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Biplanar Plating of Mandibular Fractures
A New Concept With In Vitro Testing and Comparison With the Traditional Plate-and-Screw Technique
Sara Pieri, MD;
K. Holly Gallivan, MD, MPH;
David Reiter, MD, DMD
Arch Facial Plast Surg. 2002;4:47-51.
ABSTRACT
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Objectives To introduce the concept of biplanar plating of mandibular fractures
and to present an in vitro comparison of this method with traditional use
of a single mandibular plate.
Design A device for the delivery of repetitive simulated masticatory stress
to mandibular models was developed. Using the device, we compared biplanar
with single-plate fixation of vertical mandibular body fractures by determining
cycles to failure.
Setting Tertiary care academic medical center.
Intervention A simulated masticatory force was delivered vertically to the anterior
end of polymer hemimandibles as used for in vitro teaching of plating methods.
Mobility at the fracture site was tested at intervals corresponding to 6000
chewing cycles each.
Results Of 5 specimens plated with a mandibular fixation plate, 4 developed
greater than 0.010 cm of vertical mobility at the fracture site after 12 000
cycles. Only 1 of the 5 specimens fixed with biplanar plating developed this
degree of mobility.
Conclusions Single-plate fixation of mandibular fractures is greatly enhanced by
a miniplate spanning the fracture along the inferior border. We used this
technique on 15 patients with unfavorable fractures and found it simple, secure,
and reliable. We had no complications. An inferior marginal plate serves the
same function as a tension band, and can be placed on mandibles through the
same incision as the main fixation plate without additional dissection. We
prefer this to a traditional tension band when the percutaneous route of access
to a mandibular fracture site is used.
INTRODUCTION
IN THE 60 YEARS since Adams1 described
open reduction and internal fixation of facial fractures with interosseous
stainless steel wiring, mandibular fracture repair has evolved through a series
of materials and methods. We have progressed far beyond simple wire loops
placed through burr holes in bone, and have plating systems of great sophistication
(and, in some cases, complexity). There are systems with screws having threaded
heads and shanks, systems with hollow screws for osseointegration, and even
systems with absorbable plates and screws. But the gold standard for primary
plate fixation of mandibular fractures remains the single plate on the buccal
cortex.
There are few studies in the literature on in vitro testing of mandibular
fracture fixation. Those studies that are found use synthetic or cadaver mandibles
in a common cantilever beam device. A recent article by Fedok et al2 introduced the idea of a tension band placed in a
different plane from the fixation plate (but still on the buccal cortex),
which Fedok et al termed biplanar plating. Because
we had been using this term for several years in reference to the placement
of a 1.7-mm miniplate along the inferior mandibular border in addition to
a standard 2.4-mm plate on the buccal cortex, we were stimulated by the in
vitro study by Fedok et al to test our technique against monocortical plating
with a neutral (ie, noncompression) 2.4-mm mandibular reconstruction plate.
We wanted to establish whether and to what degree the addition of a small
inferior cortex plate increases stability of fixation of mandibular body fractures.
MATERIALS AND METHODS
As with other in vitro studies, polystyrene mandibles, with a rigid
outer cortex and a trabecular medullary space, were used to simulate physiologic
properties. These uniform sample mandibles are preferred because they eliminate
the variability associated with cadaveric mandibles, and do not undergo changes
in physical properties with drying. A band saw with a fine blade was used
to create linear fractures in the body of each test mandible just distal to
the second molar, in a standardized fashion and with neither favorable nor
unfavorable angulation. Following manual reduction of the fractures, 5 of
the hemimandibles were stabilized using a standard, neutral, 2.4-mm mandibular
plate on the buccal cortex, with 2 screws on either side of the fracture.
A 1.7-mm miniplate was placed along the inferior border of 5 specimens in
a plane perpendicular to the main fixation plate, also with 2 screws on either
side of the fracture. The other 5 specimens were stabilized with neutral mandibular
plates identical to those on the buccal cortices of the first group, but without
the addition of a miniplate on the inferior cortical surface (Figure 1).
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Figure 1. Biplanar (top) and monoplanar
(bottom) plate application.
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The test mandibles were secured by a 0.794-cm stainless steel rod with
0.008 cm of clearance in precision-drilled holes through the condyles. The
fracture lines and plates were coated with a thin application of silicone
caulking to simulate the viscoelastic properties and vibration-dampening effect
of the native soft tissue adherent to in vivo fractures. Testing was conducted
in a jig that stabilized the proximal mandibular fragment on a firm elastic
polymer to simulate the muscular sling of the medial pterygoid and masseter.
Vertical forces were then applied to the central incisors by rotating a motor-driven
camshaft against the specimens to deliver forces similar in magnitude and
direction to those of natural chewing (Figure
2).
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Figure 2. The test fixture.
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The test device delivered about 12 000 "bites" per hour to 5 specimens
simultaneously, with an applied force of approximately 36 kg/cm2
at the incisal edge. For reference, the range of force per unit area on the
biting surfaces of natural teeth during biting and chewing varies from a few
grams per square centimeter to more than 150 kg/cm2. Vertical mobility
at the fracture site was determined every 30 minutes, using a dial gauge to
measure excursion of the point to which force was applied (Figure 3). The same steel flat-head screw to which force was applied
was used as the reference point for measuring mobility. Measurement was made
in hundredths of a centimeter per kilogram of distractive force (keeping in
mind that this measurement refers to movement at the measuring point, not
the fracture). The 10 model mandibles were tested for longer than 90 minutes,
during which a total of 18 000 simulated bites were delivered. Each group
of 5 was tested simultaneously. After 18 000 chewing cycles, the plates
and screws were examined to determine the mode(s) of failure (defined by obvious
loss of fixation and corresponding to fracture site mobility in excess of
0.005 cm/kg of distractive force). The distance from the point of application
of force (where mobility was measured) to the intersection of the plate with
the fracture line was 5.715 cm on all specimens. Simple geometric calculations
were used to determine the actual mobility at the fracture site, using an
estimated hypotenuse of 0.254 cm to approximate mobility within the fracture
line. This produces a value somewhat in excess of the actual mobility at the
bony interface.
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Figure 3. Measurement of mobility using
a dial gauge.
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RESULTS
The biplanar technique held 4 of 5 fractures secure through 18 000
cycles. The single-plate technique failed in 4 of 5 specimens after 12 000
cycles or less (Table 1). Because
of the small numbers in the test group, the difference just achieved significance
at P = .05 using the  2 test. However,
the Fisher exact test offered a "left-hand P" of
>.99 to support the apparent significance of this difference in so small a
pilot study. None of the plates broke, and all failures were attributable
to loss of integrity of the threads in the bone with loosening of the screws.
Interestingly, not all of the screws loosened equally on any plate. It was
the outer 2 that were loosest on all but one of the failed plates.
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Results With the Single- and Double-Plate Techniques
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COMMENT
Adams1 described open reduction and internal
fixation of facial fractures using interosseous stainless steel wiring in
1942. He found this method to be "far simpler and more satisfactory than the
use of extra-oral appliances attached to plaster headcaps,"1(p523)
and spawned the modern era of facial fracture management. The reduction and
immobilization of mandibular fractures with internal fixation subsequently
evolved from loops of stainless steel wire threaded through holes drilled
in bone to the use of plates made of stainless steel or more technologically
advanced biomaterials like chrome-cobalt alloy (Vitallium) and titanium. Despite
the wide variety of sizes, shapes, and characteristics of available plating
systems, all share the principle of direct fixation to the fracture fragments
with screws passed through holes in the plate. Furthermore, all have used
a single plate for fixation, occasionally aided by a smaller plate in the
same plane, known as a tension band, to minimize separation of the superior
limit of the fracture.
Into the 1970s, research on mandibular fracture fixation with plates
and screws was far advanced in Europe compared with the United States, resulting
in the development of an assortment of plates and techniques from overseas.
Luhr,3 in 1968, published his technique using
biocompatible chrome-cobalt alloy plates with eccentric holes, combined with
screw heads having a conical shoulder beneath the head. This produced axial
compression of the fragments across the fracture line. The dynamic compression
plate was introduced by Allgower et al4 in
1969 for use on extremity fractures. Allgower's colleague, Spiessl,5 then applied these plates to the mandible. Spiessl's
presentation in 1982 of a series of 700 complicated mandibular fractures reduced
and stabilized with various plates and techniques really focused attention
on more sophisticated methods than the simple interosseous wiring most often
used in the United States at the time. Spiessl's infection rate of 4% in 186
patients, with long-term follow-up, further impressed the North American facial
plastic surgery community. These statistics, from patients treated with the
Arbeitsgemeinschaft Osteosynthesefragen Association for the Study of Internal
Fixation system, along with the new availability of versatile plating systems
from other manufacturers, brought plate-and-screw fixation to the forefront
of mandibular fracture management by the mid-1980s.
The miniplate system was introduced by Benoit et al,6
tested by Michelet and Deymes,7 and refined
by Champy et al.8 Placing smaller plates required
less soft tissue dissection, minimizing surgical trauma yet achieving extremely
stable fracture fixation. Champy et al did some of the first in vitro studies
to determine the multiple forces at work in mastication. They also used a
compression plate and a tension band in the same plane to fix fractures in
the mandible.
Schmoker9-10 and colleagues
also performed several in vitro studies comparing and testing eccentric compression
plates and tension bands, using a cantilever beam model and synthetic mandibles.
They, too, noted that a 2-plate system provided more resistance to vertical
deformation.
Rigid internal fixation with plates and screws has been compared extensively
with intermaxillary fixation, alone and in combination with interosseous wiring.
No clear consensus or preference exists in the literature. There are several
advantages to the plate-and-screw method. Absolute immobilization of fracture
lines allows for early function of the mandible, minimizing disuse muscular
atrophy and temporomandibular joint dysfunction. Lack of time or shortened
time in an immobilization mandibular fracture provides for improved oral hygiene,
adequate nutritional intake, communication, and airway management. Plate-and-screw
repair is associated with lower infection rates and improved overall outcome
compared with interosseous wires.11 However,
Terris et al12 report in their series that
wires are more cost-effective and have a lower incidence of major complications.
Leach and Truelson13 also advocate an immobilization
mandibular fracture and interosseous wiring. They found that their patients
treated with newer techniques had a greater incidence of infection, nerve
injury, and unavailability for follow-up. Valentino et al,14
in their series of 287 patients during a 5-year period, showed that monocortical
miniplate fixation is a reliable method for achieving rigid immobilization.
They compared their results with those of others using compression plating
and found monocortical miniplate fixation to be comparable.
The key to fracture healing is rigid fixation of bone-to-bone contact.
Any mobility at the fracture site can lead to infection, poor healing, malunion,
or even nonunion and osteomyelitis. There are several forces operating on
the mandible during function. When loaded by mastication, there is a distracting
force along the alveolar ridge and a compressing force along the inferior
border. The complexity of the forces delivered to the mandible must be understood
for proper fixation of fracture sites. Distractive and compressive forces
can act along the same fracture line at different times during mastication.
Spiessl5 and Champy et al8
understood and considered this in their approaches to rigid fixation. Spiessl
applied an arch bar as a tension band to resist the distractive force along
the alveolar ridge. He advocated a compression plate at the basal border to
provide compression across the fracture. This combination provides adequate
compression along the entire length of the fracture and resists distraction
in the superior part of the fracture. As described by Marentette,15 Champy et al tested various plating schemes on cadaver
mandibles subjected to various forces, and studied the biting forces applied
to different areas of the mandible in human subjects. Armed with this knowledge,
they determined the optimal areas for plating, deemed "Champy's Ideal Line
of Osteosynthesis." The principles of Champy et al involved the use of a tension
band with monocortical screws at the superior border of the mandible and a
noncompression miniplate at the inferior border—but both plates were
in the same vertical plane. This combined the concept of stabilization with
neutralizing tension using 2 plates in the same plane.
The goal of rigid internal fixation is the achievement of rapid primary
bone healing, with solid union of the fracture fragments, without compromising
oral health and jaw function. Plate-and-screw techniques, using compression
or noncompression plating, decrease the incidences of infection, malunion,
and nonunion in patients while avoiding or decreasing time in maxillomandibular
fixation. Without time in maxillomandibular fixation, patients load the mandible
early in the bone-healing process. This requires fixation that is secure despite
the forces of mastication. Plate failure was observed by Ardary,16
who presumed the mechanism of failure to be faulty screw placement, although
he attributed loose screws to dietary noncompliance causing premature loading
of the mandible. Haug et al,17 in their studies,
reported that 100% of plate failures were due to loosening of monocortical
screws securing tensions bands at the superior border of the mandible. Suboptimal
bone health was also thought to contribute to loosening of screws under loading
forces.
In the 1998 study cited earlier, Fedok et al2
did not account for the soft tissue that suspends the native mandible, nor
did they consider the viscoelastic nature of in vivo mandibular suspension.
We attempted to simulate this by using a viscoelastic polymer to coat the
fracture and plates, and by supporting the angle of each test hemimandible
on a 2.540-cm thick roll of dense silicone polymer. We also believed that
the vector forces applied to the mandible were not accurately simulated by
the rigid fixation of the test mandibles at the condyle. By suspending the
test mandibles on a well-fitted round shaft through the condyles, rotation
of the proximal fragment is permitted, similar to that of the mandible during
chewing. We recognize that the translational component of physiologic condylar
motion is missing, but do not believe that this is important because identical
forces are being delivered to all test specimens. Furthermore, a minimal translational
component would affect all specimens slightly, if at all, and in the exact
same way.
Our device, therefore, more precisely portrays the masticatory forces
at work during function than others previously described. Because our fractures
were within the body, as opposed to through the angle, we cannot directly
compare our findings with those of Fedok et al.2
However, we conclude that biplanar plating is superior to monoplanar plating,
as did Fedok et al.
We have also used our technique on 15 mandibular fractures during the
past decade, without operative or healing complications. Because the small
plates on the inferior mandibular border are not readily demonstrable on postreduction
films, we are unable to demonstrate this radiographically.
CONCLUSIONS
Placement of a small (1.7-mm) linear plate along the inferior mandibular
border across mandibular body fractures greatly increases the stability of
traditional buccal cortex plating when exposed to the forces of mastication.
This technique is especially useful when access to extended lengths of intact
mandible is difficult and only 2 screws can be used to secure a buccal cortex
plate on either side of a fracture. The tiny plates and screws are not radiographically
demonstrable on plain postreduction films, because of their small size and
because they are placed in the horizontal plane of the inferior mandibular
cortex, presenting a small profile to the x-ray beam.
Use of a miniplate on the inferior mandibular border in addition to
a buccal cortex plate may add significant security to the repair of mandibular
body fractures and obviates the need for a tension band. Placement is quick
and easy through percutaneous access, and minimizes the extent of dissection
compared with placement of a tension band when the percutaneous route of access
is chosen.
AUTHOR INFORMATION
Accepted for publication January 23, 2001.
This study was presented at the meeting of the American Academy of Facial
Plastic and Reconstructive Surgery, Orlando, Fla, May 13, 2000.
Corresponding author: David Reiter, MD, DMD, Department of Otolaryngology–Head
and Neck Surgery, Jefferson Medical College, 925 Chestnut St, Sixth Floor,
Philadelphia, PA 19107 (e-mail: david.reiter{at}mail.tju.edu).
From the Department of Otolaryngology–Head and Neck Surgery,
Jefferson Medical College, Philadelphia, Pa.
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