The Comprehensive AOCMF Classification System: Midface Fractures - Level 3 Tutorial

Abstract

This tutorial outlines the details of the AOCMF image-based classification system for fractures of the midface at the precision level 3. The topography of the different midface regions (central midface-upper central midface, intermediate central midface, lower central midface-incorporating the naso-orbito-ethmoid region; lateral midface-zygoma and zygomatic arch, palate) is subdivided in much greater detail than in level 2 going beyond the Le Fort fracture types and its analogs. The level 3 midface classification system is presented along with guidelines to precisely delineate the fracture patterns in these specific subregions. It is easy to plot common fracture entities, such as nasal and naso-orbito-ethmoid, and their variants due to the refined structural layout of the subregions. As a key attribute, this focused approach permits to document the occurrence of fragmentation (i.e., single vs. multiple fracture lines), displacement, and bone loss. Moreover, the preinjury dental state and the degree of alveolar atrophy in edentulous maxillary regions can be recorded. On the basis of these individual features, tooth injuries, periodontal trauma, and fracture involvement of the alveolar process can be assessed. Coding rules are given to set up a distinctive formula for typical midface fractures and their combinations. The instructions and illustrations are elucidated by a series of radiographic imaging examples. A critical appraisal of the design of this level 3 midface classification is made.

Keywords: central and lateral midface; fracture classification; tooth injuries; zygoma.

Figure 1

Central midface subdivisions. UCM, upper central midface: 1, frontonasal maxillary process/medial orbital rim; 2, nasal bone; 3, upper nasal septum/ethmoidal perpendicular plate; ICM, intermediate central midface: 4, medial part of the inferior orbital rim (i.e., infraorbital margin of the maxilla—the entire orbital rim is marked as a band-like outer ring around the orbital opening); 5, anterior antral wall and parapiriform buttress; 6, area of zygomatico-maxillary crest (ZMC)—ICM part; LCM, lower central midface: 7, maxillary alveolar process with two reference lines indicating potential degrees of atrophy in edentulism; 8, lower nasal septum/vomer. The division line between UCM and ICM coincides with the demarcation between the medial and the inferior orbital rim in the inferomedial quadrant.

Figure 2

Zygoma subregions. Z, zygoma; Rl, lateral orbital rim; Ri: inferior orbital rim (infraorbital rim); W1, anterior part of orbital wall.

Figure 3

Upper dentition, FDI dental formula, ADA tooth numbering, and tooth acronyms. FDI (Fédération Dentaire Internationale) tooth numbering formula (adapted by WHO) for permanent teeth is referred to by a two-digit number, one for the quadrant and the other for the tooth order from mesial to distal. In the tooth numbering formula of the ADA (American Dental Association), the teeth are marked with consecutive numbers following a clockwise order beginning with the maxillary right third molar (1) and continuing to the mandibular right third molar (32). Individual teeth or teeth groups are often acronymed: “I” stands for incisors, “C” for canine, “PM” for premolar, and “M” for molar. To avoid confusion, two terms used conventionally in the dental nomenclature merit clarification: mesial—means toward the midline; distal—means away from the midline Note: In surgical terminology, distal is the antonym of proximal and means “away from the center,” which is toward the midline.

Figure 4

Illustration of maxilla edentulism and atrophy. (A) “atrophy grid” superimposed on a fully dentulous maxilla with permanent teeth. Three stages of atrophy are defined: 0 = no atrophy, original height of the maxilla preserved, or mild atrophy; 1 = moderate atrophy; and 2 = severe atrophy associated with loss of alveolar processes; – the atrophic region is identified by the missing teeth; (B) moderate level of atrophy (stage 1) on the left side of the patient, and severe atrophy (stage 2) on the right side; (C) severe level of atrophy (stage 2) in both premolar and molar regions; (D) complete edentulism with severe atrophy; and (E) partial central edentulism with bilateral moderate atrophy.

Figure 5

Zygoma/zygomatic arch ensemble—roadmap for charting fractures of increasing complexity and topographical extent. (A1–A5) En bloc zygoma fracture: shortcut marking—skull icons (A1–A3) and panoramic midface/orbits icon, color mode display (A4), black and white mode display (A5).(B1–B3) En bloc zygoma fracture: composition of separately marked subregions—color mode display (B1), black and white mode display (B2), marked fracture lines (red) additionally sketched (B3). (C) En bloc zygoma fracture (¼ B3) associated with a lamellar displaced orbital floor fracture (orange). (D) Multiple fracture lines at ZMC (ICM part and zygoma part) plus intermediate fragment along the infraorbital rim (ICM part) in addition to fractures displayed in (C). (E) Lamellar fracture in the lateral orbital wall running through greater wing of the sphenoid (¼ midorbit lateral wall) and the anterior flange of the zygoma (anterior lateral orbital wall) in addition to fractures displayed in (D). As the course of the fracture lines bypasses the ZSS it is left blank.(F1, F2) Multifragmentation of the antral wall of the maxillary sinus (ICM) in addition to the fractures displayed in (E). In the present AOCOIAC version fragmentation, displacement and bone loss can be indicated in the skull icons only (F1—orange subregion), in the panoramic midface/orbits icon it is marked as fractured (F2—blue) as a backlink. (G) Crack of the zygomatic process of the frontal bone (superior orbital rim) in conjunction with the lateral edge of anterior superior orbital wall in addition to fractures displayed in (F2). (H) Multiple fragments of the zygomatic arch and shearing fracture of the temporal origin in addition to fracture displayed in (G). (I) Lamellar fracture of the anterior superior orbital wall in the superolateral quadrant, a fracture line running through the piriform rim in the ICM, a unilateral naso-orbito-ethmoidal fracture through the nasal bone, the nasofrontal process, and a lamellar fracture of the medial orbital wall in addition to fractures displayed in (H). These complete an entity which is analogous to a unilateral or hemi Le Fort I, II, and III fracture. Note: Color coding of a subregion, blue denotes the presence of a fracture without any further differentiation, yellow stands for nonfragmented, nondisplaced, orange is the equivalent for fragmented, a gray crosshatching points out a bone loss. The fracture morphology features in the subregions of the graphical schemes are set to “nondisplaced,” and “no bone loss” wherever applicable. Other entries will alter the color code in correlation to the individual scenario of the injury. The subregions can be affected in various arrangements and different formations. The shown incremental order represents a random selection and intends to chart a comparable roadmap to classify distinctive midface injuries.

Figure 6

Asymmetric Le Fort Level midface fracture. Three-dimensional (3D) computed tomographic (CT) scans— (A) frontal view, (B) lateral view right, (C) lateral view left, (D) basal view—mandible removed; (E) panoramic X-ray–OPT; (F, G) 3D CT scans—oblique views, right,left (H, I) coronal CT scans. (J–M) axial CT scans; (N) sagittal CT scans—at lateral lamina of pterygoid process right, (O) at medial lamina of pterygoid process right, (P) at medial lamina of pterygoid process left, (Q) at lateral lamina of pterygoid process left, and (R) at lateral orbital rim left. (S) Level 3 Code : 92 I0i.L0.Pt0.Oim.U1m.Omil.Pt0.L0.Z0, Orbit (right): R(im).W1(im)2(i), Orbit (left): R(lm).W1(lim)2(i), This case example CMTR-92-101 is made available electronically for viewing using the AOCOIAC software at www.aocmf.org/classification. Narrative description: Le Fort analogous midface fracture (central right—types I and II/centrolateral left types I and III). Unilateral NOE fracture right—large fragments, multifragmentation of facial antral wall right, nasal skeletal fracture (multifragmanted and displaced) involving both frontonasal processes and nasal bones not reaching cranially to the nasofrontal suture. Partial Dentition (FDI): Lack of 18–14; 24–28. Maxillary alveolar process atrophy: moderate. Pterygoids: bilateral incomplete horizontal fractures, no pterygomaxillary disjunction, i.e., vertical separation. Displacement: No retrodisplacement of both maxillae, no displacement of the Le Fort I and III fragments left, multifragmentation facial antral wall right, minor displacement of frontonasal fragment right. Internal orbits: Involvement confined to anterior and midorbit sections: right, medial and inferior walls, left medial, inferior and lateral walls.

Figure 7

Zygoma Fracture left with dorsocranial displacement and antral impaction. Three-dimensional (3D) computed tomographic (CT) scans—(A) frontal view, (B) caudofrontal view, (C) oblique lateral view left, (D) caudolateral view; panoramic X-ray—(E) OPT. (F–I) coronal CT scans; (J-M) axial CT scans: sagittal CT scans—(N) next to medial orbit wall left, (O) at the level of medial orbital floor left, (P) just medial to inferior orbital fissure left. (Q) Level 3 Code : 92 m.Oil.I1.Z0i - 93 m.M0, Orbit (left)R(li).W1(li)2(li). This case example CMTR-92-102 is made available electronically for viewing using the AOCOIAC software at www.aocmf.org/classification. Narrative description: Zygoma fracture left. Details: fracture following ZFS, fragmentation along ZSS with intermediate fracture extending into the greater wing of sphenoid and the orbital flange of the zygoma, single fracture-infraorbital process, multifragmentation of facial antral wall left, ZMC and tuber region (LCM), zygomatic arch fracture. Dentition (FDI): Lack of 18–15; 26–28. Maxillary alveolar process atrophy: severe displacement: cranial and dorsal displacement (translational), antral impaction (rotation around sagittal axis through zygomatic body). Internal orbit left: Involvement confined to anterior orbital section and midorbit—anterolateral inferior and lateral fragments in juxtaposition to inferior orbital fissure.

Figure 8

Naso-orbito-ethmoidal fracture bilateral (Example 1). Imaging: Three-dimensional (3D) computed tomographic (CT) scans (A) upper frontal view, (B) frontal view, (C) lower frontal view, (D) oblique lateral view left, and (E) oblique lateral view right. (F) Level 3 Code: 92 I1i.L0.Pt.Oim.U1m.Omil.Pt1.L0.I1i.Z0i, Orbit (right)R(im).W1(im)2(im), Orbit (left)R(lim).W1(lim)2(im). This case example CMTR-92-104 is made available electronically for viewing using the AOCOIAC software at www.aocmf.org/classification. Narrative description: Displacement and large-/medium-sized fragments in a bilateral Naso Orbito Ethmoid Fracture in combination with Le Fort I, II fracture, and left zygoma fracture. Note: Exclusive involvement of midfacial structures.

Figure 9

Naso-orbito-ethmoidal fracture (Example 2)—NOE extreme Type III bilateral. Imaging: Three-dimensional (3D) computed tomographic scans (A) frontal view, (B) oblique lateral view right, and (C) oblique lateral view left. (D) Level 3 Code: 92 Z1i.I1i.L1.Pt0.Oim.U1m.Omil.Pt0.L1.I1i.Z1li - 93 m.M - 94 F1.m.F1m, Orbit (right): R(im).W1(im)2(im), Orbit (left): R(lim).W1(lim)2(lim). This case example CMTR-92-105 is made available electronically for viewing using the AOCOIAC software at www.aocmf.org/classification. Note: Involvement of midface and craniofacial transition as a consequence of fractures extending into the superomedial quadrants of the orbital rim - this is indicated by the marking of the entire frontal bone area. Narrative description: Medium-/small-sized fragments and extreme displacement (loss of interfragmentary contact) in a bilateral Naso Orbito Ethmoid Fracture in combination with a Le Fort I, II fracture, and left zyogma fracture.

Figure 10

Lateral cranio-orbito-facial Injury: fronto-spheno-zygomatico-orbital fracture. Imaging: Three-dimensional (3D) computed tomographic scans (A) frontal view, (B) lateral view left, and (C) oblique lateral view right. (D) Level 3 Code: 92 m.Omil.I1i.Z1li - 93 m.Oas.M0.A0.S1 - 94 m.F1m, Orbit (left): R(slim).W1(slim)2(slim).A(slm). This case example CMTR-92-106 is made available electronically for viewing using the AOCOIAC software at www.aocmf.org/classification. Narrative description: Large-sized fragment of left frontotemporal vault and skull base including all four orbital walls. Displaced (caudolateral) monofragment of left zygoma in continuity with infraorbital rim and antral wall, leading to an extreme diastasis of left lateral orbital wall, multifragmentation along the posterior articulations of the zygoma and in the frontotemporal transition (greater wing of sphenoid).

Figure 11

Panfacial fracture including lower central midface fracture analogous to Hemi Le Fort I fracture. Imaging: Three-dimensional (3D) computed tomographic (CT) scans—(A) frontal view, (B) oblique lateral view right, (C) oblique lateral view left, (D, E) coronal CT scans; (F, G) axial CT scans; (H, I) sagittal CT scans; 3D CT scan details—(J) superofrontal view, (K) palatal from below, (l) pterygomaxillary junction. (M) Level 3 Code : 91 P.A.S.P - 92 La.P2.L1. This case example CMTR-92-103 is made available electronically for viewing using the AOCOIAC software at www.aocmf.org/classification. Narrative description: Midface component of panfacial fracture: LCM fracture left, paramedian midline fracture of the palate; left maxillary alveolar process fracture 11–13, vertical tooth fracture 14, avulsion 15. Mandible component according to level 2: four fracture regions: condylar process bilaterally, right angle/ramus and symphyseal region. Details: Dentition (FDI) preinjury: completely dentate. Palate: Paramedian fracture left. Pterygoids: No involvement. Displacement: Anterosuperior displacement of the LCM fragment left, multifragmentation of the antral wall left, Infraorbital rim left intact. Internal orbits: No involvement.