Sunday, July 31, 2011

A Note On Use of Resorbable Plates and Screws in Pediatric Facial Fractures.......with pdf Download

The pediatric facial trauma patient provides several different considerations that are not present in the adult. First, the pediatric patient has the tremendous advantage of an accelerated ability to heal in a very short time with few complications, aided by the well-vascularized tissues of the face. Second, through the assistance of growth and an inherent ability to adapt, recovery of damaged orofacial tissues and function is much better than in the adult. Despite these advantages, certain distinctions do exist in the pediatric facial trauma patient that must be considered. This includes an appreciation of the unique characteristics and anatomy of the developing immature face, the different facial injury patterns from certain trauma risk exposures that occur in the pediatric patient, and the potential growth implications from traumatized facial structures that make long-term follow-up of these patients important. These factors, combined with the relatively limited experience of most clinicians with significant facial injuries in children due to their low incidence, may make certain treatment decisions different than what one might do in the adult. In this post, the term pediatric facial fractures will refer to fractures in those children under the age of 10 with an incomplete permanent dentition. Children older than 10 years of age are essentially treated as adults, where the advantages of resorbable fixation over metal implants are in many cases more obscure.

Resorbable Fixation Devices
Although a variety of resorbable bone fixation devices of differing polymer compositions are currently available for craniomaxillofacial applications, this author has exclusively used co-polymer plates and screws composed of 82% polylactic and 18% polyglycolic acid (PLLA-PGA, LactoSorb; Walter Lorenz Surgical, Jacksonville, FL). Their long history of uncomplicated use in cranial vault surgery, favorable biomechanical properties, and a confirmed  resorption time of 1 year or less make them ideal for the pediatric patient. The use of resorbable plates and screws involve 2 differences from similar-appearing metal devices. First, complex bending of the plates requires a heat source to allow the polymer chains to bend and not fracture. The mandible and forehead, however, have relatively flat and gently curved surfaces, which do not require enough bending to make this a concern. In the zygoma and orbit, more complex shaping of the plates may be needed. The placement of resorbable screws requires pretapping the screw threads before screw insertion, which is a 2-step process (ie, drilling and tapping).

Mandible Fractures
FIGURE 1. Resorbable plate and screw fixation (1.5 mm) of bilateral mandible fractures in a 4-year old girl. A, Reduction of left parasymphyseal 
fracture. B, Reduction of right angle fracture with a superior border plate. C, Centric occlusion obtained by free hand technique.

Pediatric mandible fractures are uncommon and have been treated by a wide variety of fixation methods. Incomplete or nondisplaced fractures as well as fractures of the subcondylar region are treated by traditional methods of a soft diet or closed reduction. Displaced fractures are better served by open reduction and internal fixation (ORIF).
Rigid metal fixation of mandibular fractures in children, however, can be complicated by a mixed dentition that can occupy the entire vertical dimension of the bone and places teeth and the inferior alveolar nerve at risk during screw insertion. In addition, on-going development of the mandible poses risk of intrabony translocation of metal plates and screws, risking potential growth and teeth disturbances and difficulty with secondary removal if needed. The goal of ORIF is a balance between stability of the fracture site and the potential risks of operative exposure of the bone. In children, this balance is particularly precarious as the implantation time of the metal devices is essentially for most of the patient’s lifetime. For these reasons, the use of resorbable fixation implants in developing facial bones is particularly appealing. Given the location of mixed dentition throughout the bone and the course of the inferior alveolar nerve, ORIF of the mandible in children uses smaller-gauge resorbable miniplates with monocortical screws. As the pediatric mandible is fairly malleable, fractures tend to be less displaced and rarely comminuted. Because the dentition is often mixed and more bone growth is expected, absolute compression of the fracture edges together is not necessary. These considerations, in conjunction with the difficulty in applying arch bars in the mixed dentition, allows for the use of a free hand technique during fracture repair. Fractures are usually exposed through an intraoral approach unless an existing laceration allows for direct access to the bone through the skin. Once the fracture site is prepared, the bone edges are manually reduced while the dentition is held together in centric occlusion by an assistant. A 1.5-mm resorbable plate with at least 2 screw holes on each side of the fracture is held along the inferior border of the mandible in tooth-bearing regions. A short drill bit (1.1 mm in diameter, 5 mm in length) is used to place bone holes through the desired screw positions on the plate. The drill holes are through the outer cortex only so as to avoid drilling into unerupted teeth. A hand-held tap (1.5 mm) is then used to cut the screw threads. Resorbable screws (1.5 mm in diameter, 4 or 5 mm in length) are inserted until flush with the plate (Figs 1, 2 ). In most cases, 1.5-mm plates usually provide adequate fixation.
FIGURE 2. Resorbable plate and screw fixation (1.5 mm) of severely displaced left mandibular parasymphyseal fracture in a 5-year-old boy. A,Magnitude of mandibular arch displacement. B, Intraoral exposure of fracture. C, Reduction and fixation of fracture with 1.5-mm plates and monocortical screws. D , Postoperative panoramic radiograph showing fracture alignment and screw holes around developing tooth buds.

The free hand technique for maintaining a centric occlusion before plate fixation works fairly well for most isolated pediatric mandibular fractures. However, alignment of the visible buccal cortex does not always guarantee a perfect occlusal result, particularly in mandibular injuries with obliquely oriented fractures. In these fracture patterns, the lingual cortex may be misaligned and a gap on this side of the mandible may persist. Unlike fixation with more rigid metal plates, resorbable plates cannot really be overbent and their physical properties merely allow them to lie passively against the bone. Such lingual misalignment cannot be easily corrected by these less rigid resorbable plates. Because this classic principle of mandibular fixation cannot be effectively used, it is therefore important to carefully check occlusal interdigitation after resorbable plate placement.
When mandibular fracture alignment cannot be easily reduced or held properly in centric occlusion, an  alternative technique is to place temporary wire ligature reduction across the fracture site (Fig 3 ). In this technique, which may require a transcutaneous approach, metal screws are placed along the inferior border and a wire ligature is placed between them to reduce the fracture. While the reduction is held in this manner, a resorbable plate is then placed on the buccal cortex along the inferior border. The wire reduction devices are subsequently removed.
FIGURE 3. Inferior border reduction technique before plate application in right mandibular parasymphyseal fracture in an 8-year-old boy. A, Fracture exposure through cervical skin incision. B , Fracture reduced by inferior border metal screws and wire ligature. C, Shows 2.0-mm plate and screw fixation. D , Metal screw and wire ligatures removed before closure.

One significant advantage of resorbable screws in the pediatric mandible is the avoidance of potential odontogenic injury. As the drill hole and tapping of the screw threads penetrate only the outer cortex, injury to developing teeth is unlikely. Even if the resorbable screw tip encroaches upon a tooth, its tip is blunt and nonpenetrating. Subsequent resorption of the screw removes any potential obstruction to tooth eruption. As such, resorbable plates and screws may be applied in even the youngest mandible, where the entire bone is composed entirely of teeth and nerve (Fig 4).

FIGURE 4. Resorbable plate and screw fixation in mandibular symphysis fracture in 3-week-old male infant. A , Fracture exposure through chin laceration. B , Shows 1.5-mm plate and screw fixation. C, Post-operative radiograph showing fracture alignment.

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