- Email: [email protected]
Imaging of high-energy midfacial trauma: what the surgeon needs to know
European Journal of Radiology 48 (2003) 17 /32 www.elsevier.com/locate/ejrad
Imaging of high-energy midfacial trauma: what the surgeon needs to know Ken F. Linnau a, Robert B. Stanley, Jr b, Danial K. Hallam a, Joel A. Gross a, F.A. Mann a,* b
a Department of Radiology, Harborview Medical Center, Box 359 728, 325 Ninth Avenue, Seattle, WA 98104-2499, USA Department of Otolaryngology */Head and Neck Surgery, Harborview Medical Center, Box 359894, 325 9th Avenue, Seattle, WA 98104-2499, USA
Received 10 June 2003; received in revised form 11 June 2003; accepted 12 June 2003
Abstract Treatment goals in severe midfacial trauma are restoration of function and appearance. Restoration of function is directed at multiple organ systems, which support visual acuity, airway patency, mastication, lacrimation, smelling, tasting, hearing, and facial expression. Victims of blunt facial trauma expect to look the same after surgical treatment as before injury. Delicate soft tissues of the midface often make cosmetic reconstructive surgery technically challenging. Generally, clinical evaluation alone does not suffice to fully characterize facial fractures associated with extensive swelling, and the deeper midface is not accessible to physical examination. Properly performed computed tomography (CT) overcomes most limitations of presurgical examination. Thus, operative approaches and sequencing of surgical repair are guided by imaging information displayed by CT. Restoration of function and appearance relies on recreating normal maxillofacial skeletal anatomy, with particular attention to position of the malar eminences, mandibular condyles, vertical dimension and orbital morphology. Due to its pivotal role in surgical planning, CT scans obtained for the evaluation of severe midfacial trauma should be designed to easily depict the imaging information necessary for clinical decision making. Learning objectives: 1. Understand the facial skeletal buttress system; 2. Understand how the pattern of derangement of the buttress system determines the need for and choice of operative approach for repair of fractures in the middle third of the face; 3. Understand the role and importance of CT and CT reformations in the detection and classification of the pattern of buttress system derangement. # 2003 Published by Elsevier Ireland Ltd. Keywords: Facial trauma; Facial fractures; Therapy; Computed tomography; 3D visualization
1. Introduction Treatment goals in patients with midfacial trauma are restoration of: 1) form (appearance), and 2) function. Restoration of appearance and function requires an accurate reconstruction of the midfacial skeletal anatomy, with particular attention to the position and 3-
* Corresponding author. Tel.: /1-206-731-3561; fax: /1-206-7318560. E-mail address: [email protected] (F.A. Mann).
dimensional orientation of the zygomata, orbital walls, and maxillary palatoalveolar complex or maxillary side of the occlusal plane. Correct spatial relocation of the zygomata restores the malar or cheek prominences and thus facial width and projection at this level. Accurate reconstruction of the orbital walls restores orbital shape and volume to prevent globe malposition and lessen the chances of ocular dysfunctions, including diplopia. Return of the maxillary side of the occlusal plane to its preinjury relationship to the skull base restores projection of the face at the level of the maxillary dentition, as well as the overall height or vertical dimension of the middle third of the face. This, in turn, optimizes function of the muscles of mastication and temporomandibular joints, something that simple
0720-048X/03/$ - see front matter # 2003 Published by Elsevier Ireland Ltd. doi:10.1016/S0720-048X(03)00205-5
18
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
interdigitation of the maxillary and mandibular teeth with maxillomandibular fixation (MMF) during healing does not insure. Most surgeons believe that surgical repair of midfacial injuries should be undertake within 7/10 days of the time of injury, prior to the onset soft tissue contraction and early fibrous tissue formation. Generally, clinical evaluation alone does not suffice to fully characterize the facial fractures at this stage, because of residual swelling in the overlying soft tissues and the inaccessibility of the deeper midface to direct physical examination (Fig. 1a). However, imaging information, displayed by properly performed computed tomography (CT) scans usually overcomes the inadequacies of the presurgical clinical examination (Fig. 1b). The imaging information is critical for the surgeon’s understanding of the extent of the injuries and, thus, the appropriate choice and sequencing of the needed operative approaches. This is particularly true if the surgeon is contemplating the use of minimally invasive (endoscopic) techniques that will similarly not allow for wide-field direct inspection of the fractures at the time of repair. The use of ‘‘modern’’ and usually more costly surgical procedures, such as stabilization of fractures with internal fixation devices (miniplates and screws, with bone grafting if necessary), is justified in most reports by improved results from the primary repair and elimination of the need for even more expensive and less effective secondary repairs or revisions [1]. Hospital administrators, third-party payers, and the victims of the trauma themselves have, therefore, developed expectations of a return to at least near-normal if not normal appearance and function following initial repair of midfacial injuries. However, the involvement in a relatively small anatomic area of multiple organ systems that support, among other things, vision, breathing, mastication, lacrmation, and facial contours and expression, makes meeting these expectations in many cases difficult, even for the experienced surgeon. It is the purpose of this presentation to show that providing the surgeon with a specific format of preoperative imaging information is the essential first step toward attaining optimum results from acute management of midfacial trauma. CT scans obtained for the evaluation of severe midfacial trauma should be designed to easily depict the imaging information necessary for clinical decision making.
1.1. Why early, comprehensive fracture management Fig. 1. Preoperative picture of a 25-year-old male polytrauma patient after high-speed motor vehicle crash shows massive facial soft-tissue swelling, limiting clinical evaluation of the face (a). Three-dimensional rendering of thin-cut maxillofacial CT scan of same patient shows highly comminuted LeFort III and NOE fractures (b).
Reduction and anatomically correct realignment of displaced fragments is most easily accomplished before the onset of early bone healing (fibrosis). Delay past the time that allows for osseous malunion means that a
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
refracture or osteotomy will be needed for movement of the displaced skeletal segments. Configuration of soft tissue is dependent on the position of underlying or adjacent bone. The anatomically realigned facial skeleton returns the soft tissue structures to their normal configuration and supports them during healing. Healing over untreated or incompletely reduced fractures may result in cicatricial contracture with permanent thickening, shortening and displacement of the soft tissue structures. Delayed or secondary repair of both bony and soft tissue defects is more challenging and its results less satisfying than primary reconstruction owing to the consequences of allowing the natural healing process to proceed before repair is completed. Reoperation through scar tissue that has resulted from previous surgical approaches increases the risk of iatrogenic complications such as lid retraction or ectropion. Note: The benefits of early, comprehensive surgical intervention may be outweighed by complicating factors including ocular and central nervous system injuries, or an overall unstable medical condition in the polytrauma patient. However, the same imaging information should be obtained in these patients if possible, so that the surgical team can consider a less comprehensive treatment plan that can be tolerated by the patient and hopefully lessen the future impact of partially treated injuries.
19
resuspend tissues elevated for fracture exposure to the repositioned bone.
2. The buttress system of the face The midface can be conceptualized as a honeycomb or lattice-like system of buttresses that has developed as a skeletal adaptation to masticatory forces that are transmitted from the teeth to the skull base (Fig. 2). This adaptation also allowed for the compartmentalization that is necessary for other physiologic facial functions. The strongest midfacial buttresses are vertically oriented in response to the large physiologic loads placed on the system by the similarly directed masticatory forces. ‘Weaker’ horizontally and sagittally oriented buttresses reinforce the vertical buttresses under the loads of mastication [2,3]. The buttress system is, therefore, less resistant to external forces such as anteroposteriorly or laterally directed impact forces, and the traumatic disruption of one buttress may weaken the lattice and cause its collapse. This collapse is not altogether a random process, and the reoccurring fracture patterns (e.g. zygomatico-maxillary complex (ZMC), naso/ orbito /ethmoidal (NOE) complex and LeFort fractures) that are observed with partial or total collapse of the lattice may actually serve to protect the delicate structures contained within the compartments of the
1.2. Examples of deformities resulting from untreated or poorly reduced fractures of the middle third of the face Globe malposition: enophthalmos with shortening of palpebral fissure height, or exophthalmos with widening of the palpebral fissure. Medial canthal ligament malposition (telecanthus): lateral displacement and rounding of the inner canthus. Shortened midface: ‘‘telescoping’’ of the maxilla upward on itself. This deformity is more often cause by overzealous closed reduction of LeFort level I and/ or II fractures than the injuries themselves. Flattened and widened midface: ‘‘dish face’’ deformity due to posterior displacement and lateral expansion of the paired midfacial components. Elongated face: ‘‘facies equina’’ deformity due to displacement of the palatoalveolar complex down the slope of the skull base, creating premature posterior occlusal contacts that force the mandible to rotate downward. Inferiorly displaced malar soft tissue pad: ‘‘hollowing’’ of the infraorbital area creates the impression of deficient support of the soft tissues by the inferior orbital rim. This deformity is usually due to failure to
Fig. 2. Buttress anatomy: line diagram showing important facial buttresses.
20
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Fig. 3. Fracture patterns: schema of fracture lines commonly seen in severe midfacial trauma.
lattice (Fig. 3). Surgical strategies for repair of midfacial fractures are based on identification of injuries and repair of the components of the buttress system that are most important for facial form and function (Fig. 4) [2,4 /6]. 2.1. Vertical buttresses (Figs. 2 and 5) 1) The nasomaxillary or medial buttress extends from the anterior maxillary alveolar process along the piriform aperture and the frontal process of the maxilla to the frontal bone in the area of the glabella. It is by definition part of the NOE complex, and as such, repair of associated NOE fractures may limit its usefulness in confirmation of accurate alignment of other midfacial fractures. 2) The bifurcated zygomaticomaxillary or lateral buttress extends from the lateral maxillary alveolar process over the malar eminence of the zygoma to the zygomatic process of the frontal bone. The
lateral facial buttress also extends in an anteroposterior (sagittal) direction from the malar eminence along the zygomatic arch to the temporal bone. This buttress is often referred to as the ‘‘key ridge’’ by orthodontists because it transmits the largest portion of occlusal forces from the teeth at the level of the maxillary first molar to the skull base. It is the indeed the key to repair of midfacial fractures at the Lefort levels. 3) The pterygomaxillary or posterior buttress extends from the posterior maxillary alveolar process along the posterior wall of the maxillary sinus (maxillary tuberosity) to the medial and lateral plates of the pterygoid process of the sphenoid bone. It is not accessible for surgical repair. 4) Although not a part of the midfacial lattice, the posterior border of the ascending ramus of the mandible is a vertical buttress that comes into play during repair of some midfacial fractures. It extends
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
21
D) The horizontally oriented portions of the mandible (symphysis and anterior portion of the body) form the caudal-most horizontal buttress of the face [8]. 2.3. Sagittal buttresses I)
The frontal bone, as it extends posteriorly as the orbital roof behind the frontal bar, provides strong support of the upper face [8]. II) The anteroposteriorly oriented posterior part of body and angle of the mandibula provide strong sagittal support of the lower face. III) The zygomatic arch (as the sagittal portion of the lateral facial buttress) supports the lateral portion of the midface. IV) The hard palate provides some relatively weak sagittal support to the lower midface by way of its articulation through the palatine bones with the pterygoid plates of the sphenoid bone.
Fig. 4. Internal fixation devices: line diagram shows sizes, locations and relationships of common titanium plates and screws (gold). Orbital medial wall and floor fractures frequently require bone grafting (gray) to restore orbital shape and volume.
from the angle through the condylar head to the skull base at the glenoid fossa of the temporomandibular joint [5]. 5) The bony nasal septum (vomer and perpendicular plate of the ethmoid bone) forms a weak central vertical buttress that must be evaluated and repaired if necessary to maintain support of the cartilaginous nasal septum and the nasal airway.
2.2. Horizontal buttresses (Figs. 2 and 5) A) The ‘frontal bar’ forms the superior-most horizontal buttress, and consists of the thickened frontal bone and superior orbital rims bridging between the frontozygomatic sutures [2]. The frontal bar serves as the key superior landmark in that the midface is suspended from it during facial stabilization [7]. B) The inferior orbital rim, a horizontal buttress in the center of the face, is important to position of the zygoma and medial orbital fragments to which the medial canthal tendon inserts [2,7]. C) The palatoalveolar complex provides horizontal buttressing just caudal to the LeFort-I-level and maintains the U-shaped configuration of the maxillary dentition.
The central midface (which is approximately the area enclosed by the Lefort I and II lines of weakness, Fig. 3) lacks strong sagittal buttress support and consequently is most vulnerable to blunt traumatic impact forces. Skeletal retrusion (‘flattening’) of the central midface, reflecting collapse of the facial buttresses, is not uncommon, especially if the NOE complex is injured [8].
3. Special considerations in repair of midfacial fractures 3.1. The zygoma: a cornerstone in the facial frame The zygoma (Fig. 6) is related to the surrounding craniofacial skeleton by two critical arcs of external contour. The horizontal external arc of contour is oriented parallel to, but slightly below, the Frankfurt Horizontal plane (FH) from the area of the lacrimal fossa around the zygoma to the zygomatic arch. The vertical arc defines the course of the lateral facial buttress [9]. Internally, the serrated edge of the orbital plate of the sphenoid bone, which forms part of the lateral orbital wall, and the orbital surface of the maxilla contribute to the orientation and position of the zygoma. The zygoma forms the upper two-thirds of the lateral buttress, and its outer surface defines the cheek or malar prominence. Postoperative spatial location of the zygoma will, therefore, play major roles in reconstruction of the buttress to re-establish correct midfacial height, as well as repositioning of the malar prominence to re-establish width and projection of the face at this level. Careful attention to anatomic realignment of all points of articulation of the zygoma to the surrounding craniofacial skeleton and stabilization of the zygoma in this position is mandatory.
22
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Fig. 5. Normal facial buttress anatomy shown on axial (a /c) and coronal (d, e) CT images, which are reconstructed orthogonal to FH plane. Labeling of buttresses corresponds with Fig. 2 and text.
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
23
accomplished with the repair of the medial and lateral vertical buttresses of the midface. The vertical mandibular ramus height (Fig. 7) defines the posterior vertical dimension (the posterior or pterygomaxillary midfacial buttress cannot be repaired) and the midfacial buttresses define the anterior vertical dimension [9]. In the presence of comminuted LeFort level midfacial fractures, overlooked or underappreciated and subsequently untreated, unilateral or bilateral displaced fractures of the condylar head and/or neck can lead to incorrect repositioning of the occlusal plane in relationship to the skull base. The lack of an intact vertical ramus buttress leads to an incorrect posterior vertical dimension, and the comminution of the midfacial buttresses themselves lessens the accuracy of the restoration of anterior vertical dimension. The usual overall effect is shortening of the middle third of the face and tipping or rotation of the occlusal plane to give a canted appearance to the maxilla if not the entire face. If the situation is further complicated by the presence of displaced palatal split and parasymphyseal mandibular fractures, both the width of the midface at the lower maxillary level and the lower third of the face at the level of the mandibular angles may also be set incorrectly to create an overly rounded frontal facial appearance (Figs. 7 and 8) [7,10]. Correction of these deformities requires maxillary and mandibular osteotomies and repositioning of multiple segments of both jaws. The status of the mandibular condylar necks and the condylar heads, including their alignment in the glenoid fossae, may on first thought seem to be insignificant in the setting of complex midfacial and mandibular fractures, but it is in these situations that evaluation for fracture dislocations of this hidden part of the facial skeleton on the preoperative imaging studies is absolutely mandatory. Fig. 6. Panfacial fractures including LeFort I, III, NOE, hard palate, and mandible, in a 16-year-old polytraumatized man, who was involved in motor vehicle crash. Three-dimensional rendering (a) from thin-cut maxillofacial CT scan shows highly comminuted fracture fragments in central midface. Both zygomata (a) are displaced lateroposteriorly and inferiorly indicative of disruption of all zygomatic articulations and both external arcs of contour. 3D rendering viewed from cranially (b) shows abnormal projection of malar prominences (arrows in b) and segmental displaced fracture of left zygomatic arch (arrowhead in b).
3.2. The mandible: a platform for maxillary reconstruction The recognized first step in repair of midfacial fractures is placement of arch bars and MMF wires so that the maxillary and mandibular teeth are correctly interdigitated. If the entire mandibular arch from condylar head to condylar head is intact or accurately reconstructed, final restoration of the relationship between the occlusal plane and the skull base is
3.3. Vertical dimension: plating at the lower maxillary level is usually the last step of buttress reconstruction Reconstruction of the midfacial buttress system usually begins with reduction and stabilization of the frontal bar to which the displaced midfacial structures are then ‘‘suspended.’’ [2,8]. This involves a step-wise reduction and fixation of any fracture line that traverses the zygomaticomaxillary buttresses between the palatoalveolar complex and the frontal bar (Fig. 8). Typically the first of these fracture lines to be repaired is the separation that occurs at the zygomaticofrontal suture line, followed by the other fracture lines in a top to bottom sequence down to the Lefort I/II level. Integrity of the hard palate should have been previously reestablished by application of MMF alone, or in combination with open reduction and repair if the correct facial width at the maxillary alveolar process and correct orientation of the teeth could not be achieved with closed techniques [2]. The palatoalveolar complex is then reattached to the
24
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Fig. 7. Mandible fractures in 46-year old woman, who fell during a seizure (a /f). No midfacial fractures. Lateral (a) and submental (b) 3D renderings, axial (c, d) and coronal (e, f) CT reformations show loss of posterior vertical dimension (upward white arrow in a, arrowheads in f), abnormal mandibular projection (forward white arrow in a), and abnormal facial width (arrowheads in b, f). Mandibular body fracture (anterior arrow in b, arrows in e) and bilaterally displaced comminuted condylar fractures (posterior arrows in b, d, f) allow both mandibular rami (arrowheads in b and f) to displace laterally and anteriorly, resulting in abnormal facial width and increased projection. Both glenoid fossae are empty (black arrow on a, asterisks on b, c) and comminuted condyles have displaced medially and inferiorly (arrows in d and f), reducing posterior vertical dimension of mandibular buttresses.
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
upper part of the buttress as the last step in the repair sequence (Fig. 8). Preferably, the vertical dimension of the midface is set and stabilized by the precise reduction and fixation of both zygomaticomaxillary buttresses. However, in the case of comminuted injuries, the side with the less severe injury is done first and used as a reference for the other lateral buttress. Repair of the medial buttresses may help in establishing vertical dimension, but typically these buttresses are even more severely injured than the lateral buttresses. In rare cases, severe comminution of the lower ends of all the vertical buttresses will require onlay split cranial bone grafts to bridge gaps of missing bone. Although these grafts do not provide the accuracy of correctly realigned in-situ bone fragments, they will allow for an adequate restoration of vertical dimension if applied appropriately. The surgeon may choose to not apply fixation devices across this last level of reduction if there is concern that the position of the condylar heads in one or both glenoid fossae has been altered by intracapsular bleeding or edema. In these cases, the MMF is not removed but rather left in place to allow the patient to adjust the position of the palatoalveolar complex as the joint abnormality resolves and the condylar head moves to its correct position. Fixation may be applied in a second procedure 1 /2 weeks later, or the MMF can be left in place for the customary 6-week period necessary for sufficient healing of non-fixated facial fractures. Although the lack of fixation at the low maxillary level could theoretically allow the patient to elongate or shorten the midface with movement of the mandible, this is more likely to occur as an iatrogenic complication of poor surgical technique in patients who do have fixation placed [1,2]. 3.4. Orbital volume: size does matter The orbit is a conical shaped compartment contained within the buttress system of the midface (Fig. 9), and collapse of the system under external impact forces places the orbital soft tissue contents at risk for injury. Fortunately the stout ring-like osseous enclosure of the orbital aperture (anterior orbital third) provides a measure of protection to these soft tissues, and the relative weakness of the very thin floor and medial wall of the middle orbital third offers a pathway for dissipation (blow-out fractures) of forces that are transmitted to the eye. The posterior orbital third is again relatively stout bone that protects the vital structures that course through the orbital apex. The distance from the orbital rim to the optic foramen ranges from 40 to 50 mm, giving a length to each orbital third of between 13 and 17 mm [1,2,11,12]. The frontal bar forms the very strong superior orbital rim and the zygoma the strong lateral rim and the lateral aspect of the inferior rim. The frontal process of the
25
maxilla contributes the medial aspect of the inferior rim. There is no true medial orbital rim but rather a smooth confluence of the frontal process of the maxilla and lacrimal bone to provide a point for the insertion of the medial canthal tendon around the lacrimal sac (Fig. 9). This insertion is important for proper function of the lacrimal pump and maintenance of the sharp angle of the medial canthus and the length of the palpebral fissure [2,11]. The orbital roof, floor and medial wall are concave relative to each other (Fig. 9), producing the greatest diameter of the orbit approximately 15 mm posterior to the inferior orbital rim. The globe is situated at this level and the orbital floor inclines upward in an inwardly convex curve behind the globe to create a relative retrobulbar constriction (Fig. 9) that maintains the position of the retrobulbar soft tissues. Posteromedially the orbital floor slopes upward into the medial orbital wall without sharp demarcation [2]. Posterolaterally, the inferior orbital fissure separates the orbital floor from the lateral orbital wall, which is formed by the greater sphenoid wing and the frontal process of the zygoma and is sometimes referred to as the sphenotemporal buttress [13]. The tip of the orbital cone is referred to as the orbital apex, into which the optic canal and superior orbital fissure open. The apex approximates intracranial structures that include the anterior clinoid process, the carotid siphon and the cavernous sinus. Reconstruction of the orbital walls can begin only after the vertical and horizontal buttresses and thus the outer ring of the orbit have been restored and stabilized (Fig. 8). This ring then serves as the anchoring point for bone grafts or alloplastic implants that replace the fragmented bone of the middle third of the orbit (Figs. 4 and 10). Recreation of the upward convexity of the normal orbital roof, the concave anterior orbital floor, the convex posterior floor, and the obtuse angle of the transition of the floor to the medial orbital wall (lamina papyracea) offer the greatest challenges to the surgeon (Fig. 10). Because of the inherent difficulty in forming an exact duplication of these gently curving osseous surfaces, over- or undercorrection may occur, leading to altered orbital volume, the primary cause of enophthalmos or less commonly exophthalmos. For example, fractures of the orbital floor almost always involve the concave portion of the floor, starting at the inferior orbital groove (locus minor resistentiae) and extending posteriorly into the retrobulbar convexity and medially at least to the junction of the floor with the medial wall [2]. Reconstruction of the entire floor defect at the level of either the concavity or the convexity will alter orbital volume as will failure to reproduce the obtuse angle with the medial wall. Orbital volume changes exceeding 1.5 ml (i.e. /5% of the normal orbital volume) may lead to an asymmetry in globe position of greater than 2 mm, a relatively small amount that will be noticeable in some
26
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Fig. 8. Vertical dimension. Same patient as in Fig. 6. Anterior 3D view (a) shows intact frontal bar and bilaterally disrupted comminuted medial and lateral buttresses, and orbital rims. Axial CT (b) shows comminution and retrusion of superior medial buttresses and nasal septum into ethmoidal cells (arrows on b). Reduction and fixation of zygomaticofrontal suture diastasis, shown on coronal CT (arrows in c), is usually first step in operative repair sequence. Longitudinal paramedian fracture repair of right hard palate (arrows in d, axial CT also shows posterior buttress fracture) is mandated prior to restoration of anterior vertical dimension of midface (vertical buttresses). Postoperative 3D renderings from CT (e, f) show internal fixation of buttresses (see also Fig. 4) and nasal bone graft (arrow in e). Bilaterally increased orbital volume is appreciated on 3D rendering (a), axial (b), and coronal (c) CT images. Right medial orbital wall is comminuted with fracture fragment (asterisk on b) impinging on right optic nerve in right orbital apex.
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
27
Fig. 9. Photography of dry bone preparation of normal left orbit. Orbital roof, floor, and medial wall are concave relative to each other anteriorly (short white arrows). More posteriorly, orbital floor inclines upward, creating retrobulbar constriction (asterisk). Medial orbital wall (long white arrow) and orbital floor (black arrow) meet at an obtuse angle without sharp demarcation. Characteristics of orbital shape need to be recreated surgically to restore correct orbital volume (see also Figs. 4 and 11). NC, nasal cavity; NB, nasal bone; LF, lacrimal fossa; O, optic foramen; SOF, superior orbital fissure; IOF, inferior orbital fissure.
patients after all swelling has subsided postoperatively [2]. Therefore, floor injuries recognized to affect more than one curved surface of the floor and/or both the floor and medial orbital wall generally require complex reconstructions with specific placement and stabilization of bone grafts or alloplastic implants (Fig. 4). 3.5. Displacement of bone fragments into the orbit and fractures involving the orbital apex Traumatic blindness (Figs. 8 and 11) occurs in about 3% of patients who suffer blunt facial trauma [13] and abnormal CT findings are present in almost all of these cases. Only rarely are both eyes affected and most often the unilateral loss of vision is diagnosed at the time of admission in an awake patient who can describe the visual disturbance. In addition to a thorough ophthalmological examination, prompt radiological evaluation is mandated in these patients, as it is possible that the images will demonstrate a condition that might respond to timely though in many cases controversial surgical intervention. Perhaps of even more importance is the demonstration of the same findings on images obtained during the evaluation of facial injuries in an unconscious or uncooperative patient following blunt trauma. Visual acuity cannot be measured in these patients and the available clinical testing is only suggestive of possible
Fig. 10. Abnormal orbital volume in same patient as Fig. 1. Left orbital floor fracture with loss of angulation in relation to medial orbital wall is shown on coronal CT reformations (a, orthogonal to FH) causing increased orbital volume and herniation of orbital contents into left maxillary sinus. Right orbital floor and volume are normal (a). Loss of relative retrobulbar orbital constriction (arrow in b) is shown on sagittal oblique CT reformations, reconstructed parallel to the optic nerve. Bone fragment is present superiorly, where normal left orbital roof curves upward (arrowhead in b).
decreased visual acuity. Because loss of vision does not automatically accompany orbital injuries of equal severity in every patient, most surgeons are hesitant to perform a ‘‘sight saving’’ surgical procedure without documentation of loss of vision. However, the medical alternative of short-term megadose steroid therapy might be considered to be an acceptable prophylactic
28
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
orbit is the equivalent of unknowingly operating on an only-seeing-eye. Many surgeons are adamant that reconstruction of an orbit that houses an only-seeingeye is contraindicated for fear that in the unlikely event of an iatrogenic injury to this eye, the patient will be totally blind. Even for patients who are alert and have no evidence of visual disturbances, the surgeon must be aware of the presence of these types of injuries so that options of a modified surgical approach that requires less surgical manipulation of the orbital soft tissues can be considered.
4. Imaging approaches CT is highly accurate at detecting and characterizing surgically important injuries. It does not, however, precisely show the magnitude of osseous fragmentation in complex fractures seen at surgery, regardless of CT technique. Maxillofacial CT delivers significant radiation dose to the orbits (potentially associated with premature lens opacification), and scan extension to include the mandible is associated with clinically meaningful radiation to the soft-tissues of the neck (e.g. thyroid), an especially important consideration in pediatric populations [15]. 4.1. Optimization of axial image acquisition (raw data)
Fig. 11. Carotid canal and optic canal fracture extension in a 25-yearold man, who fell from a height of 7 m sustaining skull base fracture. Fracture line extends into sphenoid bone at internal orifice of optic canal (arrows in a, axial CT reformations), causing traumatic optic neuropathy of the right optic nerve. Carotid canal fractures (arrows in b) may require angiographic evaluation. Use of Rowe’s maxillary disimpaction forceps may be contraindicated if LeFort fractures extend into carotid canal or orbital apex.
alternative in some of these patients while waiting for the mental status to improve [14]. In patients whose mental status has not improved but repair of the facial fractures is indicated because of the passage of time, further deferment of repair of both orbits might be appropriate if one side has findings known to be associated with loss of vision. Blindness due to the injury itself could be attributed unfairly to the surgical manipulation of the involved eye, and repair of the other
Images can be obtained either directly in axial and coronal planes, directly in either axial or coronal plane with reformations in the orthogonal plane, or as reconstruction from a CT of the cranium obtained from an appropriately prescribed study (i.e. 1.00 /1.25 mm slice thickness). In general, direct acquisition in orthogonal planes at 3 mm contiguous slice thickness has been the standard of care in outpatient practice settings. However, with the evolution of spiral CT, and especially multidetector spiral CT, 1.0 /1.25 mm thin sections in the axial plane are reformatted into the orthogonal planes, without loss of image quality, accuracy and without further radiation. For example, if a multidetector CT scanner is used for the head scan using 5 mm slice thickness, in which the 5 mm are composed of four 1.25 mm channels, postprocessing allows for separation of the information from each of those channels to create individual 1.25 mm slice thicknesses. This data can then be used to provide the raw data for maxillofacial CT planes in various spatial planes without further radiation exposure to the patient [16]. Primary axial images are obtained parallel to the FH plane using 1.0 /1.25 mm slice thickness from above the frontal sinus through the hard palate or maxillary alveolus. The scan is usually extended to include the mandible in all cases of suspected midfacial fractures to
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
29
image the entire buttress system and aid surgical planning [2,7]. Precise axial alignment of the patient’s head in the center of the scanner gantry and alignment of the scanning plane with FH (i.e. gantry tilt) are important to obtain raw data parallel to the FH plane. Only symmetric images allow cephalometric measurements (projection, width, vertical dimension) directly on CT studies for side-to-side comparison. This is especially important if surgical repair is evaluated intraoperatively [17].
4.2. Optimization and orientation of reformations Precise positioning of a severely injured patient within the CT scanner may be difficult or impossible (Fig. 12). Thin-cut axial CT images acquired with the head not in symmetric standard axial position should be considered for off-line axial reconstruction on an imaging workstation without blocking access to the CT scanner and decreasing CT throughput. This set of symmetric secondary axial images easily allows creation of orthogonal coronal and sagittal reformations. However, three reference points (left and right orbitale, left and right porion), which define the FH plane, will never lie in one single image guide (e.g. sagittal, Fig. 13), which is used for definition of the axial reformations. In our experience, intracranial reference points closer to the median sagittal plane are usually helpful. In severe cases of midfacial trauma with bilateral fracture and displacement of the inferior orbital rim (orbitale), axial CT images may be aligned parallel to FH. The nasal surface of the hard palate is commonly used as a proxy. Our experience is that the planum sphenoidale, which is normally parallel to the nasal surface of the hard palate and FH, may serve as an acceptable proxy if the hard palate is fractured in addition to both inferior orbital rims. Analogous to reconstructive surgery, we find that relating axial reformations to uninjured anatomic reference points is most successful for the creation of symmetric secondary axial images parallel to FH. In our experience, on the workstation a post-processing mode should be chosen, which displays axial, sagittal, coronal and 3D images simultaneously (Fig. 13). If both, the sagittal and coronal guide images are used with ‘oblique axes’ function, orientation of the new axial reformations will change automatically, as the sagittal and coronal axes are aligned parallel or orthogonal to the FH plane. The position of FH in relation to the axial, coronal and sagittal reformations can easily be checked on threedimensional renderings (Fig. 13). Reformations in the coronal plane should be perfectly orthogonal to the symmetric axial images, such that true coronal plane images are obtained. Sagittal plane image reformation may be performed either relative to the coronal plane or as sagittal obliques parallel to the optic
Fig. 12. Axial CT reformations in same patient as Fig. 1. Original axial CT images obtained ‘out of plane’ (a) do not allow side-to-side comparison of malar eminence position. Axial reformations reconstructed parallel to FH (b) show normal anatomy of uninjured right side in same image as injured left zygoma, allowing measurement of fracture displacement in relation to intact facial buttresses and skull base, and facilitating operative planning.
nerve (Fig. 11), if evaluating anatomic constrictions of the orbital floor and roof. Images are reconstructed using both soft tissue and bone algorithms and viewed using soft-tissue and bone windowing, respectively.
30
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Fig. 13. Reconstruction of ‘out-of-plane’ maxillofacial CT reformations of 39-year-old man after assault without fracture. For image optimization of raw data we display sagittal, coronal, axial, and 3D reformations simultaneously on workstation (a /d) with ‘oblique axes’ function active (right lower corner radio button on a /c). Aligning the sagittal axis parallel to hard palate or planum sphenoidale (horizontal lines on a) automatically carries over to coronal (b) and axial (c) reformations. Similarly, coronal axis (horizontal line in b) is oriented along uninjured bilateral symmetric anatomic landmarks (e.g. glenoid condyles, left and right porion). Resulting axial reformations are parallel to FH (left and right porion and orbitale are shown in c), which are batched for entire dataset and stored on PACS. Plane of reformation is easily checked and corrected using 3D rendering (FH in d).
5. Summary Operative planning of complex midfacial fractures depends on optimal imaging with CT scanning as the imaging modality of choice. Optimal imaging technique is dependent upon displaying the facial anatomy orthogonal to the relevant reference planes used for surgical repair, usually the FH plane.
Careful attention to patient position within the gantry of the CT scanner is the easiest way of directly obtaining symmetric axial images parallel to FH. Reformation of axial CT images parallel to FH should be considered in cases where the face is not bilaterally symmetrically positioned on the original axial images to aid side-to-side comparison of craniometric measurements during surgical repair. Coronal CT reformations should be obtained strictly orthogonal to FH.
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Differences in surgical and radiological terminology may impede inter-specialty communications (see Appendix A).
Acknowledgements We would like to thank our medical illustrator David W. Ehlert, M.A.M.S., C.M.I. for creating such great graphics (Figs. 2 /4).
31
[16] Bushberg JT, Seibert JA, Leidholdt EMJ, Boone JM. The Essential Physics of Medical Imaging, second ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2001:933. [17] Stanley RB. Use of intraoperative computed tomography during repair of orbitozygomatic fractures. Arch Facial Plast Surg 1999;1:19 /24. [18] Borman H, Ozgur F. A simple instrument to define the Frankfurt horizontal plane for soft- tissue measurements of the face. Plast Reconstr Surg 1998;102:580 /1.
Appendix A References [1] Gruss JS, Whelan MF, Rand RP, Ellenbogen RG. Lessons learnt from the management of 1500 complex facial fractures. Ann Acad Med Singapore 1999;28:677 /86. [2] Stanley RBJ. Maxillofacial trauma. In: Cummings CW, Frederikson JM, Harker LA, Schuller DE, Krause CJ, Richardson MA, editors. Otolaryngology: Head and Neck Surgery. St. Louis: Mosby-Year Book, 1998:453 /85. [3] Gentry LR, Manor WF, Turski PA, Strother CM. High-resolution CT analysis of facial struts in trauma: 1. Normal anatomy. Am J Roentgenol 1983;140:523 /32. [4] Gruss JS, Mackinnon SE. Complex maxillary fractures: role of buttress reconstruction and immediate bone grafts. Plast Reconstr Surg 1986;78:9 /22. [5] Forrest CR, Phillips JH, Prein J. LeFort fractures. In: Prein J, editor. Manual of Internal Fixation in the Cranio-Facial Skeleton. Berlin: Springer, 1998:108 /26. [6] Manson PN, Hoopes JE, Su CT. Structural pillars of the facial skeleton: an approach to the management of Le Fort fractures. Plast Reconstr Surg 1980;66:54 /62. [7] Manson PN. Organization of treatment in panfacial fractures. In: Prein J, editor. Manual of Internal Fixation in the Cranio-Facial Skeleton. Berlin: Springer, 1998:95 /107. [8] Manson PN, Clark N, Robertson B, et al. Subunit principles in midface fractures: the importance of sagittal buttresses, soft-tissue reductions, and sequencing treatment of segmental fractures. Plast Reconstr Surg 1999;103:1287 /306. [9] Stanley RB, Jr. The zygomatic arch as a guide to reconstruction of comminuted malar fractures. Arch Otolaryngol Head Neck Surg 1989;115:1459 /62. [10] Schilli W. Mandibular fractures. In: Prein J, editor. Manual of Internal Fixation in the Cranio-Facial Skeleton. Berlin: Springer, 1998:57 /93. [11] Manson PN. Orbital fractures. In: Prein J, editor. Manual of Internal Fixation in the Cranio-Facial Skeleton. Berlin: Springer, 1998:139 /47. [12] Rhea JT, Rao PM, Novelline RA. Helical CT and threedimensional CT of facial and orbital injury. Radiol Clin North Am 1999;37:489 /513. [13] Stanley RB, Jr, Sires BS, Funk GF, Nerad JA. Management of displaced lateral orbital wall fractures associated with visual and ocular motility disturbances. Plast Reconstr Surg 1998;102:972 /9. [14] Levin LA, Beck RW, Joseph MP, Seiff S, Kraker R. The treatment of traumatic optic neuropathy: the International Optic Nerve Trauma Study. Ophthalmology 1999;106:1268 /77. [15] Brenner D, Elliston C, Hall E, Berdon W. Estimated risks of radiation-induced fatal cancer from pediatric CT. Am J Roentgenol 2001;176:289 /96.
Glossary of terms frequently used with facial fracture reconstruction Buttress support Refers to the direction of force that is resisted by an osseous buttress. Not necessarily the same as bone orientation. For instance, even though the hard palate is oriented horizontally, it also resists antero-posterior impact, thus providing some sagittal buttress support Central fragment Key component of the naso /orbito /ethmoidal complex, bearing the insertion of the medial canthal ligament (MCL), located anterior to the lamina papyracea External arcs of contour Horizontal and vertical lines defining the position of the malar eminence in space [9] Frankfurt Horizontal Plane (FH) Standard craniometric reference plane used in maxillofacial surgery; passing through three of the following four reference points: the left and right porion and left and right orbitale. FH was originally introduced at an anthropological conference in Frankfurt, Germany, in 1884 [18]. Historically, FH was drawn on lateral photoor radiographs. (SYN: orbitomeatal plane, auriculo / infraorbital plane, ear /eye plane) Frontal bar Superior-most horizontal buttress. It consists of the thickened frontal bone, which bridges between the frontozygomatic sutures [2]. The superior orbital rim and the glabella are part of the frontal bar. The frontal bar serves as a key superior support in facial fracture stabilization from which the midface is suspended Maxillo-mandibular fixation (MMF) Fixing the correct interdigitation of the maxillary and mandibular teeth with arch bars and wires
32
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Medial canthal ligament (MCL) Medial tendon maintaining shape and position of the medial canthus NM Naso-maxillary buttress (SYN: medial buttress): anterior alveolar process of maxilla, along piriform aperture, frontal process of maxilla to frontal bone Occlusal plane Imaginary surface anatomically relating the cranium to the incisal edges and occluding surfaces of the teeth (SYN: bite plane) Ophthalmoplegia Paralysis of one or more of the ocular muscles Orbitale Craniometric reference point on the lowest point of the infraorbital rim Porion Craniometric reference point at top of external auditory meatus Projection Depth; refers to antero /posterior dimension of face, while ‘width’ describes left-to-right, and ‘height’ cranio / caudal dimension Quadripod fracture Anatomically incorrect term for ZMC fracture: the zygomatic bone is supported by five structures
Reid’s baseline Line connecting orbitale with center of external auditory meatus, roughly parallel to the hard palate, clinically used synonymously with FH Sphenotemporal buttress Relatively weak buttress formed by the frontal process of the zygomatic bone, the greater wing of the sphenoid bone, and the squamous portion of the temporal bone. Commonly injured in impacted fractures of the lateral orbital wall Tripod fracture Anatomically incorrect term for zygomatico /maxillary complex (ZMC) fracture: the zygomatic bone is supported by five structures Trimalar fracture Anatomically incorrect term for ZMC fracture: the zygomatic bone is supported by five structures Vertical dimension Vertical relationship of facial structures (SYN: facial height) ZM Zygomatico /maxillary buttress (SYN: lateral buttress): lateral alveolar process of maxilla, zygomatico /maxillary suture, malar eminence of zygoma, zygomatic process of frontal bone. This buttress forks at the malar eminence to give off the zygomatic arch in the sagittal direction
Imaging of high-energy midfacial trauma: what the surgeon needs to know Ken F. Linnau a, Robert B. Stanley, Jr b, Danial K. Hallam a, Joel A. Gross a, F.A. Mann a,* b
a Department of Radiology, Harborview Medical Center, Box 359 728, 325 Ninth Avenue, Seattle, WA 98104-2499, USA Department of Otolaryngology */Head and Neck Surgery, Harborview Medical Center, Box 359894, 325 9th Avenue, Seattle, WA 98104-2499, USA
Received 10 June 2003; received in revised form 11 June 2003; accepted 12 June 2003
Abstract Treatment goals in severe midfacial trauma are restoration of function and appearance. Restoration of function is directed at multiple organ systems, which support visual acuity, airway patency, mastication, lacrimation, smelling, tasting, hearing, and facial expression. Victims of blunt facial trauma expect to look the same after surgical treatment as before injury. Delicate soft tissues of the midface often make cosmetic reconstructive surgery technically challenging. Generally, clinical evaluation alone does not suffice to fully characterize facial fractures associated with extensive swelling, and the deeper midface is not accessible to physical examination. Properly performed computed tomography (CT) overcomes most limitations of presurgical examination. Thus, operative approaches and sequencing of surgical repair are guided by imaging information displayed by CT. Restoration of function and appearance relies on recreating normal maxillofacial skeletal anatomy, with particular attention to position of the malar eminences, mandibular condyles, vertical dimension and orbital morphology. Due to its pivotal role in surgical planning, CT scans obtained for the evaluation of severe midfacial trauma should be designed to easily depict the imaging information necessary for clinical decision making. Learning objectives: 1. Understand the facial skeletal buttress system; 2. Understand how the pattern of derangement of the buttress system determines the need for and choice of operative approach for repair of fractures in the middle third of the face; 3. Understand the role and importance of CT and CT reformations in the detection and classification of the pattern of buttress system derangement. # 2003 Published by Elsevier Ireland Ltd. Keywords: Facial trauma; Facial fractures; Therapy; Computed tomography; 3D visualization
1. Introduction Treatment goals in patients with midfacial trauma are restoration of: 1) form (appearance), and 2) function. Restoration of appearance and function requires an accurate reconstruction of the midfacial skeletal anatomy, with particular attention to the position and 3-
* Corresponding author. Tel.: /1-206-731-3561; fax: /1-206-7318560. E-mail address: [email protected] (F.A. Mann).
dimensional orientation of the zygomata, orbital walls, and maxillary palatoalveolar complex or maxillary side of the occlusal plane. Correct spatial relocation of the zygomata restores the malar or cheek prominences and thus facial width and projection at this level. Accurate reconstruction of the orbital walls restores orbital shape and volume to prevent globe malposition and lessen the chances of ocular dysfunctions, including diplopia. Return of the maxillary side of the occlusal plane to its preinjury relationship to the skull base restores projection of the face at the level of the maxillary dentition, as well as the overall height or vertical dimension of the middle third of the face. This, in turn, optimizes function of the muscles of mastication and temporomandibular joints, something that simple
0720-048X/03/$ - see front matter # 2003 Published by Elsevier Ireland Ltd. doi:10.1016/S0720-048X(03)00205-5
18
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
interdigitation of the maxillary and mandibular teeth with maxillomandibular fixation (MMF) during healing does not insure. Most surgeons believe that surgical repair of midfacial injuries should be undertake within 7/10 days of the time of injury, prior to the onset soft tissue contraction and early fibrous tissue formation. Generally, clinical evaluation alone does not suffice to fully characterize the facial fractures at this stage, because of residual swelling in the overlying soft tissues and the inaccessibility of the deeper midface to direct physical examination (Fig. 1a). However, imaging information, displayed by properly performed computed tomography (CT) scans usually overcomes the inadequacies of the presurgical clinical examination (Fig. 1b). The imaging information is critical for the surgeon’s understanding of the extent of the injuries and, thus, the appropriate choice and sequencing of the needed operative approaches. This is particularly true if the surgeon is contemplating the use of minimally invasive (endoscopic) techniques that will similarly not allow for wide-field direct inspection of the fractures at the time of repair. The use of ‘‘modern’’ and usually more costly surgical procedures, such as stabilization of fractures with internal fixation devices (miniplates and screws, with bone grafting if necessary), is justified in most reports by improved results from the primary repair and elimination of the need for even more expensive and less effective secondary repairs or revisions [1]. Hospital administrators, third-party payers, and the victims of the trauma themselves have, therefore, developed expectations of a return to at least near-normal if not normal appearance and function following initial repair of midfacial injuries. However, the involvement in a relatively small anatomic area of multiple organ systems that support, among other things, vision, breathing, mastication, lacrmation, and facial contours and expression, makes meeting these expectations in many cases difficult, even for the experienced surgeon. It is the purpose of this presentation to show that providing the surgeon with a specific format of preoperative imaging information is the essential first step toward attaining optimum results from acute management of midfacial trauma. CT scans obtained for the evaluation of severe midfacial trauma should be designed to easily depict the imaging information necessary for clinical decision making.
1.1. Why early, comprehensive fracture management Fig. 1. Preoperative picture of a 25-year-old male polytrauma patient after high-speed motor vehicle crash shows massive facial soft-tissue swelling, limiting clinical evaluation of the face (a). Three-dimensional rendering of thin-cut maxillofacial CT scan of same patient shows highly comminuted LeFort III and NOE fractures (b).
Reduction and anatomically correct realignment of displaced fragments is most easily accomplished before the onset of early bone healing (fibrosis). Delay past the time that allows for osseous malunion means that a
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
refracture or osteotomy will be needed for movement of the displaced skeletal segments. Configuration of soft tissue is dependent on the position of underlying or adjacent bone. The anatomically realigned facial skeleton returns the soft tissue structures to their normal configuration and supports them during healing. Healing over untreated or incompletely reduced fractures may result in cicatricial contracture with permanent thickening, shortening and displacement of the soft tissue structures. Delayed or secondary repair of both bony and soft tissue defects is more challenging and its results less satisfying than primary reconstruction owing to the consequences of allowing the natural healing process to proceed before repair is completed. Reoperation through scar tissue that has resulted from previous surgical approaches increases the risk of iatrogenic complications such as lid retraction or ectropion. Note: The benefits of early, comprehensive surgical intervention may be outweighed by complicating factors including ocular and central nervous system injuries, or an overall unstable medical condition in the polytrauma patient. However, the same imaging information should be obtained in these patients if possible, so that the surgical team can consider a less comprehensive treatment plan that can be tolerated by the patient and hopefully lessen the future impact of partially treated injuries.
19
resuspend tissues elevated for fracture exposure to the repositioned bone.
2. The buttress system of the face The midface can be conceptualized as a honeycomb or lattice-like system of buttresses that has developed as a skeletal adaptation to masticatory forces that are transmitted from the teeth to the skull base (Fig. 2). This adaptation also allowed for the compartmentalization that is necessary for other physiologic facial functions. The strongest midfacial buttresses are vertically oriented in response to the large physiologic loads placed on the system by the similarly directed masticatory forces. ‘Weaker’ horizontally and sagittally oriented buttresses reinforce the vertical buttresses under the loads of mastication [2,3]. The buttress system is, therefore, less resistant to external forces such as anteroposteriorly or laterally directed impact forces, and the traumatic disruption of one buttress may weaken the lattice and cause its collapse. This collapse is not altogether a random process, and the reoccurring fracture patterns (e.g. zygomatico-maxillary complex (ZMC), naso/ orbito /ethmoidal (NOE) complex and LeFort fractures) that are observed with partial or total collapse of the lattice may actually serve to protect the delicate structures contained within the compartments of the
1.2. Examples of deformities resulting from untreated or poorly reduced fractures of the middle third of the face Globe malposition: enophthalmos with shortening of palpebral fissure height, or exophthalmos with widening of the palpebral fissure. Medial canthal ligament malposition (telecanthus): lateral displacement and rounding of the inner canthus. Shortened midface: ‘‘telescoping’’ of the maxilla upward on itself. This deformity is more often cause by overzealous closed reduction of LeFort level I and/ or II fractures than the injuries themselves. Flattened and widened midface: ‘‘dish face’’ deformity due to posterior displacement and lateral expansion of the paired midfacial components. Elongated face: ‘‘facies equina’’ deformity due to displacement of the palatoalveolar complex down the slope of the skull base, creating premature posterior occlusal contacts that force the mandible to rotate downward. Inferiorly displaced malar soft tissue pad: ‘‘hollowing’’ of the infraorbital area creates the impression of deficient support of the soft tissues by the inferior orbital rim. This deformity is usually due to failure to
Fig. 2. Buttress anatomy: line diagram showing important facial buttresses.
20
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Fig. 3. Fracture patterns: schema of fracture lines commonly seen in severe midfacial trauma.
lattice (Fig. 3). Surgical strategies for repair of midfacial fractures are based on identification of injuries and repair of the components of the buttress system that are most important for facial form and function (Fig. 4) [2,4 /6]. 2.1. Vertical buttresses (Figs. 2 and 5) 1) The nasomaxillary or medial buttress extends from the anterior maxillary alveolar process along the piriform aperture and the frontal process of the maxilla to the frontal bone in the area of the glabella. It is by definition part of the NOE complex, and as such, repair of associated NOE fractures may limit its usefulness in confirmation of accurate alignment of other midfacial fractures. 2) The bifurcated zygomaticomaxillary or lateral buttress extends from the lateral maxillary alveolar process over the malar eminence of the zygoma to the zygomatic process of the frontal bone. The
lateral facial buttress also extends in an anteroposterior (sagittal) direction from the malar eminence along the zygomatic arch to the temporal bone. This buttress is often referred to as the ‘‘key ridge’’ by orthodontists because it transmits the largest portion of occlusal forces from the teeth at the level of the maxillary first molar to the skull base. It is the indeed the key to repair of midfacial fractures at the Lefort levels. 3) The pterygomaxillary or posterior buttress extends from the posterior maxillary alveolar process along the posterior wall of the maxillary sinus (maxillary tuberosity) to the medial and lateral plates of the pterygoid process of the sphenoid bone. It is not accessible for surgical repair. 4) Although not a part of the midfacial lattice, the posterior border of the ascending ramus of the mandible is a vertical buttress that comes into play during repair of some midfacial fractures. It extends
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
21
D) The horizontally oriented portions of the mandible (symphysis and anterior portion of the body) form the caudal-most horizontal buttress of the face [8]. 2.3. Sagittal buttresses I)
The frontal bone, as it extends posteriorly as the orbital roof behind the frontal bar, provides strong support of the upper face [8]. II) The anteroposteriorly oriented posterior part of body and angle of the mandibula provide strong sagittal support of the lower face. III) The zygomatic arch (as the sagittal portion of the lateral facial buttress) supports the lateral portion of the midface. IV) The hard palate provides some relatively weak sagittal support to the lower midface by way of its articulation through the palatine bones with the pterygoid plates of the sphenoid bone.
Fig. 4. Internal fixation devices: line diagram shows sizes, locations and relationships of common titanium plates and screws (gold). Orbital medial wall and floor fractures frequently require bone grafting (gray) to restore orbital shape and volume.
from the angle through the condylar head to the skull base at the glenoid fossa of the temporomandibular joint [5]. 5) The bony nasal septum (vomer and perpendicular plate of the ethmoid bone) forms a weak central vertical buttress that must be evaluated and repaired if necessary to maintain support of the cartilaginous nasal septum and the nasal airway.
2.2. Horizontal buttresses (Figs. 2 and 5) A) The ‘frontal bar’ forms the superior-most horizontal buttress, and consists of the thickened frontal bone and superior orbital rims bridging between the frontozygomatic sutures [2]. The frontal bar serves as the key superior landmark in that the midface is suspended from it during facial stabilization [7]. B) The inferior orbital rim, a horizontal buttress in the center of the face, is important to position of the zygoma and medial orbital fragments to which the medial canthal tendon inserts [2,7]. C) The palatoalveolar complex provides horizontal buttressing just caudal to the LeFort-I-level and maintains the U-shaped configuration of the maxillary dentition.
The central midface (which is approximately the area enclosed by the Lefort I and II lines of weakness, Fig. 3) lacks strong sagittal buttress support and consequently is most vulnerable to blunt traumatic impact forces. Skeletal retrusion (‘flattening’) of the central midface, reflecting collapse of the facial buttresses, is not uncommon, especially if the NOE complex is injured [8].
3. Special considerations in repair of midfacial fractures 3.1. The zygoma: a cornerstone in the facial frame The zygoma (Fig. 6) is related to the surrounding craniofacial skeleton by two critical arcs of external contour. The horizontal external arc of contour is oriented parallel to, but slightly below, the Frankfurt Horizontal plane (FH) from the area of the lacrimal fossa around the zygoma to the zygomatic arch. The vertical arc defines the course of the lateral facial buttress [9]. Internally, the serrated edge of the orbital plate of the sphenoid bone, which forms part of the lateral orbital wall, and the orbital surface of the maxilla contribute to the orientation and position of the zygoma. The zygoma forms the upper two-thirds of the lateral buttress, and its outer surface defines the cheek or malar prominence. Postoperative spatial location of the zygoma will, therefore, play major roles in reconstruction of the buttress to re-establish correct midfacial height, as well as repositioning of the malar prominence to re-establish width and projection of the face at this level. Careful attention to anatomic realignment of all points of articulation of the zygoma to the surrounding craniofacial skeleton and stabilization of the zygoma in this position is mandatory.
22
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Fig. 5. Normal facial buttress anatomy shown on axial (a /c) and coronal (d, e) CT images, which are reconstructed orthogonal to FH plane. Labeling of buttresses corresponds with Fig. 2 and text.
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
23
accomplished with the repair of the medial and lateral vertical buttresses of the midface. The vertical mandibular ramus height (Fig. 7) defines the posterior vertical dimension (the posterior or pterygomaxillary midfacial buttress cannot be repaired) and the midfacial buttresses define the anterior vertical dimension [9]. In the presence of comminuted LeFort level midfacial fractures, overlooked or underappreciated and subsequently untreated, unilateral or bilateral displaced fractures of the condylar head and/or neck can lead to incorrect repositioning of the occlusal plane in relationship to the skull base. The lack of an intact vertical ramus buttress leads to an incorrect posterior vertical dimension, and the comminution of the midfacial buttresses themselves lessens the accuracy of the restoration of anterior vertical dimension. The usual overall effect is shortening of the middle third of the face and tipping or rotation of the occlusal plane to give a canted appearance to the maxilla if not the entire face. If the situation is further complicated by the presence of displaced palatal split and parasymphyseal mandibular fractures, both the width of the midface at the lower maxillary level and the lower third of the face at the level of the mandibular angles may also be set incorrectly to create an overly rounded frontal facial appearance (Figs. 7 and 8) [7,10]. Correction of these deformities requires maxillary and mandibular osteotomies and repositioning of multiple segments of both jaws. The status of the mandibular condylar necks and the condylar heads, including their alignment in the glenoid fossae, may on first thought seem to be insignificant in the setting of complex midfacial and mandibular fractures, but it is in these situations that evaluation for fracture dislocations of this hidden part of the facial skeleton on the preoperative imaging studies is absolutely mandatory. Fig. 6. Panfacial fractures including LeFort I, III, NOE, hard palate, and mandible, in a 16-year-old polytraumatized man, who was involved in motor vehicle crash. Three-dimensional rendering (a) from thin-cut maxillofacial CT scan shows highly comminuted fracture fragments in central midface. Both zygomata (a) are displaced lateroposteriorly and inferiorly indicative of disruption of all zygomatic articulations and both external arcs of contour. 3D rendering viewed from cranially (b) shows abnormal projection of malar prominences (arrows in b) and segmental displaced fracture of left zygomatic arch (arrowhead in b).
3.2. The mandible: a platform for maxillary reconstruction The recognized first step in repair of midfacial fractures is placement of arch bars and MMF wires so that the maxillary and mandibular teeth are correctly interdigitated. If the entire mandibular arch from condylar head to condylar head is intact or accurately reconstructed, final restoration of the relationship between the occlusal plane and the skull base is
3.3. Vertical dimension: plating at the lower maxillary level is usually the last step of buttress reconstruction Reconstruction of the midfacial buttress system usually begins with reduction and stabilization of the frontal bar to which the displaced midfacial structures are then ‘‘suspended.’’ [2,8]. This involves a step-wise reduction and fixation of any fracture line that traverses the zygomaticomaxillary buttresses between the palatoalveolar complex and the frontal bar (Fig. 8). Typically the first of these fracture lines to be repaired is the separation that occurs at the zygomaticofrontal suture line, followed by the other fracture lines in a top to bottom sequence down to the Lefort I/II level. Integrity of the hard palate should have been previously reestablished by application of MMF alone, or in combination with open reduction and repair if the correct facial width at the maxillary alveolar process and correct orientation of the teeth could not be achieved with closed techniques [2]. The palatoalveolar complex is then reattached to the
24
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Fig. 7. Mandible fractures in 46-year old woman, who fell during a seizure (a /f). No midfacial fractures. Lateral (a) and submental (b) 3D renderings, axial (c, d) and coronal (e, f) CT reformations show loss of posterior vertical dimension (upward white arrow in a, arrowheads in f), abnormal mandibular projection (forward white arrow in a), and abnormal facial width (arrowheads in b, f). Mandibular body fracture (anterior arrow in b, arrows in e) and bilaterally displaced comminuted condylar fractures (posterior arrows in b, d, f) allow both mandibular rami (arrowheads in b and f) to displace laterally and anteriorly, resulting in abnormal facial width and increased projection. Both glenoid fossae are empty (black arrow on a, asterisks on b, c) and comminuted condyles have displaced medially and inferiorly (arrows in d and f), reducing posterior vertical dimension of mandibular buttresses.
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
upper part of the buttress as the last step in the repair sequence (Fig. 8). Preferably, the vertical dimension of the midface is set and stabilized by the precise reduction and fixation of both zygomaticomaxillary buttresses. However, in the case of comminuted injuries, the side with the less severe injury is done first and used as a reference for the other lateral buttress. Repair of the medial buttresses may help in establishing vertical dimension, but typically these buttresses are even more severely injured than the lateral buttresses. In rare cases, severe comminution of the lower ends of all the vertical buttresses will require onlay split cranial bone grafts to bridge gaps of missing bone. Although these grafts do not provide the accuracy of correctly realigned in-situ bone fragments, they will allow for an adequate restoration of vertical dimension if applied appropriately. The surgeon may choose to not apply fixation devices across this last level of reduction if there is concern that the position of the condylar heads in one or both glenoid fossae has been altered by intracapsular bleeding or edema. In these cases, the MMF is not removed but rather left in place to allow the patient to adjust the position of the palatoalveolar complex as the joint abnormality resolves and the condylar head moves to its correct position. Fixation may be applied in a second procedure 1 /2 weeks later, or the MMF can be left in place for the customary 6-week period necessary for sufficient healing of non-fixated facial fractures. Although the lack of fixation at the low maxillary level could theoretically allow the patient to elongate or shorten the midface with movement of the mandible, this is more likely to occur as an iatrogenic complication of poor surgical technique in patients who do have fixation placed [1,2]. 3.4. Orbital volume: size does matter The orbit is a conical shaped compartment contained within the buttress system of the midface (Fig. 9), and collapse of the system under external impact forces places the orbital soft tissue contents at risk for injury. Fortunately the stout ring-like osseous enclosure of the orbital aperture (anterior orbital third) provides a measure of protection to these soft tissues, and the relative weakness of the very thin floor and medial wall of the middle orbital third offers a pathway for dissipation (blow-out fractures) of forces that are transmitted to the eye. The posterior orbital third is again relatively stout bone that protects the vital structures that course through the orbital apex. The distance from the orbital rim to the optic foramen ranges from 40 to 50 mm, giving a length to each orbital third of between 13 and 17 mm [1,2,11,12]. The frontal bar forms the very strong superior orbital rim and the zygoma the strong lateral rim and the lateral aspect of the inferior rim. The frontal process of the
25
maxilla contributes the medial aspect of the inferior rim. There is no true medial orbital rim but rather a smooth confluence of the frontal process of the maxilla and lacrimal bone to provide a point for the insertion of the medial canthal tendon around the lacrimal sac (Fig. 9). This insertion is important for proper function of the lacrimal pump and maintenance of the sharp angle of the medial canthus and the length of the palpebral fissure [2,11]. The orbital roof, floor and medial wall are concave relative to each other (Fig. 9), producing the greatest diameter of the orbit approximately 15 mm posterior to the inferior orbital rim. The globe is situated at this level and the orbital floor inclines upward in an inwardly convex curve behind the globe to create a relative retrobulbar constriction (Fig. 9) that maintains the position of the retrobulbar soft tissues. Posteromedially the orbital floor slopes upward into the medial orbital wall without sharp demarcation [2]. Posterolaterally, the inferior orbital fissure separates the orbital floor from the lateral orbital wall, which is formed by the greater sphenoid wing and the frontal process of the zygoma and is sometimes referred to as the sphenotemporal buttress [13]. The tip of the orbital cone is referred to as the orbital apex, into which the optic canal and superior orbital fissure open. The apex approximates intracranial structures that include the anterior clinoid process, the carotid siphon and the cavernous sinus. Reconstruction of the orbital walls can begin only after the vertical and horizontal buttresses and thus the outer ring of the orbit have been restored and stabilized (Fig. 8). This ring then serves as the anchoring point for bone grafts or alloplastic implants that replace the fragmented bone of the middle third of the orbit (Figs. 4 and 10). Recreation of the upward convexity of the normal orbital roof, the concave anterior orbital floor, the convex posterior floor, and the obtuse angle of the transition of the floor to the medial orbital wall (lamina papyracea) offer the greatest challenges to the surgeon (Fig. 10). Because of the inherent difficulty in forming an exact duplication of these gently curving osseous surfaces, over- or undercorrection may occur, leading to altered orbital volume, the primary cause of enophthalmos or less commonly exophthalmos. For example, fractures of the orbital floor almost always involve the concave portion of the floor, starting at the inferior orbital groove (locus minor resistentiae) and extending posteriorly into the retrobulbar convexity and medially at least to the junction of the floor with the medial wall [2]. Reconstruction of the entire floor defect at the level of either the concavity or the convexity will alter orbital volume as will failure to reproduce the obtuse angle with the medial wall. Orbital volume changes exceeding 1.5 ml (i.e. /5% of the normal orbital volume) may lead to an asymmetry in globe position of greater than 2 mm, a relatively small amount that will be noticeable in some
26
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Fig. 8. Vertical dimension. Same patient as in Fig. 6. Anterior 3D view (a) shows intact frontal bar and bilaterally disrupted comminuted medial and lateral buttresses, and orbital rims. Axial CT (b) shows comminution and retrusion of superior medial buttresses and nasal septum into ethmoidal cells (arrows on b). Reduction and fixation of zygomaticofrontal suture diastasis, shown on coronal CT (arrows in c), is usually first step in operative repair sequence. Longitudinal paramedian fracture repair of right hard palate (arrows in d, axial CT also shows posterior buttress fracture) is mandated prior to restoration of anterior vertical dimension of midface (vertical buttresses). Postoperative 3D renderings from CT (e, f) show internal fixation of buttresses (see also Fig. 4) and nasal bone graft (arrow in e). Bilaterally increased orbital volume is appreciated on 3D rendering (a), axial (b), and coronal (c) CT images. Right medial orbital wall is comminuted with fracture fragment (asterisk on b) impinging on right optic nerve in right orbital apex.
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
27
Fig. 9. Photography of dry bone preparation of normal left orbit. Orbital roof, floor, and medial wall are concave relative to each other anteriorly (short white arrows). More posteriorly, orbital floor inclines upward, creating retrobulbar constriction (asterisk). Medial orbital wall (long white arrow) and orbital floor (black arrow) meet at an obtuse angle without sharp demarcation. Characteristics of orbital shape need to be recreated surgically to restore correct orbital volume (see also Figs. 4 and 11). NC, nasal cavity; NB, nasal bone; LF, lacrimal fossa; O, optic foramen; SOF, superior orbital fissure; IOF, inferior orbital fissure.
patients after all swelling has subsided postoperatively [2]. Therefore, floor injuries recognized to affect more than one curved surface of the floor and/or both the floor and medial orbital wall generally require complex reconstructions with specific placement and stabilization of bone grafts or alloplastic implants (Fig. 4). 3.5. Displacement of bone fragments into the orbit and fractures involving the orbital apex Traumatic blindness (Figs. 8 and 11) occurs in about 3% of patients who suffer blunt facial trauma [13] and abnormal CT findings are present in almost all of these cases. Only rarely are both eyes affected and most often the unilateral loss of vision is diagnosed at the time of admission in an awake patient who can describe the visual disturbance. In addition to a thorough ophthalmological examination, prompt radiological evaluation is mandated in these patients, as it is possible that the images will demonstrate a condition that might respond to timely though in many cases controversial surgical intervention. Perhaps of even more importance is the demonstration of the same findings on images obtained during the evaluation of facial injuries in an unconscious or uncooperative patient following blunt trauma. Visual acuity cannot be measured in these patients and the available clinical testing is only suggestive of possible
Fig. 10. Abnormal orbital volume in same patient as Fig. 1. Left orbital floor fracture with loss of angulation in relation to medial orbital wall is shown on coronal CT reformations (a, orthogonal to FH) causing increased orbital volume and herniation of orbital contents into left maxillary sinus. Right orbital floor and volume are normal (a). Loss of relative retrobulbar orbital constriction (arrow in b) is shown on sagittal oblique CT reformations, reconstructed parallel to the optic nerve. Bone fragment is present superiorly, where normal left orbital roof curves upward (arrowhead in b).
decreased visual acuity. Because loss of vision does not automatically accompany orbital injuries of equal severity in every patient, most surgeons are hesitant to perform a ‘‘sight saving’’ surgical procedure without documentation of loss of vision. However, the medical alternative of short-term megadose steroid therapy might be considered to be an acceptable prophylactic
28
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
orbit is the equivalent of unknowingly operating on an only-seeing-eye. Many surgeons are adamant that reconstruction of an orbit that houses an only-seeingeye is contraindicated for fear that in the unlikely event of an iatrogenic injury to this eye, the patient will be totally blind. Even for patients who are alert and have no evidence of visual disturbances, the surgeon must be aware of the presence of these types of injuries so that options of a modified surgical approach that requires less surgical manipulation of the orbital soft tissues can be considered.
4. Imaging approaches CT is highly accurate at detecting and characterizing surgically important injuries. It does not, however, precisely show the magnitude of osseous fragmentation in complex fractures seen at surgery, regardless of CT technique. Maxillofacial CT delivers significant radiation dose to the orbits (potentially associated with premature lens opacification), and scan extension to include the mandible is associated with clinically meaningful radiation to the soft-tissues of the neck (e.g. thyroid), an especially important consideration in pediatric populations [15]. 4.1. Optimization of axial image acquisition (raw data)
Fig. 11. Carotid canal and optic canal fracture extension in a 25-yearold man, who fell from a height of 7 m sustaining skull base fracture. Fracture line extends into sphenoid bone at internal orifice of optic canal (arrows in a, axial CT reformations), causing traumatic optic neuropathy of the right optic nerve. Carotid canal fractures (arrows in b) may require angiographic evaluation. Use of Rowe’s maxillary disimpaction forceps may be contraindicated if LeFort fractures extend into carotid canal or orbital apex.
alternative in some of these patients while waiting for the mental status to improve [14]. In patients whose mental status has not improved but repair of the facial fractures is indicated because of the passage of time, further deferment of repair of both orbits might be appropriate if one side has findings known to be associated with loss of vision. Blindness due to the injury itself could be attributed unfairly to the surgical manipulation of the involved eye, and repair of the other
Images can be obtained either directly in axial and coronal planes, directly in either axial or coronal plane with reformations in the orthogonal plane, or as reconstruction from a CT of the cranium obtained from an appropriately prescribed study (i.e. 1.00 /1.25 mm slice thickness). In general, direct acquisition in orthogonal planes at 3 mm contiguous slice thickness has been the standard of care in outpatient practice settings. However, with the evolution of spiral CT, and especially multidetector spiral CT, 1.0 /1.25 mm thin sections in the axial plane are reformatted into the orthogonal planes, without loss of image quality, accuracy and without further radiation. For example, if a multidetector CT scanner is used for the head scan using 5 mm slice thickness, in which the 5 mm are composed of four 1.25 mm channels, postprocessing allows for separation of the information from each of those channels to create individual 1.25 mm slice thicknesses. This data can then be used to provide the raw data for maxillofacial CT planes in various spatial planes without further radiation exposure to the patient [16]. Primary axial images are obtained parallel to the FH plane using 1.0 /1.25 mm slice thickness from above the frontal sinus through the hard palate or maxillary alveolus. The scan is usually extended to include the mandible in all cases of suspected midfacial fractures to
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
29
image the entire buttress system and aid surgical planning [2,7]. Precise axial alignment of the patient’s head in the center of the scanner gantry and alignment of the scanning plane with FH (i.e. gantry tilt) are important to obtain raw data parallel to the FH plane. Only symmetric images allow cephalometric measurements (projection, width, vertical dimension) directly on CT studies for side-to-side comparison. This is especially important if surgical repair is evaluated intraoperatively [17].
4.2. Optimization and orientation of reformations Precise positioning of a severely injured patient within the CT scanner may be difficult or impossible (Fig. 12). Thin-cut axial CT images acquired with the head not in symmetric standard axial position should be considered for off-line axial reconstruction on an imaging workstation without blocking access to the CT scanner and decreasing CT throughput. This set of symmetric secondary axial images easily allows creation of orthogonal coronal and sagittal reformations. However, three reference points (left and right orbitale, left and right porion), which define the FH plane, will never lie in one single image guide (e.g. sagittal, Fig. 13), which is used for definition of the axial reformations. In our experience, intracranial reference points closer to the median sagittal plane are usually helpful. In severe cases of midfacial trauma with bilateral fracture and displacement of the inferior orbital rim (orbitale), axial CT images may be aligned parallel to FH. The nasal surface of the hard palate is commonly used as a proxy. Our experience is that the planum sphenoidale, which is normally parallel to the nasal surface of the hard palate and FH, may serve as an acceptable proxy if the hard palate is fractured in addition to both inferior orbital rims. Analogous to reconstructive surgery, we find that relating axial reformations to uninjured anatomic reference points is most successful for the creation of symmetric secondary axial images parallel to FH. In our experience, on the workstation a post-processing mode should be chosen, which displays axial, sagittal, coronal and 3D images simultaneously (Fig. 13). If both, the sagittal and coronal guide images are used with ‘oblique axes’ function, orientation of the new axial reformations will change automatically, as the sagittal and coronal axes are aligned parallel or orthogonal to the FH plane. The position of FH in relation to the axial, coronal and sagittal reformations can easily be checked on threedimensional renderings (Fig. 13). Reformations in the coronal plane should be perfectly orthogonal to the symmetric axial images, such that true coronal plane images are obtained. Sagittal plane image reformation may be performed either relative to the coronal plane or as sagittal obliques parallel to the optic
Fig. 12. Axial CT reformations in same patient as Fig. 1. Original axial CT images obtained ‘out of plane’ (a) do not allow side-to-side comparison of malar eminence position. Axial reformations reconstructed parallel to FH (b) show normal anatomy of uninjured right side in same image as injured left zygoma, allowing measurement of fracture displacement in relation to intact facial buttresses and skull base, and facilitating operative planning.
nerve (Fig. 11), if evaluating anatomic constrictions of the orbital floor and roof. Images are reconstructed using both soft tissue and bone algorithms and viewed using soft-tissue and bone windowing, respectively.
30
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Fig. 13. Reconstruction of ‘out-of-plane’ maxillofacial CT reformations of 39-year-old man after assault without fracture. For image optimization of raw data we display sagittal, coronal, axial, and 3D reformations simultaneously on workstation (a /d) with ‘oblique axes’ function active (right lower corner radio button on a /c). Aligning the sagittal axis parallel to hard palate or planum sphenoidale (horizontal lines on a) automatically carries over to coronal (b) and axial (c) reformations. Similarly, coronal axis (horizontal line in b) is oriented along uninjured bilateral symmetric anatomic landmarks (e.g. glenoid condyles, left and right porion). Resulting axial reformations are parallel to FH (left and right porion and orbitale are shown in c), which are batched for entire dataset and stored on PACS. Plane of reformation is easily checked and corrected using 3D rendering (FH in d).
5. Summary Operative planning of complex midfacial fractures depends on optimal imaging with CT scanning as the imaging modality of choice. Optimal imaging technique is dependent upon displaying the facial anatomy orthogonal to the relevant reference planes used for surgical repair, usually the FH plane.
Careful attention to patient position within the gantry of the CT scanner is the easiest way of directly obtaining symmetric axial images parallel to FH. Reformation of axial CT images parallel to FH should be considered in cases where the face is not bilaterally symmetrically positioned on the original axial images to aid side-to-side comparison of craniometric measurements during surgical repair. Coronal CT reformations should be obtained strictly orthogonal to FH.
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Differences in surgical and radiological terminology may impede inter-specialty communications (see Appendix A).
Acknowledgements We would like to thank our medical illustrator David W. Ehlert, M.A.M.S., C.M.I. for creating such great graphics (Figs. 2 /4).
31
[16] Bushberg JT, Seibert JA, Leidholdt EMJ, Boone JM. The Essential Physics of Medical Imaging, second ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2001:933. [17] Stanley RB. Use of intraoperative computed tomography during repair of orbitozygomatic fractures. Arch Facial Plast Surg 1999;1:19 /24. [18] Borman H, Ozgur F. A simple instrument to define the Frankfurt horizontal plane for soft- tissue measurements of the face. Plast Reconstr Surg 1998;102:580 /1.
Appendix A References [1] Gruss JS, Whelan MF, Rand RP, Ellenbogen RG. Lessons learnt from the management of 1500 complex facial fractures. Ann Acad Med Singapore 1999;28:677 /86. [2] Stanley RBJ. Maxillofacial trauma. In: Cummings CW, Frederikson JM, Harker LA, Schuller DE, Krause CJ, Richardson MA, editors. Otolaryngology: Head and Neck Surgery. St. Louis: Mosby-Year Book, 1998:453 /85. [3] Gentry LR, Manor WF, Turski PA, Strother CM. High-resolution CT analysis of facial struts in trauma: 1. Normal anatomy. Am J Roentgenol 1983;140:523 /32. [4] Gruss JS, Mackinnon SE. Complex maxillary fractures: role of buttress reconstruction and immediate bone grafts. Plast Reconstr Surg 1986;78:9 /22. [5] Forrest CR, Phillips JH, Prein J. LeFort fractures. In: Prein J, editor. Manual of Internal Fixation in the Cranio-Facial Skeleton. Berlin: Springer, 1998:108 /26. [6] Manson PN, Hoopes JE, Su CT. Structural pillars of the facial skeleton: an approach to the management of Le Fort fractures. Plast Reconstr Surg 1980;66:54 /62. [7] Manson PN. Organization of treatment in panfacial fractures. In: Prein J, editor. Manual of Internal Fixation in the Cranio-Facial Skeleton. Berlin: Springer, 1998:95 /107. [8] Manson PN, Clark N, Robertson B, et al. Subunit principles in midface fractures: the importance of sagittal buttresses, soft-tissue reductions, and sequencing treatment of segmental fractures. Plast Reconstr Surg 1999;103:1287 /306. [9] Stanley RB, Jr. The zygomatic arch as a guide to reconstruction of comminuted malar fractures. Arch Otolaryngol Head Neck Surg 1989;115:1459 /62. [10] Schilli W. Mandibular fractures. In: Prein J, editor. Manual of Internal Fixation in the Cranio-Facial Skeleton. Berlin: Springer, 1998:57 /93. [11] Manson PN. Orbital fractures. In: Prein J, editor. Manual of Internal Fixation in the Cranio-Facial Skeleton. Berlin: Springer, 1998:139 /47. [12] Rhea JT, Rao PM, Novelline RA. Helical CT and threedimensional CT of facial and orbital injury. Radiol Clin North Am 1999;37:489 /513. [13] Stanley RB, Jr, Sires BS, Funk GF, Nerad JA. Management of displaced lateral orbital wall fractures associated with visual and ocular motility disturbances. Plast Reconstr Surg 1998;102:972 /9. [14] Levin LA, Beck RW, Joseph MP, Seiff S, Kraker R. The treatment of traumatic optic neuropathy: the International Optic Nerve Trauma Study. Ophthalmology 1999;106:1268 /77. [15] Brenner D, Elliston C, Hall E, Berdon W. Estimated risks of radiation-induced fatal cancer from pediatric CT. Am J Roentgenol 2001;176:289 /96.
Glossary of terms frequently used with facial fracture reconstruction Buttress support Refers to the direction of force that is resisted by an osseous buttress. Not necessarily the same as bone orientation. For instance, even though the hard palate is oriented horizontally, it also resists antero-posterior impact, thus providing some sagittal buttress support Central fragment Key component of the naso /orbito /ethmoidal complex, bearing the insertion of the medial canthal ligament (MCL), located anterior to the lamina papyracea External arcs of contour Horizontal and vertical lines defining the position of the malar eminence in space [9] Frankfurt Horizontal Plane (FH) Standard craniometric reference plane used in maxillofacial surgery; passing through three of the following four reference points: the left and right porion and left and right orbitale. FH was originally introduced at an anthropological conference in Frankfurt, Germany, in 1884 [18]. Historically, FH was drawn on lateral photoor radiographs. (SYN: orbitomeatal plane, auriculo / infraorbital plane, ear /eye plane) Frontal bar Superior-most horizontal buttress. It consists of the thickened frontal bone, which bridges between the frontozygomatic sutures [2]. The superior orbital rim and the glabella are part of the frontal bar. The frontal bar serves as a key superior support in facial fracture stabilization from which the midface is suspended Maxillo-mandibular fixation (MMF) Fixing the correct interdigitation of the maxillary and mandibular teeth with arch bars and wires
32
K.F. Linnau et al. / European Journal of Radiology 48 (2003) 17 /32
Medial canthal ligament (MCL) Medial tendon maintaining shape and position of the medial canthus NM Naso-maxillary buttress (SYN: medial buttress): anterior alveolar process of maxilla, along piriform aperture, frontal process of maxilla to frontal bone Occlusal plane Imaginary surface anatomically relating the cranium to the incisal edges and occluding surfaces of the teeth (SYN: bite plane) Ophthalmoplegia Paralysis of one or more of the ocular muscles Orbitale Craniometric reference point on the lowest point of the infraorbital rim Porion Craniometric reference point at top of external auditory meatus Projection Depth; refers to antero /posterior dimension of face, while ‘width’ describes left-to-right, and ‘height’ cranio / caudal dimension Quadripod fracture Anatomically incorrect term for ZMC fracture: the zygomatic bone is supported by five structures
Reid’s baseline Line connecting orbitale with center of external auditory meatus, roughly parallel to the hard palate, clinically used synonymously with FH Sphenotemporal buttress Relatively weak buttress formed by the frontal process of the zygomatic bone, the greater wing of the sphenoid bone, and the squamous portion of the temporal bone. Commonly injured in impacted fractures of the lateral orbital wall Tripod fracture Anatomically incorrect term for zygomatico /maxillary complex (ZMC) fracture: the zygomatic bone is supported by five structures Trimalar fracture Anatomically incorrect term for ZMC fracture: the zygomatic bone is supported by five structures Vertical dimension Vertical relationship of facial structures (SYN: facial height) ZM Zygomatico /maxillary buttress (SYN: lateral buttress): lateral alveolar process of maxilla, zygomatico /maxillary suture, malar eminence of zygoma, zygomatic process of frontal bone. This buttress forks at the malar eminence to give off the zygomatic arch in the sagittal direction