Midface Contour Irregularity

Because the Le Fort I maxillary osteotomy and advancement is performed beneath the infraorbital foramen, the midface skeleton above the foramen remains deficient in its sagittal projection. The midface skeleton is now more prominent in its lower half after Le Fort I advancement surgery and, as a result, the cheeks appear low ( Fig. 15.1 ). This imbalance is in proportion to the magnitude of sagittal skeletal advancement.

Typical facial contour sequelae after orthognathic surgery. (A) Lateral appearance of patient after Le Fort I advancement osteotomy, sagittal split, and horizontal chin osteotomies. (B) Artist’s rendition showing skeletal movements responsible for facial contour disharmonies and irregularities.

To improve midface contour some surgeons have combined zygomatic osteotomies with the Le Fort I osteotomy. More often, malar augmentation with alloplastic implants is performed at the time of the maxillary advancement procedure. Malar augmentation alone widens the midface, which tends to exaggerate an upper midface parasagittal deficiency potentially creating another imbalance. Hence, increasing the projection of the infraorbital rim is considered the critical element in creating midface balance after Le Fort I advancement, with malar augmentation often an appropriate adjunct.

Lower Face Contour Irregularity

Sagittal split osteotomy of the deficient mandible with advancement in the sagittal plane may result in ramus asymmetry and border irregularities ( Figs. 15.1 and 15.2 ). Ramus asymmetry immediately after surgery occurs when the surgeon fails to create similar osteotomies and maintain similar osteotomy gaps (with rigid fixation) on both sides. The surgeon loses control over the relation of the proximal and distal fragments because the condyle must be positioned in its fossa and the body must be positioned to correct the occlusion. The positioning of these two areas dictates ramus and angle position. In the orthognathic literature, the concern for the improper positioning of the proximal segments and condyle relates to its potential for condylar resorption and postoperative relapse. In the pre-rigid fixation era this was almost always due to counterclockwise rotation of the ramus of the mandible because wire osteosynthesis did not provide enough stability. Rigid fixation has virtually eliminated these problems related to inadequate fixation.

Acrylic model of mandible resulting after sagittal split and horizontal chin osteotomies. (A) Frontal view. Note differences in posterior mandible width and height. (B) Lateral view. Note border irregularities.

However, contour abnormalities may still occur due to incorrect positioning with resultant counterclockwise rotation or after very large movements. Clinical experience has revealed that this is due to not only the positional restraints of condylar positioning and osteotomy variability as described above, but also ramus shape changes resulting from bone atrophy ( Fig. 15.3 ). Depending on the circumstance, this atrophy may result from devascularization and/or remodeling from altered mechanotransduction forces in accordance with Wolff’s Law.

Operative findings after a previous bilateral sagittal split osteotomy (BSSO). Note bone loss beneath head of lag screw used for BSSO fixation. Skeletal devascularization or mechanotransduction are the most likely causes of bone loss.

Gaps at the osteotomy sites after sagittal osteotomy of the mandible or horizontal osteotomies of the chin with advancement can result in border irregularities. Correction of contour irregularities after skeletal rearrangement have focused on border defects at the sliding genioplasty osteotomy site, prompting some surgeons to fill the defect with hydroxyapatite. Surgical technique and the native mandible anatomy determine the presence and severity of these irregularities.

Patients with “high-angle” mandibular deficiency, which is seen in association with antegonial notching and vertically deficient rami, are predisposed to visible notching after bilateral sagittal split osteotomy (BSSO). In patients with “low-angle” mandibular deficiency, where the ramus height is adequate and there is no antegonial notching, post-BSSO border irregularities reflect technical deficiencies in creating and maintaining (assuming rigid fixation) the correct osteotomy gap geometry of the buccal cortical plates. This geometry should be the same on both sides.

The extent of parasymphyseal notching after horizontal osteotomy of the chin with advancement is also influenced by surgical technique. By making the osteotomy oblique, as the artist has depicted in Fig. 15.1 , the distal segment is shortened as it is advanced, which not only accentuates border irregularities but also causes the bone cut to exit the inferior mandibular border where the soft tissue coverage is more tenuous and exposes the notching. By lowering the bone cut anteriorly, one can eliminate or minimize the obliquity of the osteotomy and, therefore, any shortening with a more proximal inferior border exit.