve enters the mandibular foramen on the medial surface of the ramus near its center.
- It then runs downward and forward within the body of the mandible and exits at the mental foramen, which is located on the external surface midway between the alveolar process and the lower border, in the interval between the premolar teeth.
- The anteromedial margin of the mandibular foramen is guarded by an upward tonguelike projection, the lingula.
- Along its course, the inferior alveolar nerve innervates the mandibular teeth and associated soft tissue and terminates as the mental nerve, which supplies sensation to the skin and mucous membrane of the lower lip and chin.
The muscles of mastication directly attach to the surface of the mandible. The masseter and medial pterygoid muscles attach to the lateral and medial surfaces of the ramus, respectively.
- These two muscles together form the pterygomasseteric sling, which straddles the mandibular ramus.
- The temporalis muscle reaches into the external oblique ridge along the rami through its tendons and helps with opening and closing of the jaw.
The lingual nerve, before reaching the tongue, comes in close contact with the inner surface of the alveolar border of the mandible in close proximity to the mandibular third molar tooth.
An antilingula or the antilingular prominence is a lateral bony protuberance that approximately corresponds to the lingula and the entry of the inferior alveolar nerve into its canal, on the medial aspect of the mandible (FIG 1).
- This is a useful but not an entirely reliable landmark in this technique.
- The position of the lingula is posteroinferior relative to the position of the antilingula. This has been substantiated in cadaver studies.⁵

FIG 1 • A. Facial aspect of mandible demonstrating a small anatomic elevation in bone referred to as antilingula. B. Lingual aspect of mandible demonstrating position of lingula and the mandibular foramen.

PATHOGENESIS AND NATURAL HISTORY

Mandibular prognathism is a condition wherein the mandible is positioned anterior to the maxilla resulting in a malocclusion.
In the NHANES study (1989-1994), 0.3% of the US population was reported to have mandibular prognathism severe enough to require orthodontic-surgical treatment.
About 14% of the youth in the United States have a class III malocclusion. Roughly a quarter of these patients have an isolated mandibular prognathism, whereas the remaining three-quarters have a combination of maxillary deficiency in addition to mandibular protrusion.
- Often, a midface deficiency is wrongly diagnosed as mandibular prognathism, whereas in reality upon cephalometric investigation, the mandibular position may be normal.
Mandibular prognathism causes aesthetic concerns, in addition to chewing and speaking difficulties, leading patients to seek surgical treatment at a younger age.
In cases of severe mandibular prognathism, bimaxillary surgery is the preferred method of treatment (mandibular setback combined with maxillary advancement).
- This is because excessive mandibular setback may result in obstructive sleep apnea and is also subject to higher rates of relapse.
Mandibular growth can occur until late teens and early 20s in young men and several years past menarche in women.
- Surgery should be deferred until there is proof of growth cessation.

PATIENT HISTORY AND PHYSICAL FINDINGS

Patients typically present during the teenage years.
The main functional complaints related to chewing and deglutition, difficulty with speech and enunciation, and TMJ dysfunction in addition to the aesthetic concerns. Often, the malocclusion also presents as an open bite.
The patients are usually first seen by an orthodontist and eventually referred to a surgeon when ready for surgery.
Orthodontic treatment is usually undertaken for about a year and serves to align the teeth in the dental arches and remove any dental compensation.
Surgery is undertaken when the patient reaches skeletal maturity (girls 16-18 years, boys 18-20 years).
When working up for an IVRO, it is useful to note the functional status of the patient’s temporomandibular joints (TMJs). The IVRO may be preferred in patients with TMJ dysfunction over a bilateral sagittal split osteotomy (BSSO), because the condyle seats itself passively in an unloaded position during healing.
Patients with a V-shaped mandible as assessed from a norma basalis are probably better candidates for an IVRO as opposed to a BSSO for a mandibular setback (FIG 2).
The preoperative workup includes records that replicate the relationship of the jaws to the skull base, and model surgery to fabricate the surgical splints.
- Unlike in a BSSO, a splint may not be required in an IVRO in patients with stable occlusion and orthodontic setup.
- In the case of double-jaw surgery (Le Fort I advancement combined with a mandibular procedure) for severe class III malocclusion, however, two splints are made—an intermediate splint used intraoperatively to position the maxilla in its final position and a final splint to position the mandible.

IMAGING

Lateral cephalometric radiographs are obtained for cephalometric analysis.
Panoramic radiographs are obtained to determine the presence and location of mandibular third molar teeth, level of the inferior alveolar canal.
A submentovertex view of the mandible could be used in determining its shape and flare.
A CT scan may be obtained, in case virtual surgical planning is undertaken in lieu of traditional model surgery.